Exploitation of melanogenesis to develop antitumour agents specific for malignant melanoma

2002 Fiscal Year Final Research Report Summary

• Project/Area Number: 13670229
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Experimental pathology
• Research Institution: Fujita Health University
• Principal Investigator: INOUE Shigeki Fujita Health University School of Health Sciences, Departments of Clinical Immunology, Professor, 衛生学部, 教授 (30084601)
• Co-Investigator(Kenkyū-buntansha): YUKITAKE Jun Fujita Health University School of Health Sciences, Departments of Clinical Immunology, Assistant Professor, 衛生学部, 講師 (20288468) ; WAKAMATSU Kazumasa Fujita Health University School of Health Sciences, Departments of Chemistry, Associate Professor, 衛生学部, 助教授 (80131259) ; ITO Shousuke Fujita Health University School of Health Sciences, Departments of Chemistry, Professor, 衛生学部, 教授 (70121431)
• Project Period (FY): 2001 – 2002
• Keywords: Melanoma / 4-S-Cysteaminylphenol / Enantiomer / Tyrosinase / Melanogenesis

Research Abstract

Melanogenesis appears to be a unique target to develop antitumor agents specific for malignant melanoma. Among the antimelanoma compounds that we have examined, 4-S-cysteaminylphenol (4-S-CAP), a phenolic amine, was found to have the most promising antimelanoma effects. However, one problem with 4-S-CAP is its strong hypotensive effect which limits the dose that can be administered in vivo. In an attempt to overcome this problem, a potentially useful approach would appear to be to use enantiomers of 4-S-CAP homologues. We hoped mat one of the enantiomers would preferentially act as a substrate for melanoma tyrosinase while the other enantiomer might carry the hypotensive effect. Based on this rationale, we synthesized enantiomers (99% enantiomer excess) of α-Me-4-S-CAP and α-Et-4-S-CAP by coupling 4-hydroxythiophenol with the oxazolines obtained from (R)- and (S)- enantiomers of 2-amino-1-propanol and 2-amino-1-butanol, respectively. We examined the efficacy of the enantiomers of α-Me- and Et-4-S-CAP as substrates for mouse tyrosinase. The order of V_<max> values was (R)-α-Me-4-S-CAP > (R)-α-Et-4-Sr-CAP > (S)-α-Me-4-S-CAP > 4-S-CAP > (S)-α-Et-4-S-CAP. In vitro experiments showed that 50% inhibition of melanoma cell growth was achieved by all four enantiomers at ca. 10 μM for pigmented B16-F1 cells while they were 50 times less toxic to non-pigmented B16-G4F cells and were even less toxic to mouse 3T3 fibroblasts. In vivo experiments showed that intraperitoneal administration of (R)-α-Me-4-S-CAP and (S)-α-Et-4-S-CAP for 5 days (days 11-15 after tumor challenge) inhibited the subcutaneous growth of B16 melanoma by 50-60% at days 17-20 (P0.05) while the corresponding enantiomers were much less effective. These results indicate that melanogenesis is a principal mediator of the cytotoxicity of both (R)-α-Me-4-S-CAP and (S)-α-Et-4-S-CAP while tyrosinase plays a major role only in the cytotoxicity of (R)-α-Me-4-S-CAP.