Development and validation of a liquid chromatography-tandem mass spectrometry assay for the simultaneous quantitation of prednisolone and dipyridamole in human plasma and its application in a pharmacokinetic study.

We have developed and validated an accurate, sensitive, and robust LC-MS/MS method that determines the concentration of CRx-102 (the combination of prednisolone and dipyridamole) in human plasma. In this method, prednisolone, dipyridamole, and the combined internal standards (IS) prednisolone-d(6) (IS for prednisolone) and dipyridamole-d(20) (IS for dipyridamole) were extracted from 100 microL human EDTA plasma using methylbutyl ether. Calibration curves were linear over a concentration range of 0.4-200 ng/mL for prednisolone and 5-3000 ng/mL for dipyridamole. The analytes were quantitatively determined using tandem mass spectrometry operated in positive electrospray ionization in a multiple reaction monitoring (MRM) mode. This validated method has been used successfully in clinical pharmacokinetic studies of CRx-102 in healthy volunteers.

Biotransformation and in vitro assessment of metabolism-associated drug-drug interaction for CRx-102, a novel combination drug candidate.

CRx-102 is an oral synergistic combination drug which contains the cardiovascular agent, dipyridamole (DP) and a very low dose of the glucocorticoid, prednisolone (PRED). CRx-102 works through a novel mechanism of action in which DP selectively amplifies the anti-inflammatory activity of PRED without replicating its side effects. CRx-102 is in clinical trials for the treatment of osteoarthritis. Here we delineate the in vitro metabolism and explore the potential for a drug-drug interaction between the active agents in CRx-102. Our study using human hepatocyte suspensions showed that both DP and PRED were metabolized by CYP3A4 isozymes, resulting in the formation of diverse arrays of both oxidative and oxidative-reduced metabolites. Within phase 1 biotransformation, CYP3A4 was one of the pathways responsible for the metabolism of PRED, while phase 2 biotransformation played a significant role in the metabolism of DP. Glucuronidation of DP was substantial and was catalyzed by many UGT members, specifically those in the UGT1A subfamily. Based on the tandem mass (MS/MS) product ion spectra (PIS) acquired, the major metabolites of both agents, namely, monooxygenated, mono-N-deethanolaminated, dehydrogenated and O-glucuronidated metabolites of DP and the monooxygenated (e.g., 6-hydroxyl), dehydrogenated (prednisone) and reduced (20-hydroxyl) metabolites of PRED, were identified and elucidated. The affinities for DP biotransformation, including CYP3A4-mediated oxidative pathways and UGT-mediated O-glucuronidation, appeared high (K(m)<10 microM), as compared with the modest affinities of PRED biotransformation catalyzed by CYP3A4 (K(m) approximately 40-170 microM). DP, but not PRED, exerted a minimal inhibitory effect on the drug-metabolizing CYP isoforms, including CYP3A4, which was determined using a panel of CYP isoform-preferred substrate activities in pooled human liver microsomal (HLM) preparations and microsomal preparations containing the recombinant enzymes (K(i) approximately 2-12 microM). Using the DP maximal plasma concentration (C(max)) observed in the clinic and a predictive mathematical model for metabolism-associated drug-drug interaction (DDI), we have demonstrated that there is little likelihood of a pharmacokinetic interaction between the two active agents in CRx-102.