The functions and structure of ABC transporters: implications for the design of new inhibitors of Pgp and MRP1 to control multidrug resistance (MDR)

Design, synthesis, molecular modeling, in vitro and in vivo biological evaluation of potent anthranilamide derivatives as dual P-glycoprotein and CYP3A4 inhibitors

Paclitaxel (PTX) is considered the blockbuster chemotherapy treatment for cancer. Paclitaxel's (PTX) oral administration has proven to be extremely difficult, mostly because of its susceptibility to intestinal P-glycoprotein (P-gp) and cytochrome P450 (CYP3A4). The concurrent local inhibition of intestinal P-gp and CYP3A4 is a promising approach to improve the oral bioavailability of paclitaxel while avoiding potential unfavorable side effects of their systemic inhibition. Herein, we report the rational design and evaluation of novel dual potent inhibitors of P-gp and CYP3A4 using an anthranilamide derivative tariquidar as a starting point for their structural optimizations. Compound 14f, bearing N-imidazolylbenzyl side chain, was found to have potent and selective P-gp (EC50 = 28 nM) and CYP3A4 (IC50 = 223 nM) inhibitory activities with low absorption potential (Papp (A-to-B) <0.06). In vivo, inhibitor 14f improved the oral absorption of paclitaxel by 6 times in mice and by 30 times in rats as compared to vehicle, while 14f itself remained poorly absorbed. Compound 14f, possessing dual P-gp and CYP3A4 inhibitory activities, offered additional enhancement in paclitaxel oral absorption compared to tariquidar in mice. Evaluating the CYP effect of 14f on oral absorption of paclitaxel requires considering the variations in CYP expression between animal species. This study provides further medicinal chemistry advice on strategies for resolving concerns with the oral administration of chemotherapeutic agents.

Magnolol derivatives as specific and noncytotoxic inhibitors of breast cancer resistance protein (BCRP/ABCG2)

The breast cancer resistance protein (BCRP/ABCG2) transporter mediates the efflux of numerous antineoplastic drugs, playing a central role in multidrug resistance related to cancer. The absence of successful clinical trials using specific ABCG2 inhibitors reveals the urge to identify new compounds to attend this critical demand. In this work, a series of 13 magnolol derivatives was tested as ABCG2 inhibitors. Only two compounds, derivatives 10 and 11, showed partial and complete ABCG2 inhibitory effect, respectively. This inhibition was selective toward ABCG2, since none of the 13 compounds inhibited neither P-glycoprotein nor MRP1. Both inhibitors (10 and 11) were not transported by ABCG2 and demonstrated a low cytotoxic profile even at high concentrations (up to 100 µM). 11 emerged as the most promising compound of the series, considering the ratio between cytotoxicity (IG50) and ABCG2 inhibition potency (IC50), showing a therapeutic ratio (TR) higher than observed for 10 (10.5 versus 1.6, respectively). This derivative showed a substrate-independent and a mixed type of inhibition. The effect of compound 11 on the ABCG2 ATPase activity and thermostability revealed allosteric protein changes. This compound did not affect the expression levels of ABCG2 and increased the binding of the conformational-sensitive antibody 5D3. A docking study showed that 11 did not share the same binding site with ABCG2 substrate mitoxantrone. Finally, 11 could revert the chemoresistance to SN-38 mediated by ABCG2.

Synthesis of methotrexate-betulonic acid hybrids and evaluation of their effect on artificial and Caco-2 cell membranes

An efficient protocol for the synthesis of novel methotrexate-betulonic acid hybrids with a (tert-butoxycarbonylamino)-3,6-dioxa-8-octanamine (Boc-DOOA) linkage has been developed. Reaction of N-(2-(2-(2-aminoethoxy)ethoxy)ethyl)-betulonamide with methotrexate resulted in a mixture of isomeric conjugates which were separated by column chromatography. Their structures and composition have been fully established by 1H NMR, 13C spectra, FAB mass spectrometry and elemental analysis. The identity of conjugates was confirmed by LC-MS data. Membranotropic properties of the new hybrids were assessed on the basis of their interactions with artificial lipid membranes by differential scanning calorimetry (DSC) method. The ability of the conjugates to penetrate Caco-2 cells is inferior to methotrexate. Probably, this is due to the increasing lipophilicity, the affinity of these hybrid molecules for the lipid bilayer increases, which is confirmed by experiments with artificial membranes.

Mechanistic insights into the inhibition of human placental glutathione S-transferase P1-1 by abscisic and gibberellic acids: An integrated experimental and computational study

The interactions of the classic phytohormones gibberellic acid (gibberellin A3 , GA3 ) and abscisic acid (dormin, ABA), which antagonistically regulate several developmental processes and stress responses in higher plants, with human placental glutathione S-transferase P1-1 (hpGSTP1-1), an enzyme that plays a role in endo- or xenobiotic detoxification and regulation of cell survival and apoptosis, were investigated. The inhibitory potencies of ABA and GA3 against hpGSTP1, as well as the types of inhibition and the kinetic parameters, were determined by making use of both enzyme kinetic graphs and SPSS nonlinear regression models. The structural basis for the interaction between hpGSTP1-1 and phytohormones was predicted with the aid of molecular docking simulations. The IC50 values of ABA and GA3 were 5.3 and 5.0 mM, respectively. Both phytohormones inhibited hpGSTP1-1 in competitive manner with respect to the cosubstrates GSH and CDNB. When ABA was the inhibitor at [CDNB]f -[GSH]v and at [GSH]f -[CDNB]v , Vm , Km , and Ki values were statistically estimated to be 205 ± 16 μmol/min-mg protein, 1.32 ± 0.18 mM, 1.95 ± 0.25 mM and 175 ± 6 μmol/min-mg protein, 0.85 ± 0.06 mM, 1.85 ± 0.16 mM, respectively. On the other hand, the kinetic parameters Vm , Km , and Ki obtained with GA3 at [CDNB]f -[GSH]v and at [GSH]f -[CDNB]v were found to be 303 ± 14 μmol/min-mg protein, 1.77 ± 0.13 mM, 3.38 ± 0.26 mM and 249 ± 7 μmol/min-mg protein, 1.43 ± 0.07 mM, 2.89 ± 0.19 mM, respectively. Both phytohormones had the potential to engage in hydrogen-bonding and electrostatic interactions with the key residues that line the G- and H-sites of the enzyme's catalytic center. Inhibitory actions of ABA/GA3 on hpGSTP1-1 may guide medicinal chemists through the structure-based design of novel antineoplastic agents. It should be noted, however, that the same interactions may also render fetuses vulnerable to the potentially toxic effects of xenobiotics and noxious endobiotics.

MicroRNAs as the pivotal regulators of cisplatin resistance in head and neck cancers

Although, there is a high rate of good prognosis in early stage head and neck tumors, about half of these tumors are detected in advanced stages with poor prognosis. A combination of chemotherapy, radiotherapy, and surgery is the treatment option in head and neck cancer (HNC) patients. Although, cisplatin (CDDP) as the first-line drug has a significant role in the treatment of HNC patients, CDDP resistance can be observed in a large number of these patients. Therefore, identification of the molecular mechanisms involved in CDDP resistance can help to reduce the side effects and also provides a better therapeutic management. MicroRNAs (miRNAs) as the post-transcriptional regulators play an important role in drug resistance. Therefore, in the present review we investigated the role of miRNAs in CDDP response of head and neck tumors. It has been reported that the miRNAs exerted their roles in CDDP response by regulation of signaling pathways such as WNT, NOTCH, PI3K/AKT, TGF-β, and NF-kB as well as apoptosis, autophagy, and EMT process. The present review paves the way to suggest a non-invasive miRNA based panel marker for the prediction of CDDP response among HNC patients. Therefore, such diagnostic miRNA based panel marker reduces the CDDP side effects and improves the clinical outcomes of these patients following an efficient therapeutic management.

Pharmacophore Modeling Using Machine Learning for Screening the Blood-Brain Barrier Permeation of Xenobiotics

Daily exposure to xenobiotics affects human health, especially the nervous system, causing neurodegenerative diseases. The nervous system is protected by tight junctions present at the blood-brain barrier (BBB), but only molecules with desirable physicochemical properties can permeate it. This is why permeation is a decisive step in avoiding unwanted brain toxicity and also in developing neuronal drugs. In silico methods are being implemented as an initial step to reduce animal testing and the time complexity of the in vitro screening process. However, most in silico methods are ligand based, and consider only the physiochemical properties of ligands. However, these ligand-based methods have their own limitations and sometimes fail to predict the BBB permeation of xenobiotics. The objective of this work was to investigate the influence of the pharmacophoric features of protein-ligand interactions on BBB permeation. For these purposes, receptor-based pharmacophore and ligand-based pharmacophore fingerprints were developed using docking and Rdkit, respectively. Then, these fingerprints were trained on classical machine-learning models and compared with classical fingerprints. Among the tested footprints, the ligand-based pharmacophore fingerprint achieved slightly better (77% accuracy) performance compared to the classical fingerprint method. In contrast, receptor-based pharmacophores did not lead to much improvement compared to classical descriptors. The performance can be further improved by considering efflux proteins such as BCRP (breast cancer resistance protein), as well as P-gp (P-glycoprotein). However, the limited data availability for other proteins regarding their pharmacophoric interactions is a bottleneck to its improvement. Nonetheless, the developed models and exploratory analysis provide a path to extend the same framework for environmental chemicals, which, like drugs, are also xenobiotics. This research can help in human health risk assessment by a priori screening for neurotoxicity-causing agents.

GPCRs in Intracellular Compartments: New Targets for Drug Discovery

The architecture of eukaryotic cells is defined by extensive membrane-delimited compartments, which entails separate metabolic processes that would otherwise interfere with each other, leading to functional differences between cells. G protein-coupled receptors (GPCRs) are the largest class of cell surface receptors, and their signal transduction is traditionally viewed as a chain of events initiated from the plasma membrane. Furthermore, their intracellular trafficking, internalization, and recycling were considered only to regulate receptor desensitization and cell surface expression. On the contrary, accumulating data strongly suggest that GPCRs also signal from intracellular compartments. GPCRs localize in the membranes of endosomes, nucleus, Golgi and endoplasmic reticulum apparatuses, mitochondria, and cell division compartments. Importantly, from these sites they have shown to orchestrate multiple signals that regulate different cell pathways. In this review, we summarize the current knowledge of this fascinating phenomenon, explaining how GPCRs reach the intracellular sites, are stimulated by the endogenous ligands, and their potential physiological/pathophysiological roles. Finally, we illustrate several mechanisms involved in the modulation of the compartmentalized GPCR signaling by drugs and endogenous ligands. Understanding how GPCR signaling compartmentalization is regulated will provide a unique opportunity to develop novel pharmaceutical approaches to target GPCRs and potentially lead the way towards new therapeutic approaches.

A new porphyrin as selective substrate-based inhibitor of breast cancer resistance protein (BCRP/ABCG2)

The ABCG2 transporter plays a pivotal role in multidrug resistance, however, no clinical trial using specific ABCG2 inhibitors have been successful. Although ABC transporters actively extrude a wide variety of substrates, photodynamic therapeutic agents with porphyrinic scaffolds are exclusively transported by ABCG2. In this work, we describe for the first time a porphyrin derivative (4B) inhibitor of ABCG2 and capable to overcome multidrug resistance in vitro. The inhibition was time-dependent and 4B was not itself transported by ABCG2. Independently of the substrate, the porphyrin 4B showed an IC₅₀ value of 1.6 μM and a mixed type of inhibition. This compound inhibited the ATPase activity and increased the binding of the conformational-sensitive antibody 5D3. A thermostability assay confirmed allosteric protein changes triggered by the porphyrin. Long-timescale molecular dynamics simulations revealed a different behavior between the ABCG2 porphyrinic substrate pheophorbide a and the porphyrin 4B. Pheophorbide a was able to bind in three different protein sites but 4B showed one binding conformation with a strong ionic interaction with GLU446. The inhibition was selective toward ABCG2, since no inhibition was observed for P-glycoprotein and MRP1. Finally, this compound successfully chemosensitized cells that overexpress ABCG2. These findings reinforce that substrates may be a privileged source of chemical scaffolds for identification of new inhibitors of multidrug resistance-linked ABC transporters.

Cancer stem cells and strategies for targeted drug delivery

Cancer stem cells (CSCs) are a small proportion of cancer cells with high tumorigenic activity, self-renewal ability, and multilineage differentiation potential. Standard anti-tumor therapies including conventional chemotherapy, radiation therapy, and molecularly targeted therapies are not effective against CSCs, and often lead to enrichment of CSCs that can result in tumor relapse. Therefore, it is hypothesized that targeting CSCs is key to increasing the efficacy of cancer therapies. In this review, CSC properties including CSC markers, their role in tumor growth, invasiveness, metastasis, and drug resistance, as well as CSC microenvironment are discussed. Further, CSC-targeted strategies including the use of targeted drug delivery systems are examined.

NCX-4040, a Unique Nitric Oxide Donor, Induces Reversal of Drug-Resistance in Both ABCB1- and ABCG2-Expressing Multidrug Human Cancer Cells

The emergence of multidrug resistance (MDR) in the clinic is a significant problem for a successful treatment of human cancers. Overexpression of various ABC transporters (P-gp, BCRP and MRP's), which remove anticancer drugs in an ATP-dependent manner, is linked to the emergence of MDR. Attempts to modulate MDR have not been very successful in the clinic. Furthermore, no single agent has been found to significantly inhibit their functions to overcome clinical drug resistance. We have previously shown that nitric oxide (^●NO) inhibits ATPase functions of ABC transporters, causing reversal of resistance to clinically active anticancer drugs. In this study, we have used cytotoxicity and molecular docking studies to show that NCX4040, a nitric oxide donor related to aspirin, inhibited the functions of ATPase which resulted in significant reversal of resistance to both adriamycin and topotecan in P-gp- and BCRP-expressing human cancer cell lines, respectively. We also used several other cytotoxic nitric oxide donors, e.g., molsidomine and S-nitroso glutathione; however, both P-gp- and BCRP-expressing cells were found to be highly resistant to these NO-donors. Molecular docking studies showed that NCX4040 binds to the nucleotide binding domains of the ATPase and interferes with further binding of ATP, resulting in decreased activities of these transporters. Our results are extremely promising and suggest that nitric oxide and other reactive species delivered to drug resistant tumor cells by well-designed nitric oxide donors could be useful in sensitizing anticancer drugs in multidrug resistant tumors expressing various ABC transporters.

Reversal of Cancer Multidrug Resistance (MDR) Mediated by ATP-Binding Cassette Transporter G2 (ABCG2) by AZ-628, a RAF Kinase Inhibitor

Overexpression of ABCG2 remains a major impediment to successful cancer treatment, because ABCG2 functions as an efflux pump of chemotherapeutic agents and causes clinical multidrug resistance (MDR). Therefore, it is important to uncover effective modulators to circumvent ABCG2-mediated MDR in cancers. In this study, we reported that AZ-628, a RAF kinase inhibitor, effectively antagonizes ABCG2-mediated MDR in vitro. Our results showed that AZ-628 completely reversed ABCG2-mediated MDR at a non-toxic concentration (3 μM) without affecting ABCB1-, ABCC1-, or ABCC10 mediated MDR. Further studies revealed that the reversal mechanism was by attenuating ABCG2-mediated efflux and increasing intracellular accumulation of ABCG2 substrate drugs. Moreover, AZ-628 stimulated ABCG2-associated ATPase activity in a concentration-dependent manner. Docking and molecular dynamics simulation analysis showed that AZ-628 binds to the same site as ABCG2 substrate drugs with higher score. Taken together, our studies indicate that AZ-628 could be used in combination chemotherapy against ABCG2-mediated MDR in cancers.

Triple Strategies to Improve Oral Bioavailability by Fabricating Coamorphous Forms of Ursolic Acid with Piperine: Enhancing Water-Solubility, Permeability, and Inhibiting Cytochrome P450 Isozymes

As a BCS IV drug, ursolic acid (UA) has low oral bioavailability mainly because of its poor aqueous solubility/dissolution, poor permeability, and metabolism by cytochrome P450 (CYP) isozymes, such as CYP3A4. Most UA preparations demonstrated a much higher dissolution than that of its crystalline form yet a low drug concentration in plasma due to their lower consideration or evaluation for the permeability and metabolism issues. In the current study, a supramolecular coamorphous system of UA with piperine (PIP) was prepared and characterized by powder X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy. In comparison to crystalline UA and UA in physical mixture, such coamorphous system enhanced solubility (5.3-7-fold in the physiological solution) and dissolution (7-8-fold in the physiological solution within 2 h) of UA and exhibited excellent physical stability under 90-day storage conditions. More importantly, the pharmacokinetic study of coamorphous UA in rats exhibited 5.8-fold and 2.47-fold improvement in AUC0-∞ value, respectively, compared with its free and mixed crystalline counterparts. In order to further explore the mechanism of such improvement, the molecular interactions of a coamorphous system in the solid state were investigated. Fourier transform infrared spectroscopy, solid-state 13C nuclear magnetic resonance spectroscopy, and density functional theory modeling suggested that intermolecular hydrogen bonds with strong interactions newly formed between UA and PIP after coamorphization. The in vitro permeability studies across Caco-2 cell monolayer and metabolism studies by rat hepatic microsomes indicated that free PIP significantly increased the permeability of UA and inhibited the enzymatic metabolism of UA by CYP3A4. However, PIP in the coamorphous combination exhibited a much lower level in the bioenhancing than its free form arising from the synchronized dissolution characteristic of the preparation (only 60% of PIP released in comparison to its free counterpart in 2 h). The in situ loop study in rats proposed that the acid-sensitive dissolution in the stomach of the coamorphous preparation helped to improve the effective free drug concentration, thereby facilitating PIP to play its role in bioenhancing. The current study offers an exploratory strategy to overcome poor solubility/dissolution, poor permeability, and metabolism by cytochrome P450 isozymes of the BCS IV drug to improve its oral bioavailability.

6,7-Dimethoxy-2-phenethyl-1,2,3,4-tetrahydroisoquinoline amides and corresponding ester isosteres as multidrug resistance reversers

Aiming to deepen the structure-activity relationships of the two P-glycoprotein (P-gp) modulators elacridar and tariquidar, a new series of amide and ester derivatives carrying a 6,7-dimethoxy-2-phenethyl-1,2,3,4-tetrahydroisoquinoline scaffold linked to different methoxy-substituted aryl moieties were synthesised. The obtained compounds were evaluated for their P-gp interaction profile and selectivity towards the two other ABC transporters, multidrug-resistance-associated protein-1 and breast cancer resistance protein, showing to be very active and selective versus P-gp. Two amide derivatives, displaying the best P-gp activity, were tested in co-administration with the antineoplastic drug doxorubicin in different cancer cell lines, showing a significant sensitising activity towards doxorubicin. The investigation on the chemical stability of the derivatives towards spontaneous or enzymatic hydrolysis, showed that amides are stable in both models while some ester compounds were hydrolysed in human plasma. This study allowed us to identify two chemosensitizers that behave as non-transported substrates and are characterised by different selectivity profiles.

Modulating the function of ABCB1: in vitro and in vivo characterization of sitravatinib, a tyrosine kinase inhibitor

BACKGROUND

Overexpression of ATP-binding cassette (ABC) transporter is a major contributor to multidrug resistance (MDR), in which cancer cells acquire resistance to a wide spectrum of chemotherapeutic drugs. In this work, we evaluated the sensitizing effect of sitravatinib, a broad-spectrum tyrosine kinase inhibitor (TKI), on ATP-binding cassette subfamily B member 1 (ABCB1)- and ATP-binding cassette subfamily C member 10 (ABCC10)-mediated MDR.

METHODS

MTT assay was conducted to examine cytotoxicity and evaluate the sensitizing effect of sitravatinib at non-toxic concentrations. Tritium-labeled paclitaxel transportation, Western blotting, immunofluorescence analysis, and ATPase assay were carried out to elucidate the mechanism of sitravatinib-induced chemosensitization. The in vitro findings were translated into preclinical evaluation with the establishment of xenograft models.

RESULTS

Sitravatinib considerably reversed MDR mediated by ABCB1 and partially antagonized ABCC10-mediated MDR. Our in silico docking simulation analysis indicated that sitravatinib strongly and stably bound to the transmembrane domain of ABCB1 human-mouse chimeric model. Furthermore, sitravatinib inhibited hydrolysis of ATP and synchronously decreased the efflux function of ABCB1. Thus, sitravatinib could considerably enhance the intracellular concentration of anticancer drugs. Interestingly, no significant alterations of both expression level and localization of ABCB1 were observed. More importantly, sitravatinib could remarkably restore the antitumor activity of vincristine in ABCB1-mediated xenograft model without observable toxic effect.

CONCLUSIONS

The findings in this study suggest that the combination of sitrvatinib and substrate antineoplastic drugs of ABCB1 could attenuate the MDR mediated by the overexpression of ABCB1.

Erdafitinib Antagonizes ABCB1-Mediated Multidrug Resistance in Cancer Cells

ABCB1 overexpression is known to contribute to multidrug resistance (MDR) in cancers. Therefore, it is critical to find effective drugs to target ABCB1 and overcome MDR. Erdafitinib is a tyrosine kinase inhibitor (TKI) of fibroblast growth factor receptor (FGFR) that is approved by the FDA to treat urothelial carcinoma. Previous studies have demonstrated that some TKIs exhibit MDR reversal effect. In this work, we examined whether erdafitinib could reverse MDR mediated by ABCB1. The results of reversal experiments showed that erdafitinib remarkably reversed ABCB1-mediated MDR without affecting ABCG2-mediated MDR. The results of immunofluorescence and Western blot analysis demonstrated that erdafitinib did not affect the expression of ABCB1 or its cellular localization. Further study revealed that erdafitinib inhibited ABCB1 efflux function leading to increasing intracellular drug accumulation, thereby reversing MDR. Furthermore, ATPase assay indicated that erdafitinib activated the ABCB1 ATPase activity. Docking study suggested that erdafitinib interacted with ABCB1 on the drug-binding sites. In summary, this study demonstrated that erdafitinib can reverse MDR mediated by ABCB1, suggesting that combination of erdafitinib and ABCB1-substrate conventional chemotherapeutic drugs could potentially be used to overcome MDR mediated by ABCB1.

Sitravatinib, a Tyrosine Kinase Inhibitor, Inhibits the Transport Function of ABCG2 and Restores Sensitivity to Chemotherapy-Resistant Cancer Cells in vitro

Sitravatinib, also called MGCD516 or MG-516, is a broad-spectrum tyrosine kinase inhibitor (TKI) under phase III clinical evaluation. Herein, we explored the activity of sitravatinib toward multidrug resistance (MDR) by emphasizing its inhibitory effect on ATP-binding cassette super-family G member 2 (ABCG2). ABCG2 is a member of ATP-binding cassette (ABC) transporter family and plays a critical role in mediating MDR. Sitravatinb received an outstanding docking score for binding to the human ABCG2 model (PDB code: 6ETI) among thirty screened TKIs. Also, an MTT assay indicated that sitravatinib at 3 μM had the ability to restore the antineoplastic effect of various ABCG2 substrates in both drug-selected and gene-transfected ABCG2-overexpressing cell lines. In further tritium-labeled mitoxantrone transportation study, sitravatinib at 3 μM blocked the efflux function mediated by ABCG2 and as a result, increased the intracellular concentration of anticancer drugs. Interestingly, sitravatinib at 3 μM altered neither protein expression nor subcellular localization of ABCG2. An ATPase assay demonstrated that ATPase activity of ABCG2 was inhibited in a concentration-dependent manner with sitravatinib; thus, the energy source to pump out compounds was interfered. Collectively, the results of this study open new avenues for sitravatinib working as an ABCG2 inhibitor which restores the antineoplastic activity of anticancer drugs known to be ABCG2 substrates.

A Putative Efflux Transporter of the ABC Family, YbhFSR, in Escherichia coli Functions in Tetracycline Efflux and Na+(Li+)/H+ Transport

ATP-binding cassette transporters are ubiquitous in almost all organisms. The Escherichia coli genome is predicted to encode 69 ABC transporters. Eleven of the ABC transporters are presumed to be exporters, of which seven are possible drug export transporters. There has been minimal research on the function of YbhFSR, which is one of the putative drug resistance exporters. In this study, the ybhF gene of this transporter was characterized. Overexpression and knockout strains of ybhF were constructed. The ATPase activity of YbhF was studied using the malachite green assay, and the efflux abilities of knockout strains were demonstrated by using ethidium bromide (EB) as a substrate. The substrates of YbhFSR efflux, examined with the minimum inhibitory concentration (MIC), were determined to be tetracycline, oxytetracycline, chlortetracycline, doxycycline, EB, and Hoechst33342. Furthermore, tetracycline and EB efflux and accumulation experiments confirmed that the substrates of YbhFSR were tetracyclines and EB. The MIC assay and the fluorescence test results showed that tetracyclines are likely to be the major antibiotic substrate of YbhFSR. The existence of the signature NatA motif suggested that YbhFSR may also function as a Na⁺/H⁺ transporter. Overexpression of YbhF in E. coli KNabc lacking crucial Na⁺/H⁺ transporters conferred tolerance to NaCl, LiCl, and an alkaline pH. Together, the results showed that YbhFSR exhibited dual functions as a drug efflux pump and a Na⁺ (Li⁺)/H⁺ antiporter.

5-Oxo-hexahydroquinoline Derivatives and Their Tetrahydroquinoline Counterparts as Multidrug Resistance Reversal Agents

Cancer is a leading cause of death worldwide. Multidrug resistance (MDR) is a main reason of chemotherapy failure in many patients and is often related to overexpression of ATP-binding cassette (ABC) transporters, including P-glycoprotein (P-gp/ABCB1). Agents that are capable of modulation of the activity of these transporters might be effective in overcoming MDR. In this study, a new set of 1,4,5,6,7,8-hexahydro 5-oxo quinoline-3-carboxamide derivatives bearing 4-methylthiazole moiety and their tetrahydroquinoline counterparts were synthesized. MDR reversal activity of these 16 newly synthesized derivatives was tested in P-gp overexpressing MES-SA-DX5 human uterine sarcoma cells by flow cytometric determination of Rhodamine123 efflux. The effect of the most potent compounds in induction of apoptosis and alterations of cell cycle was examined in these cells by a flow cytometric method. Inherent cytotoxicity of the synthesized compounds was evaluated against MCF-7, A-549 and K562 cancer cell lines, as well as MES-SA-DX5 and their parental non-resistant MES-SA and also HEK-293 non-cancerous cells by MTT assay. Compounds A1 and A2 with 5-oxo-hexahydroquinoline structure bearing 2,4-dichlorophenyl and 4-bromophenyl moieties, respectively, and their tetrahydroquinoline counterparts B1 and B2 significantly blocked P-gp efflux, induced apoptosis and showed the highest cytotoxicities against MES-SA-DX5 cells. However, only A2 and B2 compounds were relatively selective against cancer and MDR cells as compared to non-resistant and non-cancerous cells. These findings demonstrate that 5-oxo-hexahydroquinoline and 5-oxo-tetrahydroquinoline derivatives represent promising agents with therapeutic potential in drug resistant cancers.

Proteomic Analysis Reveals that EPHX1 Contributes to 5-Fluorouracil Resistance in a Human Hepatocellular Carcinoma Cell Line

PURPOSE

The extensive drug resistance of hepatocellular carcinoma (HCC) has become a major cause of chemotherapy failure. A deeper understanding of the drug resistance mechanism of tumor cells is very significant for improving the clinical prognosis of patients with HCC.

EXPERIMENTAL DESIGN

In this study, proteomic studies on the composition of 5-fluorouracil (5-Fu) resistant Bel/5Fu cell line and its parent Bel7402 cell line by using an ionic liquid assisted proteins extraction method with the advantage of extracting plasma membrane proteins to a wider extent are performed. Then the expression level and function of differentially expressed plasma membrane proteins are verified.

RESULTS

In total, 25 plasma membrane proteins are shown differentially expressed in Bel/5Fu compared with Bel7402. Western blot analysis results further confirmed that the EPHX1 PLIN2 RAB27B SLC4A2 are upregulated in Bel/5Fu cells in accordance with the proteomics data. Moreover, cell viability assay and clonogenic survival assay results demonstrated that EPHX1 is closely related to the chemoresistance of Bel/5Fu to 5-Fu.

CONCLUSIONS AND CLINICAL RELEVANCE

Plasma membrane protein EPHX1 is closely related to the chemotherapy resistance of Bel/5Fu cells and can be used as a new drug target to improve the clinical prognosis of patients with HCC.

Reversal of drug resistance by JS-K and nitric oxide in ABCB1- and ABCG2-expressing multi-drug resistant human tumor cells

Development of resistance to chemotherapy drugs is a significant problem in treating human malignancies in the clinic. Overexpression of ABC transporter proteins, including P-170 glycoprotein (P-gp), and breast cancer resistance protein (BCRP, ABCG2) have been implicated in this multi-drug resistance (MDR). These ABC transporters are ATP-dependent efflux proteins. We have recently shown that nitric oxide (NO) inhibits the ATPase activities of P-gp, resulting in a significant enhancement of drug accumulation and the reversal of multi-drug resistance in NCI/ADR-RES cells, a P-gp-overexpressing human MDR cell line. In this study, we used [O²-(2,4-dinitrophenyl)-1-[(4-ethoxycarbonyl)-piperazin-1 yl]-diazene-1-ium-1-2-diolate] (JS-K), a tumor-specific NO-donor to study the reversal of drug resistance in both P-gp- and BCRP-overexpressing human tumor cells. We report here that while JS-K was extremely effective in reversing adriamycin resistance in the P-gp-overexpressing tumor cells (NCI/ADR-RES); it was significantly resistant to BCRP-overexpressing (MCF-7/MX) tumor cells, suggesting that JS-K may be a substrate for BCRP. Using another NO-donor (DETNO), we show that NO directly inhibits the ATP activities of BCRP, inducing significant increases in the accumulations of both Hoechst 33342 dye and topotecan, substrates for BCRP. Furthermore, NO treatment significantly reversed topotecan and mitoxantrone resistance to MCF-7/MX tumor cells. Molecular docking studies indicated that while DETNO and JS-K bind to ATP binding site in both ABC proteins, binding score was significantly reduced, compared to the ATP binding. Our results indicate that appropriately designed NO donors may find success in reversing multidrug resistance in the clinic.

Effective MDR reversers through phytochemical study of Euphorbia boetica

INTRODUCTION

Macrocyclic diterpenes from Euphorbia species were found to be promising modulators of multidrug resistance (MDR), a complex phenomenon that hampers the effectiveness of cancer therapy.

OBJECTIVE

To find new effective MDR reversers through the phytochemical study of E. boetica, including isolation and molecular derivatisation.

MATERIAL AND METHODS

The phytochemical study of E. boetica was performed through chromatographic techniques. Preliminary analysis of crude chromatographic fractions from the methanol extract was carried out by ¹ H-NMR in order to prioritise the study of those having macrocyclic diterpenes. Polyamide resin was used to remove chlorophylls. Molecular derivatisation of isolated compounds comprised hydrolysis, reduction and acylation reactions. The structural identification of compounds was performed through analysis of spectroscopic data, mainly one-dimensional- and two-dimensional-NMR. The MDR reversing activity was assessed using a combination of transport and chemosensitivity assays, in mouse lymphoma (L5178Y-MDR) and Colo320 cell models.

RESULTS

The ¹ H-NMR study of crude fractions and application of a straightforward method to remove chlorophylls, allowed the effortless isolation of two lathyrane-type diterpenes in large amounts, including the new polyester, euphoboetirane B (1). Taking advantage of the chemical functions of 1, 13 new derivatives were prepared. Several compounds showed to be promising modulators of P-glycoprotein (P-gp), in resistant cancer cells. Most of the compounds tested revealed to interact synergistically with doxorubicin.

CONCLUSION

These results corroborate the importance of macrocyclic lathyrane diterpenes as effective lead compounds for the reversal of MDR.

Role of Four ABC Transporter Genes in Pharmacogenetic Susceptibility to Breast Cancer in Jordanian Patients

Breast cancer pharmacogenetics is increasingly being explored due to chemotherapy resistance among certain classes of patients. The ATP binding cassette (ABC) transporter genes have been previously implicated in breast cancer progression and drug response. In the present study, single nucleotide polymorphisms (SNPs) from the ABCC1, ABCC2, ABCB1, and ABCG2 genes were screened in breast cancer patients and healthy volunteers from the Jordanian-Arab population. Only the ABCB1 SNPs showed a significant association with BC in Jordanian-Arab patients, and the ABCB1 SNP rs2032582 exhibited a strong genotypic association with BC. With regard to the clinical characteristics of BC, the ABCC2 SNPs rs2273697 and rs717620 were found to be significantly associated with age at breast cancer diagnosis and breastfeeding status, while the ABCB1 SNP rs1045642 was significantly associated with age at breast cancer diagnosis. In terms of pathological characteristics, the ABCC1 SNP rs35628 and the ABCB1 SNP rs2032582 were significantly associated with tumor size, the ABCC2 SNP rs2273697 was significantly associated with estrogen receptor status, and the ABCG2 SNP rs2231142 was significantly associated with axillary lymph node status. In this current study, we assume that significant genetic variants within the ABC superfamily may increase the risk of breast cancer among Jordanian women. Furthermore, these variants might be responsible for worse BC prognosis.

Tackling drug resistance with efflux pump inhibitors: from bacteria to cancerous cells

Drug resistance is a serious concern in a clinical setting jeopardizing treatment for both infectious agents and cancers alike. The wide-spread emergence of multi-drug resistant (MDR) phenotypes from bacteria to cancerous cells necessitates the need to target resistance mechanisms and prevent the emergence of resistant mutants. Drug efflux seems to be one of the preferred approaches embraced by both microbial and mammalian cells alike, to thwart the action of chemotherapeutic agents thereby leading to a drug resistant phenotype. Relative to microbes, which predominantly employs proton motive force (PMF) powered, Major Facilitator Superfamily (MFS)/Resistance Nodulation and Division (RND) classes of efflux pumps to efflux drugs, cancerous cells preferentially use ATP fuelled ATP binding cassette (ABC) transporters to extrude chemotherapeutic agents. The prevalence, evolutionary characteristics and overlapping functions of ABC transporters have been highlighted in this review. Additionally, we outline the role of ABC pumps in conferring MDR phenotype to both bacteria and cancerous cells and underscore the importance of efflux pump inhibitors (EPI) to mitigate drug resistance. Based on the literature reports and analysis, we reason out feasibility of employing bacteria as a tool to screen for EPI's targeting ABC pumps of cancerous cells.

ATP binding cassette subfamily B member 9 (ABCB9) is a prognostic indicator of overall survival in ovarian cancer

Ovarian cancer (OC) is one of the most common gynecological malignancies and owns the highest mortality rate among all gynecological malignant tumors. ATP binding cassette subfamily B member 9 (ABCB9) is an antigen processing-like (TAPL) transporter that has been found to be involved in the development and progression of various malignant tumors in accumulating reports. However, the potential role of ABCB9 in OC has never been reported.In this study, ABCB9 expression was evaluated in normal ovarian tissues and ovarian cancer tissues using The Cancer Genome Atlas (TCGA) database. And the associations between ABCB9 expression and clinical parameters of patients of OC were evaluated by Chi-square tests. Kaplan-Meier analysis and Cox regression analysis were performed to evaluate the prognostic significance of ABCB9. GSEA was performed to explore related signaling pathway.ABCB9 expression levels were significantly decreased in OC compared with normal ovarian tissues (P < .001). Low ABCB9 expression was associated with survival status (P = .0148) in OC. Kaplan-Meier analysis showed that low ABCB9 expression was associated with poor overall survival in OC (P = .0032). Multivariable Cox regression analysis indicated that low ABCB9 expression was an independent prognostic factor (HR 0.64; P = .01) in OC patients. Besides, epithelial mesenchymal transition, UV response, and TGF-β signaling were enriched in low ABCB9 expression phenotype, respectively, examined by gene set enrichment analysis.These results suggest that ABCB9 is an independent prognostic indicator in OC with certain clinical significance.

In vitro modulation of multidrug resistance by pregnane steroids and in vivo inhibition of tumour development by 7α-OBz-11α(R)-OTHP-5β-pregnanedione in K562/R7 and H295R cell xenografts

Synthetic progesterone and 5α/β-pregnane-3,20-dione derivatives were evaluated as in vitro and in vivo modulators of multidrug-resistance (MDR) using two P-gp-expressing human cell lines, the non-steroidogenic K562/R7 erythroleukaemia cells and the steroidogenic NCI-H295R adrenocortical carcinoma cells, both resistant to doxorubicin. The maximal effect in both cell lines was observed for 7α-O-benzoyloxy,11α(R)-O-tetrahydropyranyloxy-5β-pregnane-3,20-dione 4. This modulator co-injected with doxorubicin significantly decreased the tumour size and increased the survival time of immunodeficient mice xenografted with NCI-H295R or K562/R7 cells.

Structural Simplification of Natural Products

Natural products (NPs) are important sources of clinical drugs due to their structural diversity and biological prevalidation. However, the structural complexity of NPs leads to synthetic difficulties, unfavorable pharmacokinetic profiles, and poor drug-likeness. Structural simplification by truncating unnecessary substructures is a powerful strategy for overcoming these limitations and improving the efficiency and success rate of NP-based drug development. Herein, we will provide a comprehensive review of the structural simplification of NPs with a focus on design strategies, case studies, and new technologies. In particular, a number of successful examples leading to marketed drugs or drug candidates will be discussed in detail to illustrate how structural simplification is applied in lead optimization of NPs.

Nitric oxide reverses drug resistance by inhibiting ATPase activity of p-glycoprotein in human multi-drug resistant cancer cells

BACKGROUND

Development of resistance to chemotherapy drugs is a significant problem in treating human malignancies in the clinic. Overexpression of drug efflux proteins, including P-170 glycoprotein (P-gp), an ATP-dependent efflux protein, is one of the main mechanisms responsible for multi-drug resistance (MDR). Because our previous studies have shown that nitric oxide (˙NO) or its related species inhibit the ATPase activities of topoisomerase II, we hypothesized that ˙NO should also inhibit the ATPase activity of P-gp and increase drug accumulation in MDR cells, causing a reversal of drug resistance.

RESULTS

Cytotoxicity and cellular accumulation studies showed that ˙NO significantly inhibited the ATPase activity of P-gp in isolated membranes and in NCI/ADR-RES tumor cells, causing an increase in drug accumulation and reversals of adriamycin and taxol resistance in the MDR cells. While ˙NO had no effects on topoisomerase II-induced, adriamycin-dependent DNA cleavage complex formation, it significantly inhibited adriamycin-induced DNA double-strand breaks. Electron spin resonance studies showed an increase in adriamycin-dependent hydroxyl radical formation in the presence of an NO-donor.

CONCLUSIONS

The reversal of drug resistance is due to inhibition of the ATPase activity by ˙NO, resulting in enhancement of the drug accumulation in the MDR cells. Furthermore, DNA damage was not responsible for this reversal of adriamycin resistance. However, formation of adriamycin-dependent toxic free radical species and subsequent cellular damage may be responsible for the increased cytotoxicity of adriamycin by ˙NO in NCI/ADR-RES cells.

GENERAL SIGNIFICANCE

Appropriately designed NO donors would be ideal for the treatment of P-gp-overexpressing tumors in the clinic.

Hepatoprotective effect of ginsenoside Rg1 from Panax ginseng on carbon tetrachloride-induced acute liver injury by activating Nrf2 signaling pathway in mice

Oxidative stress and inflammatory response are well known to be involved in the pathogenesis of acute liver injury. This study was performed to examine the hepatoprotective effect of ginsenoside Rg1 (Rg1) against CCl4 -induced acute liver injury, and further to elucidate the involvement of Nrf2 signaling pathway in vivo and in vitro. Mice were orally administered Rg1 (15, 30, and 60 mg/kg) or sulforaphane (SFN) once daily for 1 week prior to 750 μL/kg CCl4 injection. The results showed that Rg1 markedly altered relative liver weights, promoted liver repair, increased the serum level of TP and decreased the serum levels of ALT, AST and ALP. Hepatic oxidative stress was inhibited by Rg1, as evidenced by the decrease in MDA, and increases in GSH, SOD, and CAT in the liver. Further research demonstrated that Rg1 suppressed liver inflammation response through repressing the expression levels of inflammation-related genes including TNF-α, IL-1β, IL-6, COX-2, and iNOS. In addition, Rg1 enhanced antioxidative stress and liver detoxification abilities by up-regulating Nrf2 and its target-genes such as GCLC, GCLM, HO-1, NQO1, Besp, Mrp2, Mrp3, Mrp4, and down-regulating Cyp2e1. However, the changes in Nrf2 target-genes, as well as ameliorative liver histology induced by Rg1 were abrogated by Nrf2 antagonist all-transretinoic acid in vivo and Nrf2 siRNA in vitro. Overall, the findings indicated that Rg1 might be an effective approach for the prevention against acute liver injury by activating Nrf2 signaling pathway.

Augmented anticancer activity of naringenin-loaded TPGS polymeric nanosuspension for drug resistive MCF-7 human breast cancer cells

Naringenin (NAR) is a naturally occurring plant flavonoid, found predominantly in citrus fruits, possesses a wide range of pharmacological properties. However, despite the therapeutic potential of NAR, its clinical development has been hindered due to low aqueous solubility and inefficient transport across biological membranes resulting in low bioavailability at tumor sites. In our previous studies, nanosuspension of naringenin (NARNS) was prepared using high pressure homogenization method using different polymers. D-α-Tocopheryl polyethylene glycol succinate 1000 (TPGS) was added as a co-stabilizer. All formulation characterization studies were performed. As a continuation of our previous research, current study has further evaluated the ability of the TPGS-coated NARNS, to reverse drug-resistance of P-gp-over expressing MCF-7 human breast adenocarcinoma cell line and animal model. MTT-based colorimetric assay revealed higher cytotoxic efficacy of NARNS than free NAR in MCF-7 cells. NARNS treatment significantly increased intracellular ROS level, mitochondrial membrane potential, caspase-3 activity, lipid peroxidation status (TBARS) and decreased GSH levels when compared to free NAR treatment in MCF-7 cells. It has been also noticed that the presence of apoptotic indices (membrane blebbing, nuclear fragmentation) in NARNS treated cancer cells. Further, NARNS exhibited dose-dependent in vitro antitumor activity with DLA cells. A significant increase in the life span and a decrease in the cancer cell number and tumor weight were noted in the tumor-induced mice after treatment with NARNS.

Fenbendazole acts as a moderate microtubule destabilizing agent and causes cancer cell death by modulating multiple cellular pathways

Drugs that are already clinically approved or experimentally tested for conditions other than cancer, but are found to possess previously unrecognized cytotoxicity towards malignant cells, may serve as fitting anti-cancer candidates. Methyl N-(6-phenylsulfanyl-1H benzimidazol-2-yl) carbamate [Fenbendazole, FZ], a benzimidazole compound, is a safe and inexpensive anthelmintic drug possessing an efficient anti-proliferative activity. In our earlier work, we reported a potent growth-inhibitory activity of FZ caused partially by impairment of proteasomal function. Here, we show that FZ demonstrates moderate affinity for mammalian tubulin and exerts cytotoxicity to human cancer cells at micromolar concentrations. Simultaneously, it caused mitochondrial translocation of p53 and effectively inhibited glucose uptake, expression of GLUT transporters as well as hexokinase (HK II) - a key glycolytic enzyme that most cancer cells thrive on. It blocked the growth of human xenografts in nu/nu mice model when mice were fed with the drug orally. The results, in conjunction with our earlier data, suggest that FZ is a new microtubule interfering agent that displays anti-neoplastic activity and may be evaluated as a potential therapeutic agent because of its effect on multiple cellular pathways leading to effective elimination of cancer cells.

ATP-binding cassette transporters in progression and clinical outcome of pancreatic cancer: What is the way forward?

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive diseases and is characterized by high chemoresistance, leading to the lack of effective therapeutic approaches and grim prognosis. Despite increasing understanding of the mechanisms of chemoresistance in cancer and the role of ATP-binding cassette (ABC) transporters in this resistance, the therapeutic potential of their pharmacological inhibition has not been successfully exploited yet. In spite of the discovery of potent pharmacological modulators of ABC transporters, the results obtained in clinical trials have been so far disappointing, with high toxicity levels impairing their successful administration to the patients. Critically, although ABC transporters have been mostly studied for their involvement in development of multidrug resistance (MDR), in recent years the contribution of ABC transporters to cancer initiation and progression has emerged as an important area of research, the understanding of which could significantly influence the development of more specific and efficient therapies. In this review, we explore the role of ABC transporters in the development and progression of malignancies, with focus on PDAC. Their established involvement in development of MDR will be also presented. Moreover, an emerging role for ABC transporters as prognostic tools for patients' survival will be discussed, demonstrating the therapeutic potential of ABC transporters in cancer therapy.

Doxorubicin-conjugated dexamethasone induced MCF-7 apoptosis without entering the nucleus and able to overcome MDR-1-induced resistance

Background

Doxorubicin (DOX) is the most widely used chemotherapeutic agent that has multimodal cytotoxicity. The main cytotoxic actions of DOX occur in the nucleus. The emergence of drug-resistant cancer cells that have the ability to actively efflux DOX out of the nucleus, and the cytoplasm has led to the search for a more effective derivative of this drug.

Materials and methods

We created a new derivative of DOX that was derived via simple conjugation of the 3' amino group of DOX to the dexamethasone molecule.

Results

Despite having a lower cytotoxic activity in MCF-7 cells, the conjugated product, DexDOX, exerted its actions in a manner that was different to that of DOX. DexDOX rapidly induced MCF-7 cell apoptosis without entering the nucleus. Further analysis showed that Dex-DOX increased cytosolic oxidative stress and did not interfere with the cell cycle. In addition, the conjugated product retained its cytotoxicity in multidrug resistance-1-overexpressing MCF-7 cells that had an approximately 16-fold higher resistance to DOX.

Conclusion

We have synthesized a new derivative of DOX, which has the ability to overcome multidrug resistance-1-induced resistance. This molecule may have potential as a future chemotherapeutic agent.

Delivery of siRNA in vitro and in vivo using PEI-capped porous silicon nanoparticles to silence MRP1 and inhibit proliferation in glioblastoma

BACKGROUND

Multidrug resistance-associated protein 1 (MRP1) overexpression plays a major role in chemoresistance in glioblastoma multiforme (GBM) contributing to its notorious deadly nature. Although MRP1-siRNA transfection to GBM in vitro has been shown to sensitise the cells to drug, MRP1 silencing in vivo and the phenotypic influence on the tumour and normal tissues upon MRP1 down-regulation have not been established. Here, porous silicon nanoparticles (pSiNPs) that enable high-capacity loading and delivery of siRNA are applied in vitro and in vivo.

RESULT

We established pSiNPs with polyethyleneimine (PEI) capping that enables high-capacity loading of siRNA (92 µg of siRNA/mg PEI-pSiNPs), and optimised release profile (70% released between 24 and 48 h). These pSiNPs are biocompatible, and demonstrate cellular uptake and effective knockdown of MRP1 expression in GBM by 30%. Also, siRNA delivery was found to significantly reduce GBM proliferation as an associated effect. This effect is likely mediated by the attenuation of MRP1 transmembrane transport, followed by cell cycle arrest. MRP1 silencing in GBM tumour using MRP1-siRNA loaded pSiNPs was demonstrated in mice (82% reduction at the protein level 48 h post-injection), and it also produced antiproliferative effect in GBM by reducing the population of proliferative cells. These results indicate that in vitro observations are translatable in vivo. No histopathological signs of acute damage were observed in other MRP1-expressing organs despite collateral downregulations.

CONCLUSIONS

This study proposes the potential of efficient MRP1-siRNA delivery by using PEI-capped pSiNPs in achieving a dual therapeutic role of directly attenuating the growth of GBM while sensitising residual tumour cells to the effects of chemotherapy post-resection.

AP-2α reverses vincristine-induced multidrug resistance of SGC7901 gastric cancer cells by inhibiting the Notch pathway

Multidrug resistance (MDR) remains a major clinical obstacle in the treatment of gastric cancer (GC) since it causes tumor recurrence and metastasis. The transcription factor activator protein-2α (AP-2α) has been implicated in drug-resistance in breast cancer; however, its effects on MDR of gastric cancer are far from understood. In this study, we aimed to explore the effects of AP-2α on the MDR in gastric cancer cells selected by vincristine (VCR). Decreased AP-2α levels were markedly detected by RT-PCR and Western blot in gastric cancer cell lines (BGC-823, SGC-7901, AGS, MKN-45) compared with that in the gastric epithelial cell line (GES-1). Furthermore, we found that the expression of AP-2α in SGC7901/VCR or SGC7901/adriamycin (ADR) cells was lower than in SGC7901 cells. Thus, a vector overexpressing AP-2α was constructed and used to perform AP-2α gain-of-function studies in SGC7901/VCR cells. The decreased IC50 values of the anti-cancer drugs in sensitive and resistant cells after transfect with pcDNA3.1/AP-2α were determined in SGC7901/VCR cells by MTT assay. Moreover, flow cytometry analysis indicated that overexpressed AP-2α induced cell cycle arrest in the G0/G1 phase and promoted cell apoptosis of VCR-selected SGC7901/VCR cells. RT-PCR and Western blot demonstrated that overexpressed AP-2α can significantly induce the down-regulation of Notch1, Hes-1, P-gp and MRP1 in SGC7901/VCR cells. Similar effects can be observed when Numb (Notch inhibitor) was introduced. In addition, the intracellular ADR accumulation was markedly detected in AP-2α overexpressed or Numb cells. In conclusion, our results indicate that AP-2α can reverse the MDR of gastric cancer cells, which may be realized by inhibiting the Notch signaling pathway.

microRNA-125b reverses the multidrug resistance of nasopharyngeal carcinoma cells via targeting of Bcl-2

Multidrug resistance (MDR) is a major clinical obstacle in the successful treatment of patients with metastatic nasopharyngeal carcinoma (NPC). Results from previous studies suggest that microRNAs (miRNA) may be involved in promoting MDR in multiple cancer types. However, the role of miR‑125b in modulating the MDR of NPC is elusive. In the present study, miR‑125b expression in cisplatin (DDP) ‑resistant CNE2 cells (CNE2/DDP) was compared with parental counterparts, using reverse transcription‑quantitative polymerase chain reaction. A >3‑fold reduction in miR‑125b expression levels was observed in CNE2/DDP cells compared with parental CNE2 cells. Ectopic expression of miR‑125b by transfecting CNE2/DDP cells with miR-125b mimics, increased DDP‑induced cytotoxicity, apoptosis and chemosensitivity. By contrast, suppression of miR-125b by transfecting CNE2 cells with miR‑125b inhibitors, reduced DDP‑induced cytotoxicity and apoptosis, and facilitated cisplatin resistance. The results suggest that miR‑125b may regulate the sensitivity of NPC cells to DDP by modulating the expression levels of antiapoptotic factor B-cell CLL/lymphoma 2. Collectively, the results of the present study highlight miR‑125b as a potential therapeutic target for reversing MDR in NPC.

Novel 5-oxo-hexahydroquinoline derivatives: design, synthesis, in vitro P-glycoprotein-mediated multidrug resistance reversal profile and molecular dynamics simulation study

Overexpression of the efflux pump P-glycoprotein (P-gp) is one of the important mechanisms of multidrug resistance (MDR) in many tumor cells. In this study, 26 novel 5-oxo-hexahydroquinoline derivatives containing different nitrophenyl moieties at C₄ and various carboxamide substituents at C₃ were designed, synthesized and evaluated for their ability to inhibit P-gp by measuring the amount of rhodamine 123 (Rh123) accumulation in uterine sarcoma cells that overexpress P-gp (MES-SA/Dx5) using flow cytometry. The effect of compounds with highest MDR reversal activities was further evaluated by measuring the alterations of MES-SA/Dx5 cells’ sensitivity to doxorubicin (DXR) using MTT assay. The results of both biological assays indicated that compounds bearing 2-nitrophenyl at C₄ position and compounds with 4-chlorophenyl carboxamide at C₃ demonstrated the highest activities in resistant cells, while they were devoid of any effect in parental nonresistant MES-SA cells. One of the active derivatives, 5c, significantly increased intracellular Rh123 at 100 µM, and it also significantly reduced the IC₅₀ of DXR by 70.1% and 88.7% at 10 and 25 µM, respectively, in MES-SA/Dx5 cells. The toxicity of synthesized compounds against HEK293 as a noncancer cell line was also investigated. All tested derivatives except for 2c compound showed no cytotoxicity. A molecular dynamics simulation study was also performed to investigate the possible binding site of 5c in complex with human P-gp, which showed that this compound formed 11 average H-bonds with Ser909, Thr911, Arg547, Arg543 and Ser474 residues of P-gp. A good agreement was found between the results of the computational and experimental studies. The findings of this study show that some 5-oxo-hexahydroquinoline derivatives could serve as promising candidates for the discovery of new agents for P-gp-mediated MDR reversal.

Nogo-B receptor promotes the chemoresistance of human hepatocellular carcinoma via the ubiquitination of p53 protein

Nogo-B receptor (NgBR), a type I single transmembrane domain receptor is the specific receptor for Nogo-B. Our previous work demonstrated that NgBR is highly expressed in breast cancer cells, where it promotes epithelial mesenchymal transition (EMT), an important step in metastasis. Here, we show that both in vitro and in vivo increased expression of NgBR contributes to the increased chemoresistance of Bel7402/5FU cells, a stable 5-FU (5-Fluorouracil) resistant cell line related Bel7402 cells. NgBR knockdown abrogates S-phase arrest in Bel7402/5FU cells, which correlates with a reduction in G1/S phase checkpoint proteins p53 and p21. In addition, NgBR suppresses p53 protein levels through activation of the PI3K/Akt/MDM2 pathway, which promotes p53 degradation via the ubiquitin proteasome pathway and thus increases the resistance of human hepatocellular cancer cells to 5-FU. Furthermore, we found that NgBR expression is associated with a poor prognosis of human hepatocellular carcinoma (HCC) patients. These results suggest that targeting NgBR in combination with chemotherapeutic drugs, such as 5-FU, could improve the efficacy of current anticancer treatments.

Reversal effect of ouabain on multidrug resistance in esophageal carcinoma EC109/CDDP cells by inhibiting the translocation of Wnt/β-catenin into the nucleus

The incidence of esophageal carcinoma is increasing throughout the world. A major obstacle to its treatment is acquired multidrug resistance (MDR) which results in the failure of chemotherapy and patient relapse. Here, we identified that ouabain is capable of reversing MDR to cisplatin (CDDP) in EC109/CDDP cells and explore the possible mechanisms of action. The parental and the MDR cell lines were both sensitive to ouabain with 50 % inhibitory concentration (IC50) values of 258.11 and 710.63 nM, respectively. Cisplatin cytotoxicity increased in the EC109/CDDP cells by the addition of ouabain which helps promote CDDP-induced apoptosis. Ouabain at 20 nM effectively reduced the IC50 of CDDP in EC109/CDDP cells from 36.54 to 3.39 μM. This represents a 10.78-fold increase in sensitization to CDDP. We also found that ouabain was capable of down regulating the expression of P-glycoprotein (P-gp) and Bcl-2 in a dose- and time-dependent manner. Finally, the results indicated that ouabain suppressed Wnt luciferase report (TOPFlash) activity obviously in EC109/CDDP and depressed the translocation of β-catenin into the nucleus. Moreover, ouabain showed reversal effect of MDR to CDDP in nude mouse xenograft model, and reduced the protein level of β-catenin (Y333) in tumor tissue of CDDP plus ouabain group. All data proved that ouabain has a potent β-catenin-dependent anti-MDR effect.

Extending the structure-activity relationship study of marine natural ningalin B analogues as P-glycoprotein inhibitors

In the present study, a total of 25 novel ningalin B analogues were synthesized and evaluated for their P-gp modulating activity in a P-gp overexpressed breast cancer cell line LCC6MDR. Preliminary structure-activity study shows that A ring and its two methoxy groups are important pharmacophores for P-gp inhibiting activity. Among all derivatives, 23 is the most potent P-gp modulator with EC₅₀ of 120-165 nM in reversing paclitaxel, DOX, vinblastine and vincristine resistance. It is relatively safe to use with selective index at least greater than 606 compared to verapamil. Mechanistic study demonstrates that compound 23 reverses P-gp mediated drug resistance by inhibiting transport activity of P-gp, thereby restoring intracellular drug accumulation. In summary, our study demonstrates that ningalin B analogue 23 is a non-cytotoxic and effective P-gp chemosensitizer that can be used in the future for reversing P-gp mediated clinical cancer drug resistance.

Computational predictive models for P-glycoprotein inhibition of in-house chalcone derivatives and drug-bank compounds

The human P-glycoprotein (P-gp) efflux pump is of great interest for medicinal chemists because of its important role in multidrug resistance (MDR). Because of the high polyspecificity as well as the unavailability of high-resolution X-ray crystal structures of this transmembrane protein, ligand-based, and structure-based approaches which were machine learning, homology modeling, and molecular docking were combined for this study. In ligand-based approach, individual two-dimensional quantitative structure-activity relationship models were developed using different machine learning algorithms and subsequently combined into the Ensemble model which showed good performance on both the diverse training set and the validation sets. The applicability domain and the prediction quality of the developed models were also judged using the state-of-the-art methods and tools. In our structure-based approach, the P-gp structure and its binding region were predicted for a docking study to determine possible interactions between the ligands and the receptor. Based on these in silico tools, hit compounds for reversing MDR were discovered from the in-house and DrugBank databases through virtual screening using prediction models and molecular docking in an attempt to restore cancer cell sensitivity to cytotoxic drugs.