P-glycoprotein Mediated Drug Research Articles

Highly Potent and Intestine Specific P-Glycoprotein Inhibitor to Enable Oral Delivery of Taxol.

Taxol is widely used in cancer chemotherapy; however, the oral absorption of Taxol remains a formidable challenge. Since the intestinal p-glycoprotein (P-gp) mediated drug efflux is one of the primary causes, the development of P-gp inhibitor is emerging as a promising strategy to realize Taxol's oral delivery. Because P-gp exists in many tissues, the non-selective P-gp inhibitors would lead to toxicity. Correspondingly, a potent and intestine specific P-gp inhibitor would be an ideal solution to boost the oral absorption of Taxol and avoid exogenous toxicity. Herein, we would like to report a highly potent and intestine specific P-gp inhibitor to enable oral delivery of Taxol in high efficiency. Through a multicomponent reaction and post-modification, various benzofuran-fused-piperidine derivatives were achieved and the biological evaluation identified 16 c with potent P-gp inhibitory activity. Notably, 16 c was intestine specific and showed almost none absorption (F=0.82 %), but possessing higher efficacy than Encequidar to improve the oral absorption of Taxol. In MDA-MB-231 xenograft model, the oral administration of Taxol and 16 c showed high therapeutic efficiency and low toxicity, thus providing a valuable chemotherapy strategy.

P Glycoprotein Mediated Drug Interaction between Digoxin and Orange Juice- Exploratory Study by In-vitro Approach

P.gp is an efflux transporter that plays a vital role in drug transportation. Aim: This exploratory study is aimed to find the P-glycoprotein (P-gp) mediated drug interaction between digoxin and orange juice, conducted for a period of six months. The 3D structure of the human P-gp was predicted from the peptide by molecular threading using default settings. The structural analysis and verification server and the PDB were used to assess the stereo-chemical quality of these structures. The molecular structure of P-gp in a transport cycle has been investigated using a variety of methods. Molecular docking has been performed to predict the highest binding affinity to P gp with ligands of orange juice and ligands of ketoconazole. In 50% ethyl acetate extract of orange juice was prepared and a transcellular transport study was done using MDR1 transfectants and MRP2 transfectants LLC-PK1, LLC-GAS-COL150, LLC-pCI and LLC-MRP cells grown in M199 medium supplemented with 10% fetal calf serum at 37℃ in a humidified atmosphere of 5% CO2/95% air. The minimum inhibitory concentration is found to be 125 mcg/mL. Hence, the loading concentration along with orange juice is found to be 24.562 mcg/mL and the concentration less than that is found with poor sensitivity. Whereas the concentration above 125 mcg/mL loaded with orange juice is found to inhibit P-gp. The absorbance of orange juice and digoxin was measured at 470 nm. Since digoxin is not sensitive to orange juice beyond the concentration of 125 mcg/mL, it is considered as the MIC. Hence orange juice is a moderate p-gp Inhibitor and it escalates the serum digoxin toxicity. Orange juice is inhibiting the P-gp which increases the serum toxicity levels of digoxin.

The endocytic receptor protein LRP-1 modulate P-glycoprotein mediated drug resistance in MCF-7 cells.

Multidrug resistance (MDR) is a major obstacle to successful cancer chemotherapy. A typical form of MDR is due to the overexpression of membrane transport proteins., such as Glycoprotein-P (P-gp), resulting in an increased drug efflux preventing drug cytotoxicity. P-gp is mainly localized on the plasma membrane; however, it can also be endocytosed resulting in the trafficking of P-gp in endoplasmic reticulum, Golgi, endosomes, and lysosomes. The lysosomal P-gp has been found to be capable of transporting and sequestering P-gp substrates (e.g., Doxorubicin (Dox)) into lysosomes to protect cells against cytotoxic drugs. Many translational studies have shown that low-density lipoprotein receptor-related protein-1 (LRP-1) is involved in endocytosis and regulation of signalling pathways. LRP-1 mediates the endocytosis of a diverse set of extracellular ligands that play important roles in tumor progression. Here, we investigated the involvement of LRP-1 in P-gp expression and subcellular redistribution from the cell surface to the lysosomal membrane by endocytosis and its potential implication in P-gp-mediated multidrug resistance in MCF-7 cells. Our results showed that MCF-7 resistant cells (MCF-7R) overexpressed the P-gp, LRP-1 and LAMP-1 and were 11.66-fold resistant to Dox. Our study also revealed that in MCF-7R cells, lysosomes were predominantly high density compared to sensitized cells and P-gp was localized in the plasma membrane and lysosomes. LRP-1 blockade reduced lysosomes density and level of LAMP-1 and P-gp. It also affected the subcellular distribution of P-gp. Under these conditions, we restored Dox nuclear uptake and ERK 1/2 activation thus leading to MCF-7R cell sensitization to Dox. Our data suggest that LRP-1 is able to modulate the P-gp expression and subcellular redistribution by endocytosis and to potentiate the P-gp-acquired Dox resistance.

Molecular Insights into the Mechanism of Modulatory Effects of Proton Pump Inhibitors on P-glycoprotein Mediated Drug Transport of Palbociclib and Ribociclib.

Palbociclib and ribociclib are substrates of efflux transporter, P-glycoprotein plays a key role in absorption and transport of these drugs. Proton pump inhibitors, when co-administered with them are known to show inhibitory effect on P-glycoprotein. Therefore, this study aims to investigate the role of proton pump inhibitors in inhibition of P-glycoprotein mediated efflux of palbociclib and ribociclib. A combined approach of molecular docking and ex vivo everted gut sac model was implemented to predict the potential of proton pump inhibitors i.e., omeprazole, esomeprazole, lansoprazole, pantoprazole and rabeprazole to inhibit the P-glycoprotein mediated intestinal transport of palbociclib and ribociclib and study the molecular basis of interaction taking place. Molecular docking studies revealed that omeprazole, rabeprazole and pantoprazole bound to the ATP site of nucleotide binding domain with binding energies of -27.53, -29.56 and -38.44 Kcal/mol respectively. In ex-vivo studies, rabeprazole and omeprazole, affected the absorptive permeability of palbociclib by 3.04 and 1.26 and ribociclib by 1.76 and 2.54 folds, respectively. Results of molecular docking studies and ex vivo studies highlighted that proton pump inhibitors bound to the ATP binding site to block its hydrolysis thereby inhibiting the P-glycoprotein mediated efflux of palbociclib and ribociclib. The experimental evidence presented highlights the fact that proton pump inhibitors have potential to inhibit P-glycoprotein, giving rise to drug interactions with palbociclib and ribociclib. Hence, monitoring is required while proton pump inhibitors and cyclin-dependent kinase inhibitors are being co-administered to avoid adverse events.

Translatability of in vitro Inhibition Potency to in vivo P-Glycoprotein Mediated Drug Interaction Risk

P-glycoprotein (P-gp) may limit oral drug absorption of substrate drugs due to intestinal efflux. Therefore, regulatory agencies require investigation of new chemical entities as possible inhibitors of P-gp in vitro. Unfortunately, inter-laboratory and inter-assay variability have hindered the translatability of in vitro P-gp inhibition data to predict clinical drug interaction risk. The current study was designed to evaluate the impact of potential IC50 discrepancies between two commonly utilized assays, i.e., bi-directional Madin-Darby Canine Kidney-MDR1 cell-based and MDR1 membrane vesicle-based assays. When comparing vesicle- to cell-based IC50 values (n = 28 inhibitors), non-P-gp substrates presented good correlation between assay formats, whereas IC50s of P-gp substrates were similar or lower in the vesicle assays. The IC50s obtained with a cell line expressing relatively low P-gp aligned more closely to those obtained from the vesicle assay, but passive permeability of the inhibitors did not appear to influence the correlation of IC50s, suggesting that efflux activity reduces intracellular inhibitor concentrations. IC50s obtained between two independent laboratories using the same assay type showed good correlation. Using the G-value (i.e., ratio of estimated gut concentration-to-inhibition potency) >10 cutoff recommended by regulatory agencies resulted in minimal differences in predictive performance, suggesting this cutoff is appropriate for either assay format.

Efficient Synthesis of Acylated, Dialkyl α-Hydroxy-Benzylphosphonates and Their Anticancer Activity.

An efficient method applying acyl chlorides as reagents was developed for the acylation of the hindered hydroxy group of dialkyl α-hydroxy-benzylphosphonates. The procedure did not require any catalyst. A few acylations were also performed with the SC-enantiomer of dimethyl α-hydroxy-benzylphosphonate, and the optical purity was retained. A part of the acyloxyphosphonates was tested against eight tumor cell lines of different tissue origin at c = 50 μM concentration. The compounds elicited moderate cytostatic effect against breast, skin, prostate, colon, and lung carcinomas; a melanoma cell line; and against Kaposi’s sarcoma cell lines. Then, dose-dependent cytotoxicity was assayed, and benzoylation of the α-hydroxy group was identified as a moiety that increases anticancer cytotoxicity across all cell lines. Surprisingly, a few analogues were more toxic to multidrug resistant cancer cell lines, thus evading P-glycoprotein mediated drug extrusion.

Enhancing biocatalysis of a MXene-based biomimetic plasmonic assembly for targeted cancer treatments in NIR-II biowindow

Biocatalysis-based nanomedicines have attracted considerable attention in the field of biomedicine. However, improving catalytic activity as a prerequisite for the therapeutic effect of biocatalysis is still a core scientific problem that needs to be solved urgently. Herein, an efficient strategy of plasmonic enhanced biocatalysis is proposed and applied to biomimetic photoinduced plasmonic assembly (NPD@M). The assembly consists of Nb2C plasmon (MXene), Pt nanozymes, doxorubicin (DOX) and tumor cytomembrane. After homologous targeting and internalization into tumor cells, the hot-electrons are excited from MXene under NIR-II laser irradiation remarkably facilitates the catalase-like and oxidase-like activities of Pt nanozymes to produce O2 and ROS, combining with tumor-penetrating photothermal therapy. Furthermore, DOX is released under hyperpyrexia and acidic condition, which is strengthened through the inhibition of P-glycoprotein (P-gp) mediated drug efflux caused by O2 and ROS. The results show that the HeLa cell viability reduced 38.67% by MXene enhanced nanozyme treatment compared to the nanozyme alone. The plasmonic assembly has achieved significant tumor regression in vivo. This work presents a novel plasmonic assembly for the ultra-active biocatalysis based on the plasmonic hot electrons for increasing therapeutic effect of tumor, which further promotes the development of biocatalytic nanomedicines.

ATP-responsive hollow nanocapsules for DOX/GOx delivery to enable tumor inhibition with suppressed P-glycoprotein

Multidrug resistance (MDR) restricts chemotherapy efficacy due to P-glycoprotein (P-gp) mediated drug efflux, whereas current approaches to suppressing P-gp expression suffer from intrinsic challenges, such as low transfection, high toxicity and poor specificity. Here, hollow ferric-tannic acid complex nanocapsules (HFe-TA), which can be effectively degraded by the reaction with adenosine triphosphate (ATP), are synthesized for the delivery of glucose oxidase (GOx) and doxorubicin (DOX) for tumor treatment. The findings indicate that the intracellular ATP is significantly decreased due to the combined effect of HFe-TA degradation and GOx-mediated glucose consumption. Along with this ATP down-regulation, P-gp expression of tumor cells is suppressed remarkably, which in turn promotes the intracellular accumulation and anticancer efficacy of DOX. In addition, the production of •OH by Fe ions released from HFe-TA is promoted by the by-products of the oxidation of glucose process by GOx. In consequence, HFe-TA nanocapsules loaded with DOX and GOx enable significant inhibition effect to tumors both in vitro and in vivo due to the synergistic effect of cascade reactions. This study has therefore provided an alternative therapeutic platform for effective tumor inhibition with the potential in overcoming intrinsic MDR.

N-alkylisatin-based microtubule destabilizers bind to the colchicine site on tubulin and retain efficacy in drug resistant acute lymphoblastic leukemia cell lines with less in vitro neurotoxicity

BackgroundDrug resistance and chemotherapy-induced peripheral neuropathy continue to be significant problems in the successful treatment of acute lymphoblastic leukemia (ALL). 5,7-Dibromo-N-alkylisatins, a class of potent microtubule destabilizers, are a promising alternative to traditionally used antimitotics with previous demonstrated efficacy against solid tumours in vivo and ability to overcome P-glycoprotein (P-gp) mediated drug resistance in lymphoma and sarcoma cell lines in vitro. In this study, three di-brominated N-alkylisatins were assessed for their ability to retain potency in vincristine (VCR) and 2-methoxyestradiol (2ME2) resistant ALL cell lines. For the first time, in vitro neurotoxicity was also investigated in order to establish their suitability as candidate drugs for future use in ALL treatment.MethodsVincristine resistant (CEM-VCR R) and 2-methoxyestradiol resistant (CEM/2ME2-28.8R) ALL cell lines were used to investigate the ability of N-alkylisatins to overcome chemoresistance. Interaction of N-alkylisatins with tubulin at the the colchicine-binding site was studied by competitive assay using the fluorescent colchicine analogue MTC. Human neuroblastoma SH-SY5Y cells differentiated into a morphological and functional dopaminergic-like neurotransmitter phenotype were used for neurotoxicity and neurofunctional assays. Two-way ANOVA followed by a Tukey’s post hoc test or a two-tailed paired t test was used to determine statistical significance.ResultsCEM-VCR R and CEM/2ME2-28.8R cells displayed resistance indices of > 100 to VCR and 2-ME2, respectively. CEM-VCR R cells additionally displayed a multi-drug resistant phenotype with significant cross resistance to vinblastine, 2ME2, colchicine and paclitaxel consistent with P-gp overexpression. Despite differences in resistance mechanisms observed between the two cell lines, the N-alkylisatins displayed bioequivalent dose-dependent cytotoxicity to that of the parental control cell line. The N-alkylisatins proved to be significantly less neurotoxic towards differentiated SH-SY5Y cells than VCR and vinblastine, evidenced by increased neurite length and number of neurite branch points. Neuronal cells treated with 5,7-dibromo-N-(p-hydroxymethylbenzyl)isatin showed significantly higher voltage-gated sodium channel function than those treated with Vinca alkaloids, strongly supportive of continued action potential firing.ConclusionsThe N-alkylisatins are able to retain cytotoxicity towards ALL cell lines with functionally distinct drug resistance mechanisms and show potential for reduced neurotoxicity. As such they pose as promising candidates for future implementation into anticancer regimes for ALL. Further in vivo studies are therefore warranted.

IL-17A upregulates P-glycoprotein expression in peripheral blood lymphocytes of patients with rheumatoid arthritis through TAK1

P-glycoprotein (P-gp) mediated drug efflux is the most essential mechanism of multi-drug resistance (MDR) in rheumatoid arthritis (RA). The study was undertaken to clarify the mechanism whereby IL-17 regulate the P-gp efflux function in peripheral blood lymphocytes of patients with RA. Lymphocytes from RA patients and healthy individuals were cultured with IL-17A (0, 10, 100 ng/ml), IL-17A+(5Z)-7-Oxozeaenol (TAK1 inhibitor), and IL-17A+PD98059 (ERK inhibitor), respectively. 24h later, the level of P-gp mRNA expression in peripheral blood lymphocytes was detected by RT-PCR. Meanwhile, the efflux potential of P-gp was assessed by flow cytometry using the fluorescent dye Rhodamine 123, a substrate of P-gp. In order to confirm whether the inhibitors had worked, ERK1/2 and p65, as well as their phosphorylation were detected utilising Western blot analysis. With the exception of the expression of P-gp mRNA between control and IL-17A group, the mRNA expression, as well as the function of P-gp in the different group of healthy individuals was similar, and there was no significant difference (p>0.05). However, as for the RA patients, increased expressions of P-gp mRNA and efflux function were detected in IL-17A group compared with control. Moreover, IL-17A upregulated mRNA level and function of P-gp in a concentrate dependent manner. Upregulated expression of P-gp mRNA and efflux potential of P-gp were inhibited by TAK1 or ERK inhibitors in RA peripheral blood lymphocytes. Among them, TAK1 inhibitor, (5Z) -7-Oxozeaenol, showed a significant difference (p<0.05). Also, the decreased phosphorylation levels of ERK1/2 and p65 were detected with PD98059 and (5Z) -7-Oxozeaenol addition, respectively. This study showed that inflammatory cytokines IL-17A can upregulate the mRNA expression level and drug efflux function of P-gp on lymphocytes in RA patients through TAK1, in a concentrate dependent manner, contributing to RA drug resistance. Therefore, this may represent a new target for improving the therapeutic reactivity of DMARDs in the long term for RA patients.

In Vitro Profiling for Potential Cytochrome P450 and P-Glycoprotein–Mediated Drug–Drug Interaction By Maribavir (Shp620)

Introduction Maribavir is a potent and orally bioavailable antiviral with a novel mechanism of action against cytomegalovirus (CMV). The efficacy and safety of maribavir for treatment of CMV infections are being evaluated in ongoing Phase 3 trials. Characterization of drug–drug interaction (DDI) properties of maribavir is necessary in informing potential DDIs with co-medications. Objective To evaluate the potential cytochrome p450 and p-glycoprotein–mediated drug–drug interaction by maribavir. Methods Cytochrome P450 (CYP) reversible inhibition: Probe substrates of CYPs were incubated with human liver microsomes (HLM) and maribavir. Percent remaining CYP activity was plotted against maribavir concentrations for IC50 determination. Time-dependent inhibition (TDI) for CYPs: After pre-incubation with maribavir for varying durations, percent remaining CYP activity in HLM was measured. The concentration at half-maximal inactivation (KI) and maximum inactivation rate constant (kinact) were calculated. CYP induction: After treating human hepatocytes with maribavir for three days, CYP mRNA expression was plotted against maribavir concentrations to determine half-maximal induction concentration (EC50) and maximal fold induction (Emax). P-glycroprotein (P-gp) inhibition: Bi-directional transport of digoxin in Caco-2 cells with maribavir was measured and IC50 calculated by plotting percent transporter activity against maribavir concentration. Results Maribavir is not a reversible inhibitor of CYP2A6, CYP2B6, CYP2C8, CYP2D6, CYP2E1, or CYP3A4 and is a weak inhibitor of CYP1A2, CYP2C9, and CYP2C19 (IC50 40, 18, and 35 µM). Maribavir is not a TDI of CYP1A2, CYP2C8, CYP2C9, CYP2C19, or CYP2D6 but a weak TDI for CYP3A (KI 41.2 μM, kinact 0.0117 min−1). Maribavir is not an inducer of CYP1A2 or CYP2B6 mRNA but is a weak, possibly donor-dependent inducer of CYP3A4 mRNA. Maribavir is a weak inhibitor of P-gp (IC50 33.7 µM). Conclusions Maribavir is not expected to affect exposures of substrates of major CYPs or P-gp when co-administered at therapeutic dose of 400 mg BID, based on its estimated maximal unbound plasma concentration (Cmax,u) of 0.74 μM in transplant patients with CMV infection.

Overcoming P-Glycoprotein-Mediated Drug Resistance with Noscapine Derivatives.

The antitussive agent noscapine has been shown to inhibit the proliferation of cancer cells by disruption of tubulin dynamic. However, the efficacy of several anticancer drugs that inhibit tublin dynamics (vinca alkaloids and taxanes) is reduced by the multidrug resistance phenotype. These compounds are substrates for P-glycoprotein (P-gp)-mediated extrusion from cells. Consequently, the antiproliferative activity of noscapine and a series of derivatives was measured in drug-sensitive and drug-resistant cells that overexpress P-gp. None of the noscapine derivatives displayed lower potency in cells overexpressing P-gp, thereby suggesting a lack of interaction with this pump. However, the cellular efflux of a fluorescent substrate by P-gp was potently inhibited by noscapine and most derivatives. Further investigation with purified, reconstituted P-gp demonstrated that inhibition of P-gp function was due to direct interaction of noscapine derivatives with the transporter. Moreover, coadministration of vinblastine with two of the noscapine derivatives displayed synergistic inhibition of proliferation, even in P-gp-expressing resistant cell lines. Therefore, noscapine derivatives offer a dual benefit of overcoming the significant impact of P-gp in conferring multidrug resistance and synergy with tubulin-disrupting anticancer drugs.

MiR-19b non-canonical binding is directed by HuR and confers chemosensitivity through regulation of P-glycoprotein in breast cancer

MicroRNAs and RNA-binding proteins exert regulation on >60% of coding genes, yet interplay between them is little studied. Canonical microRNA binding occurs by base-pairing of microRNA 3′-ends to complementary “seed regions” in mRNA 3′UTRs, resulting in translational repression. Similarly, regulatory RNA-binding proteins bind to mRNAs, modifying stability or translation. We investigated post-transcriptional regulation acting on the xenobiotic pump ABCB1/P-glycoprotein, which is implicated in cancer therapy resistance. We characterised the ABCB1 UTRs in primary breast cancer cells and identified UTR sequences that responded to miR-19b despite lacking a canonical binding site. Sequences did, however, contain consensus sites for the RNA-binding protein HuR. We demonstrated that a tripartite complex of HuR, miR-19b and UTR directs repression of ABCB1/P-glycoprotein expression, with HuR essential for non-canonical miR-19b binding thereby controlling chemosensitivity of breast cancer cells. This exemplifies a new cooperative model between RNA-binding proteins and microRNAs to expand the repertoire of mRNAs that can be regulated. This study suggests a novel therapeutic target to impair P-glycoprotein mediated drug efflux, and also indicates that current microRNA binding predictions that rely on seed regions alone may be too conservative.

Cyclosporin A Reversed Chemoresistance of a Patient with Pure Red Cell Aplasia Secondary to Thymoma

This case study reports on a patient who relapsed with thymoma (mixed type) nine years after tumor resection. After four courses of rescue chemotherapy (docetaxel and cisplatinum), the patient was further diagnosed with pure red cell aplasia. It was noticed that cyclosporin A (CsA), which was administered to treat aplasia, could reverse chemoresistance. Its mechanism is not completely clear, but the hypothesis of CsA inhibiting P-glycoprotein mediated drug efflux is the most acceptable.

A Prediction Method for P-glycoprotein–Mediated Drug–Drug Interactions at the Human Blood–Brain Barrier From Blood Concentration–Time Profiles, Validated With PET Data

The purpose of this study was to establish physiologically based pharmacokinetic models to predict in humans the brain concentration–time profiles and P-glycoprotein (Pgp)–mediated brain drug–drug interactions between the model Pgp substrate (R)-[11C]verapamil (VPM), the model dual Pgp/breast cancer resistance protein (BCRP) substrate [11C]tariquidar (TQD), and the Pgp inhibitor tariquidar. The model predictions were validated with results from positron emission tomography studies in humans. Using these physiologically based pharmacokinetic models, the differences between predicted and observed areas under the concentration–time curves (AUC) of VPM and TQD in the brain were within a 1.2-fold and 2.5-fold range, respectively. Also, brain AUC increases of VPM and TQD after Pgp inhibitor administration were predicted with 2.5-fold accuracy when in vitro inhibition constant or half-maximum inhibitory concentration values of tariquidar were used. The predicted rank order of the magnitude of AUC increases reflected the results of the clinical positron emission tomography studies. Our results suggest that the established models can predict brain exposure from the respective blood concentration–time profiles and rank the magnitude of the Pgp-mediated brain drug–drug interaction potential for both Pgp and Pgp/BCRP substrates in humans.

Systematic evaluation of multifunctional paclitaxel-loaded polymeric mixed micelles as a potential anticancer remedy to overcome multidrug resistance.

In this work, a novel FA-TPGS2K copolymer has been synthesized and used it to construct mixed micelles with HDP copolymer to overcome MDR effect. Furthermore, a series in vitro and in vivo evaluations have been made, which supported enough evidences for the efficient delivery of antitumor drug to MDR cells.

Intestinal P-glycoprotein: pharmacokinetic implications and approaches for enhancement of oral bioavailability of its substrates

A variety of drug transporters expressed in the body control the fate of drugs by affecting absorption, distribution, and elimination processes. In intestine, the transporters mediate the influx and efflux of endogenous or exogenous substances depending on their affinity to intestinal carrier systems as well as their chemical nature. Of prime interest are drug efflux pumps like P-glycoprotein that are recognized to pose functional role in determining the pharmacokinetics of drugs administered by peroral as well as parenteral route. Various formulation approaches are opted in order to overcome this P-glycoprotein mediated drug efflux. Moreover, broad substrate recognition by this protein and clinical implications of its inhibition lead to design and development of novel P-glycoprotein inhibitors that includes some therapeutic drugs and daily foods and beverages. Inhibition of P-glycoprotein improves intestinal absorption and tissue distribution while reducing the substrate metabolism and its elimination. Some of the pharmaceutical excipients have also shown P-glycoprotein inhibition activity. In this review, we will be discussing about the various approaches that can be explored to reduce P-glycoprotein mediated drug efflux and improve the bioavailability of its substrates.

N-alkylated isatins evade P-gp mediated efflux and retain potency in MDR cancer cell lines.

The search for novel anticancer therapeutics with the ability to overcome multi-drug resistance (MDR) mechanisms is of high priority. A class of molecules that show potential in overcoming MDR are the N-alkylated isatins. In particular 5,7-dibromo-N-alkylisatins are potent microtubule destabilizing agents that act to depolymerize microtubules, induce apoptosis and inhibit primary tumor growth in vivo. In this study we evaluated the ability of four dibrominated N-alkylisatin derivatives and the parent compound, 5,7-dibromoisatin, to circumvent MDR. All of the isatin-based compounds examined retained potency against the MDR cell lines; U937VbR and MES-SA/Dx5 and displayed bioequivalent dose-dependent cytotoxicity to that of the parental control cell lines. We show that one mechanism by which the isatin-based compounds overcome MDR is by circumventing P-glycoprotein (P-gp) mediated drug efflux. Thus, as the isatin-based compounds are not susceptible to extrusion from P-gp overexpressing tumor cells, they represent a promising alternative strategy as a stand-alone or combination therapy for treating MDR cancer.

Increased intestinal P-glycoprotein expression and activity with progression of diabetes and its modulation by epigallocatechin-3-gallate: Evidence from pharmacokinetic studies

The aim of this study was to evaluate the change in the expression and the activity of intestinal P-glycoprotein (efflux transporter) with progression of diabetes in rats. Diabetes was induced in Wistar rats using a combination of low dose streptozotocin along with high fat diet. The expression of intestinal P-glycoprotein significantly increased (P≤0.05) with the progression of diabetes which was inferred from the mRNA analysis of mdr1a and mdr1b genes in the ileum segment of rat intestine. Furthermore, a significant increase (P≤0.05) in Na+–K+ ATPase activity was observed in the ileum segment of rat intestine with the progression of diabetes. As a result of this, a significant decrease in the intestinal uptake and peroral bioavailability of the P-glycoprotein substrates (verapamil and atorvastatin) was observed along with the progression of diabetes as compared to normal animals. To address this problem of impaired drug uptake and bioavailability, a reported P-glycoprotein inhibitor, epigallocatechin-3-gallate, was experimentally evaluated. The treatment with epigallocatechin-3-gallate resulted in significant reduction in the expression and activity of P-glycoprotein and subsequent improvement in the intestinal uptake and peroral bioavailability of both verapamil and atorvastatin in normal as well as in diabetic animals. The findings of this study rationalised the use and established the mechanism of action of epigallocatechin-3-gallate to overcome P-glycoprotein mediated drug efflux and will also be helpful in therapeutic drug monitoring in diabetes.

Effects of cytochalasin congeners, microtubule-directed agents, and doxorubicin alone or in combination against human ovarian carcinoma cell lines in vitro.

BackgroundAlthough the actin cytoskeleton is vital for carcinogenesis and subsequent pathology, no microfilament-directed agent has been approved for cancer chemotherapy. One of the most studied classes of microfilament-directed agents has been the cytochalasins, mycotoxins known to disrupt the formation of actin polymers. In the present study, we sought to determine the effects of cytochalasin congeners toward human drug sensitive and multidrug resistant cell lines.MethodsSKOV3 human ovarian carcinoma and several multidrug resistant derivatives were tested for sensitivity against a panel of nine cytochalasin congeners, as well as three clinically approved chemotherapeutic agents (doxorubicin, paclitaxel, and vinblastine). In addition, verapamil, a calcium ion channel blocker known to reverse P-glycoprotein (P-gp) mediated drug resistance, was used in combination with multiple cytochalasin congeners to determine whether drug sensitivity could be increased.ResultsWhile multidrug resistant SKVLB1 had increased drug tolerance (was more resistant) to most cytochalasin congeners in comparison to drug sensitive SKOV3, the level of resistance was 10 to 1000-fold less for the cytochalasins than for any of the clinically approved agents. While cytochalasins did not appear to alter the expression of ATP binding cassette (ABC) transporters, several cytochalasins appeared to inhibit the activity of ABC transporter-mediated efflux of rhodamine 123 (Rh123), suggesting that these congeners do have affinity for drug efflux pumps. Cytochalasins also appeared to significantly decrease the F/G-actin ratio in both drug sensitive and drug resistant cells, indicative of marked microfilament inhibition. The cytotoxicity of most cytochalasin congeners could be increased with the addition of verapamil, and the drug sensitivity of resistant SKVLB1 to the clinically approved antineoplastic agents could be increased with the addition of cytochalasins. As assessed by isobolographic analysis and Chou-Talalay statistics, cytochalasin B and 21,22-dihydrocytochalasin B (DiHCB) demonstrated notable synergy with doxorubicin and paclitaxel, warranting further investigation in a tumor-bearing mammalian model.ConclusionCytochalasins appear to inhibit the activity of P-gp and potentially other ABC transporters, and may have novel activity against multidrug resistant neoplastic cells that overexpress drug efflux proteins.