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Objectives: Bcl-2 and Bcl-xL anti-apoptotic genes have been linked to treatment resistance and tumor progression in many tumors, including prostate cancer. The objectives of this study were to determine whether antisense (AS) Bcl-2 and Bcl-xL (Bcl-2/Bcl-xL) bispecific oligonucleotide (ODN) induces apoptosis and enhances chemosensitivity of paclitaxel in human androgen-independent prostate cancer PC3 cells. Methods: The potency of 5 AS ODN targeting various regions of high homology between Bcl-2 and Bcl-xL mRNA were evaluated in PC3 cells by real time PCR and Western blotting. MTT assay, flow cytometry, caspase-3 assay, and Western blotting of PARP were used to examine the effect of treatment with AS Bcl-2/Bcl-xL bispecific ODN on growth inhibition and induction of apoptosis in PC3 cells. Changes in other apoptosis-relevant genes (Bax, Bad, Bak, Mcl-1) were assessed by Western blotting. The efficacy of combined treatment with bispecific AS Bcl-2/Bcl-xL ODN + paclitaxel on PC3 cell growth was determined by MTT assay. Results: An AS-ODN with 100% sequence identity to Bcl-2 and 3-base mismatches to Bcl-xL was found to be the most potent inhibitor of both Bcl-2 and Bcl-xL expression in PC3 cells. AS Bcl-2/Bcl-xL bispecific ODN treatment reduced mRNA levels in a dose-dependent manner and at 1000 nM reduced Bcl-2 and Bcl-xL protein levels to 12 % and 19 %, respectively. Cell growth inhibition, activation of caspase-3, PARP cleavage and increases in the apoptotic sub-G1-G0 fraction were observed in PC3 cells treated with AS Bcl-2/Bcl-xL bispecific ODN. Interestingly, Mcl-1 was down-regulated as well, although levels of Bax, Bad or Bak were not altered. Furthermore, AS Bcl-2/Bcl-xL bispecific ODN enhanced paclitaxel chemosensitivity in PC3 cells reducing the concentration that reduces cell viability by 50 % (IC50) of paclitaxel from 100 nM to less than 10 nM. Conclusion: These findings illustrate that combined treatment with AS bcl-2/bcl-xL bispecific ODN plus paclitaxel could be an attractive strategy for inhibiting progression of androgen-independent prostate cancer through effective induction of apoptosis. In vivo testing is underway.

[Proc Amer Assoc Cancer Res, Volume 45, 2004]