WO2012172318A1

WO2012172318A1 - Formulations containing tropolonoids, copper salt and a solvent system

Info

Publication number: WO2012172318A1
Application number: PCT/GB2012/051320
Authority: WO
Inventors: Steven John Abbott; Jonathan Howard Cove; Gavin Donoghue; Daniel James Fitzgerald
Original assignee: Evocutis Plc
Priority date: 2011-06-17
Filing date: 2012-06-12
Publication date: 2012-12-20
Also published as: GB201110278D0

Abstract

Topical skin treatment formulation containing a combination of (a) tropone or a substituted tropone and (b) a copper salt, dissolved in a solvent system comprising (i) dimethyl isosorbide; (ii) a C1 to C9 alkyl salicylate; and (iii) a glyceryl fatty acid ester. The solvent system may also comprise an alcohol, a polyoxyalkylene-based solvent, and/or a C1 to C4 alkyl glucose ester. The formulation may be used in the treatment of microbial conditions, in particular acne or body odour. The solvent system assists in the effective dissolution of the tropone and copper salt and in targeting their delivery to relevant sites on the skin.

Description

FORMULATIONS CONTAINING TROPOLONOIDS , COPPER SALT AND A SOLVENT SYSTEM

Field of the invention

This invention relates to topical skin treatment formulations containing tropolonoids and copper salts, and to the preparation and use of such formulations.

Background to the invention

Tropolone, also known as 2-hydroxy-2,4,6-cycloheptatrien-l-one, 2-hydroxytropone and purpurocatechol, is a derivative of tropone (cyclohepta-2,4,6-trien-l-one).

Tropone, tropolone and related compounds (collectively referred to as "tropolonoids") are known to exert a variety of biological effects including anti-tumour activity, phyto growth-inhibitory activity, antimicrobial activity against bacteria and fungi, insecticidal activity, and inhibition of metalloproteinases (see for example Morita Y et al, 2003 Biol Pharm Bull 26(10): 1487-1490, and Trust TJ, 1975, Antimicrobial Agents and Chemotherapy 7(5): 500-506). Further properties of the tropolonoids, including their antibacterial activity, are described in "A fresh look at natural tropolonoids" by Bentley R, 2008 Natural Product Reports 25: 118-138.

Tropolone has also been used in personal care products as a skin conditioning agent, and has been incorporated into products such as moisturisers, sunscreens, exfoliants, anti-wrinkle formulations and shampoos. Tropolonoids such as tropolone and hinokitiol (4-isopropyltropolone) have been used as antidandruff agents, including in combination with metal salts, whilst hinokitiol has been reported to have use in promoting hair growth (Hwang & Kim, Journal of Microencapsulation, August 2008, 25(5): 351-356). Nomiya et al, in Journal of Inorganic Biochemistry, 98 (2004): 46- 60, have described complexes of hinokitiol with silver (I), aluminium (III) and cobalt (II), and their antimicrobial activities. WO-2010/055850 discloses an antiviral foam hand wash containing a polyalkylene glycol ether and hinokitiol or a metal complex thereof. JP-2009-84265 describes the use of metal-tropolone complexes in anti- Legionella products. JP-2001-40222 describes the incorporation of antimicrobial metal components and tropolone-based compounds into antimicrobial polymers.

Certain metal salts have also been used as antimicrobial and anti-acne agents. Copper and bismuth salts, for example, have been utilised as antimicrobial agents, including in anti-acne formulations - see US-2005/0123620 and US-2008/0020059 which refer to the use of various polyvalent metal compounds, including copper and bismuth salts, in the topical treatment of acne and warts; US-6,294,186 which describes a topical antimicrobial composition for the treatment of acne containing a benzoic acid analogue and a metal salt which can be a copper salt such as a halide, sulphate or salicylate; EP- 1 437 124 which describes a topical anti-acne formulation containing a hydroxyacid, a copper salt such as a sulphate or pidolate, a zinc salt, an algae extract and a

haloalkynyl carbamate; and WO-2007/096601 in which copper salts are used in combination with quinones, in particular benzo- and hydroquinones, as antimicrobial and anti-acne agents. It has since been found that combinations of tropolonoids with copper salts can be antimicrobially active, in particular against cutaneous bacteria such as propionibacteria (the bacteria involved in inflammatory acne), corynebacteria (the bacteria associated with body odour) and staphylococci. Such combinations can exhibit synergistic levels of antibacterial activity, with respect to the activities of the individual components. They can therefore be of use in the topical treatment of acne, body odour and various skin-borne bacterial infections.

In order to optimise their efficacy in vivo, it may be desirable to formulate such combinations of actives specifically for topical delivery to the skin. Such formulations should ideally solubilise the actives to an appropriate concentration, be stable during storage, and if possible target the actives more efficiently to the desired site of action. It may also be desirable for the formulations to provide a fast onset of antibacterial activity, and/or persistence of the actives at the target site for a period following topical application.

However, combinations of tropolonoids with copper salts can be difficult to formulate in a manner which delivers them efficiently to target sites in the skin. They tend to form tropolonoid-copper complexes in situ, which often have relatively low solubilities in many commonly available, cosmetically acceptable excipients: this can significantly reduce the stability of a solubilised combination of tropolonoid and copper salt. It is not therefore straightforward to identify suitable skin-compatible vehicles in which to deliver such combinations of actives. Active insolubility can in turn limit the ability to penetrate the skin, and thus to reach the pilosebaceous follicles in which cutaneous propionibacteria such as P. acnes reside.

Previous attempts to target topically delivered active substances to the pilosebaceous follicles have often been directed at transepidermal delivery, and have focused on improving the rate at which the formulated substances can penetrate and diffuse through the various layers of the skin (the stratum corneum, the epidermis and the dermis) and thence into the follicles. To this end, additives such as skin penetration enhancers and diffusion coefficient enhancers have often been added to the formulations, or the solvents used have been selected for their ability to diffuse quickly through the relevant skin layers. Partition coefficient enhancers have also been included, in order to improve partitioning of the active substances between their formulations and the skin. The resultant formulations have typically been relatively complex both to design and to manufacture. Moreover these attempts have met with only limited success and as a result, active substances often need to be formulated at relatively high concentrations to ensure that a sufficient quantity reaches the intended site of action. Again this is an issue for substances, such as certain tropolonoids, which are poorly soluble in commonly-used skin delivery vehicles and therefore difficult to formulate at effective doses.

It is an aim of the present invention to provide novel topical skin treatment formulations containing tropolonoids and copper salts, which formulations can deliver the active substances in an efficient and targeted manner, in particular to the pilosebaceous follicles.

Statements of the invention According to a first aspect of the present invention there is provided a topical skin treatment formulation containing a combination of (a) tropone or a substituted tropone and (b) a copper salt, the combination being dissolved in a solvent system, wherein the solvent system comprises: (i) dimethyl isosorbide (DMI);

(ii) a CI to C9 alkyl salicylate; and

(iii) a glyceryl fatty acid ester.

This specific combination of solvents has surprisingly been found capable of delivering a tropolonoid/copper salt combination to both the stratum corneum and the pilosebaceous follicles following topical application to the skin surface, and appears capable of overcoming many of the problems previously associated with the formulation of such actives. The invented formulation has been found to be effective as a topical antibacterial agent, including against P. acnes and S. aureus, and is thus expected to be of use as an antibacterial and anti-acne agent. Relatively few individual solvents have been found to be suitable for dissolving combinations of tropolonoids and copper salts, much less for transporting such actives through the skin to the target site of action. According to the present invention, it is necessary to use a specific mixture of solvents which together dissolve the two active substances, and deliver them effectively through the skin following topical application, and which are also acceptable for pharmaceutical and/or cosmetic use.

It is believed, although we do not wish to be bound by this theory, that a formulation according to the invention can allow the active substances to diffuse through the skin into the infundibula of the pilosebaceous follicles, where bacteria such as P. acnes reside. Thus, the active substances can be targeted to the follicles, and to micro- organisms which are present in the follicles, via the skin surface.

In an embodiment of the invention, the solvent system comprises, in addition to the components (i) to (iii): (iv) an alcohol.

In an embodiment, the solvent system comprises, in addition to the components (i) to (iii) and optionally (iv):

(v) a polyoxyalkylene-based solvent selected from polyoxyalkylene glyceryl esters, polyalkylene glycols, and mixtures thereof (in particular from polyethoxylated glyceryl esters and mixtures thereof).

In an embodiment, the solvent system comprises, in addition to the components (i) to (iii) and optionally (iv) and/or (v):

(vi) a CI to C4 alkyl glucose ester. In an embodiment, the solvent system comprises, in addition to the components (i) to (iii) and optionally (iv), (v) and/or (vi):

(vii) 2-pyrrolidone or a CI to C12 alkyl pyrrolidone.

In an embodiment, the solvent system comprises, in addition to the components (i) to (iii) and optionally (iv), (v), (vi) and/or (vii): (viii) a CI to C4 alkyl pyruvate.

The solvents (i) to (iii), optionally together with (iv), (v), (vi), (vii) and/or (viii), can together help to keep the active substances in a soluble form so that they can continue to diffuse through the skin over a longer period following topical application of the formulation - for example for 4 hours or more, or for 8 or 12 or even 16 or 20 hours or more. They also appear to lend substantivity to the formulation, as demonstrated in the examples below, causing it to linger on the skin - and thus to continue to exert its antibacterial and anti-acne effects - after application. This enhanced persistence can in turn allow the formulation to be applied for example twice or even once daily, yet to provide a sustained beneficial effect for an extended period after each application. In an embodiment, therefore, the formulation of the invention is a sustained release and/or a sustained action formulation. In an embodiment of the invention, the solvent system consists essentially of components (i) to (iii), or of components (i) to (iii) together with one or more of the optional components (iv) to (viii). In an embodiment, the solvent system comprises, or consists essentially of, components (i) to (iv), in the absence of components (v) to (viii). In an embodiment it comprises, or consists essentially of, components (i) to (v), in the absence of components (vi) to (viii). In an embodiment it comprises, or consists essentially of, components (i) to (vi), in the absence of components (vii) and (viii). In an embodiment it comprises, or consists essentially of, components (i) to (iii) together with either or both of components (iv) and (v), and optionally also with component (vi). In an embodiment it comprises, or consists essentially of, components (i) to (iii) together with either or both (suitably both) of (A) component (v) and (B) ethanol and/or tetrahydrofurfuryl alcohol (THFA).

The combination of the tropolonoid (a) and the copper salt (b) is present in the formulation as an active substance. It is typically present as an antimicrobial (in particular antibacterial) agent, and/or as an anti-acne agent.

A substituted tropone may carry one or more substituents, which may be attached to the oxygen atom of the C=0 group or more typically to carbon atoms in the cycloheptene ring. Such substituents may for example be selected from hydroxyl; alkyl and alkenyl groups; the carboxylic acid group -C0₂H or an optionally cyclic acid anydride; alkoxyl groups (in particular Ci to C₆ or Ci to C₄ alkoxyl groups such as methoxyl or ethoxyl, more particularly methoxyl); halogens such as fluoro, chloro or bromo, in particular chloro; nitro groups -N0₂; amino groups -NR₂ (where each R is independently either hydrogen or hydrocarbyl, suitably either hydrogen or Ci to C₆ alkyl, more suitably either hydrogen or Ci to C₄ alkyl, for example either hydrogen, methyl or ethyl), in particular NH₂; and in cases amide groups such as -NR-COR or - NH-COR where R is as defined above.

An alkyl or alkenyl substituent may in particular be an alkyl substituent. It may be selected from Ci to C₆ or Ci to C₄ alkyl or alkenyl groups, for instance methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or t-butyl groups, more particularly methyl, ethyl or isopropyl groups. It may itself carry one or more substituents such as those listed above; however, in an embodiment it is unsubstituted. The tropone may in particular be substituted with one or more groups selected from hydroxyl, alkoxyl and alkyl groups. It may be substituted with one or more groups selected from hydroxyl and alkyl groups. In an embodiment, it is selected from tropolone and substituted tropolones, wherein a substituted tropolone carries one or more substituents selected from those listed above, in particular alkyl groups.

A substituted tropone may be a bicyclic tropone or tropolone, which is fused to another typically 5- or 6- or 7-membered ring. The additional ring may itself carry one or more substituents, for example of the type listed above; it may contain one or more heteroatoms such as sulphur, nitrogen and/or oxygen. The additional ring may itself be fused to another ring, so that the substituted tropone is a tricyclic molecule, or in cases a tetra-, penta- or hexacyclic moiety. In cases however it may be preferred for the substituted tropone not to be multicyclic, or for the substituted tropone to be either mono- or bicyclic.

In an embodiment of the invention, the tropone is mono-substituted. In an

embodiment, it is substituted at the 2-position. In an embodiment, it is substituted with one hydroxyl group. Thus, the substituted tropone (a) may be tropolone.

In an embodiment, the tropone carries more than one substituent (for example it may be di- or tri-substituted). In such a case, one of the substituents may be a hydroxyl group, which may occupy the 2-position; the tropone may therefore be a substituted tropolone such as a hydroxytropolone (for example hydroxytropolone itself, 7- hydroxy-3 -isopropyltropolone, 7-hydroxy-4-isopropyltropolone, 2-hydroxy-4- isopropyltropolone or 7-hydroxy-3-isopropenyltropolone) or dihydroxytropolone.

Where the tropone carries more than one substituent, one of the substituents may be an alkoxyl group, in particular a methoxyl group, as in for example pygmaein and isopygmaein.

Where the tropone carries more than one substituent, one of the substituents may be an alkyl group. An alkyl group may be a Ci to C₄ alkyl group such as isopropyl, which may occupy the 4-position. Thus, the substituted tropone may be hinokitiol (also known as β-thujaplicin, 2-hydroxy-4-isopropyl-2,4,6-cycloheptatrien-l-one or 4- isopropyltropolone) or another thujaplicin.

The substituted tropone may be a hydroxytropolone acid or derivative thereof, such as stipitatic acid, stipitatonic acid, stipitalide, stipitaldehydic acid, puberulonic acid or puberulic acid.

In an embodiment, the component (a) is selected from tropolone, hinokitiol, and mixtures thereof. In an embodiment, it is tropolone. In an embodiment, it is hinokitiol. In an embodiment, it is a mixture of tropolone and hinokitiol. In certain cases, however, it may be preferred for the substituted tropone not to be hinokitiol.

In an embodiment, the component (a) is suitable for cosmetic use. In an embodiment, it is suitable for pharmaceutical (which includes veterinary) use.

In the context of the present invention, the term "copper salt" includes copper (I), (II) and (III) salts, as well as copper (I), (II) and (III) complexes. In an embodiment a copper salt in a formulation according to the invention is a copper (I) (cuprous) or copper (II) (cupric) salt, in particular a copper (II) salt.

In a formulation according to the invention, a copper salt may for instance be selected from copper carboxylates; copper halides; copper sulphadiazine; copper sulphate (in particular the pentahydrate); copper nitrate; copper carbonate; copper carbonate hydroxide; copper oxide; copper oxychloride; copper hydroxide; copper

acetylacetonate; copper PCA (pyrrolidone carboxylic acid); copper PCA

methylsilanol; copper acetyl tyrosinate methylsilanol; copper acetylmethionate; copper aminoacetylamidoimidazolyl propionate; copper picolinate; copper peptides such as copper tripeptide-1, bis (tripeptide-1) copper acetate, copper ascorbyl phosphate succinoyl tripeptide-34 and alanine/histidine/lysine copper polypeptide HC1; copper ATP; copper DNA; copper amino acid salts (eg copper glutamate, copper aspartate and copper glycinate); copper silicates; copper salts of quinolines - especially

hydroxyquino lines - and their derivatives (eg the copper salt of 8-hydroxyquinoline); copper pyrithione and other copper salts of pyridine thiols; copper phosphates, including for example sodium calcium copper phosphate and copper pyridoxal-5- phosphate; chlorophyllin copper complexes such as sodium copper chlorophyllin; copper chlorophyll,; disodium EDTA copper; and mixtures thereof.

Suitable copper carboxylates include lactate, citrate (including for example disodium cupric citrate, and copper (II) citrate dihydrate), ascorbate, acetate (either copper (I) acetate or copper (II) acetate), gluconate, laurate, myristate, palmitate, salicylate, aspirinate, stearate, succinate, tartrate, undecylenate, usnate (in particular copper (II) di-usnate), neodecanoate and ricinoleate. A carboxylate may be for example a C2 to C20, a C2 to C18, a C2 to C16, a C2 to C14, a C2 to C12, a C2 to CIO, a C2 to C8 or a C2 to C6 carboxylate. Suitable halides include copper chloride, copper bromide and copper iodide, for example copper (II) chloride or copper (I) iodide.

In an embodiment of the invention, the copper salt may be selected from copper sulphate, copper acetate, copper glycinate, copper gluconate, copper acetylmethionate, copper picolinate, copper citrate, copper PC A methylsilanol, copper acetyl tyrosinate methylsilanol, copper tripeptide-1, copper ATP, copper aspartate, copper DNA, copper carbonate hydroxide, copper pyridoxal-5-phosphate, cupric chloride, disodium cupric citrate, disodium EDTA-copper, bis (tripeptide-1) copper acetate, copper ascorbyl phosphate succinoyl tripeptide-34, chlorophyllin copper complexes, copper aminoacetylamidoimidazolyl propionate, copper chlorophyll, sodium calcium copper phosphate, alanine/histidine/lysine copper polypeptide HC1, and mixtures thereof. In each case the salt is preferably the copper (II) salt.

In another embodiment, the copper salt may be selected from copper sulphate, copper acetate, copper acetylmethionate, copper PCA, disodium EDTA-copper, chlorophyllin copper complexes (for example sodium copper chlorophyllin), copper chlorophyll, and mixtures thereof.

In a further embodiment, the copper salt may be selected from copper carboxylates and mixtures thereof. It may in particular be copper acetate, more particularly copper (II) acetate. In an embodiment, it may be preferred for the copper salt not to be a complex formed between a copper ion and a complexing agent, in particular a bi- or multi-dentate ligand.

Generally speaking a copper salt for use in the formulation of the invention may be either organic or inorganic. It may be present in an at least partially hydrated form, and may thus be formulated in the presence of an aqueous solvent. Alternatively it may take the form of a lipid-soluble salt, suitably used in the presence of an organic solvent.

In an embodiment, it may be preferred for the copper salt not to be a complex formed between a copper ion and either tropone or a substituted tropone such as tropolone or hinokitiol. In other words, it may be preferred for the formulation to be prepared using, in addition to the optionally substituted tropone (a), a first copper salt other than a copper-tropolonoid complex, even if a copper-tropolonoid complex is formed in the formulation prior to, or at the point of, use. The formulation will then contain, in addition to the copper-tropolonoid complex formed prior to or at the point of use, an additional anion or complexing agent derived from the first copper salt.

In an embodiment of the invention, the component (b) of the formulation comprises a mixture of two or more copper salts, for instance selected from those referred to above.

In an embodiment, the copper salt is suitable for cosmetic use. In an embodiment, it is suitable for pharmaceutical (which includes veterinary) use.

In a formulation according to the invention, either or both of the tropolonoid (a) and the copper salt (b) may be present in the form of a suitable derivative. In general a derivative may be acceptable for pharmaceutical (which includes veterinary) use, and/or for cosmetic use. It may be for example a salt, ester, complex or solvate, or a so-called "prodrug" form or protected form which reverts to an active form of the relevant compound at an appropriate time on or after administration. In an

embodiment of the invention, however, the optionally substituted tropone (a) is present in the form of a single, underivatised molecule of the relevant tropolonoid. In an embodiment, the copper salt (b) is present in the form of an underivatised ion, molecule or complex of the relevant species.

The concentration of the optionally substituted tropone (a) in the formulation might suitably be 0.1% w/w or greater, or 0.25 or 0.5 or 0.6 or 0.7% w/w or greater, or in cases 1 or 1.2 or 1.5 or 1.7% w/w or greater. Its concentration might be up to 5% w/w, or up to 4 or 3 or 2.5% w/w. Its concentration might for example be from 0.5 to 5% w/w, or from 0.5 to 3% w/w, or from 0.5 to 2% w/w or 0.5 to 1.5% w/w, such as about 0.7%) w/w or about 1% w/w or about 1.25% w/w or about 2% w/w.

The concentration of the copper salt in the formulation might suitably be 0.01% w/w or greater, or 0.05% w/w or greater, or 0.1 or 0.2 or 0.3 or 0.4 or 0.5% w/w or greater, or in cases 0.6 or 0.7% w/w or greater. Its concentration might be up to 5% w/w, or up to 4 or 3 or 2% w/w, or up to 1% w/w, such as from 0.05 or 0.1 to 1% w/w. It might for example be about 0.1% w/w, or about 0.5 or 0.53% w/w, or about 0.7% w/w.

The weight ratio of the tropolonoid (a) to the copper salt (b) in the formulation may be up to 100:1, for example up to 50:1 or 25:1 or 15:1 or 10:1, or up to 8:1 or 5:1 or 4:1 or 2:1. This ratio may be 1 : 100 or greater, for example 1 :50 or greater or 1 :25 or greater or 1 : 10 or greater, or 1 :5 or 1 :2 or 1 : 1 or greater. In cases it may be 1.5:1 or greater, or 2:1 or 3:1 or greater, or 5:1 or 8:1 or 10:1 or greater. It may for example be from about 15:1 to 1:1, or from about 10:1 to 1:1, or from about 5:1 to 1:1, or from about 2:1 to 1:1.

Where the formulation contains a mixture of tropolone and hinokitiol, the weight ratio of the tropolone to the hinokitiol may be up to 5 : 1 , or up to 2.5 : 1 , or up to 2: 1 or 1:1 or in cases 0.75 : 1. This ratio may be 0.1 : 1 or greater, for example 0.25 : 1 or 0.5 : 1 or greater. It may be from about 0.25 : 1 to 5 : 1 , or from about 0.25 : 1 to 3 : 1 , such as about 0.5:1 or 0.54:1 or in cases about 2.3:1.

The concentration of the DMI in the formulation may be 10% w/w or greater, or 15 or 20%) w/w or greater, or 22 or 25 or 26 or 27 or 28% w/w or greater, or in cases 30 or 35%) w/w or greater. Its concentration may be up to 35% w/w, or up to 32 or 30 or 29% w/w. In cases it may be up to 40 or even 45% w/w. Its concentration may for example be from 25 to 35% w/w, or from 20 to 30%> w/w, or from 25 to 30%> w/w, or from 27 to 30 or 33% w/w, such as about 30% w/w. In another embodiment it may be present at about 40% w/w.

The component (ii) is suitably a liquid. It may be an ester of salicylic acid with a suitable alcohol. It may be a C3 to C9 alkyl salicylate or a C5 to C9 alkyl salicylate. The alkyl group may be straight chain or branched, and/or may incorporate one or more cyclic groups. The component (ii) may for example be selected from amyl salicylate, octyl (typically ethylhexyl) salicylate, homosalate and mixtures thereof. It may in particular be homosalate, which is the ester formed from salicylic acid and 3,3,5-trimethyl cyclohexanol. The concentration of the component (ii) in the formulation may be 5% w/w or greater, or 6 or 7 or 8 or 9 or 9.5% w/w or greater. Its concentration may be up to 13% w/w, or up to 12 or 11 or 10% w/w. Its concentration may for example be from 5 to 10% w/w, or from 6 to 13% w/w, or from 9 to 11% w/w, such as about 9.6 or 10% w/w. In an embodiment, its concentration may for example be from 5 to 12% w/w, or from 6 to 11% w/w, or from 7 to 10%> w/w, such as about 8.5%) w/w.

The component (iii) is suitably a liquid. It may be for example a glyceryl mono-, di- or tri- fatty acid ester. In one embodiment it is a monoester; in another it is a diester. It may be an ester of a C 12 to C22 fatty acid, or of a C 12 to C20 fatty acid, or of a C 12 to CI 8 fatty acid, such as a glyceryl oleate or stearate. It may be an L-pyrrolidone carboxylic acid (PC A) glyceryl ester, for example of a C 12 to C22 or C 12 to C20 or C12 to C18 (in particular CI 8) fatty acid, for example PCA glyceryl oleate. It may be glyceryl diisostearate. In an embodiment it may be a diglyceride ester, in particular a diglyceride mono- or diester. In an embodiment it may be a polyglyceride ester, in particular a polyglyceride mono- or diester. In an embodiment, it is selected from PCA glyceryl esters (in particular PCA glyceryl oleate), glyceryl diisostearate, and mixtures thereof. In another embodiment, it may be preferred for the component (iii) not to be glyceryl diisostearate.

The concentration of the component (iii) in the formulation may be 2% w/w or greater, or 3 or 3.5 or 4 or 4.5 or 5% w/w or greater. Its concentration may be up to 12% w/w, or up to 10 or 8% w/w, or up to 7 or 6.5 or 6 or 5.5 or 5% w/w. Its concentration may for example be from 3 to 7% w/w, or from 4 to 6% w/w, such as about 4.8 or 5% w/w. Where the formulation comprises a mixture of two or more components (iii), the above concentration ranges suitably apply to the overall mixture. Thus, for example, the formulation may contain from 3 to 7% w/w of a first glyceryl fatty acid ester, such as PC A glyceryl dioleate, and from 3 to 7% w/w of a second glyceryl fatty acid ester, such as glyceryl diisostearate.

In an embodiment, in particular although not exclusively when the component (iii) is glyceryl diisostearate, the concentration of the component (iii) in the formulation may be up to 45% w/w, or up to 40% w/w, or up to 35 or 30 or 25 or 20%> w/w. In such a case its concentration may for example be 15% w/w or greater, or 18 or 20% w/w or greater, such as from 15 to 40 or 45% w/w or from 20 to 40% w/w, in cases about 18 to 20% w/w or about 38 to 40% w/w. A lower concentration of component (iii) may be appropriate in formulations which also contain an alcohol (or which contain more than 20% w/w of alcohol), and/or which contain one or more of the optional components (v) to (viii), in particular component (vi). Thus, in certain embodiments it may be preferred for the concentration of glyceryl diisostearate in the formulation to be 8%) w/w or less, or 7 or 6 or 5% w/w or less, or in cases to be 4 or 3 or 2% w/w or less. In some embodiments, it may be preferred for the formulation not to contain any glyceryl diisostearate. Where the solvent system comprises PC A glyceryl oleate, it may be preferred that its concentration in the overall formulation be 8% w/w or less, or 7 or 6 or 5% w/w or less, or in cases 4 or 3 or 2% w/w or less. In some embodiments, it may be preferred for the formulation not to contain any PCA glyceryl oleate. In some embodiments, it may be preferred for the formulation not to contain both glyceryl diisostearate and PCA glyceryl oleate.

The alcohol component (iv), if present, may for example be selected from CI to C3 alcohols such as ethanol and isopropyl alcohol; phenoxyethanol; l-methoxy-2- propanol; benzyl alcohol; THFA; Transcutol™ (2-(2-ethoxyethoxy)ethanol); and mixtures thereof, or from CI to C3 alcohols such as ethanol; THFA; phenoxyethanol; benzyl alcohol; and mixtures thereof. In an embodiment the alcohol is a CI to C3 alcohol, in particular ethanol. In an embodiment it is THFA. In an embodiment it is selected from ethanol, THFA and in particular mixtures thereof.

The concentration of the component (iv) in the formulation, if present, may be 5 or 8 or 10% w/w or greater, or 15% w/w or greater, or 17 or 18 or 19 or 20% w/w or greater. Its concentration may be up to 35 or 30% w/w, or up to 25 or 23 or 22 or 21 or 20% w/w. Its concentration may for example be from 10 to 20% w/w, or from 15 to 30%) w/w, or from 15 to 25% w/w, or from 15 or 18 to 22% w/w, such as about 17 or 19 or 20%) w/w or in cases about 25 or 26% w/w. Where the formulation comprises a mixture of two or more alcohol components (iv), the above concentration ranges suitably apply to the overall mixture. It may for example contain from 5 to 20% w/w of a first alcohol such as THFA, together with from 2 to 15% w/w of a second alcohol such as ethanol. In an embodiment, it contains from 5 to 15% w/w, or from7 to 13% w/w, of THFA, together with from 5 to 15% w/w, or from 7 to 13% w/w, of ethanol. In some embodiments, it may be preferred for the THFA concentration to be less than 15%) w/w, for example 14 or 13 or 12% w/w or less.

In an embodiment, where the solvent system comprises ethanol, the concentration of the ethanol in the overall formulation may be greater than 5% w/w, or greater than 6 or 7 or 8% w/w. However, it may also be preferred to maintain the ethanol concentration at 15%) w/w or lower, in particular at 10% w/w or lower, for example at 9 or 8 or 7% w/w or lower.

In an embodiment, where the solvent system comprises THFA, the concentration of the THFA in the overall formulation may be 20% w/w or less, or 17.5 or 15% w/w or less, such as 12.5 or ideally 10% w/w or less.

Where the formulation contains one or more of the optional components (vi) to (viii), in particular two or more of those components, and more particularly all three, it may be preferred for the formulation not to contain the alcohol (iv).

The component (v), if present, is suitably a liquid. In an embodiment, it is a polyoxyalkylene (polyalkoxylated) glyceryl ester, in particular a polyoxyethylene (polyethylene glycol, PEG) glyceryl ester. In an embodiment, it is a polyalkylene glycol, in particular a PEG. It suitably has a molecular weight of 350 or greater, or of 380 or 400 or 450 or greater, for example of 500 or 600 or 700 or 800 or greater.

A polyalkoxylated glyceryl ester (also known as a polyalkoxylated glyceride) is a glyceride ester of a polyalkylene glycol (typically PEG). It may contain mono-, di- or tri-glycerides, partial glycerides or mixtures thereof. It may for example be formed by esterification of a polyalkylene glycol with a glyceride oil of an appropriate chain length. The glyceride components may for example contain from 6 to 20 or from 8 to 18 carbon atoms; they may be selected from caprylic and capric glycerides and mixtures thereof. Suitable such solvents are commercially available as Glycerox™ 767 and Labrasol™, both of which are mixtures of caprylic and capric glycerides of PEGs.

A polyethoxylated glyceryl ester usable as a component (v) in the present invention may be a mixture of PEG-8 caprylic and capric glycerides, such as is commercially available as Labrasol™. In an embodiment, the component (v) may be or comprise a polyethylene glycol

(PEG), suitably a PEG having a molecular weight of 350 or greater, or of 380 or 400 or 450 or greater, for example of from 350 to 450. A suitable example might be a PEG having a molecular weight of about 400.

In an embodiment, the solvent system contains a mixture of two or more components (v). In an embodiment, the component (v) is selected from polyalkoxylated glyceryl esters, polyalkylene glycols (in particular PEGs), and mixtures thereof.

The concentration of the component (v) in the formulation, if present, may be 6% w/w or greater, or 7 or 8 or 9 or 9.5 or in cases 10% w/w or greater, or 13 or 15 or 16 or 17%) w/w or greater. Its concentration may be up to 25% w/w, or up to 23 or 22 or 21 or 20%) w/w. In cases its concentration may be up to 13% w/w, or up to 12 or 11 or 10% w/w. Its concentration may for example be from 15 to 25% w/w, or from 15 to 23%) w/w, such as about 18 or 19 or 20%> w/w. In another embodiment, its concentration may be from 6 to 13% w/w, or from 9 to 11% w/w, such as about 9.6 or 10% w/w. In an embodiment, the component (v) is present in the formulation at up to 40% w/w, or more particularly at up to 35% w/w, or up to 30%> w/w, for example from 20 to 30%> w/w or from 22 to 32% w/w or from 25 to 30%> w/w, such as about 27% w/w. In an embodiment, it is present in the formulation at up to 25% w/w, or up to 20% w/w, such as about 18% w/w. A lower concentration of component (v) may be appropriate in formulations which also contain one or more of the optional components (vi) to (viii).

Where the formulation comprises a mixture of two or more components (v), the above concentration ranges suitably apply to the overall mixture. It may for example contain from 10 to 30% w/w or from 15 to 30% w/w of a first component (v) such as a polyethoxylated glyceryl ester (eg Labrasol™), together with from 1 to 10% w/w of a second component (v) such as a PEG.

The component (vi), if present, is suitably a liquid. It may be a CI to C4 alkyl glucose mono-, di- or triester of a C12 to CI 8 (in particular CI 8) fatty acid. It may be a CI to C4 alkyl glucose diester of a C 12 to CI 8 (in particular CI 8) fatty acid, for example a CI to C4 alkyl glucose dioleate such as methyl glucose dioleate. It may be a CI to C2 alkyl glucose ester, for example a methyl glucose ester (which includes a methyl glucose diester). The concentration of the component (vi) in the formulation, if present, may be 2% w/w or greater, or 3 or 3.5 or 4 or 4.5 or 5% w/w or greater. Its concentration may be up to 8% w/w, or up to 7 or 6.5 or 6 or 5.5 or 5% w/w. Its concentration may for example be from 3 to 7% w/w, or from 4 to 5.5 or 6% w/w, such as about 4.8 or 5 % w/w.

The component (vii), if present, is suitably a liquid. It may for example be selected from CI to C12 alkyl pyrrolidones such as ethyl pyrrolidone; caprylyl pyrrolidone; lauryl pyrrolidone; and mixtures thereof. In an embodiment, it is a CI to C4 alkyl pyrrolidone, or a CI to C3 or CI to C2 alkyl pyrrolidone, in particular ethyl pyrrolidone. In an embodiment, it is 2-pyrrolidone. The concentration of the component (vi) in the formulation, if present, may be 13% w/w or greater, or 15 or 16 or 17 or 18 or 18.5 or 19% w/w or greater. Its concentration may be up to 25% w/w, or up to 24 or 23 or 22 or 21 or 20 or 19.5% w/w. Its concentration may for example be from 15 to 25% w/w, or from 18 to 21% w/w or from 18 to 20% w/w, such as about 19 or 19.1 or 20% w/w. In an embodiment, it may be preferred for the formulation not to contain the component (vii).

The component (viii), if present, is suitably a liquid. It may be for example methyl pyruvate or ethyl pyruvate, in particular ethyl pyruvate. Its concentration in the formulation may be 5% w/w or greater, or 7 or 10 or 13 or 14% w/w or greater, or in cases 15 or 17 or 18 or 18.5% w/w or greater. Its concentration may be up to 25% w/w, or up to 22 or 20 or 19.5% w/w, or in cases up to 18 or 16 or 15% w/w. Its concentration may for example be from 15 to 25% w/w, or from 18 to 20% w/w, such as about 19 or 19.1% w/w. In an embodiment, its concentration may be from 10 to 20%) w/w, or from 12 to 17% w/w, or from 12 or 13 to 16% w/w or from 14 to 15% w/w, such as about 13.5 or 14.5% w/w.

In an embodiment, a component (viii), in particular ethyl pyruvate, may be combined with an additional solvent such as THFA, for instance in a 50:50 v/v mixture, the concentration of such a mixture being typically as described above for the component (viii) alone. In an embodiment, it may be preferred for the formulation not to contain the component (viii).

The formulation of the invention should be suitable for topical application to the skin, in particular human skin. It may be adapted and/or intended for topical application to the skin. The formulation may be suitable and/or adapted and/or intended for use as a pharmaceutical formulation, or as a cosmetic. In an embodiment it is suitable and/or adapted and/or intended for use as an antibacterial preparation, and/or as an anti-acne preparation. It may be suitable and/or adapted and/or intended for use in the treatment of one or more of the conditions identified below in connection with the fourth aspect of the invention. Any component (i) to (viii) included in the formulation (and where appropriate any additional ingredient) should therefore be suitable for topical application to the skin. It should not induce unacceptable levels of irritation on application to the skin, ideally even when the formulation is applied as a "leave-on" treatment. Ideally, such components are acceptable for cosmetic use. Ideally they are acceptable for pharmaceutical (which includes veterinary) use, in particular for pharmaceutical administration to humans.

In an embodiment, the formulation does not contain water, or contains less than 5 or 2 or 1 or 0.5 or 0.1% w/w water. It may for example take the form of a non-aqueous gel. In an embodiment, it does not contain propylene glycol, or contains less than 5 or 2 or 1 or 0.5 or 0.1% w/w propylene glycol. In an embodiment, it does not contain ethanol, or contains less than 10 or 8 or 5 or 2 or 1 or 0.5 or 0.1% w/w ethanol.

The combination of the tropolonoid and the copper salt should be soluble in the solvent system, by which is meant that the solvent system is able to dissolve the combination to at least 0.01% w/w, or at least 0.05 or 0.1% w/w, or at least 0.25 or 0.5% w/w, for example to 0.8% w/w or greater or in cases 1 or 1.5 or 2 or 3 or 4% w/w or greater.

In an embodiment, the formulation of the invention contains an aliphatic amine, in particular a primary aliphatic amine. The amine may be an alkyl or alkenyl (in particular alkyl) amine, of which the alkyl or alkenyl group may be straight chain or branched. The alkyl or alkenyl group may contain one or more, or 2 or 3 or more, carbon atoms. It may contain up to 22 carbon atoms, or up to 20 or 18 or 16 carbon atoms, for example from 2 to 18 or from 3 to 16 carbon atoms. Examples of suitable amines include isopropylamine, palmitamine and mixtures thereof.

The concentration of the aliphatic amine in the formulation, if present, may be 0.1% w/w or greater, or 0.25 or 0.5%> w/w or greater, or 0.75 or 1 or 1.25 or 1.5% w/w or greater, or in cases 1.75 or 2% w/w or greater. Its concentration may be up to 5% w/w, or up to 4 or 3 or 2.5 or 2% w/w. In an embodiment, its concentration is from about 0.5 to 3 or 4%) w/w, such as about 2% w/w or about 1% w/w.

In an embodiment, the formulation contains a chelating agent, such as for example EDTA (ethylene diamine tetraacetic acid).

The concentration of the chelating agent in the formulation, if present, may be 0.05% w/w or greater, or 0.1% w/w or greater, or 0.2 or 0.3 or 0.4 or 0.5% w/w or greater. Its concentration may be up to 5% w/w, or up to 3 or 2 or 1.5 or 1% w/w, or in cases up to 0.75 or 0.5% w/w. In an embodiment, its concentration is from about 0.1 to 1% w/w, or from about 0.3 to 0.7%> w/w, such as about 0.5%> w/w.

In an embodiment, the formulation contains both an aliphatic amine and a chelating agent. In an alternative embodiment, the formulation does not contain an aliphatic amine, and/or does not contain an additional chelating agent.

In an embodiment, in particular where it is for use in the treatment of acne, the formulation of the invention may contain salicylic acid (2-hydroxybenzoic acid) or a derivative thereof. Salicylic acid is a known anti-acne agent which acts as a keratolytic and is widely used to unblock pores to help prevent whiteheads and blackheads becoming inflamed (Waller JM, Dreher F, Behnam S, Ford C, Lee C, Tiet T,

Weinstein GD, Maibach HI, "'Keratolytic' properties of benzoyl peroxide and retinoic acid resemble salicylic acid in man", Skin Pharmacol Physiol 2006;19: 283-9).

A derivative of salicylic acid may in particular be a cosmetically and/or

pharmaceutically acceptable derivative. It may be a salt, for example a metal salt or ammonium salt or vitamin salt. Suitable metal salts include the alkali metal salts (for example the sodium and potassium salts, in particular the former) and the alkaline earth metal salts (for example the calcium and magnesium salts, in particular the former). A metal salicylate may also be selected from bismuth salicylate, bismuth subsalicylate and transition metal salts such as zinc, copper or titanium salts. Other salicylate salts include MEA-salicylate and TEA-salicylate.

Other salicylic acid derivatives include salicylic acid esters, in particular alkyl esters (of which the alkyl group may be either straight chain or branched, and/or may incorporate one or more cyclic groups), more particularly CI to C20 or CI to C15 or CI to CIO or CI to C6, or in cases C12 to CI 5, alkyl esters, such as in particular methyl salicylate ("wintergreen"), capryloyl salicylic acid and homosalate (3,3,5- trimethylcyclohexyl 2-hydroxybenzoate). Further derivatives include benzyl salicylate and betaine salicylate. In cases they may include substituted salicylic acids and salts and esters thereof, such as 4-amino salicylic acid, thiosalicylic acid and their salts and esters. A salicylic acid derivative may be selected from 4-aminosalicylic acid and its salts; capryloyl salicylic acid; glucosamine salicylate; MEA-salicylate; TEA-salicylate; metal salicylates such as those listed above; thiosalicylic acid; benzyl salicylate; amyl (pentyl) and isoamyl (isopentyl) salicylates; azeloyl diethyl salicylate; betaine salicylate; butyloctyl salicylate; chitosan salicylate; dipropylene glycol and glycol salicylates; ethylhexyl (octyl) salicylate; hexanediol disalicylate; hexyl

dodecylsalicylate; hexyl salicylate; isocetyl salicylate; isodecyl salicylate; menthyl salicylate; methyl salicylate; myristyl salicylate; niacinamide salicylate; phenyl salicylate; potassium methoxysalicylate; pyridoxine salicylate; silanediol salicylate; tridecyl salicylate; trimethylsilyl trimethylsiloxy salicylate; zinc thiosalicylate; 4- acetaminophenyl salicylate; cyclohexanol, 3,3,5- trimethyl-salicylate; sodium ethylmercurithio salicylate; C12 to C15 alkyl salicylates; isopropylbenzyl salicylate; zinc glycinate salicylate; and mixtures thereof.

In an embodiment of the invention, a salicylic acid derivative may be selected from metal salicylates; alkyl salicylates of chain length CIO or greater; betaine salicylates; TEA-salicylate; MEA-salicylate; and mixtures thereof. In an embodiment, the invented formulation may contain salicylic acid, a metal salicylate, or a mixture thereof. In an embodiment, it contains salicylic acid.

In an embodiment, the salicylic acid or derivative is not a salicylanilide, for example a halogenated salicylanilide of the type referred to in GB-2 456 376. In an embodiment, the salicylic acid or derivative is not a CI to C9 alkyl salicylate, or is not a CI to C9 alkyl salicylate which is the same as component (ii) of the solvent system.

The concentration of the salicylic acid or derivative in the formulation, if present, may be 0.01% w/w or greater, or 0.05 or 0.1 % w/w or greater, or 0.25 or 0.5%> w/w or greater, for example 0.8%> w/w or greater or in cases 0.9%> w/w or greater. Its concentration may be up to 10%> w/w, or up to 5 or 3% w/w, or up to 2% w/w, or up to 1.5 or 1.2 or 1% w/w. In an embodiment, its concentration is from about 0.05 to 3% w/w, or from about 0.5 to 2% w/w, or from about 1 to 2% w/w, such as about 1% w/w.

In a specific embodiment of the invention, the solvent system comprises one or more components selected from components (vi) (ie CI to C4 alkyl glucose esters); salicylic acids and derivatives thereof; aliphatic amines; chelating agents; and combinations thereof.

In an embodiment, the formulation of the invention contains a C 12 to C20 fatty acid or mixture thereof. It may contain a C12 to C18 fatty acid or mixture thereof, or a C 14 to CI 8 fatty acid or mixture thereof, for example selected from caprylic/capric, lauric, palmitic, stearic, sapienic, arachidic, oleic and linoleic acids and mixtures thereof. One or more of the fatty acids may be a constituent of sebum, in particular human sebum: such acids include palmitic acid, sapienic acid and oleic acid, and others described by Nicolaides N in "Skin Lipids - Their Biochemical Uniqueness", Science, 1974, 186: 19-26. In an embodiment, the formulation contains oleic acid. The concentration of such a component in the formulation may be 0.05% w/w or greater, for example 0.1 or 0.2 or 0.3 or 0.4 or 0.5%> w/w or greater. Its concentration may be up to 5% w/w, or up to 2 or 1%) w/w, for example up to 0.9 or 0.8 or 0.7 or 0.6%> w/w. Its concentration may be for example from 0.3 to 0.7%> w/w, such as about 0.5 or 0.57%> w/w. In certain embodiments, however, it may be preferred for the formulation not to contain a C 12 to C20 fatty acid.

In an embodiment, the formulation contains L-pyrrolidone carboxylic acid (PC A). The concentration of the PCA in the formulation may be 0.05% w/w or greater, for example 0.1 or 0.2 or 0.3 or 0.4 or 0.5% w/w or greater. Its concentration may be up to 2 or 1.5 or 1% w/w, for example up to 0.9 or 0.8 or 0.7 or 0.6%> w/w. Its concentration may be for example from 0.2 to 1.3% w/w, or from 0.3 to 0.7% w/w, or from 0.7 to 1.3% w/w, such as about 0.5%> w/w or about 1% w/w. In certain embodiments, however, it may be preferred for the formulation not to contain PCA.

A formulation according to the invention may also contain an antioxidant. This can help to stabilise the active substance(s) present, which may be unstable in light and/or susceptible to oxidation in some solvent environments. Oxidative stability can be particularly important for formulations which are intended for use as "leave-on" products, since they can remain on the skin, exposed to both oxygen and sunlight, for extended periods. Antioxidants suitable for use in topical skin treatment formulations are well known to those skilled in the art. Where the formulation contains an antioxidant, its concentration may be 0.1% w/w or greater, or 0.2 or 0.3 or 0.4 or 0.5%> w/w or greater, or in cases 0.6 or 0.7 or 0.8%> w/w or greater. Its concentration may be up to 2 or 1.5% w/w, or up to 1.4 or 1.3 or 1.2% w/w, such as about 1% w/w. The formulation may contain one or more additional ingredients or excipients, as are known for use in topical skin treatment formulations. Those included will depend on the intended mode of application for the formulation. Examples may for instance be found in Williams' Transdermal and Topical Drug Delivery (Pharmaceutical Press, 2003) and other similar reference books. See also the Database of Cosmetic and Toiletry Formulations (CD ROM, 2005) by Ernest W Flick, published by William Andrew; the Personal Care Product Council's online database (www.ctfa-online.org); and approved ingredients lists published by regulatory authorities, for example the EU Cosmetic Ingredients list which is available online through the European Commission (see http://ec.europa.eu/enterprise/ cosmetics/ cosing) . Suitable additives may for instance include emollients, moisturisers, preservatives, stabilisers, gelling agents and other thickeners, sunscreens, colouring agents and fragrances. For use in the treatment of acne, however, it may be preferred for the formulation not to contain an emollient. In a specific embodiment, the formulation contains a fragrance, for example an essential oil or component thereof such as vanillin. In general terms, it may include a component capable of masking, at least partially, the smell of another component present in the formulation.

In an embodiment, the formulation contains one or more thickening agents, which may be gelling agents. Suitable such agents include cellulose-based thickening agents such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose and carboxymethyl celluloses. Such agents may be used in the form of a (preferably cosmetically and/or pharmaceutically acceptable) salt such as for instance the sodium salt. A thickening agent may be a polymeric thickening agent such as a carbomer, which will typically be a cross-linked acrylic acid-based polymer, for example a homopolymer of acrylic acid, cross-linked with an allyl ether: such thickeners are available for instance in the Carbopol™ range, ex- Lubrizol. In an embodiment, the formulation contains a hydroxypropyl cellulose thickening agent, for example of the type commercially available as Klucel™ from Hercules, USA. Such a thickening agent may for example have a molecular weight of 200,000 or greater, or of 300,000 or 350,000 or greater, for example from 300,000 to 500,000 or from 300,000 to 400,000.

Where the formulation contains a thickening agent, its concentration may be 0.2% w/w or greater, or 0.5%> w/w or greater, or 1 or 1.5 % w/w or greater, or in cases 5% w/w or greater. Its concentration may be up to 10%> w/w, or more usually up to 5% w/w, or up to 4 or 3 or 2.5 or 2% w/w, for example from 1 to 2.5% w/w or from 1.5 to 2.5% w/w or from 1.5 to 3% w/w or from 0.5 to 2.5% w/w or from 1 to 2% w/w. In an embodiment, the concentration of the thickening agent in the formulation is about 1.9 or 2%) w/w, or about 1 or 2% w/w, or about 2.5% w/w. In cases it may be used at 1% w/w or less. However, a suitable concentration for a thickening agent (or mixture thereof) will depend on the desired viscosity of the ultimate formulation, and on the properties of the thickening agent as well as any restrictions on its permitted levels in for example cosmetic or pharmaceutical preparations.

The formulation may contain one or more additional active agents such as

antimicrobial (in particular antibacterial) agents. For example, it may contain one or more agents selected from anti-acne agents, keratolyses, comedolytics, agents capable of normalising keratinocyte and/or sebocyte function, anti-inflammatories, antiproliferatives, antibiotics, anti-androgens, sebostatic/sebosuppressive agents, antipruritics, immunomodulators, agents which promote wound healing, additional antimicrobial agents, anti-perspirant agents, deodorants, and mixtures thereof.

An additional antimicrobial agent may be selected from biocides, disinfectants, antiseptics, antibiotics, bacteriophages, enzymes, anti-adhesins, immunoglobulins, antimicrobially active antioxidants, and mixtures thereof; it may be active as a bactericide, in particular against propionibacteria and/or staphylococci and/or coryneform bacteria. It may however be preferred for the tropolonoid and the copper salt (and where appropriate the salicylic acid or derivative) to be the only active agent(s) in the formulation, or at least to be the only antimicrobially or antibacterially active agent(s) and/or the only anti-acne active agent(s) and/or the only keratolytically active agent(s).

In a specific embodiment, a formulation according to the invention contains a combination of (a) tropone or a substituted tropone and (b) a copper salt, the combination being dissolved in a solvent system, wherein the solvent system comprises:

(1) DMI, suitably at a concentration from 25 to 35% w/w or from 25 to 30% w/w;

(2) a C5 to C9 alkyl salicylate, in particular homosalate, suitably at a concentration from 5 to 12% w/w;

(3) a glyceryl fatty acid ester, in particular a glyceryl oleate, more particularly PCA glyceryl oleate, suitably at a concentration from 2 to 8% w/w;

(4) an alcohol selected from ethanol, THFA and mixtures thereof, suitably at a concentration from 15 to 25% w/w;.

(5) a component (v) selected from polyoxyethylene glyceryl esters (in particular Labrasol™), PEGs, and mixtures thereof, suitably at a concentration from 22 to 32%) w/w; and

(6) a methyl glucose ester, in particular methyl glucose dioleate, suitably at a

concentration from 2 to 8% w/w.

Such a formulation suitably also comprises a cellulosic thickening agent, in particular hydroxypropyl cellulose, suitably at a concentration from 1 to 4% w/w. The concentration of the optionally substituted tropolone in such a formulation is suitably from 0.5 to 1.5% w/w. The concentration of the copper salt is suitably from 0.2 to 1.5% w/w or from 0.2 to 0.8% w/w.

Such a formulation also suitably comprises salicylic acid or a salicylate (in particular salicylic acid), suitably at a concentration from 0.5 to 1.5% w/w. It suitably has the form of a gel. In such a formulation, the optionally substituted tropolone is suitably either tropolone, hinokitiol, or more particularly a mixture thereof. The copper salt is suitably a copper carboxylate, for example copper acetate.

The formulation of the invention may be in the form of a fluid, for example a lotion, cream, ointment, varnish, paste, gel or other viscous or semi- viscous fluid, or a less viscous fluid such as might be used in sprays, foams, drops and dropping fluids, or aerosols. A liquid formulation may itself be formulated as suspended (for example aerosolised) liquid droplets within another fluid carrier.

The formulation may in particular be in the form of a solution, lotion, cream or gel. In an embodiment, it is a cream or gel, in particular a gel. It may comprise a formulation which is, or may be, applied to a carrier such as a sponge, swab, brush, pad, tissue, cloth, wipe, dressing (or other material designed for application to the skin) or skin patch, to facilitate its topical administration.

Where the formulation is intended for use in the treatment of body odour, it may contain an anti-perspirant such as an aluminium or aluminium-zirconium salt. It may be in the form of an aerosol, or of a roll-on or "stick" anti-perspirant or deodorant of known type, or of a gel or cream or ointment or in some cases a powder. Such formulations may contain appropriate conventional liquid or solid carriers and excipients. They may contain anti-perspirant and/or deodorant agents, and/or one or more fragrances.

A formulation according to the invention may be incorporated into, and hence applied in the form of, another product such as a hair care or in particular a skin care preparation (for example a skin cleanser, toner or moisturiser, or a shampoo); a deodorant or anti-perspirant; a cosmetic (eg a makeup product); a cleansing preparation (for example a hand, body or facial wash); a pharmaceutical (which includes veterinary) preparation; a cosmeceutical preparation; a toiletry product (for instance a bath or shower additive, a soap or a skin scrub); or a laundry or other fabric treatment product. The formulation may for example be, or be incorporated into, a wash-off skin treatment product such as a skin cleanser, or in particular a leave-on skin treatment product. The invention thus provides, according to a second aspect, a product which

incorporates a topical skin treatment formulation according to the first aspect.

A third aspect of the invention provides a method for preparing a topical skin treatment formulation according to the first aspect, the method involving dissolving a

combination of (a) tropone or a substituted tropone and (b) a copper salt, in a solvent system of the type defined above with reference to the first aspect of the invention. The components of the formulation may be mixed together in conventional manner. For example, the tropolonoid (a) and the copper salt (b) may firstly be dissolved in one or more of the components in which the combination is relatively freely soluble, prior to mixing with any components in which it is less freely soluble and any remaining ingredients of the formulation (for example thickeners, fragrances and/or antioxidants). Stirring and/or heating may be used to aid efficient mixing of ingredients, and/or dissolution of the tropolonoid and copper salt, at appropriate stages during such a process. Either or both of the tropolonoid (a) and the copper salt (b) may be individually solubilised in a suitable respective solvent prior to combining them.

According to a fourth aspect of the invention, there is provided a formulation according to the first aspect, for use in a method of therapy carried out on a living human or animal, in particular human, body. In this context the solvent system should be pharmaceutically acceptable (which includes acceptable for veterinary use). In an embodiment, the formulation is for use in the treatment of a condition which is caused by, transmitted by and/or exacerbated by (in particular either caused or transmitted by, more particularly caused by) microbial activity. The microbial activity may be bacterial or fungal activity, in particular bacterial activity. It may be propionibacterial activity, staphylococcal activity and/or corynebacterial activity, in particular propionibacterial activity.

In some embodiments, in particular when the formulation contains salicylic acid or a derivative thereof, it may be for use in the treatment of a condition (in particular a skin or skin structure condition) which is amenable to treatment by a keratolytic agent. Such conditions include for example acne, dandruff, psoriasis, calluses, corns, keratosis pilaris and warts. The formulation may be for use in the treatment of a condition which affects, or is associated with, follicles such as pilosebaceous follicles. For example, the formulation may be for use against a micro-organism which is present in the follicles, such as a staphylococcus or in particular a propionibacterium such as P. acnes, P. granulosum or P. avidum. It may be for use in the treatment of a condition which affects, or is associated with, the stratum corneum: the formulation may therefore be for use against micro-organisms which are present in the stratum corneum, for example staphylococci or coryneform bacteria, and/or it may be for use against a condition which is amenable to keratolytic treatment of the stratum corneum. In an embodiment of the fourth aspect of the invention, the formulation is for use in the treatment of a skin or skin structure condition. Such a condition may be a primary or secondary infection. It may for example be a superficial or uncomplicated skin infection amenable to local therapy. It may be caused, transmitted and/or exacerbated by a Gram-positive bacterium such as a staphylococcus or propionibacterium. It may be acne or an infection associated with acne. It may be a primary or secondary infection due to S. aureus (including MRS A) or a group A beta haemo lytic

streptococcus. Other skin and skin structure conditions which might be treated according to the invention include infected atopic eczema, superficial infected traumatic lesions, wounds, burns, ulcers, impetigo and folliculitis. In an embodiment, the formulation is for use in the treatment of acne. Acne is a multifactorial disease of the pilosebaceous follicles of the face and upper trunk, characterised by a variety of inflamed and non-inflamed lesions such as papules, pustules, nodules and open and closed comedones. Its treatment can therefore encompass the treatment (which embraces prevention or reduction) of any of these symptoms, and references to use as an anti-acne agent may be construed accordingly. In particular, the treatment of acne encompasses the treatment (including prevention) of lesions and/or scarring associated with acne. It also encompasses the inhibition of propionibacterial activity which could cause or be otherwise associated with acne or its symptoms. In the context of the present invention, it may be or involve the treatment of inflamed acne lesions. Instead or in addition, in particular when the formulation contains salicylic acid or a derivative thereof, it may be or involve the treatment of non-inflamed acne lesions. The formulation of the invention may be for use against an opportunistic infection which is caused, transmitted and/or exacerbated by (in particular caused by) propionibacteria, for instance an infected wound, burn or ulcer. It may be for use against any other infection or condition which involves or can involve

propionibacteria, for example body odour. It may be for use in the treatment (which includes prevention) of a staphylococcal infection, for example due to S. aureus.

In a further embodiment, the formulation may be for use in the treatment (which includes prevention) of body odour, for example in the axillae or feet. Human body odour is formed by the action of commensal skin bacteria, for example members of the genus Corymb acterium, on the odourless secretions of sweat glands. Other members of the bacterial human skin microflora, such as cutaneous propionibacteria and coagulase negative staphylococci, may also contribute to human body odour. Thus the formulation of the invention may be used against one or more such bacteria.

In a specific embodiment, the formulation is for use in the treatment of a condition selected from acne, staphylococcal infections, body odour, and combinations thereof.

In the context of the present invention, treatment of a condition encompasses both therapeutic and prophylactic treatment, of either an infectious or a non-infectious condition. It may involve complete or partial eradication of the condition, removal or amelioration of associated symptoms, arresting subsequent development of the condition, and/or prevention of, or reduction of risk of, subsequent occurrence of the condition. It will typically involve use of the formulation as an antimicrobial (in particular antibacterial) and/or anti-acne agent. It may involve use of the formulation as a keratolytic agent.

Treatment may involve use of the formulation to treat a condition which is caused, transmitted and/or exacerbated by (in particular caused or transmitted by, more particularly caused by), or which is associated with, microbial (in particular bacterial) bio film formation.

The treatment will be administered topically. It may for example involve applying the formulation to the skin daily, or in particular twice daily, as a leave-on formulation. For the treatment of acne, the formulation may be applied to the entire face, or to one or more regions thereof.

A fifth aspect of the invention provides the use of a formulation according to the first aspect, in the manufacture of a medicament (typically a formulation) for the treatment of a condition which is caused by, transmitted by and/or exacerbated by (in particular either caused or transmitted by, more particularly caused by) microbial activity, or of a condition (in particular a skin or skin structure condition) which is amenable to treatment by a keratolytic agent. The condition may be selected from those listed above in connection with the first to the fourth aspects of the invention. It may in particular be acne or body odour, more particularly acne.

A sixth aspect provides a method of treatment of a human or animal patient suffering from or at risk of suffering from a condition which is caused by, transmitted by and/or exacerbated by (in particular either caused or transmitted by, more particularly caused by) microbial activity, or from a condition (in particular a skin or skin structure condition) which is amenable to treatment by a keratolytic agent, the method involving administering to the patient a therapeutically (which term includes prophylactically) effective amount of a formulation according to the first aspect. The formulation may be administered in an antimicrobially and/or keratolytically effective amount. It should be administered topically. In an embodiment of the sixth aspect of the invention, the patient is suffering from the relevant condition. In an embodiment, the patient is a human patient. Again the condition may be selected from those referred to above in connection with the first to the fourth aspects of the invention.

A seventh aspect provides the use of a formulation according to the first aspect of the invention, for non-therapeutic purposes. In an embodiment of this seventh aspect, the formulation is used as a skin care agent for non-therapeutic purposes, for example for cosmetic purposes such as to improve the appearance, feel or smell of the skin. In an embodiment, it is used as an anti-body odour or in particular a deodorising agent for non-therapeutic purposes, for example for cosmetic purposes such as to improve the smell of a region of the body. It may be used as a toiletry or makeup product. According to an eighth aspect of the invention, there is provided the use of a formulation according to the first aspect, and/or of a solvent system as defined in connection with the first aspect, for the purpose of improving the delivery of a combination of (a) tropone or a substituted tropone and (b) a copper salt, to a target site in or on the skin. In this context, improving the delivery of the active combination may involve increasing the rate of its delivery, or the rate of onset of - or persistence of- its activity at the target site; increasing the amount or proportion of it which reaches the target site, or the amount or proportion which reaches the target site within a specified time period, or which remains at the target site after a specified time period; increasing control over the rate or time or quantity of delivery or the rate of onset or persistence of activity; and/or targeting the delivery more accurately to the target site or to a desired delivery time. Improving the delivery of the active combination may involve enhancing the efficacy or the perceived efficacy of the combination at the target site, which may involve increasing the speed and/or magnitude and/or duration and/or locus of the effect (typically a therapeutic effect, for example an antimicrobial and/or anti-acne effect) that the active combination has at the target site, or increasing control over the speed, magnitude, timing, duration or locus of the effect. The invention may be used to achieve any degree of improvement in the delivery of the active combination. The target site may in particular be a follicle, more particularly a pilosebaceous follicle. It may be the stratum corneum.

A formulation according to the invention may be marketed with an indication that it provides improved delivery of the active combination contained within it. Such marketing may include an activity selected from (a) enclosing the formulation in a container or package that comprises the relevant indication; (b) packaging the formulation with a package insert that comprises the indication; (c) providing the indication in a publication or sign that describes the formulation; and (d) providing the indication in a commercial which is aired for instance on the radio, television or internet. The improved delivery may be attributed, in such an indication, at least partly to the nature of the solvent system in which the active combination is dissolved. The invention may involve assessing the delivery of the active combination from the formulation during or after its preparation. It may involve assessing the delivery of the active combination both in the presence and the absence of the solvent system required by the present invention, for example so as to confirm that the solvent system contributes to improved delivery.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and do not exclude other moieties, additives, components, integers or steps. Moreover the singular encompasses the plural unless the context otherwise requires: in particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Preferred features of each aspect of the invention may be as described in connection with any of the other aspects. Other features of the invention will become apparent from the following examples. Generally speaking the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings). Thus features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. Moreover unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.

Where upper and lower limits are quoted for a property, for example for the concentration of a component in a formulation, then a range of values defined by a combination of any of the upper limits with any of the lower limits may also be implied.

In this specification, references to properties such as solubilities, liquid phases and the like are - unless stated otherwise - to properties measured under ambient conditions, ie at atmospheric pressure and at a temperature of from 18 to 25°C, for example about 20°C.

The present invention will now be further described with reference to the following non-limiting examples. Detailed description

These experiments involved preparing topical skin treatment formulations according to the invention, and testing their antimicrobial effects both in vivo and in vitro, as well as their stabilities.

Example 1 - formulations A and B

Two topical skin treatment formulations A and B according to the invention were prepared using the components and concentrations listed in Table 1. Concentrations are quoted as percentages by weight (% w/w). Neither formulation contained a thickener; they therefore had the form of solutions rather than gels. The tropolone and copper (II) acetate were present as an antibacterial combination. The combination is known to be active against the propionibacteria which are implicated in inflammatory acne, and also against corynebacteria (associated with body odour) and staphylococci. Salicylic acid was present in formulation B as an additional active; it is known for use as a keratolytic and anti-acne agent. Thus, formulations A and B may be of use as antibacterial, and in particular anti-acne, agents: they may be used to treat a range of skin and skin structure conditions, including those which are amenable to treatment using a keratolytic agent; body odour; and skin-borne bacterial infections such as staphylococcal infections.

The first four components together represented the solvent system in which the tropolone and copper salt were dissolved. The isopropylamine and EDTA were present to help stabilise the tropolone/copper salt combination in formulation B.

Table 1 - Formulations A & B

Component Formulation Formulation Source

A B

Tropolone 1 0.7 Sigma- Aldrich, UK

Copper (II) acetate 0.1 0.53 Sigma- Aldrich, UK

Salicylic acid 1 Sigma- Aldrich, UK

Isopropylamine 2 Sigma- Aldrich, UK

EDTA 0.5 Sigma- Aldrich, UK

TOTAL 100.0 100.0

The formulation was prepared as follows. Firstly the copper (II) acetate was mixed with the DMI, the homosalate and, where appropriate, the salicylic acid. This mixture was heated and stirred until most of the copper acetate had dissolved. The ethanol, glyceryl diisostearate and, where appropriate, EDTA and isopropylamine were then added, followed by heating and stirring until the solid materials had dissolved.

Tropolone was then added followed by stirring at room temperature.

In both formulations, the solvent system was capable of dissolving the

tropolone/copper acetate combination. However, formulation B provided improved solubility and stability. This is thought to be due to the inclusion of the

isopropylamine and EDTA, which are believed to be able to bind to copper ions and thus prevent formation of insoluble copper-tropolone complexes. The improved solubilising properties of the solvent system in formulation B made it possible to include a higher concentration of the copper acetate active in formulation B than in formulation A. This may also have contributed to the higher antibacterial efficacy of formulation B - see Example 2 below.

Example 2 - antimicrobial activity in vivo (formulations A and B)

These experiments used formulations A and B as described in Example 1 , containing tropolone and copper (II) acetate as antimicrobial agents. The effects of the formulations on the skin surface populations of coagulase-negative staphylococci and propionibacteria were tested on human volunteers. Each test formulation was topically applied, twice daily, to three locations on the face of a healthy human volunteer: the forehead (FH), left cheek (LC) and right cheek (RC). The skin was sampled before the treatment began, and at intervals afterwards whilst the treatment continued, using the method of Williamson-Kligman (Williamson P and Kligman AM, "A New Method for the Quantitative Investigation of Cutaneous

Bacteria", J Invest Dermatol 1965 Dec; 45(6): 498-503). Samples were collected in the mornings, in each case between 10 and 12 hours after the previously applied evening dose and before application of the morning dose.

The samples were assessed for numbers of coagulase-negative staphylococci and Propionibacterium spp by serial dilution and viable counting on suitable media (for the staphylococci, Columbia blood agar (Oxoid) containing 5% defibrinated horse blood (E & O Laboratories), and for the propionibacteria, tryptone (Oxoid, 2%), yeast extract (Oxoid, 1%), glucose (Sigma, 0.5%) agar containing 2 mg/L of furazolidone (Sigma). Colony counts, obtained following incubation at 37°C aerobically for 24 hours in the case of staphylococci and anaerobically for 7 days in the case of propionibacteria, were used to calculate the log number of bacteria per cm² of skin. It should be noted that the overwhelming majority of organisms isolated using the Columbia blood agar containing 5% defibrinated horse blood would be coagulase-negative staphylococci; however, other organisms such as Staphylococcus aureus and cutaneous

corynebacteria would also be isolated using this non-selective medium.

A decline in the numbers of bacteria present at the skin surface, over the course of the treatment period, would indicate that bacteria were being successfully inactivated not only at the skin surface but also in the follicles.

The results are shown in Tables 2a to 2c below. Table 2a relates to formulation A, Tables 2b and 2c to formulation B (tested on two subjects).

Table 2a (formulation A)

Logio change from baseline (TO)

Table 2b (formulation B; subject 1)

Table 2c (formulation B; subject 2)

In both cases, the invented formulations caused a reduction in numbers of both coagulase-negative staphylococci and propionibacteria compared to the pre-treatment values. Formulation B, containing isopropylamine and EDTA, performed better than formulation A, in particular over longer treatment periods.

These data demonstrate that a formulation containing both a tropolonoid and a copper salt, solubilised in the components (i) to (iv), can effectively deliver the two actives to the skin, including to bacteria present in the follicles. Such a formulation is therefore suitable for use as a topical antimicrobial agent, and as a topical anti-acne treatment. The additional salicylic acid component in formulation B means that the two modes of action (the keratolytic effect of the salicylic acid combined with the antibacterial activity of the tropolonoid/copper salt combination) can complement one another to provide an overall more effective treatment against acne. It can be seen that the invented formulations are effective in vivo as antimicrobial agents, against coagulase-negative staphylococci as well as against propionibacteria. They appear to be reaching the targeted follicles and once there, to be successfully acting against the resident bacteria, significantly reducing the numbers of bacteria present at the skin surface following treatment. Moreover, the antibacterial effect appears to be sustained for a significant period of time following each topical application, making the formulations suitable for use as "leave-on" skin treatment products. The data demonstrate the substantivity of the formulations, suggesting that the active substances remain in the stratum corneum, where they can continue to exert their biological effects, for some time after application to the skin. This would be consistent with delivery of the actives to the follicles via the stratum corneum.

Example 3 - formulations C to E Three further formulations C to E according to the invention were prepared using the components and concentrations listed in Table 3. Concentrations are quoted as percentages by weight. Formulations D and E contained a thickener and were in the form of gels.

Formulations C to E contained a combination of hinokitiol and copper (II) acetate as an antibacterial agent. Again, this combination is known to be active against propionibacteria such as Propionibacterium acnes NCTC 737, corynebacteria such as Corymb acterium striatum NCTC 764, and staphylococci. Salicylic acid was present as an additional anti-acne agent.

The first seven components listed in Table 3 combined to form the solvent system. Formulation C contained palmitamine as a stabiliser for the hinokitiol/copper salt mixture. The hinokitiol/copper complex formed has a better solubility profile than that of the tropolone/copper complex, allowing the use of a milder amine stabiliser and the resultant benefit of a reduction in smell. In formulations D and E, it was found possible to solubilise the active substances - even at significantly higher

concentrations - without the need for an amine stabiliser. All three of formulations C to E exhibited better long term stability than formulations A and B.

Table 3 - Formulations C to E

Component Formulation Formulation Formulation

C D E

Hydroxypropyl cellulose 2 1

(thickener)

TOTAL 100.0 100.0 100.0

The PC A glyceryl oleate was sourced from Dr Straetmans GmbH, the THFA

(tetrahydro fur fury 1 alcohol) from Sigma- Aldrich, UK, the Labrasol™ from Gattefosse and the methyl glucose dioleate from Surfachem Group Ltd. The hinokitiol and palmitamine were sourced from Sigma- Aldrich, UK, and the thickener from Honeywill & Stein.

The formulations were prepared as follows. The copper (II) acetate was mixed with the DMI, homosalate, THFA and salicylic acid. This mixture was heated and stirred until the copper acetate had dissolved. Where appropriate Labrasol™, methyl glucose dioleate, PCA glyceryl oleate, glyceryl diisostearate and/or palmitamine were then added, followed by heating and stirring until the solid materials had dissolved. The hinokitiol was then added followed by stirring at room temperature. Where appropriate, hydroxypropylcellulose was added followed by heating and stirring, and the solutions then left to gel for 2 hours. It was found that the use of PCA glyceryl oleate and methyl glucose dioleate, in formulations D and E, allowed gelling to take place using the hydroxypropyl cellulose thickener. Glyceryl diisostearate alone (as in formulation C) appeared to hinder the gelling process.

Example 4 - antimicrobial activity in vivo (formulations C to E) These experiments used formulations C to E as described in Example 3, containing hinokitiol and copper (II) acetate as antimicrobial agents. The effects of the formulations on the skin surface populations of coagulase-negative staphylococci and propionibacteria were tested on human volunteers, using the same method as in Example 2. The results are shown in Tables 4a to 4d below.

Table 4a (formulation C; subject 1)

Logio change from baseline (TO)

Coagulase-negative staphylococci Propionibacteria

Sample site/day

Forehead -3.9 ^■1.9 -3.3 -3.6 -1.9 -3.3

Left cheek -2.6 -2.8 -2.5 -0.6 -1.2 ^■1.0

Right cheek ^■1.7 ^■1.7 -1.6 -1.1 -1.1 -0.9

Table 4b (formulation C; subject 2)

Table 4c (formulation D)

Logio change from baseline (TO)

Coagulase-negative staphylococci Propionibacteria

Sample site/day Logio change from baseline (TO)

Coagulase-negative staphylococci Propionibacteria

Forehead -2.1 -3.5

Left cheek -1.7 -1.6

Right cheek -2.8 -2.4

Table 4d (formulation E)

In all three cases, the invented formulations caused a reduction in numbers of both coagulase-negative staphylococci and propionibacteria compared to the pre-treatment values. Again these data demonstrate that a formulation containing both a tropolonoid and a copper salt, solubilised in the components (i) to (v) and optionally (vi), can effectively deliver the two actives to the skin, including to bacteria present in the follicles. Such a formulation is therefore suitable for use as a topical antimicrobial agent, and as a topical anti-acne treatment. It can be effective in vivo against coagulase-negative staphylococci, as well as against propionibacteria, and can significantly reduce the numbers of bacteria present at the skin surface following treatment. Moreover, the antibacterial effect appears to be sustained for a significant period of time following each topical application, making the formulation suitable for use as a "leave-on" skin treatment product.

Example 5 - formulation F

A gel formulation F according to the invention was prepared using the components and concentrations listed in Table 5. Concentrations are quoted as percentages by weight.

This formulation contained a mixture of tropolone and hinokitiol, together with copper (II) acetate. Surprisingly, it was found that the presence of the hinokitiol improved the stability of the tropolone/copper salt combination, making it possible to solubilise the active substances, in a stable form, without the need for an amine or chelating agent. The formulation was observed to be physically stable (ie no precipitation or significant colour change) when stored for two weeks at either 4°C, room temperature or 40°C.

Table 5 - Formulation F

The formulation was prepared as follows. The copper (II) acetate was mixed with the DMI, homosalate, THFA and salicylic acid. This mixture was heated and stirred until the copper acetate had dissolved. The Labrasol™, methyl glucose dioleate and PCA glyceryl oleate were then added, followed by heating and stirring until the solid materials had dissolved. The hinokitiol was then added followed by stirring at room temperature, and afterwards the tropolone, again followed by stirring at room temperature. Finally the hydroxypropylcellulose was added, followed by heating and stirring, and the solution was left to gel for 2 hours.

Example 6 - formulations G to J Further skin treatment gel formulations G to J were prepared, according to the invention, using the components and concentrations listed in Table 6. Concentrations are quoted as percentages by weight. Formulation J was a "placebo" version of formulations G and H, containing no copper salt or tropolonoid.

Table 6

The DMI, THFA, ethanol, salicylic acid, copper (II) acetate, tropolone and hinokitiol were sourced from Sigma, UK; the homosalate from TCI, UK; the PCA glyceryl oleate as DermoFeel™ P-30 from Dr Straetmans Chemische Produkte GmbH; the Labrasol™ from Gattefosse; the methyl glucose dioleate from Surfachem, UK; the PEG 400 from Fisher Scientific, UK; and the hydroxypropyl cellulose thickener (GF Pharm) from Ashland Inc, UK.

Formulations G and H were prepared as follows. The copper (II) acetate was mixed with the DMI, homosalate and THFA. This mixture was heated and stirred until the copper acetate had dissolved. The Labrasol™, ethanol, PEG 400, methyl glucose dioleate, salicylic acid and PCA glyceryl oleate were then added, followed by heating and stirring until the solid materials had dissolved. The tropolone and/or hinokitiol were then added as required, followed by heating and stirring until the solid materials had dissolved. Finally the hydroxypropyl cellulose was added, followed by heating and stirring, and the solution was left to gel for 2 hours.

Formulation J was prepared in an analogous fashion, but omitting the copper salt and tropolonoids.

In formulation G, the mixture of tropolone and copper (II) acetate was not fully soluble: it initially formed a suspension which proceeded to settle out during storage. Surprisingly, however, it was found that the additional hinokitiol in formulation H improved the stability of the tropolone/copper salt combination, making it possible to solubilise the active substances in a stable form. Formulation H had an acceptable appearance and odour and an even consistency, the copper acetate, tropolone and hinokitiol actives being completely dissolved in the solvent system.

Formulations H and J were stored in sealed vials for two weeks at either room temperature or 40°C, in order to assess their stability. Formulation H remained physically stable (ie no precipitation, clouding or significant colour change) over the storage period. The placebo formulation J also remained stable during this period. Example 7 below demonstrates that the active-containing formulations G and H had good antibacterial activity.

Example 7 - antimicrobial activity in vitro (formulations G to J)

The in vitro antibacterial activities of formulations G to J, against both

propionibacteria and corynebacteria, were assessed as described below.

Test micro-organism

The first test organism used was Propionibacterium acnes NCTC 737. This is a propionibacterial strain and is the type strain of the genus; it is fully susceptible to antibiotics. The propionibacteria are clinically significant due to their involvement in acne. They are also opportunistic pathogens in compromised hosts. Activity observed against these micro-organisms is expected to be a good predictor of activity against acne.

The propionibacteria were cultured and maintained on Wilkins-Chalgren Anaerobe Medium (agar and broth) at pH 7.0; all cultures were incubated anaerobically at 37°C for 72 hours.

The second test organism used was Corynebacterium striatum NCTC 764. The coryneform bacterium is closely related to the aerobic diphtheroids implicated in body odour. C. striatum was cultured and maintained on Mueller-Hinton medium (agar and broth); all cultures were incubated at 37°C for 24 hours. The following tests were carried out to assess antimicrobial activity against the test organisms.

(a) Minimum inhibitory concentration (MIC) assay

This is a standard international method for quantitatively assessing the antimicrobial activity of a formulation in a liquid medium. The method used a sterile 96-well microtitre plate, capable of holding about 200 μΐ of liquid per well. The wells contained liquid culture medium and ranges of decreasing concentrations of the relevant test formulation in doubling dilutions (eg 1000, 500, 250, 125.. ^g/ml, etc.. down to 0.49 μg/ml). The culture medium was as described above.

The wells were inoculated with a liquid suspension of freshly grown micro-organism and incubated under the conditions described above. After incubation, the microtitre plate was examined visually for cloudiness in each well, which would indicate microbial growth. The MIC value was recorded as the lowest concentration of test formulation required to inhibit microbial growth, ie the lowest concentration for which the liquid in the well remained clear.

The assays were conducted in triplicate and included both negative (culture medium with no micro-organisms) and positive (culture medium plus micro-organism) controls.

Since inhibition does not necessarily indicate killing of microbial cells, merely that growth as visible to the naked eye has been inhibited, it is desirable to conduct a further test (the MBC assay described below) to establish the concentration of the test formulation needed to kill the test organism.

(b) Minimum bactericidal concentration (MBC) assay

This assay, normally carried out after an MIC assay, determines the minimum concentration of a test formulation that is lethal to the micro-organism being tested.

Following an MIC assay, a 5 μΐ sample was withdrawn from the first microtitre well that showed positive growth and from all the subsequent wells that showed no growth. These samples were then individually sub-cultured on antibiotic- free agar medium, under the incubation conditions described above. Following incubation they were examined visually for microbial growth. The MBC was taken to be the lowest test formulation concentration for which the incubated sample showed no growth.

The ratio of MIC to MBC should ideally be as close to 1 as possible. This facilitates selection of the lowest possible effective concentration of a test formulation with a reduced risk of selecting a sub-lethal concentration which could promote resistance or allow the target microbial population to recover. (c) Disc diffusion assay (DDA)

This is an internationally recognised standard method for qualitatively assessing the antimicrobial activity of a compound/formulation.

A sterile paper disc was impregnated with a sample (10 μΐ) of the test formulation. The disc was then placed on an agar plate onto which the test micro-organism had been inoculated. The plate was then incubated under the conditions described above, following which it was examined visually for signs of microbial growth. If the test formulation had antimicrobial activity, a circular zone of no growth would be obtained around the disc. The diameter of this zone of "inhibition" was measured using a ProtoCOL™ automated zone sizer (Synbiosis, Cambridge, UK). In general, a greater diameter and/or area of the zone of inhibition indicates a greater antimicrobial activity in the relevant test formulation, although other factors such as the test formulation, or the mobility of its constituents through the agar gel, may also influence the result.

Example 7a - activity against P. acnes This example used Propionibacterium acnes NCTC 737 as the test organism. MIC, MBC and DDA assays, as described above, were carried out using the test

formulations G, H and J. All experiments were performed in triplicate. The results are shown in Table 7 below.

Table 7

T The primary value represents the concentration of the formulation as a whole; the concentration of active ingredients (Cu (II) acetate, tropolone and hinokitiol) is included in parentheses. These data show that formulation J (the placebo) had no observable activity against P. acnes NCTC 737. In contrast formulations G and H, containing the tropolonoid(s) and copper salt, demonstrated significant activity against P. acnes 737. This indicates the likely activity of the invented formulations as anti-acne agents, the propionibacteria being implicated in acne.

Example 7b - activity against C. striatum

This example used Corynebacterium striatum NCTC 764 as the test organism. MIC, MBC and DDA assays, as described above, were carried out using the test

formulations G, H and J. All experiments were performed in triplicate. The results are shown in Table 8 below.

Table 8

The primary value represents the concentration of the formulation as a whole; the concentration of active ingredients (Cu (II) acetate, tropolone, and hinokitiol) is included in parentheses. * MIC (and therefore also MIC/MBC ratio) could not be determined due to the opacity of the growth media when mixed with the formulations.

The Table 8 data show that the placebo formulation J demonstrated some activity against C. striatum 764. However, the invented formulations G and H demonstrated an elevated level of activity against the micro-organism. This indicates the likely activity of the invented formulations in the treatment (including the prevention) of body odour, a condition in which the corynebacteria are implicated.

Claims

A topical skin treatment formulation containing a combination of (a) tropone or a substituted tropone and (b) a copper salt, the combination being dissolved in a solvent system, wherein the solvent system comprises:

(i) dimethyl isosorbide (DMI);

(ii) a CI to C9 alkyl salicylate; and

(iii) a glyceryl fatty acid ester.

A formulation according to claim 1 , wherein the component (a) is selected from hinokitiol, tropolone, and mixtures thereof.

A formulation according to claim 1 or claim 2, wherein the component (ii) is homosalate.

A formulation according to any one of the preceding claims, wherein the component (iii) is a glyceryl oleate such as L-pyrrolidone carboxylic acid (PCA) glyceryl oleate.

A formulation according to any one of the preceding claims, wherein the solvent system additionally comprises (iv) an alcohol.

A formulation according to any one of the preceding claims, wherein the solvent system additionally comprises (v) a polyoxyalkylene-based solvent selected from polyoxyalkylene glyceryl esters, polyalkylene glycols, and mixtures thereof, in particular from polyethoxylated glyceryl esters and mixtures thereof.

A formulation according to any one of the preceding claims, wherein the solvent system additionally comprises one or more components selected from (vi) CI to C4 alkyl glucose esters; salicylic acid and derivatives thereof;

aliphatic amines; chelating agents; and combinations thereof.

8. A formulation according to any one of the preceding claims, which is in the form of a solution, lotion or gel.

9. A product which incorporates a formulation according to any one of the

preceding claims.

10. A formulation according to any one of claims 1 to 8, for use in a method of therapy carried out on a living human or animal, in particular human, body.

11. A formulation according to any one of claims 1 to 8, for use in the treatment of a condition which is caused by, transmitted by and/or exacerbated by microbial activity, or of a condition (in particular a skin or skin structure condition) which is amenable to treatment by a keratolytic agent.

12. A formulation according to any one of claims 1 to 8, for use according to claim 11 , wherein the condition is selected from acne, staphylococcal infections, body odour, and combinations thereof.

13. A method of treatment of a human or animal patient suffering from or at risk of suffering from a condition which is caused by, transmitted by and/or exacerbated by microbial activity, or from a condition (in particular a skin or skin structure condition) which is amenable to treatment by a keratolytic agent, the method involving administering to the patient a therapeutically (which term includes prophylactically) effective amount of a formulation according to any one of claims 1 to 8.

14. Use of a formulation according to any one of claims 1 to 8, for non-therapeutic purposes.

15. Use of a formulation according to any one of claims 1 to 8, and/or of a solvent system as defined in any one of claims 1 to 8, for the purpose of improving the delivery, to a target site in or on the skin (in particular a pilosebaceous follicle), of a combination of (a) tropone or a substituted tropone and (b) a copper salt.