Expression of the inhibitors of apoptosis proteins in cisplatin-resistant prostate cancer cells

Acquired multi-drug resistance remains a major obstacle in the management of prostate cancer. The objective of this study was to examine whether chemoresistance could be due in part to the expression of the inhibitors of apoptosis proteins (IAPs). We established cisplatin-resistant LNCaP sublines. We examined the effects of cisplatin on cell growth and apoptosis in LNCaP cells and LNCaP sublines by 2-(4-lodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H- tetrazolium, monosodium salt (WST-1) assay and Hoechst 33258 staining, and analyzed cross-resistance to adriamycin, 5-fluorouracil, taxol, taxotere, and etoposide. In addition, the expression of IAP-1, IAP-2, X-linked IAP (XIAP), neuronal apoptosis inhibitory protein, and survivin was investigated by immunoblot analysis in LNCaP sublines. Although the growth rates were reduced in a dose-dependent manner by cisplatin in LNCaP sublines, the anti-proliferative effects of cisplatin were significantly decreased in LNCaP sublines compared to LNCaP cells. Cisplatin-resistant sublines, LNCaP/C1, LNCaP/ C2, and LNCaP/C3 cells, were 6.3, 9.1-, and 22.3-fold more resistant to cisplatin than LNCaP cells, respectively, and this resistance was paralleled with reduced induction of apoptosis. LNCaP/C3 cells showed cross-resistance to adriamycin, 5-fluorouracil, and etoposide whereas those cells exhibited no or only weak cross-resistance against taxol and taxotere. With the exception of survivin, all the TAPs were identified in LNCaP cells by immunoblot analysis. Interestingly, the expression of IAP-2, XIAP, and survivin gradually increased with the extent of cisplatin-resistance. Altered expression of IAP-2, XIAP, and survivin was involved in these phenotypes of cisplatin-resistant LNCaP sublines. IAPs may make an important contribution to the resistance to the apoptotic effect of cisplatin in prostate cancer.