Background: Prostate cancer that progresses after enzalutamide treatment is poorly responsive to further antiandrogen therapy, and paradoxically, rapid cycling between high and low serum testosterone concentrations (bipolar androgen therapy [BAT]) in this setting might induce tumour responses. We aimed to evaluate BAT in patients with metastatic castration-resistant prostate cancer that progressed after enzalutamide.

Methods: We did this single-centre, open-label, phase 2, multicohort study in the USA. We included patients aged 18 years or older who had histologically confirmed and radiographically documented metastatic castration-resistant prostate cancer, with no more than two previous second-line hormonal therapies, and a castrate concentration of testosterone. Patients were asymptomatic, with Eastern Cooperative Oncology Group performance status of 0-2, and did not have high-risk lesions for tumour flare (eg, >5 sites of visceral disease or bone lesions with impending fracture). For the cohort reported here, we required patients to have had progression on enzalutamide with a continued prostate-specific antigen (PSA) rise after enzalutamide treatment discontinuation. Patients received BAT, which consisted of intramuscular testosterone cipionate 400 mg every 28 days until progression and continued luteinising hormone-releasing hormone agonist therapy. Upon progression after BAT, men were rechallenged with oral enzalutamide 160 mg daily. The co-primary endpoints were investigator-assessed 50% decline in PSA concentration from baseline (PSA₅₀) for BAT (for all patients who received at least one dose) and for enzalutamide rechallenge (based on intention-to-treat analysis). These data represent the final analysis for the post-enzalutamide cohort, while two additional cohorts (post-abiraterone and newly castration-resistant prostate cancer) are ongoing. The trial is registered with ClinicalTrials.gov, number NCT02090114.

Findings: Between Aug 28, 2014, and May 18, 2016, we accrued 30 eligible patients and treated them with BAT. Nine (30%; 95% CI 15-49; p<0·0001) of 30 patients achieved a PSA₅₀ to BAT. 29 patients completed BAT and 21 proceeded to enzalutamide rechallenge, of whom 15 (52%; 95% CI 33-71; p<0·0001) achieved a PSA₅₀ response. During BAT, the only grade 3-4 adverse event occurring in more than one patient was hypertension (three [10%] patients). Other grade 3 or worse adverse events occurring during BAT in one [3%] patient each were pulmonary embolism, myocardial infarction, urinary obstruction, gallstone, and sepsis. During enzalutamide retreatment, no grade 3-4 toxicities occurred in more than one patient. No treatment-related deaths were reported during either BAT or enzalutamide retreatment.

Interpretation: BAT is a safe therapy that resulted in responses in asymptomatic men with metastatic castration-resistant prostate cancer and also resensitisation to enzalutamide in most patients undergoing rechallenge. Further studies with BAT are needed to define the potential clinical role for BAT in the management of metastatic castration-resistant prostate cancer and the optimal strategy for sequencing between androgen and antiandrogen therapies in metastatic castration-resistant prostate cancer to maximise therapeutic benefit to patients.

Funding: National Institutes of Health and National Cancer Institute.

Background: Cyclic high-dose testosterone injections, also known as bipolar androgen therapy (BAT), is a novel treatment strategy for patients with metastatic castration-resistant prostate cancer (mCRPC). BAT has shown clinical activity in prior studies enrolling men with mCRPC and may potentially restore sensitivity to prior androgen receptor (AR)-targeted agents.

Objective: To evaluate the clinical activity of BAT in patients progressing on AR-targeted therapy as well as responses to abiraterone or enzalutamide upon rechallenge after BAT.

Design, setting, and participants: RESTORE is a multicohort phase II study enrolling asymptomatic mCRPC patients after abiraterone or enzalutamide at Johns Hopkins Hospital (NCT02090114). Participants (29 after abiraterone and 30 after enzalutamide) received 400 mg testosterone cypionate intramuscularly every 28 days, with ongoing luteinizing hormone-releasing hormone agonist/antagonist treatment (ie, BAT). Following progression on BAT, patients were rechallenged with their most recent AR-targeted therapy.

Outcome measurements and statistical analysis: Coprimary endpoints were >50% decline in PSA from baseline (PSA₅₀) responses to BAT and following AR-targeted therapy rechallenge. Outcomes in the post-abiraterone cohort are presented, as well as updated results from the post-enzalutamide cohort and an exploratory AR-V7 analysis.

Results and limitations: No statistically significant difference in PSA₅₀ response rates to BAT was observed (30% [post-enzalutamide cohort] vs 17% [post-abiraterone cohort], p = 0.4). However, PSA₅₀ responses to AR-targeted therapy rechallenge were higher in the post-enzalutamide cohort (68% vs 16%, p = 0.001). The median time from enrollment to progression following rechallenge with AR-targeted therapy (ie, progression-free survival 2; PFS2) was longer in the post-enzalutamide versus post-abiraterone patients (12.8 vs 8.1 mo, p = 0.04). Outcomes were worse in patients with detectable AR-V7 in circulating tumor cells (median PFS2: 10.3 vs 7.1 mo, p = 0.005).

Conclusions: BAT shows clinical activity in mCRPC patients and may be more effective at resensitizing to enzalutamide versus abiraterone.

Patient summary: BAT is well tolerated in metastatic castration-resistant prostate cancer patients. The type of prior AR-targeted therapy might affect response to BAT as well as AR-therapy rechallenge. BAT followed by AR-targeted therapy rechallenge did not improve outcomes in AR-V7-positive patients.

Background: Cyclical, high-dose testosterone administration, termed bipolar androgen therapy (BAT), can induce clinical responses and restore sensitivity to androgen signalling inhibition in patients with previously treated castration-resistant prostate cancer (PCa) (CRPC). This trial evaluated whether BAT is a safe and effective first-line hormonal therapy for patients with CRPC.

Patients and methods: In cohort C of this single-centre, open-label, phase II, multi-cohort trial (RE-sensitizing with Supraphysiologic Testosterone to Overcome REsistance study), 29 patients with CRPC received first-line hormonal therapy with 400 mg of testosterone cypionate intramuscularly every 28 days concurrent with a luteinising hormone-releasing hormone agonist/antagonist. The primary end-point of the study was the PSA₅₀ response rate to BAT treatment.

Results: After treatment with BAT, four of 29 patients (14%; 95% confidence interval [CI]: 4-32%) experienced a PSA₅₀ response. The median radiographic progression-free survival to BAT was 8.5 months (95% CI: 6.9-15.1) for patients with metastatic CRPC. After progression on BAT, 17 of 18 patients (94%; 95% CI: 73-100%) achieved a PSA₅₀ response and 15 of 18 patients (83%; 95% CI: 59-96) achieved a PSA₉₀ response on abiraterone or enzalutamide. Twelve of 15 patients (80%; 95% CI: 52-96) with metastatic CRPC remain on abiraterone or enzalutamide with a median duration of follow-up of 11.2 months.

Conclusion: As first-line hormonal treatment for CRPC, BAT was well tolerated and resulted in prolonged disease stabilisation. After progression on BAT, patients had favourable responses to second-generation androgen receptor-targeted therapy.

Trial registration: ClinicalTrials.gov NCT02090114.

Bipolar androgen therapy (BAT) is a paradoxical treatment for castrate-resistant prostate cancer whereby testosterone levels are rapidly alternated between supraphysiologic and near-castrate concentrations. Initial studies demonstrated that BAT is safe and produces clinical responses. A trial comparing enzalutamide against BAT is ongoing.

Prostatic carcinogenesis is associated with changes in the androgen receptor (AR) axis converting it from a paracrine dependence upon stromal signaling to an autocrine-initiated signaling for proliferation and survival of prostatic cancer cells. This malignant conversion is due to gain of function changes in which the AR activates novel genomic (i.e. transcriptional) and non-genomic signaling pathways, which are not present in normal prostate epithelial cells. During further progression, additional molecular changes occur which allow these unique malignancy-dependent AR signaling pathways to be activated even in the low androgen ligand environment present following androgen ablation therapy. These signaling pathways are the result of partnering the AR with a series of other genomic (e.g. transcriptional co-activators) or non-genomic (e.g. steroid receptor co-activator (Src) kinase) signaling molecules. Thus, a combinatorial androgen receptor targeted therapy (termed CART therapy) inhibiting several points in the AR signaling cascade is needed to prevent the approximately 30,000 US males per year dying subsequent to failure of standard androgen ablation therapy. To develop such CART therapy, a series of agents targeted at specific points in the AR cascade should be used in combination with standard androgen ablative therapy to define the fewest number of agents needed to produce the maximal therapeutic anti-prostate cancer effect. As an initial approach for developing such CART therapy, a variety of new agents could be combined with luteinizing hormone-releasing hormone analogs. These include: (1) 5alpha-reductase inhibitors to inhibit the conversion of testosterone to the more potent androgen, dihydrotestosterone; (2) geldanamycin analogs to downregulate AR protein in prostate cancer cells, (3) 'bulky' steroid analogs, which can bind to AR and prevent its partnering with other co-activators/signaling molecules, and (4) small molecule kinase inhibitors to inhibit MEK, which is activated as part of the malignant AR signaling cascade.

Purpose: The use of radiation therapy (RT) in consolidating oligometastatic prostate cancer (OPCa) is a rapidly evolving treatment paradigm. We review our institutional experience using metastasis-directed therapy in the definitive management of men with OPCa.

Methods and materials: Patients with OPCa treated with definitive RT were included. The Kaplan-Meier method and multivariable Cox regression analysis were performed to assess biochemical progression-free survival (bPFS) and time to next intervention. Cumulative incidence functions were used to calculate rates of local failure. Toxicity was assessed using Common Terminology Criteria for Adverse Events (version 4).

Results: This study analyzed 156 patients with OPCa and 354 metastatic lesions with median follow-up of 24.6 months. Of 150 patients with toxicity data, 53 (35%) experienced acute grade 1 toxicity, 8 (5%) had grade 2, and none had grade 3 toxicity. Only 13 patients (9%) had late toxicities. At 24 months, the cumulative incidence of local failure was 7.4%. Median bPFS for the entire cohort was 12.9 months and 52% at 1 year. On multivariable analysis, factors associated with prolonged bPFS were peri-RT androgen deprivation therapy (ADT), lower gross tumor volume, and hormone-sensitive (HS) OPCa. Median time to next intervention, including repeat RT, was 21.6 months. Median bPFS for men with HS prostate cancer was 17.2 months compared with 7.2 months in men with castrate-resistant OPCa (P < .0001), and cumulative incidence of local failure at 24 months was lower with HS OPCa (4.8% vs 12.1%; P = .034). We analyzed 28 men with HS OPCa treated with a course of peri-RT ADT (median, 4.3 months) with recovery of testosterone. At a median follow-up of 33.5 months, 20 patients had not developed bPFS, median bPFS had not been reached, and 24-month bPFS was 77%.

Conclusions: Metastasis-directed therapy can be effective across a wide range of OPCa subtypes, but with differential efficacy. Further study is warranted to investigate the use of RT across the wide range of patients with OPCa.

Purpose: We evaluated rapid androgen cycling in combination with docetaxel for men with progressive noncastrate prostate cancers.

Patients and methods: Noncastrate patients with <or= 6 months of hormone therapy were eligible. Cohort 1 (62 patients) received six 28-day cycles of docetaxel (75 mg/m(2)), leuprolide, and 7 days of topical testosterone. Cohort 2 (38 patients) received nine 21-day cycles of docetaxel (70 mg/m(2)), leuprolide, and 3 days of testosterone. The primary end point was the proportion of patients at 18 months who achieved noncastrate testosterone levels (> 150 ng/dL) and an undetectable prostate-specific antigen (PSA; <or= 0.05, <or= 0.5, or <or= 2.0 ng/mL with prior prostatectomy, radiation therapy, or no definitive therapy, respectively). Cytochrome P450 3A4 (CYP3A4) activity and docetaxel pharmacokinetics were evaluated.

Results: A higher proportion of patients achieved the undetectable PSA outcome at 18 months in cohort 2 relative to cohort 1 (13% v 0%). The 16% incidence of febrile neutropenia was higher than that observed in patients was castration-resistant disease, which may have been related to a 50% reduction in overall docetaxel clearance in the noncastrate group. There was no alteration in CYP3A4 activity (P = .87) or docetaxel clearance (P = .88) between cycles.

Conclusion: The undetectable PSA end point allows for a rapid screening of interventions for further study. Increasing the number of docetaxel cycles after a shorter period of testosterone repletion, and a longer duration of testosterone depletion, increased the proportion of men who achieved an undetectable PSA. The higher-than-expected incidence of febrile neutropenia may have been related to the reduced overall docetaxel clearance in patients with noncastrate versus castrate testosterone levels.