An endogenous colon mitosis inhibitor reduces proliferation of colon carcinoma cells (HT 29) in serum-restricted medium.

Extracts of mouse intestine contain a colonic epithelial mitosis inhibitor that has recently been purified and identified as a tripeptide (pGlu-His-GlyOH). In order to elucidate further the biological characteristics of this peptide, the effect of the tripeptide on cell proliferation in a human colon carcinoma cell line (HT 29) was examined. The incorporation of tritiated thymidine was significantly reduced at 20-30 h after addition of the tripeptide. The dose-response relationship was bell-shaped with loss of inhibitory effect at high or low doses. The number of cells were significantly reduced at a peptide concentration of 10(-8) M at 24 h, but not at 48 or 72 h after addition of the peptide. The inhibition was reversible, and was only observed when the cells were grown in a serum-restricted medium (1%). The inhibitory effect was abolished by increasing the serum content to 10% or adding insulin to the medium.