Cytostatic activity of chlamydocin, a rapidly inactivated cyclic tetrapeptide

Abstract Chlamydocin is a cyclic tetrapeptide with an epoxi group which was isolated from cultures of Diheterospora chlamydosporia . In cultures of P- 815 mouse mastocytoma cells, the coumpound has the highest cytostatic activity found so far in our laboratory (higher than actinomycin D, amethopterin, colchicine, vincristine and others). Toxicity and oncostatic activity in animals upon drug injection is comparatively low, probably due to the fact that the drug is inactivated rapidly in blood (half life about 2·5 min). The chlamydocin-inactivating capacity of serum is lost upon heating for 30 min at 56 °C. When given as continuous or interrupted intravenous or intra-arterial infusion, chlamydocin is much more toxic in rats than by injection. Inhibition of growth of the Walker tumor is somewhat better by infusion than by injection and is abtained with much lower doses.