Cyclodextrin Reduces Intravenous Toxicity of a Model Compound.

Solubilization of new chemical entities for toxicity assessment must use excipients that do not negatively impact drug pharmacokinetics and toxicology. In this study, we investigated the tolerability of a model freebase compound, GDC-0152, solubilized by pH adjustment with succinic acid and complexation with hydroxypropyl-ß-cyclodextrin (HP-ß-CD) to enable intravenous use. Solubility, critical micelle concentration, and association constant with HP-ß-CD were determined. Blood compatibility and potential for hemolysis were assessed in vitro. Local tolerability was assessed after intravenous and subcutaneous injections in rats. A pharmacokinetic study was conducted in rats after intravenous bolus administration. GDC-0152 exhibited pH-dependent solubility that was influenced by self-association. The presence of succinic acid increased solubility in a concentration-dependent manner. HP-ß-CD alone also increased solubility, but the extent of solubility enhancement was significantly lower than succinic acid alone. Inclusion of HP-ß-CD in the solution of GDC-0152 improved blood compatibility, reduced hemolytic potential by ∼20-fold in vitro, and increased the maximum tolerated dose to 80 mg/kg.

Metabolic activation of 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine in Syrian hamsters congenic at the N-acetyltransferase 2 (NAT2) locus.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a heterocyclic amine carcinogen prevalent in the human diet. To exert its mutagenic and carcinogenic effects, PhIP undergoes bioactivation to N-hydroxy-PhIP followed by O-esterification via cytosolic acetyltransferases or sulfotransferases to form DNA adducts. We investigated the role of cytosolic acetyltransferases and sulfotransferases and the role of the N-acetyltransferase 2 genetic polymorphism on PhIP DNA-adduct levels in a congenic Syrian hamster model. DNA adduct levels were detected in all hepatic and extrahepatic tissues tested following administration of PhIP (4x100 mg/kg) or N-hydroxy-PhIP (1x50 mg/kg), with the highest levels in pancreas. DNA-adduct levels were higher in the gastrointestinal tract of rapid and slow acetylator hamsters administered N-hydroxy-PhIP. N-hydroxy-PhIP O-acetyltransferase and O-sulfotransferase activities were detected in most hepatic and extrahepatic cytosols derived from rapid and slow acetylator congenic hamsters. N-hydroxy-PhIP O-acetyltransferase activity was significantly higher (p<0.05) in liver, small intestine, and esophagus in rapid than in slow acetylator congenic hamsters. N-hydroxy-PhIP O-acetyltransferase activities correlated significantly with N-acetyltransferase 2 activities across tissues in rapid (r=0.83; p=0.0004) but not in slow (r=0.46; p=0.1142) acetylator congenic hamsters, suggesting catalysis primarily by NAT2 in rapid acetylators but NAT1 in slow acetylators. N-hydroxy-PhIP O-sulfotransferase activities did not vary with acetylator genotype. DNA-adduct levels following administration of PhIP or N-hydroxy-PhIP did not correlate with either N-hydroxy-PhIP O-acetyltransferase or O-sulfotransferase catalytic activities.