Enhanced Efficacy with Enzalutamide. Enzalutamide has greater androgen receptor (AR) binding affinity and a greater negative impact on AR nuclear import than bicalutamide with Dihydrotestosterone (DHT) as a control. In addition with enzalutamide there is no AR binding with the DNA and coac tivatior receruitment. (2) Version Date: 12/5/17 Abbreviated Title : Enzalutamide in non-met CSPC 221.2.11 Rationale for Re-Treatment of Patients with a Sec ond Course of Enzalutamide As previously stated, there is no standard of car e for patients with nmCSPC. Given that 20-40% of patients diagnosed each year with prosta te cancer (over 250,000 men in the US alone) have recurrent disease after definitive therapy, this makes up a large population of patients. The standard of care for patients with nmCSPC includes ADT and active surveillance. Generally, these patients can be followed without therapy until their PSA doubling time escalates at which time ADT is often started. ADT can be given co ntinuously or intermittently, i.e. 2-3 doses of ADT to suppress PSA, and then allow for PSA re covery. Once PSA has recovered ADT can be resumed for an intermittent basis based on PSA metrics and continued castration sensitive disease. A large study of intermittent vs. c ontinuous ADT in this population of patients has demonstrated that intermittent ADT was non-infe rior to continuous ADT in terms of overall survival. Also there were improvements in quality of life factors in patients treated with intermittent ADT. 49 Given that this trial will explore the short term benefits of a brief course of enzalutamide for 3 months, it may be prudent to evaluate if this treatment could be given for a second course and induce a second, sustained PSA decline. From a broad prostate cancer perspective, this would be valuable information moving forward if future larger trials would be considered to evaluate enzalutamide as possible alternative form of intermittent anti-androgen therapy. Such a therapy may be preferred over (intermittent) ADT from a quality of life perspective. 1.2.12 Rationale for Evaluating Changes in Te stosterone and Rela ted Hormone Levels Enzalutamide, an androgen receptor inhibitor, differs from traditional androgen deprivation therapy in its ability to inhibit the androgen re ceptor without lowering testosterone and is associated with an overall increase in testoste rone levels. Consequently , enzalutamide and other non-steroidal antiandrogens have a different side effect profile. A recent European study evaluated Enzalutamide monotherapy in hormone-naïve prostate cancer, and examined a series of hormone levels at various time points in administration to determine changes in testosterone and testosterone related hormones. 50While they found increased levels of testosterone, estradiol, and luteinizing hormone, levels were checked until the 25 week time point and only once thereafter. We seek to further elucidate this mechanism of action by obtaining hormone levels at each follow up visit, as well as pre-Enzalutamide, 1 hour post, 24 hours post, 48 hours post, and 72 hours post administration, when logistically feasible . Dr. Doug Figg’s lab is currently evaluating a murine model to demonstrate the presence of androgen receptors in the hypothalamus which may influence the levels of testos terone and relate d hormones in the serum. This pre-clinical data can also be correlated with clinical informatics that will be obtained with these serial hormonal levels. 1.2.12.1 Evaluating Immunologic Effects of Low Dose EnzalutamidePatients from the arm receiving enzalutamide al one (160 mg daily for 84 days, without ADT) have been assessed for immunologic impact from cohort 1. Peripheral blood mononuclear cells Version Date: 12/5/17 Abbreviated Title : Enzalutamide in non-met CSPC 23(PBMCs) collected from 12 patients pre and pos t enzalutamide (days 14, 28, 84, and 100) were analyzed by flow cytometry to identify 123 imm une cell subsets, including 9 standard subsets (CD4+ and CD8+ T cells, T-regulatory cells (T reg), B cells, conventional and plasmacytoid dendritic cells (cDC, pDC), natural killer cells (NK), natural killer T cells (NKT), and myeloid derived suppressor cell (MDSC)), and 114 subset s relating to maturati on and function. PBMCs were also assessed for TREC to identify rece nt thymic emigrants, and by microarray to determine changes in global gene expression. Treatment with enzalutamide induced several notable alterations in peripheral immune cells, suggesting that it has potential immune activating properties. These changes occurred early following treatment, and included an increase of NK cells, decreased frequencies of MDSCs with a suppressive phenotype (e.g. PD-L1+ MDSC, gMDSC, and CD16+ MDSC), and decreased frequencies of both CD4+ and CD8+ T-lymphocytes expressi ng the immune inhibitory checkpoint molecule CTLA4. Additionally, treatment with enzalutamide increas ed TREC levels by >75% in 7 out of 12 patients compared to pre-therapy levels (p= 0.012); naïve CD4+and CD8+ T-lymphocytes were also elevated by >25% in those patients dem onstrating the greatest increase in TREC. Gene expression analysis of PBMCs corroborated these findings, showing that enzalutamide increased activation of interferon-gamma signalingand related immune activating pathways. These preliminary findings demonstrate that short-course enzalutamide has immune activating properties in cancer patients, and support the combination of enzalutamide with immunotherapy. Since the immunologic effects are likely separate from just blocking AR (based on preclinical data serving as the rationale for this study) it would be prudent to explore the immunologic impact of lower doses of enzalutamide (i.e. 80 mg) to determine if the immune impact is preserved, while also limiting the toxicity seen with enzalutamide alone at 160 mg/day. Although enzalutamide is well tole rated, fatigue and breast tendern ess in men were frequently seen and could limit its use (independent of ADT) as an immune adjuvant. It is likely these side effects can be minimized at a lower dose. If this can be accomplished at a lower dose, it is more likely to lead to the use of enzalutamide as a possible immunologic adjuvant in other diseases where immune therapies are now approved includi ng lung cancer, bladder cancer, melanoma, and renal cancer. We planned a study to explore the immunologic ef fects in biochemically recurrent prostate cancer of enzalutamide 80 mg/day for 3 months. The data were to have been compared against the existing immune data descri bed above with enzalutamide at 160 mg/day for 3 months, however this cohort was closed before enrollment due to lack of patient interest in participation 2 ELIGIBILITY ASSESSMENT AND ENROLLMENT 2.1 E LIGIBILITY CRITERIA 2.1.1 Inclusion Criteria A. Histopathological documentation of prostate cancer confirmed in the Laboratory of Pathology at the National Institutes of Health (NIH) Clinical Version Date: 12/5/17 Abbreviated Title : Enzalutamide in non-met CSPC 24Center, or Walter Reed National Military Medical Center prior to enrollment. If no pathologic specimen is available, patients may enroll with a pathologist’s report showing a histologic diagnosis of prostate cancer and a clinical course consistent with the disease. B. Biochemical progression defined as follows: xFor patients following definitive radiation therapy: DULVHLQ36$RI ng/mL above the nadir (per RT OG-ASTRO consensus criteria). xFor patients following radical prostatectomy: rising PSA after surgical procedure. (Patients must have a PSA >2ng/ml) C. ECOG performance status of 0–1 (Karnofsky >80%, see Appendix A ). D. Patients must have a PSA doub ling time of 12 months or less. E. Patients must have a rising PSA as confirmed by 3 values done at least 1 week apart and over no less than 1 month. F. Recovery from acute toxicity related to prior therapy, including surgery and UDGLDWLRQRUQRWR[LFLW\JUDGH G. Negative CT scan/MRI and bone scan for metastatic prostate cancer. H. Hematological eligibility parameters (within 16 days before starting therapy; see Appendix D ): x*UDQXORF\WHFRXQW 000/mm3 x3ODWHOHWFRXQWPP3 x+JE g/dL I. Biochemical eligibility parameters (within 16 days before starting therapy): x+HSDWLFIXQFWLRQ E LOLUXELQPJG/ 25LQSDWLHQWVZLWK *LOEHUW¶VV\QGURPHDWRWDO ELOLUXELQ $67DQG$/7  times upper limit of normal. J. No other active malignancies within the past 36 months (with the exception of nonmelanoma skin cancers or carcinoma in situ of the bladder) or life- threatening illnesses K. Willing to travel to the NIH for follow-up visits. L. 18 years of age or older. M. Able to understand and sign informed consent.N.%DVHOLQHWHVWRVWHURQHORZHUOLPLWRIQRUPDO. O.36$QJP/ P. The effects of enzalutamide, PSA-TRICOM or the combination on the developing human fetus are unknown. For this reason, men must agree to use adequate contraception (horm onal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregna nt while her partner is participating in this study, she should inform her treating physician immediately. 2.1.2 Exclusion Criteria A.