Effect of Bcl-2 overexpression in human prostate cancer cells in vitro and in vivo

Background: Cancer cells often develop mechanisms to resist apoptosis and the extent of such anti-apoptotic ability has been shown to parallel tumor progression in various malignancies. Among various molecules implicated in regulating apoptosis pathway, bcl-2 and its family members are best characterized. Methods: To investigate the effect of bcl-2-mediated anti-apoptotic ability on tumor growth and progression in prostate cancer, a cell line overexpressing bcl-2 (LNCaP/bcl-2) was established by genetically engineering a prostate cancer cell line LNCaP. Tumor growth of LNCaP/bcl-2 was compared with the parental cell line in vitro and in vivo. Results: LNCaP/bcl-2 cells show resistance to apoptosis caused by nutrient deprivation and did not arrest when cultured in serum-free or androgen-free medium, while parental LNCaP cells or LNCaP cells transfected with the vector only (LNCaP/control) underwent extensive apoptosis on nutrient deprivation and sustained growth suppression in serum-free or androgen-free medium. When injected subcutaneously into nude mice, tumors deriving from LNCaP/bcl-2 cells grew faster compared with LNCaP/control for about 3 weeks (P = 0.02), but this effect was not evident after 5 weeks. Upon castration, the control tumors regressed but LNCaP/bcl-2-derived tumors showed resistance, as was previously reported. Conclusions: These data confirm the notion that anti-apoptotic function of bcl-2 is oncogenic and confers resistance to androgen deprivation and also indicate that it may also play a critical role in earlier stages of tumorigenesis.