Background

Flavopiridol is a cyclin-dependent kinase inhibitor in phase II clinical development for treatment of various forms of cancer. When administered with a pharmacokinetically (PK)-directed dosing schedule, flavopiridol exhibited striking activity in patients with refractory chronic lymphocytic leukemia. This study aimed to evaluate pharmacogenetic factors associated with inter-individual variability in pharmacokinetics and outcomes associated with flavopiridol therapy.

Methodology/Principal Findings

Thirty-five patients who received single-agent flavopiridol via the PK-directed schedule were genotyped for 189 polymorphisms in genes encoding 56 drug metabolizing enzymes and transporters. Genotypes were evaluated in univariate and multivariate analyses as covariates in a population PK model. Transport of flavopiridol and its glucuronide metabolite was evaluated in uptake assays in HEK-293 and MDCK-II cells transiently transfected with SLCO1B1. Polymorphisms in ABCC2, ABCG2, UGT1A1, UGT1A9, and SLCO1B1 were found to significantly correlate with flavopiridol PK in univariate analysis. Transport assay results indicated both flavopiridol and flavopiridol-glucuronide are substrates of the SLCO1B1/OATP1B1 transporter. Covariates incorporated into the final population PK model included bilirubin, SLCO1B1 rs11045819 and ABCC2 rs8187710. Associations were also observed between genotype and response. To validate these findings, a second set of data with 51 patients was evaluated, and overall trends for associations between PK and PGx were found to be consistent.

Conclusions/Significance

Polymorphisms in transport genes were found to be associated with flavopiridol disposition and outcomes. Observed clinical associations with SLCO1B1 were functionally validated indicating for the first time its relevance as a transporter of flavopiridol and its glucuronide metabolite. A second 51-patient dataset indicated similar trends between genotype in the SLCO1B1 and other candidate genes, thus providing support for these findings. Further study in larger patient populations will be necessary to fully characterize and validate the clinical impact of polymorphisms in SLCO1B1 and other transporter and metabolizing enzyme genes on outcomes from flavopiridol therapy.

A high-performance liquid chromatographic assay with tandem mass spectrometric detection was developed and validated for quantitation of the broad spectrum kinase inhibitor, flavopiridol, in human plasma. Sample preparation conditions included liquid-liquid extraction in acetonitrile (ACN), drying, and reconstitution in 20/80 water/ACN. Flavopiridol and the internal standard (IS), genistein, were separated by reversed phase chromatography using a C-18 column and a gradient of water with 25 mM ammonium formate and ACN. Electrospray ionization and detection of flavopiridol and genistein were accomplished with single reaction monitoring of m/z 402.09 > 341.02 and 271.09 > 152.90, respectively in positive-ion mode [M+H]+ on a triple quadrupole mass spectrometer. Recovery was greater than 90% throughout the linear range of 3 nM to 1,000 nM. Replicate sample analysis indicated within- and between-run accuracy and precision to be less than 13% throughout the linear range. This method has the lowest LLOQ reported to date for flavopiridol, and it allows for more accurate determination of terminal phase concentrations and improved pharmacokinetic parameter estimation in patients receiving an active dosing schedule of flavopiridol.