Abstract

Hydrolysis plays an important role in metabolic activation of prodrugs. In the current study, species and in vitro system differences in hepatic and extrahepatic hydrolysis were investigated for 11 prodrugs. Ten prodrugs in the data set are predominantly hydrolyzed by carboxylesterases (CES), whereas olmesartan medoxomil is also metabolized by carboxymethylenebutenolidase (CMBL) and paraoxonase. Metabolic stabilities were assessed in cryopreserved hepatocytes, liver S9 (LS9), intestinal S9 (IS9), kidney S9 (KS9), and plasma from human, monkey, dog, and rat. Of all the preclinical species investigated, monkey intrinsic hydrolysis clearance obtained in hepatocytes (CL_{int,hepatocytes}) were the most comparable to human hepatocyte data. Perindopril and candesartan cilexetil showed the lowest and highest CL_{int,hepatocytes}, respectively, regardless of the species investigated. Scaled intrinsic hydrolysis clearance obtained in LS9 were generally higher than CL_{int,hepatocytes} in all species investigated, with the exception of dog. In the case of human and dog intestinal S9, hydrolysis intrinsic clearance could not be obtained for CES1 substrates, but hydrolysis for CES2 and CMBL substrates was detected in IS9 and KS9 from all species. Pronounced species differences were observed in plasma; hydrolysis of CES substrates was only evident in rat. Predictability of human hepatic intrinsic clearance (CL_int,h) was assessed for eight CES1 substrates using hepatocytes and LS9; extrahepatic hydrolysis was not considered due to high stability of these prodrugs in intestinal and kidney S9. On average, predicted oral CL_int,h from hepatocyte data represented 20% of the observed value; the underprediction was pronounced for high-clearance prodrugs, consistent with the predictability of cytochrome P450/conjugation clearance from this system. Prediction bias was less apparent with LS9, in particular for high-clearance prodrugs, highlighting the application of this in vitro system for investigation of prodrugs.