Selective in vivo accumulation of N-acetyl-4-S-cysteaminylphenol in B16F10 murine melanoma and enhancement of its in vitro and in vivo antimelanoma effect by combination of buthionine sulfoximine.

Abstract

In order to develop a new chemotherapeutic agent based on exploitation of the specific metabolic pathway of malignant melanoma, a phenolic thioether, N-acetyl-4-S-cysteaminylphenol (NA-CAP), the substrate of melanin-forming enzyme, tyrosinase was developed. Our previous in vivo studies have clearly shown that this compound has a significant and selective melanocytotoxicity and antimelanoma effect. This study further examined the specificity of the antimelanoma effect of NA-CAP through the study of biodistribution and accumulation of NA-CAP in B16F10 melanoma-bearing mice. We also tested the antimelanoma effect of NA-CAP by combination treatment with buthionine sulfoximine on the growth of in vitro culture cells and in vivo B16F10 melanoma lung colonies. We found a selective accumulation of 14C-labeled NA-CAP into s.c. transplants and lung colonies of melanoma grown in C57BL mice. This accumulation was mediated by selective covalent binding of NA-CAP to the melanoma tissues. The combination of NA-CAP and buthionine sulfoximine significantly increased the chemosensitivity of B16F10 melanoma cells in vitro and reduced the number of in vivo melanoma lung colonies. We conclude that NA-CAP acts as an alkylating agent to melanoma tissue and that the combination of buthionine sulfoximine enhances the therapeutic index of this potent melanoma-specific drug through the depletion of tissue glutathione.