Tumor-induced growth-inhibitory activity isolated from the Yoshida ascites fluid by extraction with methanol

Growth-inhibitory activity was isolated from the Yoshida ascites fluid by sequential precipitation with polyethylene glycol, extraction with methanol, LH 20 Sephadex chromatography and preparative agarose gel electrophoresis. The cell non-specific activity was tumor-related as far as analogous fractions prepared from normal sera were inactive. Flow cytometric analysis indicates that the inhibition of cell growth was caused by blockage of the G1-S and possibly the G2-M phase transitions. The active component migrates electrophoretically associated to an unidentified alpha 1-antigen. In aqueous solution the molecular size of the inhibitor is ill defined, due to a tendency to autoaggregation and hydrophobic interaction with the chromatographic media. The molecular weight of the inhibitor as estimated by LH 20 Sephadex chromatography in methanol is approximately 350 daltons. This chromatographic fraction contains prostaglandin-E2 cross-reactive material in amounts suggesting the participation of a prostaglandin derivative in the observed growth-inhibitory activity.