A Multifactorial Approach to Hepatobiliary Transporter Assessment Enables Improved Therapeutic Compound Development

Abstract

The bile salt export pump (BSEP) is expressed at the canalicular domain of hepatocytes, where it serves as the primary route of elimination for monovalent bile acids (BAs) into the bile canaliculi. The most compelling evidence linking dysfunction in BA transport with liver injury in humans is found with carriers of mutations that render BSEP nonfunctional. Based on mounting evidence, there appears to be a strong association between drug-induced BSEP interference and liver injury in humans; however, causality has not been established. For this reason, drug-induced BSEP interference is best considered a susceptibility factor for liver injury as other host- or drug-related properties may contribute to the development of hepatotoxicity. To better understand the association between BSEP interference and liver injury in humans, over 600 marketed or withdrawn drugs were evaluated in BSEP expressing membrane vesicles. The example of a compound that failed during phase 1 human trials is also described, AMG 009. AMG 009 showed evidence of liver injury in humans that was not predicted by preclinical safety studies, and BSEP inhibition was implicated. For 109 of the drugs with some effect on in vitro BSEP function, clinical use, associations with hepatotoxicity, pharmacokinetic data, and other information were annotated. A steady state concentration (C(ss)) for each of these annotated drugs was estimated, and a ratio between this value and measured IC₅₀ potency values were calculated in an attempt to relate exposure to in vitro potencies. When factoring for exposure, 95% of the annotated compounds with a C(ss)/BSEP IC₅₀ ratio ≥ 0.1 were associated with some form of liver injury. We then investigated the relationship between clinical evidence of liver injury and effects to multidrug resistance-associated proteins (MRPs) believed to play a role in BA homeostasis. The effect of 600+ drugs on MRP2, MRP3, and MRP4 function was also evaluated in membrane vesicle assays. Drugs with a C(ss)/BSEP IC₅₀ ratio ≥ 0.1 and a C(ss)/MRP IC₅₀ ratio ≥ 0.1 had almost a 100% correlation with some evidence of liver injury in humans. These data suggest that integration of exposure data, and knowledge of an effect to not only BSEP but also one or more of the MRPs, is a useful tool for informing the potential for liver injury due to altered BA transport.

Tyrosine and aurora kinase inhibitors diminish transport function of multidrug resistance-associated protein (MRP) 4 and breast cancer resistance protein (BCRP)

“…Only 2 VEGFR & PDGFR and 1 BCR/ABL kinase inhibitors were found to be clinically relevant. Similar to the report of Morgan, et al, pazopanib was identified as having the potential for clinically relevant MRP4 inhibition [35]. Additionally, though the studies of Morgan, et al, also identified gefitinib as a potent inhibitor of MRP4, gefitinib-mediated inhibition of MRP4 transport activity was not deemed clinically relevant [35], which is similar to the current results.…”

“…Similar to the report of Morgan, et al, pazopanib was identified as having the potential for clinically relevant MRP4 inhibition [35]. Additionally, though the studies of Morgan, et al, also identified gefitinib as a potent inhibitor of MRP4, gefitinib-mediated inhibition of MRP4 transport activity was not deemed clinically relevant [35], which is similar to the current results. The majority of the TKI/AKIs investigated were found to potentially be clinically relevant inhibitors of BCRP, with 15 of the 20 compounds having a C ss /IC 50 ratio >0.1.…”

“…Of the 16 TKIs examined, 6 exhibited IC 50 values <10 μM (Table 2), namely, the EGFR inhibitors erlotinib, gefitinib, lapatinib and neratinib; the VEGFR & PDGFR inhibitor sorafenib; and the BCR/ABL inhibitor nilotinib. Others have reported the inhibitory potency of some TKIs against MRP4-mediated transport, particularly dasatinib, gefitinib, imatinib, lapatinib, neratinib, pazopanib, and sunitinib [35]. We found a similar IC 50 for gefinitib inhibition of MRP4 (4.48 μM) to that of Morgan, et al (4.6 μM), and a somewhat comparable IC 50 for dasatanib (18.03 μM in the present study versus 27.3 μM).…”

“…However, the IC 50 values for the remaining TKIs evaluated by Morgan, et al were notably different, which may reflect differences in the experimental conditions such as the specific transporter substrate and range of inhibitor concentrations selected for investigation (e.g. extrapolation of an IC 50 value beyond the tested concentrations) [35,36]. The majority of the potent MRP4 inhibitors fell within the EGFR TKI class with only one potent inhibitor each in the dual VEGFR & PDGFR and the BCR/ABL classes.…”

“…To provide insight to the clinical relevance of TKI/AKI inhibition of MRP4-and BCRP-mediated transport, steady-state total plasma C ss values were extracted from Micromedex and manufacturer package inserts. The C ss values were expressed as a ratio to the IC 50 for each transporter with a C ss /IC 50 ratio >0.1 regarded as having potential for clinically relevant transporter inhibition [35,38]. Although it is well-recognized that drug concentrations within cells may become more concentrated than measured C ss in patient plasma, either due to transporter-mediated accumulation or organelle binding, the use of total plasma C ss values have been recommended and are used herein in the absence of unbound intracellular drug concentration data [35,38,39].…”