Preclinical Pharmacokinetic Profiling of the Novel Anticancer Benzyl Styryl Sulfone Compound, ON 01910.Na (Estybon(TM), Rigosertib)

ON 01910.Na, a novel chemotherapeutic agent developed by Onconova Therapeutics, Inc., is primarily employed as a multi-kinase inhibitor for treatment of a variety of hematologic and solid oncologie disorders. This dissertation has set out to build upon established preclinical framework and aid in the understanding newly discovered phenomena in the clinical arena. The specific aims of this research were to: (1) develop and validate an LC-MS/MS method for the quantitation of ON 01910.Na and its potential degradants (ON 01500 and ON 012160) in a variety of preclinical matrices, (2) evaluate plasma protein binding across species (3) determine the role of phase I and phase II metabolism pathways in the rat model utilizing rodent enzymatic systems and their effect on intrinsic clearance of ON 01910.Na, (4) assess the hepatobiliary disposition of ON 01910.Na in the isolated perfused rat liver (IPRL) model through dose escalation studies, (5) investigate the potential impact of commonly concurrently administered small molecule anti-cancer compounds on the pharmacokinetic profile of ON 01910.Na, (6) study the effect of repeated oral administration on the hepatic clearance of ON 01910.Na in rats and (7) establish the effect of repeated oral administration on the clearance of ON 01910.Na in the isolated perfused liver using Mdrla deficient (Mdr1a-/-) male Sprague-Dawley rat donors.;A validated LC-MS/MS method was utilized to quantify and/or monitor ON 01910.Na, along with its possible degradants, in biological matrices including rat plasma, IPRL perfusate, bile, and Tris-HC1 and potassium phosphate buffered solutions. To validate this method, all facets of bioanalytical validation in each matrix were performed. Those included accuracy (MAPE+/-15%), recovery, method and system precision (%RSD+/-15%), linearity (r 2>0.99), range and specificity. All principles of validation were within specifications for validation of compendial methods as outlined by the United States Pharmacopeia.;ON 01910.Na was found to be extensively bound in rat and human plasma from 0.5-10 mug/mL (93.2-97.9% and 98.50-99.02% respectively), and IPRL perfusate in the range of 0.5-250 microg/mL (88.5-94.1%). Upon co-administration of oxaliplatin (4 microg/mL), doxorubicin (7 mug/mL) or gemcitabine (8 p.g/mL), significant displacement of ON 01910.Na binding from albumin at its target concentration of 250 mug/mL was observed (p=0.01).;Through metabolic profiling studies, it was discovered that metabolism was virtually non-existent in rat microsome and S9 fractions; the principle sites of phase I and II metabolism. Positive controls were used for verification of enzymatic activity of in vitro systems in phase I (7-ethoxycoumarin→7-hydroxycoumarin) and phase II (7-hydroxycoumarin→7hydroxycoumarin glucuronide) metabolism.;Dose-dependent hepatobiliary disposition of ON 01910.Na was determined through dose escalation studies in the isolated perfused rat liver (1-250 microg/mL) The results from these studies showed nonlinearity with respect to both biliary and total perfusate clearance and area under the plasma versus time concentration curve (AUC). Biliary excretion was significant with ∼46% of dose recovered in the bile over the doses evaluated. Rapid uptake and clearance was noted with an average of 11% of dose remaining in the perfusion chamber at the conclusion of the experiment.;Analogous research was done to address potential changes in pharmacokinetics upon co-administration of additional chemotherapeutic compounds; including oxaliplatin, doxorubicin and gemcitabine. Reduced exposure and half-life was noted upon addition of doxorubicin and gemcitabine to the perfusion chamber with a corresponding increase in clearance (total perfusate and biliary) with evidence of augmented bile flow. Addition of oxaliplatin did not have any apparent significant effect on hepatic function nor the pharmacokinetics of ON 01910.Na in the IPRL.;A knockout rat model (Mdrla-/-) was used to address transporter modulation after repeated chronic oral dosing of ON 01910.Na. Results with Mdrla-/- rats, contrasted to those of the wild type (WT), suggest that P-glycoprotein is not primarily responsible for the hepatic excretion of ON 01910.Na. This was confirmed by comparable increases in levels of biliary clearance, fraction of administered dose obtained in bile and cumulative excretion in both WT and Mdrla-/-knockout animal models. It was found that in both rat models, chronic dosing for 7 or 14 days led to marked reductions in ON 01910.Na exposure; as indicated by a substantial drop in AUC between control and treatment groups. Although a clear reduction in bile flow was evident in the Mdrla-/- control group rat livers as compared to WT, ON 01910.Na appeared to have a choleretic effect in this group with significantly elevated levels of bile flow after 7 or 14 days of administration (p=0.008). No such effect was witnessed in the WT cohort. Both the WT and Mdrla-/- strains also displayed elevations in biliary clearance, total hepatic clearance and fraction excreted in bile after chronic dosing however only of consequence in the Mdrla-/- model; a significance possibly attributed to biliary stimulation of compensatory mechanisms in the knockout liver. These results reflect potential modulation of alternative pathways of excretion, and not Mdrla, in the isolated perfused liver model.