bcl-xL antisense treatment induces apoptosis in breast carcinoma cells

Upregulated expression of bcl-xL is involved in the initiation and progress ion of breast cancer by inhibiting tumor cell apoptosis. Here we describe t he use of the 2'-O-methoxy-ethoxy antisense oligonucleotide 4259 targeting nucleotides 687-706 of the bcl-xL mRNA, a sequence that does not occur in t he pro-apoptotic bcl-xS transcript, to restore apoptosis in estrogen-depend ent and independent breast carcinoma cells. The antisense effect of oligonu cleotide 4259 was examined on the mRNA and protein level using real-time PC R and Western blot analysis, respectively, and the induction of cell death was investigated in viability and apoptosis assays. Treatment of MCF7 cells with oligonucleotide 4259 at a concentration of 600 nM for 20 hr decreased bcl-xL mRNA and protein levels by more than 80% and 50%, respectively. Thi s resulted in the induction of apoptosis characterized by mitochondrial cyt ochrome c release, decrease of mitochondrial transmembrane potential, and t he appearance of condensed nuclei in approximately 40% of cells. Moreover, oligonucleotide 4259 efficiently downregulated bcl-xL expression and decrea sed cell growth in the breast carcinoma cell lines T-47D, ZR-75-1, and MDA- MB-231. Our data emphasize the importance of bcl-xL as a survival factor fo r breast carcinoma cells and suggest that oligonucleotide 4259 deserves fur ther investigations for use in breast cancer therapy. Int. J. Cancer 87:582 -590, 2000. (C) 2000 Wiley-Liss, Inc.