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. Prostate 67: 1194–1201, 2007. © 2007 Wiley‐Liss, Inc.