Pomiferin targets SERCA, mTOR, and P-gp to induce autophagic cell death in apoptosis-resistant cancer cells, and reverses the MDR phenotype in cisplatin-resistant tumors in vivo.

Drug resistance in cancer has been classified as innate resistance or acquired resistance, which were characterized by apoptotic defects and ABC transporters overexpression respectively. Therefore, to preclude or reverse these resistance mechanisms could be a promising strategy to improve chemotherapeutic outcomes. In this study, a natural product from Osage Orange, pomiferin, was identified as a novel autophagy activator that circumvents innate resistance by triggering autophagic cell death via SERCA inhibition and activation of the CaMKKß-AMPK-mTOR signaling cascade. In addition, pomiferin also directly inhibited the P-gp (MDR1/ABCB1) efflux and reversed acquired resistance by potentiating the accumulation and efficacy of the chemotherapeutic agent, cisplatin. In vivo study demonstrated that pomiferin triggered calcium-mediated tumor suppression and exhibited an anti-metastatic effect in the LLC-1 lung cancer-bearing mouse model. Moreover, as an adjuvant, pomiferin potentiated the anti-tumor effect of the chemotherapeutic agent, cisplatin, in RM-1 drug-resistant prostate cancer-bearing mouse model by specially attenuating ABCB1-mediated drug efflux, but not ABCC5, thereby promoting the accumulation of cisplatin in tumors. Collectively, pomiferin may serve as a novel effective agent for circumventing drug resistance in clinical applications.

TM2, a novel semi-synthetic taxoid, exerts anti-MDR activity in NSCLC by inhibiting P-gp function and stabilizing microtubule polymerization.

Taxane agents are of particular interest in non-small cell lung carcinomas (NSCLC) treatment, while multidrug resistance (MDR) mediated by P-glycoprotein (P-gp) limits their clinical efficacy. TM2, a chemically semi-synthesized taxane derivative, exerted significant anti-cancer efficacy in vitro and in vivo, especially against vincristine-resistant and adriamycin-resistant cancer cells. In this study, the anti-cancer effect of TM2 on drug-resistant NSCLC was evaluated both in vitro and in vivo, and the mechanism underlying its anti-MDR activity was further clarified. It was found that TM2 was significantly cytotoxic to cisplatin- and paclitaxel-resistant A549 (human non-small cell lung cancer) cells that overexpressing P-gp, resulting in IC50 values of 0.19 µM and 0.12 µM. TM2 micelles (5 mg/kg, 10 mg/kg, 20 mg/kg, i.v., 21 days) inhibited the growth of MDR xenograft with the maximal inhibitory rate up to 80.4%. Moreover, TM2 caused cell cycle arrest in the G2-M phase and apoptosis in drug-resistant cells through promoting tubulin polymerization, which acted in a way similar to taxane agents. Notably, TM2 acted as a P-gp inhibitor with high binding affinity, which resulted in impaired efflux function through forming H-bonds and ATP hydrolysis to induce P-gp conformational alterations. These findings indicated that TM2 displays anti-MDR activity with the potential for the treatment of NSCLC, which can inhibit P-gp function and stabilize microtubule polymerization.

Medicinal chemistry strategies to discover P-glycoprotein inhibitors: An update.

The presence of multidrug resistance (MDR) in malignant tumors is one of the primary causes of treatment failure in cancer chemotherapy. The overexpression of the ATP binding cassette (ABC) transporter, P-glycoprotein (P-gp), which significantly increases the efflux of certain anticancer drugs from tumor cells, produces MDR. Therefore, inhibition of P-gp may represent a viable therapeutic strategy to overcome cancer MDR. Over the past 4 decades, many compounds with P-gp inhibitory efficacy (referred to as first- and second-generation P-gp inhibitors) have been identified or synthesized. However, these compounds were not successful in clinical trials due to a lack of efficacy and/or untoward toxicity. Subsequently, third- and fourth-generation P-gp inhibitors were developed but dedicated clinical trials did not indicate a significant therapeutic effect. In recent years, an extraordinary array of highly potent, selective, and low-toxicity P-gp inhibitors have been reported. Herein, we provide a comprehensive review of the synthetic and natural products that have specific inhibitory activity on P-gp drug efflux as well as promising chemosensitizing efficacy in MDR cancer cells. The present review focuses primarily on the structural features, design strategies, and structure-activity relationships (SAR) of these compounds.

[Intestinal absorption characteristics of Polygonum orientale extract in normal and isoproterenol-induced myocardial ischemia model rats via everted intestinal sac models].

The present study is to investigate the absorption characteristics of the main components in Polygonum orientale extract in normal and isoproterenol-induced myocardial ischemia model rats with everted intestinal sac models. Intestinal sac fluid samples were collected in different part of intestine(duodenum, jejunum, ileum, colon) at different time after administration of different concentration of P. orientale extract(5.0,10.0, 20.0 mg·mL~(-1)). An UPLC-TQD method was employed for the determination of six components including orientin, isoorientin, vitexin, protocatechuic acid, kaempferol-3-O-ß-D-glucoside and quercitrin in the intestinal sac samples. The absorption rate and cumulative absorption were calculated to analyze the intestinal absorption characteristics of six components in normal and myocardial ischemia model rats. The P-glycoprotein(P-gp) inhibitor was applied to investigate influence of intestinal absorption of six components in P. orientale extract. The results showed that the main absorption sites were concentrated on the duodenum at low concentration, while they were the colon at the medium concentration and the ileum at high concentration in control groups. In the condition of myocardial ischemia model, the main absorption sites focus on the ileum and jejunum at low concentration; the main absorption sites were in the ileum at the medium concentration and main absorption sites were the duodenum and ileum at high concentration. Compared with the normal group, the absorption rate and cumulative absorption of the six components significantly decreased in the model group. P-gp inhibitor markedly increased the absorption rate and cumulative absorption of six components in the model group, inferring that the 6 components may be the substrates of P-gp, and the mechanism needs further study. In this study, it is revealed that the six components of P. orientale extract can be absorbed into the intestinal sac, and it is an effective method to assess the intestinal absorption characteristics of P. orientale extract through everted intestinal sac model, providing data support for the clinical application and further development of P. orientale.

Folic Acid-Modified Nanoerythrocyte for Codelivery of Paclitaxel and Tariquidar to Overcome Breast Cancer Multidrug Resistance.

The efflux of anticancer agents mediated by P-glycoprotein (P-gp) is one of the main causes of multidrug resistance (MDR) and eventually leads to chemotherapy failure. To overcome this problem, the delivery of anticancer agents in combination with a P-gp inhibitor using nanocarrier systems is considered an effective strategy. On the basis of the physiological compatibility and excellent drug loading ability of erythrocytes, we hypothesized that nanoerythrocytes could be used for the codelivery of an anticancer agent and a P-gp inhibitor to overcome MDR in breast cancer. Herein, a folic acid-modified nanoerythrocyte system (PTX/TQR NPs@NanoRBC-PEG/FA) was prepared to simultaneously transport paclitaxel and tariquidar, and the in vitro and in vivo characteristics of this delivery system were evaluated through several experiments. The results indicated that the average diameter and surface potential of this nanocarrier system were 159.8 ± 1.4 nm and -10.98 mV, respectively. Within 120 h, sustained release of paclitaxel was observed in both pH 6.5 media and pH 7.4 media. Tariquidar release from this nanocarrier suppressed the P-gp function of MCF-7/Taxol cells and significantly increased the intracellular paclitaxel level (p < 0.01 versus the PTX group). The results of the MTT assay indicated that the simultaneous transportation of paclitaxel and tariquidar could significantly inhibit the growth of MCF-7 cells or MCF-7/Taxol cells. After 48 h of incubation with PTX/TQR NPs@NanoRBC-PEG/FA, the viability of MCF-7 cells and MCF-7/Taxol cells decreased to 7.37% and 30.2%, respectively, and the IC50 values were 2.49 µM and 6.30 µM. Pharmacokinetic results illustrated that, compared with free paclitaxel, all test paclitaxel nanoformulations prolonged the drug release time and showed similar plasma concentration-time profiles. The peak concentration (Cmax), area under the curve (AUC0-∞), and half-life (t1/2) of PTX/TQR NPs@NanoRBC-PEG/FA were 3.33 mg/L, 6.02 mg/L·h, and 5.84 h, respectively. Moreover, this active targeting nanocarrier dramatically increased the paclitaxel level in tumor tissues. Furthermore, compared with those of the other paclitaxel formulations, the cellular reactive oxygen species (ROS) and malondialdehyde (MDA) levels of the PTX/TQR NPs@NanoRBC-PEG/FA group increased by 1.38-fold (p < 0.01) and 1.36-fold (p < 0.01), respectively, and the activities of superoxide dismutase (SOD) and catalase (CAT) decreased to 67.8% (p < 0.01) and 65.4% (p < 0.001), respectively. More importantly, in vivo antitumor efficacy results proved that the PTX/TQR NPs@NanoRBC-PEG/FA group exerted an outstanding tumor inhibition effect with no marked body weight loss and fewer adverse effects. In conclusion, by utilizing the inherent and advantageous properties of erythrocytes and surface modification strategies, this biomimetic targeted drug delivery system provides a promising platform for the codelivery of an anticancer agent and a P-gp inhibitor to treat MDR in breast cancer.

SERCA and P-glycoprotein inhibition and ATP depletion are necessary for celastrol-induced autophagic cell death and collateral sensitivity in multidrug-resistant tumor cells.

Multidrug resistance (MDR) represents an obstacle in anti-cancer therapy. MDR is caused by multiple mechanisms, involving ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp), which reduces intracellular drug levels to sub-therapeutic concentrations. Therefore, sensitizing agents retaining effectiveness against apoptosis- or drug-resistant cancers are desired for the treatment of MDR cancers. The sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) pump is an emerging target to overcome MDR, because of its continuous expression and because the calcium transport function is crucial to the survival of tumor cells. Previous studies showed that SERCA inhibitors exhibit anti-cancer effects in Bax-Bak-deficient, apoptosis-resistant and MDR cancers, whereas specific P-gp inhibitors reverse the MDR phenotype of cancer cells by blocking efflux of chemotherapeutic agents. Here, we unraveled SERCA and P-gp as double targets of the triterpenoid, celastrol to reverse MDR. Celastrol inhibited both SERCA and P-gp to stimulate calcium-mediated autophagy and ATP depletion, thereby induced collateral sensitivity in MDR cancer cells. In vivo studies further confirmed that celastrol suppressed tumor growth and metastasis by SERCA-mediated calcium mobilization. To the best of our knowledge, our findings demonstrate collateral sensitivity in MDR cancer cells by simultaneous inhibition of SERCA and P-gp for the first time.

Simultaneous quantification of ondansetron and tariquidar in rat and human plasma using a high performance liquid chromatography-ultraviolet method.

Ondansetron, a widely used antiemetic agent, is a P-glycoprotein (P-gp) substrate and therefore expression of P-gp at the blood-brain barrier limits its distribution to the central nervous system (CNS), which was observed to be reversed by coadministration with P-gp inhibitors. Tariquidar is a potent and selective third-generation P-gp inhibitor, and coadministration with ondansetron has shown improved ondansetron distribution to the CNS. There is currently no reported bioanalytical method for simultaneously quantifying ondansetron with a third-generation P-gp inhibitor. Therefore, we aimed to develop and validate a method for ondansetron and tariquidar in rat and human plasma samples. A full validation was performed for both ondansetron and tariquidar, and sample stability was tested under various storage conditions. To demonstrate its utility, the method was applied to a preclinical pharmacokinetic study following coadministration of ondansetron and tariquidar in rats. The presented method will be valuable in pharmacokinetic studies of ondansetron and tariquidar in which simultaneous determination may be required. In addition, this is the first report of a bioanalytical method validated for quantification of tariquidar in plasma samples.

Constituents and Anti-Multidrug Resistance Activity of Taiwanofungus camphoratus on Human Cervical Cancer Cells.

Resistance to anti-cancer drugs is one of the main factors of treatment failure resulting in high morbidity. Among the reasons of resistance, overexpression of efflux pumps leading to multidrug resistance is an important issue that needs to be solved. Taiwanofungus camphoratus has been used as a nutritional supplement to treat various cancers. However, its effects on the resistance to chemotherapeutic agents are still unknown. In this study, we report four new chemical constituents of T. camphoratus isolated from an ether extract: camphoratins K (1) and N (2) and benzocamphorins G (3) and I (4). Furthermore, we evaluated zhankuic acids A-C for their P-glycoprotein (P-gp) inhibitory effects. The results showed that zhankuic acid A was the most potent P-gp inhibitor compound and (at 20 µM) could reverse drug resistance in human cancer cells, restoring an IC50 of 78.5 nM for doxorubicin, of 48.5 nM for paclitaxel, and of 321.5 nM for vincristine, indicating a reversal fold of 48, 38, and 45 times, respectively. This study provides support for the use of T. camphoratus in the further development of cancer therapy.

Reversal of P-glycoprotein-mediated multidrug resistance and pharmacokinetics study in rats by WYX-5.

Multidrug resistance (MDR) is one of the major obstacles confronted in cancer chemotherapy; this obstacle is mainly due to the overexpression of P-glycoprotein (P-gp). Co-administration of anticancer drugs and P-gp inhibitors is a promising approach to overcome MDR. WYX-5, a novel P-gp inhibitor, shows a notable reversal effect with low cytotoxicity in vitro. In this paper, the reversal mechanism and safety of the MDR modulator WYX-5 were explored in vitro, and evaluated for its pharmacokinetics and effects on adriamycin (ADM) metabolism in vivo. The results suggest that WYX-5 is a potent P-gp inhibitor with EC50 in nanomole range (EC50 = 204.3 ± 20.2 nmol·L-1), relative safety (therapeutic index = 446.4), which performs as a substrate of P-gp and retrains its function. Further, WYX-5 (5 mg·kg-1) had relatively ideal pharmacokinetic properties (T1/2 = 6.448 h, F = 96.05%) without interactions with ADM metabolism in vivo. In conclusion, WYX-5 may be a promising candidate for MDR cancer combined-chemotherapy research.

pH, redox and photothermal tri-responsive DNA/polyethylenimine conjugated gold nanorods as nanocarriers for specific intracellular co-release of doxorubicin and chemosensitizer pyronaridine to combat multidrug resistant cancer.

Pharmacotherapy of multidrug resistant (MDR) cancer remains a challenging task in clinic. Herein, a pH-responsive DNA and disulfide-linked polyethylenimine functionalized gold nanorod was developed for specific co-delivery of chemotherapeutic agent doxorubicin (DOX) and chemosensitizer pyronaridine (PND) to effectively overcome MDR cancer cells. DOX and PND were firstly carried by a multifunctional nanocomplex for reversing MDR cancer. The nanocomplex can responsively and rapidly release its drugs payload under acidic pH environment (pH, ~5), intracellular GSH concentration content (5 mM) and/or 808 nm NIR laser irradiation. Compared to free DOX, the nanocomplex displayed greatly increased cytotoxicity to MDR MCF-7/ADR cancer cells (IC50, 70.68:6.21 µg/mL). The application of NIR radiation further improved the DOX release and enhanced the antitumor effects of the namomedicine (IC50, drops to 2.88 µg/mL). Consequently, this new nanocomplex exerted greatly increased potency against the MDR cancer cells over free DOX (~20 fold).

One-Step Self-Assembling Nanomicelles for Pirarubicin Delivery To Overcome Multidrug Resistance in Breast Cancer.

Tumor cells can acquire multidrug resistance (MDR) as a result of drug efflux mediated by P-glycoprotein (P-gp). Here we report a targeted delivery system to carry pirarubicin (THP) to MDR breast cancer both in vitro and in vivo. PEG-derivatized vitamin E (PAMV6) amphiphiles loaded with THP were self-assembled in a single step. The PAMV6 micelles showed unimodal size distribution and high drug loading efficiency. Cytotoxicity of PAMV6/THP was higher than that of free THP on MCF-7/ADR cells but comparable to that of THP on MCF-7 cells. PAMV6/THP was able to reverse MDR more than free THP in MCF-7/ADR cells, likely reflecting the remarkably higher intracellular THP concentration in micelle-treated cells and PAMV6-mediated inhibition of P-gp activity. PAMV6/THP micelles were internalized into MCF-7/ADR cells via macropinocytosis and caveolin-mediated endocytosis, further avoiding P-gp-mediated efflux. Mechanistic studies revealed that blank PAMV6 micelles inhibited P-gp activity but did not affect P-gp expression, by significantly reducing mitochondrial membrane potential and slightly decreasing intracellular ATP levels. In a nude mouse xenograft model, PAMV6/THP led to much greater THP accumulation in tumors and much slower tumor growth than free THP. At the same time, PAMV6/THP was associated with significantly less severe bone marrow suppression and organ toxicity than free THP. Our results indicate that this PAMV6-based micelle system holds promise for combating MDR in cancer therapy.

Discovery of substituted 1,4-dihydroquinolines as novel promising class of P-glycoprotein inhibitors: First structure-activity relationships and bioanalytical studies.

Multidrug resistance (mdr) is the most important problem in the therapeutical treatment of cancer. One central problem in the resistance proceeding is the expression of transmembrane efflux pumps which transport drugs out of the cells. We developed novel substituted 1,4-dihydroquinolines as inhibitors of the transmembrane efflux pump P-glycoprotein. Structure-activity relationships are discussed for this first series. Promising active inhibitors have been identified and first bioanalytical studies have been carried out to address questions of cellular toxicity, P-gp substrate as well as mdr reversal properties.

Enhanced solubility and intestinal absorption of candesartan cilexetil solid dispersions using everted rat intestinal sacs.

OBJECTIVE: Candesartan cilexetil (CAN) is a poor aqueous soluble compound and a P-glycoprotein (P-gp) efflux pump substrate. These key factors are responsible for its incomplete intestinal absorption. METHODS: In this study, we investigated to enhance the absorption of CAN by improving its solubility and inhibiting intestinal P-gp activity. A phase solubility method was used to evaluate the aqueous solubility of CAN in PVP K30 (0.2-2%). Gibbs free energy [Formula: see text] values were all negative. Solubility was enhanced by the freeze drying technique. The in vitro dissolution was evaluated using the USP paddle method. The interaction between drug and carrier was evaluated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Differential scanning calorimetry (DSC) studies. Naringin was selected as P-gp inhibitor. Absorption studies were performed using the everted gut sac model from rat jejunum. The drug analysis was performed by HPLC. RESULTS: FTIR spectra revealed no interaction between drug and PVP K30. From XRD and DSC data, CAN was in the amorphous form, which explains the cumulative release of drug from its prepared systems. We noticed an enhancement of CAN absorption by improving its solubility and inhibiting the P-gp activity. The significant results (p < 0.05) were obtained for freeze dried solid dispersions in the presence of P-gp inhibitor than without naringin (15 mg/kg) with an absorption enhancement of 8-fold. CONCLUSION: Naringin, a natural flavonoid, has no undesirable side effects. Therefore, it could be employed as an excipient in the form of solid dispersions to increase CAN intestinal absorption and its oral bioavailability.

Adjunctive use of verapamil in patients with refractory temporal lobe epilepsy: a pilot study.

OBJECTIVE: The present study aimed to determine if adjunctive use of verapamil, as a P-glycoprotein (P-gp) inhibitor, is efficacious in decreasing seizure frequency in patients with refractory temporal lobe epilepsy. MATERIALS AND METHODS: This was an open-label pilot study. Adult patients with refractory temporal lobe epilepsy were studied. Baseline seizure type and seizure count were determined. Patients were divided randomly into two groups. Group A received verapamil 120 mg/day (n=13), and group B received 240 mg/day (n=6). All patients were followed for eight weeks. The proportion of responders, which consist of patients with more than 50% reduction in seizure frequency from baseline, was tabulated. RESULTS: Nineteen patients were studied. Seven patients (36.84%) reached the responder rate. Three patients (50%) in group B were among the responders; two of these patients achieved seizure freedom. Four patients (30.7%) in group A responded favorably to verapamil. CONCLUSION: Developing new means of improving the effectiveness of existing antiepileptic drugs is a desirable way of tackling the dilemma of medically refractory epilepsy. Hypothetically, P-gp inhibitors (e.g., verapamil) might be used to counteract the removal of AEDs from the epileptogenic tissue. Such a strategy was adopted in this non-placebo-controlled, open-label, pilot study. We observed a significant achievement in seizure control associated with adjunctive use of verapamil in patients with refractory temporal lobe epilepsy.

Functionalized Lipid Nanocarriers for Simultaneous Delivery of Docetaxel and Tariquidar to Chemoresistant Cancer Cells.

The simultaneous drug delivery efficiency of a co-loaded single-carrier system of docetaxel (DTX)- and tariquidar (TRQ)-loaded nanostructured lipid carrier (NLC) functionalized with PEG and RIPL peptide (PRN) (D^T-PRN) was compared with that of a physically mixed dual-carrier system of DTX-loaded PRN (D-PRN) and TRQ-loaded PRN (T-PRN) to overcome DTX mono-administration-induced multidrug resistance. NLC samples were prepared using the solvent emulsification evaporation technique and showed homogeneous spherical morphology, with nano-sized dispersion (<220 nm) and zeta potential values of -15 to -7 mV. DTX and/or TRQ was successfully encapsulated in NLC samples (>95% encapsulation efficiency and 73-78 µg/mg drug loading). In vitro cytotoxicity was concentration-dependent; D^T-PRN exhibited the highest MDR reversal efficiency, with the lowest combination index value, and increased the cytotoxicity and apoptosis in MCF7/ADR cells by inducing cell-cycle arrest in the G2/M phase. A competitive cellular uptake assay using fluorescent probes showed that, compared to the dual nanocarrier system, the single nanocarrier system exhibited better intracellular delivery efficiency of multiple probes to target cells. In the MCF7/ADR-xenografted mouse models, simultaneous DTX and TRQ delivery using D^T-PRN significantly suppressed tumor growth as compared to other treatments. A single co-loaded system for PRN-based co-delivery of DTX/TRQ (1:1, w/w) constitutes a promising therapeutic strategy for drug-resistant breast cancer cells.

Oral paclitaxel and encequidar in patients with breast cancer: a pharmacokinetic, safety, and antitumor activity study.

Background: Paclitaxel is widely used for the treatment of metastatic breast cancer (MBC). However, it has a low oral bioavailability due to gut extrusion caused by P-glycoprotein (P-gp). Oral paclitaxel (oPAC) may be more convenient, less resource-intensive, and more tolerable than its intravenous form. Encequidar (E) is a first-in-class, minimally absorbed, gut-specific oral P-gp inhibitor that facilitates the oral absorption of paclitaxel. Objectives: To investigate the pharmacokinetics (PK), overall response rate (ORR), and safety of weekly oral paclitaxel with encequidar (oPAC + E) in patients with advanced breast cancer. Design: This is a multicenter, single-arm, open-label study in six medical centers in Taiwan. Methods: Patients with advanced breast cancer were administered 205 mg/m2 oPAC and 12.9 mg E for 3 consecutive days weekly for up to 16 weeks. Plasma samples were collected at weeks 1 and 4. PK, ORR, and safety were evaluated. Results: In all, 28 patients were enrolled; 27 had MBC; 23 had prior chemotherapy; and 14 had ⩾2 lines of prior chemotherapy. PK were evaluable in 25 patients. Plasma paclitaxel area under the curve (AUC)(0-52 h) at week 1 (3419 ± 1475 ng h/ml) and week 4 (3224 ± 1150 ng h/ml) were equivalent. Best overall response in 28 evaluable patients was partial response (PR) in 11 (39.3%), 13 (46.4%) stable disease (SD), and 1 (3.6%) with progressive disease (PD). No patient achieved complete response (CR). The clinical benefit rate (CR + PR + SD) was 85.7%. Major adverse events among the 28 treated patients were grade 3 neutropenia (25%), grade 4 neutropenia (18%), with febrile neutropenia in 4%, and grade 3 diarrhea (4%). No treatment-related deaths occurred. Grade 2 peripheral neuropathy occurred in 1 (4%) patient and grade 3 peripheral neuropathy in 1 (4%) patient. Conclusions: oPAC + E produced a consistent therapeutic plasma paclitaxel exposure during treatment. There was a high rate of radiologically assessed clinical benefit, and a low rate of neurotoxicity which may provide advantages over IV paclitaxel. Registration: ClinicalTrials.gov Identifier: NCT03165955.

Role of natural P-gp inhibitor in the effective delivery for chemotherapeutic agents.

Multi-drug resistance has shown to be one of the leading threats faced currently in many chemotherapeutic agents. Permeability glycoprotein (P-gp) is an efflux transporter in membrane, an integral part of ATP-binding cassette (ABC) transporters widely distributed in the body for cellular uptake. It is present enormously in cancerous cells and is in charge of generating transporter mediated resistance to treatments of tumorous cells in addition to blocking the entry of chemotherapeutic drugs into the cell. Natural P-gp inhibitors are derived from natural plant sources possessing basic structures like alkaloids, flavonoids, phenolics, terpenoids, saponins, sapogenins, sterols, coumarins and miscellaneous structures acting on P-gp substrate for inhibition of multi-drug resistance via inhibiting the efflux pump. They do not depict their action on the healthy cells and thus it is proven to be more effective and less toxic than synthetic P-gp inhibitor leading to enhancement in bioavailability of chemotherapeutic drugs. The significant objective of the present review is surfing through the impact of natural P-gp inhibitors having basic structures derived from the plant sources and how it inhibits the resistance of chemotherapeutic drugs together with how well it delivers chemotherapy medicines.

Novel Pt(IV) complexes to overcome multidrug resistance in gastric cancer by targeting P-glycoprotein.

Systematic toxicity and drug resistance significantly limited FDA-approved platinum drugs for further clinical applications. In order to reverse the resistance (MDR) and enhance their anticancer efficiency, four Pt(IV) complexes (12-15) conjugating with P-glycoprotein (P-gp) inhibitors were designed and synthesized. Among them, complex 14 (IC50 = 3.37 µM) efficiently reversed cisplatin resistance in SGC-7901/CDDP cell line and increased selectivity index (6.9) against normal HL-7702 cell line. Detailed mechanisms in SGC-7901/CDDP cells assays revealed that complex 14 efficiently induced apoptosis via down-regulating expression of P-gp for enhanced intracellular uptake of platinum, arrested cells at G2/M phase, induced DNA damage and initiated mitochondrial apoptosis pathway. Further in vivo studies demonstrated that the enhanced accumulation of complex 14 contributed to tumor inhibition of 75.6% in SGC-7901/CDDP xenografts, which was much higher than cisplatin (25.9%) and oxaliplatin (43%). Moreover, the low systematic toxicity made 14 a potential novel P-gp-mediated MDR modulator.

Co-Amorphous Formulations of Furosemide with Arginine and P-Glycoprotein Inhibitor Drugs.

In this study, the amino acid arginine (ARG) and P-glycoprotein (P-gp) inhibitors verapamil hydrochloride (VER), piperine (PIP) and quercetin (QRT) were used as co-formers for co-amorphous mixtures of a Biopharmaceutics classification system (BCS) class IV drug, furosemide (FUR). FUR mixtures with VER, PIP and QRT were prepared by solvent evaporation, and mixtures with ARG were prepared by spray drying in 1:1 and 1:2 molar ratios. The solid-state properties of the mixtures were characterized with X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) in stability studies under different storage conditions. Simultaneous dissolution/permeation studies were conducted in side-by-side diffusion cells with a PAMPA (parallel artificial membrane permeability assay) membrane as a permeation barrier. It was observed with XRPD that ARG, VER and PIP formed co-amorphous mixtures with FUR at both molar ratios. DSC and FTIR revealed single glass transition values for the mixtures (except for FUR:VER 1:2), with the formation of intermolecular interactions between the components, especially salt formation between FUR and ARG. The co-amorphous mixtures were found to be stable for at least two months under an elevated temperature/humidity, except FUR:ARG 1:2, which was sensitive to humidity. The dissolution/permeation studies showed that only the co-amorphous FUR:ARG mixtures were able to enhance both the dissolution and permeation of FUR. Thus, it is concluded that formulating co-amorphous salts with ARG may be a promising option for poorly soluble/permeable FUR.

A novel fluorescence-based functional assay for human OATP1A2 and OATP1C1 identifies interaction between third-generation P-gp inhibitors and OATP1A2.

Organic anion-transporting polypeptide 1A2 (OATP1A2), expressed in the human blood-brain barrier, promotes drug uptake from the blood and hence can be exploited for central nervous system-targeted drug delivery. The thyroid transporter OATP1C1, expressed in the choroid plexus and in astrocytes, is also a potential pharmacological target. Based on their established pharmacological relevance, screening the drug interaction profile of OATP1A2 and OATP1C1 is highly desirable. However, drug interaction screens require suitable model systems and functional assays. In the current study, uptake of a set of cell-impermeable fluorescent dyes was screened in HEK-293 and A431 cell lines overexpressing OATP1A2 and OATP1C1. Based on the uptake of fluorescent dye substrates, a functional assay was developed, which was used to characterize OATP inhibitors/substrates. We identify Live/Dead Green (LDG), Live-or-Dye 488, and sulforhodamines 101, G, and B as novel fluorescent substrates of OATP1A2 and OATP1C1. We show that LDG uptake is proportional to OATP1A2/1C1 expression, allowing the isolation of cells expressing high transporter levels. Additionally, dye uptake can be used to characterize the drug interaction pattern of OATP1A2 and OATP1C1. We demonstrate that third-generation P-glycoprotein inhibitors elacridar, tariquidar, and zosuquidar inhibit OATP1A2 function. Increased toxicity of elacridar in OATP1A2-expressing cells suggests that OATP1A2 may modulate the distribution of this compound. The fluorescence-based assays developed in the current study are a good alternative of radioligand-based tests and pave the way toward high-throughput screens for OATP1A2/1C1 drug interaction studies.