Inhibition of bcl-2 enhances the efficacy of chemotherapy in renal cell carcinoma

OBJECTIVES: Renal cell cancer (RCC) is highly resistant to chemotherapy. Increased expression of the antiapoptotic gene bcl-2 in tumors is known to be associated with poor responses to systemic treatment of cancer. Down-regulation of bcl-2 expression using antisense oligonucleotides (asON) has been shown to increase chemosensitivity in clinical phase I-III studies with various cancers. However, no studies on the efficacy of this approach in RCC have been reported so far. This study aimed to evaluate whether bcl-2 asON could enhance efficacy of chemotherapy in human RCC. MATERIAL AND METHODS: Expression of bcl-2 mRNA and protein was analyzed in different RCC cell lines by RT-PCR and Western blot. Cells with high or low bcl-2 mRNA and protein expression were treated with different concentrations of bcl-2 asON in combination with cisplatin. AsON-induced down-regulation of bcl-2 mRNA and protein was documented by RT-PCR and Western blot. Treatment effects on cell viability were analyzed by colorimetric tetrazolium (MTT) assay. Immunohistochemical staining of M30-positive cells was performed for quantification of apoptotic cells. RESULTS: Transfection of high bcl-2 expressing cells with bcl-2 asON alone induced no reduction of cell viability at a concentration range from 100-1000 nM. In combination therapy, pretreatment with asON significantly enhanced MTT reduction after cisplatin treatment. IC50 concentrations of cisplatin were 1 microg/ml with and 2.7 microg/ml without prior incubation. The marked reduction of cell viability correlated with an 8-fold increase of apoptotic cells after combination treatment. Only a minor increase of cisplatin effectivity was noted after asON preincubation of cells with lower bcl-2 expression. CONCLUSIONS: The combination of cisplatin and bcl-2 antisense ON exerts significantly greater effects on cell viability and apoptosis than either agent used alone on human RCC cells. These data indicate that inhibition of bcl-2 expression may be an attractive therapeutic strategy in RCC tumors with high bcl-2 expression.