MP39-14 METFORMIN IS A NEW THERAPEUTIC STRATEGY FOR TARGETING CD44 VARIANT IN BLADDER CANCER

Abstract

INTRODUCTION AND OBJECTIVES: Metformin is an oral biguanide drug widely used to treat type 2 diabetes mellitus and has recently been shown to have an antitumor effect through selectively targeting chemotherapy-resistant cancer stem cells, characterized by CD44+CD24phenotype. We focused particularly on variant isoforms of CD44 (CD44v) which have been recently reported as new markers for targeting cancer stem cells and evaluated whether metformin could have a therapeutic role for treating bladder cancer cells with a positive CD44v phenotype. METHODS: The efficacy of metformin alone and in combination with cisplatin was examined in T24 and HT1376 bladder cancer cell lines. WST assay was used to evaluate the cytotoxicity. The expressions of CD44v were evaluated by Western blotting analysis. The percentage of CD44v-positive cells in T24 cells treated with CDDP, metformin, or both were assessed by flow cytometry. A xenograft model was used to study the effects of metformin alone and in combination with cisplatin on bladder cancer tumor growth. Mice were divided into 4 groups; (1) no treatment, (2) metformin 200 ml/ml daily p.o., (3) cisplatin 2.5 mg/kg intraperitoneally for 1 day, or (4) combined metformin (200 ml/ml) and cisplatin (2.5 mg/kg). RESULTS: CD44v was positive in T24 cells, but not in HT1376 cells and significant dose-dependent growth inhibition by metformin was observed in T24 cells but not in HT1376 cells. Cell growth inhibition relative to vehicle control was significantly higher in the combination therapy (52.1%) compared to 1mM metformin alone (77.5%) or 1mM cisplatin alone (90.2%) in T24 cells. Flow cytometry showed that the percentage of CD44v-positive cells was 29.4%, 21.7%, 45.6%, and 42.6% in vehicle control, 1mM metformin, 1mM cisplatin, and the combination, respectively. The increased CD44v-positive cell population by cisplatin was reduced by metformin. In the T24 bladder cancer xenograft model, tumor volume at day 30 for the combination therapy was 467 75 mm3, which was significantly smaller than the vehicle control (1139 136 mm3), cisplatin monotherapy (1072 160 mm3), and metformin monotherapy (857 188 mm3) (p<0.001, p1⁄40.002 and p1⁄40.006, respectively). CONCLUSIONS: Metformin targeting CD44v-positive cells showed significant antitumor effects when given in combination with cisplatin for bladder cancer. Combined metformin and cisplatin therapy might be a novel therapeutic modality for treating bladder cancer.