Evaluation of ABT-751, a novel anti-mitotic agent able to overcome multi-drug resistance, in melanoma cells

PURPOSE

Drug efflux transporter associated multi-drug resistance (MDR) is a potential limitation in the use of taxane chemotherapies for the treatment of metastatic melanoma. ABT-751 is an orally bioavailable microtubule-binding agent capable of overcoming MDR and proposed as an alternative to taxane-based therapies.

METHODS

This study compares ABT-751 to taxanes in vitro, utilizing seven melanoma cell line models, publicly available gene expression and drug sensitivity databases, a lung cancer cell line model of MDR drug efflux transporter overexpression (DLKP-A), and drug efflux transporter ATPase assays.

RESULTS

Melanoma cell lines exhibit a low but variable protein and RNA expression of drug efflux transporters P-gp, BCRP, and MDR3. Expression of P-gp and MDR3 correlates with sensitivity to taxanes, but not to ABT-751. The anti-proliferative IC50 profile of ABT-751 was higher than the taxanes docetaxel and paclitaxel in the melanoma cell line panel, but fell within clinically achievable parameters. ABT-751 IC50 was not impacted by P-gp-overexpression in DKLP-A cells, which display strong resistance to the P-gp substrate taxanes compared to DLKP parental controls. The addition of ABT-751 to paclitaxel treatment significantly decreased cell proliferation, suggesting some reversal of MDR. ATPase activity assays suggest that ABT-751 is a potential BCRP substrate, with the ability to inhibit P-gp ATPase activity.

CONCLUSION

Our study confirms that ABT-751 is active against melanoma cell lines and models of MDR at physiologically relevant concentrations, it inhibits P-gp ATPase activity, and it may be a BCRP and/or MDR3 substrate. ABT-751 warrants further investigation alone or in tandem with other drug efflux transporter inhibitors for hard-to-treat MDR melanoma.

One-step synthesis of diaryloxadiazoles as potent inhibitors of BCRP

Aim: BCRP plays a major role in the efflux of cytotoxic molecules, limiting their antiproliferative activity. We aimed to design and synthesize new BCRP inhibitors to render cancerous tumors more sensitive toward anticancer agents. Materials & methods: Based on our previous work, we conceived potential BCRP inhibitors derived from 1,3,4-oxadiazoles bearing two substituted phenyl rings. Results: Evaluating 19 derivatives, we found that 2,5-diaryl-1,3,4-oxadiazoles possessing methoxy groups were the most active. The highest activity was recorded with derivatives bearing three methoxy groups. The most active compound (3j) was selective in inhibiting BCRP and nontoxic as evidenced by cellular tests. Conclusion: 3j is a promising BCRP inhibitor thanks to its synthetic accessibility and biological profile.

Investigation into the impact of proton pump inhibitors on sertraline transport across the blood-brain barrier

As a widely used antidepressant that works by inhibiting the reuptake of serotonin, sertraline exerts an antidepressant effect depending on its concentration in the brain, which might be limited by the blood-brain barrier (BBB). It is highly possible to combine proton pump inhibitors (PPIs) with sertraline in clinical trials. Nevertheless, the role played by PPIs in regulating the transport of sertraline across the BBB remains unclear. Here, the impact of PPIs on the distribution of sertraline in the brain and the mechanisms involved were investigated. A mouse brain distribution study showed that Omeprazole (OME), Pantoprazole (PAN), Ilaprazole (ILA), and Esomeprazole (ESO) increased the area under the brain concentration-time curves (AUC) for sertraline by 2.02-, 3.18-, 3.04-, and 4.21-fold, respectively, after the 14-day administration of PPIs. Besides, PPIs significantly increased the permeability of sertraline in brain perfusion experiments, with PAN having the highest rank order, followed by ILA, OME, and ESO. In the tail suspension test (TST), co-administration PPI groups showed significantly shorter immobility time than the control group. In vitro, four PPIs inhibited sertraline efflux in breast cancer resistance protein (BCRP)-overexpressing MDCKII cells, and showed a mixed inhibition type. In this study, PPIs were further found to inhibit the mRNA and protein expression of brain BCRP. To sum up, the findings of this study revealed that PPIs could enhance the brain distribution and antidepressant effect of sertraline, which may be attributed to the inhibition of BCRP expression at the BBB by PPIs.

Breast Cancer Resistance Protein Limits Fetal Transfer of Tadalafil in Mice

Tadalafil, a phosphodiesterase 5 (PDE5) inhibitor, is a candidate therapeutic agent for fetal growth restriction and hypertensive disorders of pregnancy. In this study, we elucidated the fetal transfer of tadalafil in comparison with that of sildenafil, the first PDE5 inhibitor to be approved. We also examined the contributions of multidrug resistance protein 1 (MDR1) and breast cancer resistance protein (BCRP) to fetal transfer. Tadalafil or sildenafil was administered to wild-type, Mdr1a/b-double-knockout or Bcrp-knockout pregnant mice by continuous infusion from gestational day (GD) 14.5 to 17.5, and the fetal-to-maternal plasma concentration ratio of unbound drug (unbound F/M ratio) was evaluated at GD 17.5. The values of unbound F/M ratio of tadalafil and sildenafil in wild-type mice were 0.80 and 1.6, respectively. The unbound F/M ratio of tadalafil was increased to 1.1 and 1.7 in Mdr1a/b-knockout and Bcrp-knockout mice, respectively, while the corresponding values for sildenafil were equal to or less than that in wild-type mice, respectively. A transcellular transport study revealed that basal-to-apical transport of both tadalafil and sildenafil was significantly higher than transport in the opposite direction in MDCKII-BCRP cells. Our research reveals that tadalafil is a newly identified substrate of human and mouse BCRP, and it appears that the fetal transfer of tadalafil is, at least in part, attributed to the involvement of BCRP within the placental processes in mice. The transfer of sildenafil to the fetus was not significantly constrained by BCRP, even though sildenafil was indeed a substantial substrate for BCRP.

Dissimilar Effect of P-Glycoprotein and Breast Cancer Resistance Protein Inhibition on the Distribution of Erlotinib to the Retina and Brain in Humans and Mice

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are two ATP-binding cassette efflux transporters that are coexpressed at the human blood-brain barrier (BBB) and blood-retina barrier (BRB). While pharmacological inhibition of P-gp and/or BCRP results in increased brain distribution of dual P-gp/BCRP substrate drugs, such as the tyrosine kinase inhibitor erlotinib, the effect of P-gp and/or BCRP inhibition on the retinal distribution of such drugs has hardly been investigated. In this study, we used positron emission tomography (PET) imaging to assess the effect of transporter inhibition on the distribution of [11C]erlotinib to the human retina and brain. Twenty two healthy volunteers underwent two PET scans after intravenous (i.v.) injection of a microdose (<5 μg) of [11C]erlotinib, a baseline scan, and a second scan either with concurrent i.v. infusion of tariquidar to inhibit P-gp (n = 5) or after oral intake of single ascending doses of erlotinib (300 mg, 650 mg, or 1000 mg, n = 17) to saturate erlotinib transport. In addition, transport of [3H]erlotinib to the retina and brain was assessed in mice by in situ carotid perfusion under various drug transporter inhibition settings. In comparison to the baseline PET scan, coadministration of tariquidar or erlotinib led to a significant decrease of [11C]erlotinib total volume of distribution (VT) in the human retina by -25 ± 8% (p ≤ 0.05) and -41 ± 16% (p ≤ 0.001), respectively. In contrast, erlotinib intake led to a significant increase in [11C]erlotinib VT in the human brain (+20 ± 16%, p ≤ 0.001), while administration of tariquidar did not result in any significant changes. In situ carotid perfusion experiments showed that both P-gp and BCRP significantly limit the distribution of erlotinib to the mouse retina and brain but revealed a similar discordant effect at the mouse BRB and BBB following co-perfusion with tariquidar and erlotinib as in humans. Co-perfusion with prototypical inhibitors of solute carrier transporters did not reveal a significant contribution of organic cation transporters (e.g., OCTs and OCTNs) and organic anion-transporting polypeptides (e.g., OATP2B1) to the retinal and cerebral distribution of erlotinib. In conclusion, we observed a dissimilar effect after P-gp and/or BCRP inhibition on the retinal and cerebral distribution of [11C]erlotinib. The exact mechanism for this discrepancy remains unclear but may be related to the function of an unidentified erlotinib uptake carrier sensitive to tariquidar inhibition at the BRB. Our study highlights the great potential of PET to study drug distribution to the human retina and to assess the functional impact of membrane transporters on ocular drug distribution.

Expression, Function and Trafficking of the Human ABCG2 Multidrug Transporter Containing Mutations in an Unstructured Cytoplasmic Loop

The human ABCG2 multidrug transporter plays a crucial role in the absorption and excretion of xeno- and endobiotics, contributes to cancer drug resistance and the development of gout. In this work, we have analyzed the effects of selected variants, residing in a structurally unresolved cytoplasmic region (a.a. 354-367) of ABCG2 on the function and trafficking of this protein. A cluster of four lysines (K357-360) and the phosphorylation of a threonine (T362) residue in this region have been previously suggested to significantly affect the cellular fate of ABCG2. Here, we report that the naturally occurring K360del variant in human cells increased ABCG2 plasma membrane expression and accelerated cellular trafficking. The variable alanine replacements of the neighboring lysines had no significant effect on transport function, and the apical localization of ABCG2 in polarized cells has not been altered by any of these mutations. Moreover, in contrast to previous reports, we found that the phosphorylation-incompetent T362A, or the phosphorylation-mimicking T362E variants in this loop had no measurable effects on the function or expression of ABCG2. Molecular dynamics simulations indicated an increased mobility of the mutant variants with no major effects on the core structure of the protein. These results may help to decipher the potential role of this unstructured region within this transporter.

Placental BCRP transporter reduces cadmium accumulation and toxicity in immortalized human trophoblasts

Cadmium (Cd) is a ubiquitous environmental metal detectable in most pregnant women. Animal and human studies demonstrate that in utero exposure to Cd reduces birth weight and impairs perinatal growth due to placental toxicity. BCRP is a prominent transporter that can efflux xenobiotics from the placenta. This study sought to investigate Cd transport and toxicity in cultured human BeWo trophoblasts with reduced expression and function of the placental barrier transporter BCRP. Knockdown (KD) of BCRP protein expression and function in BeWo trophoblasts increased the intracellular accumulation of Cd by 100% following treatment with 1 μM CdCl2. No change in the expression of Cd uptake transporters was observed between control and BCRP-KD cells. Reduced BCRP expression impaired viability of BeWo cells exposed to CdCl2 for 48 hr (BCRP-KD IC50: 11 μM, control cells IC50: 18 μM). Moreover, BCRP-KD cells were more sensitive to CdCl2-induced cytotoxicity compared to control BeWo cells. CdCl2 treatment strongly induced the expression of the metal-binding protein metallothionein (MT) in both control and BCRP-KD cells, with significantly greater MT upregulation in Cd-treated BCRP-KD cells. These data suggest that the BCRP transporter reduces Cd accumulation in syncytiotrophoblasts, which may be one mechanism to reduce subsequent toxicity to the placenta and developing fetus.

Implications of BCRP modulation on PTZ-induced seizures in mice: Role of ko143 and metformin as adjuvants to lamotrigine

Blood-brain barrier (BBB) efflux transporters' overexpression hinders antiepileptic drug brain entry. Breast cancer resistance protein (BCRP) is a major BBB efflux transporter. In the present work, BCRP's role as a mechanism that might contribute to drug-resistant epilepsy (DRE) in a mouse model of acute seizures was studied with further assessment of the effect of its inhibition by ko143 and metformin (MET) on lamotrigine (LTG) bioavailability and efficacy. 42 male mice divided into 6 groups: G1: Normal control, G2: LTG-injected healthy mice: LTG 20 mg/kg i.p., G3: Acute seizures (A.S) mice: Pentylenetetrazole (PTZ) 50 mg/kg i.p., G4: LTG-treated A.S mice: LTG 20 mg/kg + PTZ 50 mg/kg i.p., G5: Ko143 + LTG treated A.S mice: Ko143 15 mg/kg i.p. before LTG + PTZ, G6: MET + LTG treated A.S mice: MET 200 mg/kg i.p. before LTG + PTZ. Seizures severity, serum, brain LTG, and brain BCRP were assessed. PTZ group experienced the highest seizure frequency and brain BCRP expression. Ko143 and MET groups showed a significant decrease in brain BCRP with subsequent improvement in brain LTG level and better seizure control. BCRP has a significant role in epilepsy resistance and its inhibition with ko143 or MET adds value to DRE management.

Inhibition of efflux transporters by poly ADP-ribose polymerase inhibitors

Poly ADP-ribose polymerase (PARP) inhibitors have been approved for the treatment of various cancers. They share a similar mechanism of action but have differences in pharmacokinetic characteristics and potential for drug-drug interactions (DDI). This study evaluated the potential ATP-binding cassette transporter-mediated interactions between PARP inhibitors (niraparib, olaparib and rucaparib) and statins (atorvastatin and rosuvastatin). We studied the inhibitory activity of PARP inhibitors on breast cancer resistance protein (BCRP), multidrug resistance-associated protein 3 (MRP3) and P-glycoprotein (P-gp) using vesicular transport assays and determined the concentrations required for 50% inhibition (IC50 ). Then, we predicted the increase of statin exposure followed by the administration of PARP inhibitors using a mechanistic static model. Rucaparib was the strongest inhibitor of BCRP-mediated rosuvastatin transport (IC50 13.7 μM), followed by niraparib (42.6 μM) and olaparib (216 μM). PARP inhibitors did not affect MRP3. While niraparib appeared to inhibit P-gp, the inhibition showed large variability. The inhibition of intestinal BCRP by rucaparib, niraparib and olaparib was predicted to elevate rosuvastatin exposure by 52%, 37% and 24%, respectively. The interactions between PARP inhibitors and rosuvastatin are probably of minor clinical significance alone, but combined with other predisposing factors, they may increase the risk of rosuvastatin-associated adverse effects.

Structural Basis of the Allosteric Inhibition of Human ABCG2 by Nanobodies

ABCG2 is an ATP-binding cassette transporter that exports a wide range of xenobiotic compounds and has been recognized as a contributing factor for multidrug resistance in cancer cells. Substrate and inhibitor interactions with ABCG2 have been extensively studied and small molecule inhibitors have been developed that prevent the export of anticancer drugs from tumor cells. Here, we explore the potential for inhibitors that target sites other than the substrate binding pocket of ABCG2. We developed novel nanobodies against ABCG2 and used functional analyses to select three inhibitory nanobodies (Nb8, Nb17 and Nb96) for structural studies by single particle cryo-electron microscopy. Our results showed that these nanobodies allosterically bind to different regions of the nucleotide binding domains. Two copies of Nb8 bind to the apex of the NBDs preventing them from fully closing. Nb17 binds near the two-fold axis of the transporter and interacts with both NBDs. Nb96 binds to the side of the NBD and immobilizes a region connected to key motifs involved in ATP binding and hydrolysis. All three nanobodies prevent the transporter from undergoing conformational changes required for substrate transport. These findings advance our understanding of the molecular basis of modulation of ABCG2 by external binders, which may contribute to the development of a new generation of inhibitors. Furthermore, this is the first example of modulation of human multidrug resistance transporters by nanobodies.

In vitro identification of decreased function phenotype ABCG2 variants

Reduced activity of efflux transporter ABCG2, caused e.g., by inhibition or decreased function genetic variants, can increase drug absorption and plasma levels. ABCG2 has one clinically significant single nucleotide variant Q141K (c.421C>A), which leads to decreased protein levels and transport activity. In addition to Q141K, ABCG2 has over 500 rare (<1% minor allele frequency) nonsynonymous variants, but their functionality remains unknown. We studied the transport activity and abundance of 30 rare ABCG2 variants. The variants were transiently expressed in HEK293 cells. Transport activity and protein abundance were measured from inside-out crude membrane vesicles. Results were normalised to the reference ABCG2, while Q141K was used to categorise variants into decreased and normal function phenotypes based on their apparent transport activity. Fourteen variants (G80E, D128V, T434M, Q437R, C438R, C438W, C438Y, L479S, P480L, S486N, T512N, S519P, G553D and K647E) had similar or lower apparent transport activity than Q141K and thus were categorised as having a decreased function phenotype. Protein abundance could not explain all of the observed changes in transport activity: Only six variants (D128V, Q437R, C438R, S519P, G553D, and K647E) had similar or lower abundance compared to Q141K. The decreased function variants may increase systemic drug exposure and therefore cause interindividual variability in pharmacokinetics. In the future, in vitro phenotype classification may help to design personalised drug treatments.

Genetic Predictors of Antipsychotic Efflux Impairment via Blood-Brain Barrier: Role of Transport Proteins

Antipsychotic (AP)-induced adverse drug reactions (ADRs) are a current problem of biological and clinical psychiatry. Despite the development of new generations of APs, the problem of AP-induced ADRs has not been solved and continues to be actively studied. One of the important mechanisms for the development of AP-induced ADRs is a genetically-determined impairment of AP efflux across the blood-brain barrier (BBB). We present a narrative review of publications in databases (PubMed, Springer, Scopus, Web of Science E-Library) and online resources: The Human Protein Atlas; GeneCards: The Human Gene Database; US National Library of Medicine; SNPedia; OMIM Online Mendelian Inheritance in Man; The PharmGKB. The role of 15 transport proteins involved in the efflux of drugs and other xenobiotics across cell membranes (P-gp, TAP1, TAP2, MDR3, BSEP, MRP1, MRP2, MRP3, MRP4, MRP5, MRP6, MRP7, MRP8, MRP9, BCRP) was analyzed. The important role of three transporter proteins (P-gp, BCRP, MRP1) in the efflux of APs through the BBB was shown, as well as the association of the functional activity and expression of these transport proteins with low-functional and non-functional single nucleotide variants (SNVs)/polymorphisms of the ABCB1, ABCG2, ABCC1 genes, encoding these transport proteins, respectively, in patients with schizophrenia spectrum disorders (SSDs). The authors propose a new pharmacogenetic panel "Transporter protein (PT)-Antipsychotic (AP) Pharmacogenetic test (PGx)" (PTAP-PGx), which allows the evaluation of the cumulative contribution of the studied genetic biomarkers of the impairment of AP efflux through the BBB. The authors also propose a riskometer for PTAP-PGx and a decision-making algorithm for psychiatrists. Conclusions: Understanding the role of the transportation of impaired APs across the BBB and the use of genetic biomarkers for its disruption may make it possible to reduce the frequency and severity of AP-induced ADRs, since this risk can be partially modified by the personalized selection of APs and their dosing rates, taking into account the genetic predisposition of the patient with SSD.

Regulation of BCRP expression and sulfasalazine pharmacokinetics by the nuclear receptor REV-ERBα

BCRP (breast cancer resistance protein) is a crucial efflux transporter involved in the regulation of the pharmacokinetics and pharmacodynamics of a wide range of drugs. Herein, we aimed to investigate a potential role for the nuclear receptor REV-ERBα in the regulation of BCRP expression and sulfasalazine (a BCRP probe substrate) pharmacokinetics.Regulation of BCRP expression by REV-ERBα was assessed using Rev-erbα^-/- mice and AML12 and CT26 cells. Pharmacokinetic analysis was performed with Rev-erbα^-/- and wild-type mice after sulfasalazine administration.We found that the expression levels of BCRP mRNA and protein were downregulated in the liver and small intestine of Rev-erbα-dificient mice. In line with this, Rev-erbα ablation increased the systemic exposures of oral sulfasalazine.Positive regulation of BCRP expression and function by REV-ERBα was furtherly confirmed in AML12 and CT26 cells. Moreover, indirect regulation of Bcrp expression by REV-ERBα was potentially mediated by a negative transcription factor DEC2, which is a downstream target of REV-ERBα.In conclusion, REV-ERBα positively regulates BCRP expression in mice, thereby affecting sulfasalazine pharmacokinetics.

A pharmacokinetic drug-drug interaction study between rosuvastatin and emvododstat, a potent anti-SARS-CoV-2 (COVID-19) DHODH (dihydroorotate dehydrogenase) inhibitor

A therapeutic agent that targets both viral replication and the hyper-reactive immune response would offer a highly desirable treatment for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; COVID-19) management. Emvododstat (PTC299) was found to be a potent inhibitor of immunomodulatory and inflammation-related processes by the inhibition of dihydroorotate dehydrogenase (DHODH) to reduce SARS-CoV-2 replication. DHODH is the rate-limiting enzyme of the de novo pyrimidine nucleotide biosynthesis pathway. This drug interaction study was performed to determine whether emvododstat was an inhibitor of breast cancer resistance protein (BCRP) transporters in humans. Potential drug-drug interactions (DDIs) between emvododstat and a BCRP transporter substrate (rosuvastatin) were investigated by measuring plasma rosuvastatin concentrations before and after emvododstat administration. There was no apparent difference in rosuvastatin plasma exposure. The geometric means of maximum plasma rosuvastatin concentrations (Cmax ) were 4369 (rosuvastatin) and 5141 pg/mL (rosuvastatin + emvododstat) at 4 h postdose. Geometric mean rosuvastatin area under the concentration-time curve (AUC) from time 0 to the last measurable plasma concentration was 45 616 and 48 975 h·pg/mL when administered alone and after 7 days of b.i.d. emvododstat dosing, respectively. Geometric least squares mean ratios for Cmax and AUC were approximately equal to 1. Overall, administration of multiple doses of 100 mg emvododstat b.i.d. for 7 days in combination with a single dose of rosuvastatin was safe and well tolerated. Emvododstat can be safely administered with other BCRP substrate drugs. Hence, pharmacokinetic DDI mediated via BCRP inhibition is not expected when emvododstat and BCRP substrates are coadministered.

Usefulness of a humanized tricellular static transwell blood-brain barrier model as a microphysiological system for drug development applications. - A case study based on the benchmark evaluations of blood-brain barrier microphysiological system

Microphysiological system (MPS), a new technology for in vitro testing platforms, have been acknowledged as a strong tool for drug development. In the central nervous system (CNS), the blood‒brain barrier (BBB) limits the permeation of circulating substances from the blood vessels to the brain, thereby protecting the CNS from circulating xenobiotic compounds. At the same time, the BBB hinders drug development by introducing challenges at various stages, such as pharmacokinetics/pharmacodynamics (PK/PD), safety assessment, and efficacy assessment. To solve these problems, efforts are being made to develop a BBB MPS, particularly of a humanized type. In this study, we suggested minimal essential benchmark items to establish the BBB-likeness of a BBB MPS; these criteria support end users in determining the appropriate range of applications for a candidate BBB MPS. Furthermore, we examined these benchmark items in a two-dimensional (2D) humanized tricellular static transwell BBB MPS, the most conventional design of BBB MPS with human cell lines. Among the benchmark items, the efflux ratios of P-gp and BCRP showed high reproducibility in two independent facilities, while the directional transports meditated through Glut1 or TfR were not confirmed. We have organized the protocols of the experiments described above as standard operating procedures (SOPs). We here provide the SOPs with the flow chart including entire procedure and how to apply each SOP. Our study is important developmental step of BBB MPS towards the social acceptance, which enable end users to check and compare the performance the BBB MPSs.

ATP-binding cassette efflux transporters and MDR in cancer

Of the many known multidrug resistance (MDR) mechanisms, ATP-binding cassette (ABC) transporters expelling drug molecules out of cells is a major factor limiting the efficacy of present-day anticancer drugs. In this review, we highlights updated information on the structure, function, and regulatory mechanisms of major MDR-related ABC transporters, such as P-glycoprotein (P-gp), multidrug resistance protein 1 (MRP1), and breast cancer resistance protein (BCRP), and the effect of modulators on their functions. We also provide focused information on different modulators of ABC transporters that could be utilized against the emerging MDR crisis in cancer treatment. Finally, we discuss the importance of ABC transporters as therapeutic targets in light of future strategic planning for translating ABC transporter inhibitors into clinical practice.

Inhibitors of ABCG2-mediated multidrug resistance: Lead generation through computer-aided drug design

Human breast cancer resistance protein (BCRP), known also as ABCG2, plays a major role in multiple drug resistance (MDR) in tumor cells. Through this ABC transporter, cancer cells acquire the ability of resistance to structurally and functionally unrelated anticancer drugs. Nowadays, the design of ABCG2 inhibitors as potential agents to enhance the chemotherapy efficacy is an interesting strategy. In this context, we have used computer-aided drug design (CADD) based on available data of a large series of potent inhibitors from our groups as an approach in guiding the design of effective ABCG2 inhibitors. We report therein the results on the use of the FLAPpharm method to elucidate the pharmacophoric features of one of the ABCG2 binding sites involved in the regulation of the basal ATPase activity of the transporter. The predictivity of the model was evaluated by testing three predicted compounds which were found to induce high inhibitory activity of BCRP, in the nanomolar range for the best of them.

Recent advances in the in vitro and in vivo methods to assess impact of P-glycoprotein and breast cancer resistance protein transporters in central nervous system drug disposition

One challenge in central nervous system (CNS) drug discovery has been ensuring the blood-brain barrier (BBB) penetration of compounds at an efficacious concentration that provides suitable safety margins for clinical investigation. Research providing for the accurate prediction of brain penetration of compounds during preclinical discovery is important to a CNS program. In the BBB, P-glycoprotein (P-gp) (ABCB1) and breast cancer resistance protein (BCRP) (ABCG2) transporters have been demonstrated to play a major role in the active efflux of endogenous compounds and xenobiotics out of the brain microvessel cells and back to the systemic circulation. In the past 10 years, there has been significant technological improvement in the sensitivity of quantitative proteomics methods, in vivo imaging, in vitro methods of organoid and microphysiological systems, as well as in silico quantitative physiological based pharmacokinetic and systems pharmacology models. Scientists continually leverage these advancements to interrogate the distribution of compounds in the CNS which may also show signals of substrate specificity of P-gp and/or BCRP. These methods have shown promise toward predicting and quantifying the unbound concentration(s) within the brain relevant for efficacy or safety. In this review, the authors have summarized the in vivo, in vitro, and proteomics advancements toward understanding the contribution of P-gp and/or BCRP in restricting the entry of compounds to the CNS of either healthy or special populations. Special emphasis has been provided on recent investigations on the application of a proteomics-informed approach to predict steady-state drug concentrations in the brain. Moreover, future perspectives regarding the role of these transporters in newer modalities are discussed.

Novel inhibitors of breast cancer resistance protein (BCRP, ABCG2) among marketed drugs

Drug-drug interactions (DDIs) are a major concern for the safe use of medications. Breast cancer resistance protein (BCRP) is a clinically relevant ATP-binding cassette (ABC) transporter for drug disposition. Inhibition of BCRP increases the plasma concentrations of BCRP substrate drugs, which potentially could lead to adverse drug reactions. The aim of the present study was to identify BCRP inhibitors amongst a library of 232 commonly used drugs and anticancer drugs approved by the United States Food and Drug Administration (FDA). BCRP inhibition studies were carried out using the vesicular transport assay. We found 75 drugs that reduced the relative transport activity of BCRP to less than 25% of the vehicle control and were categorized as strong inhibitors. The concentration required for 50% inhibition (IC₅₀) was determined for 13 strong inhibitors that were previously poorly characterized for BCRP inhibition. The IC₅₀ ranged from 1.1 to 11 µM, with vemurafenib, dabigatran etexilate and everolimus being the strongest inhibitors. According to the drug interaction guidance documents from the FDA and the European Medicines Agency (EMA), in vivo DDI studies are warranted if the theoretical intestinal luminal concentration of a drug exceeds its IC₅₀ by tenfold. Here, the IC₅₀ values for eight of the drugs were 100-fold lower than their theoretical intestinal luminal concentration. Moreover, a mechanistic static model suggested that vemurafenib, bexarotene, dabigatran etexilate, rifapentine, aprepitant, and ivacaftor could almost fully inhibit intestinal BCRP, increasing the exposure of concomitantly administered rosuvastatin over 90%. Therefore, clinical studies are warranted to investigate whether these drugs cause BCRP-mediated DDIs in humans.

Design, Synthesis and Biological Evaluation of Quinazolinamine Derivatives as Breast Cancer Resistance Protein and P-Glycoprotein Inhibitors with Improved Metabolic Stability

A series of twenty-two quinazolinamine derivatives showing potent inhibitory activities on breast cancer resistance protein (BCRP) and p-glycoprotein (P-gp) were synthesized. A cyclopropyl-containing quinazolinamine 22 was identified as a dual BCRP and P-gp inhibitor, while azide-containing quinazolinamine 33 showed BCRP inhibitory activity. These lead compounds were further investigated in a battery of mechanistic experiments. Compound 22 changed the localization of BCRP and P-gp in cells, thus inhibiting the efflux of anticancer drugs by the two ATP-binding cassette (ABC) transporters. In addition, both 22 and 33 significantly stimulated the ATP hydrolysis of the BCRP transporter, indicating that they can be competitive substrates of the BCRP transporter, and thereby increase the accumulation of mitoxantrone in BCRP-overexpressing H460/MX20 cells. Azide derivative 33, exhibited a greater inhibitory effect on BCRP after UV activation and can serve as a valuable probe for investigating the interactions of quinazolinamine derivatives with BCRP. Notably, the dual BCRP and P-gp inhibitors 4-5, 22-24, 27, and BCRP inhibitor 33 showed improved metabolic stability compared to Ko143.

OAT, OATP, and MRP Drug Transporters and the Remote Sensing and Signaling Theory

The coordinated movement of organic anions (e.g., drugs, metabolites, signaling molecules, nutrients, antioxidants, gut microbiome products) between tissues and body fluids depends, in large part, on organic anion transporters (OATs) [solute carrier 22 (SLC22)], organic anion transporting polypeptides (OATPs) [solute carrier organic (SLCO)], and multidrug resistance proteins (MRPs) [ATP-binding cassette, subfamily C (ABCC)]. Depending on the range of substrates, transporters in these families can be considered multispecific, oligospecific, or (relatively) monospecific. Systems biology analyses of these transporters in the context of expression patterns reveal they are hubs in networks involved in interorgan and interorganismal communication. The remote sensing and signaling theory explains how the coordinated functions of drug transporters, drug-metabolizing enzymes, and regulatory proteins play a role in optimizing systemic and local levels of important endogenous small molecules. We focus on the role of OATs, OATPs, and MRPs in endogenous metabolism and how their substrates (e.g., bile acids, short chain fatty acids, urate, uremic toxins) mediate interorgan and interorganismal communication and help maintain and restore homeostasis in healthy and disease states.

COVID-19 drugs: potential interaction with ATP-binding cassette transporters P-glycoprotein and breast cancer resistance protein

Background

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2, has resulted in acute respiratory distress, fatal systemic manifestations (extrapulmonary as well as pulmonary), and premature mortality among many patients. Therapy for COVID-19 has focused on the treatment of symptoms and of acute inflammation (cytokine storm) and the prevention of viral infection. Although the mechanism of COVID-19 is not fully understood, potential clinical targets have been identified for pharmacological, immunological, and vaccinal approaches.

Area covered

Pharmacological approaches including drug repositioning have been a priority for initial COVID-19 therapy due to the time-consuming nature of the vaccine development process. COVID-19 drugs have been shown to manage the antiviral infection cycle (cell entry and replication of proteins and genomic RNA) and anti-inflammation. In this review, we evaluated the interaction of current COVID-19 drugs with two ATP-binding cassette transporters [P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP)] and potential drug-drug interactions (DDIs) among COVID-19 drugs, especially those associated with P-gp and BCRP efflux transporters.

Expert opinion

Overall, understanding the pharmacodynamic/pharmacokinetic DDIs of COVID-19 drugs can be useful for pharmacological therapy in COVID-19 patients.

Effects of ABCB1 polymorphisms on the transport of ponatinib into the cerebrospinal fluid in Japanese Philadelphia chromosome-positive acute lymphoblastic leukaemia patients

The effects of polymorphisms of ABCB1 and ABCG2 on the dose-adjusted plasma trough concentrations and cerebrospinal fluid (CSF)-to-plasma ratios of ponatinib were evaluated. Blood (C₄ ) and CSF (CSF₄ ) concentrations at 4 h after administration were determined. The median (95% confidence interval) CSF₄ -to-C₄ ratio of ponatinib in subjects homozygous for ABCB1 variants 1236T/T, 2677T/T + T/A or 3435T/T were significantly higher than that in a group of subjects with other genotypes (P = .026, .012 and .015, respectively). The median (95% confidence interval) CSF₄ -to-C₄ ratio of ponatinib in 4 patients with the combination of ABCB1 variants 1236T/T-2677T/T + T/A-3435T/T was 2.62% (1.42-3.42%); this ratio was significantly higher than that in subjects with other genotypes (1.08% [0.89-1.47%]; P = .006). The brain distribution of ponatinib was affected by ABCB1 polymorphisms and therefore seems to be modulated by P-glycoprotein at the blood-brain and blood-CSF barriers.

The Role of ABC Transporters in Skin Cells Exposed to UV Radiation

ABC transporters are expressed in skin cells to protect them against harmful xenobiotics. Moreover, these transmembrane proteins have a number of additional functions that ensure skin homeostasis. This review summarizes the current knowledge about the role of specific ABC proteins in the skin, including multi-drug resistance transporters (MDR1/3), the transporter associated with antigen processing 1/2 (TAP1/2), the cystic fibrosis transmembrane conductance regulator (CFTR), sulfonylurea receptors (SUR1/2), and the breast cancer resistance protein (BCRP). Additionally, the effect of UV radiation on ABC transporters is shown. The exposure of skin cells to UV radiation often leads to increased activity of ABC transporters-as has been observed in the case of MDRs, TAPs, CFTR, and BCRP. A different effect of oxidative stress has been observed in the case of mitochondrial SURs. However, the limited data in the literature-as indicated in this article-highlights the limited number of experimental studies dealing with the role of ABC transporters in the physiology and pathophysiology of skin cells and the skin as a whole. At the same time, the importance of such knowledge in relation to the possibility of daily exposure to UV radiation and xenobiotics, used for both skin care and the treatment of its diseases, is emphasized.

Characterization of a Potent, Selective, and Safe Inhibitor, Ac15(Az8)2, in Reversing Multidrug Resistance Mediated by Breast Cancer Resistance Protein (BCRP/ABCG2)

Overexpression of breast cancer resistance transporter (BCRP/ABCG2) in cancers has been explained for the failure of chemotherapy in clinic. Inhibition of the transport activity of BCRP during chemotherapy should reverse multidrug resistance. In this study, a triazole-bridged flavonoid dimer Ac15(Az8)2 was identified as a potent, nontoxic, and selective BCRP inhibitor. Using BCRP-overexpressing cell lines, its EC50 for reversing BCRP-mediated topotecan resistance was 3 nM in MCF7/MX100 and 72 nM in S1M180 in vitro. Mechanistic studies revealed that Ac15(Az8)2 restored intracellular drug accumulation by inhibiting BCRP-ATPase activity and drug efflux. It did not down-regulate the cell surface BCRP level to enhance drug retention. It was not a transport substrate of BCRP and showed a non-competitive relationship with DOX in binding to BCRP. A pharmacokinetic study revealed that I.P. administration of 45 mg/kg of Ac15(Az8)2 resulted in plasma concentration above its EC50 (72 nM) for longer than 24 h. It increased the AUC of topotecan by 2-fold. In an in vivo model of BCRP-overexpressing S1M180 xenograft in Balb/c nude mice, it significantly reversed BCRP-mediated topotecan resistance and inhibited tumor growth by 40% with no serious body weight loss or death incidence. Moreover, it also increased the topotecan level in the S1M180 xenograft by 2-fold. Our results suggest that Ac15(Az8)2 is a promising candidate for further investigation into combination therapy for treating BCRP-overexpressing cancers.

Chicken xenobiotic receptor upregulates the BCRP/ABCG2 transporter

The transporter breast cancer resistance protein (BCRP, encoded by ABCG2) influences the bioavailability and elimination of numerous substrate drugs during clinical therapy. The xenobiotic-sensing nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) reportedly regulate functional expression of BCRP in mammalian species. However, it is unknown whether chicken xenobiotic receptor (CXR) regulates the expression and activity of BCRP. This study aimed to investigate the role of CXR in regulation of BCRP in chicken using in vitro and in vivo models. CXR was expressed in the main drug-metabolizing tissues of chickens, and its expression correlated well with that of the prototypical target genes CYP2H1 and ABCG2. BCRP expression was upregulated, and transporter activity was increased, in chicken primary hepatocytes exposed to the CXR agonist metyrapone. Using RNA interference and ectopic expression techniques to manipulate the cellular CXR status, we confirmed that ABCG2 gene regulation depended on CXR. In vivo experiments showed that metyrapone induced BCRP in the liver, kidney, duodenum, and jejunum of chickens. Coadministration of metyrapone significantly changed the pharmacokinetic behavior of orally administered florfenicol (substrate of chicken BCRP), with a lower C_max (4.62 vs. 7.35 µg/mL, P < 0.01) and AUC_0-t (15.83 vs. 24.18 h·mg/L, P < 0.01) as well as a higher T_max (0.96 vs. 0.79 h, P < 0.05) and Cl/F (0.13 vs. 0.08 L/h/kg, P < 0.05). Together, our data suggest that CXR is involved in regulation of BCRP, and consequently, coadministration of a CXR agonist can affect the pharmacokinetic behavior of an orally administered BCRP substrate.

Augmented Therapeutic Potential of EC-Synthetic Retinoids in Caco-2 Cancer Cells Using an In Vitro Approach

Colorectal cancer therapies have produced promising clinical responses, but tumor cells rapidly develop resistance to these drugs. It has been previously shown that EC19 and EC23, two EC-synthetic retinoids, have single-agent preclinical anticancer activity in colorectal carcinoma. Here, isobologram analysis revealed that they have synergistic cytotoxicity with retinoic acid receptor (RAR) isoform-selective agonistic retinoids such as AC261066 (RARβ2-selective agonist) and CD437 (RARγ-selective agonist) in Caco-2 cells. This synergism was confirmed by calculating the combination index (lower than 1) and the dose reduction index (higher than 1). Flow cytometry of combinatorial IC₅₀ (the concentration causing 50% cell death) confirmed the cell cycle arrest at the SubG₀-G₁ phase with potentiated apoptotic and necrotic effects. The reported synergistic anticancer activity can be attributed to their ability to reduce the expression of ATP-binding cassette (ABC) transporters including P-glycoprotein (P-gp1), breast cancer resistance protein (BCRP) and multi-drug resistance-associated protein-1 (MRP1) and Heat Shock Protein 70 (Hsp70). This adds up to the apoptosis-promoting activity of EC19 and EC23, as shown by the increased Caspase-3/7 activities and DNA fragmentation leading to DNA double-strand breaks. This study sheds the light on the possible use of EC-synthetic retinoids in the rescue of multi-drug resistance in colorectal cancer using Caco-2 as a model and suggests new promising combinations between different synthetic retinoids. The current in vitro results pave the way for future studies on these compounds as possible cures for colorectal carcinoma.

Ivermectin induces chicken BCRP/ABCG2 expression and function: Involvement of CXR signaling pathway and mRNA stabilization

Ivermectin is a macrocyclic lactone antiparasitic drug widely used in human and veterinary medicine. Previous studies indicated that ivermectin could interact with P-glycoprotein, being a good inducer and substrate; however, it is unknown whether ivermectin affects BCRP of chicken. In this study, we found that ivermectin distinctly affected the expression of BCRP in a time- and concentration-dependent up-regulatory way in chicken primary hepatocytes. Subsequent series of experiments showed that the BCRP induction is related with the increase of CXR expression and, promoting CXR translocations to the nucleus and enhancing the stability of Abcg2 mRNA at the post-transcriptional level by ivermectin. Furthermore, we observed that ivermectin also enhanced the stability of Abcg2 mRNA at the post-transcriptional level by Act-D chase assay. We got the similar results by in vivo test that ivermectin-induced BCRP and CXR expression in pharmacologically important tissues, and decreased the apparent permeability coefficient of florfenicol (substrate of chicken BCRP). In conclusion, the results indicated that ivermectin could induce chicken BCRP expression and function through the transcriptional CXR signaling pathway and post-transcriptional mRNA stabilization.

Developing an In Vitro to In Vivo Extrapolation (IVIVE) Model to Predict Human Milk-to-Plasma Drug Concentration Ratios

Determining the amount of drug transferred into human milk is critical for benefit-risk analysis of taking medication while breastfeeding. In this study, we developed an in vitro and in vivo extrapolation (IVIVE) model to predict human milk/plasma (M/P) drug concentration ratios. Drug unionized fractions at pH 7.0 (F_ni,7.0) and 7.4 (F_ni,7.4), drug fractions unbound in human plasma (f_up) and milk (f_um), and in vitro cell permeability in both directions (efflux ratio, ER) were incorporated into the IVIVE model. A multiple regression E_max model was chosen to predict f_um from f_up and polar surface area (PSA). A total of 97 drugs with experimental ER from Caco-2 cells were used to test the IVIVE model. The M/P ratios predicted by the IVIVE model had a 1.93-fold geometric mean fold error (GMFE) and 72% of predictions were within two-fold error (Pw2FE), which were superior to the performance of previously reported five models. The IVIVE model showed a reasonable prediction accuracy for passive diffusion drugs (GMFE = 1.71-fold, Pw2FE = 82%, N = 50), BCRP substrates (BCRP: GMFE = 1.91-fold, Pw2FE = 60%, N = 5), and substrates of P-gp and BCRP (GMFE = 1.74-fold, Pw2FE = 75%, N = 8) and a lower prediction performance for P-gp substrates (GMFE = 2.51-fold, Pw2FE = 55%, N = 22). By fitting the observed M/P ratios of 39 P-gp substrates, an optimized ER (1.61) was generated to predict the M/P ratio of P-gp substrates using the developed IVIVE model. Compared with currently available in vitro models, the developed IVIVE model provides a more accurate prediction of the drug M/P ratio, especially for passive diffusion drugs. The model performance is expected to be further improved when more experimental f_um and ER data are available.

The potential roles of retinoids in combating drug resistance in cancer: implications of ATP-binding cassette (ABC) transporters

Multidrug resistance (MDR) means that tumour cells become unresponsive during or after the course of treatment to one or more of chemotherapeutic drugs. Chemotherapeutic resistance critically limits the treatment outcomes and remains a key challenge for clinicians. The alternation in intracellular drug concentration through the modulation of its transport across the plasma membrane is the major cause for MDR and is adopted by various mediators, including ATP-requiring enzymes (ATPases). Among these ATPases, ABC transporters have been extensively studied, and found to be highly implicated in tumorigenesis and MDR. The present review sheds light on the documented effects of retinoids on ABC enzymes to understand their mechanism in combating cancer cell resistance. This would open the gate to test the mechanism and applicability of different new synthetic retinoids in literature and market as modulators of ATP-dependent efflux pumping activity, and promote their applicability in diminishing anti-cancer drug resistance.

Pharmacokinetics of Temsavir, the Active Moiety of the HIV-1 Attachment Inhibitor Prodrug, Fostemsavir, Coadministered with Cobicistat, Etravirine, Darunavir/Cobicistat, or Darunavir/Ritonavir with or without Etravirine in Healthy Participants

Fostemsavir is a prodrug of temsavir, a first-in-class attachment inhibitor that binds directly to HIV-1 gp120, preventing initial viral attachment and entry into host CD4⁺ T cells with demonstrated efficacy in phase 2 and 3. Temsavir is a P-glycoprotein and breast cancer resistance protein (BCRP) substrate; its metabolism is mediated by esterase and CYP3A4 enzymes. Drugs that induce or inhibit CYP3A, P-glycoprotein, and BCRP may affect temsavir concentrations. Understanding potential drug-drug interactions (DDIs) following fostemsavir coadministration with antiretrovirals approved for HIV-1-infected treatment-experienced patients, including darunavir plus cobicistat (DRV/c) or DRV plus low-dose ritonavir (DRV/r) and etravirine, is clinically relevant. Open-label, single-sequence, multiple-dose, multicohort DDI studies were conducted in healthy participants (n = 46; n = 32). The primary objective was to assess the effects of DRV/r, etravirine, DRV/r plus etravirine, cobicistat, and DRV/c on temsavir systemic exposures; safety was a secondary objective. Compared with fostemsavir alone, coadministration with DRV/r increased the temsavir maximum observed plasma concentration (C_max), area under the concentration-time curve in one dosing interval (AUC_tau), and plasma trough concentration (C_tau) by 52%, 63%, and 88%, respectively, while etravirine decreased the temsavir C_max, AUC_tau, and C_tau by ∼50% each. DRV/r plus etravirine increased the temsavir C_max, AUC_tau, and C_tau by 53%, 34%, and 33%, respectively. Compared with fostemsavir alone, coadministration with cobicistat increased the temsavir C_max, AUC_tau, and C_tau by 71%, 93%, and 136%, respectively; DRV/c increased the temsavir C_max, AUC_tau, and C_tau by 79%, 97%, and 124%, respectively. Fostemsavir with all combinations was generally well tolerated. No dose adjustment is required for fostemsavir when coadministered with strong CYP3A inhibitors, P-glycoprotein inhibitors, and modest inducers, including regimens with DRV/r, DRV/c, cobicistat, etravirine, and DRV/r plus etravirine based on the therapeutic margin for temsavir (ClinicalTrials.gov registration no. NCT02063360 and NCT02277600).

Exploration of novel phthalazinone derivatives as potential efflux transporter inhibitors for reversing multidrug resistance and improving the oral absorption of paclitaxel

Chemotherapy is an important means of cancer treatment. However, overexpression of efflux transporters (including but not limited to P-gp and BCRP) can lead to resistance to cancer chemotherapy. Multiple-target inhibitors of efflux transporter can be overcome the resistance and improve the oral bioavailability of chemotherapy drugs. Therefore, we designed and synthesized a series of phthalazinone ring derivatives (1-20) with different aromatic heterocycles substituents on the amide bond for dual inhibition of P-gp and BCRP. Most target compounds significantly increased the accumulation of P-gp substrates in the chemo-resistant cancer cell lines by inhibiting the efflux of transporters. Compound 19 in particular showed stronger MDR reversal compared to Gefitinib and Verapamil, and comparable to that of the BCRP inhibitor Ko143. In addition, compound 19 improved intestinal absorption of paclitaxel (PTX) and enhanced the bioavailability of the orally administered drug in vivo.

Practical Application of Rodent Transporter Knockout Models to assess Brain Penetration in Drug Discovery

BACKGROUND & OBJECTIVE

Compound X is a drug candidate for the treatment of neurodegenerative diseases. Its brain distribution was evaluated as part of the lead identification and optimization of early drug discovery.

METHODS

The brain distribution of compound X was studied in genetic transporter knockout rodent models, in vivo models with a chemical inhibitor and in vitro transporter cell systems.

RESULTS

Compound X was found to be a substrate for human Breast Cancer-Resistance Protein (BCRP) in vitro (efflux ratio 8.1) and rodent Bcrp in vivo (Kp,uuKO/Kp,uuWT = 0.15/0.057 = 2.7, p < 0.05) but not a substrate for human P-glycoprotein (P-gp) in vitro (efflux ratio 1.0) nor rodent P-gp in vivo (Kp,uuKO/Kp,uuWT = 0.056/0.051 = 1.1, p > 0.05). When both transporters were knocked out in vivo, Kp,uu increased to 0.51 ± 0.02. Similar patterns observed across compounds with related chemistry corroborated structure-activity relationship.

CONCLUSION

While in vitro assays showed compound X to be a substrate for human BCRP and not P-gp, in vivo studies indicated a synergistic effect between rodent efflux transporters. However, this only accounted for ~50% of restricted BBB-transport, suggesting involvement from other efflux transporters. Given Kp,uu is a key criterion for assessing technical quality of CNS candidates before progression into clinical development, it is important to identify relevant screening assays for a better understanding of low Kp,uu and brain distribution in pre-clinical models for translation to humans.

Novel microtubule inhibitor SQ overcomes multidrug resistance in MCF-7/ADR cells by inhibiting BCRP function and mediating apoptosis

The occurrence of multidrug resistance (MDR) is one of the impediments in the clinical treatment of breast cancer, and MDR breast cancer has abnormally high breast cancer resistance protein (BCRP/ABCG2) expression. However, there are currently no clinical drugs that inhibit this target. Our previous study found that 2-Methoxy-5((3,4,5-trimethosyphenyl)seleninyl) phenol (SQ0814061/SQ), a small molecule drug with low toxicity to normal tissues, could target microtubules, inhibit the proliferation of breast cancer, and reduce its migration and invasion abilities. However, the effect and the underlying mechanism of SQ on MDR breast cancers are still unknown. Therefore, in this study, we investigated the effect of SQ on adriamycin-resistant MCF-7 (MCF-7/ADR) cells and explored the underlying mechanism. The MTT assay showed that SQ had potent cytotoxicity to MCF-7/ADR cells. In particular, the results of western blot and flow cytometry proved that SQ could effectively inhibit the expression of BCRP in MCF-7/ADR cells to decrease its drug delivery activity. In addition, SQ could block the cell cycle at G2/M phase in parental and MCF-7/ADR cells, thereby mediating cell apoptosis, which was related with the inhibition of PI3K-Akt-MDM2 pathway. Taken together, our findings indicate that SQ overcomes multidrug resistance in MCF-7/ADR cells by inhibiting BCRP function and mediating apoptosis through PI3K-Akt-MDM2 pathway inhibition.

Magnolol and Honokiol Inhibited the Function and Expression of BCRP with Mechanism Exploration

Breast cancer resistance protein (BCRP), one of the ATP-binding cassette (ABC) transporters, was associated with the multidrug resistance (MDR) of chemotherapy. Magnolol (MN) and honokiol (HK) are major bioactive polyphenols of Magnolia officinalis. This study investigated the effects of MN and HK on the function and expression of BCRP for the purpose of developing BCRP inhibitor to overcome MDR. Cell lines including MDCKII-BCRP and MDCKII-WT were used for evaluating the function and expression of BCRP. The results showed that MN (100-12.5 µM) and HK (100-12.5 µM) significantly decreased the function of BCRP by 80~12% and 67~14%, respectively. In addition, MN and HK were verified as substrates of BCRP. Furthermore, MN and HK reduced the protein expression of BCRP, and inhibited the phosphorylation of epidermal growth factor receptor (EGFR) and phosphatidylinositol 3-kinase (PI3K). In conclusion, both MN and HK decreased the function and expression of BCRP via EGFR/PI3K signaling pathway. Therefore, both compounds were promising candidates for reversing the MDR of chemotherapy.

Risk of Hematologic Events With Coadministration of Methotrexate and the Breast Cancer Resistance Protein Inhibitor Febuxostat

BACKGROUND

The breast cancer resistance protein (BCRP) is a key drug transporter found in the liver, kidney, central nervous system, and gastrointestinal tract. Due to the wide expression of BCRP, interactions of other drugs with methotrexate (MTX) may differ in oral and intravenous MTX users, and understanding of these interactions may be useful in preventing severe adverse events. Febuxostat, a urate-lowering drug, inhibits BCRP.

OBJECTIVE

The objective of this study was to clarify the differences in the drug-drug interaction profiles of oral and intravenous methotrexate, associated with BCRP.

METHODS

We analyzed the Japanese Adverse Drug Event Report database and compared the frequency of hematologic events in patients taking oral and intravenous MTX, with or without the concomitant use of febuxostat or allopurinol. Hematologic events were defined as pancytopenia and neutropenia. Multiple logistic regression analysis was then used to identify the risk factors for hematologic events in oral and intravenous MTX users.

RESULTS

We identified 8 453 oral and 810 intravenous MTX users with 546 and 126 cases of hematologic events, respectively. Compared with those not using febuxostat, a disproportionate number of hematologic events was observed in intravenous MTX users concomitantly using febuxostat (P < 0.01). The multivariate logistic analysis of intravenous MTX users showed that hematologic events were significantly associated with febuxostat use (P < 0.01) and age ≥ 60 years (P < 0.01).

CONCLUSION AND RELEVANCE

Our findings suggest that patients being treated with intravenous MTX who concomitantly use febuxostat may be at an increased risk of hematologic events, presumably due to BCRP-mediated drug-drug interaction.

Assessment of Transporter-Mediated Drug Interactions for Enasidenib Based on a Cocktail Study in Patients With Relapse or Refractory Acute Myeloid Leukemia or Myelodysplastic Syndrome

As a first-in-class, selective, potent inhibitor of the isocitrate dehydrogenase-2 (IDH2) mutant protein, enasidenib was approved by the US Food and Drug Administration in 2017 for the treatment of adult patients with relapsed or refractory acute myeloid leukemia with an isocitrate dehydrogenase-2 mutation. An in vitro study showed that enasidenib at clinically relevant concentrations has effects on multiple drug metabolic enzymes and transporters, including inhibition of P-glycoprotein, breast cancer resistance protein, organic anion transporter (OAT) P1B1, and OATP1B3 transporters. Therefore, a drug-drug interaction study was conducted to assess the impact of enasidenib at steady state on the pharmacokinetics of several probe compounds in patients with relapsed or refractory acute myeloid leukemia or myelodysplastic syndrome, including the probes herein described in this article, digoxin and rosuvastatin. Results from 8 patients (all Asian) with a mean age of 67.1 years showed that following coadministration of enasidenib (100 mg, 28-day once-daily schedule) for 28 days (at steady state), digoxin's (0.25 mg) area under the plasma concentration-time curve from time 0 to 30 days was 1.2-fold (90% confidence interval, 0.9-1.6), compared with digoxin alone. Following coadministration of enasidenib (100 mg, 28-day once-daily schedule) for 28 days (at steady state), rosuvastatin's (10 mg) area under the plasma concentration-time curve from time 0 to infinity was 3.4-fold (90% confidence interval, 2.6-4.5) compared with rosuvastatin alone. These results should serve as the basis for dose recommendations for drugs that are substrates of P-glycoprotein, breast cancer resistance protein, OATP1B1, and OATP1B3 transporters, when used concomitantly with enasidenib.

Piceatannol, a Structural Analog of Resveratrol, Is an Apoptosis Inducer and a Multidrug Resistance Modulator in HL-60 Human Acute Myeloid Leukemia Cells

Acute myeloid leukemia is characterized by uncontrolled clonal proliferation of abnormal myeloid progenitor cells. Despite recent advances in the treatment of this disease, the prognosis and overall long-term survival for patients remain poor, which drives the search for new chemotherapeutics and treatment strategies. Piceatannol, a polyphenolic compound present in grapes and wine, appears to be a promising chemotherapeutic agent in the treatment of leukemia. The aim of the present study was to examine whether piceatannol induces autophagy and/or apoptosis in HL-60 human acute myeloid leukemia cells and whether HL-60 cells are able to acquire resistance to piceatannol toxicity. We found that piceatannol at the IC90 concentration of 14 µM did not induce autophagy in HL-60 cells. However, it induced caspase-dependent apoptosis characterized by phosphatidylserine externalization, disruption of the mitochondrial membrane potential, caspase-3 activation, internucleosomal DNA fragmentation, PARP1 cleavage, chromatin condensation, and fragmentation of cell nuclei. Our findings also imply that HL-60 cells are able to acquire resistance to piceatannol toxicity via mechanisms related to MRP1 activity. Our results suggest that the use of piceatannol as a potential chemotherapeutic agent may be associated with the risk of multidrug resistance, warranting its use in combination with other chemotherapeutic agents.

A phase 1, open-label, drug-drug interaction study of rucaparib with rosuvastatin and oral contraceptives in patients with advanced solid tumors

Purpose

This study aimed at evaluating the effect of rucaparib on the pharmacokinetics of rosuvastatin and oral contraceptives in patients with advanced solid tumors and the safety of rucaparib with and without coadministration of rosuvastatin or oral contraceptives.

Methods

Patients received single doses of oral rosuvastatin 20 mg (Arm A) or oral contraceptives ethinylestradiol 30 µg + levonorgestrel 150 µg (Arm B) on days 1 and 19 and continuous doses of rucaparib 600 mg BID from day 5 to 23. Serial blood samples were collected with and without rucaparib for pharmacokinetic analysis.

Results

Thirty-six patients (n = 18 each arm) were enrolled and received at least 1 dose of study drug. In the drug–drug interaction analysis (n = 15 each arm), the geometric mean ratio (GMR) of maximum concentration (C_max) with and without rucaparib was 1.29 for rosuvastatin, 1.09 for ethinylestradiol, and 1.19 for levonorgestrel. GMR of area under the concentration–time curve from time zero to last quantifiable measurement (AUC_0–last) was 1.34 for rosuvastatin, 1.43 for ethinylestradiol, and 1.56 for levonorgestrel. There was no increase in frequency of treatment-emergent adverse events (TEAEs) when rucaparib was given with either of the probe drugs. In both arms, most TEAEs were mild in severity and considered unrelated to study treatment.

Conclusion

Rucaparib 600 mg BID weakly increased the plasma exposure to rosuvastatin or oral contraceptives. Rucaparib safety profile when coadministered with rosuvastatin or oral contraceptives was consistent with that of rucaparib monotherapy. Dose adjustments of rosuvastatin and oral contraceptives are not necessary when coadministered with rucaparib.

ClinicalTrials.gov NCT03954366; Date of registration May 17, 2019.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00280-021-04338-7.

Ginkgo biloba leaf extract suppresses intestinal human breast cancer resistance protein expression in mice: Correlation with gut microbiota

In this study, we investigated the effects of treatment with Gingko biloba leaf extract (GLE) on intestinal transporter expression and gut microbiota composition in mice and the correlation between intestinal transporter expression and gut microbiota composition in mice. When GLE was orally administered to mice, intestinal BCRP expression was significantly suppressed. Pharmacokinetic studies showed that the maximum plasma concentration and area under the curve values of sulfasalazine were increased more than twice by treatment with GLE compared with those in the control group. GLE treatment significantly decreased the populations of Proteobacteria and Deferribacteres at the phylum level. Correlation analysis showed that BCRP expression was positively or negatively correlated with the composition of gut bacteria. In Caco-2 cells, GLE treatment did not affect BCRP expression, but treatment with the lysates of GLE-treated mouse feces significantly suppressed BCRP expression. These findings demonstrate that the suppression of intestinal BCRP expression following GLE treatment may occur through modulation of the gut microbiota composition. Thus, the present study suggests that modulation of gut microbiota composition may cause drug transporter-mediated herb-drug interactions.

Expression levels of ABCG2 and CD61 genes in breast cancer tissues of Iranian population

Breast cancer as the most common female cancer is a malignancy with heterogeneous course. Dysregulation of several genes has been associated with development of this malignancy. Among these genes are the stem cell markers CD61 and breast cancer resistance protein (BCRP or ATP-binding cassette super-family G member 2 (ABCG2)). ABCG2 is one of the major efflux transporters implicated in multidrug resistance in cancer cells. In the present study, we compared expression of CD61 and ABCG2 transcripts between 30 breast cancer tissues and matched adjacent non-cancerous tissues (ANCTs) using real time qPCR technique. There was no significant difference in expression of CD61 or ABCG2 between tumoral tissues and ANCTs (Expression ratios = 1.21 and 0.98, P values = 0.55 and 0.96, respectively). There was a trend toward association between relative expression of CD61 (tumoral tissues versus ANCTs) and patients' age (P = 0.05) in a way that older patients tended to over-express this marker in their tumoral tissues compared with the matched ANCTs. Moreover, there was a significant association between expression of this gene and tumor size (P = 0.04) in a way that all tumors with sizes less than 2 cm showed down-regulation of CD61 (as compared with the matched ANCTs). Expression of CD61 was significantly higher in tumor tissues with extracapsular nodal extension compared with confined lesions (P = 0.007). Moreover, expression of ABCG2 was significantly higher in tumor tissues of patients aged less than 55 years compared with older patients (P = 0.04). There was no significant correlation between expression of CD61 and ABCG2 either in tumoral tissues or in ANCTs. The current investigation shows association or trends toward association between expression of two cancer stem cell markers and some clinical data of breast cancer patients such as extracapsular nodal extension, age and tumor size which might imply their importance in the pathogenesis of breast cancer.

Meta-Analysis of Food Effect on Oral Absorption of Efflux Transporter Substrate Drugs: Does Delayed Gastric Emptying Influence Drug Transport Kinetics?

The oral route of drug administration is the most convenient method of drug delivery, but it is associated with variable bioavailability. Food is one of the major factors that affect oral drug absorption by influencing drug properties (e.g., solubility and dissolution rate) and physiological factors (e.g., metabolism and transport across the gastrointestinal tract). The aim of this work was to investigate the effect of food on the high-affinity intestinal efflux transporter substrate drugs. We hypothesized that transport efficiency is higher in the fed state as compared to the fasted state because of the lower intestinal lumen drug concentration due to prolonged gastric emptying time. A systematic analysis of reported clinical food-effect (FE) studies on 311 drugs was performed and the association of the efflux transport efficiency was investigated on the FE magnitude, i.e., changes in maximal plasma concentration and area under the plasma concentration-time profile curve for both solubility and permeability-limited drugs. In total, 124 and 88 drugs showed positive and negative FE, respectively, whereas 99 showed no FE. As expected, the solubility-limited drugs showed positive FE, but interestingly, drugs with a high potential for efflux transport, were associated with negative FE. Moreover, a high-fat diet was associated with a higher magnitude of negative FE for high-affinity efflux transporter substrates as compared to a low-fat diet. To account for changes in drug absorption after food intake, the prolonged gastric emptying time should be considered in the physiologically based pharmacokinetic (PBPK) modeling of orally absorbed efflux transporter substrate drugs.

The Role of ABCG2 in the Pathogenesis of Primary Hyperuricemia and Gout-An Update

Urate homeostasis in humans is a complex and highly heritable process that involves i.e., metabolic urate biosynthesis, renal urate reabsorption, as well as renal and extrarenal urate excretion. Importantly, disturbances in urate excretion are a common cause of hyperuricemia and gout. The majority of urate is eliminated by glomerular filtration in the kidney followed by an, as yet, not fully elucidated interplay of multiple transporters involved in the reabsorption or excretion of urate in the succeeding segments of the nephron. In this context, genome-wide association studies and subsequent functional analyses have identified the ATP-binding cassette (ABC) transporter ABCG2 as an important urate transporter and have highlighted the role of single nucleotide polymorphisms (SNPs) in the pathogenesis of reduced cellular urate efflux, hyperuricemia, and early-onset gout. Recent publications also suggest that ABCG2 is particularly involved in intestinal urate elimination and thus may represent an interesting new target for pharmacotherapeutic intervention in hyperuricemia and gout. In this review, we specifically address the involvement of ABCG2 in renal and extrarenal urate elimination. In addition, we will shed light on newly identified polymorphisms in ABCG2 associated with early-onset gout.

Effect of Upadacitinib on the Pharmacokinetics of Rosuvastatin or Atorvastatin in Healthy Subjects

This phase 1, 2‐part, 2‐period, open‐label, drug‐drug interaction study evaluated the potential for pharmacokinetic interactions between upadacitinib and rosuvastatin, an organic anion transporting polypeptide (OATP) 1B1 and breast cancer resistance protein substrate, or atorvastatin, a cytochrome P450 3A, OATP1B1, and OATP1B3 substrate, in 36 healthy volunteers. During period 1, a single dose of rosuvastatin (5 mg; part 1) or atorvastatin (10 mg; part 2) was administered on day 1, followed by a washout period of 5 days. During period 2, once‐daily doses of upadacitinib extended‐release (30 mg) were administered on days 1 to 10, and a single dose of rosuvastatin (5 mg; part 1) or atorvastatin (10 mg; part 2) was administered 1 hour after the upadacitinib dose on day 7. Serial blood samples were collected for assays of drug concentrations. In Part 1, rosuvastatin maximum observed plasma concentration (C_max) and area under the plasma concentration–time curve from time 0 to infinity (AUC_inf) were 23% and 33% lower, respectively, when administered with upadacitinib relative to when administered alone. In part 2, atorvastatin C_max and AUC_inf was 11% and 23% lower, respectively, when administered with upadacitinib relative to when administered alone. The C_max and AUC_inf of the active metabolite ortho‐hydroxyatorvastatin remained unchanged. Administration of a single 5‐mg dose of rosuvastatin or a single 10‐mg dose of atorvastatin had no relevant effect on upadacitinib C_max or area under the plasma concentration–time curve. These results demonstrated that upadacitinib has no clinically relevant effect on the pharmacokinetics of rosuvastatin and atorvastatin or on substrates transported by OATP1B or breast cancer resistance protein.

Translational CNS Steady-State Drug Disposition Model in Rats, Monkeys, and Humans for Quantitative Prediction of Brain-to-Plasma and Cerebrospinal Fluid-to-Plasma Unbound Concentration Ratios

Capturing unbound drug exposure in the brain is crucial to evaluate pharmacological effects for drugs acting on the central nervous system. However, to date, there are no reports of validated prediction models to determine the brain-to-plasma unbound concentration ratio (K_p,uu,brain) as well as the cerebrospinal fluid (CSF)-to-plasma unbound concentration ratio (K_p,uu,CSF) between humans and other species. Here, we developed a translational CNS steady-state drug disposition model to predict K_p,uu,brain and K_p,uu,CSF across rats, monkeys, and humans by estimating the relative activity factors (RAF) for MDR1 and BCRP in addition to scaling factors (γ and σ) using the molecular weight, logD, CSF bulk flow, and in vitro transport activities of these transporters. In this study, 68, 26, and 28 compounds were tested in the rat, monkey, and human models, respectively. Both the predicted K_p,uu,brain and K_p,uu,CSF values were within the 3-fold range of the observed values (71, 73, and 79%; 79, 88, and 78% of the compounds, respectively), indicating successful prediction of K_p,uu,brain and K_p,uu,CSF in the three species. The overall predictivity of the RAF approach is consistent with that of the relative expression factor (REF) approach. As the established model can predict K_p,uu,brain and K_p,uu,CSF using only in vitro and physicochemical data, this model would help avoid ethical issues related to animal use and improve CNS drug discovery workflow.

Bisphenol A Inhibits the Transporter Function of the Blood-Brain Barrier by Directly Interacting with the ABC Transporter Breast Cancer Resistance Protein (BCRP)

The breast cancer resistance protein (BCRP) is an important efflux transporter in the blood-brain barrier (BBB), protecting the brain from a wide range of substances. In this study, we investigated if BCRP function is affected by bisphenol A (BPA), a high production volume chemical used in common consumer products, as well as by bisphenol F (BPF) and bisphenol S (BPS), which are used to substitute BPA. We employed a transwell-based in vitro cell model of iPSC-derived brain microvascular endothelial cells, where BCRP function was assessed by measuring the intracellular accumulation of its substrate Hoechst 33342. Additionally, we used in silico modelling to predict if the bisphenols could directly interact with BCRP. Our results showed that BPA significantly inhibits the transport function of BCRP. Additionally, BPA was predicted to bind to the cavity that is targeted by known BCRP inhibitors. Taken together, our findings demonstrate that BPA inhibits BCRP function in vitro, probably by direct interaction with the transporter. This effect might contribute to BPA’s known impact on neurodevelopment.

Direct Comparison of the Prediction of the Unbound Brain-to-Plasma Partitioning Utilizing Machine Learning Approach and Mechanistic Neuropharmacokinetic Model

The mechanistic neuropharmacokinetic (neuroPK) model was established to predict unbound brain-to-plasma partitioning (K_p,uu,brain) by considering in vitro efflux activities of multiple drug resistance 1 (MDR1) and breast cancer resistance protein (BCRP). Herein, we directly compare this model to a computational machine learning approach utilizing physicochemical descriptors and efflux ratios of MDR1 and BCRP-expressing cells for predicting K_p,uu,brain in rats. Two different types of machine learning techniques, Gaussian processes (GP) and random forest regression (RF), were assessed by the time and cluster-split validation methods using 640 internal compounds. The predictivity of machine learning models based on only molecular descriptors in the time-split dataset performed worse than the cluster-split dataset, whereas the models incorporating MDR1 and BCRP efflux ratios showed similar predictivity between time and cluster-split datasets. The GP incorporating MDR1 and BCRP in the time-split dataset achieved the highest correlation (R² = 0.602). These results suggested that incorporation of MDR1 and BCRP in machine learning is beneficial for robust and accurate prediction. K_p,uu,brain prediction utilizing the neuroPK model was significantly worse compared to machine learning approaches for the same dataset. We also investigated the predictivity of K_p,uu,brain using an external independent test set of 34 marketed drugs. Compared to machine learning models, the neuroPK model showed better predictive performance with R² of 0.577. This work demonstrates that the machine learning model for K_p,uu,brain achieves maximum predictive performance within the chemical applicability domain, whereas the neuroPK model is applicable more widely beyond the chemical space covered in the training dataset.

Structural Basis of Drug Recognition by the Multidrug Transporter ABCG2

ABCG2 is an ATP-binding cassette (ABC) transporter whose function affects the pharmacokinetics of drugs and contributes to multidrug resistance of cancer cells. While its interaction with the endogenous substrate estrone-3-sulfate (E₁S) has been elucidated at a structural level, the recognition and recruitment of exogenous compounds is not understood at sufficiently high resolution. Here we present three cryo-EM structures of nanodisc-reconstituted, human ABCG2 bound to anticancer drugs tariquidar, topotecan and mitoxantrone. To enable structural insight at high resolution, we used Fab fragments of the ABCG2-specific monoclonal antibody 5D3, which binds to the external side of the transporter but does not interfere with drug-induced stimulation of ATPase activity. We observed that the binding pocket of ABCG2 can accommodate a single tariquidar molecule in a C-shaped conformation, similar to one of the two tariquidar molecules bound to ABCB1, where tariquidar acts as an inhibitor. We also found single copies of topotecan and mitoxantrone bound between key phenylalanine residues. Mutagenesis experiments confirmed the functional importance of two residues in the binding pocket, F439 and N436. Using 3D variability analyses, we found a correlation between substrate binding and reduced dynamics of the nucleotide binding domains (NBDs), suggesting a structural explanation for drug-induced ATPase stimulation. Our findings provide additional insight into how ABCG2 differentiates between inhibitors and substrates and may guide a rational design of new modulators and substrates.

Resveratrol promotes liver regeneration in drug-induced liver disease in mice

Studies suggest that the bioactive polyphenolic compound resveratrol (RESV, trans-isomer), found naturally in certain foods such as red grapes and peanuts, may be able to ameliorate liver damage. However, the effects and efficacy of long-term treatment with RESV remain unclear. Here, we used an acetaminophen (APAP; 400 mg/kg/d for 15 days) overdose model to induce liver damage in C56BL/6 mice. Three days after the intoxication was stopped, we observed biochemical, histological and ultrastructural alterations in the livers of these mice. The APAP-treated animals were then given RESV (10 mg/kg/d) for 60 days. Blood and tissue were analyzed at days 7, 30 and 60. Our data show that long-term RESV treatment (60 days) ameliorates the liver injury caused by APAP intoxication, restoring histological features, ultrastructural organization and serum biochemical parameters (albumin, alanine aminotransferase). Ck18- and F4/80-positive cells (indicators of hepatocyte recovery) were reestablished and the number of α-SMA positive cells was normalized after long-term RESV treatment. Additionally, downregulation of the drug transporter BCRP was observed. Electron microscopy revealed that treatment with RESV was effective in restoring the shape and size of hepatic microvilli and normalizing both the number and viability of mitochondria. Taken together, these results indicate that long-term treatment with RESV is effective in alleviating liver injury caused by APAP administration.

Interaction of Phytocompounds of Echinacea purpurea with ABCB1 and ABCG2 Efflux Transporters

Preparations of Echinacea purpurea (E. purpurea) are widely used for the management of upper respiratory infections, influenza, and common cold, often in combination with other conventional drugs. However, the potential of phytochemical constituents of E. purpurea to cause herb-drug interactions via ABCB1 and ABCG2 efflux transporters remains elusive. The purpose of this study was to investigate the impact of E. purpurea-derived caffeic acid derivatives (cichoric acid and echinacoside) and tetraenes on the mRNA and protein expression levels as well as on transport activity of ABCB1 and ABCG2 in intestinal (Caco-2) and liver (HepG2) cell line models. The safety of these compounds was investigated by estimating EC₂₀ values of cell viability assays in both cell lines. Regulation of ABCB1 and ABCG2 protein in these cell lines were analyzed after 24 h exposure to the compounds at 1, 10, and 50 μg/mL. Bidirectional transport of 0.5 μg/mL Hoechst 33342 and 5 μM rhodamine across Caco-2 monolayer and profiling for intracellular concentrations of the fluorophores in both cell lines were conducted to ascertain inhibition effects of the compounds. Cichoric acid showed no cytotoxic effect, while the EC₂₀ values of tetraenes and echinacoside were 45.0 ± 3.0 and 52.0 ± 4.0 μg/mL in Caco-2 cells and 28.0 ± 4.3 and 62.0 ± 9.9 μg/mL in HepG2 cells, respectively. In general, the compounds showed heterogeneous induction of ABCB1 with the strongest 3.6 ± 1.2-fold increase observed for 10 μg/mL tetraenes in Caco-2 cells (p < 0.001). However, the compounds did not induce ABCG2. None of the phytocompounds inhibited significantly net flux of the fluorophores across Caco-2 monolayers. Overall, tetraenes moderately induced ABCB1 but not ABCG2 in Caco-2 and HepG2 cells while no compound significantly inhibited activity of these transporters at clinically relevant concentration to cause herb-drug interactions.