CDP-323

CT7758, a carboxylate containing α4β1/α4/β7 integrin antagonist, was characterized for its pharmacokinetic profile in various in vitro and in vivo assays in support of clinical development. The oral bioavailability of CT7758 was 4% in mice, 2% in rats, 7-55% in dogs, and 0.2% in cynomolgus monkeys. The low bioavailability in rodents and monkey results from low intestinal absorption as evidenced by a low fraction absorbed in the rat portal vein model (3%), low-to-medium permeability in Caco-2 cells (≤1.3 × 10(-6) cm/s) with evidences of polarized efflux, and high polar surface area (104 Å). In rodents and cynomolgus monkeys, the total plasma clearance was moderate to high (≥50% hepatic blood flow QH) and associated with a short elimination half-life (≤1 hour). This contrast with the dog data which showed a much lower clearance (6% QH) and a longer t1/2 (2.4 hours). The volume of distribution (Vz) also varied significantly across species with value of 5.5, 2.8, 0.24, and 0.93 l/kg in mouse, rat, dog, and cynomolgus monkey, respectively. In vitro assays demonstrated that active hepatic uptake accounted for most of the in vivo clearance and was the source of the large species variability. In vitro uptake assays predicted a total plasma clearance in humans in the low range (33% QH), a finding subsequently confirmed in the clinic. Assays in OAPT1B1-transfected cells demonstrated active uptake transport through this transporter. The prospect of limited absorption in human prompted the synthesis an ethyl ester prodrug, CDP323, which demonstrated higher in vitro permeability, increased oral bioavailability, as well as efficient in vivo release of its active moiety CT7758.

We identified the enzyme(s) involved in the hydrolysis of the ethyl ester prodrug CDP323 (C28H29BrN403) and characterized its transesterification in the presence of ethanol with special emphasis on the risks of drug-drug interaction. The hydrolysis of CDP323 was evaluated in vitro using human liver and intestinal microsomes and recombinant human carboxylesterases (hCES1 and 2) and was shown to be approximately 20-fold higher in human liver microsomes when compared with human intestinal microsomes and in hCES1 when compared with hCES2. Nonspecific inhibitors of carboxylesterases significantly inhibited the hydrolysis of CDP323 (>80% inhibition) while specific inhibitors of CES2, acetylcholine esterase, arylesterase, and butyrylcholinesterase did not impair the hydrolysis reaction. The effect of ethanol on the kinetic parameters for hydrolysis was investigated, demonstrating that at high concentration (2%), Michaelis-Menten constant (Km), maximum velocity (Vmax), and intrinsic clearance (CLint) for the formation of the hydrolyzed product were decreased (∼40%). The use of deuterated ethanol allowed more mechanistic investigations of the transesterification mechanism and showed that the intrinsic clearance based on parent loss was not impaired in the presence of alcohol. Overall, our data demonstrate that CDP323 is mainly hydrolyzed by hCES1 and is prone to transesterification in the presence of ethanol. Transesterification mechanisms compete with hydrolysis without impairing the overall clearance of the ester prodrug. Based on in vitro results, the risk of a clinically significant drug-drug interaction with ethanol is anticipated to be low.