Targeting melanin-associated disorders mediated by related-dicopper enzymes: from structure/activity relationship to biological applications – 2Cu-TargMelanin

The project is focused on tyrosinase (Ty), a copper-containing metalloenzyme which to date remains poorly characterized. Ty belongs to the type-3 copper-containing enzymes that contain a coupled binuclear active site. Ty is the key enzyme involved in melanins (protective pigments) biosynthesis. It catalyzes the rate-limiting step, the oxidation of the amino acid tyrosine to 3,4-dihydroxyphenylalanine (Dopa) and subsequently to Dopa-quinone, which is then converted by multi-step reactions to melanin pigments. Ty is widely distributed in nature in many organisms with slightly different forms. In mammals, the final products of Ty activity are melanins, pigments responsible for the skin, eyes and hair color. Melanins are produced in melanocytes, cells located in the basal layer of the dermis after further chemical transformations involving Ty and Ty-related proteins (TRP-1 and TRP-2). This multistep process leads to the formation of eumelanin (the most protective melanins). Accumulation of high levels of melanins causes a variety of disorders as cutaneous hyperpigmentation (melasma, naevi'..) and ocular retinitis pigmentosa. A number of treatments exist for these conditions and the most prominent ones function as inhibitors of Ty activity. Ty inhibition is thus now the well-known approach against increased production and accumulation of melanins. Despite the numbers of Ty inhibitors described in vitro, very few are efficient under clinical trials. Among them the most widely used (1,4-dihydroquinone and kojic acid ) in medical prescriptions to achieve hypopigmentation and skin-whitening agent for cosmetic products, have been proven to be cytotoxic and mutagenic agents. In this context there is an urgent need for new strategies for the rational conception of Ty-inhibitors. In addition to efficiency of inhibition (low KI) others parameters related to cytotoxicity, solubility, skin and cellular penetration parameters should be considered. Therefore the main objectives of this project are to enhance the fundamental knowledge about inhibition of Ty and its related proteins via a novel and rational approach based on bio-inorganic chemistry, combining enzymes and models studies. Understanding the way of action of our targets would allow rationally designed inhibitors to emerge. Such products will be searched among a family of natural compounds recently discovered by one of the partners as potent Ty inhibitors and from design of new compounds. Aware of the health and efficacy concerns related to existing drugs, we consider the present multidisciplinary approach to develop specific and safe inhibitors. The partners involved in the project combine complementary expertise associating enzyme biochemistry, bioinorganic chemistry, computational chemistry and organic synthesis. Iterative feedbacks between partners are of importance to take advantage of all these expertise. The specific aims of the proposed research are as follows: i) From models and enzymes studies (experimental and theoritical), establishment of structural and mechanistic aspects of inhibition in Ty for the rational design of inhibitors, ii) Design and synthesis of new specific inhibitors, iii) Biological evaluation of synthesized inhibitors, including tests on enzymes, cellular tests on human melanocytes and tests to evaluate the cytotoxic effects. There is no doubt that a better understanding at a molecular level will open new fields for future development of potent and specific inhibitors for pharmaceutical and cosmetic industries.