Baseline serum testosterone and differential efficacy of bipolar androgen therapy and enzalutamide in the randomized TRANSFORMER trial.

Bipolar androgen therapy (BAT) is effective in a subset of metastatic castration-resistant prostate cancer (mCRPC) patients. Treatment selection biomarkers are needed due to other therapies that can be equally efficacious. We performed post-hoc analysis to determine whether baseline serum testosterone (T) is a treatment selection marker in the TRANSFORMER study, a randomized trial of abiraterone-pretreated mCRPC patients assigned to BAT (n = 94) or enzalutamide (n = 101). The findings suggest that patients with poor outcomes to abiraterone and serum T ≥ 20 ng/dL may benefit preferentially from BAT over enzalutamide. Baseline testosterone could be considered in the treatment selection process when BAT is an option.

Association of PARP inhibitor treatment on the prevalence and progression of clonal hematopoiesis in patients with advanced prostate cancer.

BACKGROUND: Poly ADP-ribose polymerase (PARP) inhibitors are approved for the treatment of some men with advanced prostate cancer. Rare but serious side effects include myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). The impact of PARP inhibitors on clonal hematopoiesis (CH), a potential precursor lesion associated with MDS and AML, is incompletely understood in prostate cancer. We hypothesized that PARP inhibitors would increase CH prevalence and abundance. METHODS: We prospectively enrolled participants with advanced prostate cancer treated with PARP inhibitors. The presence of CH was assessed from leukocytes using an ultra-deep error-corrected dual unique molecular identifiers sequencing method targeting 49 genes most commonly mutated in CH and myeloid malignancies. Variant allele frequencies (VAF) of ≥0.5% were considered clinically significant. Blood samples were collected before and after PARP inhibitor treatment. RESULTS: Ten men were enrolled; mean age of 67 years. Six patients had Gleason 7 disease, and four had Gleason ≥8 disease at diagnosis. Nine had localized disease at diagnosis, and eight had prior treatment with radiation. The mean time between pre- and post-treatment blood samples was 11 months (range 2.6-31 months). Six patients (60%) had CH identified prior to PARP inhibitor treatment, three with multiple clones. Of 11 CH clones identified in follow-up, 5 (45%) appeared or increased after treatment. DNMT3A, TET2, and PPM1D were the most common CH alterations observed. The largest post-treatment increase involved the PPM1D gene. CONCLUSION: CH alterations are frequently found after treatment with PARP inhibitors in patients with prostate cancer and this may be one mechanism by which PARP inhibitors lead to increased risk of MDS/AML.

Characterization of structural, biochemical, pharmacokinetic, and pharmacodynamic properties of the LSD1 inhibitor bomedemstat in preclinical models.

INTRODUCTION: Lysine-specific demethylase 1 (LSD1) is emerging as a critical mediator of tumor progression in metastatic castration-resistant prostate cancer (mCRPC). Neuroendocrine prostate cancer (NEPC) is increasingly recognized as an adaptive mechanism of resistance in mCRPC patients failing androgen receptor axis-targeted therapies. Safe and effective LSD1 inhibitors are necessary to determine antitumor response in prostate cancer models. For this reason, we characterize the LSD1 inhibitor bomedemstat to assess its clinical potential in NEPC as well as other mCRPC pathological subtypes. METHODS: Bomedemstat was characterized via crystallization, flavine adenine dinucleotide spectrophotometry, and enzyme kinetics. On-target effects were assessed in relevant prostate cancer cell models by measuring proliferation and H3K4 methylation using western blot analysis. In vivo, pharmacokinetic (PK) and pharmacodynamic (PD) profiles of bomedemstat are also described. RESULTS: Structural, biochemical, and PK/PD properties of bomedemstat, an irreversible, orally-bioavailable inhibitor of LSD1 are reported. Our data demonstrate bomedemstat has >2500-fold greater specificity for LSD1 over monoamine oxidase (MAO)-A and -B. Bomedemstat also demonstrates activity against several models of advanced CRPC, including NEPC patient-derived xenografts. Significant intra-tumoral accumulation of orally-administered bomedemstat is measured with micromolar levels achieved in vivo (1.2 ± 0.45 µM at the 7.5 mg/kg dose and 3.76 ± 0.43 µM at the 15 mg/kg dose). Daily oral dosing of bomedemstat at 40 mg/kg/day is well-tolerated, with on-target thrombocytopenia observed that is rapidly reversible following treatment cessation. CONCLUSIONS: Bomedemstat provides enhanced specificity against LSD1, as revealed by structural and biochemical data. PK/PD data display an overall safety profile with manageable side effects resulting from LSD1 inhibition using bomedemstat in preclinical models. Altogether, our results support clinical testing of bomedemstat in the setting of mCRPC.

A Phase 1/2 multicenter trial of DKN-01 as monotherapy or in combination with docetaxel for the treatment of metastatic castration-resistant prostate cancer (mCRPC).

BACKGROUND: Dickkopf-related protein 1 (DKK1) is a Wingless-related integrate site (Wnt) signaling modulator that is upregulated in prostate cancers (PCa) with low androgen receptor expression. DKN-01, an IgG4 that neutralizes DKK1, delays PCa growth in pre-clinical DKK1-expressing models. These data provided the rationale for a clinical trial testing DKN-01 in patients with metastatic castration-resistant PCa (mCRPC). METHODS: This was an investigator-initiated parallel-arm phase 1/2 clinical trial testing DKN-01 alone (monotherapy) or in combination with docetaxel 75 mg/m2 (combination) for men with mCRPC who progressed on ≥1 AR signaling inhibitors. DKK1 status was determined by RNA in-situ expression. The primary endpoint of the phase 1 dose escalation cohorts was the determination of the recommended phase 2 dose (RP2D). The primary endpoint of the phase 2 expansion cohorts was objective response rate by iRECIST criteria in patients treated with the combination. RESULTS: 18 pts were enrolled into the study-10 patients in the monotherapy cohorts and 8 patients in the combination cohorts. No DLTs were observed and DKN-01 600 mg was determined as the RP2D. A best overall response of stable disease occurred in two out of seven (29%) evaluable patients in the monotherapy cohort. In the combination cohort, five out of seven (71%) evaluable patients had a partial response (PR). A median rPFS of 5.7 months was observed in the combination cohort. In the combination cohort, the median tumoral DKK1 expression H-score was 0.75 and the rPFS observed was similar between patients with DKK1 H-score ≥1 versus H-score = 0. CONCLUSION: DKN-01 600 mg was well tolerated. DKK1 blockade has modest anti-tumor activity as a monotherapy for mCRPC. Anti-tumor activity was observed in the combination cohorts, but the response duration was limited. DKK1 expression in the majority of mCRPC is low and did not clearly correlate with anti-tumor activity of DKN-01 plus docetaxel.

Bipolar androgen therapy plus nivolumab for patients with metastatic castration-resistant prostate cancer: the COMBAT phase II trial.

Cyclic high-dose testosterone administration, known as bipolar androgen therapy (BAT), is a treatment strategy for patients with metastatic castration-resistant prostate cancer (mCRPC). Here, we report the results of a multicenter, single arm Phase 2 study (NCT03554317) enrolling 45 patients with heavily pretreated mCRPC who received BAT (testosterone cypionate, 400 mg intramuscularly every 28 days) with the addition of nivolumab (480 mg intravenously every 28 days) following three cycles of BAT monotherapy. The primary endpoint of a confirmed PSA50 response rate was met and estimated at 40% (N = 18/45, 95% CI: 25.7-55.7%, P = 0.02 one-sided against the 25% null hypothesis). Sixteen of the PSA50 responses were achieved before the addition of nivolumab. Secondary endpoints included objective response rate (ORR), median PSA progression-free survival, radiographic progression-free survival (rPFS), overall survival (OS), and safety/tolerability. The ORR was 24% (N = 10/42). Three of the objective responses occurred following the addition of nivolumab. After a median follow-up of 17.9 months, the median rPFS was 5.6 (95% CI: 5.4-6.8) months, and median OS was 24.4 (95% CI: 17.6-31.1) months. BAT/nivolumab was well tolerated, resulting in only five (11%) drug related, grade-3 adverse events. In a predefined exploratory analysis, clinical response rates correlated with increased baseline levels of intratumoral PD-1 + T cells. In paired metastatic tumor biopsies, BAT induced pro-inflammatory gene expression changes that were restricted to patients achieving a clinical response. These data suggest that BAT may augment antitumor immune responses that are further potentiated by immune checkpoint blockade.

Prognostic and therapeutic potential of senescent stromal fibroblasts in prostate cancer.

The stromal component of the tumour microenvironment in primary and metastatic prostate cancer can influence and promote disease progression. Within the prostatic stroma, fibroblasts are one of the most prevalent cell types associated with precancerous and cancerous lesions; they have a vital role in the structural composition, organization and integrity of the extracellular matrix. Fibroblasts within the tumour microenvironment can undergo cellular senescence, which is a stable arrest of cell growth and a phenomenon that is emerging as a recognized hallmark of cancer. Supporting the idea that cellular senescence has a pro-tumorigenic role, a subset of senescent cells exhibits a senescence-associated secretory phenotype (SASP), which, along with increased inflammation, can promote prostate cancer cell growth and survival. These cellular characteristics make targeting senescent cells and/or modulating SASP attractive as a potential preventive or therapeutic option for prostate cancer.

Third generation quinoline-3-carboxamide transcriptional disrupter of HDAC4, HIF-1α, and MEF-2 signaling for metastatic castration-resistant prostate cancer.

BACKGROUND: The quinoline-3-carboxamide, Tasquinimod (TasQ), is orally active as a maintenance therapy with an on-target mechanism-of-action via allosteric binding to HDAC4. This prevents formation of the HDAC4/NCoR1/HDAC3 complex, disrupting HIF-1α transcriptional activation and repressing MEF-2 target genes needed for adaptive survival signaling in the compromised tumor micro environment. In phase 3 clinical testing against metastatic castration-resistant prostate cancer(mCRPC), TasQ (1 mg/day) increased time-to-progression, but not overall survival. METHODS: TasQ analogs were chemically synthesized and tested for activity compared to the parental compound. These included HDAC4 enzymatic assays, qRT-PCR and western blot analyses of gene and protein expression following treatment, in vitro and in vivo efficacy against multiple prostate cancer models including PDXs, pharmacokinetic analyses,AHR binding and agonist assays, SPR analyses of binding to HDAC4 and NCoR1, RNAseq analysis of in vivo tumors, 3D endothelial sprouting assays, and a targeted kinase screen. Genetic knockout or knockdown controls were used when appropriate. RESULTS: Here, we document that, on this regimen (1 mg/day), TasQ blood levels are 10-fold lower than the optimal concentration (≥2 µM) needed for anticancer activity, suggesting higher daily doses are needed. Unfortunately, we also demonstrate that TasQ is an arylhydrocarbon receptor (AHR) agonist, which binds with an EC50 of 1 µM to produce unwanted off-target side effects. Therefore, we screened a library of TasQ analogsto maximize on-target versus off-target activity. Using this approach, we identified ESATA-20, which has ~10-fold lower AHR agonism and 5-fold greater potency against prostate cancer patient-derived xenografts. CONCLUSION: This increased therapeuticindex nominates ESATA-20 as a lead candidate forclinical development as an orally active third generation quinoline-3-carboxamide analog thatretains its on-target ability to disrupt HDAC4/HIF-1α/MEF-2-dependent adaptive survival signaling in the compromisedtumor microenvironment found in mCRPC.

Liver Fibrosis Scores and Prostate Cancer Risk and Mortality in the Atherosclerosis Risk in Communities Study.

Subclinical liver impairment due to fibrosis could influence the development and detectability of prostate cancer. To investigate the association between liver fibrosis and prostate cancer incidence and mortality, we included 5,284 men (mean age: 57.6 years, 20.1% Black) without cancer or liver disease at Visit 2 in the Atherosclerosis Risk in Communities study. Liver fibrosis was assessed using the aspartate aminotransferase to platelet ratio index, fibrosis 4 index (FIB-4), and nonalcoholic fatty liver disease fibrosis score (NFS). Over 25 years, 215 Black and 511 White men were diagnosed with prostate cancer, and 26 Black and 51 White men died from the disease. We estimated HRs for total and fatal prostate cancer using Cox regression. FIB-4 [quintile 5 vs. 1: HR = 0.47, 95% confidence interval (CI): 0.29-0.77, Ptrend = 0.004] and NFS (HR = 0.56, 95% CI: 0.33-0.97, Ptrend = 0.03) were inversely associated with prostate cancer risk in Black men. Compared with no abnormal score, men with ≥1 abnormal score had a lower prostate cancer risk if they were Black (HR = 0.46, 95% CI: 0.24-0.89), but not White (HR = 1.04, 95% CI: 0.69-1.58). Liver fibrosis scores did not appear to be associated with fatal prostate cancer in Black or White men. Among men without a clinical diagnosis of liver disease, higher liver fibrosis scores were associated with lower incidence of prostate cancer in Black men, but not in White men, and not with fatal prostate cancer in either race. Further research is needed to understand the influence of subclinical liver disease on prostate cancer development versus detectability and the racial differences observed. PREVENTION RELEVANCE: Investigating the link between liver fibrosis and prostate cancer risk and mortality, our study reveals the potential influence of liver health on prostate cancer development and on detection using PSA test, urging further research to understand the differential findings by race and to optimize prevention and intervention strategies.

Bipolar Androgen Therapy Followed by Androgen Receptor Inhibition as Sequential Therapy for Prostate Cancer.

Inhibition of androgen receptor (AR) signaling has been the mainstay of treatment of advanced prostate cancer (PCa) for the past 80 years. Combination and sequential AR-inhibiting therapies are highly effective palliative therapy, but they are not curative. All patients eventually develop resistance to primary castrating therapy [ie, castration-resistant PCa (CRPC)]. At this point, they are treated with subsequent lines of secondary AR inhibitory therapies. However, resistance to these agents also develops and patients progress to a state we have termed complete androgen inhibition-resistant PCa. This phase of the disease is associated with poor prognosis. At this point, treatment shifts to non-hormonal cytotoxic therapies (eg, chemotherapy and radiopharmaceuticals). However, the majority of PCas remain addicted to signaling through AR throughout the course of the disease. Resistant PCa cells adaptively upregulate AR activity, despite castration and AR inhibitors, via mechanisms such as AR overexpression, gene amplification, mutation, and expression of ligand-independent variants to permit sustained liganded and non-liganded AR signaling. Studies dating back nearly 30 years indicate that high expression of AR induced by prolonged castration becomes a vulnerability of CRPC cells in vitro and in mouse xenografts to supraphysiologic androgen (SPA), which induces cell death and growth arrest in this context. Based on these studies, we developed a counterintuitive treatment called bipolar androgen therapy (BAT) for patients with CRPC, in which SPA is administered intermittently to result in cycling of serum testosterone from the polar extremes of supraphysiologic to near-castrate levels. This rapid cycling is intended to disrupt the adaptive of AR regulation associated with chronic exposure to high or low levels of testosterone, while simultaneously targeting the spectrum of AR expression present in heterogeneous CRPC tumors. We have now tested BAT in >250 patients with CRPC. Here we present a review of these clinical studies, which have demonstrated collectively that BAT can be safely given to men with CRPC, improves quality of life, and produces therapeutic responses in ~30% of patients. As expected, resistance to BAT is associated with adaptive downregulation of AR expression. Intriguingly, this downregulation is associated with restoration of sensitivity to subsequent AR inhibitor therapies.

Neoadjuvant enoblituzumab in localized prostate cancer: a single-arm, phase 2 trial.

B7 homolog 3 (B7-H3; CD276), a tumor-associated antigen and possible immune checkpoint, is highly expressed in prostate cancer (PCa) and is associated with early recurrence and metastasis. Enoblituzumab is a humanized, Fc-engineered, B7-H3-targeting antibody that mediates antibody-dependent cellular cytotoxicity. In this phase 2, biomarker-rich neoadjuvant trial, 32 biological males with operable intermediate to high-risk localized PCa were enrolled to evaluate the safety, anti-tumor activity and immunogenicity of enoblituzumab when given before prostatectomy. The coprimary outcomes were safety and undetectable prostate-specific antigen (PSA) level (PSA0) 1 year postprostatectomy, and the aim was to obtain an estimate of PSA0 with reasonable precision. The primary safety endpoint was met with no notable unexpected surgical or medical complications, or surgical delay. Overall, 12% of patients experienced grade 3 adverse events and no grade 4 events occurred. The coprimary endpoint of the PSA0 rate 1 year postprostatectomy was 66% (95% confidence interval 47-81%). The use of B7-H3-targeted immunotherapy in PCa is feasible and generally safe and preliminary data suggest potential clinical activity. The present study validates B7-H3 as a rational target for therapy development in PCa with larger studies planned. The ClinicalTrials.gov identifier is NCT02923180.

The testosterone paradox of advanced prostate cancer: mechanistic insights and clinical implications.

The discovery of the benefits of castration for prostate cancer treatment in 1941 led to androgen deprivation therapy, which remains a mainstay of the treatment of men with advanced prostate cancer. However, as early as this original publication, the inevitable development of castration-resistant prostate cancer was recognized. Resistance first manifests as a sustained rise in the androgen-responsive gene, PSA, consistent with reactivation of the androgen receptor axis. Evaluation of clinical specimens demonstrates that castration-resistant prostate cancer cells remain addicted to androgen signalling and adapt to chronic low-testosterone states. Paradoxically, results of several studies have suggested that treatment with supraphysiological levels of testosterone can retard prostate cancer growth. Insights from these studies have been used to investigate administration of supraphysiological testosterone to patients with prostate cancer for clinical benefits, a strategy that is termed bipolar androgen therapy (BAT). BAT involves rapid cycling from supraphysiological back to near-castration testosterone levels over a 4-week cycle. Understanding how BAT works at the molecular and cellular levels might help to rationalize combining BAT with other agents to achieve increased efficacy and tumour responses.

Androgen receptor activity in prostate cancer dictates efficacy of bipolar androgen therapy through MYC.

Testosterone is the canonical growth factor of prostate cancer but can paradoxically suppress its growth when present at supraphysiological levels. We have previously demonstrated that the cyclical administration of supraphysiological androgen (SPA), termed bipolar androgen therapy (BAT), can result in tumor regression and clinical benefit for patients with castration-resistant prostate cancer. However, predictors and mechanisms of response and resistance have been ill defined. Here, we show that growth inhibition of prostate cancer models by SPA required high androgen receptor (AR) activity and were driven in part by downregulation of MYC. Using matched sequential patient biopsies, we show that high pretreatment AR activity predicted downregulation of MYC, improved clinical response, and prolonged progression-free and overall survival for patients on BAT. BAT induced strong downregulation of AR in all patients, which is shown to be a primary mechanism of acquired resistance to SPA. Acquired resistance was overcome by alternating SPA with the AR inhibitor enzalutamide, which induced adaptive upregulation of AR and resensitized prostate cancer to SPA. This work identifies high AR activity as a predictive biomarker of response to BAT and supports a treatment paradigm for prostate cancer involving alternating between AR inhibition and activation.

Clinical Efficacy of Bipolar Androgen Therapy in Men with Metastatic Castration-Resistant Prostate Cancer and Combined Tumor-Suppressor Loss.

Bipolar androgen therapy (BAT) relies on oscillating levels of serum testosterone as a way to treat patients with metastatic castration-resistant prostate cancer (mCRPC). Aggressive-variant prostate cancers typically require combination chemotherapy and are frequently associated with loss-of-function mutations in tumor suppressor genes. Here we report clinical outcomes after BAT among patients with mCRPC harboring pathogenic alterations in at least two of three genes: TP53, PTEN, and RB1. In this setting, BAT induced a meaningful PSA50 response rate, progression-free survival and overall survival, particularly in patients without prior chemotherapy. Patient summary: Bipolar androgen therapy, in which drugs are used to raise testosterone levels and then allow them to decrease again in a cycle, may be a safe and effective treatment for prostate cancer that is resistant to testosterone suppression and has mutations in tumor suppressor genes. A randomized study comparing this approach to chemotherapy is needed to confirm the findings.

Molecular and Clinical Characterization of Patients With Metastatic Castration Resistant Prostate Cancer Achieving Deep Responses to Bipolar Androgen Therapy.

BACKGROUND: Bipolar androgen therapy (BAT) is an emerging treatment strategy for men with metastatic castration resistant prostate cancer (mCRPC) whereby serum testosterone is cycled from supraphysiologic to near-castrate levels each month. BAT has been shown to induce clinical responses in a significant proportion of patients, some of which are extreme. We explored the clinical and molecular characteristics of patients with mCRPC who achieved deep responses to BAT. METHODS: We conducted a retrospective analysis of patients with mCRPC treated with BAT at Johns Hopkins. We identified 22 of 114 (19%) patients with mCRPC who achieved ≥70% PSA reductions upon treatment with BAT. All patients were treated using 400 mg testosterone cypionate intramuscularly every 28 days, together with continuous LHRH agonist therapy. Clinical-grade DNA sequencing was obtained using commercially available assays. RESULTS: Somatic next-generation sequencing was obtained for 15 of 22 (68%) patients. Of these 15 extreme PSA responders with sequencing data available, All 15 of 15 (100%) harbored a pathogenic mutation in TP53 and/or a homologous recombination DNA repair (HRD) gene. Among the subset of patients with measureable disease (N = 15), 10 patients (67%) achieved an objective response including one patient with a complete response. The median radiographic progression-free survival of these deep PSA responders was 11.3 months (95% CI, 7.9-25.0 months). CONCLUSIONS: We observed an enrichment of TP53 and HRD mutations in mCRPC patients with extreme PSA responses to BAT, with durability lasting about a year. These data support the hypothesis that BAT may most benefit patients with DNA repair-deficient mCRPC. Further studies of BAT in biomarker-selected mCRPC populations (ie, TP53/HRD-mutated) are warranted.

Mipsagargin: The Beginning-Not the End-of Thapsigargin Prodrug-Based Cancer Therapeutics.

Søren Brøgger Christensen isolated and characterized the cell-penetrant sesquiterpene lactone Thapsigargin (TG) from the fruit Thapsia garganica. In the late 1980s/early 1990s, TG was supplied to multiple independent and collaborative groups. Using this TG, studies documented with a large variety of mammalian cell types that TG rapidly (i.e., within seconds to a minute) penetrates cells, resulting in an essentially irreversible binding and inhibiting (IC50~10 nM) of SERCA 2b calcium uptake pumps. If exposure to 50-100 nM TG is sustained for >24-48 h, prostate cancer cells undergo apoptotic death. TG-induced death requires changes in the cytoplasmic Ca2+, initiating a calmodulin/calcineurin/calpain-dependent signaling cascade that involves BAD-dependent opening of the mitochondrial permeability transition pore (MPTP); this releases cytochrome C into the cytoplasm, activating caspases and nucleases. Chemically unmodified TG has no therapeutic index and is poorly water soluble. A TG analog, in which the 8-acyl groups is replaced with the 12-aminododecanoyl group, afforded 12-ADT, retaining an EC50 for killing of <100 nM. Conjugation of 12-ADT to a series of 5-8 amino acid peptides was engineered so that they are efficiently hydrolyzed by only one of a series of proteases [e.g., KLK3 (also known as Prostate Specific Antigen); KLK2 (also known as hK2); Fibroblast Activation Protein Protease (FAP); or Folh1 (also known as Prostate Specific Membrane Antigen)]. The obtained conjugates have increased water solubility for systemic delivery in the blood and prevent cell penetrance and, thus, killing until the TG-prodrug is hydrolyzed by the targeting protease in the vicinity of the cancer cells. We summarize the preclinical validation of each of these TG-prodrugs with special attention to the PSMA TG-prodrug, Mipsagargin, which is in phase II clinical testing.

Supraphysiologic Testosterone Induces Ferroptosis and Activates Immune Pathways through Nucleophagy in Prostate Cancer.

The discovery that androgens play an important role in the progression of prostate cancer led to the development of androgen deprivation therapy (ADT) as a first line of treatment. However, paradoxical growth inhibition has been observed in a subset of prostate cancer upon administration of supraphysiologic levels of testosterone (SupraT), both experimentally and clinically. Here we report that SupraT activates cytoplasmic nucleic acid sensors and induces growth inhibition of SupraT-sensitive prostate cancer cells. This was initiated by the induction of two parallel autophagy-mediated processes, namely, ferritinophagy and nucleophagy. Consequently, autophagosomal DNA activated nucleic acid sensors converge on NFκB to drive immune signaling pathways. Chemokines and cytokines secreted by the tumor cells in response to SupraT resulted in increased migration of cytotoxic immune cells to tumor beds in xenograft models and patient tumors. Collectively, these findings indicate that SupraT may inhibit a subset of prostate cancer by activating nucleic acid sensors and downstream immune signaling. SIGNIFICANCE: This study demonstrates that supraphysiologic testosterone induces two parallel autophagy-mediated processes, ferritinophagy and nucleophagy, which then activate nucleic acid sensors to drive immune signaling pathways in prostate cancer.

Targeting the spectrum of immune checkpoints in prostate cancer.

Introduction: The proven efficacy of the cellular vaccine sipuleucel-T in 2010 led to optimism about immunotherapeutic approaches for the treatment of prostate cancer. Some surmised that prostate cancer might be an ideal target for immune-mediated killing given that the prostate is not an essential organ and expresses unique proteins including prostate-specific antigen, prostate-specific membrane antigen, and prostatic acid phosphatase that could be targeted without side effects. Subsequently, antibodies that inhibit the T cell checkpoints PD1 and CTLA4 were shown to stimulate antitumor immune responses, leading to tumor regression in several cancer types. These therapies have since been tested in several studies as treatments for prostate cancer, but appear to have limited efficacy in molecularly unselected patients.Areas covered: In this review, we discuss these studies and evaluate features of prostate cancer and its host environment that may render it generally resistant to CTLA4 and PD1 blockade. We provide an overview of alternate immune checkpoints that may hold greater significance in this disease.Expert opinion: Combination therapies to target multiple layers of alternate immune checkpoints may be required for an effective immune response to prostate cancer. We discuss combination therapies currently being investigated.