Cellular Changes in Prostate Cancer Cells Induced by Intermittent Androgen Suppression

Long-term treatment outcomes of intermittent androgen deprivation therapy for relapsed prostate cancer after radical prostatectomy

PURPOSE

Intermittent androgen deprivation therapy is an effective treatment for metastatic prostate cancer. However, no study to date has evaluated the long-term outcomes of this treatment among patients with prostate cancer after radical prostatectomy. We retrospectively examined the treatment outcomes of patients with prostate-specific antigen recurrence who underwent radical prostatectomy at our department.

MATERIALS AND METHODS

Of the 690 patients who underwent radical prostatectomy for local prostate cancer between 1988 and 2011, 129 patients who received androgen deprivation therapy for prostate-specific antigen recurrence were included in this study. Patient characteristics, luteinizing hormone-releasing hormone agonist administration, and outcomes were compared between the intermittent androgen deprivation group (n = 66) and the continuous androgen deprivation therapy group (n = 63). The non-recurrence and overall survival rates were compared between groups.

RESULTS

Thirty-six patients (27.9%) experienced recurrence after luteinizing hormone-releasing hormone agonist administration. The 5-year non-recurrence rate and 10-year overall survival rate were higher in the intermittent group (92.9%) than in the continuous group (92.9 vs 57.9%, P < 0.001; and 95.9% vs 84.3%, P = 0.047, respectively). Furthermore, 63 patients (48.8%) showed a PSA nadir of less than 0.01 ng/mL after initiation of luteinizing hormone-releasing hormone agonist; among these patients, the non-recurrence rate was significantly higher in the intermittent androgen deprivation group (P = 0.003).

CONCLUSIONS

Intermittent androgen deprivation therapy for prostate specific antigen recurrence after radical prostatectomy contributed to improvement of the non-recurrence rate and overall survival, and can be considered an effective therapy for better prognosis.

Testosterone Replacement Therapy and Risk of Favorable and Aggressive Prostate Cancer

Purpose The association between exposure to testosterone replacement therapy (TRT) and prostate cancer risk is controversial. The objective was to examine this association through nationwide, population-based registry data. Methods We performed a nested case-control study in the National Prostate Cancer Register of Sweden, which includes all 38,570 prostate cancer cases diagnosed from 2009 to 2012, and 192,838 age-matched men free of prostate cancer. Multivariable conditional logistic regression was used to examine associations between TRT and risk of prostate cancer (overall, favorable, and aggressive). Results Two hundred eighty-four patients with prostate cancer (1%) and 1,378 control cases (1%) filled prescriptions for TRT. In multivariable analysis, no association was found between TRT and overall prostate cancer risk (odds ratio [OR], 1.03; 95% CI, 0.90 to 1.17). However, patients who received TRT had more favorable-risk prostate cancer (OR, 1.35; 95% CI, 1.16 to 1.56) and a lower risk of aggressive prostate cancer (OR, 0.50; 95% CI, 0.37 to 0.67). The increase in favorable-risk prostate cancer was already observed within the first year of TRT (OR, 1.61; 95% CI, 1.10 to 2.34), whereas the lower risk of aggressive disease was observed after > 1 year of TRT (OR, 0.44; 95% CI, 0.32 to 0.61). After adjusting for previous biopsy findings as an indicator of diagnostic activity, TRT remained significantly associated with more favorable-risk prostate cancer and lower risk of aggressive prostate cancer. Conclusion The early increase in favorable-risk prostate cancer among patients who received TRT suggests a detection bias, whereas the decrease in risk of aggressive prostate cancer is a novel finding that warrants further investigation.

Radioimmunotherapy of prostate cancer targeting human kallikrein-related peptidase 2

Background

Prostate cancer ranks as the second most lethal malignancy in the Western world. Previous targeting of prostate-specific antigen and human kallikrein-related peptidase 2, two related enzymes abundantly expressed in prostatic malignancies, with radioimmunoconjugates intended for diagnostic purposes, have proven successful in rodent prostate cancer (PCa) models. In this study, we investigated the uptake and therapeutic efficacy of ¹⁷⁷Lu-m11B6, a human kallikrein-related peptidase 2 (hK2)-targeting radioimmunoconjugate in a pre-clinical setting.

Methods

The murine 11B6 antibody, m11B6, with high affinity for hK2, was labeled with ¹⁷⁷Lu. Therapy planning was done from a biokinetic study in LNCaP xenografts, and therapeutic activities of ¹⁷⁷Lu-m11B6 were administered to groups of mice. Body weight and general conditions of the mice were followed over a period of 120 days.

Results

The tumor uptake in LNCaP xenografts was 30 ± 8.2 % injected activity per gram 1 week post-injection. In vivo targeting was hK2-specific as verified by a 2.5-fold decrease in tumor uptake in pre-dosed xenografts or by a fourfold lower tumor accumulation in hK2-negative DU 145 xenografts. Therapy showed a dose-dependent efficacy in LNCaP xenografts treated with ¹⁷⁷Lu-m11B6. No therapeutic effect was seen in the control groups. The median survival for the lowest given activity of ¹⁷⁷Lu-m11B6 was 88 days compared to that of 38 days in mice given labeled non-specific IgG. For the higher administrated activities, total tumor regression was seen with minimal normal organ toxicity.

Conclusions

We have proven the possibility of radioimmunotherapy targeting hK2 in subcutaneous prostate cancer xenografts. ¹⁷⁷Lu-m11B6 exhibited high therapeutic efficacy, with low observed toxicity. Additionally, an evaluation of the concept of pre-therapy planning using a dosimetry model was included in this radioimmunotherapy study.

Experimental evidence of persistent androgen-receptor-dependency in castration-resistant prostate cancer

In the majority of castration-resistant prostate cancer (CRPC), prostate-specific antigen (PSA), product of a gene that is almost exclusively regulated by the androgen receptor (AR), still acts as a serum marker reflecting disease burden, indicating that AR signaling is activated even under castrate level of serum androgen. Accumulated evidence shows that transcriptional ability of AR is activated both in ligand-dependent and -independent manners in CRPC cells. Some androgen-independent sublines derived from originally androgen-dependent LNCaP prostate cancer cells overexpress the AR and PSA, for which silencing the AR gene suppresses cellular proliferation. The overexpression of the AR confers androgen-independent growth ability on androgen-dependent prostate cancer cells. Some patient-derived prostate cancer xenograft lines also acquire castration-resistant growth ability secreting PSA. More recent publications have shown that the AR activated in CRPC cells regulates distinct gene sets from that in androgen-dependent status. This concept provides very important insights in the development of novel anti-prostate cancer drugs such as new generation anti-androgens and CYP17 inhibitors.

Androgen receptor (AR) aberrations in castration-resistant prostate cancer

Genetic aberrations affecting the androgen receptor (AR) are rare in untreated prostate cancers (PCs) but have been found in castration-resistant prostate cancers (CRPCs). Further, successful treatment with novel endocrine therapies indicates that CRPCs remain androgen-sensitive. Known AR aberrations include amplification of the AR gene leading to the overexpression of the receptor, point mutations of AR resulting in promiscuous ligand usage, and constitutively active AR splice variants. Gain, or amplification, of the AR gene is one of the most frequent genetic alterations observed in CRPCs. Up to 80% of CRPCs have been reported to carry an elevated AR gene copy number, and about 30% have a high-level amplification of the gene. AR mutations are also commonly observed and have been found in approximately 10-30% of the CRPC treated with antiandrogens; however, the frequency and significance of AR splice variants is still unclear. Because AR aberrations are found almost exclusively in CRPC, these alterations must have been selected for during therapy. Interestingly, these aberrations lead to activation of the receptor, despite treatment-induced emergence of therapy-resistant tumor clones. Therefore, future novel treatment strategies should focus on suppressing AR activity in CRPC.

Hormones and prostate carcinogenesis: Androgens and estrogens

Prostate cancer is the leading non-skin malignancy detected in US males and the second cause of death due to male cancer in the US. Androgenic hormones are generally believed to be causatively associated with prostate carcinogenesis, but human evidence, mostly epidemiological, for this is minimal. Circulating hormone levels are not associated with the risk of prostate cancer and neither are polymorphisms in various genes encoding the androgen metabolizing enzymes or androgen receptors. Evidence in support of the involvement of androgens in prostate cancer development is derived from clinical trials with 5α-reductase inhibitors, which reduced the risk by approximately 25%. Animal studies using rat models, however, provide clear evidence that testosterone can induce prostate cancer and can act as a strong tumor promoter in concert with genotoxic carcinogens. One such genotoxic factor may be 17β-estradiol, which is generated from testosterone by the aromatase enzyme. Estradiol can be converted to catecholestrogens, which through redox cycling, generate reactive metabolites that can adduct the DNA and potentially lead to mutations. Animal studies and limited human evidence suggest that estrogens can be involved in prostate carcinogenesis by such a genotoxic mechanism. However, how androgens exert their tumor-promoting effect is not clear. It is likely that hormonal and non-hormonal factors as well as genetic and non-genetic (environmental) factors interact in a highly complex and poorly understood manner to determine the risk of prostate cancer.

Intermittent androgen suppression for prostate cancer

Although androgen deprivation therapy (ADT) has been a cornerstone of the management of prostate cancer for more than 50 years, controversy remains regarding its optimum application. Intermittent androgen suppression (IAS) has been researched since the mid-1980s as a way of reducing the adverse effects and cost of continuous androgen suppression. With preclinical evidence suggesting a potential benefit in terms of time to androgen independence, IAS has been the focus of a number of clinical phase II and III trials. Overall, these trials suggest that IAS is neither inferior nor superior to continuous androgen suppression, with respect to time to castration resistance and cancer-specific survival, but has significant advantages in terms of adverse effects, quality of life and cost. A number of unresolved questions remain, however, including how to select patients for therapy, the optimum duration of therapy, when to restart therapy after the off cycle, and how to define progression to castration-resistant disease. Landmark randomized clinical trials comparing IAS to continuous androgen suppression are in progress and will hopefully answer many of these questions. In future, the use of second-line drugs in the off-treatment phase holds potential for delaying disease progression in men on IAS. At present, men with advanced disease who are deemed candidates for ADT should be informed of IAS as a treatment option, considered experimental from an informed consent point of view, but promising based on current evidence.

Expression of X-linked inhibitor of apoptosis protein in human prostate cancer specimens with and without neo-adjuvant hormonal therapy

PURPOSE

X-linked inhibitor of apoptosis (XIAP) has high affinity and strong inhibitory activity on apoptosis-related caspase-3. The relationships between expression of XIAP and cleaved caspase-3, and response to neo-adjuvant hormonal therapy (NHT) remain elusive. The aim was to investigate whether NHT influences with XIAP expression in prostate cancer patients. In addition, the relationship between XIAP expression and apoptosis in patients who did or did not receive NHT was also investigated.

METHODS

Eighty-three patients who had undergone radical prostatectomy were examined retrospectively and divided into NHT group (n = 40) and non-NHT group (n = 43). Immunohistochemistry was used to analyze the expressions of XIAP and cleaved caspase-3. The apoptotic cells reconfirmed the number of terminal deoxynucleotidyl transferase-mediated nick and labeling (TUNEL)-positive cells.

RESULTS

In the non-NHT group, the proportion of TUNEL-positive cells correlated with expression of cleaved caspase-3 (r = 0.592, P < 0.001), and the expression of XIAP correlated negatively with that of cleaved caspase-3 and TUNEL-positive cells (r = -0.464, P < 0.001 and r = 0.431, P = 0.002, respectively). The expression of cleaved caspase-3, but not that of XIAP, was higher in NHT group than non-NHT group (P = 0.017). In the NHT group, there was no significant correlation between XIAP expression and cleaved caspase-3 expression or the proportion of TUNEL-positive cells.

CONCLUSIONS

NHT did not influence XIAP expression. We speculate that the inhibition of XIAP expression may reinforce the apoptotic effect of NHT and improve the prognosis in patients with prostate cancer.

Intermittent androgen deprivation for locally advanced and metastatic prostate cancer: results from a randomised phase 3 study of the South European Uroncological Group

BACKGROUND

Few randomised studies have compared intermittent hormonal therapy (IHT) with continuous therapy for the treatment of advanced prostate cancer (PCa).

OBJECTIVE

To determine whether intermittent therapy is associated with a shorter time to progression.

DESIGN, SETTING, AND PARTICIPANTS

766 patients with locally advanced or metastatic PCa received a 3-mo induction treatment. The 626 patients whose prostate-specific antigen (PSA) level decreased to <4 ng/ml or to 80% below the initial value were randomised.

INTERVENTION

Patients received cyproterone acetate (CPA) 200mg for 2 wk and then monthly depot injections of a luteinising hormone-releasing hormone (LHRH) analogue plus 200mg of CPA daily during induction. Patients randomised to the intermittent arm ceased treatment, while those randomised to the continuous arm received 200mg of CPA daily plus an LHRH analogue.

MEASUREMENTS

Primary outcome measurement was time to subjective or objective progression. Secondary outcomes were survival and quality of life (QoL). Time off therapy in the intermittent arm was also recorded.

RESULTS AND LIMITATIONS

127 patients from the intermittent arm and 107 patients from the continuous arm progressed, with a hazard ratio (HR) of 0.81 (95% confidence interval [CI]: 0.63-1.05, p=0.11). There was no difference in survival, with an HR of 0.99 (95% CI: 0.80-1.23) and 170 deaths in the intermittent arm and 169 deaths in the continuous arm. The greater number of cancer deaths in the intermittent treatment arm (106 vs 84) was balanced by a greater number of cardiovascular deaths in the continuous arm (52 vs 41). Side-effects were more pronounced in the continuous arm. Men treated with intermittent therapy reported better sexual function. Median time off therapy for the intermittent patients was 52 wk (95% CI: 39.4-65.7).

CONCLUSIONS

IHT should be considered for use in routine practice because it is associated with no reduction in survival, no clinically meaningful impairment in QoL, better sexual activity, and considerable economic benefit to the individual and the community.