Abstract
The cytotoxicity of the (-)- and (+)-isomers and the quinone metabolite gossypolone prepared from the naturally occurring polyphenolic dialdehyde gossypol were compared using two human melanoma cell lines (SK-mel-19 and SK-mel-28) with a similar growth rate, one melanotic (melanin content of 69 pg/cell) and one amelanotic (melanin content of 10 pg/cell). Results from two viability assays (MTT and flow cytometry) showed that the cytotoxicity of racemic gossypol was identical for both cell lines (50% inhibition of cell growth IC50 = 22 microM). Gossypolone at equimolar concentrations was inactive in the amelanotic cell line and as potent as racemic gossypol in the melanotic cell line. (-)-Gossypol was significantly more active in both cell lines compared with the (+)-isomer. The cytotoxic effect of (-)-gossypol was both concentration and time dependent. Under serum-free conditions, the cytotoxicity of both enantiomers was increased, suggesting that serum protein binding may play a role in the differential toxicity of these isomers in vitro. Morphological changes after exposure to (-)-gossypol included shrinkage and loss of adherence. Cell sensitivity to the (-)-isomer was five-fold greater (IC50 = 4 microM) using a clonogenic assay. At equimolar concentrations, (-)-gossypol was more cytotoxic to both cell lines than the clinically used drugs cisplatin, dacarbazine and melphalan. The results of this study suggest that (-)-gossypol may be of potential therapeutic benefit in melanoma patients.
Published Version
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