P-glycoprotein, CYP3A, and Plasma Carboxylesterase Determine Brain Disposition and Oral Availability of the Novel Taxane Cabazitaxel (Jevtana) in Mice

ABCB1 attenuates brain exposure to the KRASG12C inhibitor opnurasib whereas binding to mouse carboxylesterase 1c influences its plasma exposure

Opnurasib (JDQ443) is a newly developed oral KRASG12C inhibitor, with a binding mechanism distinct from the registered KRASG12C inhibitors sotorasib and adagrasib. Phase I and II clinical trials for opnurasib in NSCLC are ongoing. We evaluated the pharmacokinetic roles of the ABCB1 (P-gp/MDR1) and ABCG2 (BCRP) efflux and OATP1 influx transporters, and of the metabolizing enzymes CYP3A and CES1 in plasma and tissue disposition of oral opnurasib, using genetically modified cell lines and mouse models. In vitro, opnurasib was potently transported by human (h)ABCB1 and slightly by mouse (m)Abcg2. In Abcb1a/b- and Abcb1a/b;Abcg2-deficient mice, a significant ∼100-fold increase in brain-to-plasma ratios was observed. Brain penetration was unchanged in Abcg2-/- mice. ABCB1 activity in the blood-brain barrier may therefore potentially limit the efficacy of opnurasib against brain metastases. The Abcb1a/b transporter activity could be almost completely reversed by co-administration of elacridar, a dual ABCB1/ABCG2 inhibitor, increasing the brain penetration without any behavioral or postural signs of acute CNS-related toxicity. No significant pharmacokinetic roles of the OATP1 transporters were observed. Transgenic human CYP3A4 did not substantially affect the plasma exposure of opnurasib, indicating that opnurasib is likely not a sensitive CYP3A4 substrate. Interestingly, Ces1-/- mice showed a 4-fold lower opnurasib plasma exposure compared to wild-type mice, whereas no strong effect was seen on the tissue distribution. Plasma Ces1c therefore likely binds opnurasib, increasing its retention in plasma. The obtained pharmacokinetic insights may be useful for further optimization of the clinical efficacy and safety of opnurasib, and might reveal potential drug-drug interaction risks.

Interplay of Ritonavir-Boosted Oral Cabazitaxel with the Organic Anion-Transporting Polypeptide (OATP) Uptake Transporters and Carboxylesterase 1 in Mice

Intravenously administered chemotherapeutic cabazitaxel is used for palliative treatment of prostate cancer. An oral formulation would be more patient-friendly and reduce the need for hospitalization. We therefore study determinants of the oral pharmacokinetics of cabazitaxel in a ritonavir-boosted setting, which reduces the CYP3A-mediated first-pass metabolism of cabazitaxel. We here assessed the role of organic anion-transporting polypeptides (OATPs) in the disposition of orally boosted cabazitaxel and its active metabolites, using the Oatp1a/b-knockout and the OATP1B1/1B3-transgenic mice. These transporters may substantially affect plasma clearance and hepatic and intestinal drug disposition. The pharmacokinetics of cabazitaxel and DM2 were not significantly affected by Oatp1a/b and OATP1B1/1B3 activity. In contrast, the plasma AUC0-120 min of DM1 in Oatp1a/b-/- was 1.9-fold (p < 0.05) higher than that in wild-type mice, and that of docetaxel was 2.4-fold (p < 0.05) higher. We further observed impaired hepatic uptake and intestinal disposition for DM1 and docetaxel in the Oatp-ablated strains. None of these parameters showed rescue by the OATP1B1 or -1B3 transporters in the humanized mouse strains, suggesting a minimal role of OATP1B1/1B3. Ritonavir itself was also a potent substrate for mOatp1a/b, showing a 2.9-fold (p < 0.0001) increased plasma AUC0-120 min and 3.5-fold (p < 0.0001) decreased liver-to-plasma ratio in Oatp1a/b-/- compared to those in wild-type mice. Furthermore, we observed the tight binding of cabazitaxel and its active metabolites, including docetaxel, to plasma carboxylesterase (Ces1c) in mice, which may complicate the interpretation of pharmacokinetic and pharmacodynamic mouse studies. Collectively, these results will help to further optimize (pre)clinical research into the safety and efficacy of orally applied cabazitaxel.

Coadministration of ABCB1/P-glycoprotein inhibitor elacridar improves tissue distribution of ritonavir-boosted oral cabazitaxel in mice

Developing an oral formulation for the chemotherapeutic cabazitaxel might improve its patient-friendliness, costs, and potentially exposure profile. Cabazitaxel oral availability is restricted by CYP3A-mediated first-pass metabolism, but can be substantially boosted with the CYP3A inhibitor ritonavir. We here tested whether adding the ABCB1/P-glycoprotein inhibitor elacridar to ritonavir-boosted oral cabazitaxel could further improve its tissue exposure using wild-type, CYP3A4-humanized and Abcb1a/b-/- mice. The plasma AUC0-2h of cabazitaxel was increased 2.3- and 1.9-fold in the ritonavir- and ritonavir-plus-elacridar groups of wild-type, and 10.5- and 8.8-fold in CYP3A4-humanized mice. Elacridar coadministration did not influence cabazitaxel plasma exposure. The brain-to-plasma ratio of cabazitaxel was not increased in the ritonavir group, 7.3-fold in the elacridar group and 13.4-fold in the combined booster group in wild-type mice. This was 0.4-, 4.6- and 3.6-fold in CYP3A4-humanized mice, illustrating that Abcb1 limited cabazitaxel brain exposure also during ritonavir boosting. Ritonavir itself was also a potent substrate for the Abcb1 efflux transporter, limiting its oral availability (3.3-fold) and brain penetration (10.6-fold). Both processes were fully reversed by elacridar. The tissue disposition of ritonavir-boosted oral cabazitaxel could thus be markedly enhanced by elacridar coadministration without affecting the plasma exposure. This approach should be verified in selected patient populations.

Predictability of human exposure by human-CYP3A4-transgenic mouse models: A meta-analysis

First-in-human dose predictions are primarily based on no-observed-adverse-effect levels in animal studies. Predictions from these animal models are only as effective as their ability to predict human results. To narrow the gap between human and animals, researchers have, among other things, focused on the replacement of animal cytochrome P450 (CYP) enzymes with their human counterparts (called humanization), especially in mice. Whereas research in humanized mice is extensive, the emphasis has been particularly on qualitative rather than quantitative predictions. Because the CYP3A4 enzyme is most involved in the metabolism of clinically used drugs, most benefit was expected from CYP3A4 models. There are several applications of these mouse models regarding in vivo CYP3A4 functionality, one of which might be their capacity to help improve first-in-human (FIH) dose predictions for CYP3A4-metabolized drugs. To evaluate whether human-CYP3A4-transgenic mouse models are better predictors of human exposure compared to the wild-type mouse model, we performed a meta-analysis comparing both mouse models in their ability to accurately predict human exposure of small-molecule drugs metabolized by CYP3A4. Results showed that, in general, the human-CYP3A4-transgenic mouse model had similar accuracy in the prediction of human exposure compared to the wild-type mouse model, suggesting that there is limited added value in humanization of the mouse Cyp3a enzymes if the primary aim is to acquire more accurate FIH dose predictions. Despite the results of this meta-analysis, corrections for interspecies differences through extension of human-CYP3A4-transgenic mouse models with pharmacokinetic modeling approaches seems a promising contribution to more accurate quantitative predictions of human pharmacokinetics.

Pharmacokinetics of the KRASG12C inhibitor adagrasib is limited by CYP3A and ABCB1, and influenced by binding to mouse plasma carboxylesterase 1c

Adagrasib (Krazati™) is the second FDA-approved specific KRASG12C inhibitor for non-small cell lung cancer (NSCLC) patients harboring this mutation. The impact of the drug efflux transporters ABCB1 and ABCG2, and the drug-metabolizing enzymes CYP3A and carboxylesterase 1 (CES1) on the pharmacokinetics of oral adagrasib were studied using genetically modified mouse models. Adagrasib was potently transported by human ABCB1 and modestly by mouse Abcg2 in vitro. In Abcb1a/b-/- and Abcb1a/b;Abcg2-/- mice, the brain-to-plasma ratios were enhanced by 33- and 55-fold, respectively, compared to wild-type mice, whereas ratios in Abcg2-/- mice remained unchanged. The influence of ABC transporters was completely reversed by coadministration of the dual ABCB1/ABCG2 inhibitor elacridar, increasing the brain penetration in wild-type mice by 41-fold while no signs of acute CNS toxicity were observed. Tumor ABCB1 overexpression may thus confer adagrasib resistance. Whereas the ABC transporters did not affect adagrasib plasma exposure, CYP3A and Ces1 strongly impacted its apparent oral availability. The plasma AUC0-8 h was significantly enhanced by 2.3-fold in Cyp3a-/- compared to wild-type mice, and subsequently 4.3-fold reduced in transgenic CYP3A4 mice, indicating substantial CYP3A-mediated metabolism. Adagrasib plasma exposure was strongly reduced in Ces1-/- compared to wild-type mice, but tissue exposure was slightly increased, suggesting that adagrasib binds to plasma Ces1c in mice and is perhaps metabolized by Ces1. This binding could complicate interpretation of mouse studies, especially since humans lack circulating CES1 enzyme(s). Our results may be useful to further optimize the clinical safety and efficacy of adagrasib, and give more insight into potential drug-drug interactions risks.

Natural deletion of mouse carboxylesterases Ces1c/d/e impacts drug metabolism and metabolic syndrome development

Mammalian carboxylesterase 1 enzymes can hydrolyze many xenobiotic chemicals and endogenous lipids. We here identified and characterized a mouse strain (FVB/NKI) in which three of the eight Ces1 genes were spontaneously deleted, removing Ces1c and Ces1e partly, and Ces1d entirely. We studied the impact of this Ces1c/d/e deficiency on drug and lipid metabolism and homeostasis. Ces1c/d/e-/- mice showed strongly impaired conversion of the anticancer prodrug irinotecan to its active metabolite SN-38 in plasma, spleen and lung. Plasma hydrolysis of the oral anticancer prodrug capecitabine to 5-DFCR was also profoundly reduced in Ces1c/d/e-/- mice. Our findings resolved previously unexplained FVB/NKI pharmacokinetic anomalies. On a medium-fat diet, Ces1c/d/e-/- female mice exhibited moderately higher body weight, mild inflammation in gonadal white adipose tissue (gWAT), and increased lipid load in brown adipose tissue (BAT). Ces1c/d/e-/- males showed more pronounced inflammation in gWAT and an increased lipid load in BAT. On a 5-week high-fat diet exposure, Ces1c/d/e deficiency predisposed to developing obesity, enlarged and fatty liver, glucose intolerance and insulin resistance, with severe inflammation in gWAT and increased lipid load in BAT. Hepatic proteomics analysis revealed that the acute phase response, involved in the dynamic cycle of immunometabolism, was activated in these Ces1c/d/e-/- mice. This may contribute to the obesity-related chronic inflammation and adverse metabolic disease in this strain. While Ces1c/d/e deficiency clearly exacerbated metabolic syndrome development, long-term (18-week) high-fat diet exposure overwhelmed many, albeit not all, observed phenotypic differences.

The roles of the human ATP-binding cassette transporters P-glycoprotein and ABCG2 in multidrug resistance in cancer and at endogenous sites: future opportunities for structure-based drug design of inhibitors

The ATP-binding cassette (ABC) transporters P-glycoprotein (P-gp) and ABCG2 are multidrug transporters that confer drug resistance to numerous anti-cancer therapeutics in cell culture. These findings initially created great excitement in the medical oncology community, as inhibitors of these transporters held the promise of overcoming clinical multidrug resistance in cancer patients. However, clinical trials of P-gp and ABCG2 inhibitors in combination with cancer chemotherapeutics have not been successful due, in part, to flawed clinical trial designs resulting from an incomplete molecular understanding of the multifactorial basis of multidrug resistance (MDR) in the cancers examined. The field was also stymied by the lack of high-resolution structural information for P-gp and ABCG2 for use in the rational structure-based drug design of inhibitors. Recent advances in structural biology have led to numerous structures of both ABCG2 and P-gp that elucidated more clearly the mechanism of transport and the polyspecific nature of their substrate and inhibitor binding sites. These data should prove useful helpful for developing even more potent and specific inhibitors of both transporters. As such, although possible pharmacokinetic interactions would need to be evaluated, these inhibitors may show greater effectiveness in overcoming ABC-dependent multidrug resistance in combination with chemotherapeutics in carefully selected subsets of cancers. Another perhaps even more compelling use of these inhibitors may be in reversibly inhibiting endogenously expressed P-gp and ABCG2, which serve a protective role at various blood-tissue barriers. Inhibition of these transporters at sanctuary sites such as the brain and gut could lead to increased penetration by chemotherapeutics used to treat brain cancers or other brain disorders and increased oral bioavailability of these agents, respectively.

The intravenous to oral switch of taxanes: strategies and current clinical developments

The taxanes paclitaxel, docetaxel and cabazitaxel are important anticancer agents that are widely used as intravenous treatment for several solid tumor types. Switching from intravenous to oral treatment can be more convenient for patients, improve cost-effectiveness and reduce the demands of chemotherapy treatment on hospital care. However, oral treatment with taxanes is challenging because of pharmaceutical and pharmacological factors that lead to low oral bioavailability. This review summarizes the current clinical developments in oral taxane treatment. Intravenous parent drugs, strategies in the oral switch, individual agents in clinical trials, challenges and further perspectives on treatment with oral taxanes are subsequently discussed.

Microtubule-targeting anticancer drug eribulin induces drug efflux transporter P-glycoprotein

This study examined the effects of microtubule-targeting anticancer drugs (paclitaxel, cabazitaxel, and eribulin) on the expression of drug efflux transporter P-glycoprotein, which is encoded by MDR1. Paclitaxel and eribulin induced MDR1 promoter activity in a concentration-dependent manner, while cabazitaxel had little effect in human intestinal epithelial LS174T cells. Overexpression of the nuclear receptor pregnane X receptor (PXR) gene (NR1I2) enhanced paclitaxel- and eribulin-induced MDR1 activation, but expression of the nuclear receptor co-repressor silencing mediator for retinoid and thyroid receptors (SMRT) gene (NCOR2) repressed MDR1 activation. Eribulin increased the mRNA and protein expression of P-glycoprotein in LS174T cells. Cellular uptake of rhodamine 123 and calcein-acetoxymethyl ester (calcein-AM), P-glycoprotein substrates, decreased in paclitaxel- or eribulin-treated LS174T cells. Eribulin also increased MDR1 promoter activity in human breast cancer MCF7 cells. The results suggest that the microtubule-targeting anticancer drug eribulin can induce the drug efflux transporter P-glycoprotein via PXR in human intestinal and breast cancer cells and thus influence the efficacy of anticancer drugs.

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Eribulin activates the P-glycoprotein gene (MDR1) promoter in human intestinal LS174T and breast cancer MCF7 cells.

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Eribulin increases mRNA and protein expression of P-glycoprotein in human intestinal LS174T cells.

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Eribulin can induce P-glycoprotein and modulate the efficacy of anticancer drugs.

Structural Perspectives of the CYP3A Family and Their Small Molecule Modulators in Drug Metabolism

Cytochrome P450 enzymes function to catalyze a wide range of reactions, many of which are critically important for drug response. Members of the human cytochrome P450 3A (CYP3A) family are particularly important in drug clearance, and they collectively metabolize more than half of all currently prescribed medications. The ability of these enzymes to bind a large and structurally diverse set of compounds increases the chances of their modulating or facilitating drug metabolism in unfavorable ways. Emerging evidence suggests that individual enzymes in the CYP3A family play discrete and important roles in catalysis and disease progression. Here we review the similarities and differences among CYP3A enzymes with regard to substrate recognition, metabolism, modulation by small molecules, and biological consequence, highlighting some of those with clinical significance. We also present structural perspectives to further characterize the basis of these comparisons.

Revisiting the role of ABC transporters in multidrug-resistant cancer

Most patients who die of cancer have disseminated disease that has become resistant to multiple therapeutic modalities. Ample evidence suggests that the expression of ATP-binding cassette (ABC) transporters, especially the multidrug resistance protein 1 (MDR1, also known as P-glycoprotein or P-gp), which is encoded by ABC subfamily B member 1 (ABCB1), can confer resistance to cytotoxic and targeted chemotherapy. However, the development of MDR1 as a therapeutic target has been unsuccessful. At the time of its discovery, appropriate tools for the characterization and clinical development of MDR1 as a therapeutic target were lacking. Thirty years after the initial cloning and characterization of MDR1 and the implication of two additional ABC transporters, the multidrug resistance-associated protein 1 (MRP1; encoded by ABCC1)), and ABCG2, in multidrug resistance, interest in investigating these transporters as therapeutic targets has waned. However, with the emergence of new data and advanced techniques, we propose to re-evaluate whether these transporters play a clinical role in multidrug resistance. With this Opinion article, we present recent evidence indicating that it is time to revisit the investigation into the role of ABC transporters in efficient drug delivery in various cancer types and at the blood-brain barrier.

Therapeutic Potential and Utility of Elacridar with Respect to P-glycoprotein Inhibition: An Insight from the Published In Vitro, Preclinical and Clinical Studies

The occurrence of efflux mechanisms via Permeability-glycoprotein (P-gp) recognized as an important physiological process impedes drug entry or transport across membranes into tissues. In some instances, either low oral bioavailability or lack of brain penetration has been attributed to P-gp mediated efflux activity. Therefore, the objective of development of P-gp inhibitors was to facilitate the attainment of higher drug exposures in tissues. Many third-generation P-gp inhibitors such as elacridar, tariquidar, zosuquidar, etc. have entered clinical development to fulfil the promise. The body of evidence from in vitro and in vivo preclinical and clinical data reviewed in this paper provides the basis for an effective blockade of P-gp efflux mechanism by elacridar. However, clinical translation of the promise has been elusive not just for elacridar but also for other P-gp inhibitors in this class. The review provides introspection and perspectives on the lack of clinical translation of this class of drugs and a broad framework of strategies and considerations in the potential application of elacridar and other P-gp inhibitors in oncology therapeutics.

Towards better dose individualisation: metabolic phenotyping to predict cabazitaxel pharmacokinetics in men with prostate cancer

BACKGROUND

Cabazitaxel is approved for treatment of castration-resistant metastatic prostate cancer. The current dosing strategy of cabazitaxel is based on body surface area (BSA). Body surface area is known as a poor predictor for total systemic exposure to drugs, since it does not take into account variability in activity of metabolising enzymes, necessary for clearance of drugs. As exposure to cabazitaxel is related to treatment response, it is essential to develop a better individualised dosing strategy.

METHODS

Ten patients with metastatic castration-resistant prostate cancer, who received cabazitaxel dosed on BSA as a part of routine palliative care, were enrolled in this study. Midazolam was administered as phenotyping probe for cytochrome P450 isoenzyme 3A (CYP3A). The relationship between midazolam and cabazitaxel clearance was investigated using non-linear mixed effects modelling.

RESULTS

The clearance of Midazolam highly correlated with cabazitaxel clearance (R=0.74). Midazolam clearance significantly (P<0.004) explained the majority (∼60%) of the inter-individual variability in cabazitaxel clearance in the studied population.

CONCLUSIONS

Metabolic phenotyping of CYP3A using midazolam is a promising strategy to individualise cabazitaxel dosing. Before clinical application, a randomised study is warranted.

Breast cancer resistance protein (BCRP/ABCG2) and P-glycoprotein (P-gp/ABCB1) transport afatinib and restrict its oral availability and brain accumulation

Afatinib is a highly selective, irreversible inhibitor of EGFR and HER-2. It is orally administered for the treatment of patients with EGFR mutation-positive types of metastatic NSCLC. We investigated whether afatinib is a substrate for the multidrug efflux transporters ABCB1 and ABCG2 and whether these transporters influence oral availability and brain and other tissue accumulation of afatinib. We used in vitro transport assays to assess human (h)ABCB1-, hABCG2- or murine (m)Abcg2-mediated transport of afatinib. To study the single and combined roles of Abcg2 and Abcb1a/1b in oral afatinib disposition, we used appropriate knockout mouse strains. Afatinib was transported well by hABCB1, hABCG2 and mAbcg2 in vitro. Upon oral administration of afatinib, Abcg2^-/-, Abcb1a/1b^-/- and Abcb1a/1b^-/-;Abcg2^-/- mice displayed a 4.2-, 2.4- and 7-fold increased afatinib plasma AUC_0-24 compared with wild-type mice. Abcg2-deficient strains also displayed decreased afatinib plasma clearance. At 2h, relative brain accumulation of afatinib was not significantly altered in the single knockout strains, but 23.8-fold increased in Abcb1a/1b^-/-;Abcg2^-/- mice compared to wild-type mice. Abcg2 and Abcb1a/1b restrict oral availability and brain accumulation of afatinib. Inhibition of these transporters may therefore be of clinical importance for patients with brain (micro)metastases positioned behind an intact blood-brain barrier.

The impact of Organic Anion-Transporting Polypeptides (OATPs) on disposition and toxicity of antitumor drugs: Insights from knockout and humanized mice

It is now widely accepted that organic anion-transporting polypeptides (OATPs), especially members of the OATP1A/1B family, can have a major impact on the disposition and elimination of a variety of endogenous molecules and drugs. Owing to their prominent expression in the sinusoidal plasma membrane of hepatocytes, OATP1B1 and OATP1B3 play key roles in the hepatic uptake and plasma clearance of a multitude of structurally diverse anti-cancer and other drugs. Here, we present a thorough assessment of the currently available OATP1A and OATP1B knockout and transgenic mouse models as key tools to study OATP functions in vivo. We discuss recent studies using these models demonstrating the importance of OATPs, primarily in the plasma and hepatic clearance of anticancer drugs such as taxanes, irinotecan/SN-38, methotrexate, doxorubicin, and platinum compounds. We further discuss recent work on OATP-mediated drug-drug interactions in these mouse models, as well as on the role of OATP1A/1B proteins in the phenomenon of hepatocyte hopping, an efficient and flexible way of liver detoxification for both endogenous and exogenous substrates. Interestingly, glucuronide conjugates of both the heme breakdown product bilirubin and the protein tyrosine kinase-targeted anticancer drug sorafenib are strongly affected by this process. The clinical relevance of variation in OATP1A/1B activity in patients has been previously revealed by the effects of polymorphic variants and drug-drug interactions on drug toxicity. The development of in vivo tools to study OATP1A/1B functions has greatly advanced our mechanistic understanding of their functional role in drug pharmacokinetics, and their implications for therapeutic efficacy and toxic side effects of anticancer and other drug treatments.

Cytochrome P450 and Non-Cytochrome P450 Oxidative Metabolism: Contributions to the Pharmacokinetics, Safety, and Efficacy of Xenobiotics

The drug-metabolizing enzymes that contribute to the metabolism or bioactivation of a drug play a crucial role in defining the absorption, distribution, metabolism, and excretion properties of that drug. Although the overall effect of the cytochrome P450 (P450) family of drug-metabolizing enzymes in this capacity cannot be understated, advancements in the field of non-P450-mediated metabolism have garnered increasing attention in recent years. This is perhaps a direct result of our ability to systematically avoid P450 liabilities by introducing chemical moieties that are not susceptible to P450 metabolism but, as a result, may introduce key pharmacophores for other drug-metabolizing enzymes. Furthermore, the effects of both P450 and non-P450 metabolism at a drug's site of therapeutic action have also been subject to increased scrutiny. To this end, this Special Section on Emerging Novel Enzyme Pathways in Drug Metabolism will highlight a number of advancements that have recently been reported. The included articles support the important role of non-P450 enzymes in the clearance pathways of U.S. Food and Drug Administration-approved drugs over the past 10 years. Specific examples will detail recent reports of aldehyde oxidase, flavin-containing monooxygenase, and other non-P450 pathways that contribute to the metabolic, pharmacokinetic, or pharmacodynamic properties of xenobiotic compounds. Collectively, this series of articles provides additional support for the role of non-P450-mediated metabolic pathways that contribute to the absorption, distribution, metabolism, and excretion properties of current xenobiotics.