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Drug resistance is a big problem in cancer treatment and one of the most prominent mechanisms underlain is overexpression of ATP-binding cassette (ABC) transporters, particularly ABCB1, ABCC1 and ABCG2. Inhibition of ABC transporters is an important approach to overcome drug resistance. The inositol-requiring enzyme 1α (IRE1α), an arm of unfolded protein response (UPR), splices XBP1 mRNA to generate an active transcription factor XBP1s. UPR is implicated in drug resistance. However, the underlying mechanism is unclear. We found that the anticancer drugs such as 5-fluorouracil (5-FU) activated the IRE1α-XBP1 pathway to induce the expression of ABCB1, ABCC1 and ABCG2 in colon cancer cells. Inhibition of IRE1α RNase activity with small molecule 4μ8c suppressed the drug-induced expression of these ABC transporters and sensitized 5-FU-resistant colon cancer cells to drug treatment. In vivo xenograft assay indicates that administration of 4μ8C substantially enhanced the efficacy of 5-FU chemotherapy on 5-FU-resistant colon cancer cells. These results suggest that IRE1α-targeting might be a strategy to cope with drug resistance of colon cancer.

Breast cancer is the most frequent malignancy in women. Multidrug resistance due to overexpression of ABC drug transporters is a common cause of chemotherapy failure and disease recurrence. Genistein (GNT) is a phytoestrogen present in soybeans and hormone supplements. We investigated the effect of GNT on the expression and function of ABC transporters in MCF-7 and MDA-MB-231 breast cancer cell lines. Results demonstrated an induction at the protein level of ABCC1 and ABCG2 and of ABCC1 in MCF-7 and MDA-MB-231, respectively. MCF-7 cells showed a concomitant increase in doxorubicin and mitoxantrone efflux and resistance, dependent on ABCG2 activity. ABCC1 induction by GNT in MDA-MB-231 cells modified neither drug efflux nor chemoresistance due to simultaneous acute inhibition of the transporter activity by GNT. All inductions took place at the translational level, as no increment in mRNA was observed and protein increase was prevented by cycloheximide. miR-181a, already demonstrated to inhibit ABCG2 translation, was down-regulated by GNT, explaining translational induction. Effects were independent of classical estrogen receptors. Results suggest potential nutrient-drug interactions that could threaten chemotherapy efficacy, especially in ABCG2-expressing tumors treated with substrates of this transporter. Fil: Rigalli, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Fisiología Experimental. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Fisiología Experimental; Argentina. University of Heidelberg; Alemania Fil: Tocchetti, Guillermo Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Fisiología Experimental. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Fisiología Experimental; Argentina Fil: Arana, Maite Rocío. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Fisiología Experimental. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Fisiología Experimental; Argentina Fil: Villanueva, Silvina Stella Maris. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Fisiología Experimental. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Fisiología Experimental; Argentina Fil: Catania, Viviana Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Fisiología Experimental. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Fisiología Experimental; Argentina Fil: Theile, Dirk. University of Heidelberg; Alemania Fil: Ruiz, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Fisiología Experimental. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Fisiología Experimental; Argentina Fil: Weiss, Johanna. University of Heidelberg; Alemania

Oncogenic pituitary homeobox 2 (PITX2), a de facto master regulator of developmental organ asymmetry, previously upregulated multidrug resistance (MDR) P-glycoprotein ABCB1 in A498 renal cell carcinoma (RCC) cells. The role of PITX2 isoforms in MDR cancers was investigated. Data mining correlated elevated PITX2 in >30% of cancers analyzed, maximally in colon (4.4-fold), confirmed in co-immunostaining of colon and renal cancer microarrays wherein ABCB1 concomitantly increased in RCC. Drug-resistant colorectal adenocarcinoma Colo320DM cells exhibited increased nuclear PITX2 (40-fold), PITX2 promoter activity (27-fold) and ABCB1 (8000-fold) compared to drug-sensitive Colo205. ABCB1 inhibitor PSC833/valspodar or PITX2 siRNA reversed doxorubicin resistance. Nuclei from Colo320DM and A498 cells harbored PITX2A/B1 and PITX2A/B1/B2/Cα/Cβ, respectively. ChIP-qPCR evidenced PITX2 promoter binding in drug exporters ABCB1, ABCC1, ABCG2 and importer hOCT3/SLC22A3. In A498, 786-O, Caki-1, Colo320DM, and Caco2 cells, PITX2 siRNA diminished exporters, increased hOCT3/SLC22A3 expression and activity, and reverted vincristine resistance. Heterologous PITX2 expression induced ABCB1, repressed hOCT3/SLC22A3, enhanced vincristine resistance and diminished proliferation inhibition wherein PITX2A and PITX2C were most effective. Furthermore, PITX2 activity and MDR depended on phosphorylation by GSK3 in A498 cells. Conclusively, oncogenic PITX2 limits sensitizing drug uptake and potentiates cytoprotective drug efflux, contributing to MDR phenotype.

The development of multidrug resistance (MDR) to chemotherapy remains a major challenge in the treatment of cancer. Numerous mechanisms have been recognized that cause MDR, but one of the most important mechanisms is overexpression of adenosine triphosphate (ATP)-binding cassette (ABC) transporters, through which the efflux of various anticancer drugs against their concentration gradients is powered by ATP. In recent years, small molecular tyrosine kinase inhibitors (TKIs) have been developed for treatment in various human cancers overexpressing epidermal growth factor receptor (EGFR). At the same time, some TKIs have been shown to be capable of inhibiting ABC transporter-mediated MDR. Dacomitinib (PF-00299804) is a second generation, irreversible TKI, which has shown positive anticancer activities in some preclinical and clinical trials. As many TKIs are substrates or inhibitors of ABC transporters, this study investigates whether dacomitinib could interact with ABC subfamily members that mediate MDR, including ABCB1 (P-gp), ABCG2 (BCRP) and ABCC1 (MRP1). The results showed that dacomitinib at 1.0 μM significantly reversed drug resistance mediated by ABCB1 and ABCG2, but not ABCC1, doing so by antagonizing the drug efflux function in ABCB1- and ABCG2-overexpressing cell lines. The reversal effect on ABCB1-overexpressing cells is more potent than that on ABCG2-overexpressing cells. In addition, dacomitinib at reversal concentration affected neither the protein expression level nor the localization of ABCB1 and ABCG2. Therefore, the mechanisms of this modulating effect are likely to be the following: first, as an inhibitor of ABCB1 or ABCG2 transporters, dacomitinib binds to drug-substrate site in transmembrane domains (TMD) stably in a noncompetitive manner; or second, dacomitinib inhibits ATPase activity and maintains the stability of TMD conformation in a concentration-dependent manner thereby inhibiting the drug efflux function of ABCB1 or ABCG2 transporter. This study provides a useful combinational therapeutic strategy with dacomitinib and substrates of ABCB1 and/or ABCG2 transporters in ABCB1- or ABCG2-overexpressing cancers.

To better understand the response of HCC to EGFR inhibition, we analyzed factors connected to the resistance of HCC cells against gefitinib. Sensitive HCC3 cells co-expressed EGFR and ErbB3 but lacked kinase-domain mutations in EGFR. Interestingly, expression of MVP was restricted to resistant cell lines, whereas ABCB1 and ABCC1 showed no association with gefitinib resistance. Moreover, ectopic MVP expression in HCC3 cells decreased gefitinib sensitivity, increased AKT phosphorylation and reduced the expression of inflammatory pathway-associated genes, whereas silencing of MVP in Hep3B and HepG2 cells increased sensitivity. These findings suggest MVP as a novel player in resistance against EGFR inhibition.

Sunitinib is an ATP-competitive multi-targeted tyrosine kinase inhibitor. In this study, we evaluated the possible interaction of sunitinib with P-glycoprotein (P-gp, ABCB1), multidrug resistance protein 1 (MRP1, ABCC1), breast cancer resistance protein (BCRP, ABCG2) and lung-resistance protein (LRP) in vitro . Our results showed that sunitinib completely reverse drug resistance mediated by ABCG2 at a non-toxic concentration of 2.5 μM and has no significant reversal effect on ABCB1-, ABCC1- and LRP-mediated drug resistance, although a small synergetic effect was observed in combining sunitinib and conventional chemotherapeutic agents in ABCB1 overexpressing MCF-7/adr and parental sensitive MCF-7 cells, ABCC1 overexpressing C-A120 and parental sensitive KB-3-1 cells. Sunitinib significantly increased intracellular accumulation of rhodamine 123 and doxorubicin and remarkably inhibited the efflux of rhodamine 123 and methotrexate by ABCG2 in ABCG2-overexpressing cells, and also profoundly inhibited the transport of [ 3 H]-methotrexate by ABCG2. However, sunitinib did not affect the expression of ABCG2 at mRNA or protein levels. In addition, sunitinib did not block the phosphorylation of Akt and Erk1/2 in ABCG2-overexpressing or parental sensitive cells. Overall, we conclude that sunitinib reverses ABCG2-mediated MDR through inhibiting the drug efflux function of ABCG2. These findings may be useful for cancer combinational therapy with sunitinib in the clinic.

The effects of oleanolic acid (OA) on ABCB1 and ABCC1 activities were studied in a cell line constitutively expressing both proteins. It was observed that OA did not alter ABCB1 activity, but inhibited the activity of ABCC1 protein. This inhibition was reversible and only occurred in the presence of OA. In addition, OA did not alter the expression of ABCC1 mRNA. These results suggest that OA could be a good choice in the treatment of MDR tumours, either as a chemotherapic itself in tumours bearing ABCB1, or as an adjuvant in the chemotherapy of ABCC1 expressing tumours.

Membrane transporters play important roles in mediating chemosensitivity and -resistance of tumor cells. ABC transporters, such as ABCB1/MDR1, ABCC1/MRP1 and ABCG2/BCRP, are frequently associated with decreased cellular accumulation of anticancer drugs and multidrug resistance of tumors. SLC transporters, such as folate, nucleoside, and amino acid transporters, commonly increase chemosensitivity by mediating the cellular uptake of hydrophilic drugs. Ion channels and pumps variably affect sensitivity to anticancer therapy by modulating viability of tumor cells. A pharmacogenomic approach, using correlations between drug potency and transporter gene expression in multiple cancer cell lines, has shown promise for identifying potential drug-transporter relationships and predicting anticancer drug response, in an effort to optimize chemotherapy for individual patients.

Among the ABC proteins, some members including ABCB1, ABCC1, ABCC2 and ABCG2 are believed to contribute to multidrug resistance of cancer chemotherapy. In addition, the broad substrate-specificity and apical localization of the ABCB1 and ABCC2 in mucosal epithelium of intestine and hepatocyte give them a protective role against xenobiotics. The inter-individual variations in activity and expression levels of ABCB1 and ABCC2, thus, might affect on drug response and response to toxic substrates. In this review, I focus on (1) physiological and toxicological relevance of ABCB1 and ABCC2, and on (2) genetic variations of ABCB1 and ABCC2 genes and their association with biochemical function, expression level and tumor incidence.

Multidrug resistance is a major obstacle to cancer treatment and leads to poor prognosis for the patient. Multidrug resistance-associated protein 1 (MRP1) can confer drug resistance in vitro and MRP1 may play a role in the development of drug resistance in several cancers including acute myeloid leukaemia, small cell lung cancer, T-cell leukaemia and neuroblastoma. The majority of patients with neuroblastoma present with widely disseminated disease at diagnosis and despite intensive treatment, the prognosis for such patients is dismal. There is increasing evidence for the involvement of the MYCN oncogene, and its down-stream target, MRP1, in the development of multidrug resistance in neuroblastoma. Given the importance of MRP1 overexpression in neuroblastoma, MRP1 inhibition may be a clinically relevant approach to improving patient outcome in this disease.