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.