Selective toxicity of NSC73306 in MDR1-positive cells as a new strategy to circumvent multidrug resistance in cancer

New immunomodulatory anticancer quinazolinone-based thalidomide analogs: design, synthesis and biological evaluation

Aim: The current work is an extension to our previous work for the development of new thalidomide analogs.Materials & methods: Quinazolinone-based molecules carrying a glutarimide moiety have been designed, synthesized and biologically evaluated for immunomodulatory and anticancer activity.Results: Compounds 7d and 12 showed considerable immunomodulatory properties in comparison to thalidomide. 7d and 12 significantly reduced TNF-α levels in HepG-2 cells from 162.5 to 57.4 pg/ml and 49.2 pg/ml, respectively, compared with 53.1 pg/ml reported for thalidomide. Moreover, they caused 69.33 and 77.74% reduction in NF-κB P65, respectively, compared with 60.26% reduction for thalidomide. Similarly, they reduced VEGF from 432.5 to 161.3 pg/ml and 132.8 pg/ml, respectively, in comparison to 153.2 pg/ml reported for thalidomide. The two new derivatives, 7d and 12 also showed about eightfold increases in caspase-8 levels in cells treated with them. These results were slightly better than those of thalidomide. The obtained results revealed that Compound 12 had better immunomodulatory properties than thalidomide, with stronger effects on TNF-α, NF-κB P65, VEGF and caspase-8.Conclusion: This work indicates that compounds 7d and 12 have interesting biological properties that should be further evaluated and modified in order to develop clinically useful thalidomide analogs.

Discovery of Potent Isoquinolinequinone N-Oxides to Overcome Cancer Multidrug Resistance

Multidrug resistance (MDR) of human tumors has resulted in an immediate need to develop appropriate new drugs. This work outlines the development of 20 potent IQQ N-oxide derivatives in two isomeric families, both exhibiting nanomolar GI50 against human tumor cell lines. Preliminary NCI-60 tumor screening sees the C(6) isomers achieve a mean GI50 > 2 times lower than the corresponding C(7) isomers. MDR evaluation of nine selected compounds reveals that each presents lower GI50 concentrations in two MDR tumor cell lines. Four of the series display nanomolar GI50 values against MDR cells, having selectivity ratios up to 2.7 versus the sensitive (parental) cells. The most potent compound 25 inhibits the activity of drug efflux pumps in MDR cells, causes significant ROS accumulation, and potently inhibits cell proliferation, causing alterations in the cell cycle profile. Our findings are confirmed by 3D spheroid models, providing new candidates for studies against MDR cancers.

Copper(II) Complexes with Isomeric Morpholine-Substituted 2-Formylpyridine Thiosemicarbazone Hybrids as Potential Anticancer Drugs Inhibiting Both Ribonucleotide Reductase and Tubulin Polymerization: The Morpholine Position Matters

The development of copper(II) thiosemicarbazone complexes as potential anticancer agents, possessing dual functionality as inhibitors of R2 ribonucleotide reductase (RNR) and tubulin polymerization by binding at the colchicine site, presents a promising avenue for enhancing therapeutic effectiveness. Herein, we describe the syntheses and physicochemical characterization of four isomeric proligands H2L3-H2L6, with the methylmorpholine substituent at pertinent positions of the pyridine ring, along with their corresponding Cu(II) complexes 3-6. Evidently, the position of the morpholine moiety and the copper(II) complex formation have marked effects on the in vitro antiproliferative activity in human uterine sarcoma MES-SA cells and the multidrug-resistant derivative MES-SA/Dx5 cells. Activity correlated strongly with quenching of the tyrosyl radical (Y•) of mouse R2 RNR protein, inhibition of RNR activity in the cancer cells, and inhibition of tubulin polymerization. Insights into the mechanism of antiproliferative activity, supported by experimental results and molecular modeling calculations, are presented.

Evaluation of anticancer activity of novel platinum(II) bis(thiosemicarbazone) complex against breast cancer

The study aims to synthesize a novel bis(thiosemicarbazone) derivative based on platinum (thioPt) and evaluate its anticancer properties against MFC-7 and MDA-MB-231 breast cancer cells. A new platinum complex was synthesised by reacting K2PtCl4 with 2,2'-(1,2-diphenylethane-1,2-diylidene)bis(hydrazine-1-carbothioamide) in ethanol in the presence of K2CO3. In the obtained complex, the platinum atom is coordinated by a conjugated system = N-NC-S-The structures of the new compound were characterised using NMR spectroscopy, HR MS, IR, and X-ray structural analysis. The obtained results of the cytotoxicity assay indicate that compound thioPt had potent anticancer activity (MCF-7: 61.03 ± 3.57 µM, MDA-MB-231: 60.05 ± 5.40 µM) with less toxicity against normal MCF-10A breast epithelial cells, even compared to the reference compound (cisplatin). In addition, subsequent experiments found that thioPt induces apoptosis through both an extrinsic (↑caspase 8 activity) and intrinsic (↓ΔΨm) pathway, which ultimately leads to an increase in active caspase 3/7 levels. The induction of autophagy and levels of proteins involved in this process (LC3A/B and Beclin-1) were examined in MCF-7 and MDA-MB-231 breast cancer cells exposed to tested compounds (thio, thioPt, cisPt) at a concentration of 50 µM for 24 h. Based on these results, it can be concluded that thio and thioPt do not significantly affect the autophagy process. This demonstrates their superiority over cisplatin, which can stimulate cancer cell survival through its effect on stimulation of autophagy.

Schiff bases and their metal complexes to target and overcome (multidrug) resistance in cancer

Overcoming multidrug resistance (MDR) is one of the major challenges in cancer therapy. In this respect, Schiff base-related compounds (bearing a R1R2CNR3 bond) gained high interest during the past decades. Schiff bases are considered privileged ligands for various reasons, including the easiness of their preparation and the possibility to form complexes with almost all transition metal ions. Schiff bases and their metal complexes exhibit many types of biological activities and are used for the treatment and diagnosis of various diseases. Until now, 13 Schiff bases have been investigated in clinical trials for cancer treatment and hypoxia imaging. This review represents the first collection of Schiff bases and their complexes which demonstrated MDR-reversal activity. The areas of drug resistance covered in this article involve: 1) Modulation of ABC transporter function, 2) Targeting lysosomal ABCB1 overexpression, 3) Circumvention of ABC transporter-mediated drug efflux by alternative routes of drug uptake, 4) Selective activity against MDR cancer models (collateral sensitivity), 5) Targeting GSH-detoxifying systems, 6) Overcoming apoptosis resistance by inducing necrosis and paraptosis, 7) Reactivation of mutated p53, 8) Restoration of sensitivity to DNA-damaging anticancer therapy, and 9) Overcoming drug resistance through modulation of the immune system. Through this approach, we would like to draw attention to Schiff bases and their metal complexes representing highly interesting anticancer drug candidates with the ability to overcome MDR.

ABCB1-dependent collateral sensitivity of multidrug-resistant colorectal cancer cells to the survivin inhibitor MX106-4C

AIMS

To investigate the collateral sensitivity (CS) of ABCB1-positive multidrug resistant (MDR) colorectal cancer cells to the survivin inhibitor MX106-4C and the mechanism.

METHODS

Biochemical assays (MTT, ATPase, drug accumulation/efflux, Western blot, RT-qPCR, immunofluorescence, flow cytometry) and bioinformatic analyses (mRNA-sequencing, reversed-phase protein array) were performed to investigate the hypersensitivity of ABCB1 overexpressing colorectal cancer cells to MX106-4C and the mechanisms. Synergism assay, long-term selection, and 3D tumor spheroid test were used to evaluate the anti-cancer efficacy of MX106-4C.

RESULTS

MX106-4C selectively killed ABCB1-positive colorectal cancer cells, which could be reversed by an ABCB1 inhibitor, knockout of ABCB1, or loss-of-function ABCB1 mutation, indicating an ABCB1 expression and function-dependent mechanism. MX106-4C's selective toxicity was associated with cell cycle arrest and apoptosis through ABCB1-dependent survivin inhibition and activation on caspases-3/7 as well as modulation on p21-CDK4/6-pRb pathway. MX106-4C had good selectivity against ABCB1-positive colorectal cancer cells and retained this in multicellular tumor spheroids. In addition, MX106-4C could exert a synergistic anti-cancer effect with doxorubicin or re-sensitize ABCB1-positive cancer cells to doxorubicin by reducing ABCB1 expression in the cell population via long-term exposure.

CONCLUSIONS

MX106-4C selectively kills ABCB1-positive MDR colorectal cancer cells via a novel ABCB1-dependent survivin inhibition mechanism, providing a clue for designing CS compound as an alternative strategy to overcome ABCB1-mediated colorectal cancer MDR.

Fighting Multidrug Resistance with Ruthenium-Cyclopentadienyl Compounds: Unveiling the Mechanism of P-gp Inhibition

The search for more effective and selective drugs to overcome cancer multidrug resistance is urgent. As such, a new series of ruthenium-cyclopentadienyl ("RuCp") compounds with the general formula [Ru(η5-C5H4R)(4,4'-R'-2,2'-bipy)(PPh3)] were prepared and fully characterized. All compounds were evaluated toward non-small cell lung cancer cells with different degrees of cisplatin sensitivity (A549, NCI-H2228, Calu-3, and NCI-H1975), showing better cytotoxicity than the first-line chemotherapeutic drug cisplatin. Compounds 2 and 3 (R' = -OCH3; R = CHO (2) or CH2OH (3)) further inhibited the activity of P-gp and MRP1 efflux pumps by impairing their catalytic activity. Molecular docking calculations identified the R-site P-gp pocket as the preferred one, which was further validated using site-directed mutagenesis experiments in P-gp. Altogether, our results unveil the first direct evidence of the interaction between P-gp and "RuCp" compounds in the modulation of P-gp activity and establish them as valuable candidates to circumvent cancer MDR.

Green synthesis, anti-proliferative evaluation, docking, and MD simulations studies of novel 2-piperazinyl quinoxaline derivatives using hercynite sulfaguanidine-SA as a highly efficient and reusable nanocatalyst

In this study, the immobilization of sulfaguanidine-SA on the surface of FeAl2O4 (hercynite) MNPs (magnetic nanoparticles) as a novel acid nanocatalyst has been successfully reported for the synthesis of 2-(piperazin-1-yl) quinoxaline derivatives via a one-pot multiple-component reaction under green conditions. The products were characterized by SEM, TEM, TGA, EDS, BET technique, VSM, and FTIR. This series of novel 2-piperazinyl quinoxaline derivatives containing isatin-based thio/semicarbazones and/or Schiff bases of Metformin were evaluated for anticancer activity against both human ovarian and colon-derived tumor cell lines by MTT colorimetric assay. Although most of the investigated hybrid compounds exhibited excellent anti-proliferative activities and high selectivity index (SI) values, the promising compounds N'-[4-(quinoxaline-2-yl)-piperazine-1-yl]methyl-5-chloro-1-H-indole,2,3-dion-3-metformin 4c and N'-[4-(quinoxaline-2-yl)-piperazine-1-yl]methyl-5-bromo-1-H-indole,2,3-dion-3-metformin 4b proved to be the most potent anti-proliferative agents (IC50 values < 1 μM). Molecular docking and dynamics simulation suggest that these hybrid compounds can be wrapped in the catalytic cavity of c-Kit tyrosine kinase receptor and the binding pocket of P-glycoprotein with high scores. Thus, 2-piperazinyl quinoxaline linked isatin-based N-Mannich bases of metformin and/or thio/semicarbazones might be served as suitable candidates for further investigations to develop a new generation of multi-target cancer chemotherapy agents.

The anti-estrogen receptor drug, tamoxifen, is selectively Lethal to P-glycoprotein-expressing Multidrug resistant tumor cells

BACKGROUND

P-glycoprotein (P-gp), a member of the ATP Binding Cassette B1 subfamily (ABCB1), confers resistance to clinically relevant anticancer drugs and targeted chemotherapeutics. However, paradoxically P-glycoprotein overexpressing drug resistant cells are "collaterally sensitive" to non-toxic drugs that stimulate its ATPase activity.

METHODS

Cell viability assays were used to determine the effect of low concentrations of tamoxifen on the proliferation of multidrug resistant cells (CHO^RC5 and MDA-Doxo⁴⁰⁰), expressing P-gp, their parental cell lines (AuxB1 and MDA-MB-231) or P-gp-CRISPR knockout clones of AuxB1 and CHO^RC5 cells. Western blot analysis was used to estimate P-gp expression in different cell lines. Apoptosis of tamoxifen-induced cell death was estimated by flow cytometry using Annexin-V-FITC stained cells. Oxidative stress of tamoxifen treated cells was determined by measuring levels of reactive oxygen species and reduced thiols using cell-permeant 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) and 5,5-dithio-bis-(2-nitrobenzoic acid) DTNB, respectively.

RESULTS

In this report, we show that P-gp-expressing drug resistant cells (CHO^RC5 and MDA-Doxo⁴⁰⁰) are collaterally sensitive to the anti-estrogen tamoxifen or its metabolite (4-hydroxy-tamoxifen). Moreover, P-gp-knockout clones of CHO^RC5 cells display complete reversal of collateral sensitivity to tamoxifen. Drug resistant cells exposed to low concentrations of tamoxifen show significant rise in reactive oxygen species, drop of reduced cellular thiols and increased apoptosis. Consistent with the latter, CHO^RC5 cells expressing high levels of human Bcl-2 (CHO^RC5-Bcl-2) show significant resistance to tamoxifen. In addition, the presence of the antioxidant N-acetylcysteine or P-gp ATPase inhibitor, PSC-833, reverse the collateral sensitivity of resistant cells to tamoxifen. By contrast, the presence of rotenone (specific inhibitor of mitochondria complex I) synergizes with tamoxifen.

CONCLUSION

This study demonstrates the use of tamoxifen as collateral sensitivity drug that can preferentially target multidrug resistant cells expressing P-gp at clinically achievable concentrations. Given the widespread use of tamoxifen in the treatment of estrogen receptor-positive breast cancers, this property of tamoxifen may have clinical applications in treatment of P-gp-positive drug resistant breast tumors.

Down-regulation of ABCB1 by Collateral Sensitivity Drugs Reverses Multidrug Resistance and Up-regulates Enolase I

The emergence of drug resistance remains an obstacle in the clinical treatment of cancer. Recent developments in the studies of drug resistance have identified compounds such as verapamil and tamoxifen that specifically target ABCB1-expressing multidrug resistant (MDR) cells, through an ATP-dependent ROS-generating mechanism. In this report, we demonstrate that treatment of ABCB1-expressing multidrug resistant cells (CHORC5 or MDA-Doxo400) or individual clones of the latter with sub-lethal concentrations of tamoxifen or verapamil down-regulates ABCB1 protein and mRNA expression in surviving clones. Consequently, tamoxifen- and verapamil-treated cells show increased sensitivity to chemotherapeutic drugs (e.g., colchicine and doxorubicin) and decreased sensitivity to collateral sensitivity drugs (e.g., verapamil and tamoxifen). Importantly, we show for the first time that down-regulation of ABCB1 expression resulting from tamoxifen treatment and CRISPR-knockout of ABCB1 expression up-regulate α-enolase (enolase I) protein levels and activity. These findings demonstrate a possible effect of ABCB1 expression on the metabolic homeostasis of MDR cells. Moreover, given the use of tamoxifen to prevent the recurrence of estrogen receptor-positive breast cancer, the findings of this study may be clinically important in modulating activity of other drugs.

Emerging on-chip electrokinetic based technologies for purification of circulating cancer biomarkers towards liquid biopsy: A review

Early detection of cancer can significantly reduce mortality and save lives. However, the current cancer diagnosis is highly dependent on costly, complex, and invasive procedures. Thus, a great deal of effort has been devoted to exploring new technologies based on liquid biopsy. Since liquid biopsy relies on detection of circulating biomarkers from biofluids, it is critical to isolate highly purified cancer-related biomarkers, including circulating tumor cells (CTCs), cell-free nucleic acids (cell-free DNA and cell-free RNA), small extracellular vesicles (exosomes), and proteins. The current clinical purification techniques are facing a number of drawbacks including low purity, long processing time, high cost, and difficulties in standardization. Here, we review a promising solution, on-chip electrokinetic-based methods, that have the advantage of small sample volume requirement, minimal damage to the biomarkers, rapid, and label-free criteria. We have also discussed the existing challenges of current on-chip electrokinetic technologies and suggested potential solutions that may be worthy of future studies.

The phenothiazine, trifluoperazine, is selectively lethal to ABCB1-expressing multidrug resistant cells

P-glycoprotein, member of the B-subfamily of the ATP-binding cassette (ABC) superfamily (e.g., ABCB1), has been demonstrated to confer resistance to clinically relevant anticancer drugs. Paradoxically, ABCB1-expressing multidrug resistant (MDR) cells are hypersensitivity or collateral sensitivity to non-toxic drugs. In this report, we demonstrate the capacity of trifluoperazine (TFP), a calmodulin inhibitor, to confer a collateral sensitivity onto ABCB1-overexpressing MDR cells. We show TFP-induced collateral sensitivity to be linked to ABCB1 expression and ATPase activity, as such phenotype is abolished in ABCB1-knockout MDR cells (CHO^RC5^ΔABCB1 clones A1-A3) or with inhibitors of ABCB1 ATPase. TFP-induced collateral sensitivity is mediated by apoptotic cell death, due to enhanced oxidative stress. The findings in this study show for first time the use TFP as a collateral sensitivity drug, at clinically relevant concentrations. Moreover, given the use of trifluoperazine in the treatment for symptoms of schizophrenia and the role of ABCB1 transporter in tissue blood barriers and other physiologic functions, the finding in this study may have implications beyond cancer chemotherapy.

Selective Cytotoxicity of Piperine Over Multidrug Resistance Leukemic Cells

Multidrug resistance (MDR) is the main challenge in the treatment of chronic myeloid leukemia (CML), and P-glycoprotein (P-gp) overexpression is an important mechanism involved in this resistance process. However, some compounds can selectively affect MDR cells, inducing collateral sensitivity (CS), which may be dependent on P-gp. The aim of this study was to investigate the effect of piperine, a phytochemical from black pepper, on CS induction in CML MDR cells, and the mechanisms involved. The results indicate that piperine induced CS, being more cytotoxic to K562-derived MDR cells (Lucena-1 and FEPS) than to K562, the parental CML cell. CS was confirmed by analysis of cell metabolic activity and viability, cell morphology and apoptosis. P-gp was partially required for CS induction. To investigate a P-gp independent mechanism, we analyzed the possibility that poly (ADP-ribose) polymerase-1 (PARP-1) could be involved in piperine cytotoxic effects. It was previously shown that only MDR FEPS cells present a high level of 24 kDa fragment of PARP-1, which could protect these cells against cell death. In the present study, piperine was able to decrease the 24 kDa fragment of PARP-1 in MDR FEPS cells. We conclude that piperine targets selectively MDR cells, inducing CS, through a mechanism that might be dependent or not on P-gp.

Relation of Metal-Binding Property and Selective Toxicity of 8-Hydroxyquinoline Derived Mannich Bases Targeting Multidrug Resistant Cancer Cells

Simple Summary

Effective treatment of cancer is often limited by the resistance of cancer cells to chemotherapy. A well-described mechanism supporting multidrug resistance (MDR) relies on the efflux of toxic drugs from cancer cells, mediated by P-glycoprotein (Pgp). Circumventing Pgp-mediated resistance is expected to make a significant contribution to improved therapy of malignancies. Interestingly, MDR cells exhibit paradoxical hypersensitivity towards a diverse set of anticancer chelators. In this study we explore the relation of chemical and structural properties influencing metal binding and toxicity of a set of 8-hydroxyquinoline derivatives to reveal key characteristics governing “MDR-selective” activity. We find that subtle changes in the stability and redox activity of the biologically relevant metal complexes significantly influence MDR-selective toxicity. Our results underline the importance of chelation in MDR-selective toxicity, suggesting that the collateral sensitivity of MDR cells may be targeted by preferential iron deprivation or the formation of redox-active copper(II) complexes.

Abstract

Resistance to chemotherapeutic agents is a major obstacle in cancer treatment. A recently proposed strategy is to target the collateral sensitivity of multidrug resistant (MDR) cancer. Paradoxically, the toxicity of certain metal chelating agents is increased, rather than decreased, by the function of P-glycoprotein (Pgp), which is known to confer resistance by effluxing chemotherapeutic compounds from cancer cells. We have recently characterized and compared the solution’s chemical properties including ligand protonation and the metal binding properties of a set of structurally related 8-hydroxyquinoline derived Mannich bases. Here we characterize the impact of the solution stability and redox activity of their iron(III) and copper(II) complexes on MDR-selective toxicity. Our results show that the MDR-selective anticancer activity of the studied 8-hydroxyquinoline derived Mannich bases is associated with the iron deprivation of MDR cells and the preferential formation of redox-active copper(II) complexes, which undergo intracellular redox-cycling to induce oxidative stress.

Overexpression of ABCB1 and ABCG2 contributes to reduced efficacy of the PI3K/mTOR inhibitor samotolisib (LY3023414) in cancer cell lines

LY3023414 (samotolisib) is a promising new dual inhibitor of phosphoinositide 3-kinase (PI3K) and mammalian target of rapamycin (mTOR). Currently, multiple clinical trials are underway to evaluate the efficacy of LY3023414 in patients with various types of cancer. However, the potential mechanisms underlying acquired resistance to LY3023414 in human cancer cells still remain elusive. In this study, we investigated whether the overexpression of ATP-binding cassette (ABC) drug transporters such as ABCB1 and ABCG2, one of the most common mechanisms for developing multidrug resistance, may potentially reduce the efficacy of LY3023414 in human cancer cells. We demonstrated that the intracellular accumulation of LY3023414 in cancer cells was significantly reduced by the drug efflux function of ABCB1 and ABCG2. Consequently, the cytotoxicity and efficacy of LY3023414 for inhibiting the activation of the PI3K pathway and induction of G0/G1 cell-cycle arrest were substantially reduced in cancer cells overexpressing ABCB1 or ABCG2, which could be restored using tariquidar or Ko143, respectively. Furthermore, stimulatory effect of LY3023414 on the ATPase activity of ABCB1 and ABCG2, as well as in silico molecular docking analysis of LY3023414 binding to the substrate-binding pockets of these transporters provided additional insight into the manner in which LY3023414 interacts with both transporters. In conclusion, we report that LY3023414 is a substrate for ABCB1 and ABCG2 transporters implicating their role in the development of resistance to LY3023414, which can have substantial clinical implications and should be further investigated.

Mycoplasma Infection Mediates Sensitivity of Multidrug-Resistant Cell Lines to Tiopronin: A Cautionary Tale

We previously reported that some, but not all, multidrug-resistant cells that overexpressed various drug-resistance transporters were collaterally sensitive to tiopronin. In recent follow-up studies, we discovered that sensitivity to tiopronin in the original study was mediated by infection of the cells by a human-specific strain of mycoplasma. These results strongly support the need to constantly monitor cells for mycoplasma infection and keep stored samples of all cells that are used for in vitro studies.

Recent advances in isatin hybrids as potential anticancer agents

The isatin framework is a useful template for the development of novel anticancer agents. This is exemplified by the fact that several isatin-based anticancer agents, such as semaxanib, sunitinib, nintedanib, and hesperadin, are already in use or under clinical trials for the treatment of diverse kinds of cancers. Isatin-based hybrids could be obtained by incorporating other anticancer pharmacophores into the isatin skeleton and they have the potential to overcome drug resistance with reduced side effects. Thus, isatin-based hybrids may provide attractive scaffolds for the development of novel anticancer agents. This review covers the recent advances of isatin-based hybrids with anticancer activity, covering articles published between 2001 and 2019. The anticancer activities of these molecules and the structure-activity relationships are also discussed. The purpose of this review article is to set up the direction for the design and development of isatin-based hybrids with high efficacy and low toxicity.

Thiosemicarbazone-metal complexes exhibiting cytotoxicity in colon cancer cell lines through oxidative stress

Colorectal cancer is the third most common type of cancer and has a high incidence in developed countries. At present, specific treatments are being required to allow individualized therapy depending on the molecular alteration on which the drug may act. The aim of this project is to evaluate whether HPTSC and HPTSC* thiosemicarbazones (HPTSC = pyridine-2-carbaldehyde thiosemicarbazone and HPTSC* = pyridine-2-carbaldehyde 4N-methylthiosemicarbazone), and their complexes with different transition metal ions as Cu(II), Fe(III) and Co(III), have antitumor activity in colon cancer cells (HT-29 and SW-480), that have different oncogenic characteristics. Cytotoxicity was evaluated and the involvement of oxidative stress in its mechanism of action was analyzed by quantifying the superoxide dismutase activity, redox state by quantification of the thioredoxin levels and reduced/oxidized glutathione rate and biomolecules damage. The apoptotic effect was evaluated by measurements of the levels of caspase 9 and 3 and the index of histones. All the metal-thiosemicarbazones have antitumor activity mediated by oxidative stress. The HPTSC*-Cu was the compound that showed the best antitumor and apoptotic characteristics for the cell line SW480, that is KRAS gene mutated.

Unshielding Multidrug Resistant Cancer through Selective Iron Depletion of P-Glycoprotein-Expressing Cells

Clinical evidence shows that following initial response to treatment, drug-resistant cancer cells frequently evolve and, eventually, most tumors become resistant to all available therapies. We compiled a focused library consisting of >500 commercially available or newly synthetized 8-hydroxyquinoline (8OHQ) derivatives whose toxicity is paradoxically increased rather than decreased by the activity of P-glycoprotein (Pgp), a transporter conferring multidrug resistance (MDR). Here, we deciphered the mechanism of action of NSC297366 that shows exceptionally strong Pgp-potentiated toxicity. Treatment of cells with NSC297366 resulted in changes associated with the activity of potent anticancer iron chelators. Strikingly, iron depletion was more pronounced in MDR cells due to the Pgp-mediated efflux of NSC297366-iron complexes. Our results indicate that iron homeostasis can be targeted by MDR-selective compounds for the selective elimination of multidrug resistant cancer cells, setting the stage for a therapeutic approach to fight transporter-mediated drug resistance. SIGNIFICANCE: Modulation of the MDR phenotype has the potential to increase the efficacy of anticancer therapies. These findings show that the MDR transporter is a "double-edged sword" that can be turned against resistant cancer.

Recent advances in microfluidic methods in cancer liquid biopsy

Early cancer detection, its monitoring, and therapeutical prediction are highly valuable, though extremely challenging targets in oncology. Significant progress has been made recently, resulting in a group of devices and techniques that are now capable of successfully detecting, interpreting, and monitoring cancer biomarkers in body fluids. Precise information about malignancies can be obtained from liquid biopsies by isolating and analyzing circulating tumor cells (CTCs) or nucleic acids, tumor-derived vesicles or proteins, and metabolites. The current work provides a general overview of the latest on-chip technological developments for cancer liquid biopsy. Current challenges for their translation and their application in various clinical settings are discussed. Microfluidic solutions for each set of biomarkers are compared, and a global overview of the major trends and ongoing research challenges is given. A detailed analysis of the microfluidic isolation of CTCs with recent efforts that aimed at increasing purity and capture efficiency is provided as well. Although CTCs have been the focus of a vast microfluidic research effort as the key element for obtaining relevant information, important clinical insights can also be achieved from alternative biomarkers, such as classical protein biomarkers, exosomes, or circulating-free nucleic acids. Finally, while most work has been devoted to the analysis of blood-based biomarkers, we highlight the less explored potential of urine as an ideal source of molecular cancer biomarkers for point-of-care lab-on-chip devices.

Design, synthesis and biological evaluation of selective survivin inhibitors

The differential distribution between cancer cells and normal adult tissues makes survivin a very attractive cancer drug target. We have previously reported a series of novel selective survivin inhibitors with the most potent compound MX106 reaching nanomolar activity in several cancer cell lines. Further optimization of the MX106 scaffold leads to the discovery of more potent and more selective survivin inhibitors. Various structural modifications were synthesized and their anticancer activities were evaluated to determine the structure activity relationships for this MX106 scaffold. In vitro anti-proliferative assays using two human melanoma cell lines showed that several new analogs have improved potency compared to MX106. Very interestingly, these new analogs generally showed significantly higher potency against P-glycoprotein overexpressed cells compared with the corresponding parental cells, suggesting that these compounds may strongly sensitize tumors that have high expressions of the P-glycoprotein drug efflux pumps. Western blotting analysis confirmed that the new MX106 analogs maintained their mechanism of actions by selectively suppressing survivin expression level among major inhibitors of apoptotic proteins and induced strong apoptosis in melanoma tumor cells.

Anticancer Thiosemicarbazones: Chemical Properties, Interaction with Iron Metabolism, and Resistance Development

SIGNIFICANCE

During the past decades, thiosemicarbazones were clinically developed for a variety of diseases, including tuberculosis, viral infections, malaria, and cancer. With regard to malignant diseases, the class of α-N-heterocyclic thiosemicarbazones, and here especially 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (Triapine), was intensively developed in multiple clinical phase I/II trials. Recent Advances: Very recently, two new derivatives, namely COTI-2 and di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC) have entered phase I evaluation. Based on the strong metal-chelating/metal-interacting properties of thiosemicarbazones, interference with the cellular iron (and copper) homeostasis is assumed to play an important role in their biological activity.

CRITICAL ISSUES

In this review, we summarize and analyze the data on the interaction of (α-N-heterocyclic) thiosemicarbazones with iron, with the special aim of bridging the current knowledge on their mode of action from chemistry to (cell) biology. In addition, we highlight the difference to classical iron(III) chelators such as desferrioxamine (DFO), which are used for the treatment of iron overload.

FUTURE DIRECTIONS

We want to emphasize that thiosemicarbazones are not solely removing iron from the cells/organism. In contrast, they should be considered as iron-interacting drugs influencing diverse biological pathways in a complex and multi-faceted mode of action. Consequently, in addition to the discussion of physicochemical properties (e.g., complex stability, redox activity), this review contains an overview on the diversity of cellular thiosemicarbazone targets and drug resistance mechanisms.

Novel Potent ABCB1 Modulator, Phenethylisoquinoline Alkaloid, Reverses Multidrug Resistance in Cancer Cell

ATP-binding cassette (ABC) transporters, which are concerned with the efflux of anticancer drugs from cancer cells, have a pivotal role in multidrug resistance (MDR). In particular, ABCB1 is a well-known ABC transporter that develops MDR in many cancer cells. Some ABCB1 modulators can reverse ABCB1-mediated MDR; however, no modulators with clinical efficacy have been approved. The aim of this study was to identify novel ABCB1 modulators by using high-throughput screening. Of the 5861 compounds stored at Tohoku University, 13 compounds were selected after the primary screening via a fluorescent plate reader-based calcein acetoxymethylester (AM) efflux assay. These 13 compounds were validated in a flow cytometry-based calcein AM efflux assay. Two isoquinoline derivatives were identified as novel ABCB1 inhibitors, one of which was a phenethylisoquinoline alkaloid, (±)-7-benzyloxy-1-(3-benzyloxy-4-methoxyphenethyl)-1,2,3,4-tetrahydro-6-methoxy-2-methylisoquinoline oxalate. The compound, a phenethylisoquinoline alkaloid, was subsequently evaluated in the cytotoxicity assay and shown to significantly enhance the reversal of ABCB1-mediated MDR. In addition, the compound activated the ABCB1-mediated ATP hydrolysis and inhibited the photolabeling of ABCB1 with [¹²⁵I]-iodoarylazidoprazosin. Furthermore, the compound also reversed the resistance to paclitaxel without increasing the toxicity in the ABCB1-overexpressing KB-V1 cell xenograft model. Overall, we concluded that the newly identified phenethylisoquinoline alkaloid reversed ABCB1-mediated MDR through direct interaction with the substrate-binding site of ABCB1. These findings may contribute to the development of more potent and less toxic ABCB1 modulators, which could overcome ABCB1-mediated MDR.

Metal transport capabilities of anticancer copper chelators

In the present study, several Cu chelators [2,2'-biquinoline, 8-hydroxiquinoline (oxine), ammonium pyrrolidinedithiocarbamate (APDTC), Dp44mT, dithizone, neocuproine] were used to study Cu uptake, depletion and localization in different cancer cell lines. To better understand the concentration dependent fluctuations in the Cu intracellular metal content and Cu-dependent in vitro antiproliferative data, the conditional stability constants of the Cu complex species of the investigated ligands were calculated. Each investigated chelator increased the intracellular Cu content on HT-29 cells causing Cu accumulation depending on the amount of the free Cu(II). Copper accumulation was 159 times higher for Dp44mT compared to the control. Investigating a number of other transition metals, intracellular accumulation of Cd was observed only for two chelators. Intracellular Zn content slightly decreased (cca. 10%) for MCF-7 cells, while a dramatic decrease was observed on MDA-MB-231 ones (cca. 50%). A similar decrease was observed for HCT-116, while Zn depletion for HT-29 corresponded to cca. 20%. The IC₅₀ values were registered for the investigated four cell lines at increasing external Cu(II) concentration, namely, MDA-MB-231 cells had the lowest IC₅₀ values for Dp44mT ranging between 7 and 35 nM. Thus, Zn depletion could be associated with lower IC₅₀ values. Copper depletion was observed for all ligands being less pronounced for Dp44mT and neocuproine. Copper localization and its colocalization with Zn were determined by μ-XRF imaging. Loose correlation (0.57) was observed for the MCF-7 cells independently of the applied chelator. Similarly, a weak correlation (0.47) was observed for HT-29 cells treated with Cu(II) and oxine. Colocalization of Cu and Zn in the nucleus of HT-29 cells was observed for Dp44mT (correlation coefficient of 0.85).

Big Data Approaches for Modeling Response and Resistance to Cancer Drugs

Despite significant progress in cancer research, current standard-of-care drugs fail to cure many types of cancers. Hence, there is an urgent need to identify better predictive biomarkers and treatment regimes. Conventionally, insights from hypothesis-driven studies are the primary force for cancer biology and therapeutic discoveries. Recently, the rapid growth of big data resources, catalyzed by breakthroughs in high-throughput technologies, has resulted in a paradigm shift in cancer therapeutic research. The combination of computational methods and genomics data has led to several successful clinical applications. In this review, we focus on recent advances in data-driven methods to model anticancer drug efficacy, and we present the challenges and opportunities for data science in cancer therapeutic research.

Kallikrein-related peptidase 6 induces chemotherapeutic resistance by attenuating auranofin-induced cell death through activation of autophagy in gastric cancer

Kallikrein-related peptidase 6 (KLK6) is a biomarker of gastric cancer associated with poor prognosis. Mechanisms by which KLK6 could be exploited for chemotherapeutic use are unclear. We evaluated auranofin (AF), a compound with cytotoxic effects, in KLK6-deficient cells, and we investigated whether KLK6 expression induces autophagy and acquisition of drug resistance in gastric cancer. Using cultured human cells and a mouse xenograft model, we investigated how KLK6 affects antitumor-reagent-induced cell death and autophagy. Expression levels of KLK6, p53, and autophagy marker LC3B were determined in gastric cancer tissues. We analyzed the effects of knockdown/overexpression of KLK6, LC3B, and p53 on AF-induced cell death in cancer cells. Increased KLK6 expression in human gastric cancer tissues and cells inhibited AF-induced cell motility due to increased autophagy and p53 levels. p53 dependent induction of KLK6 expression increased autophagy and drug resistance, whereas KLK6 silencing decreased the autophagy level and increased drug sensitivity. During AF-induced cell death, KLK6 and LC3B colocalized to autophagosomes, associated with p53, and were then trafficked to the cytosol. In the xenograft model of gastric cancer, KLK6 expression decreased AF-induced cell death and KLK6-induced autophagy increased AF resistance. Taken together, the data suggest that the induction of autophagic processes through KLK6 expression may increase acquisition of resistance to AF. Our findings may contribute to a new paradigm for tumor therapeutics.

Cell Migration Related to MDR-Another Impediment to Effective Chemotherapy?

Multidrug resistance, mediated by members of the ATP-binding cassette (ABC) proteins superfamily, has become one of the biggest obstacles in conquering tumour progression. If the chemotherapy outcome is considered successful, when the primary tumour volume is decreased or completely abolished, modulation of ABC proteins activity is one of the best methods to overcome drug resistance. However, if a positive outcome is represented by no metastasis or, at least, elongation of remission-free time, then the positive effect of ABC proteins inhibition should be compared with the several side effects it causes, which may inflict cancer progression and decrease overall patient health. Clinical trials conducted thus far have shown that the tested ABC modulators add limited or no benefits to cancer patients, as some of them are merely toxic and others induce unwanted drug–drug interactions. Moreover, the inhibition of certain ABC members has been recently indicated as potentially responsible for increased fibroblasts migration. A better understanding of the complex role of ABC proteins in relation to cancer progression may offer novel strategies in cancer therapy.

Asclepiasterol, a novel C21 steroidal glycoside derived from Asclepias curassavica, reverses tumor multidrug resistance by down-regulating P-glycoprotein expression

Multidrug resistance (MDR) mediated by P-glycoprotein (P-gp) is a major cause of cancer therapy failure. In this study, we identified a novel C₂₁ steroidal glycoside, asclepiasterol, capable of reversing P-gp-mediated MDR. Asclepiasterol (2.5 and 5.0μM) enhanced the cytotoxity of P-gp substrate anticancer drugs in MCF-7/ADR and HepG-2/ADM cells. MDR cells were more responsive to paclitaxel in the presence of asclepiasterol, and colony formation of MDR cells was only reduced upon treatment with a combination of asclepiasterol and doxorubicin. Consistent with these findings, asclepiasterol treatment increased the intracellular accumulation of doxorubicin and rhodamine 123 (Rh123) in MDR cells. Asclepiasterol decreased expression of P-gp protein without stimulating or suppressing MDR1 mRNA levels. Asclepiasterol-mediated P-gp suppression caused inhibition of ERK1/2 phosphorylation in two MDR cell types, and EGF, an activator of the MAPK/ERK pathway, reversed the P-gp down-regulation, implicating the MAPK/ERK pathway in asclepiasterol-mediated P-gp down-regulation. These results suggest that asclepiasterol could be developed as a modulator for reversing P-gp-mediated MDR in P-gp-overexpressing cancer variants.

Doxorubicin synergism and resistance reversal in human neuroblastoma BE(2)C cell lines: An in vitro study with dextran-catechin nanohybrids

Hybrid nanocarrier consisting in nanographene oxide coated by a dextran-catechin conjugate was proposed in the efforts to find more efficient Neuroblastoma treatment with Doxorubicin chemotherapy. The dextran-catechin conjugate was prepared by immobilized laccase catalysis and its peculiar reducing ability exploited for the synthesis of the hybrid carrier. Raman spectra and DSC thermograms were recorded to check the physicochemical properties of the nanohybrid, while DLS measurements, SEM, TEM, and AFM microscopy allowed the determination of its morphological and dimensional features. A pH dependent Doxorubicin release was observed, with 30 and 75% doxorubicin released at pH 7.4 and 5.0, respectively. Viability assays on parental BE(2)C and resistant BE(2)C/ADR cell lines proved that the high anticancer activity of dextran-catechin conjugate (IC₅₀ 19.9 ± 0.6 and 18.4 ± 0.7 µg mL^-1) was retained upon formation of the nanohybrids (IC₅₀ 24.8 ± 0.7 and 22.9 ± 1 µg mL^-1). Combination therapy showed a synergistic activity between doxorubicin and either bioconjugate or nanocarrier on BE(2)C. More interestingly, on BE(2)C/ADR we recorded both the reversion of doxorubicin resistance mechanism as a consequence of decreased P-gp expression (Western Blot analysis) and a synergistic effect on cell viability, confirming the proposed nanohybrid as a very promising starting point for further research in neuroblastoma treatment.

Tomentodione M sensitizes multidrug resistant cancer cells by decreasing P-glycoprotein via inhibition of p38 MAPK signaling

In this study, we investigated the mechanism by which tomentodione M (TTM), a novel natural syncarpic acid-conjugated monoterpene, reversed multi-drug resistance (MDR) in cancer cells. TTM increased the cytotoxicity of chemotherapeutic drugs such as docetaxel and doxorubicin in MCF-7/MDR and K562/MDR cells in a dose- and time-dependent manner. TTM reduced colony formation and enhanced apoptosis in docetaxel-treated MCF-7/MDR and K562/MDR cells, and it enhanced intracellular accumulation of doxorubicin and rhodamine 123 in MDR cancer cells by reducing drug efflux mediated by P-gp. TTM decreased expression of both P-gp mRNA and protein by inhibiting p38 MAPK signaling. Similarly, the p38 MAPK inhibitor SB203580 reversed MDR in cancer cells by decreasing P-gp expression. Conversely, p38 MAPK-overexpressing MCF-7 and K562 cells showed higher P-gp expression than controls. These observations indicate that TTM reverses MDR in cancer cells by decreasing P-gp expression via p38 MAPK inhibition.

Schiff base derived from thiosemicarbazone and anthracene showed high potential in overcoming multidrug resistance in vitro with low drug resistance index

Multidrug resistance (MDR) is a huge obstacle in cancer chemotherapeutics. Overcoming MDR is a great challenge for anticancer drug discovery. Here, DNA binding and cytotoxicity of Schiff base L1 and L2 were explored to assess their efficiency in fighting cancer and overcoming the MDR. L1 and L2 could treat extremely chemoresistant MCF-7/ADR cell as drug-sensitive cell, with drug resistance index (DRI) <2.13, showing high potential in overcoming the MDR. The apoptotic ratio induced by L1 and L2 was low for both MCF-7 and MCF-7/ADR cells. L1 and L2 induced an impairment of cell cycle progression of MCF-7 and MCF-7/ADR cell lines and suppressed cell growth by perturbing progress through the G0/G1 phase, with L2 causing more profound effect, which might account for lower drug resistance after L2 treatment. The molecular docking revealed weak interaction between L1/L2 and P-glycoprotein (P-gp), the most important drug efflux pump and intracellular Rhodamine 123 accumulation indicated that the activity of P-gp was not inhibited by L1 and L2. Combined with the cellular uptake results, it implied that L1 and L2 could bypass P-gp efflux to exert anticancer activity.

Alpha-Mangostin Reverses Multidrug Resistance by Attenuating the Function of the Multidrug Resistance-Linked ABCG2 Transporter

The ATP-binding cassette (ABC) drug transporter ABCG2 can actively efflux a wide variety of chemotherapeutic agents out of cancer cells and subsequently reduce the intracellular accumulation of these drugs. Therefore, the overexpression of ABCG2 often contributes to the development of multidrug resistance (MDR) in cancer cells, which is one of the major obstacles to successful cancer chemotherapy. Moreover, ABCG2 is highly expressed in various tissues including the intestine and blood-brain barrier (BBB), limiting the absorption and bioavailability of many therapeutic agents. For decades, the task of developing a highly effective synthetic inhibitor of ABCG2 has been hindered mostly by the intrinsic toxicity, the lack of specificity, and complex pharmacokinetics. Alternatively, considering the wide range of diversity and relatively nontoxic nature of natural products, developing potential modulators of ABCG2 from natural sources is particularly valuable. α-Mangostin is a natural xanthone derived from the pericarps of mangosteen (Garcinia mangostana L.) with various pharmacological purposes, including suppressing angiogenesis and inducing cancer cell growth arrest. In this study, we demonstrated that at nontoxic concentrations, α-mangostin effectively and selectively inhibits ABCG2-mediated drug transport and reverses MDR in ABCG2-overexpressing MDR cancer cells. Direct interactions between α-mangostin and the ABCG2 drug-binding site(s) were confirmed by stimulation of ATPase activity and by inhibition of photolabeling of the substrate-binding site(s) of ABCG2 with [¹²⁵I]iodoarylazidoprazosin. In summary, our findings show that α-mangostin has great potential to be further developed into a promising modulator of ABCG2 for reversing MDR and for its use in combination therapy for patients with MDR tumors.

Molecular docking, PASS analysis, bioactivity score prediction, synthesis, characterization and biological activity evaluation of a functionalized 2-butanone thiosemicarbazone ligand and its complexes

2-Butanone thiosemicarbazone ligand was prepared by condensation reaction between thiosemicarbazide and butanone. The ligand was characterized by ¹H NMR, ¹³C NMR, FT-IR, mass spectrometry and UV spectroscopic studies. Docking studies were performed to study inhibitory action against topoisomerase II (Topo II) and ribonucleoside diphosphate reductase (RR) enzymes. Inhibition constants (K_i ) of the ligand were 437.87 and 327.4 μM for the two enzymes, respectively. The ligand was tested for its potential anticancer activity against two cancer cell lines MDA-MB-231 and A549 using MTT assay and was found to exhibit good activity at higher doses with an IC₅₀ = 80 μM against human breast cancer cell line MDA-MB-231. On the other hand, no significant activity was obtained against the lung carcinoma cell line A549. Antibacterial activity of the ligand was tested against Staphylococcus aureus and E. coli using the disc diffusion method. Ligand did not exhibit any significant antibacterial activity. Four complexes of Co(III), Fe(II), Cu(II), and Zn(II) were prepared with the ligand and characterized by various spectroscopic studies. Low molar conductance values were obtained for all complexes displaying non-electrolyte nature except in Co(III) complex. As expected, complexation with metal ions significantly increased the cytotoxicity of the ligand against the tested cell lines viz. IC₅₀ values of <20 μM for Co, Fe, and Zn complexes and approx. 80 μM against MDA cells versus IC₅₀ value of <20 μM for Co and Cu complexes and that of 30 and 50 μM for Fe and Zn complexes, respectively, against A549 cells. The Cu complex was found to be active against E. coli and S. aureus with MIC values in the range of 6-10 mg/mL. Other than Cu, only Co complex was found to possess antibacterial activity with MIC values of 5-10 mg/mL when tested against S. aureus. Bioactivity score and Prediction of Activity Spectra for Substances (PASS) analysis also depicted the drug-like nature of ligand and complexes.

Stimulus-Responsive Short Peptide Nanogels for Controlled Intracellular Drug Release and for Overcoming Tumor Resistance

Multidrug resistance (MDR) poses a major burden to cancer treatment. As one important factor contributing to MDR, overexpression of P-glycoprotein (P-gp) results in a reduced intracellular drug accumulation. Hence, the ability to effectively block the efflux protein and to accumulate the therapeutics in cancer cells is of great significance in clinical practice. In this work, we successfully developed a smart stimulus-responsive short peptide-assembled system, termed as PD/VER nanogels, which synergistically combined the acid-activatable antitumor prodrug doxorubicin (Dox) with the P-gp inhibitor verapamil (VER) for reversing MDR. Systematic studies demonstrated that such an inhibitor-encapsulated nanogel could effectively enhance the accumulation of Dox in resistant cancer cells, thereby revealing significantly higher antitumor activity compared to free Dox molecules. This work showed that the assembly of bioactive agents with a synergistic effect into nano-drugs could provide a useful strategy to overcome cancer drug resistance.

Prognostic Value and Implication for Chemotherapy Treatment of ABCB1 in Epithelial Ovarian Cancer: A Meta-Analysis

Background

Chemotherapy resistance is reported to correlate with up-regulation of anti-tumor agent transporter ABCB1 (p-gp) in epithelial ovarian cancer (EOC), but the results remain controversial. To reconcile the results, a systematic review followed by meta-analysis was performed to assess the association between high ABCB1 status or ABCB1 gene variants and overall survival (OS), progression free survival (PFS), and total response rate (TR) in patients with EOC.

Materials and Methods

Electronic searches were performed using Pubmed, EMBASE, Web of Science and Chinese Wanfang databases from January 1990 to February 2016. Summary hazard ratio (HR), risk ratio (RR) and 95% confidence intervals (CIs) were combined using fixed or random-effects models as appropriate.

Results

Thirty-eight retrospective studies of 8607 cases qualified for meta-analysis were identified. Our results suggested that ABCB1 over-expression was significantly associated with unfavorable OS (HR = 1.54; 95% CI, 1.25–1.90), PFS (HR = 1.49; 95% CI, 1.22–1.82) and TR (RR = 0.63; 95% CI, 0.54–0.75). After adjustment for age, clinical stage, residual disease, histological type and tumor grade, high ABCB1 status remained to be a significant risk factor for adverse OS and PFS. Patients with recurrent ABCB1 positivity suffered from poorer OS than those with primary ABCB1 positivity. However, stratified by chemotherapy regimen, inverse correlation between high ABCB1 status and poor OS, PFS and TR were only found in patients underwent platinum-based chemotherapy but not in patients received standard platinum/paclitaxel-based chemotherapy. No evidence was found for any association between ABCB1 gene polymorphisms and OS, PFS or TR.

Conclusion

High ABCB1 status is significantly associated with chemo-resistance and poor prognosis in patients with EOC. Large-scale, prospective studies are needed to assess the clinical value of ABCB1 expression in EOC more accurately.

Novel mechanisms and approaches to overcome multidrug resistance in the treatment of ovarian cancer

Ovarian cancer remains the leading cause of gynecological cancer-related mortality despite the advances in surgical techniques and chemotherapy drugs over the past three decades. Multidrug resistance (MDR) to chemotherapy is the major cause of treatment failure. Previous research has focused mainly on strategies to reverse MDR by targeting the MDR1 gene encoded P-glycoprotein (Pgp) with small molecular compound inhibitors. However, prior Pgp inhibitors have shown very limited clinical success because these agents have relatively low potency and high toxicity. Therefore, identification of more specific and potent new inhibitors would be useful. In addition, emerging evidence suggests that cancer stem cells (CSCs), deregulated non-coding RNA (ncRNA), autophagy, and tumor heterogeneity also contribute significantly to drug sensitivity/resistance in ovarian cancer. This review summarizes these novel mechanisms of MDR and evaluates several new concepts to overcome MDR in the treatment of ovarian cancer. These new strategies include overcoming MDR with more potent and specific Pgp inhibitors, targeting CSCs and ncRNA, modulating autophagy signaling pathway, and targeting tumor heterogeneity.