A-803467, a tetrodotoxin-resistant sodium channel blocker, modulates ABCG2-mediated MDR in vitro and in vivo

Clinical relevance of stem cells in lung cancer

Lung cancer is the major cause of cancer-related deaths worldwide, it has one of the lowest 5-year survival rate, mainly because it is diagnosed in the late stage of the disease. Lung cancer is classified into two groups, small cell lung cancer (SCLC) and non-SCLC (NSCLC). In turn, NSCLC is categorized into three distinct cell subtypes: Adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. NSCLC is the most common lung cancer, accounting for 85% of all lung cancers. Treatment for lung cancer is linked to the cell type and stage of the disease, involving chemotherapy, radiation therapy, and surgery. Despite improvements in therapeutic treatments, lung cancer patients show high rates of recurrence, metastasis, and resistance to chemotherapy. Lung stem cells (SCs) are undifferentiated cells capable of self-renewal and proliferation, are resistant to chemotherapy and radiotherapy and, due to their properties, could be involved in the development and progression of lung cancer. The presence of SCs in the lung tissue could be the reason why lung cancer is difficult to treat. The identification of lung cancer stem cells biomarkers is of interest for precision medicine using new therapeutic agents directed against these cell populations. In this review, we present the current knowledge on lung SCs and discuss their functional role in the initiation and progression of lung cancer, as well as their role in tumor resistance to chemotherapy.

Anticancer effect of Indanone-based thiazolyl hydrazone derivative on p53 mutant colorectal cancer cell lines: An in vitro and in vivo study

Colorectal cancer is a major health problem, and it is the third most diagnosed cancer in the United States. The current treatment for colorectal cancer includes irinotecan, a topoisomerase I inhibitor, and other targeted drugs, such as bevacizumab and regorafenib. The low response rates and incidence of high toxicity caused by these drugs instigated an evaluation of the anticancer efficacy of a series of 13 thiazolyl hydrazone derivatives of 1-indanone, and four compounds among them show favorable anticancer activity against some of the tested colorectal cancer cell lines with IC₅₀ values ranging from 0.41 ± 0.19 to 6.85 ± 1.44 μM. It is noteworthy that one of the indanone-based thiazolyl hydrazone (ITH) derivatives, N-Indan-1-ylidene-N’-(4-Biphenyl-4-yl-thiazol-2-yl)-hydrazine (ITH-6), has a better cytotoxicity profile against p53 mutant colorectal cancer cells HT-29, COLO 205, and KM 12 than a p53 wild-type colorectal cancer cell line, such as HCT 116. Mechanistic studies show that ITH-6 arrests these three cancer cell lines in the G2/M phase and induces apoptosis. It also causes a rise in the reactive oxygen species level with a remarkable decrease in the glutathione (GSH) level. Moreover, ITH-6 inhibits the expression of NF-κB p65 and Bcl-2, which proves its cytotoxic action. In addition, ITH-6 significantly decreased tumor size, growth rate, and tumor volume in mice bearing HT-29 and KM 12 tumor xenografts. Moreover, CRISPR/Cas9 was applied to establish an NF-κB p65 gene knockout HT-29 cell line model to validate the target of ITH-6. Overall, the results suggest that ITH-6 could be a potential anticancer drug candidate for p53 mutant colorectal cancers.

Ion Channel Involvement in Tumor Drug Resistance

Over 90% of deaths in cancer patients are attributed to tumor drug resistance. Resistance to therapeutic agents can be due to an innate property of cancer cells or can be acquired during chemotherapy. In recent years, it has become increasingly clear that regulation of membrane ion channels is an important mechanism in the development of chemoresistance. Here, we review the contribution of ion channels in drug resistance of various types of cancers, evaluating their potential in clinical management. Several molecular mechanisms have been proposed, including evasion of apoptosis, cell cycle arrest, decreased drug accumulation in cancer cells, and activation of alternative escape pathways such as autophagy. Each of these mechanisms leads to a reduction of the therapeutic efficacy of administered drugs, causing more difficulty in cancer treatment. Thus, targeting ion channels might represent a good option for adjuvant therapies in order to counteract chemoresistance development.

A Phenylfurocoumarin Derivative Reverses ABCG2-Mediated Multidrug Resistance In Vitro and In Vivo

The ATP-binding cassette subfamily G member 2 (ABCG2) transporter is involved in the development of multidrug resistance in cancer patients. Many inhibitors of ABCG2 have been reported to enhance the chemosensitivity of cancer cells. However, none of these inhibitors are being used clinically. The aim of this study was to identify novel ABCG2 inhibitors by high-throughput screening of a chemical library. Among the 5812 compounds in the library, 23 compounds were selected in the first screening, using a fluorescent plate reader-based pheophorbide a (PhA) efflux assay. Thereafter, to validate these compounds, a flow cytometry-based PhA efflux assay was performed and 16 compounds were identified as potential inhibitors. A cytotoxic assay was then performed to assess the effect these 16 compounds had on ABCG2-mediated chemosensitivity. We found that the phenylfurocoumarin derivative (R)-9-(3,4-dimethoxyphenyl)-4-((3,3-dimethyloxiran-2-yl)methoxy)-7H-furo [3,2-g]chromen-7-one (PFC) significantly decreased the IC₅₀ of SN-38 in HCT-116/BCRP colon cancer cells. In addition, PFC stimulated ABCG2-mediated ATP hydrolysis, suggesting that this compound interacts with the substrate-binding site of ABCG2. Furthermore, PFC reversed the resistance to irinotecan without causing toxicity in the ABCG2-overexpressing HCT-116/BCRP cell xenograft mouse model. In conclusion, PFC is a novel inhibitor of ABCG2 and has promise as a therapeutic to overcome ABCG2-mediated MDR, to improve the efficiency of cancer chemotherapy.

VKNG-1 Antagonizes ABCG2-Mediated Multidrug Resistance via p-AKT and Bcl-2 Pathway in Colon Cancer: In Vitro and In Vivo Study

The emergence of multidrug resistance (MDR) to chemotherapeutic drugs is a major problem in the therapy of cancer. Knowledge of the mechanisms of drug resistance in cancer is necessary for developing efficacious therapies. ATP-binding cassette (ABC) transporters are transmembrane proteins that efflux chemotherapeutic drugs from cancer cells, thereby producing MDR. Our research efforts have led to the discovery of VKNG-1, a compound that selectively inhibits the ABCG2 transporter and reverses resistanctabe to standard anticancer drugs both in vitro and in vivo. VKNG-1, at 6 µM, selectively inhibited ABCG2 transporter and sensitized ABCG2-overexpressing drug-resistant cancer cells to the ABCG2 substrate anticancer drugs mitoxantrone, SN-38, and doxorubicin in ABCG2-overexpressing colon cancers. VKNG- 1 reverses ABCG2-mediated MDR by blocking ABCG2 efflux activity and downregulating ABCG2 expression at the mRNA and protein levels. Moreover, VKNG-1 inhibits the level of phosphorylated protein kinase B (PKB/p-AKT), and B-cell lymphoma-2 (Bcl-2) protein which may overcome resistance to anticancer drugs. However, the in vitro translocation of ABCG2 protein did not occur in the presence of 6 µM of VKNG-1. In addition, VKNG-1 enhanced the anticancer efficacy of irinotecan in ABCG2- overexpressing mouse tumor xenografts. Overall, our results suggest that VKNG-1 may, in combination with certain anticancer drugs, represent a treatment to overcome ABCG2-mediated MDR colon cancers.

Lipid-Saporin Nanoparticles for the Intracellular Delivery of Cytotoxic Protein to Overcome ABC Transporter-Mediated Multidrug Resistance In Vitro and In Vivo

Although the judicious use of anticancer drugs that target one or more receptor tyrosine kinases constitutes an effective strategy to attenuate tumor growth, drug resistance is commonly encountered in cancer patients. The ATP-binding cassette transporters are one of the major contributors to the development of multidrug resistance as their overexpression significantly decreases the intracellular concentration and thus, the efficacy of certain anticancer drugs. Therefore, the development of treatment strategies that would not be susceptible to efflux or excretion by specific ABC transporters could overcome resistance to treatment. Here, we investigated the anticancer efficacy of saporin, a ribosome-inactivating protein. Since saporin has poor permeability across the cell membrane, it was encapsulated in a lipid-based nanoparticle system (EC16-1) that effectively delivered the formulation (EC16-1/saporin) intracellularly and produced anti-cancer efficacy. EC16-1/saporin, at nanomolar concentrations, significantly inhibited the cellular proliferation of parental and ABCB1- and ABCG2-overexpressing cancer cells. EC16-1/saporin did not significantly alter the subcellular localization of ABCB1 and ABCG2. In addition, EC16-1/saporin induced apoptosis in parental and ABCB1- and ABCG2-overexpressing cancer cells. In a murine model system, EC16-1/saporin significantly inhibited the tumor growth in mice xenografted with parental and ABCB1- and ABCG2-overexpressing cancer cells. Our findings suggest that the EC16-1/saporin combination could potentially be a novel therapeutic treatment in patients with parental or ABCB1- and ABCG2-positive drug-resistant cancers.

Preclinical development of a novel BCR-ABL T315I inhibitor against chronic myeloid leukemia

Chronic Myeloid Leukemia (CML) is a myeloproliferative neoplasm primarily due to the presence of the BCR-ABL fusion gene that produces the constitutively active protein, BCR-ABL. Imatinib, a BCR-ABL-targeted drug, is a first-line drug for the treatment of CML. Resistance to imatinib occurs as a result of mutations in the BCR-ABL kinase domains. In this study, we evaluated S116836, a novel BCR-ABL inhibitor, for its anti-cancer efficacy in the wild-type (WT) and T315I mutant BCR-ABL. S116836 was efficacious in BaF3 cells with WT or T315I mutated BCR-ABL genotypes. S116836 inhibits the phosphorylation of BCR-ABL and its downstream signaling in BaF3/WT and BaF3/T315I cells. Mechanistically, S116836 arrests the cells in the G0/G1 phase of cell cycle, induces apoptosis, increases ROS production, and decreases GSH production in BaF3/WT and BaF3/T315I cells. Moreover, in mouse tumor xenografts, S116836 significantly inhibits the growth and volume of tumors expressing the WT or T315I mutant BCR-ABL without causing significant cardiotoxicity. Overall, our results indicate that S116836 significantly inhibits the imatinib-resistant T315I BCR-ABL mutation and could be a novel drug candidate for treating imatinib-resistant CML patients.

Ciprofloxacin Enhances the Chemosensitivity of Cancer Cells to ABCB1 Substrates

ABCB1 is one of the major drug efflux transporters that is known to cause multidrug resistance (MDR) in cancer patients receiving chemotherapy for the treatment of solid tumors and hematological malignancies. Inhibition of ABCB1 efflux function is important for maintaining the intracellular concentration of chemotherapeutic drugs. Here, we evaluated ciprofloxacin for its ability to reverse MDR caused by the overexpression of ABCB1. Cytotoxicity of ciprofloxacin was determined by the MTT assay. The chemosensitizing effects of ciprofloxacin were determined in combination with ABCB1 substrates. The intracellular accumulation and efflux of ABCB1 substrates was measured by a scintillation counter, and protein expression was determined by the Western blotting. Vanadate-sensitive ATPase assay was performed to determine the effect of ciprofloxacin on the ATPase activity of ABCB1, and docking analysis was done to determine the interaction of ciprofloxacin with ABCB1. Ciprofloxacin significantly potentiated the cytotoxic effects of ABCB1 substrates in ABCB1-overexpressing cells. Furthermore, ciprofloxacin increased the intracellular accumulation and decreased the efflux of [³H]-paclitaxel without altering the expression of ABCB1. Ciprofloxacin stimulated the ATPase activity of ABCB1 in a concentration-dependent manner. Our findings showed that ciprofloxacin potently inhibits the ABCB1 efflux function and it has potential to be developed as a combination anticancer therapy.

Puerarin Relieves Paclitaxel-Induced Neuropathic Pain: The Role of Nav1.8 β1 Subunit of Sensory Neurons

Currently there is no effective treatment available for clinical patients suffering from neuropathic pain induced by chemotherapy paclitaxel. Puerarin is a major isoflavonoid extracted from the Chinese medical herb kudzu root, which has been used for treatment of cardiovascular disorders and brain injury. Here, we found that puerarin dose-dependently alleviated paclitaxel-induced neuropathic pain. At the same time, puerarin preferentially reduced the excitability and blocked the voltage-gated sodium (Na_v) channels of dorsal root ganglion (DRG) neurons from paclitaxel-induced neuropathic pain rats. Furthermore, puerarin was a more potent blocker of tetrodotoxin-resistant (TTX-R) Na_v channels than of tetrodotoxin-sensitive (TTX-S) Na_v channels in chronic pain rats’ DRG neurons. In addition, puerarin had a stronger blocking effect on Na_v1.8 channels in DRG neurons of neuropathic pain rats and β1 subunit siRNA can abolish this selective blocking effect on Na_v1.8. Together, these results suggested that puerarin may preferentially block β1 subunit of Na_v1.8 in sensory neurons contributed to its anti-paclitaxel induced neuropathic pain effect.

Bulleyaconitine A attenuates hyperexcitability of dorsal root ganglion neurons induced by spared nerve injury: The role of preferably blocking Nav1.7 and Nav1.3 channels

Background

Oral administration of Bulleyaconitine A, an extracted diterpenoid alkaloid from Aconitum bulleyanum plants, is effective for treating chronic pain in rats and in human patients, but the underlying mechanisms are poorly understood.

Results

As the hyperexcitability of dorsal root ganglion neurons resulting from the upregulation of voltage-gated sodium (Nav) channels has been proved critical for development of chronic pain, we tested the effects of Bulleyaconitine A on Nav channels in rat spared nerve injury model of neuropathic pain. We found that Bulleyaconitine A at 5 nM increased the threshold of action potentials and reduced the firing rate of dorsal root ganglion neurons in spared nerve injury rats but not in sham rats. Bulleyaconitine A preferably blocked tetrodotoxin-sensitive Nav channels over tetrodotoxin-resistant ones in dorsal root ganglion neurons of spared nerve injury rats. Bulleyaconitine A was more potent for blocking Nav1.3 and Nav1.7 than Nav1.8 in cell lines. The half maximal inhibitory concentration (IC₅₀) values for resting Nav1.3, Nav1.7, and Nav1.8 were 995.6 ± 139.1 nM, 125.7 ± 18.6 nM, and 151.2 ± 15.4 μM, respectively, which were much higher than those for inactivated Nav1.3 (20.3 ± 3.4 pM), Nav1.7 (132.9 ± 25.5 pM), and Nav1.8 (18.0 ± 2.5 μM). The most profound use-dependent blocking effect of Bulleyaconitine A was observed on Nav1.7, less on Nav1.3, and least on Nav1.8 at IC₅₀ concentrations. Bulleyaconitine A facilitated the inactivation of Nav channels in each subtype.

Conclusions

Preferably blocking tetrodotoxin-sensitive Nav1.7 and Nav1.3 in dorsal root ganglion neurons may contribute to Bulleyaconitine A’s antineuropathic pain effect.

Voruciclib, a Potent CDK4/6 Inhibitor, Antagonizes ABCB1 and ABCG2-Mediated Multi-Drug Resistance in Cancer Cells

Background/Aims: The overexpression of ATP-Binding Cassette (ABC) transporters has known to be one of the major obstacles impeding the success of chemotherapy in drug resistant cancers. In this study, we evaluated voruciclib, a CDK 4/6 inhibitor, for its chemo-sensitizing activity in ABCB1- and ABCG2- overexpressing cells. Methods: Cytotoxicity and reversal effect of voruciclib was determined by MTT assay. The intracellular accumulation and efflux of ABCB1 and ABCG2 substrates were measured by scintillation counter. The effects on expression and intracellular localization of ABCB1 and ABCG2 proteins were determined by Western blotting and immunofluorescence, respectively. Vanadate-sensitive ATPase assay was done to determine the effect of voruciclib on the ATPase activity of ABCB1 and ABCG2. Flow cytometric analysis was done to determine the effect of voruciclib on apoptosis of ABCB1 and ABCG2-overexpressing cells and docking analysis was done to determine the interaction of voruciclib with ABCB1 and ACBG2 protein. Results: Voruciclib significantly potentiated the effect of paclitaxel and doxorubicin in ABCB1-overexpressing cells, as well as mitoxantrone and SN-38 in ABCG2-overexpressing cells. Voruciclib moderately sensitized ABCC10- overexpressing cells to paclitaxel, whereas it did not alter the cytotoxicity of substrates of ABCC1. Furthermore, voruciclib increased the intracellular accumulation and decreased the efflux of substrate anti-cancer drugs from ABCB1- or ABCG2-overexpressing cells. However, voruciclib did not alter the expression or the sub-cellular localization of ABCB1 or ABCG2. Voruciclib stimulated the ATPase activity of both ABCB1 and ABCG2 in a concentration-dependent manner. Lastly, voruciclib exhibited a drug-induced apoptotic effect in ABCB1- or ABCG2- overexpressing cells. Conclusion: Voruciclib is currently a phase I clinical trial drug. Our findings strongly support its potential use in combination with conventional anti-cancer drugs for cancer chemotherapy.

A novel anticancer agent SNG1153 inhibits growth of lung cancer stem/progenitor cells

Lung cancer is the leading cause of cancer-related death in both men and women. Lung cancer contains a small population of cancer cells with stem-like features known as cancer stem cells (CSCs). CSCs are often more resistant to current therapeutic treatments. Thus, it is urgent to develop a novel agent that is able to inhibit CSCs growth. In this study, we examined the ability of SNG1153, a novel chemical agent to inhibit the growth of lung CSCs. We found that SNG1153 inhibited growth and induced apoptosis in established lung cancer cells. We also found that SNG1153 inhibited the tumorsphere formation and decreased CD133-positive (lung CSC marker) cancer cells. SNG1153 was able to attenuate tumor formation in NOD/SCID (non-obese diabetic/severe combined immunodeficient) mice injected with lung tumorsphere cells. We further demonstrated that SNG1153 induced β-catenin phosphorylation and down-regulated β-catenin. Our results thus demonstrate that SNG1153 effectively inhibits the growth of lung CSCs and suggest that SNG1153 may be a novel therapeutic agent to treat human lung cancer.

Design, synthesis and biological evaluation of benzamide and phenyltetrazole derivatives with amide and urea linkers as BCRP inhibitors

Breast cancer resistant protein (BCRP/ABCG2), a 72kDa plasma membrane transporter protein is a member of ABC transporter superfamily. Increased expression of BCRP causes increased efflux and therefore, reduced intracellular accumulation of many unrelated chemotherapeutic agents leading to multidrug resistance (MDR). A series of 31 benzamide and phenyltetrazole derivatives with amide and urea linkers has been synthesized to serve as potential BCRP inhibitors in order to overcome BCRP-mediated MDR. The target derivatives were tested for their cytotoxicity and reversal effects in human non-small cell lung cancer cell line H460 and mitoxantrone resistant cell line H460/MX20 using the MTT assay. In the benzamide series, compounds 6 and 7 exhibited a fold resistance of 1.51 and 1.62, respectively at 10µM concentration which is similar to that of FTC, a known BCRP inhibitor. Compounds 27 and 31 were the most potent analogues in the phenyltetrazole series with amide linker with a fold resistance of 1.39 and 1.32, respectively at 10µM concentration. For the phenyltetrazole series with urea linker, 38 exhibited a fold resistance of 1.51 which is similar than that of FTC and is the most potent compound in this series. The target compounds did not exhibit reversal effect in P-gp overexpressing resistant cell line SW620/Ad300 suggesting that they are selective BCRP inhibitors.

GSK1904529A, a Potent IGF-IR Inhibitor, Reverses MRP1-Mediated Multidrug Resistance

Overexpression of multidrug-resistant efflux transporters is one of the major causes of chemotherapy failure. MRP1, a 190 kDa efflux transporter, confers resistance to a wide of range of chemotherapeutic drugs. Here we study the cellular effects of GSK1904529A in reversing MRP1-mediated drug resistance. Cytotoxicity of GSK1904529A was determined by MTT assay. Reversal effects of GSK1904529A in combination with MRP1 substrates were determined. The intracellular accumulation and efflux of MRP1 substrate was measured by scintillation counter and protein expression was determined by Western blotting analysis. Cell cycle effects of GSK1904529A in combination with MRP1 substrates were determined by flow cytometric analysis. GSK1904529A, at non-toxic concentrations, enhanced the cytotoxicity of MRP1 substrates in HEK293/MRP1 cells. Furthermore, GSK1904529A increased the intracellular accumulation of [³ H]-vinblastine by inhibiting the efflux function of MRP1. GSK1904529A did not alter the expression level of MRP1, induced a G0/G1 phase cell cycle arrest. Our results indicated that GSK1904529A significantly increased the sensitivity of MRP1 overexpressing cells to chemotherapeutic agents. Furthermore, GSK1904529A enhanced the efficacy of chemotherapeutic drugs that are substrates of MRP1. J. Cell. Biochem. 118: 3260-3267, 2017. © 2017 Wiley Periodicals, Inc.

Regorafenib overcomes chemotherapeutic multidrug resistance mediated by ABCB1 transporter in colorectal cancer: In vitro and in vivo study

Chemotherapeutic multidrug resistance (MDR) is a significant challenge to overcome in clinic practice. Several mechanisms contribute to MDR, one of which is the augmented drug efflux induced by the upregulation of ABCB1 in cancer cells. Regorafenib, a multikinase inhibitor targeting the RAS/RAF/MEK/ERK pathway, was approved by the FDA to treat metastatic colorectal cancer and gastrointestinal stromal tumors. We investigated whether and how regorafenib overcame MDR mediated by ABCB1. The results showed that regorafenib reversed the ABCB1-mediated MDR and increased the accumulation of [³H]-paclitaxel in ABCB1-overexpressing cells by suppressing efflux activity of ABCB1, but not altering expression level and localization of ABCB1. Regorafenib inhibited ATPase activity of ABCB1. In mice bearing resistant colorectal tumors, regorafenib raised the intratumoral concentration of paclitaxel and suppressed the growth of resistant colorectal tumors. But regorafenib did not induce cardiotoxicity/myelosuppression of paclitaxel in mice. Strategy to reposition one FDA-approved anticancer drug regorafenib to overcome the resistance of another FDA-approved, widely used chemotherapeutic paclitaxel, may be a promising direction for the field of adjuvant chemotherapy. This study provides clinical rationale for combination of conventional chemotherapy and targeted anticancer agents.

Thiazole-valine peptidomimetic (TTT-28) antagonizes multidrug resistance in vitro and in vivo by selectively inhibiting the efflux activity of ABCB1

Multidrug resistance (MDR) attenuates the chemotherapy efficacy and increases the probability of cancer recurrence. The accelerated drug efflux mediated by ATP-binding cassette (ABC) transporters is one of the major MDR mechanisms. This study investigated if TTT-28, a newly synthesized thiazole-valine peptidomimetic, could reverse ABCB1-mediated MDR in vitro and in vivo. TTT-28 reversed the ABCB1-mediated MDR and increased the accumulation of [³H]-paclitaxel in ABCB1 overexpressing cells by selectively blocking the efflux function of ABCB1, but not interfering with the expression level and localization of ABCB1. Animal study revealed that TTT-28 enhanced the intratumoral concentration of paclitaxel and promoted apoptosis, thereby potently inhibiting the growth of ABCB1 overexpressing tumors. But TTT-28 did not induce the toxicity (cardiotoxicity/myelosuppression) of paclitaxel in mice. In this study, we synthesized and evaluated a novel selective inhibitor of ABCB1 (TTT-28) with high efficacy and low toxicity. The identification and characterization of this new thiazole-valine peptidomimetic will facilitate design and synthesis of a new generation of ABCB1 inhibitors, leading to further research on multidrug resistance and combination chemotherapy. Furthermore, the strategy that co-administer MDR-ABCB1 inhibitor to overcome the resistance of one FDA approved, widely used chemotherapeutic paclitaxel, may be promising direction for the field of adjuvant chemotherapy.

Modulating the function of ATP-binding cassette subfamily G member 2 (ABCG2) with inhibitor cabozantinib

Cabozantinib (XL184) is a small molecule tyrosine kinase receptor inhibitor, which targets c-Met and VEGFR2. Cabozantinib has been approved by the Food and Drug Administration to treat advanced medullary thyroid cancer and renal cell carcinoma. In the present study, we evaluated the ability of cabozantinib to modulate the function of the ATP-binding cassette subfamily G member 2 (ABCG2) by sensitizing cells that are resistant to ABCG2 substrate antineoplastic drugs. We used a drug-selected resistant cell line H460/MX20 and three ABCG2 stable transfected cell lines ABCG2-482-R2, ABCG2-482-G2, and ABCG2-482-T7, which overexpress ABCG2. Cabozantinib, at non-toxic concentrations (3 or 5μM), sensitized the ABCG2-overexpressing cells to mitoxantrone, SN-38, and topotecan. Our results indicate that cabozantinib reverses ABCG2-mediated multidrug resistance by antagonizing the drug efflux function of the ABCG2 transporter instead of downregulating its expression. The molecular docking analysis indicates that cabozantinib binds to the drug-binding site of the ABCG2 transporter. Overall, our findings demonstrate that cabozantinib inhibits the ABCG2 transporter function and consequently enhances the effect of the antineoplastic agents that are substrates of ABCG2. Cabozantinib may be a useful agent in anticancer treatment regimens for patients who are resistant to ABCG2 substrate drugs.