A randomized phase 1 study of testosterone replacement for patients with low-risk castration-resistant prostate cancer

Bipolar Androgen Therapy: When Excess Fuel Extinguishes the Fire

Androgen deprivation therapy (ADT) remains the cornerstone of advanced prostate cancer treatment. However, the progression towards castration-resistant prostate cancer is inevitable, as the cancer cells reactivate androgen receptor signaling and adapt to the castrate state through autoregulation of the androgen receptor. Additionally, the upfront use of novel hormonal agents such as enzalutamide and abiraterone acetate may result in long-term toxicities and may trigger the selection of AR-independent cells through "Darwinian" treatment-induced pressure. Therefore, it is crucial to develop new strategies to overcome these challenges. Bipolar androgen therapy (BAT) is one such approach that has been devised based on studies demonstrating the paradoxical inhibitory effects of supraphysiologic testosterone on prostate cancer growth, achieved through a variety of mechanisms acting in concert. BAT involves rapidly alternating testosterone levels between supraphysiological and near-castrate levels over a period of a month, achieved through monthly intramuscular injections of testosterone plus concurrent ADT. BAT is effective and well-tolerated, improving quality of life and potentially re-sensitizing patients to previous hormonal therapies after progression. By exploring the mechanisms and clinical evidence for BAT, this review seeks to shed light on its potential as a promising new approach to prostate cancer treatment.

The testosterone paradox of advanced prostate cancer: mechanistic insights and clinical implications

The discovery of the benefits of castration for prostate cancer treatment in 1941 led to androgen deprivation therapy, which remains a mainstay of the treatment of men with advanced prostate cancer. However, as early as this original publication, the inevitable development of castration-resistant prostate cancer was recognized. Resistance first manifests as a sustained rise in the androgen-responsive gene, PSA, consistent with reactivation of the androgen receptor axis. Evaluation of clinical specimens demonstrates that castration-resistant prostate cancer cells remain addicted to androgen signalling and adapt to chronic low-testosterone states. Paradoxically, results of several studies have suggested that treatment with supraphysiological levels of testosterone can retard prostate cancer growth. Insights from these studies have been used to investigate administration of supraphysiological testosterone to patients with prostate cancer for clinical benefits, a strategy that is termed bipolar androgen therapy (BAT). BAT involves rapid cycling from supraphysiological back to near-castration testosterone levels over a 4-week cycle. Understanding how BAT works at the molecular and cellular levels might help to rationalize combining BAT with other agents to achieve increased efficacy and tumour responses.

The role of testosterone in men's health: is it time for a new approach?

PURPOSE

Because of many unanswered questions regarding men's health, a literature review was performed to better understand the role of testosterone and testosterone replacement therapy (TRT) in the management of hypogonadism and aging related prostate gland diseases (ARPGD) including prostate cancer (PCa) and benign prostatic hyperplasia (BPH) with lower urinary tract symptoms (LUTS).

METHODS

The PubMed database was screened for pertinent peer reviewed articles published during the last four decades that culminated in the positions and recommendations in this paper.

RESULTS

Hypogonadism seriously impacts men's health, and the diagnosis remains controversial. The incidence of ARPGD is projected to increase worldwide and treatment still has significant limitations. There is compelling evidence that lower, not higher, testosterone levels trigger the development of PCa and BPH through androgen receptor over-expression. TRT was found to be safe and effective in treating hypogonadism including in PCa survivors and those harboring PCa. There is also evidence that TRT might reduce the incidence and prevalence of ARPGD.

CONCLUSIONS AND RECOMMENDATIONS

This review synthesizes a wide-ranging compendium of basic science and clinical research that strongly encourages altering the present approach to diagnosing and treating men with hypogonadism and ARPGD. These findings underscore the importance of avoiding significant testosterone decline and support the use of TRT. Ten recommendations are offered as a framework for the way forward. It is now time for clinicians, payers, researchers, funding agencies, professional associations, and patient advocacy groups to embrace this new paradigm to increase longevity and improve the quality of life.

High-dose-androgen-induced autophagic cell death to suppress the Enzalutamide-resistant prostate cancer growth via altering the circRNA-BCL2/miRNA-198/AMBRA1 signaling

Androgen deprivation therapy (ADT) is a gold standard treatment for advanced PCa. However, most patients eventually develop the castration-resistant prostate cancer (CRPC) that progresses rapidly despite ongoing systemic androgen deprivation. While early studies indicated that high physiological doses of androgens might suppress rather than promote PCa cell growth in some selective CRPC patients, the exact mechanism of this opposite effect remains unclear. Here we found that Enzalutamide-resistant (EnzR) CRPC cells can be suppressed by the high-dose-androgen (dihydrotestosterone, DHT). Mechanism dissection suggested that a high-dose-DHT can suppress the circular RNA-BCL2 (circRNA-BCL2) expression via transcriptional regulation of its host gene BCL2. The suppressed circRNA-BCL2 can then alter the expression of miRNA-198 to modulate the AMBRA1 expression via direct binding to the 3′UTR of AMBRA1 mRNA. The consequences of high-dose-DHT suppressed circRNA-BCL2/miRNA-198/AMBRA1 signaling likely result in induction of the autophagic cell death to suppress the EnzR CRPC cell growth. Preclinical studies using in vivo xenograft mouse models also demonstrated that AMBRA1-shRNA to suppress the autophagic cell death can weaken the effect of high-dose-DHT on EnzR CRPC tumors. Together, these in vitro and in vivo data provide new insights for understanding the mechanisms underlying high-dose-DHT suppression of the EnzR CRPC cell growth, supporting a potential therapy using high-dose-androgens to suppress CRPC progression in the future.

Role of PI3K-AKT-mTOR Pathway as a Pro-Survival Signaling and Resistance-Mediating Mechanism to Therapy of Prostate Cancer

Androgen deprivation therapy (ADT) and androgen receptor (AR)-targeted therapy are the gold standard options for treating prostate cancer (PCa). These are initially effective, as localized and the early stage of metastatic disease are androgen- and castration-sensitive. The tumor strongly relies on systemic/circulating androgens for activating AR signaling to stimulate growth and progression. However, after a certain point, the tumor will eventually develop a resistant stage, where ADT and AR antagonists are no longer effective. Mechanistically, it seems that the tumor becomes more aggressive through adaptive responses, relies more on alternative activated pathways, and is less dependent on AR signaling. This includes hyperactivation of PI3K-AKT-mTOR pathway, which is a central signal that regulates cell pro-survival/anti-apoptotic pathways, thus, compensating the blockade of AR signaling. The PI3K-AKT-mTOR pathway is well-documented for its crosstalk between genomic and non-genomic AR signaling, as well as other signaling cascades. Such a reciprocal feedback loop makes it more complicated to target individual factor/signaling for treating PCa. Here, we highlight the role of PI3K-AKT-mTOR signaling as a resistance mechanism for PCa therapy and illustrate the transition of prostate tumor from AR signaling-dependent to PI3K-AKT-mTOR pathway-dependent. Moreover, therapeutic strategies with inhibitors targeting the PI3K-AKT-mTOR signal used in clinic and ongoing clinical trials are discussed.

Testosterone Replacement Therapy in Men with Untreated or Treated Prostate Cancer: Do We Have Enough Evidences?

PURPOSE

To investigate the oncologic safety of testosterone replacement therapy (TRT) in men with untreated or treated prostate cancer.

MATERIALS AND METHODS

We systematically searched PubMed, Embase, and Cochrane library database from January 1941 to March 2019.

RESULTS

In total, 36 articles met the eligibility criteria for this systematic review. They included a total of 2,459 TRT-treated patients, with a median of 20 patients per study (range: 1-1,142). Except for four studies, all were single-armed studies with poor quality scores (median MINOR, 9 of 24). Of the 36 studies, prostate cancer was managed through active surveillance (AS), in 5 studies; radical prostatectomy, in 11 studies; radiation therapy, in 5 studies; multiple intervention modalities, in 5 studies; and systemic therapy, in 9 studies. In comparison with TRT-treated and untreated patients, the pooled risk ratio (RR) was not significantly higher than one in comparisons of risk for disease progression (pooled RR, 0.83; 95% confidence interval, 0.57-1.21). The results of systematic review implied that TRT might be harmful in men with advanced disease (progression rate: 38.5%-100.0%), who undergo AS (15.4%-57.1%), and who successfully treated but having high-risk disease (0.0%-50.0%).

CONCLUSIONS

Compared to TRT-untreated patients, TRT-treated patients may not have increased risks for disease progression in prostate cancer. However, the quality of currently available evidence is extremely poor. TRT may be harmful in men with advanced disease burden, in those with untreated prostate cancer undergoing AS, and in those with successfully treated prostate cancer but having high-risk disease.

High estrogen receptor alpha activation confers resistance to estrogen deprivation and is required for therapeutic response to estrogen in breast cancer

Estrogen receptor alpha (ER)-positive breast cancer is commonly treated with endocrine therapies, including antiestrogens that bind and inhibit ER activity, and aromatase inhibitors that suppress estrogen biosynthesis to inhibit estrogen-dependent ER activity. Paradoxically, treatment with estrogens such as 17b-estradiol can also be effective against ER+ breast cancer. Despite the known efficacy of estrogen therapy, the lack of a predictive biomarker of response and understanding of the mechanism of action have contributed to its limited clinical use. Herein, we demonstrate that ER overexpression confers resistance to estrogen deprivation through ER activation in human ER+ breast cancer cells and xenografts grown in mice. However, ER overexpression and the associated high levels of ER transcriptional activation converted 17b-estradiol from a growth-promoter to a growth-suppressor, offering a targetable therapeutic vulnerability and a potential means of identifying patients likely to benefit from estrogen therapy. Since ER+ breast cancer cells and tumors ultimately developed resistance to continuous estrogen deprivation or continuous 17b-estradiol treatment, we tested schedules of alternating treatments. Oscillation of ER activity through cycling of 17b-estradiol and estrogen deprivation provided long-term control of patient-derived xenografts, offering a novel endocrine-only strategy to manage ER+ breast cancer.

The role of androgen therapy in prostate cancer: from testosterone replacement therapy to bipolar androgen therapy

Testosterone replacement therapy (TRT) is the primary treatment for male testosterone deficiency. This therapy raises concerns over the risk of prostate cancer (PC), because testosterone has historically been considered the fuel for PC. We discuss the re-evaluation of the relationship between androgen and PC, and highlight the safety of TRT in the treatment of symptomatic men with testosterone deficiency who have low-risk disease after treatment for localized PC with surgery or radiation. Furthermore, we review the clinical application and potential mechanisms of bipolar androgen therapy (BAT) in the treatment of castration-resistant PC, emphasizing that much remains to be done before BAT can be broadly applied.

Bipolar androgen therapy in prostate cancer: Current evidences and future perspectives

Testosterone suppression by androgen deprivation therapy is the cornerstone of prostate cancer treatment. New-generation hormone therapies improved overall survival in castration-resistant prostate cancer. More recent trials showed a further increase in overall survival when enzalutamide or abiraterone are associated with androgen deprivation therapy in hormone-sensitive disease. However, a higher clonal pressure may lead to the upregulation of alternative pathways for cancer progression and to dedifferentiated diseases that would probably respond poorly to subsequent treatments. In this contest, new strategies that could be able to delay or even revert resistance are needed. The bipolar androgen therapy is an under-investigation treatment that consists in periodical oscillation between castration levels and supraphysiological levels of testosterone in order to prevent the adaptation of prostate cancer cells to a low-androgen environment. This review aims to underline the biological rationale of bipolar androgen therapy and gather evidences from the most recent clinical trials.

Evaluation of the genomic alterations in the androgen receptor gene during treatment with high-dose testosterone for metastatic castrate-resistant prostate cancer

INTRODUCTION

Castration resistant prostate cancer (CRPC) has been characterized by a reactivation of the androgen receptor (AR) signaling pathway via alterations in androgen metabolism and AR aberrations. High-dose testosterone (HDT) is emerging as an active treatment in metastatic CRPC, however, biomarkers of response are unknown. We hypothesized that responses to HDT might impact the genomic expression of AR alterations found in circulating-tumor DNA (ctDNA).

METHODS

Retrospective analysis of mCRPC patients treated with HDT (testosterone cypionate q 2-4 weeks) with available clinical and somatic genomic data using a commercially available assay (Guardant360, Redwood City, CA). Clinical outcomes included PSA response (PSA50), time to PSA progression (TPP) and safety.

RESULTS

A total of 33 mCRPC patients were treated with ≥2 testosterone cypionate injections. ctDNA testing revealed alterations in AR (39%), TP53 (48%), and DNA repair genes (12%). HDT was given for median of 4.0 months (95% CI, 2.6-5.3) with 24% of PSA50. Twenty patients were re-challenged with abiraterone (n = 2) or enzalutamide (n = 18) with 30% PSA50. Significant (grade ≥3) adverse events were observed in 5% of patients (grade 4 thrombocytopenia and asthenia). Patients with median baseline ctDNA% of ≥1.10 had numerically worse TPP outcomes and all patients with AR alterations exhibited decreased AR expression post-HDT (n = 9), yet no association between clinical outcomes and ctDNA findings was observed.

CONCLUSIONS

HDT led to a decrease in AR copy number and mutations which was independent from responses to therapy. Further understanding of the genomic alterations as potential predictor of response to HDT is needed.

Supraphysiological androgens suppress prostate cancer growth through androgen receptor-mediated DNA damage

Prostate cancer (PC) is initially dependent on androgen receptor (AR) signaling for survival and growth. Therapeutics designed to suppress AR activity serve as the primary intervention for advanced disease. However, supraphysiological androgen (SPA) concentrations can produce paradoxical responses leading to PC growth inhibition. We sought to discern the mechanisms by which SPA inhibits PC and to determine if molecular context associates with anti-tumor activity. SPA produced an AR-mediated, dose-dependent induction of DNA double-strand breaks (DSBs), G0/G1 cell cycle arrest and cellular senescence. SPA repressed genes involved in DNA repair and delayed the restoration of damaged DNA which was augmented by PARP1 inhibition. SPA-induced DSBs were accentuated in BRCA2-deficient PCs, and combining SPA with PARP or DNA-PKcs inhibition further repressed growth. Next-generation sequencing was performed on biospecimens from PC patients receiving SPA as part of ongoing Phase II clinical trials. Patients with mutations in genes mediating homology-directed DNA repair were more likely to exhibit clinical responses to SPA. These results provide a mechanistic rationale for directing SPA therapy to PCs with AR amplification or DNA repair deficiency, and for combining SPA therapy with PARP inhibition.

The Role of Testosterone Therapy in the Setting of Prostate Cancer

PURPOSE OF REVIEW

The role of testosterone in the development of prostate cancer and the safety of testosterone therapy (TTh) after prostate cancer treatment, or in the setting of active surveillance, remains controversial. There are many concerns about using TTh in men, particularly those with a history of prostate cancer, ranging from a possible increased risk of cardiovascular disease to cancer progression or recurrence. With many prostate cancer patients living longer, and hypogonadism having significant morbidity, much care must go into the decision to treat. Here, we review the literature investigating the effects of testosterone on the prostate as well as the efficacy and safety of exogenous testosterone in men with a history of prostate cancer.

RECENT FINDINGS

The improvement in quality of life with TTh is well studied and understood, while the argument for significantly increased risk of cancer or other adverse effects is much less robust. Neither increased rates of prostate cancer, cancer recurrence, or cardiovascular risk have been well established. In men with high-risk prostate cancer, evidence in the setting of TTh is very limited, and TTh should be used with caution. The fears of TTh causing or worsening prostate cancer do not appear to be well supported by available data. Though more studies are needed to definitively determine the safety of TTh in men with prostate cancer, consideration should be given to treatment of hypogonadal men with a history of CaP.

Supraphysiologic Testosterone Therapy in the Treatment of Prostate Cancer: Models, Mechanisms and Questions

Since Huggins defined the androgen-sensitive nature of prostate cancer (PCa), suppression of systemic testosterone (T) has remained the most effective initial therapy for advanced disease although progression inevitably occurs. From the inception of clinical efforts to suppress androgen receptor (AR) signaling by reducing AR ligands, it was also recognized that administration of T in men with castration-resistant prostate cancer (CRPC) could result in substantial clinical responses. Data from preclinical models have reproducibly shown biphasic responses to T administration, with proliferation at low androgen concentrations and growth inhibition at supraphysiological T concentrations. Many questions regarding the biphasic response of PCa to androgen treatment remain, primarily regarding the mechanisms driving these responses and how best to exploit the biphasic phenomenon clinically. Here we review the preclinical and clinical data on high dose androgen growth repression and discuss cellular pathways and mechanisms likely to be involved in mediating this response. Although meaningful clinical responses have now been observed in men with PCa treated with high dose T, not all men respond, leading to questions regarding which tumor characteristics promote response or resistance, and highlighting the need for studies designed to determine the molecular mechanism(s) driving these responses and identify predictive biomarkers.

The Role of Testosterone in the Treatment of Castration-Resistant Prostate Cancer

Most men with metastatic prostate cancer who are treated with androgen deprivation therapy will eventually develop castration-resistant disease. In this review, we examine the molecular mechanisms that constitute castration resistance and how these processes may be exploited using testosterone-based therapies. We detail how the utilization of superphysiologic doses of testosterone at regular intervals, followed by a rapid clearance of testosterone through continued chemical castration, also known as bipolar androgen therapy, offers an especially promising therapeutic approach. We investigate the historical basis for this modality, detail recent early-phase clinical trials that have demonstrated the feasibility and efficacy of this treatment, and describe an ongoing clinical trial comparing this modality to a currently accepted standard of care, enzalutamide, for castration-resistant prostate cancer. Finally, we explore how this treatment modality will continue to be refined in the future.

Effects of Testosterone on Benign and Malignant Conditions of the Prostate

PURPOSE OF THE REVIEW

This review summarizes the current literature regarding the effects of testosterone therapy (TTh) on common disorders of the prostate.

RECENT FINDINGS

Testosterone therapy has gained credibility over the last several decades as a potentially safe co-treatment modality for men with benign and malignant prostatic conditions. Our understanding of the effects of testosterone on the prostate continues to evolve with ongoing clinical and basic science research. Findings of these studies have reinvigorated the debate over the effects of testosterone on benign and malignant disorders of the prostate, including BPH, chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), and prostate cancer.

SUMMARY

Despite the burgeoning body of data claiming the safety and efficacy of TTh in common prostatic conditions (including BPH, CP/CPPS, and prostate cancer), diligent monitoring, appropriate patient selection, and informed consent are critical until more definitive studies are performed.

Growth Inhibition by Testosterone in an Androgen Receptor Splice Variant-Driven Prostate Cancer Model

BACKGROUND

Castration resistance creates a significant problem in the treatment of prostate cancer. Constitutively active splice variants of androgen receptor (AR) have emerged as drivers for resistance to androgen deprivation therapy, including the next-generation androgen-AR axis inhibitors abiraterone and enzalutamide. In this study, we describe the characteristics of a novel castration-resistant prostate cancer (CRPC) model, designated JDCaP-hr (hormone refractory).

METHODS

JDCaP-hr was established from an androgen-dependent JDCaP xenograft model after surgical castration. The expression of AR and its splice variants in JDCaP-hr was evaluated by immunoblotting and quantitative reverse transcription-polymerase chain reaction. The effects of AR antagonists and testosterone on JDCaP-hr were evaluated in vivo and in vitro. The roles of full-length AR (AR-FL) and AR-V7 in JDCaP-hr cell growth were evaluated using RNA interference.

RESULTS

JDCaP-hr acquired a C-terminally truncated AR protein during progression from the parental JDCaP. The expression of AR-FL and AR-V7 mRNA was upregulated by 10-fold in JDCaP-hr compared with that in JDCaP, indicating that the JDCaP and JDCaP-hr models simulate castration resistance with some clinical features, such as overexpression of AR and its splice variants. The AR antagonist bicalutamide did not affect JDCaP-hr xenograft growth, and importantly, testosterone induced tumor regression. In vitro analysis demonstrated that androgen-independent prostate-specific antigen secretion and cell proliferation of JDCaP-hr were predominantly mediated by AR-V7. JDCaP-hr cell growth displayed a bell-shaped dependence on testosterone, and it was suppressed by physiological concentrations of testosterone. Testosterone induced rapid downregulation of both AR-FL and AR-V7 expression at physiological concentrations and suppressed expression of the AR target gene KLK3.

CONCLUSIONS

Our findings support the clinical value of testosterone therapy, including bipolar androgen therapy, in the treatment of AR-overexpressed CRPC driven by AR splice variants that are not clinically actionable at present. Prostate 76:1536-1545, 2016. © 2016 Wiley Periodicals, Inc.

Advances in hormonal therapies for hormone naïve and castration-resistant prostate cancers with or without previous chemotherapy

Hormonal manipulation plays a significant role in the treatment of advanced hormone naïve prostate cancer and castration-resistant prostate cancer (CRPC) with or without previous chemotherapy. Combination of gonadotropin releasing hormone (GnRH) agonists and androgen receptor (AR) antagonists (combined androgen blockade; CAB) is the first line therapy for advanced hormone naïve prostate cancer, but current strategies are developing novel GnRH antagonists to overcome disadvantages associated with GnRH agonist monotherapy and CAB in the clinical setting. Abiraterone acetate and enzalutamide are hormonal agents currently available for patients with CRPC and are both shown to improve overall survival versus placebo. Recently, in clinical trials, testosterone has been administered in cycles with existing surgical and chemical androgen deprivation therapies (ADT) (intermittent therapy) to CRPC patients of different stages (low risk, metastatic) to abate symptoms of testosterone deficiency and reduce cost of treatment from current hormonal therapies for patients with CRPC. This review will provide an overview on the therapeutic roles of hormonal manipulation in advanced hormone naïve and castration-resistant prostate cancers, as well as the development of novel hormonal therapies currently in preclinical and clinical trials.

Challenges to treat hypogonadism in prostate cancer patients: implications for endocrinologists, urologists and radiotherapists

The literature suggests that the serum testosterone level required for maximum androgen receptor (AR) binding may be in the range of nanomolar and above this range of concentrations; this sexual hormone may not significantly affect tumour biology. This assumption is supported by clinical studies showing that cell proliferation markers did not change when serum T levels increased after exogenous T treatment in comparison to subjects treated with placebo. However, a considerable part of the global scientific community remains sceptical regarding the use of testosterone replacement therapy (TRT) in men suffering from hypogonadism and prostate cancer (Pca). The negative attitudes with respect to testosterone supplementation in men with hypogonadism and Pca may be justified by the relatively low number of clinical and preclinical studies that specifically dealt with how androgens affect Pca biology. More controversial still is the use of TRT in men in active surveillance or at intermediate or high risk of recurrence and treated by curative radiotherapy. In these clinical scenarios, clinicians should be aware that safety data regarding TRT are scanty limiting our ability to draw definitive conclusions on this important topic. In this review we critically discuss the newest scientific evidence concerning the new challenges in the treatment of men with hypogonadal condition and Pca providing new insights in the pharmacological and psychological approaches.

Caffeic acid phenethyl ester induced cell cycle arrest and growth inhibition in androgen-independent prostate cancer cells via regulation of Skp2, p53, p21Cip1 and p27Kip1

Prostate cancer (PCa) patients receiving the androgen ablation therapy ultimately develop recurrent castration-resistant prostate cancer (CRPC) within 1–3 years. Treatment with caffeic acid phenethyl ester (CAPE) suppressed cell survival and proliferation via induction of G1 or G2/M cell cycle arrest in LNCaP 104-R1, DU-145, 22Rv1, and C4–2 CRPC cells. CAPE treatment also inhibited soft agar colony formation and retarded nude mice xenograft growth of LNCaP 104-R1 cells. We identified that CAPE treatment significantly reduced protein abundance of Skp2, Cdk2, Cdk4, Cdk7, Rb, phospho-Rb S807/811, cyclin A, cyclin D1, cyclin H, E2F1, c-Myc, SGK, phospho-p70S6kinase T421/S424, phospho-mTOR Ser2481, phospho-GSK3α Ser21, but induced p21^Cip1, p27^Kip1, ATF4, cyclin E, p53, TRIB3, phospho-p53 (Ser6, Ser33, Ser46, Ser392), phospho-p38 MAPK Thr180/Tyr182, Chk1, Chk2, phospho-ATM S1981, phospho-ATR S428, and phospho-p90RSK Ser380. CAPE treatment decreased Skp2 and Akt1 protein expression in LNCaP 104-R1 tumors as compared to control group. Overexpression of Skp2, or siRNA knockdown of p21^Cip1, p27^Kip1, or p53 blocked suppressive effect of CAPE treatment. Co-treatment of CAPE with PI3K inhibitor LY294002 or Bcl-2 inhibitor ABT737 showed synergistic suppressive effects. Our finding suggested that CAPE treatment induced cell cycle arrest and growth inhibition in CRPC cells via regulation of Skp2, p53, p21^Cip1, and p27^Kip1.

Testosterone therapy in men with prostate cancer: literature review, clinical experience, and recommendations

For several decades any diagnosis of prostate cancer (PCa) has been considered an absolute contraindication to the use of testosterone (T) therapy in men. Yet this prohibition against T therapy has undergone recent re-examination with refinement of our understanding of the biology of androgens and PCa, and increased appreciation of the benefits of T therapy. A reassuringly low rate of negative outcomes has been reported with T therapy after radical prostatectomy (RP), radiation treatments, and in men on active surveillance. Although the number of these published reports are few and the total number of treated men is low, these experiences do provide a basis for consideration of T therapy in selected men with PCa. For clinicians considering offering this treatment, we recommend first selecting patients with low grade cancers and undetectable prostate-specific antigen following RP. Further research is required to define the safety of T therapy in men with PCa. However, many patients symptomatic from T deficiency are willing to accept the potential risk of PCa progression or recurrence in return for the opportunity to live a fuller and happier life with T therapy.

Effect of bipolar androgen therapy for asymptomatic men with castration-resistant prostate cancer: results from a pilot clinical study

Targeting androgen receptor (AR) axis signaling by disrupting androgen-AR interactions remains the primary treatment for metastatic prostate cancer. Unfortunately, all men develop resistance to primary castrating therapy and secondary androgen deprivation therapies (ADTs). Resistance develops in part because castration-resistant prostate cancer (CRPC) cells adaptively up-regulate AR levels through overexpression, amplification, and expression of ligand-independent variants in response to chronic exposure to a low-testosterone environment. However, preclinical models suggest that AR overexpression represents a therapeutic liability that can be exploited via exposure to supraphysiologic testosterone to promote CRPC cell death. Preclinical data supported a pilot study in which 16 asymptomatic CRPC patients with low to moderate metastatic burden were treated with testosterone cypionate (400 mg intramuscular; day 1 of 28) and etoposide (100 mg oral daily; days 1 to 14 of 28). After three cycles, those with a declining prostate-specific antigen (PSA) continued on intermittent testosterone therapy monotherapy. Castrating therapy was continued to suppress endogenous testosterone production, allowing for rapid cycling from supraphysiologic to near-castrate serum testosterone levels, a strategy termed bipolar androgen therapy (BAT). BAT was well tolerated and resulted in high rates of PSA (7 of 14 evaluable patients) and radiographic responses (5 of 10 evaluable patients). Although all men showed eventual PSA progression, four men remained on BAT for ≥1 year. All patients (10 of 10) demonstrated PSA reductions upon receiving androgen-ablative therapies after BAT, suggesting that BAT may also restore sensitivity to ADTs. BAT shows promise as treatment for CRPC and should be further evaluated in larger trials.

Androgen suppresses the proliferation of androgen receptor-positive castration-resistant prostate cancer cells via inhibition of Cdk2, CyclinA, and Skp2

The majority of prostate cancer (PCa) patient receiving androgen ablation therapy eventually develop castration-resistant prostate cancer (CRPC). We previously reported that androgen treatment suppresses Skp2 and c-Myc through androgen receptor (AR) and induced G1 cell cycle arrest in androgen-independent LNCaP 104-R2 cells, a late stage CRPC cell line model. However, the mechanism of androgenic regulation of Skp2 in CRPC cells was not fully understood. In this study, we investigated the androgenic regulation of Skp2 in two AR-positive CRPC cell line models, the LNCaP 104-R1 and PC-3^AR Cells. The former one is an early stage androgen-independent LNCaP cells, while the later one is PC-3 cells re-expressing either wild type AR or mutant LNCaP AR. Proliferation of LNCaP 104-R1 and PC-3^AR cells is not dependent on but is suppressed by androgen. We observed in this study that androgen treatment reduced protein expression of Cdk2, Cdk7, Cyclin A, cyclin H, Skp2, c-Myc, and E2F-1; lessened phosphorylation of Thr14, Tyr15, and Thr160 on Cdk2; decreased activity of Cdk2; induced protein level of p27^Kip1; and caused G1 cell cycle arrest in LNCaP 104-R1 cells and PC-3^AR cells. Overexpression of Skp2 protein in LNCaP 104-R1 or PC-3^AR cells partially blocked accumulation of p27^Kip1 and increased Cdk2 activity under androgen treatment, which partially blocked the androgenic suppressive effects on proliferation and cell cycle. Analyzing on-line gene array data of 214 normal and PCa samples indicated that gene expression of Skp2, Cdk2, and cyclin A positively correlates to each other, while Cdk7 negatively correlates to these genes. These observations suggested that androgen suppresses the proliferation of CRPC cells partially through inhibition of Cyclin A, Cdk2, and Skp2.

Difference in protein expression profile and chemotherapy drugs response of different progression stages of LNCaP sublines and other human prostate cancer cells

Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, 80-90% of the patients who receive androgen ablation therapy ultimately develop recurrent tumors in 12-33 months after treatment with a median overall survival time of 1-2 years after relapse. LNCaP is a commonly used cell line established from a human lymph node metastatic lesion of prostatic adenocarcinoma. We previously established two relapsed androgen receptor (AR)-rich androgen-independent LNCaP sublines 104-R1 (androgen depleted for 12 months) and 104-R2 cells (androgen depleted for 24 months) from AR-positive androgen-dependent LNCaP 104-S cells. LNCaP 104-R1 and 104-R2 mimics the AR-positive hormone-refractory relapsed tumors in patients receiving androgen ablation therapy. Androgen treatment stimulates proliferation of 104-S cells, but causes growth inhibition and G1 cell cycle arrest in 104-R1 and 104-R2 cells. We investigated the protein expression profile difference between LNCaP 104-S vs. LNCaP 104-R1, 104-R2, PC-3, and DU-145 cells as well as examined the sensitivity of these prostate cancer cells to different chemotherapy drugs and small molecule inhibitors. Compared to 104-S cells, 104-R1 and 104-R2 cells express higher protein levels of AR, PSA, c-Myc, Skp2, BCL-2, P53, p-MDM2 S166, Rb, and p-Rb S807/811. The 104-R1 and 104-R2 cells express higher ratio of p-Akt S473/Akt, p-EGFR/EGFR, and p-Src/Src, but lower ratio of p-ERK/ERK than 104-S cells. PC-3 and DU-145 cells express higher c-Myc, Skp2, Akt, Akt1, and phospho-EGFR but less phospho-Akt and phospho-ERK. Overexpression of Skp2 increased resistance of LNCaP cells to chemotherapy drugs. Paclitaxel, androgen, and inhibitors for PI3K/Akt, EGFR, Src, or Bcl-2 seem to be potential choices for treatment of advanced prostate cancers. Our study provides rationale for targeting Akt, EGFR, Src, Bcl-2, and AR signaling as a treatment for AR-positive relapsed prostate tumors after hormone therapy.

Testosterone boosts for treatment of castration resistant prostate cancer: an experimental implementation of intermittent androgen deprivation

BACKGROUND

The primary therapeutic target for non-organ-confined prostate cancer is the androgen receptor (AR). Main strategies to ablate AR function are androgen depletion and direct receptor blockade by AR antagonists. However, incurable castration resistant prostate cancer (CRPC) develops resistance mechanisms to cope with trace amounts of androgen including AR overexpression and mutation in the AR ligand binding domain.

METHODS

The CRPC cell model VCaP derivative of a prostate cancer bone metastasis was used in vitro and in nude mice in vivo to examine the effects of immediate testosterone boost on CRPC cells. In addition, a testosterone tolerant cell model was established by incremental acclimatization of VCaP cells to 1 nM testosterone. The effects of androgen withdrawal and testosterone boosts on gene expression were assessed by quantitative real-time polymerase chain reaction, ELISA, and Western blots. Tumor cell proliferation was evaluated with a BrdU test.

RESULTS

Testosterone boosts on CRPC VCaP cells eliminate tumor cells to a higher extent than androgen withdrawal in androgen tolerant cells. The pronounced decrease of tumor cell proliferation was accompanied by a marked downregulation of AR expression regarding full-length AR and splice variant AR V7.

CONCLUSIONS

Acquiring castration resistance of prostate cancer cells by AR overexpression and amplification obviously sensitizes such cells to testosterone concentrations as low as physiological values. This introduces novel therapeutic means to treat CRPC with non-toxic measures and may find clinical implementation in intermittent androgen deprivation regimens.

New platinum(II) complexes conjugated at position 7α of 17β-acetyl-testosterone as new combi-molecules against prostate cancer: design, synthesis, structure-activity relationships and biological evaluation

Prostate cancer is a major public health problem worldwide and, more specifically, new treatments for hormone-refractory cancers are highly sought by several research groups. Although platinum(II)-based chemotherapy and other strategies grow in interest to treat castration-resistant prostate cancer (CRPC), they still exhibit modest activity on CRPC and overall patient survival. In this study, we designed and prepared new combi-molecules using 17β-acetyl-testosterone and amino acid platinum(II) complexes linked at the position 7α to target and to improve the antiproliferative activity of platinum(II)-based chemotherapy on prostate cancer cells. Twelve chemical intermediates and six new combi-molecules were prepared and characterized. Structure-activity relationships studies show that the platinum complex moiety is essential for an optimal cytocidal activity. Moreover, stereochemistry of the amino acid involved in the platinum complexes had only minor effects on the antiproliferative activity whereas pyridinyl (10a and b) and thiazolyl (10f) complexes exhibited the highest cytocidal activities that are significantly superior to that of cisplatin used as control on human prostate adenocarcinoma LNCaP (AR+), PC3 (AR-) and DU145 (AR-). Compounds 10a, b and f arrested the cell cycle progression in S-phase and induced double strand breaks as confirmed by the phosphorylation of histone H2AX into γH2AX. Compounds 10a and f showed 33 and 30% inhibition, respectively of the growth of HT-1080 tumors grafted onto chick chorioallantoic membranes. Finally, compounds 10a and 10f exhibited low toxicity on the chick embryos (18 and 21% of death, respectively), indicating that these new combi-molecules might be a promising new class of anticancer agents for prostate cancer.

Dentatin Induces Apoptosis in Prostate Cancer Cells via Bcl-2, Bcl-xL, Survivin Downregulation, Caspase-9, -3/7 Activation, and NF-κB Inhibition

This study was set to investigate antiproliferative potential of dentatin (a natural coumarin isolated from Clausena excavata Burm. F) against prostate cancer and to delineate the underlying mechanism of action. Treatment with dentatin dose-dependently inhibited cell growth of PC-3 and LNCaP prostate cancer cell lines, whereas it showed less cytotoxic effects on normal prostate epithelial cell line (RWPE-1). The inhibitory effect of dentatin on prostate cancer cell growth was due to induction of apoptosis as evidenced by Annexin V staining and cell shrinkage. We found that dentatin-mediated accumulation of reactive oxygen species (ROS) and downregulated expression levels of antiapoptotic molecules (Bcl-2, Bcl-xL, and Survivin), leading to disruption of mitochondrial membrane potential (MMP), cell membrane permeability, and release of cytochrome c from the mitochondria into the cytosol. These effects were associated with induction of caspase-9, -3/7 activities, and subsequent DNA fragmentation. In addition, we found that dentatin inhibited TNF-α-induced nuclear translocation of p65, suggesting dentatin as a potential NF-κB inhibitor. Thus, we suggest that dentatin may have therapeutic value in prostate cancer treatment worthy of further development.

Testosterone promotes DNA damage response under oxidative stress in prostate cancer cell lines

BACKGROUND

Sustained chronic inflammation and oxidative stress in the prostate promote prostate carcinogenesis. The process of oncogenic transformation leads to enhanced DNA damage and activates the checkpoint network that functions as an inducible barrier against cancer progression. Here, we analyzed the effects of testosterone on the DNA damage response in prostate cancer cells to assess whether testosterone functions a barrier to cancer progression under the oxidative stress.

METHODS

We examined the effects of testosterone on components of the DNA damage response pathway, including ATM (ataxia-telangiectasia-mutated kinase), H2AX (histone H2AX variant), and Chk2 (checkpoint kinase2) in prostate cancer cell lines, treated with various concentration of hydrogen peroxide (H(2) O(2) ). Cellular apoptosis was quantified by poly (ADP-ribose) polymerase (PARP) cleavage and flow cytometry.

RESULTS

H(2) O(2) induced apoptosis and phosphorylation of ATM, Chk2, and H2AX in LNCaP cells. An ATM inhibitor, Ku55933, reduced H(2) O(2) -induced apoptosis in LNCaP and 22Rv1 cells. Androgen treatments increased H(2) O(2) -induced activation of the DNA damage response and PARP cleavage, but not when the H(2) O(2) -treated cells were also treated with the anti-androgen flutamide. The ATM inhibitor Ku55933 inhibited androgen-induced phosphorylation of ATM and PARP cleavage.

CONCLUSIONS

DNA damage responses play important roles in the maintenance of the cell homeostasis in response to oxidative stress. Our results indicated that under oxidative stress androgen signaling may induce apoptosis by activating the DNA damage response.

Cardiometabolic complications after androgen deprivation therapy in a man with prostate cancer: effects of 3 years intermittent testosterone supplementation

Androgen deprivation therapy (ADT) for prostate carcinoma (PCa) may cause cardiometabolic complications unless intermittent androgen blockade (IAB) is instituted. An 80-year-old caucasian man was diagnosed intermediate grade (Gleason 4 + 3) PCa and was treated with continuous ADT with triptorelin plus bicalutamide. After 6 months of treatment, he experienced an acute myocardial infarction and 1 month after hospitalization he came to our outpatient clinic for fatigue, weight gain, and hyperglycemia. Due to iatrogenic hypogonadism, we decided to proceed with IAB, but after 3 months ADT withdrawal his serum testosterone (T) was still 0.5 ng/mL. Due to very low concomitant PSA levels (0.1 ng/mL) he was then proposed intermittent T-gel supplementation (Tostrex(®)) which was initiated according to the following scheme: 6 months on and 3 months off. T-gel dose was titrated tri-weekly in order to achieve T plasma levels below 3.49 ng/mL. After 6 months on, his serum T raised to a mean value of about 2.0 ng/mL without increments in PSA. After overall 12 months on, his serum T peaked to a mean value of 3.0 ng/mL while a delay in PSA rise was seen after 24 months (0.6 ng/mL) but remained stable until the last observation carried forward (LOCF), at 45 months. No clinical and biochemical PCa progression were observed at LOCF. Reversion of iatrogenic metabolic syndrome started after 6 months of T supplementation without using any add-on treatment. This case provides support that once regression of PCa growth is attained, T supplementation may be administered in well differentiated PCa, especially if IAB is not successful in reverting iatrogenic hypogonadism and its associated cardiac and metabolic complications.

Growth hormone, insulin-like growth factor 1, and insulin signaling-a pharmacological target in body wasting and cachexia

Cachexia is an irreversible process that can develop in the course of chronic disease. It is characterized by the remodeling of the metabolic, inflammatory, and endocrine pathways. Insulin, growth hormone (GH), and insulin-like growth factor 1 (IGF-1) are involved in glucose, protein, and fat metabolism, which regulates body composition. In body wasting and cachexia, their signaling is impaired and causes anabolic/catabolic imbalance. Important mechanisms include inflammatory cytokines and neurohormonal activation. Remodeled post-receptor insulin, GH, and IGF-1 pathways constitute a potential target for pharmacological treatment in the setting of body wasting and cachexia. Peroxisome proliferator-activated receptor gamma agonists, drugs inhibiting angiotensin II action (angiotensin II antagonists and inhibitors of angiotensin-converting enzyme), and testosterone, which interfere with post-receptor pathways of insulin, GH, and IGF-1, were investigated as pharmacological intervention targets and various clinically important implications were reported. There are several other potential targets, but their treatment feasibility and applicability is yet to be established.

Androgens as therapy for androgen receptor-positive castration-resistant prostate cancer

Prostate cancer is the most frequently diagnosed non-cutaneous tumor of men in Western countries. While surgery is often successful for organ-confined prostate cancer, androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, this therapy is associated with several undesired side-effects, including increased risk of cardiovascular diseases. Shortening the period of androgen ablation therapy may benefit prostate cancer patients. Intermittent Androgen Deprivation therapy improves quality of life, reduces toxicity and medical costs, and delays disease progression in some patients. Cell culture and xenograft studies using androgen receptor (AR)-positive castration-resistant human prostate cancers cells (LNCaP, ARCaP, and PC-3 cells over-expressing AR) suggest that androgens may suppress the growth of AR-rich prostate cancer cells. Androgens cause growth inhibition and G1 cell cycle arrest in these cells by regulating c-Myc, Skp2, and p27Kip via AR. Higher dosages of testosterone cause greater growth inhibition of relapsed tumors. Manipulating androgen/AR signaling may therefore be a potential therapy for AR-positive advanced prostate cancer.

Androgen suppresses proliferation of castration-resistant LNCaP 104-R2 prostate cancer cells through androgen receptor, Skp2, and c-Myc

Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, this therapy is associated with several undesired side-effects, including increased risk of cardiovascular diseases. To study if termination of long-term androgen ablation and restoration of testosterone levels could suppress the growth of relapsed hormone-refractory prostate tumors, we implanted testosterone pellets in castrated nude mice carrying androgen receptor (AR)-positive LNCaP 104-R2 cells, which relapsed from androgen-dependent LNCaP 104-S cells after long-term androgen deprivation. 104-R2 tumor xenografts regressed after testosterone pellets were implanted. Of 33 tumors, 24 adapted to elevation of testosterone level and relapsed as androgen-insensitive tumors. Relapsed tumors (R2Ad) expressed less AR and prostate-specific antigen. We then studied the molecular mechanism underlying the androgenic regulation of prostate cancer cell proliferation. Androgen suppresses proliferation of 104-R2 by inducing G(1) cell cycle arrest through reduction of S-phase kinase-associated protein 2 (Skp2) and c-Myc, and induction of p27(Kip1). 104-R2 cells adapted to androgen treatment and the adapted cells, R2Ad, were androgen-insensitive cells with a slower growth rate and low protein level of AR, high levels of c-Myc and Skp2, and low levels of p27(Kip1). Nuclear AR and prostate-specific antigen expression is present in 104-R2 cells but not R2Ad cells when androgen is absent. Overexpression of AR in R2Ad cells regenerated an androgen-repressed phenotype; knockdown of AR in 104-R2 cells generated an androgen-insensitive phenotype. Overexpression of Skp2 and c-Myc in 104-R2 cells blocked the growth inhibition caused by androgens. We concluded that androgens cause growth inhibition in LNCaP 104-R2 prostate cancer cells through AR, Skp2, and c-Myc.

Androgen hypersensitivity in prostate cancer: molecular perspectives on androgen deprivation therapy strategies

Androgen deprivation therapy is initially successful in treating advanced prostate cancer. However, after a period of time tumors inevitably recur. Improved understanding of the various biochemical causes of resistance to hormonal therapy is of crucial importance for developing more effective therapeutic strategies in this cohort of patients. This review discusses the preclinical evidence for androgen hypersensitivity (AH), as a mechanism by which tumors become hormone-refractory (HR). We propose that the growth of some such tumors may be not only stimulated by, but also dependent on low hormone levels, and furthermore, that normal hormone concentrations can have an inhibitory effect on growth. The incidence and importance of AH merits further investigation both in preclinical studies and during clinical trials of intermittent androgen withdrawal or testosterone replacement. We suggest that a subset of HR prostate cancer patients who have androgen-hypersensitive tumors could be particularly amenable to these treatments. Finally, potential approaches for developing biomarkers to identify such patients are explored.

Bipolar androgen therapy: the rationale for rapid cycling of supraphysiologic androgen/ablation in men with castration resistant prostate cancer

Androgen ablation is highly effective palliative therapy for metastatic prostate cancer but eventually all men relapse. New findings demonstrating that androgen receptor (AR) expression continues in androgen ablated patients has resulted in the classification "Castration Resistant Prostate Cancer" (CRPC) and has led to the development of new second-line "anti-ligand" hormonal agents. In this background is the paradoxical observation that the growth of some AR-expressing "androgen sensitive" human prostate cancer cells can be inhibited by supraphysiologic levels of androgens. This response may be due to effects of high-dose androgen on inhibiting re-licensing of DNA in cells expressing high levels of AR. It may also be due to recently described effects of androgen in inducing double strand DNA breaks. Based on available preclinical data described in this review demonstrating the effects of supraphysiologic levels of testosterone on inhibition of growth of CRPC xenografts, we initiated a clinical trial in men with CRPC testing the effect of monthly treatments with an intramuscular (IM) depot injection of testosterone. This IM formulation achieves supraphysiologic levels of testosterone that cannot be achieved with standard testosterone gel-based applications. The supraphysiologic testosterone level is followed by a rapid drop to castrate levels of testosterone with each cycle of therapy. This "bipolar androgen therapy" will not allow time for prostate cancer cells to adapt their AR expression in response to environmental conditions. The goal is to determine if a clinical response can be achieved through this non-adaptive rapid cycling approach in men with CRPC.

An in vitro model for preclinical testing of endocrine therapy combinations for prostate cancer

BACKGROUND

Even though patients with prostate cancer commonly respond to endocrine treatment, in most cases the disease progresses to castration resistant prostate cancer (CRPC). Our objective was to generate a novel cell line model representing the endocrine treatment naive prostate cancer for testing treatments that target the androgen receptor (AR) and androgen metabolism.

METHODS

After culturing DuCaP cells 20 passages with additional 1 nM R1881, DuCaP-N(aive) cell line was developed and validated for testing endocrine therapy combinations. Cell viability, apoptosis and cell cycle distribution were assessed in DuCaP and DuCaP-N when interfering with the hormonal content.

RESULTS

Addition of 1 nM R1881 to DuCaP reduces cell viability and induces cell cycle inhibition and apoptosis. Eventually, an androgen accustomed DuCaP-N cell line developed. An antiandrogen (bicalutamide), a histone deacetylase (HDAC) inhibitor (trichostatin A) and a 5alpha-reductase (SRD5A) inhibitor (finasteride) reduce cell viability, and their combinations give a synergistic response in inducing apoptosis.

CONCLUSIONS

The TMPRSS2-ERG expressing DuCaP-N cell line represents human prostate cancer prior to endocrine treatment, and its parental DuCaP cell line is a model for CRPC. These cell lines can be used for preclinical evaluation of compounds that target the androgenic pathway.

Words of wisdom. Re: Phase 1 trial of high-dose exogenous testosterone in patients with castration-resistant metastatic prostate cancer. Morris MJ, Huang D, Kelly WK, et al. Eur Urol 2009;56:237-44

Laboratory studies suggest that castration-resistant prostate cancer (CRPC) cell growth is suppressed by supraphysiologic doses of testosterone (T). In this study, 12 men received high doses of T transdermally for 7 d, for 4 mo, or until progression.The approach was safe and toxicity was mild, but responses were modest. Because serum T did not reach intended supraphysiologic levels, the authors urged more clinical testing.

Androgen receptor signaling and mutations in prostate cancer

Normal and neoplastic growth of the prostate gland are dependent on androgen receptor (AR) expression and function. Androgenic activation of the AR, in association with its coregulatory factors, is the classical pathway that leads to transcriptional activity of AR target genes. Alternatively, cytoplasmic signaling crosstalk of AR by growth factors, neurotrophic peptides, cytokines or nonandrogenic hormones may have important roles in prostate carcinogenesis and in metastatic or androgen-independent (AI) progression of the disease. In addition, cross-modulation by various nuclear transcription factors acting through basal transcriptional machinery could positively or negatively affect the AR or AR target genes expression and activity. Androgen ablation leads to an initial favorable response in a significant number of patients; however, almost invariably patients relapse with an aggressive form of the disease known as castration-resistant or hormone-refractory prostate cancer (PCa). Understanding critical molecular events that lead PCa cells to resist androgen-deprivation therapy is essential in developing successful treatments for hormone-refractory disease. In a significant number of hormone-refractory patients, the AR is overexpressed, mutated or genomically amplified. These genetic alterations maintain an active presence for a highly sensitive AR, which is responsive to androgens, antiandrogens or nonandrogenic hormones and collectively confer a selective growth advantage to PCa cells. This review provides a brief synopsis of the AR structure, AR coregulators, posttranslational modifications of AR, duality of AR function in prostate epithelial and stromal cells, AR-dependent signaling, genetic changes in the form of somatic and germline mutations and their known functional significance in PCa cells and tissues.

Differential androgen receptor signals in different cells explain why androgen-deprivation therapy of prostate cancer fails

Prostate cancer is one of the major causes of cancer-related death in the western world. Androgen-deprivation therapy (ADT) for the suppression of androgens binding to the androgen receptor (AR) has been the norm of prostate cancer treatment. Despite early success to suppress prostate tumor growth, ADT eventually fails leading to recurrent tumor growth in a hormone-refractory manner, even though AR remains to function in hormone-refractory prostate cancer. Interestingly, some prostate cancer survivors who received androgen replacement therapy had improved quality of life without adverse effect on their cancer progression. These contrasting clinical data suggest that differential androgen/AR signals in individual cells of prostate tumors can exist in the same or different patients, and may be used to explain why ADT of prostate cancer fails. Such a hypothesis is supported by the results obtained from transgenic mice with selective knockout of AR in prostatic stromal vs epithelial cells and orthotopic transplants of various human prostate cancer cell lines with AR over-expression or knockout. These studies concluded that AR functions as a stimulator for prostate cancer proliferation and metastasis in stromal cells, as a survival factor of prostatic cancer epithelial luminal cells, and as a suppressor for prostate cancer basal intermediate cell growth and metastasis. These dual yet opposite functions of the stromal and epithelial AR may challenge the current ADT to battle prostate cancer and should be taken into consideration when developing new AR-targeting therapies in selective prostate cancer cells.