Selective inhibition of MDR1 (ABCB1) by HM30181 increases oral bioavailability and therapeutic efficacy of paclitaxel

Co-release of paclitaxel and encequidar from amorphous solid dispersions increase oral paclitaxel bioavailability in rats

The oral bioavailability of paclitaxel is limited due to low solubility and high affinity for the P-glycoprotein (P-gp) efflux transporter. Here we hypothesized that maximizing the intestinal paclitaxel levels through apparent solubility enhancement and controlling thesimultaneous release of both paclitaxel and the P-gp inhibitor encequidar from amorphous solid dispersions (ASDs) would increase the oral bioavailability of paclitaxel. ASDs of paclitaxel and encequidar in polyvinylpyrrolidone K30 (PVP-K30), hydroxypropylmethylcellulose 5 (HPMC-5), and hydroxypropylmethylcellulose 4 K (HPMC-4K) were hence prepared by freeze-drying. In vitro dissolution studies showed that both compounds were released fastest from PVP-K30, then from HPMC-5, and slowest from HPMC-4K ASDs. The dissolution of paclitaxel from all polymers resulted in stable concentration levels above the apparent solubility. The pharmacokinetics of paclitaxel after oral administration to male Sprague-Dawley rats was investigated with or without 1 mg/kg encequidar, as amorphous solids or polymer-based ASDs. The bioavailability of paclitaxel increased 3- to 4-fold when administered as polymer-based ASDs relative to solid amorphous paclitaxel. However, when amorphous paclitaxel was co-administered with encequidar, either as an amorphous powder or as a polymer-based ASD, the bioavailability increased 2- to 4-fold, respectively. Interestingly, a noticeable increase in paclitaxel bioavailability of 24-fold was observed when paclitaxel and encequidar were co-administered as HPMC-5-based ASDs. We, therefore, suggest that controlling the dissolution rate of paclitaxel and encequidar in order to obtain simultaneous and timed release from polymer-based ASDs is a strategy to increase oral paclitaxel bioavailability.

Evaluation of Encequidar as An Intestinal P-gp and BCRP Specific Inhibitor to Assess the Role of Intestinal P-gp and BCRP in Drug-Drug Interactions

PURPOSE

The differences between intestinal and systemic (hepatic and renal) P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) roles in drug disposition are difficult to define. Accordingly, we characterized Encequidar (ECD) as an intestinal P-gp and BCRP specific inhibitor to evaluate their role in drug disposition.

METHODS

We assessed the in vitro and in vivo inhibition potential of ECD towards human and animal P-gp and BCRP.

RESULTS

ECD is a potent inhibitor with a high degree of selectivity in inhibiting human P-gp (hP-gp) over human BCRP (hBCRP) (IC50s of 0.0058 ± 0.0006 vs. > 10 µM, respectively). In contrast, ECD is a potent inhibitor of rat and cynomolgus monkey BCRP (IC50 ranged from 0.059 to 0.18 µM). While the AUC of IV paclitaxel (PTX) was significantly increased by elacridar (ELD) (P < 0.05) but not ECD in rats (15 mg/kg; PO) (2.55- vs. 0.93-fold), that of PO PTX was significantly elevated to a similar extent between the inhibitors (39.5- vs. 33.5-fold). Similarly, the AUC of PO sulfasalazine (SFZ) was dramatically increased by ELD and ECD (16.6- vs. 3.04-fold) although that of IV SFZ was not significantly affected by ELD and ECD in rats (1.18- vs. 1.06-fold). Finally, a comparable ECD-induced increase of the AUC of PO talinolol in cynomolgus monkeys was observed compared with ELD (2.14- vs. 2.12-fold).

CONCLUSIONS

ECD may allow an in-depth appraisal of the role of intestinal efflux transporter(s) in drug disposition in animals and humans through local intestinal drug interactions.

An oral triple pill-based cocktail effectively controls acute myeloid leukemia with high translation

Acute myeloid leukemia (AML) is a deadly hematological malignancy characterized by oncogenic translational addiction that results in over-proliferation and apoptosis evasion of leukemia cells. Various chemo- and targeted therapies aim to reverse this hallmark, but most show only modest efficacy. Here we report a single oral pill containing a low-dose triple small molecule-based cocktail, a highly active anti-cancer therapy (HAACT) with unique mechanisms that can effectively control AML. The cocktail comprises oncogenic translation inhibitor HHT, drug efflux pump P-gpi ENC and anti-apoptotic protein Bcl-2i VEN. Mechanistically, the cocktail can potently kill both leukemia stem cells (LSC) and bulk leukemic cells via co-targeting oncogenic translation, apoptosis machinery, and drug efflux pump, resulting in deep and durable remissions of AML in diverse model systems. We also identified EphB4/Bcl-xL as the cocktail response biomarkers. Collectively, our studies provide proof that a single pill containing a triple combination cocktail might be a promising avenue for AML therapy.

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.

Predicting disruptions to drug pharmacokinetics and the risk of adverse drug reactions in non-alcoholic steatohepatitis patients

The liver plays a central role in the pharmacokinetics of drugs through drug metabolizing enzymes and transporters. Non-alcoholic steatohepatitis (NASH) causes disease-specific alterations to the absorption, distribution, metabolism, and excretion (ADME) processes, including a decrease in protein expression of basolateral uptake transporters, an increase in efflux transporters, and modifications to enzyme activity. This can result in increased drug exposure and adverse drug reactions (ADRs). Our goal was to predict drugs that pose increased risks for ADRs in NASH patients. Bibliographic research identified 71 drugs with reported ADRs in patients with liver disease, mainly non-alcoholic fatty liver disease (NAFLD), 54 of which are known substrates of transporters and/or metabolizing enzymes. Since NASH is the progressive form of NAFLD but is most frequently undiagnosed, we identified other drugs at risk based on NASH-specific alterations to ADME processes. Here, we present another list of 71 drugs at risk of pharmacokinetic disruption in NASH, based on their transport and/or metabolism processes. It encompasses drugs from various pharmacological classes for which ADRs may occur when used in NASH patients, especially when eliminated through multiple pathways altered by the disease. Therefore, these results may inform clinicians regarding the selection of drugs for use in NASH patients.

Discovery of a Flavonoid FM04 as a Potent Inhibitor to Reverse P-Glycoprotein-Mediated Drug Resistance in Xenografts and Improve Oral Bioavailability of Paclitaxel

Biotransformation of flavonoid dimer FD18 resulted in an active metabolite FM04. It was more druggable because of its improved physicochemical properties. FM04 (EC50 = 83 nM) was 1.8-fold more potent than FD18 in reversing P-glycoprotein (P-gp)-mediated paclitaxel (PTX) resistance in vitro. Similar to FD18, FM04 chemosensitized LCC6MDR cells towards multiple anticancer drugs by inhibiting the transport activity of P-gp and restoring intracellular drug levels. It stimulated the P-gp ATPase by 3.3-fold at 100 μM. Different from FD18, FM04 itself was not a transport substrate of P-gp and presumably, it cannot work as a competitive inhibitor. In the human melanoma MDA435/LCC6MDR xenograft, the co-administration of FM04 (28 mg/kg, I.P.) with PTX (12 mg/kg, I.V.) directly modulated P-gp-mediated PTX resistance and caused a 56% (*, p < 0.05) reduction in tumor volume without toxicity or animal death. When FM04 was administered orally at 45 mg/kg as a dual inhibitor of P-gp/CYP2C8 or 3A4 enzymes in the intestine, it increased the intestinal absorption of PTX from 0.2% to 14% in mice and caused about 57- to 66-fold improvement of AUC as compared to a single oral dose of PTX. Oral co-administration of FM04 (45 mg/kg) with PTX (40, 60 or 70 mg/kg) suppressed the human melanoma MDA435/LCC6 tumor growth with at least a 73% (***, p < 0.001) reduction in tumor volume without serious toxicity. Therefore, FM04 can be developed into a novel combination chemotherapy to treat cancer by directly targeting the P-gp overexpressed tumors or potentiating the oral bioavailability of P-gp substrate drugs.

The Tetrahydroisoquinoline Scaffold in ABC Transporter Inhibitors that Act as Multidrug Resistance (MDR) Reversers

BACKGROUND

The failure of anticancer chemotherapy is often due to the development of resistance to a variety of anticancer drugs. This phenomenon is called multidrug resistance (MDR) and is related to the overexpression of ABC transporters, such as P-glycoprotein, multidrug resistance- associated protein 1 and breast cancer resistance protein. Over the past few decades, several ABC protein modulators have been discovered and studied as a possible approach to evade MDR and increase the success of anticancer chemotherapy. Nevertheless, the co-administration of pump inhibitors with cytotoxic drugs, which are substrates of the transporters, does not appear to be associated with an improvement in the therapeutic efficacy of antitumor agents. However, more recently discovered MDR reversing agents, such as the two tetrahydroisoquinoline derivatives tariquidar and elacridar, are characterized by high affinity towards the ABC proteins and by reduced negative properties. Consequently, many analogs of these two derivatives have been synthesized, with the aim of optimizing their MDR reversal properties.

OBJECTIVE

This review aims to describe the MDR modulators carrying the tetraidroisoquinoline scaffold reported in the literature in the period 2009-2021, highlighting the structural characteristics that confer potency and/or selectivity towards the three ABC transport proteins.

RESULTS AND CONCLUSION

Many compounds have been synthesized in the last twelve years showing interesting properties, both in terms of potency and selectivity. Although clear structure-activity relationships can be drawn only by considering strictly related compounds, some of the compounds reviewed could be promising starting points for the design of new ABC protein inhibitors.

The effect and mechanistic study of encequidar on reversing the resistance of SW620/AD300 cells to doxorubicin

Encequidar, a gut-specific P-glycoprotein (P-gp) inhibitor, makes oral paclitaxel possible, and has been used in clinical treatment of metastatic breast cancer, however, its pharmacological effect and mechanism of reversal of drug resistance in drug-resistant colon cancer cells SW620/AD300 are still unknown. Herein, we first synthesized encequidar and demonstrated that it could inhibit the transport activity of P-gp, reduced doxorubicin (DOX) efflux, enhanced DOX cytotoxicity and promoted tumor-apoptosis in SW620/AD300 cells. Metabolomic analysis of cell samples was performedusing liquid chromatography Q-Exactive mass spectrometer, the results of metabolite enrichment analysis and pathway analysis showed that the combination of encequidar and DOX could: i) significantly affect the citric acid cycle (TCA cycle) and reduce the energy supply required for P-gp to exert its transport activity; ii) affect the metabolism of glutathione, which is the main component of the anti-oxidative stress system, and reduce the ability of cells to resist oxidative stress; iii) increase the intracellular reactive oxygen species (ROS) production and enhance ROS-induced cell damage and lipid peroxidation, which in turn restore the sensitivity of drug-resistant cells to DOX. In conclusion, these results provide sufficient data support for the therapeutical application of the P-gp inhibitor encequidar to reverse MDR, and are of great significance to further understand the therapeutic advantages of encequidar in anti-tumor therapy and guide clinical rational drug use.

A commentary on the use of pharmacoenhancers in the pharmaceutical industry and the implication for DMPK drug discovery strategies

Paxlovid, a drug combining nirmatrelvir and ritonavir, was designed for the treatment of COVID-19 and its rapid development has led to emergency use approval by the FDA to reduce the impact of COVID-19 infection on patients.In order to overcome potentially suboptimal therapeutic exposures, nirmatrelvir is dosed in combination with ritonavir to boost the pharmacokinetics of the active product.Here we consider examples of drugs co-administered with pharmacoenhancers.Pharmacoenhancers have been adopted for multiple purposes such as ensuring therapeutic exposure of the active product, reducing formation of toxic metabolites, changing the route of administration, and increasing the cost-effectiveness of a therapy.We weigh the benefits and risks of this approach, examining the impact of technology developments on drug design and how enhanced integration between cross-discipline teams can improve the outcome of drug discovery.

A phase Ib study of Oraxol (oral paclitaxel and encequidar) in patients with advanced malignancies

PURPOSE

Oraxol is an oral formulation of paclitaxel administered with a novel, minimally absorbed P-glycoprotein inhibitor encequidar (HM30181A). This phase Ib study was conducted to determine the maximum-tolerated dose (MTD) of Oraxol administered at a fixed dose for up to 5 consecutive days in patients with advanced malignancies.

METHODS

Part 1 of this study utilized a 3 + 3 dose-escalation design to determine the MTD of oral paclitaxel 270 mg plus oral encequidar 15 mg administered daily. Dose escalation was achieved by increasing the number of consecutive dosing days per week (from 2 to 5 days per week). Dosing occurred for 3 consecutive weeks out of a 4-week cycle. Part 2 treated additional patients at the MTD to determine tolerability and recommended phase II dose (RP2D). Adverse events, tumor responses, and pharmacokinetic profiles were assessed.

RESULTS

A total of 34 patients (n = 24 in Part 1, n = 10 in Part 2) received treatment. The MTD of Oraxol was determined to be 270 mg daily × 5 days per week per protocol definition and this was declared the RP2D. The most common treatment-related adverse events were fatigue, neutropenia, and nausea/vomiting. Hypersensitivity-type reactions were not observed. Of the 28 patients evaluable for response, 2 (7.1%) achieved partial response and 18 (64.3%) achieved stable disease. Pharmacokinetic analysis showed rapid absorption of paclitaxel when administered orally following encequidar. Paclitaxel daily exposure was comparable following 2-5 days dose levels.

CONCLUSION

The oral administration of encequidar with paclitaxel was safe, achieved clinically relevant paclitaxel levels, and showed evidence of anti-tumor activity.

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

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

Discovery and Characterization of Potent Dual P-Glycoprotein and CYP3A4 Inhibitors: Design, Synthesis, Cryo-EM Analysis, and Biological Evaluations

Targeted concurrent inhibition of intestinal drug efflux transporter P-glycoprotein (P-gp) and drug metabolizing enzyme cytochrome P450 3A4 (CYP3A4) is a promising approach to improve oral bioavailability of their common substrates such as docetaxel, while avoiding side effects arising from their pan inhibitions. Herein, we report the discovery and characterization of potent small molecule inhibitors of P-gp and CYP3A4 with encequidar (minimally absorbed P-gp inhibitor) as a starting point for optimization. To aid in the design of these dual inhibitors, we solved the high-resolution cryo-EM structure of encequidar bound to human P-gp. The structure guided us to prudently decorate the encequidar scaffold with CYP3A4 pharmacophores, leading to the identification of several analogues with dual potency against P-gp and CYP3A4. In vivo, dual P-gp and CYP3A4 inhibitor 3a improved the oral absorption of docetaxel by 3-fold as compared to vehicle, while 3a itself remained poorly absorbed.

Oral etoposide and zosuquidar bioavailability in rats: Effect of co-administration and in vitro-in vivo correlation of P-glycoprotein inhibition

P-glycoprotein inhibitors, like zosuquidar, have widely been used to study the role of P-glycoprotein in oral absorption. Still, systematic studies on the inhibitor dose-response relationship on intestinal drug permeation are lacking. In the present study, we investigated the effect of 0.79 nM-2.5 μM zosuquidar on etoposide permeability across Caco-2 cell monolayers. We also investigated etoposide pharmacokinetics after oral or IV administration to Sprague Dawley rats with co-administration of 0.063–63 mg/kg zosuquidar, as well as the pharmacokinetics of zosuquidar itself. Oral zosuquidar bioavailability was 2.6–4.2%, while oral etoposide bioavailability was 5.5 ± 0.9%, which increased with increasing zosuquidar doses to 35 ± 5%. The intestinal zosuquidar concentration required to induce a half-maximal increase in bioavailability was estimated to 180 μM. In contrast, the IC₅₀ of zosuquidar on etoposide permeability in vitro was only 5–10 nM, and a substantial in vitro-in vivo discrepancy of at least four orders of magnitude was thereby identified. Overall, the present study provides valuable insights for future formulation development that applies fixed dose combinations of P-glycoprotein inhibitors to increase the absorption of poorly permeable P-glycoprotein substrate drugs.

Pharmaceutical Formulations with P-Glycoprotein Inhibitory Effect as Promising Approaches for Enhancing Oral Drug Absorption and Bioavailability

P-glycoprotein (P-gp) is crucial in the active transport of various substrates with diverse structures out of cells, resulting in poor intestinal permeation and limited bioavailability following oral administration. P-gp inhibitors, including small molecule drugs, natural constituents, and pharmaceutically inert excipients, have been exploited to overcome P-gp efflux and enhance the oral absorption and bioavailability of many P-gp substrates. The co-administration of small molecule P-gp inhibitors with P-gp substrates can result in drug–drug interactions and increased side effects due to the pharmacological activity of these molecules. On the other hand, pharmaceutically inert excipients, including polymers, surfactants, and lipid-based excipients, are safe, pharmaceutically acceptable, and are not absorbed from the gut. Notably, they can be incorporated in pharmaceutical formulations to enhance drug solubility, absorption, and bioavailability due to the formulation itself and the P-gp inhibitory effects of the excipients. Different formulations with inherent P-gp inhibitory activity have been developed. These include micelles, emulsions, liposomes, solid lipid nanoparticles, polymeric nanoparticles, microspheres, dendrimers, and solid dispersions. They can bypass P-gp by different mechanisms related to their properties. In this review, we briefly introduce P-gp and P-gp inhibitors, and we extensively summarize the current development of oral drug delivery systems that can bypass and inhibit P-gp to improve the oral absorption and bioavailability of P-gp substrates. Since many drugs are limited by P-gp-mediated efflux, this review is helpful for designing suitable formulations of P-gp substrates to enhance their oral absorption and bioavailability.

Discovery of Encequidar, First-in-Class Intestine Specific P-glycoprotein Inhibitor

Many chemotherapeutics, such as paclitaxel, are administered intravenously as they suffer from poor oral bioavailability, partly because of efflux mechanism of P-glycoprotein in the intestinal epithelium. To date, no drug has been approved by the U.S. Food and Drug Administration (FDA) that selectively blocks this efflux pump. We sought to identify a compound that selectively inhibits P-glycoprotein in the gastrointestinal mucosa with poor oral bioavailability, thus eliminating the issues such as bone marrow toxicity associated with systemic inhibition of P-glycoprotein. Here, we describe the discovery of highly potent, selective, and poorly orally bioavailable P-glycoprotein inhibitor 14 (encequidar). Clinically, encequidar was found to be well tolerated and minimally absorbed; and importantly, it enabled the oral delivery of paclitaxel.

Itraconazole synergistically increases therapeutic effect of paclitaxel and 99mTc-MIBI accumulation, as a probe of P-gp activity, in HT-29 tumor-bearing nude mice

P-glycoprotein (P-gp), is an important efflux pump involved in chemotherapy resistance in human colon cancer. We investigated the efficacy of itraconazole as a P-gp inhibitor and its therapeutic synergistic relationship to paclitaxel through 99mTc-MIBI accumulation in HT-29 tumor-bearing nude mice. Histopathological screening along with in vitro experiments was done for further assessment. Itraconazole successfully inhibited P-gp mediated 99mTc-MIBI efflux, increasing its in vitro accumulation in itraconazole-receiving dishes. Notably, the co-administration of itraconazole with paclitaxel significantly enhanced the in vitro cytotoxicity effect of paclitaxel in itraconazole + paclitaxel wells containing HT-29 cells. Compared to the control, tumor volume in mice treated with itraconazole, paclitaxel and itraconazole +paclitaxel showed growth suppression approximately by 36.21, 60.02, and 73.3% respectively. And compared to paclitaxel group, the nude mice co-treated with paclitaxel and itraconazole showed suppression of tumor growth by about 33.31 % at the end of the treatment period. Also the biodistribution result showed that the co-administration of itraconazole with paclitaxel raised the mean tumor radioactivity accumulation compared to control and paclitaxel group. When given paclitaxel alone, the ID% of hepatic and cardiac tissue was reduced while co-administration of itraconazole with paclitaxel increased 99mTc-MIBI accumulation in these organs. Furthermore, the histopathological findings confirmed the biodistribution results. These results demonstrate that although monotherapy with itraconazole or paclitaxel has anti-tumor activity against HT-29 human colorectal cancer, a synergistic anti-tumor activity can be achieved when itraconazole is co-administered with paclitaxel. Also, 99mTc-MIBI is an effective radiotracer for monitoring response to treatment in MDR tumors.

Exploring pharmacogenetics of paclitaxel- and docetaxel-induced peripheral neuropathy by evaluating the direct pharmacogenetic-pharmacokinetic and pharmacokinetic-neuropathy relationships

Introduction: Peripheral neuropathy (PN) is an adverse effect of several classes of chemotherapy including the taxanes. Predictive PN biomarkers could inform individualized taxane treatment to reduce PN and enhance therapeutic outcomes. Pharmacogenetics studies of taxane-induced PN have focused on genes involved in pharmacokinetics, including enzymes and transporters. Contradictory findings from these studies prevent translation of genetic biomarkers into clinical practice. Areas covered: This review discusses the progress toward identifying pharmacogenetic predictors of PN by assessing the evidence for two independent associations; the effect of pharmacogenetics on taxane pharmacokinetics and the evidence that taxane pharmacokinetics affects PN. Assessing these direct relationships allows the reader to understand the progress toward individualized taxane treatment and future research opportunities. Expert opinion: Paclitaxel pharmacokinetics is a major determinant of PN. Additional clinical trials are needed to confirm the clinical benefit of individualized dosing to achieve target paclitaxel exposure. Genetics does not meaningfully contribute to paclitaxel pharmacokinetics and may not be useful to inform dosing. However, genetics may contribute to PN sensitivity and could be useful for estimating patients' optimal paclitaxel exposure. For docetaxel, genetics has not been demonstrated to have a meaningful effect on pharmacokinetics and there is no evidence that pharmacokinetics determines PN.

HM30181A, a potent P-glycoprotein inhibitor, potentiates the absorption and in vivo antitumor efficacy of paclitaxel in an orthotopic brain tumor model

Objective:

Delivery of chemotherapeutic drugs to the brain has remained a major obstacle in the treatment of glioma, owing to the presence of the blood-brain barrier and the activity of P-gp, which pumps its substrate back into the systemic circulation. The aim of the present study was to develop an intravenous formulation of HM30181A (HM) to inhibit P-gp in the brain to effectively deliver paclitaxel (PTX) for the treatment of malignant glioma.

Methods:

Two formulations of solubilized HM were designed on the basis of different solid dispersion strategies: i) spray-drying [polyvinlypyrrolidone (PVP)-HM] and ii) solvent evaporation [HP-β-cyclodextrin (cyclodextrin)-HM]. The P-gp inhibition of these 2 formulations was assessed on the basis of rhodamine 123 uptake in cancer cells. Blood and brain pharmacokinetic parameters were also determined, and the antitumor effect of cyclodextrin-HM with PTX was evaluated in an orthotopic glioma xenograft mouse model.

Results:

Although both PVP-HM and cyclodextrin-HM formulations showed promising P-gp inhibition activity in vitro, cyclodextrin-HM had a higher maximum tolerated dose in mice than did PVP-HM. Pharmacokinetic study of cyclodextrin-HM revealed a plasma concentration plateau at 20 mg/kg, and the mice began to lose weight at doses above this level. Cyclodextrin-HM (10 mg/kg) administered with PTX at 10 mg/kg showed optimal antitumor activity in a mouse model, according to both tumor volume measurement and survival time (P < 0.05).

Conclusions:

In a mouse orthotopic brain tumor model, the intravenous co-administration of cyclodextrin-HM with PTX showed potent antitumor effects and therefore may have potential for glioma therapy in humans.

Desirable drug-drug interactions or when a matter of concern becomes a renewed therapeutic strategy

Drug-drug interactions are sometimes considered to be detrimental and responsible for adverse effects. In some cases, however, some are stakeholders of the efficiency of the treatment and this combinatorial strategy is exploited by some drug associations, including levodopa (L-Dopa) and dopadecarboxylase inhibitors, β-lactam antibiotics and clavulanic acid, 5-fluorouracil (5-FU) and folinic acid, and penicillin and probenecid. More recently, some drug-drug combinations have been integrated in modern drug design strategies, aiming to enhance the efficiency of already marketed drugs with new compounds acting not only as synergistic associations, but also as real boosters of activity. In this review, we provide an update of examples of such strategies, with a special focus on microbiology and oncology.

Tetrazoles as anticancer agents: A review on synthetic strategies, mechanism of action and SAR studies

Cancer is a leading cause of death worldwide. Even after the availability of numerous drugs and treatments in the market, scientists and researchers are focusing on new therapies because of their resistance and toxicity issues. The newly synthesized drug candidates are able to demonstrate in vitro activity but are unable to reach clinical trials due to their rapid metabolism and low bioavailability. Therefore there is an imperative requisite to expand novel anticancer negotiators with tremendous activity as well as in vivo efficacy. Tetrazole is a promising pharmacophore which is metabolically more stable and acts as a bioisosteric analogue for many functional groups. Tetrazole fragment is often castoff with other pharmacophores in the expansion of novel anticancer drugs. This is the first systematic review that emphasizes on contemporary strategies used for the inclusion of tetrazole moiety, mechanistic targets along with comprehensive structural activity relationship studies to provide perspective into the rational design of high-efficiency tetrazole-based anticancer drug candidates.

Affinity-Based Protein Profiling Reveals Cellular Targets of Photoreactive Anticancer Inhibitors

Affinity-based protein profiling has proven to be a powerful method in target identification of bioactive molecules. Here, this technology was applied in two photoreactive anticancer inhibitors, arenobufagin and HM30181. Using UV irradiation, these photoreactive reagents can covalently cross-link to target proteins, leading to a covalent binding with target proteins. Moreover, the cellular on/off targets of these two molecules, including ATP1A1, MDR1, PARP1, DDX5, NOP2, RAB6A, and ERGIC1 were first identified by affinity-based protein profiling and bioimaging approaches. The protein hit, PARP1, was further validated to be involved in the function of the anticancer effects.

Effect of treatment period with LC478, a disubstituted adamantayl derivative, on P-glycoprotein inhibition: its application to increase docetaxel absorption in rats

1. Treatment periods of P-glycoprotein (P-gp) inhibitors have revealed different efficacies. We have previously reported dose-dependent inhibition of P-gp in single-treatment with LC478. However, whether repeated treatment with LC478 can inhibit P-gp even at its ineffective single-treatment dose remains unknown. 2. Therefore, the purpose of this study was to assess the effect of repeated treatment (i.e., 7-day treatment) with LC478 on P-gp known to affect docetaxel bioavailability in rats. Effects of LC478 on P-gp mediated efflux and expression in MDCK-MDR1 cells, P-gp ATPase activity, and binding site with P-gp were evaluated.3. The 7-day treatment with LC478 increased docetaxel absorption via intestinal P-gp inhibition in rats. Intestinal concentrations of LC478 were 8.31-10.3 μM in rats after 7-day treatment of LC478. These concentrations were close to 10 μM that reduced P-gp mediated docetaxel efflux and P-gp expression in MDCK-MDR1 cells. Considering that intestinal LC478 concentrations after 1-day treatment were 2.68-4.19 μM, higher LC478 concentrations after 7-day treatment might have driven P-gp inhibition and increased docetaxel absorption. LC478 might competitively inhibit P-gp considering its stimulated ATPase activity and its binding site with nucleotide binding domain of P-gp. 4. Therefore, repeated treatment with LC478 can determine its feasibility for P-gp inhibition and changing docetaxel bioavailability.

Recent advances in the search of BCRP- and dual P-gp/BCRP-based multidrug resistance modulators

The development of multidrug resistance (MDR) is one of the major challenges to the success of chemotherapy treatment of cancer. This phenomenon is often associated with the overexpression of the ATP-binding cassette (ABC) transporters P-gp (P-glycoprotein, ABCB1), multidrug resistance-associated protein 1, ABCC1 and breast cancer resistance protein, ABCG2 (BCRP). These transporters are constitutively expressed in many tissues playing relevant protective roles by the regulation of the permeability of biological membranes, but they are also overexpressed in malignant tissues. P-gp is the first efflux transporter discovered to be involved in cancer drug resistance, and over the years, inhibitors of this pump have been disclosed to administer them in combination with chemotherapeutic agents. Three generations of inhibitors of P-gp have been examined in preclinical and clinical studies; however, these trials have largely failed to demonstrate that coadministration of pump inhibitors elicits an improvement in therapeutic efficacy of antitumor agents, although some of the latest compounds show better results. Therefore, new and innovative strategies, such as the fallback to natural products and the discover of dual activity ligands emerged as new perspectives. BCRP is the most recently ABC protein identified to be involved in multidrug resistance. It is overexpressed in several haematological and solid tumours together with P-gp, threatening the therapeutic effectiveness of different chemotherapeutic drugs. The chemistry of recently described BCRP inhibitors and dual P-gp/BCRP inhibitors, as well as their preliminary pharmacological evaluation are discussed, and the most recent advances concerning these kinds of MDR modulators are reviewed.

Reversal effect of ginsenoside Rh2 on oxaliplatin-resistant colon cancer cells and its mechanism

Chemotherapy is an important treatment modality for colon cancer, however, drug resistance is the main factor leading to treatment failure. Ginsenoside Rh2 (G-Rh2), the main bioactive metabolite of ginseng, is known to possess the ability to potently induce cell apoptosis, inhibit cell proliferation and reverse multidrug resistance in a variety of cancer cells. The present study examined the effect of G-Rh2 on oxaliplatin (L-OHP)-resistant colon cancer cells and its potential mechanism. L-OHP-resistant colon cancer cells (LoVo/L-OHP) and LoVo cells were used in the present study. The effect of G-Rh2 on LoVo/L-OHP and LoVo cell proliferation was measured using a 3-(4,5 dimethylthiazol-z-yl)-3,5-diphenyltetrazolium bromide assay. The effects of G-Rh2 on LoVo/L-OHP and LoVo cell apoptosis were detected by flow cytometry. The mRNA and protein expression of apoptosis-related genes Bax, Bcl-2 and caspase-3, drug resistance-related genes P-glycoprotein (P-gp) and Smad4, were determined in LoVo/L-OHP and LoVo cells treated with G-Rh2 by reverse transcription-quantitative polymerase chain reaction and western blot analyses. G-Rh2 treatment significantly inhibited the proliferation and induced the apoptosis of LoVo/L-OHP and LoVo cells. In addition, G-Rh2 treatment resulted in a significant increase in pro-apoptotic factors, Bax and caspase-3, and decrease in anti-apoptotic factor Bcl-2 in the LoVo/L-OHP and LoVo cells. Furthermore, G-Rh2 treatment significantly decreased the levels of P-gp and increased the levels of Smad4 in the LoVo/L-OHP and LoVo cells. It was found that L-OHP had no significant effects on LoVo/L-OHP cell proliferation or apoptosis, whereas G-Rh2 + L-OHP treatment significantly inhibited LoVo/L-OHP cell proliferation and induced apoptosis. L-OHP had no significant effects on the expression of P-gp, Smad4, Bcl-2, Bax or caspase-3 in LoVo/L-OHP cells. Treatment with G-Rh2 + L-OHP significantly reduced the expression of P-gp and Bcl-2, and enhanced the expression levels of Smad4, Bax and caspase-3. These findings demonstrated that G-Rh2 reversed the drug resistance of LoVo/L-OHP cells to L-OHP, and this may be mediated by inhibiting cell proliferation and promoting apoptosis and regulating the expression of drug resistance genes. These results suggest that G-Rh2 may function as a potent anticancer drug for drug resistance in colon cancer treatment.

10-Phenyltriazoyl Artemisinin is a Novel P-glycoprotein Inhibitor that Suppresses the Overexpression and Function of P-glycoprotein

Background:

The effect of drugs on ATP-binding cassette transporters, especially permeabilityglycoprotein (P-gp), is an important consideration during new anti-cancer drug development.

Objective:

In this context, the effects of a newly synthesized artemisinin derivative, 10-(4-phenyl-1H-1,2,3- triazol)-artemisinin (5a), were evaluated on P-gp expression and function.

Methods:

Reverse transcript polymerase chain reaction and immunoblotting techniques were used to determine the effect of 5a on P-gp expression in LS174T cells. In addition, the ability of 5a to work as either a substrate or an inhibitor of P-gp was investigated through different methods.

Results:

The results revealed that 5a acts as a novel P-gp inhibitor that dually suppresses the overexpression and function of P-glycoprotein. Co-treatment of LS174T cell line, human colon adenocarcinoma cell line, with 5a and paclitaxel recovered the anticancer effect of paclitaxel by controlling the acquired drug resistance pathway. The overexpression of P-gp induced by rifampin and paclitaxel in a colorectal cell line was suppressed by 5a which could be a novel inhibitory substrate inhibiting the transport of paclitaxel by P-gp.

Conclusion:

The results revealed that 5a can be classified as a type B P-gp inhibitor (with both substrate and inhibitor activities) with an additional function of suppressing P-gp overexpression. The results might be clinically useful in the development of anticancer drugs against cancers with multidrug resistance.

LC478, a Novel Di-Substituted Adamantyl Derivative, Enhances the Oral Bioavailability of Docetaxel in Rats

P-glycoprotein (P-gp)-mediated efflux of docetaxel in the gastrointestinal tract mainly impedes its oral chemotherapy. Recently, LC478, a novel di-substituted adamantyl derivative, was identified as a non-cytotoxic P-gp inhibitor in vitro. Here, we assessed whether LC478 enhances the oral bioavailability of docetaxel in vitro and in vivo. LC478 inhibited P-gp mediated efflux of docetaxel in Caco-2 cells. In addition, 100 mg/kg of LC478 increased intestinal absorption of docetaxel, which led to an increase in area under plasma concentration-time curve (AUC) and absolute bioavailability of docetaxel in rats. According to U.S. FDA criteria (I, an inhibitor concentration in vivo tissue)/(IC₅₀, inhibitory constant in vitro) >10 determines P-gp inhibition between in vitro and in vivo. The values 15.6–20.5, from (LC478 concentration in intestine, 9.37–12.3 μM)/(IC₅₀ of LC478 on P-gp inhibition in Caco-2 cell, 0.601 μM) suggested that 100 mg/kg of LC478 sufficiently inhibited P-gp to enhance oral absorption of docetaxel. Moreover, LC478 inhibited P-gp mediated efflux of docetaxel in the ussing chamber studies using rat small intestines. Our study demonstrated that the feasibility of LC478 as an ideal enhancer of docetaxel bioavailability by P-gp inhibition in dose (concentration)-dependent manners.

Effects of Piperazine Derivative on Paclitaxel Pharmacokinetics

Paclitaxel (PTX) is an anticancer agent that is used to treat many cancers but it has a very low oral bioavailability due, at least in part, to the drug efflux transporter, P-glycoprotein (P-gp). Therefore, this study was performed to enhance oral bioavailability of PTX. In this study, we investigated the effects of several piperazine derivatives on P-gp function in vitro. Compound 4 was selected as the most potent P-gp inhibitor from the in vitro results for examining the pharmacokinetic (PK) changes of PTX in rats. Compound 4 increased the AUC_inf of PTX without alterations in the C_max value. The elimination half-life was extended and the oral clearance decreased. Additionally, the T_max was delayed or widened in the treatment groups. Therefore, the bioavailability (BA) of PTX was improved 2.1-fold following the co-administration of 5 mg/kg of the derivative. A piperazine derivative, compound 4, which was confirmed as a substantial P-gp inhibitor in vitro increased the BA of PTX up to 2-fold by a lingering absorption, in part due to inhibition of intestinal P-gp and a low oral clearance of PTX. These results suggest that co-administering compound 4 may change the PK profile of PTX by inhibiting P-gp activity in the body.

Seco-4-methyl-DCK derivatives as potent chemosensitizers

Twenty-five seco-4-methyl-DCK derivatives were designed, synthesized and evaluated for chemoreversal activity when combined with paclitaxel or vincristine in two drug-resistant cancer cell lines (A2780/T and KB-V) respectively. Most of the new compounds displayed moderate to significant MDR reversal activities in the P-gp overexpressing A2780/T and KB-V cells. Especially, compounds 7o and 7y showed the most potent chemosensitization activities with more than 496 and 735 reversal ratios at a concentration of 10 μM. Unexpectedly the newly synthesized compounds did not show chemosensitization activities observed in a non-P-gp overexpressing cisplatin resistant human ovarian cancer cell line (A2780/CDDP), implying that the MDR reversal effects might be associated with P-gp overexpression. Moreover, these compounds did not exhibit significant antiproliferative activities against nontumorigenic cell lines (HUVEC, HOSEC and T29) compared to the positive control verapamil at the tested concentration, which suggested better safety than verapamil. The pharmacological actions of the compounds will be studied further to explore their merit for development as novel candidates to overcome P-gp mediated MDR cancer.

Further enhanced dissolution and oral bioavailability of docetaxel by coamorphization with a natural P-gp inhibitor myricetin

The current study aims to improve the dissolution and oral bioavailability of a BCS IV drug docetaxel (DOC) by coamorphization with a natural P-gp inhibitor myricetin (MYR). A single-phase coamorphous form of DOC with MYR in a 1:1 molar ratio was prepared by solvent-evaporation method and characterized by differential scanning calorimetry, thermogravimetric analysis and powder X-ray diffraction. In comparison to crystalline DOC, amorphous DOC showed similar equilibrium aqueous solubility, temporary improvement in the intrinsic dissolution rate (IDR) and supersaturated dissolution; while coamorphous DOC-MYR exhibited a persistent enhanced IDR and prolonged highly supersaturated dissolution. In addition, coamorphous DOC-MYR demonstrated significantly superior physical stability compared to amorphous DOC under the long-term storage condition and accelerated condition. Compared with oral administration of crystalline DOC to rats, amorphous DOC showed a significant increase in C_max (2.6-fold) and a marginal increase in AUC (1.3-fold) of DOC; but coamorphous DOC-MYR performed a 3.9-fold higher C_max and 3.1-fold higher AUC. In conclusion, coamorphization of DOC with MYR was a promising approach to enhance both dissolution and oral absorption of poorly soluble and permeable DOC.

ERp57‑small interfering RNA silencing can enhance the sensitivity of drug‑resistant human ovarian cancer cells to paclitaxel

ERp57 has been identified to be associated with the chemoresistance of human ovarian cancer. However, its biological roles in the chemoresistance phenotype remain unclear. In the present study, the association of ERp57 with paclitaxel‑resistant cellular behavior was investigated and the sensitivity enhancement of chemoresistant human ovarian cancer cells to paclitaxel was examined using ERp57‑small interfering (si)RNA silencing. Cell viability, cell proliferation, cell apoptosis and cell migration were detected using an MTT assay, clonogenic assay, flow cytometry analysis and transwell assay. Furthermore, mRNA expression levels of ERp57 and protein expression levels of ERp57, STAT3, phosphorylated STAT3, PCNA, nucelolin, TUBB3, P-gp, vimentin, Bcl-2, Bax, Bcl-xl, p53, MMP1, MMP2 and MMP9 of paclitaxel-sensitive human SKOV3 ovarian cancer cells were compared with paclitaxel-resistant counterpart SKOV3/tax using the real-time PCR and western blot analysis. ERp57 was highly expressed in the paclitaxel‑resistant SKOV3/tax cells, and experimental results concluded that the paclitaxel‑resistance phenotype was due primarily to the activation of the STAT3 signaling pathway. ERp57 overexpression by lentiviral particle infection decreased the sensitivity of SKOV3 cells to paclitaxel. Furthermore, ERp57‑siRNA silencing restored paclitaxel sensitivity of SKOV3/tax cells. Notably, the IC50 value of ERp57‑siRNA silenced SKOV3/tax cells was reduced to the original level and colony survival was significantly decreased in comparison with that of SKOV3/tax cells. Additionally, co‑treatment of ERp57‑siRNA silencing and paclitaxel could inhibit the STAT3 signaling pathway and downregulate the expression levels of downstream proteins. Notably, ERp57‑siRNA and 100 nM paclitaxel co‑treatment downregulated Bcl‑2, Bcl‑xl, MMP2, MMP9, TUBB3 and P‑gp expression levels and upregulated the expression of Bax protein. Furthermore, co‑treatment promoted change of the isoform of p53 to p53/p47. Bioinformatics analyses supported the experimental observations that ERp57 was associated with drug resistance in ovarian cancer. The present study implies that ERp57 is a potential therapeutic target for the treatment of paclitaxel‑resistant human ovarian cancer.

Effects of aripiprazole on pupillometric parameters related to pharmacokinetics and pharmacogenetics after single oral administration to healthy subjects

BACKGROUND

Pupillometry is used for the detection of autonomic dysfunction related to numerous diseases and drug administration. Genetic variants in cytochrome P450 ( CYP2D6, CYP3A4), dopamine receptor ( DRD2, DRD3), serotonin receptor ( HTR2A, HTR2C) and ATP-binding cassette subfamily B ( ABCB1) genes were previously associated with aripiprazole response.

AIMS

Our aim was to evaluate if aripiprazole affects pupil contraction and its relationship with pharmacokinetics and pharmacogenetics.

METHODS

Thirty-two healthy volunteers receiving a 10 mg single oral dose of aripiprazole were genotyped for 15 polymorphisms in ABCB1, CYP2D6, DRD2, DRD3, HTR2A and HTR2C genes by reverse transcription polymerase chain reaction. Aripiprazole and dehydro-aripiprazole plasma concentrations were measured by high-performance liquid chromatography tandem mass spectrometry. Pupil examination was performed by automated pupillometry.

RESULTS

Aripiprazole caused pupil constriction and reached the peak value at C_max. HTR2A rs6313 T allele carriers and HTR2C rs3813929 C/T subjects showed higher maximum constriction velocity and maximum pupil diameter. Besides, Gly/Gly homozygotes for DRD3 rs6280 showed significantly lower maximum constriction velocity values. A/G heterozygotes for DRD2 rs6277 showed higher total time taken by the pupil to recover 75% of the initial resting size values. CYP2D6 intermediate metabolisers showed higher area under the curve, C_max and T_1/2 than extensive metabolisers. ABCB1 G2677T/A A/A homozygotes had greater T_1/2 in comparison with C/C homozygotes. ABCB1 C3435T T allele carriers and C1236T C/T subjects showed greater area under the curve than C/C homozygotes.

CONCLUSIONS

Aripiprazole affects pupil contraction, which could be a secondary effect through dopamine and serotonin receptors. Pupillometry could be a useful tool to assess autonomic nervous system activity during antipsychotic treatment.

Synthesis and antiproliferative activities of doxorubicin thiol conjugates and doxorubicin-SS-cyclic peptide

Myocardial toxicity and drug resistance caused by drug efflux are major limitations of doxorubicin (Dox)-based chemotherapy. Dox structure modification could be used to develop conjugates with an improved biological profile, such as antiproliferative activity and higher cellular retention. Thus, Dox thiol conjugates, Dox thiol (Dox-SH), thiol-reactive Dox-SS-pyridine (SS = disulfide), and a Dox-SS-cell-penetrating cyclic peptide, Dox-SS-[C(WR)₄K], were synthesized. Dox was reacted with Traut's reagent to generate Dox-SH. The thiol group was activated by the reaction with dithiodipyridine to afford the corresponding Dox-SS-Pyridine (Dox-SS-Pyr). A cyclic cell-penetrating peptide containing a cysteine residue [C(WR)₄K] was prepared using Fmoc solid-phase strategy. Dox-SS-Py was reacted with the free sulfhydryl of cysteine in [C(WR)₄K] to generate Dox-SS-[C(WR)₄K] as a Dox-cyclic peptide conjugate. Cytotoxicity of the compounds was examined in human embryonic kidney (HEK-293), human ovarian cancer (SKOV-3), human fibrosarcoma (HT-1080), and human leukemia (CCRF-CEM) cells. Dox-SH and Dox-SS-pyridine were found to have significantly higher or comparable cytotoxicity when compared to Dox in HEK-293, HT-1080, and CCRF-CEM cells after 24 h and 72 incubation, presumably because of higher activity and retention of the compounds in these cells. Furthermore, Dox-SS-[C(WR)₄K] showed significantly higher cytotoxic activity in HEK-293, HT-1080, and SKOV-3 cells when compared with Dox after 72 h incubation. Dox-SS-Pyr exhibited higher cellular uptake than Dox-SS-[C(WR)₄K] in HT-1080 and HEK-293 cells as shown by flow cytometry. Fluorescence microscopy exhibited that Dox-SS-Pyr, Dox-SH, and Dox-SS-[C(WR)₄K] localized in the nucleus as shown in four cell lines, HT-1080, SKOV-3, MDA-MB-468, and MCF-7. Of note, Dox-SS-[C(WR)₄K] was significantly less toxic in mouse myoblast cells compared to Dox at the same concentration. Further mechanistic study demonstrated that the level of intracellular reactive oxygen species (ROS) in myoblast cells exposed to Dox-SS-[C(WR)₄K] was reduced in comparison of Dox when co-treated with FeCl₂. These data indicate that Dox-SH, Dox-SS-Pyr, and Dox-SS-[C(WR)₄K] have the potential to be further examined as Dox alternatives and anticancer agents.

Intestinal P-glycoprotein inhibitors, benzoxanthone analogues

OBJECTIVES

The inhibitors of P-glycoprotein (P-gp) which limits an access of exogenous compounds in the luminal membrane of the intestine have been studied to enhance the intestinal P-gp-mediated absorption of anticancer drugs.

METHODS

Inhibition of the efflux pump by synthesized benzoxanthone derivatives was investigated in vitro and in vivo. MCF-7/ADR cell line was used for cytotoxicity assay and [³ H]-daunomycin (DNM) accumulation/efflux study. Eight benzoxanthone analogues were tested for their effects on DNM cytotoxicity. Among them, three analogues were selected for the accumulation/efflux and P-gp ATPase studies. Paclitaxel (PTX), a P-gp substrate anticancer drug, was orally administered to rats with/without compound 1 (8,10-bis(thiiran-2-ylmethoxy)-7H-benzo[c]xanthen-7-one). The pharmacokinetic parameters of PTX in the presence/absence of compound 1 were evaluated from the plasma concentration-time profiles.

KEY-FINDINGS

Compound 1 increased the DNA accumulation to 6.5-fold and decreased the DNM efflux to approximately 1/2 in the overexpressing P-gp cell line. Relative bioavailability (RB) of PTX in rats was significantly increased up to 3.2-fold by compound 1 (0.5 or 2 mg/kg).

CONCLUSIONS

Benzoxanthone analogue, compound 1 is strongly suggested to be a promising inhibitor of P-gp to improve an oral absorption of compounds for cancer therapy.

2-Trifluoromethyl-2-Hydroxypropionamide Derivatives as Novel Reversal Agents of ABCG2 (BCRP)-Mediated Multidrug Resistance: Synthesis and Biological Evaluations

It has been postulated that one of the biggest impediments to a successful chemotherapy is the phenomena of multidrug resistance (MDR) in cancer cells. One of the main mechanisms of MDR is overexpression of the ATP-binding cassette (ABC) transporters in cancer cells which alters absorption, distribution, metabolism, and excretion of various chemotherapeutic drugs. Efforts have been made to find effective inhibitors of ABC transporters. However, none has been approved clinically. This study shows that a novel compound 3-chloro-N-(2-hydroxyphenyl)-4-(3,3,3-trifluoro-2-hydroxy-2-methylpropanamido) benzamide (compound 7d), one of the 2-trifluoromethyl-2-hydroxypropionamide derivatives could reverse ABCG2 (BCRP)-mediated MDR. Cytotoxicity studies show that compound 7d sensitizes the ABCG2-overexpressing cells to chemotherapeutic drugs mitoxantrone and SN-38, which are well-established substrates of the ABCG2 transporter. Western blotting results indicate that compound 7d does not significantly alter the protein level of the ABCG2 transporter. Accumulation and efflux studies demonstrate that compound 7d increases intracellular accumulation of mitoxantrone by inhibiting the function of ABCG2. Overall, these findings indicate a potential use for compound 7d as an adjuvant agent for chemotherapy to inhibit the function of the clinically relevant ABC transporter and sensitize tumor cells to chemotherapeutic drugs. J. Cell. Biochem. 118: 2420-2429, 2017. © 2017 Wiley Periodicals, Inc.

Functional characterization of ABCB4 mutations found in progressive familial intrahepatic cholestasis type 3

Multidrug resistance 3 (MDR3), encoded by the ATP-binding cassette, subfamily B, member 4 gene (ABCB4), localizes to the canalicular membrane of hepatocytes and translocates phosphatidylcholine from the inner leaflet to the outer leaflet of the canalicular membrane. Progressive familial intrahepatic cholestasis type 3 (PFIC3) is a rare hepatic disease caused by genetic mutations of ABCB4. In this study, we characterized 8 ABCB4 mutations found in PFIC3 patients, using in vitro molecular assays. First, we examined the transport activity of each mutant by measuring its ATPase activity using paclitaxel or phosphatidylcholine. Then, the pathogenic mechanisms by which these mutations affect MDR3 were examined through immunoblotting, cell surface biotinylation, and immunofluorescence. As a result, three ABCB4 mutants showed significantly reduced transport activity. Among these mutants, one mutation A364V, located in intracellular domains, markedly decreased MDR3 expression on the plasma membrane, while the others did not affect the expression. The expression of MDR3 on the plasma membrane and transport activity of A364V was rescued by a pharmacological chaperone, cyclosporin A. Our study provides the molecular mechanisms of ABCB4 mutations and may contribute to the understanding of PFIC3 pathogenesis and the development of a mutation-specific targeted treatment for PFIC3.

Korean red ginseng extract enhances paclitaxel distribution to mammary tumors and its oral bioavailability by P-glycoprotein inhibition

1. Drug efflux by P-glycoprotein (P-gp) is a common resistance mechanism of breast cancer cells to paclitaxel, the primary chemotherapy in breast cancer. As a means of overcoming the drug resistance-mediated failure of paclitaxel chemotherapy, the potential of Korean red ginseng extract (KRG) as an adjuvant chemotherapy has been reported only in in vitro. Therefore, we assessed whether KRG alters P-gp mediated paclitaxel efflux, and therefore paclitaxel efficacy in in vitro and vivo models. 2. KRG inhibited P-gp protein expression and transcellular efflux of paclitaxel in MDCK-mdr1 cells, but KRG was not a substrate of P-gp ATPase. In female rats with mammary tumor, the combination of paclitaxel with KRG showed the greater reduction of tumor volumes, lower P-gp protein expression and higher paclitaxel distribution in tumors, and greater oral bioavailability of paclitaxel than paclitaxel alone. 3. From these results, KRG increased systemic circulation of oral paclitaxel and its distribution to tumors via P-gp inhibition in rats and under the current study conditions.

Effect of HM30181 mesylate salt-loaded microcapsules on the oral absorption of paclitaxel as a novel P-glycoprotein inhibitor

The purpose of this study was to develop HM30181 mesylate salt (HM30181M)-loaded microcapsules as a novel P-glycoprotein inhibitor for enhancing the oral absorption of paclitaxel. The effect of various carriers including hydrophilic polymers and solvents on the solubility of HM30181M were evaluated. Among the hydrophilic polymers and solvents tested, HPMC and methylene chloride (and ethanol) provided the highest HM30181M solubility. Numerous HM30181M-loaded microcapsules were prepared with HPMC, silicon dioxide and acidifying agents using a spray-drying technique, and their solubility, dissolution and physicochemical properties were evaluated. Furthermore, a pharmacokinetic study was performed after oral administration of paclitaxel alone, simultaneously with HM30181M powder or HM30181M-loaded microcapsules to rats. Among the acidifying agents investigated, phosphoric acid provided the best improvement in the solubility and dissolution of HM30181M. Moreover, the microcapsule composed of HM30181M, HPMC, silicon dioxide and phosphoric acid at a weight ratio of 3:6:3:2 remarkably enhanced the solubility and dissolution of HM30181M compared with the HM30181M powder alone. The microcapsules were spherical in shape, had a reduced particle size of about 7μm, and contained HM30181M in an amorphous state. Furthermore, this microcapsule significantly enhanced HM30181M absorption, making it about 1.7-fold faster and 1.6-fold greater after simultaneous administration, leading to about 70- and 2-fold improved oral bioavailability of paclitaxel compared with paclitaxel alone and the simultaneous administration with HM30181M powder, respectively. Thus, this novel microcapsule could be a potential candidate for effective P-glycoprotein inhibition during oral administration of paclitaxel.

Single-cell pharmacokinetic imaging reveals a therapeutic strategy to overcome drug resistance to the microtubule inhibitor eribulin

Eribulin mesylate was developed as a potent microtubule-targeting cytotoxic agent to treat taxane-resistant cancers, but recent clinical trials have shown that it eventually fails in many patient subpopulations for unclear reasons. To investigate its resistance mechanisms, we developed a fluorescent analog of eribulin with pharmacokinetic (PK) properties and cytotoxic activity across a human cell line panel that are sufficiently similar to the parent drug to study its cellular PK and tissue distribution. Using intravital imaging and automated tracking of cellular dynamics, we found that resistance to eribulin and the fluorescent analog depended directly on the multidrug resistance protein 1 (MDR1). Intravital imaging allowed for real-time analysis of in vivo PK in tumors that were engineered to be spatially heterogeneous for taxane resistance, whereby an MDR1-mApple fusion protein distinguished resistant cells fluorescently. In vivo, MDR1-mediated drug efflux and the three-dimensional tumor vascular architecture were discovered to be critical determinants of drug accumulation in tumor cells. We furthermore show that standard intravenous administration of a third-generation MDR1 inhibitor, HM30181, failed to rescue drug accumulation; however, the same MDR1 inhibitor encapsulated within a nanoparticle delivery system reversed the multidrug-resistant phenotype and potentiated the eribulin effect in vitro and in vivo in mice. Our work demonstrates that in vivo assessment of cellular PK of an anticancer drug is a powerful strategy for elucidating mechanisms of drug resistance in heterogeneous tumors and evaluating strategies to overcome this resistance.

The role of ABC transporters in ovarian cancer progression and chemoresistance

Over 80% of ovarian cancer patients develop chemoresistance which results in a lethal course of the disease. A well-established cause of chemoresistance involves the family of ATP-binding cassette transporters, or ABC transporters that transport a wide range of substrates including metabolic products, nutrients, lipids, and drugs across extra- and intra-cellular membranes. Expressions of various ABC transporters, shown to reduce the intracellular accumulation of chemotherapy drugs, are increased following chemotherapy and impact on ovarian cancer survival. Although clinical trials to date using ABC transporter inhibitors have been disappointing, ABC transporter inhibition remains an attractive potential adjuvant to chemotherapy. A greater understanding of their physiological functions and role in ovarian cancer chemoresistance will be important for the development of more effective targeted therapies. This article will review the role of the ABC transporter family in ovarian cancer progression and chemoresistance as well as the clinical attempts used to date to reverse chemoresistance.

Effects of HM30181, a P-glycoprotein inhibitor, on the pharmacokinetics and pharmacodynamics of loperamide in healthy volunteers

AIMS

HM30181 is a third generation P-glycoprotein (P-gp) inhibitor currently under development. The objectives of this study were to evaluate the effects of a single dose of HM30181 on the pharmacodynamics and pharmacokinetics of loperamide, a P-gp substrate, and to compare them with those of quinidine.

METHODS

Eighteen healthy male subjects were administered loperamide alone (period 1) or with loperamide plus quinidine or HM30181 in period 2 or 3, respectively. In period 3, subjects randomly received one of three HM30181 doses: 15, 60 or 180 mg. Changes in pupil size, alertness, oxygen saturation and the oral bioavailability of loperamide were assessed in each period. In addition, the pharmacokinetics of HM30181 were determined.

RESULTS

Pupil size, alertness and oxygen saturation did not change over time when loperamide alone or loperamide plus HM30181 was administered while HM30181 significantly increased the systemic exposure to loperamide, i.e. the geometric mean ratio (90% confidence interval) of AUC(0,tlast ) for loperamide with and without HM30181 was 1.48 (1.08, 2.02). Co-administered quinidine significantly increased the systemic exposure to loperamide 2.2-fold (1.53, 3.18), which also markedly reduced pupil size, resulting in a decrease of 24.7 mm h in the area under the effect curve of pupil size change from baseline compared with loperamide alone.

CONCLUSIONS

HM30181 inhibits P-gp mainly in the intestinal endothelium, which can be beneficial because pan-inhibition of P-gp, particularly in the brain, could lead to detrimental adverse events. Further studies are warranted to investigate adequately the dose-exposure relationship of HM30181, along with its duration of effect.

HM30181 Derivatives as Novel Potent and Selective Inhibitors of the Breast Cancer Resistance Protein (BCRP/ABCG2)

The breast cancer resistance protein (BCRP, ABCG2) belongs to the superfamily of ATP binding-cassette (ABC) proteins. In addition to other physiological functions, it transports potentially cell-damaging compounds out of the cell using the energy from ATP hydrolysis. Certain tumors overexpressing BCRP were found to become resistant against various anticancer drugs. In previous work, we found that tariquidar analogues lacking the tetrahydroisoquinoline moiety selectively inhibit BCRP. In the present study, we synthesized 21 derivatives of the third-generation P-gp inhibitor HM30181, which is structurally related to tariquidar. The compounds were tested for their inhibitory activities against BCRP and screened against P-glycoprotein (P-gp, ABCB1) and multidrug resistance protein 1 (MRP1, ABCC1) to confirm the selectivity toward BCRP. The most potent compounds are selective toward BCRP and 2-fold more potent than the reference Ko143. Qualitative structure-activity relationship (SAR) analysis revealed that the presence of a methoxy group in the ortho or para position of at least one phenyl ring is beneficial for inhibitory activity. Furthermore, the cytotoxicity and multidrug resistance (MDR)-reversal ability of selected compounds were investigated. It was shown that they have a low cytotoxicity and the ability to reverse the BCRP-mediated SN-38 resistance.

Triapine-mediated ABCB1 induction via PKC induces widespread therapy unresponsiveness but is not underlying acquired triapine resistance

Although triapine is promising for treatment of advanced leukemia, it failed against solid tumors due to widely unknown reasons. To address this issue, a new triapine-resistant cell line (SW480/tria) was generated by drug selection and investigated in this study. Notably, SW480/tria cells displayed broad cross-resistance against several known ABCB1 substrates due to high ABCB1 levels (induced by promoter hypomethylation). However, ABCB1 inhibition did not re-sensitize SW480/tria cells to triapine and subsequent analysis revealed that triapine is only a weak ABCB1 substrate without significant interaction with the ABCB1 transport function. Interestingly, in chemo-naive, parental SW480 cells short-time (24 h) treatment with triapine stimulated ABCB1 expression. These effects were based on activation of protein kinase C (PKC), a known response to cellular stress. In accordance, SW480/tria cells were characterized by elevated levels of PKC. Together, this led to the conclusion that increased ABCB1 expression is not the major mechanism of triapine resistance in SW480/tria cells. In contrast, increased ABCB1 expression was found to be a consequence of triapine stress-induced PKC activation. These data are especially of importance when considering the choice of chemotherapeutics for combination with triapine.