Development of an in vitro primary screen for skin depigmentation and antimelanoma agents

An in vitro cell culture assay was developed to identify inhibitors of melanogenesis and agents which produce cytostatic or cytotoxic effects specifically in melanocytes. A total of 50 compounds related to tyrosine, dihydroxyphenylalanine, and hydroquinone (HQ) were tested in vitro in order to determine their effects upon a murine melanocyte cell line, Mel-Ab, that produces copious amounts of melanin in culture. The agents that demonstrated an inhibition of growth or pigment production by 50% (IC50) at < 100 micrograms/ml were considered active. The cytotoxicity of melanocyte-active compounds were also tested in vitro on a control nonmelanocyte cell line (HT 1080), using a simple crystal violet staining method to quantitate adherent cell number after treatment. The cell culture assay was validated with known potent melanocyte cytotoxic agents, including HQ and 4-S-cysteaminylphenol (4-S-CAP). Although most cytotoxic chemicals were nonspecific in this primary screen (i.e. killing both Mel-Ab and HT-1080 cells), several of the compounds tested exhibited high melanocyte-specific cytotoxicity, similar to HQ and 4-S-CAP. Potentially these compounds may be useful as either antimelanoma or skin depigmentation agents. All of the compounds identified as active in this primary screen were cytotoxic or cytostatic to melanocytes, except for the methyl ester of gentisic acid, which uniquely inhibited the de novo synthesis of melanin without cytotoxicity.