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 n M of the synthetic androgen methyltrienolone (R1881), whereas 0.01 n M 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 n M , whereas 0.1 n M 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 non-steroidal 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. © 1999 Cancer Research Campaign

The major obstacle in the management of advanced prostate cancer is the occurrence of resistance to endocrine therapy. Although the androgen receptor (AR) has been linked to therapy failure, the underlying escape mechanisms have not been fully clarified. Being closely related to the AR, the glucocorticoid receptor (GR) has been suggested to play a role in enzalutamide and docetaxel resistance. Given that glucocorticoids are frequently applied to prostate cancer patients, it is essential to unravel the exact role of the GR in prostate cancer progression. Assessment of GR expression and functional significance in tissues from 177 prostate cancer patients, including 14 lymph node metastases, as well as in several human prostate cancer models, including androgen-dependent, androgen-independent, and long-term antiandrogen-treated cell lines. Although GR expression is reduced in primary prostate cancer tissue, it is restored in metastatic lesions. Relapse patients with high GR experience shortened progression-free survival. GR is significantly increased upon long-term abiraterone or enzalutamide treatment in the majority of preclinical models, thus identifying GR upregulation as an underlying mechanism for cells to bypass AR blockade. Importantly, GR inhibition by RNAi or chemical blockade results in impaired proliferation and 3D-spheroid formation in all tested cell lines. GR upregulation seems to be a common mechanism during antiandrogen treatment and supports the notion that targeting the GR pathway combined with antiandrogen medication may further improve prostate cancer therapy. .

Currently available methods for treatment of human prostatic carcinoma aim to inactivate the androgen receptor (AR) by androgen deprivation or blockade with anti-androgens. Failure of endocrine therapy and tumor progression is characterized by androgenindependent growth despite high levels of AR expression in metastatic disease. We inhibited AR expression in LNCaP prostate tumor cells by using antisense AR oligodeoxynucleotides (ODNs) and explored whether antisense AR treatment would be conceivable as a therapy for advanced prostate cancer. Among the various AR antisense ODNs tested, a 15-base ODN targeting the CAG repeats encoding the poly-glutamine region of the AR (as750/15) was found to be most effective. Treatment of LNCaP cells with as750/15 reduced AR expression to ϳ2% within 24 hours compared with mock-treated controls. AR down-regulation resulted in significant cell growth inhibition, strongly reduced secretion of the androgen-regulated prostate-specific antigen, reduction of epidermal growth factor receptor expression, and an increase in apoptotic cells. Mis-sense and mismatched control ODNs had no or only slight effects. Antisense inhibition was also very efficient in LNCaP-abl cells, a subline established after long-term androgen ablation of LNCaP cells, resulting in inhibition of AR expression and cell proliferation that was similar to that seen for parental LNCaP cells. This study shows that inhibition of AR expression by antisense AR ODNs may be a promising new approach for treatment of advanced human prostate cancer. Cancer Gene Therapy (2000) 7, 997-1007

Prostate cancer (PCa) is one of the most common causes of male cancer-related death in Western nations. The cellular response to androgens is mediated via the androgen receptor (AR), a ligand-inducible transcription factor whose dysregulation plays a key role during PCa development and progression following androgen deprivation therapy, the current mainstay systemic treatment for advanced PCa. Thus, a better understanding of AR signaling and new strategies to abrogate AR activity are essential for improved therapeutic intervention. Consequently, a large number of experimental cell culture models have been established to facilitate in vitro investigations into the role of AR signaling in PCa development and progression. These different model systems mimic distinct stages of this heterogeneous disease and exhibit differences with respect to AR expression/status and androgen responsiveness. Technological advances have facilitated the development of in vitro systems that more closely reflect the physiological setting, for example via the use of three-dimensional coculture to study the interaction of prostate epithelial cells with the stroma, endothelium, immune system and tissue matrix environment. This review provides an overview of the most commonly used in vitro cell models currently available to study AR signaling with particular focus on their use in addressing key questions relating to the development and progression of PCa. It is hoped that the continued development of in vitro models will provide more biologically relevant platforms for mechanistic studies, drug discovery and design ensuring a more rapid transfer of knowledge from the laboratory to the clinic.