Pharmacokinetics of IDX184, a liver-targeted oral prodrug of 2'-methylguanosine-5'-monophosphate, in the monkey and formulation optimization for human exposure.

IDX184 is a phosphoramidate prodrug of 2'-methylguanosine-5'-monophosphate, developed to treat patients infected with hepatitis C virus. A mass balance study of radiolabeled IDX184 and pharmacokinetic studies of IDX184 in portal vein-cannulated monkeys revealed relatively low IDX184 absorption but higher exposure of IDX184 in the portal vein than in the systemic circulation, indicating >90 % of the absorbed dose was subject to hepatic extraction. Systemic exposures to the main metabolite, 2'-methylguanosine (2'-MeG), were used as a surrogate for liver levels of the pharmacologically active entity 2'-MeG triphosphate, and accordingly, systemic levels of 2'-MeG in the monkey were used to optimize formulations for further clinical development of IDX184. Capsule formulations of IDX184 delivered acceptable levels of 2'-MeG in humans; however, the encapsulation process introduced low levels of the genotoxic impurity ethylene sulfide (ES), which necessitated formulation optimization. Animal pharmacokinetic data guided the development of a tablet with trace levels of ES and pharmacokinetic performance equal to that of the clinical capsule in the monkey. Under fed conditions in humans, the new tablet formulation showed similar exposure to the capsule used in prior clinical trials.

Overcoming stability challenges in the quantification of tissue nucleotides: determination of 2'-C-methylguanosine triphosphate concentration in mouse liver.

A conventional, rapid and high throughput method for tissue extraction and accurate and selective LC-MS/MS quantification of 2'-C-methylguanosine triphosphate (2'-MeGTP) in mouse liver was developed and qualified. Trichloroacetic acid (TCA) was used as the tissue homogenization reagent that overcomes instability challenges of liver tissue nucleotide triphosphates due to instant ischemic degradation to mono- and diphosphate nucleotides. Degradation of 2'-MeGTP was also minimized by harvesting livers using in situ clamp-freezing or snap-freezing techniques. The assay also included a sample clean-up procedure using weak anion exchange solid phase extraction followed by ion exchange chromatography and tandem mass spectrometry detection. The linear assay range was from 50 to 10000 pmol/mL concentration in liver homogenate (250-50000 pmol/g in liver tissue). The method was qualified over three intraday batches for accuracy, precision, selectivity and specificity. The assay was successfully applied to pharmacokinetic studies of 2'-MeGTP in liver tissue samples after single oral doses of IDX184, a nucleotide prodrug inhibitor of the viral polymerase for the treatment of hepatitis C, to mice. The study results suggested that the clamp-freezing liver collection method was marginally more effective in preventing 2'-MeGTP degradation during liver tissue collection compared to the snap-freezing method.

Exploration of the African green monkey as a preclinical pharmacokinetic model: intravenous pharmacokinetic parameters.

The value of cynomolgus and rhesus monkeys to predict human pharmacokinetic parameters has been well established in recent years. However, practical limitations on cost and accessibility can often be a deterrent to obtain data in these valuable species, and the characterization of the predictive power of other nonhuman primates would be useful. Therefore, the present investigation was designed to evaluate the pharmacokinetics of a test set of marketed compounds in the African green monkey, to compare the pharmacokinetics of these agents between nonhuman primate species, and to validate the ability of the African green monkey to predict human pharmacokinetics. Intravenous pharmacokinetics were evaluated for 11 test compounds in this study and compared with data from rats, dogs, cynomolgus/rhesus monkeys, and humans. The results from this investigation indicate that African green monkeys deliver reasonable prediction of human clearance and mean residence time and volume of distribution, although somewhat less accurately than cynomolgus and rhesus monkeys, particularly for volume of distribution, potentially because of body size or composition or experimental design differences. Furthermore, use of an optimized clearance prediction algorithm from the literature enhanced predictivity over a simple liver blood flow-based extrapolation methodology. The data from this study show that African green monkeys have the potential to be used as a surrogate for cynomolgus or rhesus monkeys in preclinical pharmacokinetic studies, particularly for the study of clearance processes, and should be considered as an alternate nonhuman primate test species.