Quantitative turbidimetric assay for potency evaluation of colchicine-like drugs.

A modified Shelanski method has been applied to quantitatively compare cochicine-like drugs with regard to their inhibition of the rate of rat brain tubulin polymerisation $\text{in vitro}$. The potency of six known microtubule-disrupting drugs was in increasing order: griseofulvin < colchicine < podophyllotoxin < rotenone < vinblastine < vincristine. Two other drugs which have been claimed to interfere with microtubules, melatonin and isopropyl-n-phenylcarbamate were inactive. Methyl benzimidazol-2-yl-carbamate showed only a marginal effect. The usefulness of the method in screening colchicine-like drugs is discussed.