Molecular Modeling Studies to Probe the Binding Hypothesis of Novel Lead Compounds against Multidrug Resistance Protein ABCB1.

The expression of drug efflux pump ABCB1/P-glycoprotein (P-gp), a transmembrane protein belonging to the ATP-binding cassette superfamily, is a leading cause of multidrug resistance (MDR). We previously curated a dataset of structurally diverse and selective inhibitors of ABCB1 to develop a pharmacophore model that was used to identify four novel compounds, which we showed to be potent and efficacious inhibitors of ABCB1. Here, we dock the inhibitors into a model structure of the human transporter and use molecular dynamics (MD) simulations to report the conformational dynamics of human ABCB1 induced by the binding of the inhibitors. The binding hypotheses are compared to the wider curated dataset and those previously reported in the literature. Protein-ligand interactions and MD simulations are in good agreement and, combined with LipE profiling, statistical and pharmacokinetic analyses, are indicative of potent and selective inhibition of ABCB1.

Synergistic Inhibitory Effect of Quercetin and Cyanidin-3O-Sophoroside on ABCB1.

The human ABCB1 (P-glycoprotein, Pgp) protein is an active exporter expressed in the plasma membrane of cells forming biological barriers. In accordance with its broad substrate spectrum and tissue expression pattern, it affects the pharmacokinetics of numerous chemotherapeutic drugs and it is involved in unwanted drug-drug interactions leading to side effects or toxicities. When expressed in tumor tissues, it contributes to the development of chemotherapy resistance in malignancies. Therefore, the understanding of the molecular details of the ligand-ABCB1 interactions is of crucial importance. In a previous study, we found that quercetin (QUR) hampers both the transport and ATPase activity of ABCB1, while cyandin-3O-sophroside (C3S) stimulates the ATPase activity and causes only a weak inhibition of substrate transport. In the current study, when QUR and C3S were applied together, both a stronger ATPase inhibition and a robust decrease in substrate transport were observed, supporting their synergistic ABCB1 inhibitory effect. Similar to cyclosporine A, a potent ABCB1 inhibitor, co-treatment with QUR and C3S shifted the conformational equilibrium to the "inward-facing" conformer of ABCB1, as it was detected by the conformation-selective UIC2 mAb. To gain deeper insight into the molecular details of ligand-ABCB1 interactions, molecular docking experiments and MD simulations were also carried out. Our in silico studies support that QUR and C3S can bind simultaneously to ABCB1. The most favourable ligand-ABCB1 interaction is obtained when C3S binds to the central substrate binding site and QUR occupies the "access tunnel". Our results also highlight that the strong ABCB1 inhibitory effect of the combined treatment with QUR and C3S may be exploited in chemotherapy protocols for the treatment of multidrug-resistant tumors or for improving drug delivery through pharmacological barriers.

Low-dose Pimecrolimus, an FDA-approved Calcineurin Inhibitor, Sensitizes Drug-resistant Cancer Cells via Strong P-gp Inhibition.

BACKGROUND/AIM: Co-treatment with calcineurin inhibitors, such as tacrolimus and cyclosporin A, can sensitize chemotherapy-resistant cancer cells with P-glycoprotein (P-gp)-over-expression. Pimecrolimus (PIME) is a clinically available calcineurin inhibitor with a structure similar to that of tacrolimus. Whether PIME can sensitize P-gp-over-expressing resistant cancer cells remains unclear. MATERIALS AND METHODS: Cell viability assay, annexin V analyses, cellular morphology and density observation with a microscope, western-blotting, fluorescence-activated cell sorting (FACS), and analysis for P-gp inhibitory activity were performed to investigate the mechanism of action. RESULTS: PIME exhibited strong cytotoxicity to vincristine (VIC)-treated drug-resistant cell lines (KBV20C and MCF-7/ADR) over-expressing P-gp. Co-treatment with VIC and PIME increased apoptosis and down-regulated the ERK signaling pathway, resulting in G2 arrest. PIME could be co-administered with vinorelbine or eribulin to sensitize resistant KBV20C or MCF-7/ADR cancer cells. Moreover, PIME strongly inhibited the efflux of both rhodamine 123 and calcein-AM substrates through P-gp after 4 h of treatment, indicating that VIC+PIME sensitized cancer cells by inhibiting VIC efflux via direct PIME binding to P-gp. Low doses of PIME, tacrolimus, and cyclosporin A showed similar sensitizing efficiencies in resistant KBV20C cells. These drugs showed similar P-gp inhibitory activities using both rhodamine 123 and calcein-AM substrates, suggesting that calcineurin inhibitors generally have strong P-gp inhibitory activities that sensitize drug-resistant cancer cells with P-gp over-expression. CONCLUSION: PIME, currently used in clinics, can be repositioned for treating patients with P-gp-over-expressing resistant cancer (stem) cells.

Inhibitors of ABCB1 and ABCG2 overcame resistance to topoisomerase inhibitors in small cell lung cancer.

BACKGROUND: Small cell lung cancer (SCLC) is a highly aggressive disease with a poor prognosis. Although most patients initially respond to topoisomerase inhibitors, resistance rapidly emerges. The aim, therefore, is to overcome resistance to topoisomerase I (irinotecan) or II (etoposide) inhibitors in SCLCs. METHODS: To identify key factors in the chemoresistance of SCLCs, we established four cell lines resistant to etoposide or an active metabolite of irinotecan, SN-38, from SCLC cell lines and evaluated RNA profiles using parental and newly established cell lines. RESULTS: We found that the drug efflux protein, ATP-binding cassette sub-family B member 1 (ABCB1), was associated with resistance to etoposide, and ATP-binding cassette sub-family G member 2 (ABCG2) was associated with resistance to SN-38 by RNA sequencing. The inhibition of ABCB1 or ABCG2 in each resistant cell line induced synergistic apoptotic activity and promoted drug sensitivity in resistant SCLC cells. The ABC transporter inhibitors, elacridar and tariquidar, restored sensitivity to etoposide or SN-38 in in vitro and in vivo studies, and promoted apoptotic activity and G2-M arrest in resistant SCLC cells. CONCLUSIONS: ABC transporter inhibitors may be a promising therapeutic strategy for the purpose of overcoming resistance to topoisomerase inhibitors in patients with SCLC.

Statins Increase the Bioavailability of Fixed-Dose Combination of Sofosbuvir/Ledipasvir by Inhibition of P-glycoprotein.

BACKGROUND: Coadministration of statins and direct acting antiviral agents is frequently used. This study explored the effects of both atorvastatin and lovastatin on pharmacokinetics of a fixed-dose combination of sofosbuvir/ledipasvir "FDCSL". METHODS: 12 healthy volunteers participated in a randomized, three-phase crossover trial and were administered a single atorvastatin dose 80 mg plus tablet containing 400/90 mg FDCSL, a single lovastatin dose 40 mg plus tablet containing 400/90 mg FDCSL, or tablets containing 400/90 mg FDCSL alone. Liquid chromatography-tandem mass spectrometry was used to analyze plasma samples of sofosbuvir, ledipasvir and sofosbuvir metabolite "GS-331007" and their pharmacokinetic parameters were determined. RESULTS: Atorvastatin caused a significant rise in sofosbuvir bioavailability as explained by increasing in AUC0-∞ and Cmax by 34.36% and 11.97%, respectively. In addition, AUC0-∞ and Cmax of GS-331007 were increased by 73.73% and 67.86%, respectively after atorvastatin intake. Similarly, co-administration of lovastatin with FDCSL increased the bioavailability of sofosbuvir, its metabolite (AUC0-∞ increase by 17.2%, 17.38%, respectively, and Cmax increase by 12.03%, 22.24%, respectively). However, neither atorvastatin nor lovastatin showed a change in ledipasvir bioavailability. Hepatic elimination was not affected after statin intake with FDCSL. Compared to lovastatin, atorvastatin showed significant increase in AUC0-∞ and Cmax of both sofosbuvir and its metabolite. CONCLUSIONS: Both atorvastatin and lovastatin increased AUC of sofosbuvir and its metabolite after concurrent administration with FDCSL. Statins' P-glycoprotein inhibition is the attributed mechanism of interaction. The increase in sofosbuvir bioavailability was more pronounced after atorvastatin intake. Close monitoring is needed after co-administration of atorvastatin and FDCSL.

Ko143 Reverses MDR in Glioblastoma via Deactivating P-Glycoprotein, Sensitizing a Resistant Phenotype to TMZ Treatment.

BACKGROUND/AIM: Over-expression of both P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP) has been associated with multidrug-resistance in glioblastoma (GBM). Though previously studied broad-spectrum inhibitors of drug efflux pumps have failed to progress in clinical studies due to in vivo toxicity, research into clinically viable targeted inhibitors is needed. This study evaluated the effects of Ko143, a non-toxic analog of fumitremorgin C, on temozolomide (TMZ) efficacy in resistant glioblastoma stem cells. MATERIALS AND METHODS: We used ATP-Glo assay to determine cell viabilities and flow cytometry to perform cell cycle analysis. Comparative gene expression was analysed through RT-qPCR. RESULTS: TMZ IC50 decreased 41.07% (p<0.01) in the resistant phenotype when delivered in combination with Ko143. Additionally, the TMZ-resistant phenotype (GBM146) displayed 44-fold greater P-gp expression than the TMZ-sensitive phenotype (GBM9) (p<0.01), yet a 0.6-fold lower BCRP expression. Ko143 potentiates TMZ efficacy and likely inhibits P-glycoprotein more potently than previously indicated. CONCLUSION: Further development of non-toxic, targeted inhibitors of drug efflux pumps for use in combinatorial chemotherapy may improve glioblastoma patient prognosis.

Repositioning application of polyoxyethylene (20) sorbitan monooleate on ocular drug resistance and cancer multi-drug resistance by inhibiting the ATPase activity of human multidrug resistance protein 1 and P-glycoprotein.

Drug efflux transporters were highly related to the clinical drug resistance issues, such as cancer multi-drug resistance (MDR) and ocular drug resistance. In the present study, with the focus on human multi-drug resistance protein 1 (MRP1) and P-glycoprotein (P-gp), the inhibitory kinetics of polyoxyethylene (20) sorbitan monooleate (Tween 80) on both drug binding sites and ATPase were in-depth evaluated. We used the stable-cloned ABCB1/Flp-In™-293 and ABCC1/Flp-In™-293 cell lines, and inside-out membrane vesicles for underlying mechanisms investigation while used the drug induced cancer MDR cell line KB/VIN and human retinal pigmented epithelium cell line ARPE-19 for efficacy evaluation. Results showed that Tween 80 exhibited non-competitive inhibition on the doxorubicin efflux of P-gp and MRP1, with the inhibitory affinity 0.00195% (14.89 µM) and 0.00245% (18.7 µM), respectively. Tween 80 inhibited the basal ATPase activity of P-gp and MRP1 in a dose-dependent manner (0.0002-0.02%) and demonstrated significant reversing effects on the doxorubicin, paclitaxel, and vincristine resistance at the concentration of 0.001% (7.63 µM). This was the first thorough study revealing the interactions between Tween 80 and P-gp or MRP1 at a molecular level and these findings suggested that Tween 80 was a potential candidate for future combinatorial regimens applied in the "drug resistance" issue.

Discovery of the Triazolo[1,5-a]Pyrimidine-Based Derivative WS-898 as a Highly Efficacious and Orally Bioavailable ABCB1 Inhibitor Capable of Overcoming Multidrug Resistance.

Targeting P-glycoprotein (ABCB1 or P-gp) has been recognized as a promising strategy to overcome multidrug resistance. Here, we reported our medicinal chemistry efforts that led to the discovery of the triazolo[1,5-a]pyrimidine derivative WS-898 as a highly effective ABCB1 inhibitor capable of reversing paclitaxel (PTX) resistance in drug-resistant SW620/Ad300, KB-C2, and HEK293/ABCB1 cells (IC50 = 5.0, 3.67, and 3.68 nM, respectively), more potent than verapamil and zosuquidar. WS-898 inhibited the efflux function of ABCB1, thus leading to decreased efflux and increased intracellular PTX concentration in SW620/Ad300 cells. The cellular thermal shift assay indicated direct engagement of WS-898 to ABCB1. Furthermore, WS-898 stimulated the ATPase activity of ABCB1 but had minimal effects on cytochrome P450 3A4 (CYP3A4). Importantly, WS-898 increased PTX sensitization in vivo without obvious toxicity. The results suggest that WS-898 is a highly effective triazolo[1,5-a]pyrimidine-based ABCB1 inhibitor and shows promise in reversing ABCB1-mediated PTX resistance.

Cinnamophilin overcomes cancer multi-drug resistance via allosterically modulating human P-glycoprotein on both drug binding sites and ATPase binding sites.

Cancer multi-drug resistance (MDR) caused by P-glycoprotein (P-gp) efflux is a critical unresolved clinical concern. The present study analyzed the effect of cinnamophilin on P-gp inhibition and MDR reversion. The effect of cinnamophilin on P-gp was investigated through drug efflux assay, ATPase assay, MDR1 shift assay, and molecular docking. The cancer MDR-reversing ability and mechanisms were analyzed through cytotoxicity and combination index (CI), cell cycle, and apoptosis experiments. P-gp efflux function was significantly inhibited by cinnamophilin without influencing the drug's expression or conformation. Cinnamophilin uncompetitively inhibited the efflux of doxorubicin and rhodamine 123 and exhibited a distinct binding behavior compared with verapamil, the P-gp standard inhibitor. The half maximal inhibitory concentration of cinnamophilin for doxorubicin and rhodamine 123 efflux was 12.47 and 11.59 µM, respectively. In regard to P-gp energy consumption, verapamil-stimulated ATPase activity was further enhanced by cinnamophilin at concentrations of 0.1, 1, 10, and 20 µM. In terms of MDR reversion, cinnamophilin demonstrated synergistic cytotoxic effects when combined with docetaxel, vincristine, or paclitaxel. The CI was < 0.7 in all experimental combination treatments. The present study showed that cinnamophilin possesses P-gp-modulating effects and cancer MDR resensitizing ability.

Crystallographic studies of piperazine derivatives of 3-methyl-5-spirofluorenehydantoin in search of structural features of P-gp inhibitors.

5-Spirofluorenehydantoin derivatives show efflux modulating, cytotoxic and antiproliferative effects in sensitive and resistant mouse T-lymphoma cells. In order to extend the knowledge available about the pharmacophoric features responsible for the glycoprotein P (P-gp) inhibitory properties of arylpiperazine derivatives of 3-methyl-5-spirofluorenehydantoin, we have performed crystal structure analyses for 1-[3-(3'-methyl-2',4'-dioxospiro[fluorene-9,5'-imidazolidin]-1'-yl)propyl]-4-phenylpiperazine-1,4-diium dichloride monohydrate, C29H32N4O22+·2Cl-·H2O (1), 3'-methyl-1'-{3-[4-(4-nitrophenyl)piperazin-1-yl]propyl}spiro[fluorene-9,5'-imidazolidine]-2',4'-dione, C29H29N5O4·H2O (2), 3'-methyl-1'-{5-[4-(4-nitrophenyl)piperazin-1-yl]pentyl}spiro[fluorene-9,5'-imidazolidine]-2',4'-dione, C31H33N5O4 (3), and 1-benzyl-4-[5-(3'-methyl-2',4'-dioxospiro[fluorene-9,5'-imidazolidin]-1'-yl)pentyl]piperazine-1,4-diium dichloride 0.613-hydrate, C32H38N4O22+·2Cl-·0.613H2O (4). Structure 3 is anhydrous but the other three structures crystallize with water present. The investigated compounds crystallize in the monoclinic crystal system, with the space group P21/n for 1 and 3, and P21/c for 2 and 4. The cations of salts 1 and 4 are doubly protonated, with the protons located on the N atoms of the piperazine rings. The packing of 1 and 4 in the crystals is dominated by intermolecular N-H...Cl and O-H...Cl hydrogen bonds. In the crystal structure of 2, the intermolecular interactions are dominated by O-H...O and O-H...N hydrogen bonds, while in 3, which is lacking in classic hydrogen-bond donors, it is C-H...O contacts that dominate. Additionally, we have performed induced-fit docking studies for the investigated compounds docked to the P-gp human homology model.

Cell death-inducing activities via P-glycoprotein inhibition of the constituents isolated from fruits of Nandina domestica.

Two new pyrrole alkaloids methyl-E-mangolamide (1) and methyl-Z-mangolamide (2), four new megastigmane glycosides nandinamegastigmanes I-IV (3-6), and eight known compounds (7-14) were isolated from the methanol extract of the fruits of Nandina domestica. The structures of the new compounds were elucidated based on chemical and spectroscopic evidence. The absolute stereochemistry of nandinamegastigmane I (3) was established upon comparing the experimental and predicted electronic circular dichroism (ECD) data. Among the isolated compounds, 1 and 2 showed cell death-inducing activity on the Adriamycin-treated HeLa cells. In addition, one of the mechanisms for cell death-inducing activity of 1 and 2 was suggested as inhibition of P-glycoprotein.

Isobavachalcone as an Active Membrane Perturbing Agent and Inhibitor of ABCB1 Multidrug Transporter.

Isobavachalcone (IBC) is an active substance from the medicinal plant Psoralea corylifolia. This prenylated chalcone was reported to possess antioxidative, anti-inflammatory, antibacterial, and anticancer activities. Multidrug resistance (MDR) associated with the over-expression of the transporters of vast substrate specificity such as ABCB1 (P-glycoprotein) belongs to the main causes of cancer chemotherapy failure. The cytotoxic, MDR reversing, and ABCB1-inhibiting potency of isobavachalcone was studied in two cellular models: human colorectal adenocarcinoma HT29 cell line and its resistant counterpart HT29/Dx in which doxorubicin resistance was induced by prolonged drug treatment, and the variant of MDCK cells transfected with the human gene encoding ABCB1. Because MDR modulators are frequently membrane-active substances, the interaction of isobavachalcone with model phosphatidylcholine bilayers was studied by means of differential scanning calorimetry. Molecular modeling was employed to characterize the process of membrane permeation by isobavachalcone. IBC interacted with ABCB1 transporter, being a substrate and/or competitive inhibitor of ABCB1. Moreover, IBC intercalated into model membranes, significantly affecting the parameters of their main phospholipid phase transition. It was concluded that isobavachalcone interfered both with the lipid phase of cellular membrane and with ABCB1 transporter, and for this reason, its activity in MDR cancer cells was presumptively beneficial.

The inhibition of ABCB1/MDR1 or ABCG2/BCRP enables doxorubicin to eliminate liver cancer stem cells.

Two ATP-binding cassette transporters, ABCB1/MDR1 and ABCG2/BCRP, are considered the most critical determinants for chemoresistance in hepatocellular carcinoma. However, their roles in the chemoresistance in liver cancer stem cells remain elusive. Here we explored the role of inhibition of MDR1 or ABCG2 in sensitizing liver cancer stem cells to doxorubicin, the most frequently used chemotherapeutic agent in treating liver cancer. We show that the inhibition of MDR1 or ABCG2 in Huh7 and PLC/PRF/5 cells using either pharmacological inhibitors or RNAi resulted in the elevated level of intracellular concentration of doxorubicin and the accompanied increased apoptosis as determined by confocal microscopy, high-performance liquid chromatography, flow cytometry, and annexin V assay. Notably, the inhibition of MDR1 or ABCG2 led to the reversal of the chemoresistance, as evident from the enhanced death of the chemoresistant liver cancer stem cells in tumorsphere-forming assays. Thus, the elevation of effective intracellular concentration of doxorubicin via the inhibition of MDR1 or ABCG2 represents a promising future strategy that transforms doxorubicin from a traditional chemotherapy agent into a robust killer of liver cancer stem cells for patients undergoing transarterial chemoembolization.

Multifunctional nanoplatforms co-delivering combinatorial dual-drug for eliminating cancer multidrug resistance.

Clinically, the primary cause of chemotherapy failure belongs to the occurrence of cancer multidrug resistance (MDR), which directly leads to the recurrence and metastasis of cancer along with high mortality. More and more attention has been paid to multifunctional nanoplatform-based dual-therapeutic combination to eliminate resistant cancers. In addition to helping both cargoes improve hydrophobicity and pharmacokinetic properties, increase bioavailability, release on demand and enhance therapeutic efficacy with low toxic effects, these smart co-delivery nanocarriers can even overcome drug resistance. Here, this review will not only present different types of co-delivery nanocarriers, but also summarize targeted and stimuli-responsive combination nanomedicines. Furthermore, we will focus on the recent progress in the co-delivery of dual-drug using such intelligent nanocarriers for surmounting cancer MDR. Whereas it remains to be seriously considered that there are some knotty issues in the fight against MDR of cancers via using co-delivery nanoplatforms, including limited intratumoral retention, the possible changes of combinatorial ratio under complex biological environments, drug release sequence from the nanocarriers, and subsequent free-drug resistance after detachment from the nanocarriers. It is hoped that, with the advantage of continuously developing nanomaterials, two personalized therapeutic agents in combination can be better exploited to achieve the goal of cooperatively combating cancer MDR, thus advancing the time to clinical transformation.

Comprehensive Exploration of Medications That Affect the Bleeding Risk of Oral Anticoagulant Users.

Oral anticoagulants (OACs) pose a major bleeding risk, which may be increased or decreased by concomitant medications. To explore medications that affect the bleeding risk of OACs, we conducted a nested case-control study including 554 bleeding cases (warfarin, n = 327; direct OACs [DOACs], n = 227) and 1337 non-bleeding controls (warfarin, n = 814; DOACs, n = 523), using a Japanese health insurance database from January 2005 to June 2017. Major bleeding risk associated with exposure to concomitant medications within 30 d of the event/index date was evaluated, and adjusted odds ratios (aORs) were calculated using logistic regression analysis. Several antihypertensive drugs, such as amlodipine and bisoprolol, were associated with a decreased risk of bleeding (warfarin + amlodipine [aOR, 0.64; 95% confidence interval (CI): 0.41-0.98], DOACs + bisoprolol [aOR, 0.51; 95% CI, 0.33-0.80]). As hypertension is considered a significant risk factor for intracranial bleeding in antithrombotic therapy, antihypertensive drugs may suppress intracranial bleeding. In contrast, telmisartan, a widely used antihypertensive drug, was associated with an increased risk of bleeding [DOACs + telmisartan (aOR, 4.87; 95% CI, 1.84-12.91)]. Since telmisartan is an inhibitor of P-glycoprotein (P-gp), the elimination of rivaroxaban and apixaban, which are substrates of P-gp, is hindered, resulting in increased blood levels of both drugs, thereby increasing the risk of hemorrhage. In conclusion, antihypertensive drugs may improve the safety of OACs, and the pharmacokinetic-based drug interactions of DOACs must be considered.

Rapid Increase of Gastrointestinal P-Glycoprotein Functional Activity in Response to Etoposide Stimulation.

We previously reported that exposure of human colon adenocarcinoma (Caco-2) cells to the bitter substance phenylthiocarbamide (PTC) rapidly enhanced the transport function of P-glycoprotein (P-gp). In this study, we investigated the short-term effect of etoposide, another bitter-tasting P-gp substrate, on P-gp transport function in the same cell line. We found that etoposide exposure significantly increased both the P-gp protein level in the plasma membrane fraction and the efflux rate of rhodamine123 (Rho123) in Caco-2 cells within 10 min. The efflux ratio (ratio of the apparent permeability coefficient in the basal-to-apical direction to that in the apical-to-basal direction) of Rho123 in etoposide-treated cells was also significantly increased compared with the control. These results indicated that etoposide rapidly enhances P-gp function in Caco-2 cells. In contrast, P-gp expression in whole cells at both the mRNA and protein level was unchanged by etoposide exposure, compared with the levels in non-treated cells. Furthermore, etoposide increased the level of phosphorylated ezrin, radixin and moesin (P-ERM) proteins in the plasma membrane fraction of Caco-2 cells within 10 min. P-gp functional changes were blocked by YM022, an inhibitor of cholecystokinin (CCK) receptor. These results suggest that etoposide induces release of CCK, causing activation of the CCK receptor followed by phosphorylation of ERM proteins, which recruit intracellular P-gp for trafficking to the gastrointestinal membrane, thereby increasing the functional activity of P-gp.

Jatrophane diterpenoids as multidrug resistance modulators from Euphorbia sororia.

Eight new jatrophane diterpenoids, Euphosorophane F-M (1-8), as well as fourteen known jatrophane diterpenoids (9-22) were separated and purified from the fructus of Euphorbia sororia, and the chemical structures were determined based on extensive spectroscopic analysis, 1D, 2D NMR and HRESIMS data included. Their absolute configurations of compounds 1, 2, 9, and 22 were elucidated by X-ray crystallographic analysis. These jatrophane diterpenoids showed lower cytotoxicity and compounds 3, 4, 11, 12, 13, 14, and 20 revealed promising multidrug resistance (MDR) reversal ability as modulators compared to verapamil (VRP) by MTT assay. The structure-activity relationship (SAR) exhibited that the absence of keto-carbonyl at C-9 and C-14 was essential to MDR reversal activity and the acyloxies substitution at C-5, C-7, C-8, and C-14 also made the activity difference. Euphosorophane I (4) particularly unfold greater potency (EC50 = 1.82 µM) in reversing P-gp-mediated resistance to doxorubicin (DOX). As shown by fluorescence microscopy, 4 promoted intracellular accumulation of rhodamine 123 (Rh123) and DOX in a dose-dependentmanner than VRP. Flow cytometry indicated that 4 inhibitedP-glycoprotein (P-gp) -dependentRh123 efflux in drug-resistant MCF-7/ADR cells. 4 stimulated P-gp-ATPase activity in a concentration-dependent way and inhibited DOX transport activity. Western blot and real-time qPCR results further illustrated that 4 exhibited superior MDR reversal effect in MCF-7/ADR cells attributed to the activation of ATPase rather than the upregulation of P-gp expression and mRNA levels. In addition, 4 bond to the drug-binding site of P-gp predicted by the molecular docking analysis. Collectively, these results indicated that 4 efficiently reversed P-gp-mediated MDR via inhibiting the ABCB1 drug efflux function. 4 with the advantage of low toxicity and efficient could be used as an adjuvanttherapy drug for breast cancer.

Computer-Aided Search for 5-Arylideneimidazolone Anticancer Agents Able To Overcome ABCB1-Based Multidrug Resistance.

ABCB1 modulation is an interesting strategy in the search for new anticancer agents that can overcome multidrug resistance (MDR). Hence, 17 new 5-arylideneimidazolones containing an amine moiety, as potential ABCB1 inhibitors, were designed, synthesized, and investigated. The series was tested in both parental (PAR) and multidrug-resistant (MDR) ABCB1-overexpressing T-lymphoma cancer cells using cytotoxicity assays. The ABCB1-modulating activity was examined in rhodamine 123 accumulation tests, followed by Pgp-Glo™ Assay to determine the influence of the most active compounds on ATPase activity. Lipophilic properties were assessed both, in silico and experimentally (RP-TLC). Pharmacophore-based molecular modelling toward ABCB1 modulation was performed. The studies allowed the identification of anticancer agents (p-fluorobenzylidene derivatives) more potent than doxorubicin, with highly selective action on MDR T-lymphoma cells (selectivity index >40). Most of the investigated compounds showed ABCB1-modulating action; in particular, two 5-benzyloxybenzylidene derivatives displayed activity nearly as strong as that of tariquidar.

Chiral Transplacental Pharmacokinetics of Fexofenadine: Impact of P-Glycoprotein Inhibitor Fluoxetine Using the Human Placental Perfusion Model.

PURPOSE: Fexofenadine is a well-identified in vivo probe substrate of P-glycoprotein (P-gp) and/or organic anion transporting polypeptide (OATP). This work aimed to investigate the transplacental pharmacokinetics of fexofenadine enantiomers with and without the selective P-gp inhibitor fluoxetine. METHODS: The chiral transplacental pharmacokinetics of fexofenadine-fluoxetine interaction was determined using the ex vivo human placenta perfusion model (n = 4). In the Control period, racemic fexofenadine (75 ng of each enantiomer/ml) was added in the maternal circuit. In the Interaction period, racemic fluoxetine (50 ng of each enantiomer/mL) and racemic fexofenadine (75 ng of each enantiomer/mL) were added to the maternal circulation. In both periods, maternal and fetal perfusate samples were taken over 90 min. RESULTS: The (S)-(-)- and (R)-(+)-fexofenadine fetal-to-maternal ratio values in Control and Interaction periods were similar (~0.18). The placental transfer rates were similar between (S)-(-)- and (R)-(+)-fexofenadine in both Control (0.0024 vs 0.0019 min-1) and Interaction (0.0019 vs 0.0021 min-1) periods. In both Control and Interaction periods, the enantiomeric fexofenadine ratios [R-(+)/S-(-)] were approximately 1. CONCLUSIONS: Our study showed a low extent, slow rate of non-enantioselective placental transfer of fexofenadine enantiomers, indicating a limited fetal fexofenadine exposure mediated by placental P-gp and/or OATP2B1. The fluoxetine interaction did not affect the non-enantioselective transplacental transfer of fexofenadine. The ex vivo placental perfusion model accurately predicts in vivo placental transfer of fexofenadine enantiomers with remarkably similar values (~0.17), and thus estimates the limited fetal exposure.

Discovery of new pyrimidopyrrolizine/indolizine-based derivatives as P-glycoprotein inhibitors: Design, synthesis, cytotoxicity, and MDR reversal activities.

Targeting P-glycoprotein (P-gp, ABCB1 transporter), which plays an essential role in multi-drug resistance (MDR) in cancers, with new cytotoxic agents is a promising strategy in cancer chemotherapy. In the current study, we report the synthesis of thirteen novel pyrimidopyrrolizine, pyrimidoindolizine, and diazepinopyrrolizine derivatives. The new compounds exhibited cytotoxic activities against MCF7, A2780 and HT29 cancer cell lines (IC50 = 0.02-19.58 µM) and MRC5 (IC50 = 0.17-20.57 µM). The six most active compounds (23b, 24a,b and, 31c-e) were evaluated for their MDR reversal activities in MCF7/ADR cells. Mechanistic study using real-time PCR revealed the ability of compound 31c to inhibit P-gp. In addition, compound 31c increased the accumulation of Rho123 inside MCF7/ADR cells in a dose-dependent manner compared to verapamil. Compound 31c arrested the cell cycle of MCF7 cells at the G1 phase. Compound 31c also caused a significant dose-dependent increase of early and late apoptotic events. Molecular docking analysis revealed a high binding affinity for compound 31c toward P-gp. Like zosuquidar, compound 31c displayed one hydrogen bond and several hydrophobic interactions with amino acids in P-gp. These results indicated that compound 31c represents a potential anticancer candidate with MDR reversal activity.