Cordycepin Resensitizes T24R2 Cisplatin-Resistant Human Bladder Cancer Cells to Cisplatin by Inactivating Ets-1 Dependent MDR1 Transcription

Tumor cell resistance to anti-cancer drugs is a major obstacle in tumor therapy. In this study, we investigated the mechanism of cordycepin-mediated resensitization to cisplatin in T24R2 cells, a T24-derived cell line. Treatment with cordycepin or cisplatin (2 μg/mL) alone failed to induce cell death in T24R2 cells, but combination treatment with these drugs significantly induced apoptosis through mitochondrial pathways, including depolarization of mitochondrial membranes, decrease in anti-apoptotic proteins Bcl-2, Bcl-xL, and Mcl-1, and increase in pro-apoptotic proteins Bak and Bax. High expression levels of MDR1 were the cause of cisplatin resistance in T24R2 cells, and cordycepin significantly reduced MDR1 expression through inhibition of MDR1 promoter activity. MDR1 promoter activity was dependent on transcription factor Ets-1 in T24R2 cells. Although correlation exists between MDR1 and Ets-1 expression in bladder cancer patients, active Ets-1, Thr38 phosphorylated form (pThr38), was critical to induce MDR1 expression. Cordycepin decreased pThr-38 Ets-1 levels and reduced MDR1 transcription, probably through its effects on PI3K signaling, inducing the resensitization of T24R2 cells to cisplatin. The results suggest that cordycepin effectively resensitizes cisplatin-resistant bladder cancer cells to cisplatin, thus serving as a potential strategy for treatment of cancer in patients with resistance to anti-cancer drugs.

Cordycepin Resensitizes T24R2, Cisplatin-resistant Human Bladder Cancer Cell, to Cisplatin by Inhibiting the AKT-mediated Ets-1 Activation

Resistance of tumor cells to anticancer drugs is a major obstacle in tumor therapy. In this study, we investigated the mechanism of cordycepin-mediated resensitization to cisplatin inT24R2, a derived T24 cell line. Treatment with cordycepin or cisplatin (2 g/ml) alone could not induce cell death of T24R2, but combination treatment of these drugs significantly induced apoptosis of the cells through mitochondrial pathway including depolarization of mitochondrial membrane, decrease of anti-apoptotic proteins, Bcl-2, Bcl-xL, and Mcl-1, and increase of pro-apoptotic proteins, Bak and Bax. . High expression of MDR1 was the cause of cisplatin resistance in T24R2, and cordycepin significantly reduced MDR1 expression through inhibition of MDR1 promoter activity. MDR1 promoter activity was dependent on a transcription factor, Ets-1, in T24R2 cells. Although there is a correlation between MDR1 and Ets-1 expression in bladder cancer patients, active Ets-1, Thr-38 phosphorylated form (pThr-38), was critical to induce MDR1 expression. Cordycepin decreased pThr-38 Ets-1 level through inhibition of AKT, which reduced MDR1 transcription and induced the resensitization of T24R2 to cisplatin. The results suggest that cordycepin effectively resensitizes cisplatin-resistant bladder cancer cells to cisplatin, thus serving as a potential strategy for treatment of anti-cancer drug resistant patients.

Abstract 225: HSF-1 Knockout Induces Multidrug Resistance Gene (MDR1b) and Enhances Drug Extrusion in the Heart

Heat shock factor-1 (HSF-1), a transcription factor of heat shock proteins, is known to interfere with the transcriptional activity of many oncogenic and anti-inflammatory factors. In the present work we have discovered that HSF-1 ablation induced multidrug resistance gene (MDR1b) in the heart and increased the expression of P-glycoprotein (P-gp, ABCB1), an ATP binding cassette that is usually associated with multidrug resistant cancer cells, and it could successfully extrude doxorubicin (Dox) to alleviate Dox-induced heart failure and reduce mortality in mice. Cardiac MRI showed that Dox-induced left ventricular dysfunction was significantly reduced in HSF-1 -/- mice. NF-B nuclear translocation and DNA binding activity were higher in Dox-treated HSF-1 -/- mice. IB, the NF-B inhibitor, was depleted due to enhanced IKK-α activity. In parallel, MDR1b gene expression and a large increase in P-gp, and lowering Dox loading were observed in HSF-1 -/- mouse hearts. However, application of the P-gp antagonist, Verapamil, increased Dox loading in HSF-1 -/- cardiomyocytes, deteriorated cardiac function in HSF-1 -/- mice, and decreased survival. MDR1 promoter activity (as determined by luciferase reporter gene assay), was higher in HSF-1 -/- cardiomyocytes, whereas a mutant MDR1 promoter with heat shock elements (HSE) mutation showed increased activity only in HSF-1 +/+ cardiomyocytes. However, deletion of both HSE and NF- κB binding motifs diminished the luciferase luminescence, suggesting that HSF-1 competitively inhibits MDR1 promoter activity. Thus, since high levels of HSF-1 is attributed to poor prognosis of cancer, systemic down regulation of HSF-1 before chemotherapy is a potential therapeutic approach to ameliorate the chemotherapeutics-induced cardiotoxicity and enhance cancer prognosis.