Increased resistance to trail-induced apoptosis in prostate cancer cells selected in the presence of bicalutamide.

Background: Following prolonged treatment with the non-steroidal anti-androgen bicalutamide (Casodex), LNCaP cells have become resistant to this drug. Previously, we found that the bicalutamide-refractory subline LNCaP-Bic acquires a growth advantage and does not respond to androgenic stimulation. In the present study, we have asked whether changes in response to the tumor-selective apoptosis inducer TNF-related apoptosis-inducing ligand (TRAIL) occur in LNCaP-Bic cells.

Methods: LNCaP and LNCaP-Bic cells were incubated with increasing concentrations of TRAIL and apoptosis rate was analyzed using FACS. Expression of death receptors (DR), adaptor protein Fas-associated death domain (FADD), members of the Bcl-2 family, and caspases were investigated by Western blot.

Results: The percentage of cells undergoing apoptosis was lower in LNCaP-Bic in comparison to LNCaP cells. There were no major differences in death receptor expression between control LNCaP and bicalutamide-selected cells. Surprisingly, treatment with TRAIL increased the levels of Bcl-2 by 50% in LNCaP-Bic cells. The ratio cleaved caspase/procaspase-8 was substantially lower in LNCaP-Bic cells.

Conclusions: Reduced sensitivity to TRAIL-induced apoptosis is a novel mechanism relevant to resistance to bicalutamide in prostate cancer. Inability of TRAIL to cause programmed cell death might be caused by multiple perturbations in the TRAIL-signaling pathway.