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

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.