Development Of Chemoresistance In Cancer Research Articles

Knockdown of BAP31 Downregulates Galectin-3 to Inhibit the Wnt/β-Catenin Signaling Pathway to Modulate 5-FU Chemosensitivity and Cancer Stemness in Colorectal Cancer.

Increased stemness is causally linked to the development of chemoresistance in cancers. B-cell receptor-associated protein 31 (BAP31) has been identified to play an oncogenic role in many types of cancer. However, the role of BAP31 in 5-fluorouracil (5-FU) chemosensitivity and stemness of colorectal cancer (CRC) is still unknown. The aim of this study was to investigate the biological function and molecular mechanism of BAP31 in regulating 5-FU chemosensitivity and stemness. The correlation between BAP31 expression and 5-FU chemosensitivity was examined using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide and colony formation assays. Cancer stemness was analyzed using tumor sphere formation and Western blot assays. Western blot and immunofluorescence analyses of the knockdown cell lines were performed to explore the possible mechanisms. Finally, we investigated the function of BAP31 by constructing xenograft nude mouse models in vivo. In this study, we demonstrated that BAP31 was increased in CRC cells, and knockdown of BAP31 reduced the half maximal inhibitory concentration (IC50) of 5-FU, while this effect was reversed by overexpression of BAP31. In addition, knockdown of BAP31 substantially reduced the stemness of CRC cells in vitro. Consistently, knockdown of BAP31 significantly suppressed the tumorigenicity and stemness of CRC in vivo. The functional study further suggested that knockdown of BAP31 downregulated galectin-3 to inhibit the accumulation of β-catenin, which in turn repressed the transcription of downstream target genes (c-MYC, SOX2) of the Wnt/β-catenin signaling pathway. Knockdown of BAP31 reduced stemness by inhibiting the Wnt/β-catenin signaling pathway to increase 5-FU chemosensitivity. Importantly, intrabodies against BAP31 suppressed tumor growth and enhanced the antitumor effects of 5-FU in vivo. Therefore, using intrabodies against BAP31 may be a strategy for improving the antitumor effect of 5-FU in CRC.

Effects of trans-(±)-kusunokinin on chemosensitive and chemoresistant ovarian cancer cells.

Ovarian cancer ranks eighth in cancer incidence and mortality among women worldwide. Cisplatin-based chemotherapy is commonly used for patients with ovarian cancer. However, the clinical efficacy of cisplatin is limited due to the occurrence of adverse side effects and development of cancer chemoresistance during treatment. Trans-(±)-kusunokinin has been previously reported to inhibit cell proliferation and induce cell apoptosis in various cancer cell types, including breast, colon and cholangiocarcinoma. However, the potential effects of (±)-kusunokinin on ovarian cancer remains unknown. In the present study, chemosensitive ovarian cancer cell line A2780 and chemoresistant ovarian cancer cell lines A2780cis, SKOV-3 and OVCAR-3 were treated with trans-(±)-kusunokinin to investigate its potential effects. MTT, colony formation, apoptosis and multi-caspase assays were used to determine cytotoxicity, the ability of single cells to form colonies, induction of apoptosis and multi-caspase activity, respectively. Moreover, western blot analysis was performed to determine the proteins level of topoisomerase II, cyclin D1, CDK1, Bax and p53-upregulated modulator of apoptosis (PUMA). The results demonstrated that trans-(±)-kusunokinin exhibited the strongest cytotoxicity against A2780cis cells with an IC50 value of 3.4 µM whilst also reducing the colony formation of A2780 and A2780cis cells. Trans-(±)-kusunokinin also induced the cells to undergo apoptosis and increased multi-caspase activity in A2780 and A2780cis cells. This compound significantly downregulated topoisomerase II, cyclin D1 and CDK1 expression, but upregulated Bax and PUMA expression in both A2780 and A2780cis cells. In conclusion, trans-(±)-kusunokinin suppressed ovarian cancer cells through the inhibition of colony formation, cell proliferation and the induction of apoptosis. This pure compound could be a potential targeted therapy for ovarian cancer treatment in the future. However, studies in an animal model and clinical trial need to be performed to support the efficacy and safety of this new treatment.

Resistance to platinum-based cancer drugs: a special focus on epigenetic mechanisms.

Chemoresistance is a significant clinical challenge, limiting the drug response in cancer. Several mechanisms associated with drug resistance have been characterized, and the role of epigenetics in generating resistance to platinum-based drugs has been clarified. Epigenetic mechanisms such as DNA methylation, histone modification, long noncoding RNA, and microRNA affect the expression of genes implicated in absorption, distribution, metabolism and excretion (ADME) of drugs, and other non-ADME genes that encode enzymes involved in the processes of cell proliferation, DNA repair, apoptosis and signal transduction key in the development of chemoresistance in cancer, specifically in platinum-based drugs. This review summarizes current discoveries in epigenetic regulation implicated in platinum drug resistance in cancer and the main clinical trials based on epigenetic therapy, evaluating their potential synergy with platinum-based drugs.

MiR-221/222-Mediated Inhibition of Autophagy Promotes Dexamethasone Resistance in Multiple Myeloma.

Inherent or acquired resistance to chemotherapeutic drugs is still an obstacle for the treatment of multiple myeloma (MM). MicroRNA dysregulation is related to the development of chemoresistance in cancers. However, its role in chemoresistance of MM is largely unknown. Here we demonstrated that miR-221/222 were upregulated in plasma cells from patientswith MM, especially those with relapsed or refractory disease. Moreover, expression levels of miR-221/222 were inversely correlated with dexamethasone (Dex) sensitivity of human MM cell lines. Importantly, we found that Dex induced pro-death autophagy in MM cells and the inhibition of autophagy significantly decreased Dex-induced cell death. Mechanistically, autophagy-related gene 12 (ATG12) was identified as a novel target gene of miR-221/222, and miR-221/222 overexpressioninhibited autophagy by directly targeting ATG12 and the p27kip (p27)-mammalian target of rapamycin (mTOR) pathway. Indeed, Dex treatment decreased the expression of miR-221/222, thereby activating the ATG12/p27-mTOR autophagy-regulatory axis and inducing cell death in Dex-sensitive MM cells. Furthermore, both invitro and invivo results showed that the inhibitions of miR-221/222 increased the expression of ATG12 and p27 and functionally induced extended autophagy and cell death of MM cells. In conclusion, our findings demonstrated the crucial role of the miR-221/222-ATG12/p27-mTOR autophagy-regulatory axis in Dex resistance of MM, and they suggest potential prediction and treatmentstrategies for glucocorticoid resistance.

Bcl-2 Antiapoptotic Family Proteins and Chemoresistance in Cancer.

Cancer is a daunting global problem confronting the world's population. The most frequent therapeutic approaches include surgery, chemotherapy, radiotherapy, and more recently immunotherapy. In the case of chemotherapy, patients ultimately develop resistance to both single and multiple chemotherapeutic agents, which can culminate in metastatic disease which is a major cause of patient death from solid tumors. Chemoresistance, a primary cause of treatment failure, is attributed to multiple factors including decreased drug accumulation, reduced drug-target interactions, increased populations of cancer stem cells, enhanced autophagy activity, and reduced apoptosis in cancer cells. Reprogramming tumor cells to undergo drug-induced apoptosis provides a promising and powerful strategy for treating resistant and recurrent neoplastic diseases. This can be achieved by downregulating dysregulated antiapoptotic factors or activation of proapoptotic factors in tumor cells. A major target of dysregulation in cancer cells that can occur during chemoresistance involves altered expression of Bcl-2 family members. Bcl-2 antiapoptotic molecules (Bcl-2, Bcl-xL, and Mcl-1) are frequently upregulated in acquired chemoresistant cancer cells, which block drug-induced apoptosis. We presently overview the potential role of Bcl-2 antiapoptotic proteins in the development of cancer chemoresistance and overview the clinical approaches that use Bcl-2 inhibitors to restore cell death in chemoresistant and recurrent tumors.

Emerging Roles for Modulation of microRNA Signatures in Cancer Chemoprevention

miRNAs are small endogenous non-coding RNAs, approximately 21-nucleotides in length, which are shown to regulate an array of cellular processes such as differentiation, cell cycle, cell proliferation, apoptosis, and angiogenesis which are important in cancer. miRNAs can function as both tumor promoters (oncomiRs) or tumor suppressors by their ability to target numerous biomolecules that are important in carcinogenesis. Aberrant expression of miRNAs is correlated with the development and progression of tumors, and the reversal of their expression has been shown to modulate the cancer phenotype suggesting the potential of miRNAs as targets for anti-cancer drugs. Several chemopreventive phytochemicals like epigallocatechin-3-gallate, curcumin, isoflavones, indole-3-carbinol, resveratrol, and isothiocyanate have been shown to modulate the expression of numerous miRNAs in cancer cells that lead to either abrogation of tumor growth or sensitization of cancer cells to chemotherapeutic agents. This review focuses on the putative role(s) of miRNAs in different aspects of tumorigenesis and at various stages of early drug discovery that makes them a promising class of drug targets for chemopreventive intervention in cancer. We summarize the current progress in the development of strategies for miRNA-based anti-cancer therapies. We also explore the modulation of miRNAs by various cancer chemopreventive agents and the role of miRNAs in drug metabolism. We will discuss the role of miRNAs in cancer stem cells and epithelial-to-mesenchymal transition; and talk about how modulation of miRNA expression relates to altered glycosylation patterns in cancer cells. In addition, we consider the role of altered miRNA expression in carcinogenesis induced by various agents including genotoxic and epigenetic carcinogens. Finally, we will end with a discussion on the potential involvement of miRNAs in the development of cancer chemoresistance. Taken together, a better understanding of the complex role(s) of miRNAs in cancer may help in designing better strategies for biomarker discovery or drug targeting of miRNAs and/or their putative protein targets.

ABCG2 is a direct transcriptional target of hedgehog signaling and involved in stroma-induced drug tolerance in diffuse large B-cell lymphoma

Successful treatment of diffuse large B-cell lymphoma (DLBCL) is frequently hindered by development of resistance to conventional chemotherapy resulting in disease relapse and high mortality. High expression of anti-apoptotic and/or drug transporter proteins induced by oncogenic signaling pathways has been implicated in the development of chemoresistance in cancer. Previously, our studies showed high expression of ATP-binding cassette drug transporter ABCG2 in DLBCL correlated inversely with disease-free and failure-free survival. In this study, we have implicated activated hedgehog (Hh) signaling pathway as a key factor behind high ABCG2 expression in DLBCL through direct upregulation of ABCG2 gene transcription. We have identified a single binding site for GLI transcription factors in the ABCG2 promoter and established its functionality using luciferase reporter, site-directed mutagenesis and chromatin-immunoprecipitation assays. Furthermore, in DLBCL tumor samples, significantly high ABCG2 and GLI1 levels were found in DLBCL tumors with lymph node involvement in comparison to DLBCL tumor cells collected from pleural and/or peritoneal effusions. This suggests a role for the stromal microenvironment in maintaining high levels of ABCG2 and GLI1. Accordingly, in vitro co-culture of DLBCL cells with HS-5 stromal cells increased ABCG2 mRNA and protein levels by paracrine activation of Hh signaling. In addition to ABCG2, co-culture of DLBCL cells with HS-5 cells also resulted in increase expression of the antiapoptotic proteins BCL2, BCL-xL and BCL2A1 and in induced chemotolerance to doxorubicin and methotrexate, drugs routinely used for the treatment of DLBCL. Similarly, activation of Hh signaling in DLBCL cell lines with recombinant Shh N-terminal peptide resulted in increased expression of BCL2 and ABCG2 associated with increased chemotolerance. Finally, functional inhibition of ABCG2 drug efflux activity with fumitremorgin (FTC) or inhibition of Hh signaling with cyclopamine-KAAD abrogated the stroma-induced chemotolerance suggesting that targeting ABCG2 and Hh signaling may have therapeutic value in overcoming chemoresistance in DLBCL.

Stroma-Induced Increase In ABCG2 Expression Is Involved In Resistance to Chemotherapy In Diffuse Large B-Cell Lymphoma

AbstractAbstract 972Successful treatment of diffuse large B-cell lymphoma (DLBCL) is frequently hindered by development of resistance to conventional chemotherapy resulting in disease relapse and high mortality. High expression of anti-apoptotic and/or drug transporter proteins induced by oncogenic signaling pathways has been implicated in the development of chemoresistance in cancer. However, the cellular mechanisms responsible for drug resistance and treatment failure in DLBCL are poorly understood and their elucidation could lead to development of new therapeutic approaches. Activated Hedgehog (HH) signaling was identified in our laboratory to contribute to DLBCL cell survival and proliferation. We also found that inhibiting HH signaling resulted in decrease of BCL-2 protein and mRNA levels in ABC DLBCL cells but not in GC DLBCL cells, and that the resistance to apoptosis to HH inhibition observed in GC DLBCL cells can be overcome using the BCL2 inhibitor YC137. (Leukemia 2010;24:1025). We also found that the drug transporter protein ABCG2 is a potential prognostic factor in DLBCL given that its expression (as detected by immunohistochemistry) inversely correlated with overall survival and failure-free survival (Mod Pathol 2009;22:1312). Here, we investigate potential mechanistic connections between HH signaling and chemoresistance in DLBCL. Using chromatin immunoprecipitation (ChIP), site directed mutagenesis and luciferase reporter based assays, we confirmed the presence of a GLI-1 transcription factor-binding site in the ABCG2 gene promoter and we established ABCG2 gene as a direct downstream target of HH signaling. We also characterized the baseline expression and functionality of ABCG2 in DLBCL cell lines and explored the role of stroma in modulating its expression levels as well as the expression of other drug transporters (MDR1 and ABCC1) and the levels of the anti-apoptotic proteins, BCL-2, BCL2A1 and BCL-xL. Co-culturing DLBCL cell lines (BJAB and DOHH2) with human bone marrow stromal cells (HS5) resulted in decreased chemosensitivity to doxorubicin and methotrexate that was associated to marked increased expression levels of the drug transporters ABCG2, MDR1 and ABCC1 as well as of the expression levels of BCL2, BCL2A1 and BCL-xL. Our results also showed that pharmacologic inhibition of the activity of ABCG2, using fumitremorgin C and glefanine, significantly increased the chemosensitivity of BJAB and DOHH2 cells in the presence of stromal cells. However, this effect was not seen in the absence of stromal cells. Collectively, our data confirm that the stromal cells plays a role in inducing chemoresistance in DLBCL and that this effect is in part mediated by inducing high expression of drug protein transporters and antiapoptotic proteins. Inhibition of HH signaling as well as inhibition of drug transporters abrogates the stroma-induced chemoresistance suggesting that targeting these molecules may have a therapeutic value for the treatment of DLBCL. Disclosures:No relevant conflicts of interest to declare.