Antitumor Activity of YM155, a Selective Small-Molecule Survivin Suppressant, Alone and in Combination with Docetaxel in Human Malignant Melanoma Models

Abstract

Aggressive cell growth and chemoresistance are notorious obstacles in melanoma therapy. Accumulating evidence suggests that survivin is preferentially expressed in cancer cells and plays a crucial role in cell division and apoptosis dysfunction. Here, we evaluated the therapeutic potential of YM155, a selective survivin suppressant, alone and in combination with docetaxel using human melanoma models. A375 and SK-MEL-5 human malignant melanoma cells were treated with siRNA, YM155, and/or docetaxel, and cell viability, mRNA and protein expression levels, cell-cycle distribution, and immunohistochemical staining were then evaluated. Furthermore, the efficacy of YM155 combined with docetaxel was further examined in established xenograft models. Survivin suppression was sufficient to induce spontaneous apoptosis of melanoma cells. YM155 showed nanomolar antiproliferative effects and induced tumor regression in established melanoma xenograft models. Docetaxel showed antitumor activity against melanoma cells, although it also induced survivin upregulation and G(2)/M mitotic arrest; however, cotreatment with YM155 decreased survivin expression below basal levels. Combination treatment of YM155 and docetaxel induced a greater rate of apoptosis than the sum of the single-treatment rates and promoted tumor regression without enhanced body weight loss in the melanoma xenograft models. Survivin is responsible for the inherent low levels of spontaneous apoptosis in melanoma cells. The concomitant combination of YM155 with docetaxel diminished the accumulation of survivin in G(2)/M mitotic arrest, and induced more intense apoptosis compared with each single treatment. YM155 in combination with docetaxel is well tolerated and shows greater efficacy than either agent alone in mouse xenograft models.