The effect of antisense Bcl-2 oligonucleotides on Bcl-2 protein expressionand apoptosis in human bladder transitional cell carcinoma

Purpose: Bcl-2 is an important determinant of transitional cell carcinoma o f the bladder recurrence and progression as well as a factor in patient res ponse to chemotherapy or radiotherapy. We determined Bcl-2 down-regulation after antisense oligonucleotide therapy and synergism with mitomycin C in t ransitional cell carcinoma of the bladder. Materials and Methods: Bcl-2 protein was quantified using flow cytometry an d immunohistochemistry in 4 bladder cancer cell lines, in bladder washings from 6 patients with carcinoma in situ and in 16 patient tumor samples. The synergistic effects of antisense oligonucleotides G3139 and 2009, and mito mycin C were investigated in 4 cell lines, while 2009 down-regulation was e xamined in 20 tumor explants in an ex vivo model. Results: Bcl-2 protein expression was found in all 4 cell lines and in 5 of the 6 cell populations derived from patients with carcinoma in situ. Of th e 16 tumors 7 were classified positive by frozen section immunohistochemist ry and quantitative flow cytometry. G3139 and 2009 down-regulated Bel-2 pro tein expression in all 4 cell lines and 2009 down-regulated Bcl-2 protein e xpression in half of the Bel-2 positive tumor specimens. There was only evi dence in 1 cell line, T24/83, that Bcl-2 protein expression down-regulation enhanced mitomycin C induced apoptotic cell death. Conclusions: Bel-2 was expressed in a significant proportion of bladder tum ors and in carcinoma in situ. Therefore, antisense oligonucleotides represe nt a viable strategy for Bcl-2 protein down-regulation. However, it may not always translate into an increased level of mitomycin C induced apoptosis in transitional cell carcinoma of the bladder.