A simplified approach to predict CYP3A-mediated drug-drug interactions at early drug discovery: validation with clinical data.

1. The present study evaluates which factors should be incorporated into a simplified approach to reasonably predict CYP3A-mediated drug-drug interaction (DDI) at an early drug discovery stage. 2. CYP3A IC50 values were obtained using human liver microsomes (HLM) and hepatocytes. Plasma and microsomal protein binding and in vitro hepatocyte partition coefficient (Kp) were also determined for 10 drugs. Therapeutic human maximum plasma concentrations (Cmax) were retrieved from the literature. DDI predictions were performed using an equation incorporating the fraction of the substrate metabolized by CYP3A with the total or free plasma Cmax, with or without correction for hepatocyte Kp. 3. Based on the Ki data from HLM, the use of total Cmax provided a prediction of DDI within 2-fold of the observed clinical values for 9 out of 10 drugs. 4. In comparison, free drug corrections for both Cmax and Ki values from HLM led to an underprediction of DDI (>3-fold error for five drugs). 5. Data from hepatocytes showed, in general, lower prediction accuracy than data from HLM. 6. CYP3A-mediated DDIs can be predicted with a high level of accuracy based on Ki estimates from HLM data and the total therapeutic plasma Cmax of the inhibitors. This approach should be widely applicable to the assessment of clinically significant DDIs risk in early drug discovery programs.

The liver partition coefficient-corrected inhibitory quotient and the pharmacokinetic-pharmacodynamic relationship of directly acting anti-hepatitis C virus agents in humans.

Pharmacokinetic-pharmacodynamic (PK-PD) data analyses from early hepatitis C virus (HCV) clinical trials failed to show a good correlation between the plasma inhibitory quotient (IQ) and antiviral activity of different classes of directly acting antiviral agents (DAAs). The present study explored whether use of the liver partition coefficient-corrected IQ (LCIQ) could improve the PK-PD relationship. Animal liver partition coefficients (Kp(liver)) were calculated from liver to plasma exposure ratios. In vitro hepatocyte partition coefficients (Kp(hep)) were determined by the ratio of cellular to medium drug concentrations. Human Kp(liver) was predicted using an in vitro-in vivo proportionality method: the species-averaged animal Kp(liver) multiplied by the ratio of human Kp(hep) over those in animals. LCIQ was calculated using the IQ multiplied by the predicted human Kp(liver). Our results demonstrated that the in vitro-in vivo proportionality approach provided the best human Kp(liver) prediction, with prediction errors of <45% for all 5 benchmark drugs evaluated (doxorubicin, verapamil, digoxin, quinidine, and imipramine). Plasma IQ values correlated poorly (r(2) of 0.48) with maximum viral load reduction and led to a corresponding 50% effective dose (ED(50)) IQ of 42, with a 95% confidence interval (CI) of 0.1 to 148534. In contrast, the LCIQ-maximum VLR relationship fit into a typical sigmoidal curve with an r(2) value of 0.95 and an ED(50) LCIQ of 121, with a 95% CI of 83 to 177. The present study provides a novel human Kp(liver) prediction model, and the LCIQ correlated well with the viral load reductions observed in short-term HCV monotherapy of different DAAs and provides a valuable tool to guide HCV drug discovery.

Animal models of acute moderate hypoxia are associated with a down-regulation of CYP1A1, 1A2, 2B4, 2C5, and 2C16 and up-regulation of CYP3A6 and P-glycoprotein in liver.

In humans, indirect evidence suggests that hypoxia reduces the rate of biotransformation of drugs cleared by cytochrome P450 (P450) subfamilies CYP1A, 2B, and 2C. The aim of this study was to assess whether acute moderate hypoxia modulates the expression of CYP2B4, 2C5, and 2C16 in vivo, and to determine whether the changes in hepatic P450 are conveyed by serum mediators. Moreover, because hypoxia increases the expression of P-glycoprotein in vitro, we examined whether in vivo acute moderate hypoxia modulates the expression of several membrane transporters in the liver. Rabbits and rats were exposed to a fractional concentration of oxygen of 8% for 48 h to generate a stable arterial partial pressure of O2 of 34 +/- 1 mm Hg. Compared with rabbits breathing room air, hypoxia in rabbits reduced the amount of CYP1A1, 1A2, 2B4, 2C5, and 2C16 proteins and increased the expression of CYP3A6. Sera of rabbits with hypoxia were fractionated by size exclusion chromatography, the fractions were tested for their ability to modify the expression of P450 isoforms, and serum mediators were identified through neutralization experiments. The serum mediators responsible for the down-regulation of P450 isoforms were interferon-gamma, interleukin-1beta (IL-1beta), and IL-2. In vivo, in rats, hypoxia increased the mRNA and protein expression of P-glycoprotein but did not affect the mRNA of breast cancer resistance protein and organic anion-transporting polypeptide 2. It is concluded that in vivo, hypoxia down-regulates rabbit hepatic CYP1A1, 1A2, 2B4, 2C5, and 2C16 and up-regulates CYP3A6. CYP3A11 and P-glycoprotein were up-regulated in the livers of hypoxic rats.