Approaches to Better Predict Fetal Drug Exposure, Renal DDIs and CNS Drug Efficacy

This ISSX webinar will feature three presentations! The webinar will also recognize graduate students and postdoctoral fellows from academia who carried out transporter-related research and presented their work in the form of a poster at the 2023 North American ISSX meeting. The graduate student presenters will be introduced by their mentors, who will also participate in the question and answer portion of the webinar.

PREDICTION AND VERIFICATION OF FETAL EXPOSURE TO DUAL BCRP/P-GP DRUG SUBSTRATES USING THE PROTEOMICS INFORMED EFFLUX RATIO-RELATIVE EXPRESSION FACTOR (ER-REF) APPROACH AND PBPK MODELING AND SIMULATION

To inform fetal drug safety, it is important to determine or predict fetal drug exposure throughout pregnancy. The former is not possible in the first or second trimester. In contrast, at the time of birth, fetal drug exposure, relative to maternal exposure, can be estimated as Kp,uu (unbound fetal umbilical venous (UV) plasma area under the curve (AUC)/unbound maternal plasma (MP) AUC), provided the observed UV/MP values, spanning the dosing interval, are available from multiple maternal-fetal dyads. However, this fetal Kp,uu cannot be extrapolated to other drugs. To overcome the above limitations, we have used an efflux ratio-relative expression factor (ER-REF) approach to successfully predict the fetal Kp,uu of P-gp substrates. Because many drugs taken by pregnant people are also BCRP substrates, here, we extend this approach to drugs that are effluxed by both placental BCRP and P-gp or P-gp alone. To verify our predictions, we chose drugs for which UV/MP data were available at term: glyburide and imatinib (both BCRP and P-gp substrates) and nelfinavir (only P-gp substrate). First, the ER of the drugs was determined using Transwells and MDCKII cells expressing either BCRP or P-gp. Then, the ER was scaled using the proteomics-informed REF value to predict the fetal Kp,uu of the drug at term. The ER-REF predicted fetal Kp,uu of glyburide (0.43), imatinib (0.42), and nelfinavir (0.40) fell within two-fold of the corresponding in vivo fetal Kp,uu (0.44, 0.37, and 0.46, respectively). These data confirm that the ER-REF approach can successfully predict fetal drug exposure to BCRP/ P-gp and P-gp substrates, at term.

METABOLOMICS-BASED BIOMARKER APPROACH FOR IDENTIFICATION AND VALIDATION OF CLINICAL ENDOGENOUS BIOMARKERS OF RENAL ORGANIC ANION TRANSPORTERS

Endogenous substrates of drug transporters can be used as phenotypic biomarkers to predict transporter-mediated drug-drug interactions (DDIs), drug toxicity, and inter-individual variability in transport function. Inhibition of renal organic anion transporter (OAT) 1 and 3-mediated uptake and multidrug resistance-associated protein (MRP) 2 and 4-mediated efflux can increase plasma concentration and decrease urine amount of endogenous substrates, respectively, which can be used as clinical biomarkers. We identified and validated clinically relevant biomarkers of OAT1/3 and MRP2/4 using a state-of-the-art metabolomics-based DMET biomarker discovery (MDBD) approach. Untargeted metabolomics of the plasma and urine samples collected from a clinical furosemide/probenecid pharmacokinetic DDI study (n=16) yielded >10,000 features (m/z values) that were either increased or decreased in plasma and urine samples in the presence of probenecid (dual OAT/MRP inhibitor). Features that were significantly increased in plasma (1.5 to 10-fold) and were either decreased or non-significantly increased in urine samples were characterized as putative OAT1/3 biomarkers. Similarly, identification of putative MRP2/4 biomarkers included features that were significantly decreased in urine (by >45%) with non-significant change in plasma. Putative OAT1/3 biomarkers (m/z range, 130-384) belonged to the following pathways: tryptophan metabolites, steroids, peptides, glucuronide conjugates, and fatty acids. MRP2/4 biomarkers (m/z range, 110-510) were majorly bile acids, fatty acids, steroids, glycosides, and peptides. In vitro validation of the identified OAT1/3 biomarkers confirmed 12 putative OAT1 substrates as OAT1 biomarkers (>1.4-fold uptake in transporter over-expressing cells, p-value <0.05), 17 as OAT3 biomarkers and 21 as dual OAT1/3 biomarkers. This high-throughput and robust MDBD approach to identify and validate biomarkers is applicable beyond transporters.          

HOW MUCH IS ENOUGH? BI-907828: A MDM2-P53 ANTAGONIST WITH LIMITED BBB PENETRATION BUT POTENT EFFICACY IN GLIOBLASTOMA MDM2–p53 inhibition may be effective in glioblastoma (GBM). This study evaluates the pharmacokinetics/pharmacodynamics of BI-907828, a potent antagonist of MDM2, in GBM, and demonstrates a translational paradigm with a focus on a unified “Delivery – Potency – Efficacy” relationship in drug development for central nervous system(CNS) tumors. BI-907828 was tested for cytotoxicity and MDM2–p53 pathway inhibition. Systemic pharmacokinetics and transport mechanisms controlling CNS distribution were evaluated in mice. BI-907828 free fractions in cell media, mouse and human specimens were measured to determine “active” unbound concentrations. Efficacy measures, including overall survival and target expression were assessed in mouse orthotopic GBM xenografts. BI-907828 exhibited potent inhibition of MDM2–p53 pathway and promoted cell death in GBM TP53 wild-type cells. MDM2-amplified cells are highly sensitive to BI-907828, with an effective unbound concentration of 0.1 nmol/L. The CNS distribution of BI-907828 is limited by blood–brain barrier (BBB) efflux mediated by P-gp, resulting in a Kp,uu_brain of 0.002. Despite this seemingly “poor” BBB penetration, weekly administration of 10 mg/kg BI-907828 extended median survival of orthotopic GBM108 xenografts from 28 to 218 days (P < 0.0001). This excellent efficacy can be attributed to high potency, resulting in a limited, yet effective, exposure in the CNS. These studies show that efficacy of BI-907828 in orthotopic models is related to high potency even though its CNS distribution is limited by BBB efflux. Therefore, a comprehensive understanding of all aspects of the “Delivery – Potency – Efficacy” relationship is warranted in drug discovery and development, especially for treatment of CNS tumors.