Purpose Abiraterone acetate (AA) is a standard of care for metastatic castration-resistant prostate cancer (CRPC). Despite a large food effect, AA was administered under fasting conditions in its pivotal trials. We sought to test the hypothesis that low-dose AA (LOW; 250 mg with a low-fat meal) would have comparable activity to standard AA (STD; 1,000 mg fasting) in patients with CRPC. Patients and Methods Patients (n = 72) with progressive CRPC from seven institutions in the United States and Singapore were randomly assigned to STD or LOW. Both arms received prednisone 5 mg twice daily. Prostate-specific antigen (PSA) was assessed monthly, and testosterone/dehydroepiandrosterone sulfate were assessed every 12 weeks with disease burden radiographic assessments. Plasma was collected for drug concentrations. Log change in PSA, as a pharmacodynamic biomarker for efficacy, was the primary end point, using a noninferiority design. Progression-free survival (PFS), PSA response (≥ 50% reduction), change in androgen levels, and pharmacokinetics were secondary end points. Results Thirty-six patients were accrued to both arms. At 12 weeks, there was a greater effect on PSA in the LOW arm (mean log change, -1.59) compared with STD (-1.19), and noninferiority of LOW was established according to predefined criteria. The PSA response rate was 58% in LOW and 50% in STD, and the median PFS was approximately 9 months in both groups. Androgen levels decreased similarly in both arms. Although there was no difference in PSA response or PFS, abiraterone concentrations were higher in STD. Conclusion Low-dose AA (with low-fat breakfast) is noninferior to standard dosing with respect to PSA metrics. Given the pharmacoeconomic implications, these data warrant consideration by prescribers, payers, and patients. Additional studies are indicated to assess the long-term efficacy of this approach.

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Purpose: Although androgen deprivation therapy (ADT) and androgen receptor (AR) signaling inhibitors are effective in metastatic prostate cancer, resistance occurs in most patients. This phase I/II trial assessed the safety, pharmacokinetic impact, and efficacy of the glucocorticoid receptor (GR) antagonist mifepristone in combination with enzalutamide for castration-resistant prostate cancer (CRPC). Patients and Methods: One hundred and six patients with CRPC were accrued. Phase I subjects were treated with enzalutamide monotherapy at 160 mg per day for 28 days to allow steady-state accumulation. Patients then entered the dose escalation combination portion of the study. In phase II, patients were randomized 1:1 to either receive enzalutamide alone or enzalutamide plus mifepristone. The primary endpoint was PSA progression-free survival (PFS), with radiographic PFS, and PSA response rate (RR) as key secondary endpoints. Circulating tumor cells were collected before randomization for exploratory translational biomarker studies. Results: We determined a 25% dose reduction in enzalutamide, when added to mifepristone, resulted in equivalent drug levels compared with full-dose enzalutamide and was well tolerated. However, the addition of mifepristone to enzalutamide following a 12-week enzalutamide lead-in did not delay time to PSA, radiographic or clinical PFS. The trial was terminated early due to futility. Conclusions: This is the first prospective trial of dual AR–GR antagonism in CRPC. Enzalutamide combined with mifepristone was safe and well tolerated but did not meet its primary endpoint. The development of more specific GR antagonists combined with AR antagonists, potentially studied in an earlier disease state, should be explored.

We determined the RP2D of tasquinimod combined with cabazitaxel to be 0.5 mg daily following a 3 week lead-in of tasquinimod 0.25 mg with growth factor support. No unexpected toxicities occurred. Prostate 77: 385-395, 2017. © 2016 Wiley Periodicals, Inc.

91 Background: Resistance to androgen receptor (AR) targeted therapies is common in mCRPC. Glucocorticoid receptor (GR) expression increases with AR inhibition in patients (pts) and blockade of GR signaling inhibits CRPC growth in preclinical models when combined with AR blockade. We thus conducted a phase I/II open label trial of Enz combined with Mif, a GR, AR, and progesterone receptor antagonist for pts with mCRPC to assess the feasibility and impact on disease progression with dual AR/GR antagonism. Methods: The phase I dose escalation portion assessed the safety of the two-drug combination and a recommended phase II dose (R2PD) was determined based on safety, pharmacokinetic and endocrine assessments. In the phase II portion, patients (pts) received 12 weeks of Enz (160mg/day) followed by randomization to Enz alone or Enz plus Mif with PSA-progression free survival (PFS) as the primary endpoint. 42 pts were to randomize to each arm to provide 80% power to detect a hazard ratio of 0.6, with a one-sided alpha of 0.1; there was a planned interim futility analysis after 50% of progression events. Results: 106 pts (18 phase I/88 phase II) were enrolled. Pts had a median age of 70 (range 53-89) and baseline PSA of 12.8 (range 0.1-755). 34% of pts received prior docetaxel. The RP2D was 120mg/day Enz and 300mg/day Mif. In phase II, 33 patients were randomized to each arm, with well-balanced baseline demographics. 22 pts were not randomized (15 due to disease progression, 2 due to toxicity, and 5 due to the interim study analysis). The interim analysis showed no difference between arms in PSA-PFS (hazard ratio = 1.34, p=0.395), 12-month PSA-PFS of 31% in both arms, and per-protocol, the trial was stopped. Toxicities were similar in the arms, e.g. fatigue (12% vs. 14%), hot flashes (6% vs. 5%), and pain (4% vs. 4%). Conclusions: The addition of Mif to Enz following a 12-week Enz lead-in did not delay time to PSA progression. Further analyses of secondary endpoints, including translational biomarkers such as hormone levels, GR/AR-v7 expression in circulating tumor cells and cell free DNA analyses are ongoing. Clinical trial information: NCT02012296.

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Background: Docetaxel prednisone is a standard of care for men with metastatic castration-resistant prostate cancer (mCRPC), and plasma vascular endothelial growth factor (VEGF) levels are a poor prognostic factor in this population; therefore, we evaluated the combination of docetaxel prednisone with pazopanib, an oral VEGF receptor inhibitor, for safety and preliminary efficacy. Methods: This is a two-site phase 1b Department of Defense Prostate Cancer Clinical Trials Consortium trial of docetaxel, prednisone, and pazopanib once daily and ongoing androgen deprivation therapy and prophylactic pegfilgrastim in men with mCRPC. The primary endpoint was safety and the determination of a maximum tolerated dose (MTD) through a dose-escalation and expansion design; secondary endpoints included progression-free and overall survival (OS), prostate specific antigen (PSA) declines, radiographic responses, and pharmacokinetic and plasma angiokine biomarker analyses.Results: Twenty-five men were treated over six dose levels. Pegfilgrastim was added to the regimen after myelosuppression limited dose escalation. With pegfilgrastim, our target MTD of docetaxel 75 mg/m 2 q3 weeks; prednisone 10 mg daily; and pazopanib 800 mg daily was reached. Eleven additional patients were accrued at this dose level for a total of 36 patients. Dose-limiting toxicities included neutropenia, syncope, and hypertension. Three deaths attributed to study treatment occurred. The objective response rate was 31%; median PFS was 14.1 months (95% confidence interval [CI]: 7.1 and 22.2); and OS was 18.6 months (95% CI: 11.8 and 22.2). Conclusions:The combination of docetaxel, prednisone, and pazopanib (with pegfilgrastim) was tolerable at full doses and demonstrated promising efficacy in a relatively poor risk patients with mCRPC. Further development of predictive biomarkers may enrich for patients who receive clinical benefit from this regimen. K E Y W O R D Scastration-resistant, chemotherapy, docetaxel, metastatic, overall survival, pazopanib, progression-free survival, prostate cancer