Determination of intestinal permeability of rigosertib (ON 01910.Na, Estybon): Correlation with systemic exposure

Abstract

Objectives: Rigosertib (ON 01910.Na, Estybon) is a novel, anticancer agent undergoing phase 3 clinical trials for a lead indication against myelodysplastic syndromes (MDS). In this research, the permeability of rigosertib was evaluated using the in-situ perfused rat intestine (IPRI) model to support development of an oral formulation for rigosertib for treating cancer patients. Methods: Experiments (n = 6 per group) were conducted using male Sprague-Dawley rats. Studies evaluated permeability across various intestinal segments and assessed the dose-linearity of absorption over the entire intestinal length. Drug concentrations in the portal and jugular vein were collected to correlate permeability parameters with presystemic and systemic exposure. Key findings: Rigosertib permeability was highest in the jejunum, although parameter estimates indicated that rigosertib was a medium permeability compound. The compound displayed nonlinear absorption in the IPRI model, suggesting a saturable transport process. Transport inhibition studies using Caco-2 cells demonstrated that rigosertib was a P-glycoprotein (P-gp) substrate. Absolute bioavailability of rigosertib (10 and 20 mg/kg, 1-h infusion) in rats was estimated to be 10-15%. However, the fraction absorbed in humans predicted from IPRI data (52%) was consistent with published clinical data for rigosertib (35% oral bioavailability). Conclusions: The results of this research indicated that rigosertib is a promising candidate for oral delivery. Further studies are needed to evaluate the potential impact of P-gp and other intestinal transporters on the oral absorption of this promising anticancer agent. © 2013 Royal Pharmaceutical Society.