Characterization of HOXB13 expression patterns in localized and metastatic castration-resistant prostate cancer.

HOXB13 is a key lineage homeobox transcription factor that plays a critical role in the differentiation of the prostate gland. Several studies have suggested that HOXB13 alterations may be involved in prostate cancer development and progression. Despite its potential biological relevance, little is known about the expression of HOXB13 across the disease spectrum of prostate cancer. To this end, we validated a HOXB13 antibody using genetic controls and investigated HOXB13 protein expression in murine and human developing prostates, localized prostate cancers, and metastatic castration-resistant prostate cancers. We observed that HOXB13 expression increases during later stages of murine prostate development. All localized prostate cancers showed HOXB13 protein expression. Interestingly, lower HOXB13 expression levels were observed in higher-grade tumors, although no significant association between HOXB13 expression and recurrence or disease-specific survival was found. In advanced metastatic prostate cancers, HOXB13 expression was retained in the majority of tumors. While we observed lower levels of HOXB13 protein and mRNA levels in tumors with evidence of lineage plasticity, 84% of androgen receptor-negative castration-resistant prostate cancers and neuroendocrine prostate cancers (NEPCs) retained detectable levels of HOXB13. Notably, the reduced expression observed in NEPCs was associated with a gain of HOXB13 gene body CpG methylation. In comparison to the commonly used prostate lineage marker NKX3.1, HOXB13 showed greater sensitivity in detecting advanced metastatic prostate cancers. Additionally, in a cohort of 837 patients, 383 with prostatic and 454 with non-prostatic tumors, we found that HOXB13 immunohistochemistry had a 97% sensitivity and 99% specificity for prostatic origin. Taken together, our studies provide valuable insight into the expression pattern of HOXB13 during prostate development and cancer progression. Furthermore, our findings support the utility of HOXB13 as a diagnostic biomarker for prostate cancer, particularly to confirm the prostatic origin of advanced metastatic castration-resistant tumors. © 2023 The Pathological Society of Great Britain and Ireland.

Metastatic Penile Squamous Cell Carcinoma Responsive to Enfortumab Vedotin.

Penile squamous cell carcinoma is a rare disease with very limited data to guide treatment decisions. In particular, there is minimal evidence for effective therapies in the metastatic setting. Here, we present a case of metastatic penile squamous cell carcinoma with response to the Nectin-4 inhibitor enfortumab-vedotin-ejfv (EV). EV was selected due to the evidence of the high expression of Nectin-4 in squamous cell carcinomas, including penile carcinoma. The patient had both radiographic and symptomatic improvement after two cycles of treatment, despite having been treated with multiple prior lines of traditional chemotherapy. This case provides support for the use of antibody-drug conjugates (ADC), including EV, in this disease with few other options in the advanced setting. Further studies examining Nectin-4 and ADCs in penile squamous cell carcinoma should be completed, as high-quality evidence is needed to guide treatment after initial progression for these patients.

TrkA overexpression in non-tumorigenic human breast cell lines confers oncogenic and metastatic properties.

BACKGROUND/PURPOSE: TrkA overexpression occurs in over 20% of breast cancers, including triple-negative breast cancers (TNBC), and has recently been recognized as a potential driver of carcinogenesis. Recent clinical trials of pan-Trk inhibitors have demonstrated targeted activity against tumors harboring NTRK fusions, a relatively rare alteration across human cancers. Despite this success, current clinical trials have not investigated TrkA overexpression as an additional therapeutic target for pan-Trk inhibitors. Here, we evaluate the cancerous phenotypes of TrkA overexpression relative to NTRK1 fusions in human cells and assess response to pharmacologic Trk inhibition. EXPERIMENTAL DESIGN/METHODS: To evaluate the clinical utility of TrkA overexpression, a panel of TrkA overexpressing cells were developed via stable transfection of an NTRK1 vector into the non-tumorigenic breast cell lines, MCF10A and hTERT-IMEC. A panel of positive controls was generated via stable transfection with a CD74-NTRK1 fusion vector into MCF10A cells. Cells were assessed via various in vitro and in vivo analyses to determine the transformative potential and targetability of TrkA overexpression. RESULTS: TrkA overexpressing cells demonstrated transformative phenotypes similar to Trk fusions, indicating increased oncogenic potential. TrkA overexpressing cells demonstrated growth factor-independent proliferation, increased PI3Kinase and MAPKinase pathway activation, anchorage-independent growth, and increased migratory capacity. These phenotypes were abrogated by the addition of the pan-Trk inhibitor, larotrectinib. In vivo analysis demonstrated increased tumorgenicity and metastatic potential of TrkA overexpressing breast cancer cells. CONCLUSIONS: Herein, we demonstrate TrkA overexpressing cells show increased tumorgenicity and are sensitive to pan-Trk inhibitors. These data suggest that TrkA overexpression may be an additional target for pan-Trk inhibitors and provide a targeted therapy for breast cancer patients.

Undetectable Tumor Cell-Free DNA in a Patient With Metastatic Breast Cancer With Complete Response and Long-Term Remission.

The ability to serially monitor tumor-derived cell-free DNA (cfDNA) brings with it the potential to measure response to anticancer therapies and detect minimal residual disease (MRD). This report describes a patient with HER2-positive metastatic breast cancer with an exceptional response to trastuzumab and nab-paclitaxel who remains in complete remission several years after cessation of therapy. Next-generation sequencing of the patient's primary tumor tissue showed several mutations, including an oncogenic hotspot PIK3CA mutation. A sample of cfDNA was collected 6 years after her last therapy and then analyzed for mutant PIK3CA using digital PCR. No detectable mutations associated with the primary tumor were found despite assaying >10,000 genome equivalents, suggesting that the patient had achieved a molecular remission. Results of this case study suggest that serial monitoring of MRD using liquid biopsies could provide a useful method for individualizing treatment plans for patients with metastatic disease with extreme responses to therapy. However, large-scale clinical studies are needed to validate and implement these techniques for patient care.

NDRG1 links p53 with proliferation-mediated centrosome homeostasis and genome stability.

The tumor protein 53 (TP53) tumor suppressor gene is the most frequently somatically altered gene in human cancers. Here we show expression of N-Myc down-regulated gene 1 (NDRG1) is induced by p53 during physiologic low proliferative states, and mediates centrosome homeostasis, thus maintaining genome stability. When placed in physiologic low-proliferating conditions, human TP53 null cells fail to increase expression of NDRG1 compared with isogenic wild-type controls and TP53 R248W knockin cells. Overexpression and RNA interference studies demonstrate that NDRG1 regulates centrosome number and amplification. Mechanistically, NDRG1 physically associates with γ-tubulin, a key component of the centrosome, with reduced association in p53 null cells. Strikingly, TP53 homozygous loss was mutually exclusive of NDRG1 overexpression in over 96% of human cancers, supporting the broad applicability of these results. Our study elucidates a mechanism of how TP53 loss leads to abnormal centrosome numbers and genomic instability mediated by NDRG1.

PIK3CA mutations and TP53 alterations cooperate to increase cancerous phenotypes and tumor heterogeneity.

BACKGROUND/PURPOSE: The combined contributions of oncogenes and tumor suppressor genes toward carcinogenesis remain poorly understood. Elucidation of cancer gene cooperativity can provide new insights leading to more effective use of therapies. EXPERIMENTAL DESIGN/METHODS: We used somatic cell genome editing to introduce singly and in combination PIK3CA mutations (E545K or H1047R) with TP53 alterations (R248W or knockout), to assess any enhanced cancerous phenotypes. The non-tumorigenic human breast epithelial cell line, MCF10A, was used as the parental cell line, and resultant cells were assessed via various in vitro assays, growth as xenografts, and drug sensitivity assays using targeted agents and chemotherapies. RESULTS: Compared to single-gene-targeted cells and parental controls, cells with both a PIK3CA mutation and TP53 alteration had increased cancerous phenotypes including cell proliferation, soft agar colony formation, aberrant morphology in acinar formation assays, and genomic heterogeneity. Cells also displayed varying sensitivities to anti-neoplastic drugs, although all cells with PIK3CA mutations showed a relative increased sensitivity to paclitaxel. All cell lines remained non-tumorigenic. CONCLUSIONS: This cell line panel provides a resource for further elucidating cooperative genetic mediators of carcinogenesis and response to therapies.

MACROD2 overexpression mediates estrogen independent growth and tamoxifen resistance in breast cancers.

Tamoxifen is effective for treating estrogen receptor-alpha (ER) positive breast cancers. However, few molecular mediators of tamoxifen resistance have been elucidated. Here we describe a previously unidentified gene, MACROD2 that confers tamoxifen resistance and estrogen independent growth. We found MACROD2 is amplified and overexpressed in metastatic tamoxifen-resistant tumors. Transgene overexpression of MACROD2 in breast cancer cell lines results in tamoxifen resistance, whereas RNAi-mediated gene knock down reverses this phenotype. MACROD2 overexpression also leads to estrogen independent growth in xenograft assays. Mechanistically, MACROD2 increases p300 binding to estrogen response elements in a subset of ER regulated genes. Primary breast cancers and matched metastases demonstrate MACROD2 expression can change with disease evolution, and increased expression and amplification of MACROD2 in primary tumors is associated with worse overall survival. These studies establish MACROD2 as a key mediator of estrogen independent growth and tamoxifen resistance, as well as a potential novel target for diagnostics and therapy.

A human prostatic bacterial isolate alters the prostatic microenvironment and accelerates prostate cancer progression.

Inflammation is associated with several diseases of the prostate including benign enlargement and cancer, but a causal relationship has not been established. Our objective was to characterize the prostate inflammatory microenvironment after infection with a human prostate-derived bacterial strain and to determine the effect of inflammation on prostate cancer progression. To this end, we mimicked typical human prostate infection with retrograde urethral instillation of CP1, a human prostatic isolate of Escherichia coli. CP1 bacteria were tropic for the accessory sex glands and induced acute inflammation in the prostate and seminal vesicles, with chronic inflammation lasting at least 1 year. Compared to controls, infection induced both acute and chronic inflammation with epithelial hyperplasia, stromal hyperplasia, and inflammatory cell infiltrates. In areas of inflammation, epithelial proliferation and hyperplasia often persist, despite decreased expression of androgen receptor (AR). Inflammatory cells in the prostates of CP1-infected mice were characterized at 8 weeks post-infection by flow cytometry, which showed an increase in macrophages and lymphocytes, particularly Th17 cells. Inflammation was additionally assessed in the context of carcinogenesis. Multiplex cytokine profiles of inflamed prostates showed that distinct inflammatory cytokines were expressed during prostate inflammation and cancer, with a subset of cytokines synergistically increased during concurrent inflammation and cancer. Furthermore, CP1 infection in the Hi-Myc mouse model of prostate cancer accelerated the development of invasive prostate adenocarcinoma, with 70% more mice developing cancer by 4.5 months of age. This study provides direct evidence that prostate inflammation accelerates prostate cancer progression and gives insight into the microenvironment changes induced by inflammation that may accelerate tumour initiation or progression.

Secreted protein, acidic and rich in cysteine-like 1 (SPARCL1) is down regulated in aggressive prostate cancers and is prognostic for poor clinical outcome.

Prostate cancer is the second leading cause of cancer death among United States men. However, disease aggressiveness is varied, with low-grade disease often being indolent and high-grade cancer accounting for the greatest density of deaths. Outcomes are also disparate among men with high-grade prostate cancer, with upwards of 65% having disease recurrence even after primary treatment. Identification of men at risk for recurrence and elucidation of the molecular processes that drive their disease is paramount, as these men are the most likely to benefit from multimodal therapy. We previously showed that androgen-induced expression profiles in prostate development are reactivated in aggressive prostate cancers. Herein, we report the down-regulation of one such gene, Sparcl1, a secreted protein, acidic and rich in cysteine (SPARC) family matricellular protein, during invasive phases of prostate development and regeneration. We further demonstrate a parallel process in prostate cancer, with decreased expression of SPARCL1 in high-grade/metastatic prostate cancer. Mechanistically, we demonstrate that SPARCL1 loss increases the migratory and invasive properties of prostate cancer cells through Ras homolog gene family, member C (RHOC), a known mediator of metastatic progression. By using models incorporating clinicopathologic parameters to predict prostate cancer recurrence after treatment, we show that SPARCL1 loss is a significant, independent prognostic marker of disease progression. Thus, SPARCL1 is a potent regulator of cell migration/invasion and its loss is independently associated with prostate cancer recurrence.

An in vitro CRISPR screen of cell-free DNA identifies apoptosis as the primary mediator of cell-free DNA release.

ABTRACT: Clinical circulating cell-free DNA (cfDNA) testing is now routine, however test accuracy remains limited. By understanding the life-cycle of cfDNA, we might identify opportunities to increase test performance. Here, we profile cfDNA release across a 24-cell line panel and utilize a cell-free CRISPR screen (cfCRISPR) to identify mediators of cfDNA release. Our panel outlines two distinct groups of cell lines: one which releases cfDNA fragmented similarly to clinical samples and purported as characteristic of apoptosis, and another which releases larger fragments associated with vesicular or necrotic DNA. Our cfCRISPR screens reveal that genes mediating cfDNA release are primarily involved with apoptosis, but also identify other subsets of genes such as RNA binding proteins as potential regulators of cfDNA release. We observe that both groups of cells lines identified primarily produce cfDNA through apoptosis. These results establish the utility of cfCRISPR, genetically validate apoptosis as a major mediator of DNA release in vitro, and implicate ways to improve cfDNA assays.

Wnt signaling though beta-catenin is required for prostate lineage specification.

Androgens initiate a complex network of signals within the UGS that trigger prostate lineage commitment and bud formation. Given its contributions to organogenesis in other systems, we investigated a role for canonical Wnt signaling in prostate development. We developed a new method to achieve complete deletion of beta-catenin, the transcriptional coactivator required for canonical Wnt signaling, in early prostate development. Beta-catenin deletion abrogated canonical Wnt signaling and yielded prostate rudiments that exhibited dramatically decreased budding and failed to adopt prostatic identity. This requirement for canonical Wnt signaling was limited to a brief critical period during the initial molecular phase of prostate identity specification. Deletion of beta-catenin in the adult prostate did not significantly affect organ homeostasis. Collectively, these data establish that beta-catenin and Wnt signaling play key roles in prostate lineage specification and bud outgrowth.

Activation of Dendritic Cells Isolated from the Blood of Patients with Prostate Cancer by Ex Vivo Fluid Shear Stress Stimulation.

Prostate cancer is one of the most common cancers among men in the United States and a leading cause of cancer-related death in men. Treatment options for patients with advanced prostate cancer include hormone therapies, chemotherapies, radioligand therapies, and immunotherapies. Provenge (sipuleucel-T) is an autologous cancer-vaccine-based immunotherapy approved for men with asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). Administration of sipuleucel-T involves leukapheresis of patient blood to isolate antigen-presenting cells (APCs), including dendritic cells (DCs), and subsequent incubation of isolated APCs with both an antigen, prostatic acid phosphatase (PAP), and granulocyte macrophage-colony stimulating factor (GM-CSF) before their infusion back into the patient. Although sipuleucel-T has been shown to improve overall survival, other meaningful outcomes, such as prostate-specific antigen (PSA) levels and radiographic response, are inconsistent. This lack of robust response may be due to limited ex vivo activation of DCs using current protocols. Earlier studies have shown that many cell types can be activated ex vivo by external forces such as fluid shear stress (FSS). We hypothesize that novel fluid shear stress technologies and methods can be used to improve ex vivo efficacy of prostate cancer DC activation in prostate cancer. Herein, we report a new protocol for activating DCs from patients with prostate cancer using ex vivo fluid shear stress. Ultimately, the goal of these studies is to improve DC activation to expand the efficacy of therapies such as sipuleucel-T. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Sample collection and DC isolation Basic Protocol 2: Determination and application of fluid shear stress Basic Protocol 3: Flow cytometry analysis of DCs after FSS stimulation.

NOTCH1 PEST domain variants are responsive to standard of care treatments despite distinct transformative properties in a breast cancer model.

Activating variants in the PEST region of NOTCH1 have been associated with aggressive phenotypes in human cancers, including triple-negative breast cancer (TNBC). Previous studies suggested that PEST domain variants in TNBC patients resulted in increased cell proliferation, invasiveness, and decreased overall survival. In this study, we assess the phenotypic transformation of activating NOTCH1 variants and their response to standard of care therapies. AAV-mediated gene targeting was used to isogenically incorporate 3 NOTCH1 variants, including a novel TNBC frameshift variant, in two non-tumorigenic breast epithelial cell lines, MCF10A and hTERT-IMEC. Two different variants at the NOTCH1 A2241 site (A2441fs and A2441T) both demonstrated increased transformative properties when compared to a non-transformative PEST domain variant (S2523L). These phenotypic changes include proliferation, migration, anchorage-independent growth, and MAPK pathway activation. In contrast to previous studies, activating NOTCH1 variants did not display sensitivity to a gamma secretase inhibitor (GSI) or resistance to chemotherapies. This study demonstrates distinct transformative phenotypes are specific to a given variant within NOTCH1 and these phenotypes do not correlate with sensitivities or resistance to chemotherapies or GSIs. Although previous studies have suggested NOTCH1 variants may be prognostic for TNBC, our study does not demonstrate prognostic ability of these variants and suggests further characterization would be required for clinical applications.

Single cell analysis of cribriform prostate cancer reveals cell intrinsic and tumor microenvironmental pathways of aggressive disease.

Cribriform prostate cancer, found in both invasive cribriform carcinoma (ICC) and intraductal carcinoma (IDC), is an aggressive histological subtype that is associated with progression to lethal disease. To delineate the molecular and cellular underpinnings of ICC/IDC aggressiveness, this study examines paired ICC/IDC and benign prostate surgical samples by single-cell RNA-sequencing, TCR sequencing, and histology. ICC/IDC cancer cells express genes associated with metastasis and targets with potential for therapeutic intervention. Pathway analyses and ligand/receptor status model cellular interactions among ICC/IDC and the tumor microenvironment (TME) including JAG1/NOTCH. The ICC/IDC TME is hallmarked by increased angiogenesis and immunosuppressive fibroblasts (CTHRC1+ASPN+FAP+ENG+) along with fewer T cells, elevated T cell dysfunction, and increased C1QB+TREM2+APOE+-M2 macrophages. These findings support that cancer cell intrinsic pathways and a complex immunosuppressive TME contribute to the aggressive phenotype of ICC/IDC. These data highlight potential therapeutic opportunities to restore immune signaling in patients with ICC/IDC that may afford better outcomes.

Molecular effects of genistein on male urethral development.

PURPOSE: The increasing incidence of hypospadias is partly attributed to increased gestational exposure to endocrine disruptors. We investigated the effects of genistein, the primary phytoestrogen in soy, on the molecular program of male urethral development. MATERIALS AND METHODS: Female mice were fed diets supplemented with genistein (500 mg/kg diet) or control diets before breeding and throughout gestation. Urethras from embryonic day 17.5 male fetuses were harvested, and RNA was prepared, amplified, labeled and hybridized on whole genome microarrays. Data were analyzed using packages from the R/Bioconductor project. Immunohistochemical analysis and immunoblotting were used to confirm the activity of MAPK and the presence of Ntrk1 and Ntrk2 during urethral development. RESULTS: Gestational exposure to genistein altered the urethral expression of 277 genes (p <0.008). Among the most affected were hormonally regulated genes, including IGFBP-1, Kap and Rhox5. Differentially expressed genes were grouped into functional pathways of cell proliferation, adhesion, apoptosis and tube morphogenesis (p <0.0001), and were enriched for members of the MAPK (p <0.00001) and TGF-ß (p <0.01) signaling cascades. Differentially expressed genes preferentially contained ELK1, Myc/Max, FOXO, HOX and ER control elements. The MAPK pathway was active, and its upstream genistein affected tyrosine kinase receptors Ntrk1 and Ntrk2 were present in the developing male urethra. CONCLUSIONS: Gestational exposure to genistein contributes to hypospadias by altering pathways of tissue morphogenesis, cell proliferation and cell survival. In particular, genes in the MAPK and TGF-ß signaling pathways and those controlled by FOXO, HOX and ER transcription factors are disrupted.

Dimeric naphthoquinones, a novel class of compounds with prostate cancer cytotoxicity.

OBJECTIVES: • To evaluate the cytotoxicity of dimeric naphthoquinones (BiQs) in prostate cancer cells. • To assess the interaction of dimeric naphthoquinones with common therapies including radiation and docetaxel. MATERIALS AND METHODS: • The cytotoxicity of 12 different dimeric naphthoquinones was assessed in androgen-independent (PC-3, DU-145) and androgen-responsive (LNCaP, 22RV1) prostate cancer cell lines and in prostate epithelial cells (PrECs). • BiQ2 and BiQ11 were selected for determination of dose response, effects on colony formation and initial exploration into mechanism of action. • Synergistic effects with radiation and docetaxel were explored using colony-forming and MTT assays. RESULTS: • At concentrations of 15µM, BiQ2, BiQ3, BiQ11, BiQ12, and BiQ15 demonstrated cytotoxicity in all prostate cancer cell lines. • Treatment with BiQs limited the ability of prostate cancer cells to form colonies in clonogenic assays. • Exposure of prostate cancer to BiQs increased cellular reactive oxygen species (ROS), decreased ATP production, and promoted apoptosis. • BiQ cytotoxicity was independent of NADP(H):quinone oxidoreductase 1 (NQO1) activity in PrECs, PC-3 and 22RV1, but not DU-145 cells. • Exposure of prostate cancer cells to radiation before treatment with BiQs increased their activity allowing for inhibitory effects well below the IC(50) s of these compounds in PrECs. • Co-administration of BiQs with docetaxel had minimal additive effects. CONCLUSIONS: • Dimeric naphthoquinones represent a new class of compounds with prostate cancer cytotoxicity and synergistic effects with radiation. The cytotoxic effect of these agents is probably contributed to by the accumulation of ROS and mitochondrial dysfunction. • Further studies are warranted to better characterize this class of potential chemo-therapeutics.

Cribriform Prostate Cancer: Clinical Pathologic and Molecular Considerations.

Intraductal cribriform (IDC) and invasive cribriform morphologies are associated with worse prostate cancer outcomes. Limited retrospective studies have associated IDC and cribriform morphology with germline mutations in DNA repair genes, particularly BRCA2. These findings, which prompted the National Comprehensive Cancer Network (NCCN) Guidelines for Prostate Cancer and Genetic/Familial High- Risk Assessment to consider germline testing for individuals with IDC/cribriform histology, have been questioned in a recent prospective study. A deepened understanding of the molecular mechanisms driving disease aggressiveness in cribriform morphology is critical to provide more clarity in clinical decision making. This review summarizes the current understanding of IDC and cribriform prostate cancer, with an emphasis on clinical outcomes and molecular alterations.

A distinct repertoire of cancer-associated fibroblasts is enriched in cribriform prostate cancer.

Outcomes for men with localized prostate cancer vary widely, with some men effectively managed without treatment on active surveillance, while other men rapidly progress to metastatic disease despite curative-intent therapies. One of the strongest prognostic indicators of outcome is grade groups based on the Gleason grading system. Gleason grade 4 prostate cancer with cribriform morphology is associated with adverse outcomes and can be utilized clinically to improve risk stratification. The underpinnings of disease aggressiveness associated with cribriform architecture are not fully understood. Most studies have focused on genetic and molecular alterations in cribriform tumor cells; however, less is known about the tumor microenvironment in cribriform prostate cancer. Cancer-associated fibroblasts (CAFs) are a heterogeneous population of fibroblasts in the tumor microenvironment that impact cancer aggressiveness. The overall goal of this study was to determine if cribriform prostate cancers are associated with a unique repertoire of CAFs. Radical prostatectomy whole-tissue sections were analyzed for the expression of fibroblast markers (ASPN in combination with FAP, THY1, ENG, NT5E, TNC, and PDGFRß) in stroma adjacent to benign glands and in Gleason grade 3, Gleason grade 4 cribriform, and Gleason grade 4 noncribriform prostate cancer by RNAscope®. Halo® Software was used to quantify percent positive stromal cells and expression per positive cell. The fibroblast subtypes enriched in prostate cancer were highly heterogeneous. Both overlapping and distinct populations of low abundant fibroblast subtypes in benign prostate stroma were enriched in Gleason grade 4 prostate cancer with cribriform morphology compared to Gleason grade 4 prostate cancer with noncribriform morphology and Gleason grade 3 prostate cancer. In addition, gene expression was distinctly altered in CAF subtypes adjacent to cribriform prostate cancer. Overall, these studies suggest that cribriform prostate cancer has a unique tumor microenvironment that may distinguish it from other Gleason grade 4 morphologies and lower Gleason grades.

Castration-mediated IL-8 promotes myeloid infiltration and prostate cancer progression.

Unlike several other tumor types, prostate cancer rarely responds to immune checkpoint blockade (ICB). To define tumor cell intrinsic factors that contribute to prostate cancer progression and resistance to ICB, we analyzed prostate cancer epithelial cells from castration-sensitive and -resistant samples using implanted tumors, cell lines, transgenic models and human tissue. We found that castration resulted in increased expression of interleukin-8 (IL-8) and its probable murine homolog Cxcl15 in prostate epithelial cells. We showed that these chemokines drove subsequent intratumoral infiltration of tumor-promoting polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs), which was largely abrogated when IL-8 signaling was blocked genetically or pharmacologically. Targeting IL-8 signaling in combination with ICB delayed the onset of castration resistance and increased the density of polyfunctional CD8 T cells in tumors. Our findings establish a novel mechanism by which castration mediates IL-8 secretion and subsequent PMN-MDSC infiltration, and highlight blockade of the IL-8/CXCR2 axis as a potential therapeutic intervention.