Depigmentation of black guinea pig skin by topical application of cysteaminylphenol, cysteinylphenol, and related compounds.

Phenol and catechol were combined with sulfur to develop new melanocytotoxic agents. Among these synthetic compounds, 4-S-cysteaminylphenol (4-S-CAP) and 4-S-cysteinylphenol (4-S-CP), which showed an in vivo antimelanoma effect, were evaluated for cytotoxicity to normal epidermal melanocytes using hydroquinone (HQ) as the control. Topical application of 4-S-CAP on the skin of black guinea pigs revealed a marked depigmentation of black skin. 4-S-Cysteinylphenol also showed some depigmenting potency. 2-S-Cysteinylhydroquinone, which was made by combining cystine with HQ, on the other hand, did not show any depigmenting effect. Depigmentation of black skin by 4-S-CAP appeared to derive from: a decrease in the number of functioning melanocytes; a decrease in the number of melanosomes synthesized within the melanocytes and transferred to keratinocytes; and destruction of the membranous organelles of the melanocytes. None of these degenerative changes was observed in the keratinocytes, indicating the selective effect of 4-S-CAP on melanocytes.