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Sipuleucel-T (sip-T) is a Food and Drug Administration (FDA)-approved autologous cellular immunotherapy for metastatic castration-resistant prostate cancer (mCRPC). We hypothesized that combining sip-T with interleukin (IL)-7, a homeostatic cytokine that enhances both B and T cell development and proliferation, would augment and prolong antigen-specific immune responses against both PA2024 (the immunogen for sip-T) and prostatic acid phosphatase (PAP). Fifty-four patients with mCRPC treated with sip-T were subsequently enrolled and randomized 1:1 into observation (n=26) or IL-7 (n=28) arms of a phase II clinical trial (NCT01881867). Recombinant human (rh) IL-7 (CYT107) was given weekly×4. Immune responses were evaluated using flow cytometry, mass cytometry (CyTOF), interferon (IFN)-γ ELISpot, 3H-thymidine incorporation, and ELISA. Treatment with rhIL-7 was well tolerated. For the rhIL-7-treated, but not observation group, statistically significant lymphocyte subset expansion was found, with 2.3-2.6-fold increases in CD4+T, CD8+T, and CD56bright NK cells at week 6 compared with baseline. No significant differences in PA2024 or PAP-specific T cell responses measured by IFN-γ ELISpot assay were found between rhIL-7 and observation groups. However, antigen-specific T cell proliferative responses and humoral IgG and IgG/IgM responses significantly increased over time in the rhIL-7-treated group only. CyTOF analyses revealed pleiotropic effects of rhIL-7 on lymphocyte subsets, including increases in CD137 and intracellular IL-2 and IFN-γ expression. While not powered to detect clinical outcomes, we found that 31% of patients in the rhIL-7 group had prostate specific antigen (PSA) doubling times of >6 months, compared with 14% in the observation group. Treatment with rhIL-7 led to a significant expansion of CD4+ and CD8+ T cells, and CD56bright natural killer (NK) cells compared with observation after treatment with sip-T. The rhIL-7 treatment also led to improved antigen-specific humoral and T cell proliferative responses over time as well as to increased expression of activation markers and beneficial cytokines. This is the first study to evaluate the use of rhIL-7 after sip-T in patients with mCRPC and demonstrates encouraging results for combination approaches to augment beneficial immune responses.

PurposeRadical prostatectomy (RP) alone is often inadequate in curing men with clinically localized, high-risk prostate cancer (PC). We hypothesized that chemohormonal therapy (CHT) with androgen-deprivation therapy plus docetaxel before RP would improve biochemical progression-free survival (BPFS) over RP alone.Patients and methodsMen with clinically localized, high-risk PC were assigned to RP alone or neoadjuvant CHT with androgen deprivation plus docetaxel (75 mg/m2 body surface area every 3 weeks for 6 cycles) and RP. The primary end point was 3-year BPFS. Biochemical failure was defined as a serum prostate-specific antigen level > 0.2 ng/mL that increased on 2 consecutive occasions that were at least 3 months apart. Secondary end points included 5-year BPFS, overall BPFS, local recurrence, metastasis-free survival (MFS), PC-specific mortality, and overall survival (OS).ResultsIn total, 788 men were randomly assigned. Median follow-up time was 6.1 years. The overall rates of grade 3 and 4 adverse events during chemotherapy were 26% and 19%, respectively. No difference was seen in 3-year BPFS between neoadjuvant CHT plus RP and RP alone (0.89 v 0.84, respectively; 95% CI for the difference, -0.01 to 0.11; P = .11). Neoadjuvant CHT was associated with improved overall BPFS (hazard ratio [HR], 0.69; 95% CI, 0.48 to 0.99), improved MFS (HR, 0.70; 95% CI, 0.51 to 0.95), and improved OS (HR, 0.61; 95% CI, 0.40 to 0.94) compared with RP alone.ConclusionThe primary study end point, 3-year BPFS, was not met. Although some improvement was seen in secondary end points, any potential benefit must be weighed against toxicity. Our data do not support the routine use of neoadjuvant CHT and RP in patients with clinically localized, high-risk PC at this time.

Enzalutamide (MDV3100) is a second generation Androgen Receptor (AR) antagonist with proven efficacy in the treatment of castration resistant prostate cancer (CRPC). The majority of treated patients, however, develop resistance and disease progression and there is a critical need to identify novel targetable pathways mediating resistance. The purpose of this study was to develop and extensively characterize a series of enzalutamide-resistant prostate cancer cell lines. Four genetically distinct AR-positive and AR-pathway dependent prostate cancer cell lines (CWR-R1, LAPC-4, LNCaP, VCaP) were made resistant to enzalutamide by long-term culture (> 6 months) in enzalutamide. Extensive characterization of these lines documented divergent in vitro growth characteristics and AR pathway modulation. Enzalutamide-resistant LNCaP and CWR-R1 cells, but not LAPC-4 and VCAP cells, demonstrated increased castration-resistant and metastatic growth in vivo. Global gene expression analyses between short-term enzalutamide treated vs. enzalutamide-resistant cells identified both AR pathway and non-AR pathway associated changes that were restored upon acquisition of enzalutamide resistance. Further analyses revealed very few common gene expression changes between the four resistant cell lines. Thus, while AR-mediated pathways contribute in part to enzalutamide resistance, an unbiased approach across several cell lines demonstrates a greater contribution toward resistance via pleiotropic, non-AR mediated mechanisms.

The function and clinical utility of stem cell markers in metastatic castration-resistant prostate cancer (mCRPC) remains unresolved, and their expression may confer important therapeutic opportunities for staging and therapy. In the adult human prostate, CD133 (PROM1) expression identifies infrequent prostate epithelial progenitor cells and putative cancer stem cells. Previous work demonstrated an association with CD133 and cancer cell proliferation using in vitro model systems. The primary objective here was to investigate the expression of CD133 in circulating tumor cells (CTCs) from patients with mCRPC and to test the hypothesis that patients with mCRPC had CD133-positive CTCs associated with increased cell proliferation, changes in the androgen receptor (AR) protein expression, or AR nuclear co-localization. We utilized ImageStreamX technology, which combines flow cytometry and fluorescence microscopy, to capture and analyze CD45-negative/EpCAM-positive CTCs for CD133, Ki-67, and AR. All patient samples (20/20) contained CD133-positive populations of CTCs, and on average 50.9 ± 28.2% (range of 18.2% to 100%) of CTCs were CD133-positive. CD133-positive CTCs have increased Ki-67 protein expression compared to CD133-negative CTCs, implying that CD133-positive CTCs may have greater proliferative potential when compared to their CD133-negative counterparts. CD133-positive and CD133-negative CTCs have similar levels of AR protein expression and cellular co-localization with nuclear markers, implying that CD133 expression is independent of AR pathway activity and an AR-independent marker of mCRPC proliferation. These studies demonstrate the presence of CD133-positive populations in CTCs from mCRPC with increased proliferative potential.

PurposePatients previously treated with ketoconazole were excluded from phase III trials of abiraterone acetate due to potential overlapping mechanism of action. The purpose of this study was to determine the clinical utility of abiraterone and its impact on circulating androgens following ketoconazole.Experimental designChemotherapy-naïve patients with progressive metastatic castration-resistant prostate cancer (mCRPC) and prior ketoconazole therapy ≥28 days received abiraterone acetate 1,000 mg daily and prednisone 5 mg twice daily. The primary endpoint was the proportion of patients with PSA response, defined as ≥30% PSA decline at 12 weeks. H0 = 0.30 versus H1 = 0.50 (α = 0.05, power = 0.83). Circulating androgen levels were measured using liquid chromatography tandem mass spectrometry.ResultsThirty-nine patients were included in the final analysis. Twenty (51%; 95% confidence interval, 36%-66%) patients had ≥30% PSA decline; the null hypothesis was rejected. Sixteen (41%) had ≥50% PSA decline. Median PFS (progression-free survival) was 16 weeks; median radiographic PFS (rPFS) was 36 weeks. Samples for measurement of baseline androgens were available in 37 patients. The PSA response proportion was 59% in 29 patients with DHEA ≥ limit of quantitation (LOQ), compared with 13% in 8 patients with DHEA < LOQ (P = 0.042). Median PFS was 6 and 16 weeks in DHEA < LOQ and DHEA ≥ LOQ patients, respectively (P = 0.017); median rPFS was 14 and 36 weeks in DHEA < LOQ and DHEA ≥ LOQ patients, respectively (P < 0.001).ConclusionsAbiraterone demonstrates modest clinical efficacy in mCRPC patients previously treated with ketoconazole. Patients with DHEA ≥ LOQ were more likely to demonstrate PSA responses and longer PFS. Analysis of circulating androgens merits further investigation as a biomarker for response to androgen synthesis inhibitor therapy.

BACKGROUND: Many current therapies for metastatic castration-resistant prostate cancer (mCRPC) are aimed at AR signaling; however, resistance to these therapies is inevitable. To personalize CRPC therapy in an individual with clinical progression despite maximal AR signaling blockade, it is important to characterize the status of AR activity within their cancer. Biopsies of bone metastases are invasive and frequently fail to yield sufficient tissue for further study. Evaluation of circulating tumor cells (CTCs) offers an alternative, minimally invasive mechanism to characterize and study late-stage disease. The goal of this study was to evaluate the utility of CTC interrogation with respect to the AR as a potential novel therapeutic biomarker in patients with mCRPC. METHODS: Fifteen mL of whole blood was collected from patients with progressive, metastatic mCRPC, the mononuclear cell portion was isolated, and fluorescence-activated cell sorting (FACS) was used to isolate and evaluate CTCs. A novel protocol was optimized to use ImageStreamX to quantitatively analyze AR expression and subcellular localization within CTCs. Co-expression of AR and the proliferation marker Ki67 was also determined using ImageStreamX. RESULTS: We found inter-patient and intra-patient heterogeneity in expression and localization of AR. Increased AR expression and nuclear localization are associated with elevated co-expression of Ki-67, consistent with the continued role for AR in castration-resistant disease. Despite intra-patient heterogeneity, CTCs from patients with prior exposure to abiraterone had increased AR expression compared to CTCs from patients who were abiraterone-naïve. CONCLUSIONS: As our toolbox for targeting AR function expands, our ability to evaluate AR expression and function within tumor samples from patients with late-stage disease will likely be a critical component of the personalized management of advanced prostate cancer. AR expression and nuclear localization varies within patients and between patients; however it remains associated with markers of proliferation. This supports a molecularly diverse AR-centric pathobiology imparting castration-resistance.

Despite new treatments for castrate-resistant prostate cancer (CRPC), the prognosis of patients with CRPC remains bleak due to acquired resistance to androgen receptor (AR)-directed therapy. The glucocorticoid receptor (GR) and AR share several transcriptional targets, including the anti-apoptotic genes serum and glucocorticoid-regulated kinase 1 (SGK1) and Map kinase phosphatase 1 (MKP1)/dual specificity phosphatase 1 (DUSP1). Because GR expression increases in a subset of primary prostate cancer (PC) following androgen deprivation therapy, we sought to determine whether GR activation can contribute to resistance to AR-directed therapy. We studied CWR-22Rv1 and LAPC4 AR/GR-expressing PC cell lines following treatment with combinations of the androgen R1881, AR antagonist MDV3100, GR agonist dexamethasone, GR antagonists mifepristone and CORT 122928, or the SGK1 inhibitor GSK650394. Cell lines stably expressing GR (NR3C1)-targeted shRNA or ectopic SGK1-Flag were also studied in vivo. GR activation diminished the effects of the AR antagonist MDV3100 on tumor cell viability. In addition, GR activation increased prostate-specific antigen (PSA) secretion and induced SGKI and MKP1/DUSP gene expression. Glucocorticoid-mediated cell viability was diminished by a GR antagonist or by co-treatment with the SGK1 inhibitor GSK650394. In vivo, GR depletion delayed castrate-resistant tumor formation, while SGK1-Flag-overexpressing PC xenografts displayed accelerated castrate-resistant tumor initiation, supporting a role for SGK1 in GR-mediated CRPC progression. We studied several PC models before and following treatment with androgen blockade and found that increased GR expression and activity contributed to tumor-promoting PC cell viability. Increased GR-regulated SGK1 expression appears, at least in part, to mediate enhanced PC cell survival. Therefore, GR and/or SGK1 inhibition may be useful adjuncts to AR blockade for treating CRPC.