VINCA ALKALOIDS ENHANCE THE HALF-LIFE OF TUMOR ORNITHINE DECARBOXYLASE

Naturally occurring vinca alkaloids, vincristine and vinblastine, at m icromolar concentrations enhanced the ornithine decarboxylase activity in a dose-response manner in primary cultures of Ehrlich ascites carc inoma cells. After 8 h of culture in the presence or absence of vinbla stine, cycloheximide was added to the medium, a 4.5-fold increase in t he half-life of the ornithine decarboxylase activity was observed in v inblastine-treated cells. This effect is probably due to the inhibitio n of the intracellular enzyme degradation by the vinca alkaloids.