calcein-am and Chemical-and-Drug-Induced-Liver-Injury

PF-022 (1) is a novel polycyclic benzothiophene kinase inhibitor selective for mitogen-activated protein kinase-activated protein kinase 2 (MK2). Compound 1 emerged as an inhibitor bearing submicromolar potency against MK2 (IC50 5 nM) and demonstrated projected human pharmacokinetics sufficient for oral dosing. However, following a single, oral administration of 1 to beagle dogs, animals experienced an acute liver injury characterized by increases in biomarkers associated with hepatotoxicity; particularly noteworthy was the reversible elevation in bile salts and total bilirubin. Accompanying this observation was an ADME appraisal which included hepatic bioactivation of 1 in multiple species and the in vitro inhibition of P-glycoprotein (P-gp; IC50 21 μM). Simply attenuating the bioactivation via structural modification proved ineffective in improving the in vivo tolerability of this polycyclic scaffold. Hence, disruption of hepatobiliary transporters by the compound series was hypothesized as the likely mechanism contributing to the acute hepatotoxicity. Indeed, closer in vitro examination employing transporter gene overexpressing MDCK cell lines and membrane vesicles revealed potent compound-dependent inhibition of human multi-drug resistance-associated protein 2 (MRP2/ABCC2; IC50 38 μM) and bile salt export pump (BSEP/ABCB11; IC50 10 μM), two crucial hepatobiliary transport proteins accountable for bilirubin and bile salt homeostasis, respectively. Subsequent introduction of pKa-altering modifications to a second generation compound PF029 proved successful in reducing its affinity for these key efflux transporters (MRP2 IC50 >>80 μM; BSEP IC50 > 70 μM; P-gp > 90 μM), consequently mitigating this overt organ toxicity in dogs.

Topics: Animals; Area Under Curve; ATP Binding Cassette Transporter, Subfamily B, Member 1; Bile; Carrier Proteins; Cell Line; Chemical and Drug Induced Liver Injury; Dogs; Drug Resistance, Multiple; Fluoresceins; Fluorescent Dyes; Liver; Male; Multidrug Resistance-Associated Protein 2; Multidrug Resistance-Associated Proteins; Protein Kinase Inhibitors; Taurocholic Acid

CP-724,714, a potent and selective orally active HER2 tyrosine kinase inhibitor, was discontinued from clinical development due to unexpected hepatotoxicity in cancer patients. Based on the clinical manifestation of the toxicity, CP-724,714 likely exerted its hepatotoxicity via both hepatocellular injury and hepatobiliary cholestatic mechanisms. The direct cytotoxic effect, hepatobiliary disposition of CP-724,714, and its inhibition of active canalicular transport of bile constituents were evaluated in established human hepatocyte models and in vitro transporter systems. CP-724,714 exhibited direct cytotoxicity using human hepatocyte imaging assay technology with mitochondria identified as a candidate organelle for its off-target toxicity. Additionally, CP-724,714 was rapidly taken up into human hepatocytes, partially via an active transport process, with an uptake clearance approximately fourfold higher than efflux clearance. The major human hepatic uptake transporter, OATP1B1, and efflux transporters, multidrug resistance protein 1 (MDR1) and breast cancer resistance protein, were involved in hepatobiliary clearance of CP-724,714. Furthermore, CP-724,714 displayed a concentration-dependent inhibition of cholyl-lysyl fluorescein and taurocholate (TC) efflux into canaliculi in cryopreserved and fresh cultured human hepatocytes, respectively. Likewise, CP-724,714 inhibited TC transport in membrane vesicles expressing human bile salt export pump with an IC(50) of 16 microM. Finally, CP-724,714 inhibited the major efflux transporter in bile canaliculi, MDR1, with an IC(50) of approximately 28 microM. These results suggest that inhibition of hepatic efflux transporters contributed to hepatic accumulation of drug and bile constituents leading to hepatocellular injury and hepatobiliary cholestasis. This study provides likely explanations for clinically observed adverse liver effects of CP-724,714.

Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Bile; Bile Acids and Salts; Calcium; Carrier Proteins; Cells, Cultured; Chemical and Drug Induced Liver Injury; Enzyme Inhibitors; Fluoresceins; Hepatocytes; Humans; Liver; Liver-Specific Organic Anion Transporter 1; Membrane Potentials; Mitochondrial Membranes; Multidrug Resistance-Associated Protein 2; Multidrug Resistance-Associated Proteins; Neoplasm Proteins; Quinazolines; Receptor, ErbB-2