To study the mechanisms whereby
androgen-dependent
tumors relapse in patients undergoing
androgen blockade, we developed a novel progression model for
prostate cancer. The PC346C cell line, established from a transurethral resection of a primary
tumor, expresses wild-type (wt)
androgen receptor (AR) and secretes
prostate-specific antigen (PSA). Optimal proliferation of PC346C requires
androgens and is inhibited by the
antiandrogen hydroxyflutamide. Orthotopic injection in the dorsal-lateral prostate of castrated athymic nude mice did not produce
tumors, whereas fast
tumor growth occurred in
sham-operated males. Three
androgen-independent sublines were derived from PC346C upon long-term in vitro
androgen deprivation: PC346DCC, PC346Flu1 and PC346Flu2. PC346DCC exhibited
androgen-insensitive growth, which was not inhibited by
flutamide. AR and PSA were detected at very low levels, coinciding with background AR activity in a reporter assay, which suggests that these cells have bypassed the AR pathway. PC346Flu1 and PC346Flu2 were derived by culture in
steroid-stripped medium supplemented with
hydroxyflutamide. PC346Flu1 strongly upregulated AR expression and showed 10-fold higher AR activation than the parental PC346C. PC346Flu1 proliferation was inhibited in vitro by
R1881 at 0.1 nM concentration, consistent with a slower
tumor growth rate in intact males than in castrated mice. PC346Flu2 carries the well-known T877A AR mutation, causing the receptor to become activated by diverse nonandrogenic
ligands including
hydroxyflutamide. Array-based comparative genomic hybridization revealed little change between the various PC346 lines. The common alterations include gain of chromosomes 1, 7 and 8q and loss of 13q, which are frequently found in
prostate cancer. In conclusion, by in vitro
hormone manipulations of a unique
androgen-dependent cell line expressing wtAR, we successfully reproduced common AR modifications observed in
hormone-refractory
prostate cancer: downregulation, overexpression and mutation.