A highly sensitive, rapid assay method has been developed and validated for the estimation of abiraterone (ART) in rat and human plasma with liquid chromatography coupled to tandem mass spectrometry and electrospray ionization in the positive-ion mode. The assay procedure involves extraction of ART and phenacetin (internal standard, IS) from rat and human plasma with a simple protein precipitation extraction process. Chromatographic separation was achieved using an isocratic mobile (10 mm ammonium acetate:acetonitrile, 10:90, v/v) at a flow-rate of 0.70 mL/min on an Atlantis dC(18) column maintained at 40 °C with a total run time of 3.5 min. The MS/MS ion transitions monitored were 350.3 → 156.0 for ART and 180.2 → 110.1 for IS. Method validation was performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 0.20 ng/mL and the linearity range extended from 0.20 to 201 ng/mL. The intra- and inter-day precisions were in the ranges 2.39-10.4 and 4.84-9.53% in rat plasma and 3.82-10.8 and 6.97-8.94% in human plasma.

The results met the acceptance criteria. The validated method was successfully applied to characterize the pharmacokinetic parameters of Orteronel in rat plasma.

Background and objective: Concurrent usage of proton pump inhibitors and their effect on survival and medication termination has been found in individuals receiving protein kinase inhibitor chemotherapy. To investigate the drug-drug interaction mechanism between CDK inhibitors and proton pump inhibitors, the in-silico docking approach was designed by applying computer simulation modules to predict the binding and inhibitory potential. Method: The interaction potential of proton pump inhibitors and CDK inhibitors was predicted utilising molecular docking techniques that employed Schrödinger algorithms to capture the dynamics of the CYP450 enzyme-inhibitor interaction between PPIs and CDK inhibitors. Additionally, the human liver microsomes assay was used to determine the in vitro half-maximal inhibitory concentration (IC50) of proton pump inhibitors and the inactivation of CDK inhibitors via CYP3A4. Results: Proton pump inhibitors alter the conformation of the CYP3A4 and CYP2C19 enzymes and interact with the heme prosthetic group, as determined by docking studies. It may result in the suppression of CDK inhibitors' metabolism via competitive inhibition at the binding site of an enzyme. Omeprazole and rabeprazole both significantly block midazolam's 1′-hydroxylation by CYP3A4 in vitro, with IC50 values of 9.86µM and 9.71µM, respectively. When omeprazole and rabeprazole are co-incubated in human liver microsomes at a 30µM concentration equivalent to the Cmax of omeprazole and rabeprazole, rabeprazole significantly prolongs the metabolic clearance of palbociclib, whereas omeprazole affects the ribociclib CYP3A4-mediated metabolism. Conclusion: Using dynamic models, we determined that proton pump inhibitors such as rabeprazole and omeprazole indeed have the potential to cause clinically significant drug-drug interactions with CDK inhibitors in the treatment of estrogen receptor (ER) positive and HER2-positive breast cancer. As a result, it is suggested to use caution when prescribing proton pump inhibitors to these individuals.