Abstract

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 (K_m), maximum velocity (V_max), and intrinsic clearance (CL_int) 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.