Enzyme induction in freshly isolated human hepatocytes

DESCRIPTION (provided by applicant): This is Phase I of an SBIR grant application. The overall goal of this project is to enable the pharmaceutical industry to conduct high-throughput screening (HTS) studies with Fa2N-4 cells, a new cell line created by immortalizing human hepatocytes with SV-40 virus, in order to identify those drug candidates that will likely cause clinically significant drug-drug interactions as a result of their ability to induce (up-regulate) the expression of cytochrome P450 (CYP) and other drug-metabolizing/transporting enzymes. Enzyme induction by drugs and other agents (such as herbal agent St. John's Wort) is a serious cause of drug-drug interactions; it is responsible for the loss of therapeutic effect of life-saving drugs (such as anti-HIV, anti-cancer and anti-coagulant drugs) and life- modifying drugs (such as oral contraceptive steroids). The US-FDA now considers enzyme induction to be an obstacle to drug approval (i.e., grounds for disapproval), especially for drugs intended for use in combination with anti-HIV or other drugs used to treat life-threatening diseases. Enzyme induction occurs in a highly species-specific manner, such that studies aimed at assessing clinical outcome must be conducted in a human-based system. Currently, the use of primary cultures of human hepatocytes represents the "gold standard" for evaluating enzyme-induction potential in vitro, but this approach is limited by an inadequate (and erratic) supply of non-transplantable human liver. Human-derived hepatic cell lines, such as HepG2 cells, do not respond appropriately to those drugs that cause clinically significant enzyme induction because they lack a functional PXR/CAR signaling pathway. However, this signaling pathway is functional in the new line of immortalized human hepatocytes (Fa2N-4 cells), which suggests that these cells can be used to identify drug candidates as enzyme inducers, which will save millions of dollars in failed drug development costs, as well as improve drug safety by reducing the incidence of drug-drug interactions, which are reported to be one of the leading causes of adverse drug reactions (ADRs), which in turn are one of the leading causes of preventable death in the United States.