A 125I-radiolabelled probe for vinblastine and vindesine radioimmunoassays: applications to measurements of vindesine plasma levels in man after intravenous injections and long-term infusions.

The transformation of vinblastine into a reactive acid azide was used for the preparation of a vindesine-glycyl-tyrosine conjugate. This conjugate was radiolabelled [125I] and used as a tracer for the radioimmunoassay of vinblastine and vindesine with antisera developed by the Eli Lilly Research Laboratories and by ourselves. Its higher specific activity as compared to tritiated vinblastine significantly increases the sensitivity of the assay (0.05 microgram/1 as compared to 0.6 microgram/1). It was then possible to monitor vindesine plasma levels for more than 60 h after intravenous bolus injection and to evaluate the elimination rates more accurately. When plasma levels were also measurable using tritiated vinblastine a satisfactory agreement was observed with determinations performed with radioiodinated vindesine-glycyl-tyrosine. Furthermore, the use of a gamma-emitting probe simplifies the radioimmunoassay procedure and accordingly increases its reproducibility. A few examples of vindesine level measurements in human plasma collected after bolus intravenous injection and during long-term infusion are given.