Switch from antagonist to agonist of the androgen receptor bicalutamide is associated with prostate tumour progression in a new model system.
Advanced prostate cancer is treated by androgen ablation and/or androgen receptor (AR) antagonists. In order to investigate the mechanisms relevant to the development of therapy-resistant tumours, we established a new tumour model which closely resembles the situation in patients who receive androgen ablation therapy. Androgen-sensitive LNCaP cells were kept in androgen-depleted medium for 87 passages. The new LNCaP cell subline established in this manner, LNCaP-abl, displayed a hypersensitive biphasic proliferative response to androgen until passage 75. Maximal proliferation of LNCaP-abl cells was achieved at 0.001 nM of the synthetic androgen methyltrienolone (R1881), whereas 0.01 nM of this compound induced the same effect in parental cells. At later passages (> 75), androgen exerted an inhibitory effect on growth of LNCaP-abl cells. The non-steroidal anti-androgen bicalutamide stimulated proliferation of LNCaP-abl cells. AR protein expression in LNCaP-abl cells increased approximately fourfold. The basal AR transcriptional activity was 30-fold higher in LNCaP-abl than in LNCaP cells. R1881 stimulated reporter gene activity in LNCaP-abl cells even at 0.01 nM, whereas 0.1 nM of R1881 was needed for induction of the same level of reporter gene activity in LNCaP cells. Bicalutamide that acts as a pure antagonist in parental LNCaP cells showed agonistic effects on AR transactivation activity in LNCaP-abl cells and was not able to block the effects of androgen in these cells. The non-steroidal AR blocker hydroxyflutamide exerted stimulatory effects on AR activity in both LNCaP and LNCaP-abl cells; however, the induction of reporter gene activity by hydroxyflutamide was 2.4- to 4-fold higher in the LNCaP-abl subline. The changes in AR activity were associated neither with a new alteration in AR cDNA sequence nor with amplification of the AR gene. Growth of LNCaP-abl xenografts in nude mice was stimulated by bicalutamide and repressed by testosterone. In conclusion, our results show for the first time that the nonsteroidal anti-androgen bicalutamide acquires agonistic properties during long-term androgen ablation. These findings may have repercussions on the natural course of prostate cancer with androgen deprivation and on strategies of therapeutic intervention.
Culig
Z
Z
Department of Urology, University of Innsbruck, Austria.
Hoffmann
J
J
Erdel
M
M
Eder
I E
IE
Hobisch
A
A
Hittmair
A
A
Bartsch
G
G
Utermann
G
G
Schneider
M R
MR
Parczyk
K
K
Klocker
H
H
D000726:Androgen Antagonists / Q000494:pharmacology*; D059002:Androgen Receptor Antagonists; D000728:Androgens; D000813:Anilides / Q000494:pharmacology*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002455:Cell Division; D006801:Humans; D008024:Ligands; D008297:Male; D051379:Mice; D009368:Neoplasm Transplantation; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D009570:Nitriles; D017430:Prostate-Specific Antigen / Q000096:biosynthesis; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000032:analysis; D011944:Receptors, Androgen / Q000187:drug effects*; D014105:Tosyl Compounds; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D000726:Androgen Antagonists; D059002:Androgen Receptor Antagonists; D000728:Androgens; D000813:Anilides; D000970:Antineoplastic Agents; D008024:Ligands; D009570:Nitriles; D012333:RNA, Messenger; D011944:Receptors, Androgen; D014105:Tosyl Compounds; C053541:bicalutamide; D017430:Prostate-Specific Antigen