DETERMINATION OF FLAVOPIRIDOL (L86-8275, NSC-649890) IN HUMAN PLASMA BY REVERSED-PHASE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

Purpose: Flavopiridol is a flavone which inhibits several cyclin-depen dent kinases, and exhibits potent growth inhibitory activity against a number of human cell lines both in vitro, and when grown as xenograft s in mice. It is currently being evaluated in a phase I clinical trial at the National Cancer Institute. The objective of this project was t o develop and validate an analytical method for the assay of flavopiri dol to be studied during clinical trials. Methods: Flavopiridol was is olated from human plasma samples by extraction with t-butylmethyl ethe r following alkalinization with borate buffer (pH 8.0). The extract wa s evaporated, the residue was dissolved in mobile phase, and analyzed by reverse-phase high-pressure liquid chromatography. Chromatography w as accomplished with a polymer-based C-18 column eluted with a mobile phase consisting of methanol-phosphate buffer, pH 11.0 (53:47 v/v). El ectrochemical detection (ECD) was employed. Results: Flavopiridol was recovered from human plasma with an efficiency of 85-87%. Calibration curves were linear over the concentration range 10-500 nM (4.4-219 ng/ ml). Plasma standard concentrations were measured with an accuracy and precision ranging from 3.2% to 10%. Regression analysis of flavopirid ol concentrations of 15 clinical trial plasma samples ranging in conce ntration from approximately 50 to 4000 muM quantitated by both ECD and mass spectrometry showed close agreement. The equation of the regress ion line was y=1.02x+8 with a correlation coefficient of 0.969. Contin uous infusion of flavopiridol in four patients for 72 h at a rate of 5 0 mg/m(2) per day, resulted in mean steady-state plasma concentrations of from 200 to 300 nM. Levels declined in a biexponential manner foll owing termination of the infusion, falling to approximately 10 nM afte r 48 h. Conclusions: An analytical method for the assay of flavopirido l in human plasma was developed with sensitivity to at least 10 nM. Th e assay is accurate, precise and specific, and is suitable for determi nation of plama flavopiridol concentrations for pharmacokinetic studie s during clinical trials.