Evidence for a colon chalone

The molecular weight fractions of 10,000-50,000 daltons prepared from "used" medium obtained during cultivation of human colon carcinoma cells (SW-48) in vitro inhibited the proliferation and DNA synthesis of these cells. Fractions exceeding 50,000 daltons were not inhibitory; those less than 10,000 daltons were cytotoxic. The inhibitory fraction did not affect either proliferation of human fibroblasts or transformation of human lymphocytes in vitro. Similar fractions from the colon mucosa of other species inhibited the proliferation of SW-48 cells, whereas extracts of dog jejunum or lung did not. This mitotic inhibition was completely reversible and could be destroyed by preincubation with trypsin. Therefore, colon cells appear to contain a cell- (but not species) specific, endogenous mitotic inhibitor or chalone.