Inhibition of tubulin-microtubule polymerization by drugs of the Vinca alkaloid class.

A series of Vinca alkaloids were found to block polymerization of crude tubulin extracts of porcine brain in a dose-dependent manner. This appears to be a specific effect occurring at low concentrations of drug. The concentration of vinblastine that prevents polymerization by 50% was 4.3 x 10(-7) mole/liter for a tubulin concentration of 3.0 mg/ml, and this concentration is consistent with levels achieved in vivo following routine pharmacological doses in humans.