Abstract
A preclinical drug candidate, MRK-1, was found to elicit tumor regression in a mouse xenograft model. Analysis of samples from these studies revealed significant levels of two circulating metabolites whose identities were confirmed by comparison to authentic standards using liquid chromatography-mass spectrometry (LC-MS/MS). These metabolites were found to have similar in vitro potency to MRK-1 against the pharmacological target and were therefore thought to contribute towards the observed efficacy. In order to predict this contribution in humans, a pharmacokinetic (PK) modeling approach was developed. At the efficacious dose, the mouse steady state unbound areas under the plasma concentration time curves (AUCs) of the active metabolites were normalized by their in vitro potency compared to MRK-1. These normalized metabolite AUCs were added to that of MRK-1 to yield a composite efficacious unbound AUC, expressed as "parent drug equivalents", which was used as the target AUC for predictions of the human efficacious dose. In vitro and preclinical PK studies afforded predictions of the PK of MRK-1 and the two active metabolites in human as well as the relative pathway flux to each metabolite. These were used to construct a PK model (Berkeley Madonna, v 8.3.18, Berkeley Madonna Inc., University of California, Berkeley, CA) and predict the human dose required to achieve the target "parent equivalents" exposure. These predictions were used to inform on the feasibility of the human dose in terms of size, frequency, formulation and likely safety margins as well as to aid design of preclinical safety studies.
- animal/nonclinical/preclinical
- anticancer agents
- drug development/discovery
- hepatocytes
- metabolite identification
- modeling and simulation
- pharmacokinetics
- The American Society for Pharmacology and Experimental Therapeutics