藥物動力學/毒性研究


Webinar Series Abstracts

One of these is Not Like the Other: a Comparison of USFDA and EMA Guidance in the Conduct of Enzyme Induction Studies In Vitro
Presenter: David Stresser

In 2012, the USFDA published an updated draft “Guidance for Industry: Drug Interaction Studies” and the European Medicine Agency issued its “Guideline on the Investigation of Drug Interactions.” These documents provide specific and general guidance for conducting in vivo and in vitro investigations of drug interaction potential. Importantly, they also serve to reduce uncertainty among practitioners tasked with providing information to these agencies for review.

Ideally, guidance documents originating from various regulatory agencies would be fully harmonized, but logistical and practical challenges are considerable. In this webinar, we provide a detailed comparison of the recommendations provided from both agencies concerning the conduct of enzyme induction studies in vitro. Included in this comparison are recommendations concerning the test system, the endpoints measured, how an enzyme inducer and non-inducer are defined, the mathematical models, and several other parameters. While there are many similarities, there are also notable contrasts. Most practitioners will elect to seek marketing approval in the United States and in European Union countries. Therefore a strong understanding of recommendations for enzyme induction, as well as other drug-interaction testing recommendations, is essential to develop a single, comprehensive testing strategy. The aims of this presentation are to help elucidate the major differences between the two sets of recommendations.


Recombinant Enzymes as a Model System for Drug Profiling Studies
Presenter: Chris Patten

The majority of current drugs are eliminated by metabolism through one or more of the various biotransformation pathways in liver and non-hepatic tissue. The identification of the critical pathways for drug transformation (reaction phenotyping) and the rate of parent drug elimination (metabolic stability) are typically determined using in vitro model systems. Recombinant drug metabolism enzymes, which contain a single cDNA-expressed enzyme, are a convenient and highly validated enzyme source for both reaction phenotyping and metabolic stability studies. This webinar will focus on the specific methods for reaction phenotyping and metabolic stability testing using recombinant enzymes as the model system. Emphasis will be placed on P450s. The details of the methodologies will be discussed, along with topics that include a comparison of cDNA-expression systems, as well as scaling in vitro data to predict in vivo PK parameters (IV-IVE) using BD Supersomes™ with pre-determined ISEF/RAF values.


CYP Activity Levels in Human Livers: Trends and Impact on Designing Pooled Human Liver Microsome Reagents for Metabolic Stability, CYP Inhibition and Reaction Phenotyping
Presenter: Charles Crespi

Human liver microsomes are a key reagent for preclinical drug lead optimization and safety assessment research. The majority of these materials are prepared from donor livers that could not be used for transplantation. However, transplantation practices have changed and this may impact the characteristics of livers that are available for research. We have analyzed CYP activity levels in microsomes prepared from livers donated over several decades. The impact of gender, age, date of donation and other factors will be discussed. The use of this information to rationally design a pooled human liver microsome product, BD UltraPool™, will be demonstrated and the characteristics of this product relative to statistical predictions discussed.


Evaluation of mRNA and Enzyme Activity: EC50 and Emax as Endpoints in Human Hepatocyte Induction Studies to Predict Clinical Inducers and Non-inducers of CYP3A4
Presenter: George Zhang

Recent guidance from the FDA and EMA advocates the use of human hepatocytes as the test system for evaluating cytochrome P450 induction potential. Both agencies indicate that use of hepatocytes that have been prequalified for response to known clinical inducers and non-inducers are acceptable and/or preferred for certain model applications. In addition, the use of mRNA alone is suggested as the necessary endpoint to evaluate induction response (except in cases where enzyme stabilization is suspected as a mechanism). However, the applicability of using prequalified hepatocytes as the test system, and the use of mRNA alone as a response endpoint, has not been widely demonstrated. To this end, we have examined the induction response from a set of 20 compounds, including established clinical inducers and non-inducers of CYP3A4/5, in cryopreserved hepatocytes from three donors. The endpoint examined was CYP3A4 mRNA, typically over 8 concentration points in an effort to enable calculation of EC50 and Emax. Results were used to determine relative induction scores (RIS) and R3 values that may classify a drug candidate as a potential clinical inducer. The results and merits of these and other parameters for evaluating the induction potential of drug candidates will be discussed.


Overview of In Vitro Methods for Studying Drug Glucuronidation
Presenter: Chris Patten

Glucuronidation is as a major pathway for the metabolism and elimination of drugs in humans. It is second only to P450 for the metabolic clearance of currently marketed drugs. The glucuronidation reaction is catalyzed by the Phase 2 enzyme UDP-glucuronosyltransferase (UGT), which like the P450s exists as a superfamily of enzymes with broad and overlapping substrate specificities. Identification of the UGT isoforms important for the glucuronidation of new chemical entities is essential for predicting and avoiding the risk of adverse reactions due to either drug-drug interactions or genetic polymorphisms. This webinar will provide an in depth overview of in vitro methods for studying UGT pathways. Important parameters for setting up UGT assays using tissue fractions and recombinant UGT enzymes will be discussed, as well as the methods and tools currently available for conducting UGT reaction phenotyping studies.


In Vitro ABC Transporter Models and Alignment with USFDA and EMA Guidelines (part 1 of 2)
Presenter: Na Li

Much clinical evidence exists demonstrating that membrane transporters can be the key determinants of drug disposition, efficacy and safety profiles. Transporter mediated drug-drug interaction can result in severe drug side effects, causing early termination of a drug development project or withdrawal of drugs from the market. The newly published regulatory guidance concerning drug-drug interaction testing from the USFDA and EMA have listed a series of clinically relevant ABC transporters and SLC transporters. In this webinar, we will focus on in vitro ABC transporter models that align with the agency’s guidance and suitability to study drug interaction with these transporters. Our next webinar will focus on SLC transporter models.


In Vitro SLC Transporter Models and Alignment with USFDA and EMA Guidelines (part 2 of 2)
Presenter: Na Li

The newly published regulatory guidance concerning drug-drug interaction testing from the USFDA and the EMA have listed a series of clinically relevant ABC transporters and SLC transporters. In this webinar, we will describe in vitro SLC transporter models aligned with the agency’s guidance and applications in studying drug-drug interaction. The pros and cons of each in vitro model will be discussed. Much clinical evidence exists demonstrating that membrane transporters can be the key determinants of drug disposition, efficacy and safety profiles. Transporter mediated drug-drug interaction can result in severe drug side effects, causing early termination of a drug development project or withdrawal of drugs from the market.