Multidrug Resistance Reversal Activity Research Articles

Pentasaccharide resin glycosides with multidrug resistance reversal activities from the seeds of Pharbitis nil

Pharbitins A–G (1–7) were isolated from the seeds of Pharbitis nil; 2 showed MDR reversal activity via inhibition of P-gp.

Quercetin-glutamic acid conjugate with a non-hydrolysable linker; a novel scaffold for multidrug resistance reversal agents through inhibition of P-glycoprotein

Previously, we have reported remarkable effect of a quercetin-glutamic acid conjugate to reverse multidrug resistance (MDR) of cancer cells to a broad spectrum of anticancer agents through inhibition of P-glycoprotein (Pgp)-mediated drug efflux. Due to the hydrolysable nature, MDR-reversal activity of the quercetin conjugate was attributed to its hydrolysis product, quercetin. However, several lines of evidence demonstrated that the intact quercetin-glutamic acid conjugate has stronger MDR-reversal activity than quercetin. In order to evaluate this hypothesis and to identify a novel scaffold for MDR-reversal agents, we prepared quercetin conjugates with a glutamic acid attached at the 7-O position via a non-hydrolysable linker. Pgp inhibition assay, Pgp ATPase assay, and MDR-reversal activity assay were performed, and the non-hydrolysable quercetin conjugates showed significantly higher activities compared with those of quercetin. Unfortunately, the quercetin conjugates were not as effective as verapamil in Pgp-inhibition and thereby reversing MDR, but it is worth to note that the structurally modified quercetin conjugates with a non-cleavable linker showed significantly improved MDR-reversal activity compared with quercetin. Taken together, the quercetin conjugates with appropriate structural modifications were shown to have a potential to serve as a scaffold for the design of novel MDR-reversal agents.

Design, synthesis and evaluation of the multidrug resistance-reversing activity of pyridine acid esters of podophyllotoxin in human leukemia cells

Multidrug resistance (MDR) is the main cause for chemotherapeutic failure in cancer treatment. To overcome MDR, a serious of pyridine acid esters of podophyllotoxin was synthesized and their antiproliferation activities were evaluated against two human chronic myeloid leukemia cell lines in vitro. Most of them exhibited potent growth inhibition with IC50 values in the nanomolar range as well as markedly reduced resistance factors. The most potent compound, Y8 exhibited an IC50 of 0.046±0.003μM against resistance K562/ADR cells, showing more significant than that of adriamycin and etoposide, respectively. Furthermore, Y8 efficiently triggered cell cycle arrest at S phase and simultaneously induced apoptosis in K562/ADR cells. Meanwhile, Y8 also regulated the expression levels of cell cycle- and apoptosis-related proteins. Additionally, Y8 stimulated the ERK1/2 signalling and reduced the expression of Pgp protein. Finally, on the basis of results obtained using U0126, an ERK1/2 inhibitor, the ERK1/2 signalling pathway was proposed for the multidrug resistance-reversing effect of Y8 in K562/ADR cells. Together, Y8 could be a novel potential MDR reversal agent for the treatment of drug-resistant leukemia.

Abstract 2144: Next generation inhibitors to reverse ABCB1 transport mediated multidrug resistance in cancer

Abstract The therapeutic efficacy of anticancer drugs is often limited by chemoresistance. Cancer can present intrinsic or acquired resistance to chemotherapy drugs through different mechanisms of multidrug resistance (MDR). The accelerated drug efflux facilitated by overexpression of ATP-binding cassette (ABC) transporters is one of the key mechanisms of MDR. Specifically, overexpression of ABCB1 (MDR1, P-gp) is known to be a major cause of resistance to structurally dissimilar anticancer drugs such as paclitaxel and doxorubicin. To circumvent ABC transport mediated MDR, many small molecules and kinase inhibitors have been researched and employed to retain the efficacy of the anticancer drugs. Though many small molecule inhibitors demonstrate to be useful reversal agents, understanding the mechanisms at a molecular level is important in order to design candidate drug inhibitors which are safe, selective and effective. To investigate the functional groups and molecular structures which can efficiently reverse ABCB1-mediated MDR, multiple series of thiazole-valine peptide compounds were designed, synthesized and tested in vitro. The results indicated BTT-10A was most effective in sensitizing ABCB1-mediated resistance to anticancer drugs. Both transfected and drug-selected cell lines overexpressing the ABCB1 transporter were utilized in this study. We identified BTT-10A, at nontoxic concentrations (10 μM), to have optimal MDR reversal activity through cell viability MTT cytotoxicity and reversal bioassays. BTT-10A sensitized resistant cells to the anticancer drugs in a concentration dependent manner, without downregulating the transporter expression. BTT-10A significantly increased the accumulation of ABCB1 anticancer substrate drugs by blocking the efflux function of ABCB1 transporter, as demonstrated by significant increased [3H]-paclitaxel accumulation, and increased intracellular doxorubicin accumulation through immunofluorescent detection in ABCB1 overexpressing cells. Alongside these findings, docking studies showed site-1 to be the preferable binding site for BTT-10A within the drug-binding pocket of human ABCB1 homology model. Therefore, we report that BTT-10A antagonizes MDR by inhibiting the efflux activity of the overexpressed ABCB1 transporter. These findings reveal more evidence of specific molecular structure and function of ABCB1-mediated MDR reversal agents. The therapeutic application of BTT-10A co-administered with ABCB1 substrate anticancer drugs holds promise for cancer patients resistant to specific chemotherapies, overexpressing the ABCB1 transporter. Further in vivo studies will be conducted using drug resistant xenograft models. This research will help inspire further investigations of ABC transport-mediated MDR in cancer, to find the next generation of targeted and safe reversal agents to combat chemoresistance. Citation Format: Anna Maria Barbuti, Bhargav A. Patel, Tanaji T. Talele, Zhe-Sheng Chen. Next generation inhibitors to reverse ABCB1 transport mediated multidrug resistance in cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2144.

Involucratusins A-H: Unusual Cadinane Dimers from Stahlianthus involucratus with Multidrug Resistance Reversal Activity.

Three novel cadinane dimers, involucratusins A–C (1–3), five unique nor-cadinane-dimers, involucratusins D–H (4–8), together with a known compound (9) were isolated from the rhizomes of Stahlianthus involucratus. Their challenging structures and absolute configurations were determined by spectroscopic data, CD experimentation, chemical conversions and single-crystal X-ray diffraction. Compounds 1–3 are unusual cadinane dimers with new connection and novel cores. Compound 4 is a unique nor-cadinane-dimer, and 5 and 6 are two pairs of hemiketal racemates with novel dinor-cadinane-dimer backbone. Compounds 7 and 8 represent unusual dodecanor-cadinane-dimer and tetradecanor-cadinane-dimer carbon skeletons, respectively. The possible biogenetic pathways of 1–8 were proposed, involving nucleophilic addition, SN2 nucleophilic displacement, [3 + 3] benzannulation, oxidative cleavage, decarboxylation, and oxidative phenol coupling reactions. Multidrug resistance (MDR) reversal activity assay of the isolates were evaluated in doxorubicin-resistant human breast cancer cells (MCF-7/DOX). The combined use of these novel cadinane dimers at a concentration of 10 μM increased the cytotoxicity of doxorubicin by 2.2–5.8-fold. It is the first report about the MDR reversal activity of cadinane dimers.

Effects of Psoralen as an Anti-tumor Agent in Human Breast Cancer MCF-7/ADR Cells.

Psoralen is a major active component of Psoralea corylifolia. In the present study, we analyzed psoralen-induced changes in human breast cancer MCF-7/ADR cells and investigated the underlying mechanisms of the anticancer effect on MCF-7/ADR cells. We measured cell viability by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay to evaluate the cytotoxicity and multidrug resistance (MDR) reversal activity of psoralen. The cell cycle distribution and apoptosis, accumulation and efflux of rhodamine123 (Rh123), and P-glycoprotein (P-gp) expression levels of MCF-7/ADR cells treated with psoralen were all detected by flow cytometry (FCM). We assessed P-gp ATPase activity by monitoring ATP consumption. We evaluated the activity of nuclear factor-kappaB (NF-κB) and the expression of E-cadherin, vimentin and α-smooth muscle actin (SMA) involved in regulating epithelial-mesenchymal transition (EMT). The results showed that psoralen inhibited the proliferation of MCF-7/ADR cells as shown by G0/G1 phase arrest rather than encouraging apoptosis. It was also observed that psoralen reversed MDR through inhibiting ATPase activity rather than reducing P-gp expression. Our results further showed that psoralen inhibited the migration abilities of MCF-7/ADR cells by repressing EMT possibly through inhibiting the activation of NF-κB. Our findings provided a systematic and detailed description of the anti-cancer effect of psoralen on MCF-7/ADR cells for the exploration of natural compounds as novel anticancer agents.

Diterpenoid constituents of Euphorbia macrorrhiza

Ten diterpenoids, named macrorilone A–B, macroripremyrsinone A, macrorilathyrone A–B, macrorieuphorone A–B and macroricasbalone A–C, together with ten known diterpenoids, jatrophalone, sikkimenoids A–D, jatrophodione A, latilagascenes F, jolkinol B, 15β-O-benzoyl-5α-hydroxyisolathyrol and jatrophalactone were isolated from the whole plant of Euphorbia macrorrhiza C.A. Mey. These diterpenoids belong to six skeleton-types, including jatropholane, premyrsinane, lathyrane, euphoractin, casbene and rhamnofolane diterpenoids. Their structures were elucidated by extensive analysis of 1D, 2D NMR and HRESIMS spectroscopic data. The absolute configurations of macrorilone B, macroripremyrsinone A and macrorilathyrone A were established by comparing their experimental and calculated electronic circular dichroism (ECD) spectra. Several of the isolated compounds exhibited weak cytotoxicity against the KB and KBv200 cell lines with IC50 values ranging from 21.19 to 47.87μM. Some also showed multidrug resistance (MDR) reversal activity, among which macrorilathyrone B exhibited a remarkable inhibitory effect on P-gp-mediated drug exclusion.

Design, Synthesis, and Biological Evaluation of Novel Cholesteryl Peptides with Anticancer and Multidrug Resistance-Reversing Activities.

Antimicrobial peptides have been suggested as promising chemotherapeutics for cancer therapy due to their efficient antitumor activity and lower toxicity to benign cells. In previous study, we find the peptide B1 presents specific cytotoxicity to cancer cells. As hydrophobicity plays a pivotal role in the anticancer activity of peptide, we introduce cholesterol-like moiety (3β-amino-5-cholestene) to the N-terminus of B1 expect to ameliorate the anticancer activity of B1. Biological evaluations revealed that target peptides show improved anticancer activity. The peptides can also penetrate into the cytoplasm and activating mitochondria-cytochrome c apoptosis pathway. Besides, the peptides acted on multidrug-resistant cells and had multidrug resistance-reversing activity. It is therefore suggested these peptides might be promising candidates for oncotherapy.

Suppression of MAPK Signaling and Reversal of mTOR-Dependent MDR1-Associated Multidrug Resistance by 21α-Methylmelianodiol in Lung Cancer Cells.

Lung cancer is the leading cause of cancer-related deaths worldwide and remains the most prevalent. Interplay between PI3K/AMPK/AKT and MAPK pathways is a crucial effector in lung cancer growth and progression. These signals transduction protein kinases serve as good therapeutic targets for non-small cell lung cancer (NSCLC) which comprises up to 90% of lung cancers. Here, we described whether 21α-Methylmelianodiol (21α-MMD), an active triterpenoid derivative of Poncirus trifoliate, can display anticancer properties by regulating these signals and modulate the occurrence of multidrug resistance in NSCLC cells. We found that 21α-MMD inhibited the growth and colony formation of lung cancer cells without affecting the normal lung cell phenotype. 21α-MMD also abrogated the metastatic activity of lung cancer cells through the inhibition of cell migration and invasion, and induced G0/G1 cell cycle arrest with increased intracellular ROS generation and loss of mitochondrial membrane integrity. 21α-MMD regulated the expressions of PI3K/AKT/AMPK and MAPK signaling which drove us to further evaluate its activity on multidrug resistance (MDR) in lung cancer cells by specifying on P-glycoprotein (P-gp)/MDR1-association. Employing the established paclitaxel-resistant A549 cells (A549-PacR), we further found that 21α-MMD induced a MDR reversal activity through the inhibition of P-gp/MDR1 expressions, function, and transcription with regained paclitaxel sensitivity which might dependently correlate to the regulation of PI3K/mTOR signaling pathway. Taken together, these findings demonstrate, for the first time, the mechanistic evaluation in vitro of 21α-MMD displaying growth-inhibiting potential with influence on MDR reversal in human lung cancer cells.

Quercetin–POM (pivaloxymethyl) conjugates: Modulatory activity for P-glycoprotein-based multidrug resistance

BackgroundWe previously demonstrated that the bioactivity of quercetin could be improved through conjugation with a hydrolysable pivaloxymethyl (POM) group. PurposePresent study aimed to evaluate MDR (multidrug resistance)-modulatory activity of the quercetin–POM conjugates. Study design/methodsMDR-modulatory activity was determined by measuring cytotoxicity of various anticancer agents to MDR MES-SA/Dx5 cell lines upon combination with the quercetin–POM conjugates. ResultsThe quercetin–7-O-POM conjugate (7-O-POM-Q) was significantly more potent than quercetin in reversing MDR, which recovered the cytotoxicity of various anticancer agents with EC50 values of 1.1–1.3 µM. A series of mechanistic studies revealed that 7-O-POM-Q competes with verapamil in binding to the same drug-binding site of the major MDR target, Pgp (P-glycoprotein), and inhibits Pgp-mediated drug efflux with a similar potency as verapamil. The physicochemical properties of 7-O-POM-Q were then evaluated, which confirmed that 7-O-POM-Q has remarkably enhanced cellular uptake and intracellular localization compared with quercetin. Additionally, it is noteworthy that 7-O-POM-Q undergoes slow hydrolysis to quercetin over a prolonged period of time. ConclusionThe quercetin–POM conjugate showed significantly improved MDR-reversing activity compared with quercetin, which could be attributed to its capacity to maintain high intracellular concentrations.

Co-delivery of rapamycin- and piperine-loaded polymeric nanoparticles for breast cancer treatment

P-glycoprotein (P-gp) efflux is the major cause of multidrug resistance (MDR) in tumors when using anticancer drugs, moreover, poor bioavailability of few drugs is also due to P-gp efflux in the gut. Rapamycin (RPM) is in the clinical trials for breast cancer treatment, but its P-gp substrate property leads to poor oral bioavailability and efficacy. The objective of this study is to formulate and evaluate nanoparticles of RPM, along with a chemosensitizer (piperine, PIP) for improved oral bioavailability and efficacy. Poly(d,l-lactide-co-glycolide) (PLGA) was selected as polymer as it has moderate MDR reversal activity, which may provide additional benefits. The nanoprecipitation method was used to prepare PLGA nanoparticles with particle size below 150 nm, loaded with both drugs (RPM and PIP). Prepared nanoparticles showed sustained in vitro drug release for weeks, with initial release kinetics of zero order with non-Fickian transport, subsequently followed by Higuchi kinetics with Fickian diffusion. An everted gut sac method was used to study the effect of P-gp efflux on drug transport. This reveals that the uptake of the RPM (P-gp substrate) has been increased in the presence of chemosensitizer. Pharmacokinetic studies showed better absorption profile of RPM from polymeric nanoparticles compared to its suspension counterpart and improved bioavailability of 4.8-folds in combination with a chemosensitizer. An in vitro cell line study indicates higher efficacy of nanoparticles compared to free drug solution. Results suggest that the use of a combination of PIP with RPM nanoparticles would be a promising approach in the treatment of breast cancer.

Evaluation of dual P-gp-BCRP inhibitors as nanoparticle formulation

Overcoming multidrug resistance (MDR) in cancer is a major challenge and efforts are on-going to develop inhibitors against the most characterized and ubiquitous MDR transporters: P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP1) and breast cancer resistance protein (BCRP). Recently reported, two 4-anilinoquinazolines (compounds 1 and 2), demonstrate potential MDR reversal activity against BCRP and to a lesser extent, P-gp. In this work, we formulated the compounds as polymeric nanoparticles (NPs) and assessed their MDR inhibitory activity in relevant BCRP and P-gp over-expressing cell line models. Particles in the size range 300–365nm with a loading efficiency of 69% (compound 1 NP) and 77% (compound 2 NP) respectively were obtained. BCRP inhibition was observed in Hoechst 33342 and pheophorbide A assays while P-gp inhibition was evaluated in calcein AM and rhodamine-123 assays. In cytotoxicity studies, while BCRP expressing cells showed complete reversal of drug resistance in nearly all treatment groups (both compounds and their respective NP); a higher reversal in NP treated group was obtained as compared with inhibitory compound treated group in P-gp expressing cells. These results demonstrate promising inhibitory activity of both formulations, especially against P-gp expressing cells; which is possibly due to a prolonged presence of encapsulated compounds in NPs and consequently a prolonged sensitization of transmembrane drug transporter. These formulations can therefore be considered as dual-transporter inhibitors and it is imperative to investigate both inhibitors in animal models of MDR owing to the presence of multiple efflux transporters in several cancer models.

Reversal of P-glycoprotein-mediated multidrug resistance in MCF-7/Adr cancer cells by sesquiterpene coumarins

In the present study, fifteen sesquiterpene coumarins were isolated and purified from different Ferula species, and were tested for their MDR reversal properties. Enhancement of doxorubicin cytotoxicity in MCF-7/Adr cells (doxorubicin resistant derivatives of MCF-7 cells overexpressing P-gp), when combined with very non-toxic concentrations of the sesquiterpene coumarins (50μM) including umbelliprenin, farnesiferol B, farnesiferol C and lehmferin, proved significant MDR reversal activity of these coumarins. Flow cytometric efflux assay confirmed that the intracellular accumulation of Rho123 was significantly increased in MCF-7/Adr cells when treated with sesquiterpene coumarins. A deeper insight into the structure–activity relationship of sesquiterpene coumarins revealed that ring-opened drimane-type sesquiterpene coumarins including farnesiferol B, farnesiferol C and lehmferin possessed the best inhibitory effects on P-gp pump efflux and they could be considered as lead scaffolds for further structure modifications.

Multidrug resistance–reversal effects of resin glycosides from Dichondra repens

Investigation of hydrophobic extract of Dichondra repens (Convolvulaceae) led to the isolation of three new resin glycosides dichondrins A–C (1–3), and three known resin glycosides cus-1, cus-2, and cuse 3. All the isolated resin glycosides with an acyclic core were evaluated for their multidrug resistance reversal activities, and the combined use of these compounds at a concentration of 25μM increased the cytotoxicity of vincristine by 1.03–1.78-fold.

Natural lignans from Arctium lappa modulate P-glycoprotein efflux function in multidrug resistant cancer cells

Arctium lappa is a well-known traditional medicinal plant in China (TCM) and Europe that has been used for thousands of years to treat arthritis, baldness or cancer. The plant produces lignans as secondary metabolites which have a wide range of bioactivities. Yet, their ability to reverse multidrug resistance (MDR) in cancer cells has not been explored. In this study, we isolated six lignans from A. lappa seeds, namely arctigenin, matairesinol, arctiin, (iso)lappaol A, lappaol C, and lappaol F. The MDR reversal potential of the isolated lignans and the underlying mechanism of action were studied using two MDR cancer cell lines, CaCo2 and CEM/ADR 5000 which overexpress P-gp and other ABC transporters. In two-drug combinations of lignans with the cytotoxic doxorubicin, all lignans exhibited synergistic effects in CaCo2 cells and matairesinol, arctiin, lappaol C and lappaol F display synergistic activity in CEM/ADR 5000 cells. Additionally, in three-drug combinations of lignans with the saponin digitonin and doxorubicin MDR reversal activity was even stronger enhanced. The lignans can increase the retention of the P-gp substrate rhodamine 123 in CEM/ADR 5000 cells, indicating that lignans can inhibit the activity of P-gp. Our study provides a first insight into the potential chemosensitizing activity of a series of natural lignans, which might be candidates for developing novel adjuvant anticancer agents.

Preparation and study of the physicochemical properties of psoralen-doxorubicin nanostructured lipid carriers

The purpose of the present study was to prepare psoralen-doxorubicin nanostructured lipid carriers (PSO-DOX-NLC) with better physicochemical properties for further study on its multidrug resistance reversal activity on leukemia cells. PSO-DOX-NLC was synthesized by emulsion evaporation and solidification at a low temperature. PSO-DOX-NLC morphology and particle size were examined using transmission electron microscopy, and Zeta potential was determined using photon correlation spectroscopy; encapsulation efficiency was also investigated. The results showed that PSO-DOX-NLC possessed a rounded structure, with a mean (± SD) particle size of 128.7±1.8 nm, a polydispersity index of 0.22±0.01, a Zeta potential of 20.17±0.31 mV, a psoralen encapsulation rate of 76.56% and a doxorubicin encapsulation rate of 89.48%. Thus, PSO-DOX-NLC prepared by emulsion evaporation and solidification at a low temperature had good physicochemical properties.

Aliphatic acid-conjugated antimicrobial peptides – potential agents with anti-tumor, multidrug resistance-reversing activity and enhanced stability

Compared with traditional therapeutics, antimicrobial peptides as novel anti-tumor agents have prominent advantages of higher specificity and circumvention of multi-drug resistance. In a previous study, we found that B1, an antimicrobial peptide derived from Cathelicidin-BF15, presented specific anti-tumor activity against several tumor cells. Since aliphatic chain-conjugated peptides have shown ameliorative activity and stability, we conjugated aliphatic acids with different lengths to the amino terminal of B1. All the conjugated peptides exhibited improved anti-tumor activity over B1. Further investigations revealed that the peptides were capable of disrupting the cell membrane, stimulating cytochrome c release into the cytosol, which results in apoptosis. The peptides also acted against multidrug resistant cells and had multidrug resistance-reversing effects. Additionally, conjugation of aliphatic acid enhanced the peptide stability in plasma. In summary, aliphatic acid-modified peptides might be promising anti-tumor agents in the future.

A Synthesis of Lamellarins via Regioselective Assembly of 1,2,3-Differentially Substituted 5,6-Dihydropyrrolo[2,1-a]Isoquinoline Core

A modular synthesis of the marine natural products lamellarins has been developed. The key reactions utilized are C3-selective Vilsmeier-Haack formylation followed by iterative bromination/cross-coupling of the 5,6-dihydropyrrolo[2,1-a]isoquinoline core. The 1,2-diaryl-5,6-dihydropyrrolo[2,1-a]isoquinoline-3-carbaldehyde thus synthesized was readily converted to the lamellarin skeleton by mean of palladium-catalyzed oxidative lactonization. INTRODUCTION Lamellarins constitute an important class of natural products of marine origin. Since the first isolation of lamellarins A–D from Lamellaria sp. by Faulkner in 1985, more than 50 lamellarins (A–Z, α–χ, A1– A6, and O1–O2, including their acetate and sulfate derivatives) have been isolated from marine organisms such as tunicates, sponges, and prosobranches. With a very few exceptions, lamellarins possess a unique 14-phenyl-6H-[1]benzopyrano[4’,3’:4,5]pyrrolo[2,1-a]isoquinolin-6-one ring system (Figure 1). Furthermore, these lamellarins exhibit various interesting biological activities including potent antiproliferative activity against several cancer cell lines, multi-drug resistance (MDR) reversal activity, anti-HIV activity, topoisomerase I inhibitory activity, inhibition of mitochondrial function, and protein kinases inhibitory activity. Because of their unique structure and significant biological activities, lamellarins have attracted considerable attention from organic and medicinal chemists. Consequently, various synthetic methods for the preparation of lamellarins have been exploited so far. The synthetic methods can be classified broadly into two categories: one utilizes formation of the pyrrole core as the key step and the other employs regioselective functionalization of the pre-existing pyrrole core. Compared to the former approaches, the latter syntheses are more effective because a wide range of natural and artificial lamellarins can be obtained easily by simple modification of 782 HETEROCYCLES, Vol. 91, No. 4, 2015

Cytotoxic and multidrug resistance reversal activities of novel 1,4-dihydropyridines against human cancer cells

Multidrug resistance (MDR) caused by P-glycoprotein (P-gp, ABCB1, MDR-1) transporter over-expression in cancer cells substantially limits the effectiveness of chemotherapy. 1,4-Dihydropyridines (DHPs) derivatives possess several pharmacological activities. In this study, 18 novel asymmetrical DHPs bearing 3-pyridyl methyl carboxylate and alkyl carboxylate moieties at C3 and C5 positions, respectively, as well as nitrophenyl or hetero aromatic rings at C4 were synthesized and tested for MDR reversal with the aim of establishing a structure–activity relationship (SAR) for these agents. Effect of these compounds on P-gp mediated MDR was assessed in P-gp over-expressing MES-SA/DX5 doxorubicin resistant cells by flow cytometric detection of rhodamine 123 efflux. MDR reversal was further examined as the alteration of doxorubicin׳s IC50 in MES-SA/DX5 cells in the presence of DHPs by MTT assay and was compared to nonresistant MES-SA cells. Direct anticancer effect was examined against 4 human cancer cells including HL-60, K562, MCF-7 and LS180. Calcium channel blocking (CCB) activity was also measured as a potential side effect. Most DHPs, particularly compounds bearing 3-nitrophenyl (A2B2 and A3B2) and 4-nitrophenyl (A3B1 and A4B1) moieties at C4 significantly inhibited rhodamine 123 efflux at 5–25µM, showing that the mechanism of MDR reversal by these agents is P-gp transporter modulation. Same derivatives were also able to selectively lower the resistance of MES-SA/DX5 to doxorubicin. A2B2 bearing ethyl carboxylate at C5 had also high direct antitumoral effect (IC50 range: 3.77–15.60μM). Our findings suggest that SAR studies of DHPs may lead to the discovery of novel MDR reversal agents.

Design, synthesis and evaluation of novel triazole core based P-glycoprotein-mediated multidrug resistance reversal agents

A novel series of triazol-N-ethyl-tetrahydroisoquinoline based compounds were designed and synthesized via click chemistry. Most of the synthesized compounds showed P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) reversal activities. Among them, compound 7 with little cytotoxicity towards GES-1 cells (IC50 >80μM) and K562/A02 cells (IC50 >80μM) exhibited more potency than verapamil (VRP) on increasing anticancer drug accumulation in K562/A02 cells. Moreover, compound 7 could significantly reverse MDR in a dose-dependent manner and also persist longer chemo-sensitizing effect than VRP with reversibility. Further mechanism studies revealed that compound 7 in reversing MDR revealed that it could remarkably increase the intracellular accumulation of both rhodamine-123 (Rh123) and adriamycin (ADM) in K562/A02 cells as well as inhibit their efflux from the cells. These results suggested that compound 7 showed more potency than the classical P-gp inhibitor VRP under the same conditions, which may be a promising P-gp-mediated MDR modulator for further development.