Understanding the Impact of BCRP and PGP Efflux Transporters on the Disposition of Their Endogenous, Xenobiotic and Dietary Substrates
Breast Cancer Resistant Protein (BCRP) and P-glycoprotein (PGP) are membrane-bound efflux transporters that transport multiple chemical classes of compounds and act as barriers to tissue permeability, thereby regulating tissue exposure of their substrates. The role of these transporters in therapeutic resistance of their xenobiotic substrates due to their expression and efflux function at target organs/tissues, especially in brain and intestine, is well established, which has fueled investigation toward identification of their inhibitors. Multiple clinically used drugs and dietary chemicals have been reported to inhibit these transporters and potentially increase the exposure of concomitantly administered BCRP and/or PGP substrates, which might be desirable (to increase efficacy of the substrate drug) as well as undesirable (as it can affect the disposition of the substrate in tissues where it might cause toxicity). Therefore, drug-drug and food-drug interactions with BCRP and PGP are a major concern in drug development, as recognized by US Food and Drug Administration (FDA), European Medicines Agency (EMA) and International Transporter Consortium (ITC).
BCRP and PGP transporters are also known to transport endogenous substrates and have been associated with important physiological functions. This includes an inflammatory bowel disease-like phenotype associated with a non-functional PGP polymorphism (Ala893), while a loss of function mutation in BCRP (Q141K) is known to be positively associated with gout and negatively associated with Parkinson’s syndrome. Although a few endogenous substrates of BCRP and PGP have been identified, a systemic understanding of their physiological function and effect on the endogenous metabolome is still lacking.
In the current studies, utilizing untargeted metabolomics, coupled with transcriptomic analysis, we sought to understand the endogenous function of Bcrp and/Pgp transporters in rats, by comparing the plasma and cerebrospinal fluid metabolome of wild-type and Bcrp-Pgp double knockout rats. Our findings revealed several putative novel endogenous/dietary substrates of Bcrp and Pgp transporters and established a novel understanding of the physiological function of these transporters. We also identified the anesthetic/analgesic ketamine as a putative substrate of Bcrp and Pgp, and found that ketamine pharmacokinetics (PK), as well as pharmacodynamics (PD), are affected by these efflux transporters. Importantly, the Bcrp-Pgp inhibitor, elacridar, was found to alter the PD of ketamine, indicating that ketamine might be prone toward drug-drug interactions (DDIs) associated with Bcrp-Pgp inhibitors. Finally, utilizing a Bcrp dietary substrate, Pheophorbide A (PhA), we developed an in vivo assay for the assessment of DDI due to inhibition of Bcrp at enterocytes. Our results demonstrated that PhA can be potentially used to create a reliable, high-throughput and less expensive in vivo assay for determining Bcrp-mediated DDIs