A new endogenous inhibitor for mouse melanoma cells

A standardized protocol for assessing regulators of pigmentation

Varied effects of chemical or biological compounds on mammalian pigmentation have been reported by many groups, but to date, no standardized method has established necessary and/or optimal parameters for testing such agents. A standardized method has been developed to screen compounds with potential effects on pigmentation. The protocol comprises basic parameters to analyze melanogenic effects and allows for further characterization of candidate compounds, providing important insights into their mechanism of action. In this protocol (termed STOPR, for standardized testing of pigmentation regulators), compounds are initially screened using purified tyrosinase and are then tested on melanocytes in culture. After treatment of melanocytes with potentially bioactive compounds, cell proliferation and viability, total melanin accumulated, and melanogenic potential are measured. This protocol is an important first step in characterizing chemical regulation of effects on melanogenesis. When bioactive candidate compounds are identified, testing may proceed for pharmacological or otherwise commercial applications in coculture and/or organ culture models followed by in vivo testing. As an application of this method, results for compounds known to stimulate and/or inhibit melanogenesis (including arbutin, hydroquinone, kojic acid, melanocyte-stimulating hormone, and thymidine dimers) as well as some commercial skin whiteners are reported.

The identification of a cell culture inhibitor in a tumour extract

An extract of Harding-Passey mouse melanoma was found to inhibit the proliferation of the same cell line grown in culture when measured by both thymidine incorporation and by the increase in cell number. The active ingredient was purified by ultrafiltration, column chromatography and preparative electrophoresis. The purified material was identified by mass spectrometry and by gas chromatography as spermidine. The partially purified material reversed the methylglyoxal Bis-guanyl hydrazone (Methyl-GAG) inhibition of cultured cells to the same extent as spermidine. Very low concentrations of Methyl-GAG were found to suppress the spermidine inhibition of thymidine incorporation into cells. The inhibitor extracted from melanoma tumours behaved in the same way as spermidine at all Methyl-GAG concentrations. Thus, it is unlikely that the active ingredient in the biological extract is anything other than spermidine.