Utilization of in vitro Caco‐2 permeability and liver microsomal half‐life screens in discovering BMS‐488043, a novel HIV‐1 attachment inhibitor with improved pharmacokinetic properties

Optimizing pharmacokinetic properties to improve oral exposure is a common theme in modern drug discovery. In the present work, in vitro Caco‐2 permeability and microsomal half‐life screens were utilized in an effort to guide the structure-activity relationship in order to improve the pharmacokinetic properties of novel HIV‐1 attachment inhibitors. The relevance of the in vitro screens to in vivo pharmacokinetic properties was first demonstrated with a number of program compounds at the early stage of lead optimization. The Caco‐2 permeability, tested at 200 µM, was quantitatively predictive of in vivo oral absorption, with complete absorption occurring at a Caco‐2 permeability of 100 nm/s or higher. The liver microsomal half‐life screen, conducted at 1 µM substrate concentration, can readily differentiate low‐, intermediate‐, and high‐clearance compounds in rats, with a nearly 1:1 correlation in 12 out of 13 program compounds tested. Among the >100 compounds evaluated, BMS‐488043 emerged as a lead, exhibiting a Caco‐2 permeability of 178 nm/s and a microsomal half‐life predictive of a low clearance (4 mL/min/kg) in humans. These in vitro characteristics translated well to the in vivo setting. The oral bioavailability of BMS‐488043 in rats, dogs, and monkeys was 90%, 57%, and 60%, respectively. The clearance was low in all three species tested, with a terminal half‐life ranging from 2.4 to 4.7 h. Furthermore, the oral exposure of BMS‐488043 was significantly improved (6‐ to 12‐fold in rats and monkeys) compared to the prototype compound BMS‐378806 that had a suboptimal Caco‐2 permeability (51 nm/s) and microsomal half‐life. More importantly, the improvements in preclinical pharmacokinetics translated well to humans, leading to a >15‐fold increase in the human oral exposure of BMS‐488043 than BMS‐378806 and enabling a clinical proof‐of‐concept for this novel class of anti‐HIV agents. The current studies demonstrated the valuable role of in vitro ADME screens in improving oral pharmacokinetics at the lead optimization stage. © 2009 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2135-2152, 2010