Radioimmunoassays for the Vinca alkaloids, vinblastine and vincristine.

Radioimmunoassays for the chemotherapeutic alkaloids, vinblastine (VLB) and vincristine (VCR) were developed that could determine less than 1 pmol of each compound in the homologous hapten-antibody reaction. The anti-VCR serum bound VCR 200 times more effectively than VLB, demonstrating a high specificity in spite of the structural similarity of the drugs. Several other chemotherapeutic drugs showed no significant cross-reactivity. The assays were used to measure plasma levels of the alkaloids in rabbits treated with the drugs and to determine immunoreactive drug equivalents in extracts of the periwinkle plant following fractionation by high-pressure liquid chromatography.