EZH2 inhibition activates a dsRNA-STING-interferon stress axis that potentiates response to PD-1 checkpoint blockade in prostate cancer

Prostate cancers are considered to be immunologically 'cold' tumors given the very few patients who respond to checkpoint inhibitor (CPI) therapy. Recently, enrichment of interferon-stimulated genes (ISGs) predicted a favorable response to CPI across various disease sites. The enhancer of zeste homolog-2 (EZH2) is overexpressed in prostate cancer and known to negatively regulate ISGs. In the present study, we demonstrate that EZH2 inhibition in prostate cancer models activates a double-stranded RNA-STING-ISG stress response upregulating genes involved in antigen presentation, Th1 chemokine signaling and interferon response, including programmed cell death protein 1 (PD-L1) that is dependent on STING activation. EZH2 inhibition substantially increased intratumoral trafficking of activated CD8+ T cells and increased M1 tumor-associated macrophages, overall reversing resistance to PD-1 CPI. Our study identifies EZH2 as a potent inhibitor of antitumor immunity and responsiveness to CPI. These data suggest EZH2 inhibition as a therapeutic direction to enhance prostate cancer response to PD-1 CPI.

Nascent Prostate Cancer Heterogeneity Drives Evolution and Resistance to Intense Hormonal Therapy

BACKGROUND

Patients diagnosed with high risk localized prostate cancer have variable outcomes following surgery. Trials of intense neoadjuvant androgen deprivation therapy (NADT) have shown lower rates of recurrence among patients with minimal residual disease after treatment. The molecular features that distinguish exceptional responders from poor responders are not known.

OBJECTIVE

To identify genomic and histologic features associated with treatment resistance at baseline.

DESIGN, SETTING, AND PARTICIPANTS

Targeted biopsies were obtained from 37 men with intermediate- to high-risk prostate cancer before receiving 6 mo of ADT plus enzalutamide. Biopsy tissues were used for whole-exome sequencing and immunohistochemistry (IHC).

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

We assessed the relationship of molecular features with final pathologic response using a cutpoint of 0.05 cm3 for residual cancer burden to compare exceptional responders to incomplete and nonresponders. We assessed intratumoral heterogeneity at the tissue and genomic level, and compared the volume of residual disease to the Shannon diversity index for each tumor. We generated multivariate models of resistance based on three molecular features and one histologic feature, with and without multiparametric magnetic resonance imaging estimates of baseline tumor volume.

RESULTS AND LIMITATIONS

Loss of chromosome 10q (containing PTEN) and alterations to TP53 were predictive of poor response, as were the expression of nuclear ERG on IHC and the presence of intraductal carcinoma of the prostate. Patients with incompletely and nonresponding tumors harbored greater tumor diversity as estimated via phylogenetic tree reconstruction from DNA sequencing and analysis of IHC staining. Our four-factor binary model (area under the receiver operating characteristic curve [AUC] 0.89) to predict poor response correlated with greater diversity in our cohort and a validation cohort of 57 Gleason score 8-10 prostate cancers from The Cancer Genome Atlas. When baseline tumor volume was added to the model, it distinguished poor response to NADT with an AUC of 0.98. Prospective use of this model requires further retrospective validation with biopsies from additional trials.

CONCLUSIONS

A subset of prostate cancers exhibit greater histologic and genomic diversity at the time of diagnosis, and these localized tumors have greater fitness to resist therapy.

PATIENT SUMMARY

Some prostate cancer tumors do not respond well to a hormonal treatment called androgen deprivation therapy (ADT). We used tumor volume and four other parameters to develop a model to identify tumors that will not respond well to ADT. Treatments other than ADT should be considered for these patients.

Low Abundance of Circulating Tumor DNA in Localized Prostate Cancer

PURPOSE

Despite decreased screening-based detection of clinically insignificant tumors, most diagnosed prostate cancers are still indolent, indicating a need for better strategies for detection of clinically significant disease before treatment. We hypothesized that patients with detectable circulating tumor DNA (ctDNA) were more likely to harbor aggressive disease.

METHODS

We applied ultra-low-pass whole-genome sequencing to profile cell-free DNA from 112 patients diagnosed with localized prostate cancer and performed targeted resequencing of plasma DNA for somatic mutations previously identified in matched solid tumor in nine cases. We also performed similar analyses of data from patients with metastatic prostate cancer.

RESULTS

In all cases of localized prostate cancer, even in clinically high-risk patients who subsequently had recurrent disease, ultra-low-pass whole-genome sequencing and targeted resequencing did not detect ctDNA in plasma acquired before surgery or before recurrence. In contrast, using both approaches, ctDNA was detected in patients with metastatic prostate cancer.

CONCLUSION

Our findings demonstrate clear differences between localized and advanced prostate cancer with respect to the dissemination and detectability of ctDNA. Because allele-specific alterations in ctDNA are below the threshold for detection in localized prostate cancer, other approaches to identify cell-free nucleic acids of tumor origin may demonstrate better specificity for aggressive disease.

A case report of multiple primary prostate tumors with differential drug sensitivity

Localized prostate cancers are genetically variable and frequently multifocal, comprising spatially distinct regions with multiple independently-evolving clones. To date there is no understanding of whether this variability can influence management decisions for patients with prostate tumors. Here, we present a single case from a clinical trial of neoadjuvant intense androgen deprivation therapy. A patient was diagnosed with a large semi-contiguous tumor by imaging, histologically composed of a large Gleason score 9 tumor with an adjacent Gleason score 7 nodule. DNA sequencing demonstrates these are two independent tumors, as only the Gleason 9 tumor harbors single-copy losses of PTEN and TP53. The PTEN/TP53-deficient tumor demonstrates treatment resistance, selecting for subclones with mutations to the remaining copies of PTEN and TP53, while the Gleason 7 PTEN-intact tumor is almost entirely ablated. These findings indicate that spatiogenetic variability is a major confounder for personalized treatment of patients with prostate cancer.

Oligomerization of p53 Precedes its Association with Dynein and Nuclear Accumulation

Previous studies have identified several proteins that associate with microtubules and the dynein motor complex including p53, the glucocorticoid and the vitamin D receptors, and the APC (adenomatous polyposis coli) protein; but neither the residues important for this interaction nor the physical state of the proteins involved have been clarified. We observed in SN12C cells harboring a mutant p53 truncated at amino acid 336, impaired nuclear localization and impaired association with dynein. This finding was confirmed and extended by examining a series of truncated p53 proteins that identified residues 336 to 348 as crucial for association with dynein and nuclear transport. Point mutations identified the importance of residues involved in p53 oligomerization in this process, establishing a p53 oligomer as the cargo for dynein transport. The association of cytosolic p53 oligomers with dynein occurs independent of microtubules indicating that following this association, the p53/dynein complex then associates with microtubules and is transported to the peri-nuclear region. These studies suggest that mutations or modifications that affect p53 oligomerization not only interfere with DNA binding but also with its intracellular distribution. They also highlight the importance of an intact microtubule network in the trafficking of crucial cellular proteins.

MEIS1 down-regulation by MYC mediates prostate cancer development through elevated HOXB13 expression and AR activity

Localized prostate cancer develops very slowly in most men, with the androgen receptor (AR) and MYC transcription factors amongst the most well-characterized drivers of prostate tumorigenesis. Canonically, MYC up-regulation in luminal prostate cancer cells functions to oppose the terminally differentiating effects of AR. However, the effects of MYC up-regulation are pleiotropic and inconsistent with a poorly proliferative phenotype. Here we show that increased MYC expression and activity are associated with the down-regulation of MEIS1, a HOX-family transcription factor. Using RNA-seq to profile a series of human prostate cancer specimens laser capture microdissected on the basis of MYC immunohistochemistry, MYC activity, and MEIS1 expression were inversely correlated. Knockdown of MYC expression in prostate cancer cells increased the expression of MEIS1 and increased the occupancy of MYC at the MEIS1 locus. Finally, we show in laser capture microdissected human prostate cancer samples and the prostate TCGA cohort that MEIS1 expression is inversely proportional to AR activity as well as HOXB13, a known interacting protein of both AR and MEIS1. Collectively, our data demonstrate that elevated MYC in a subset of primary prostate cancers functions in a negative role in regulating MEIS1 expression, and that this down-regulation may contribute to MYC-driven development and progression.

Assessment of Androgen Receptor Splice Variant-7 as a Biomarker of Clinical Response in Castration-Sensitive Prostate Cancer

PURPOSE

Therapies targeting the androgen receptor (AR) have improved the outcome for patients with castration-sensitive prostate cancer (CSPC). Expression of the constitutively active AR splice variant-7 (AR-V7) has shown clinical utility as a predictive biomarker of AR-targeted therapy resistance in castration-resistant prostate cancer (CRPC), but its importance in CSPC remains understudied.

EXPERIMENTAL DESIGN

We assessed different approaches to quantify AR-V7 mRNA and protein in prostate cancer cell lines, patient-derived xenograft (PDX) models, publicly available cohorts, and independent institutional clinical cohorts, to identify reliable approaches for detecting AR-V7 mRNA and protein and its association with clinical outcome.

RESULTS

In CSPC and CRPC cohorts, AR-V7 mRNA was much less abundant when detected using reads across splice boundaries than when considering isoform-specific exonic reads. The RM7 AR-V7 antibody had increased sensitivity and specificity for AR-V7 protein detection by immunohistochemistry (IHC) in CRPC cohorts but rarely identified AR-V7 protein reactivity in CSPC cohorts, when compared with the EPR15656 AR-V7 antibody. Using multiple CRPC PDX models, we demonstrated that AR-V7 expression was exquisitely sensitive to hormonal manipulation. In CSPC institutional cohorts, AR-V7 protein quantification by either assay was associated neither with time to development of castration resistance nor with overall survival, and intense neoadjuvant androgen-deprivation therapy did not lead to significant AR-V7 mRNA or staining following treatment. Neither pre- nor posttreatment AR-V7 levels were associated with volumes of residual disease after therapy.

CONCLUSIONS

This study demonstrates that further analytical validation and clinical qualification are required before AR-V7 can be considered for clinical use in CSPC as a predictive biomarker.

Progression of prostate cancer reprograms MYC-mediated lipid metabolism via lysine methyltransferase 2A

BACKGROUND

The activities of MYC, the androgen receptor, and its associated pioneer factors demonstrate substantial reprogramming between early and advanced prostate cancer. Although previous studies have shown a shift in cellular metabolic requirements associated with prostate cancer progression, the epigenetic regulation of these processes is incompletely described. Here, we have integrated chromatin immunoprecipitation sequencing (ChIP-seq) and whole-transcriptome sequencing to identify novel regulators of metabolism in advanced prostate tumors characterized by elevated MYC activity.

RESULTS

Using ChIP-seq against MYC, HOXB13, and AR in LNCaP cells, we observed redistribution of co-bound sites suggestive of differential KMT2A activity as a function of MYC expression. In a cohort of 177 laser-capture microdissected foci of prostate tumors, KMT2A expression was positively correlated with MYC activity, AR activity, and HOXB13 expression, but decreased with tumor grade severity. However, KMT2A expression was negatively correlated with these factors in 25 LuCaP patient-derived xenograft models of advanced prostate cancer and 99 laser-capture microdissected foci of metastatic castration-resistant prostate cancer. Stratified by KMT2A expression, ChIP-seq against AR and HOXB13 in 15 LuCaP patient-derived xenografts showed an inverse association with sites involving genes implicated in lipid metabolism, including the arachidonic acid metabolic enzyme PLA2G4F. LuCaP patient-derived xenograft models grown as organoids recapitulated the inverse association between KMT2A expression and fluorine-18 labeled arachidonic acid uptake in vitro.

CONCLUSIONS

Our study demonstrates that the epigenetic activity of transcription factor oncogenes exhibits a shift during prostate cancer progression with distinctive phenotypic effects on metabolism. These epigenetically driven changes in lipid metabolism may serve as novel targets for the development of novel imaging agents and therapeutics.

Molecular and histopathologic correlates of imaging and biological responses to neoadjuvant GnRH agonist plus enzalutamide for high risk prostate cancer

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Background: AR directed therapies are standard of care for metastatic prostate cancer, and their use for high-risk localized disease may improve survival. Previous trials showed low rates of complete pathologic responses to neoadjuvant ADT. The underlying biology and molecular features of tumors that fail to respond remain unknown. Methods: Men with localized prostate cancer with high risk features received 6 months of GnRH agonist plus enzalutamide. mpMRI was performed at baseline and prior to RP. MRI-US fusion guided biopsies were performed at study enrollment. RP specimens were sectioned in the same plane as mpMRI. Imaging and anatomical landmarks on pre- and post-treatment mpMRI were used to match targeted biopsies to RPs. IHC stains including AR, GR, and SYP were performed to guide laser capture microdissection (LCM) and characterization of residual disease. DNA was extracted from LCM biopsy and RP tissues. Whole exome sequencing with somatic mutation calling and copy number analysis was performed. Results: Most patients showed incomplete pathologic responses despite reductions in tumor volume. Several patients harbored multiple tumor clones prior to treatment, distinguished by distinct copy number alterations and mutations in biopsies. Alignment of biopsies to pre- and post-treatment mpMRI correlated with imaging response and histopathology of matched RP sections. Minimal genomic divergence from untreated clones on biopsy suggested intrinsic resistance, while extensive divergence indicated selection for pre-existing subclones. Most residual tumor was AR- and GR-positive adenocarcinoma, with some regions of AR-negative Panneth cell-like differentiation positive for synaptophysin. AR-V7 was rare in residual tumor and < 1% cells were positive for KI-67. The most common alteration in all samples was single-copy loss of chromosome 16q overlapping with ZFHX3. Conclusions: Our approach of repeated sampling by matching targeted biopsies to mpMRI demonstrates feasibility in comparing mpMRI response, pathologic treatment response, and the underlying genomic features that drive tumor development versus treatment resistance. Clinical trial information: NCT02430480.

Abstract 2510: Combining genetic and histopathologic features to predict response to anti-androgen therapy in aggressive prostate cancer

Background: Genetic alterations in lethal, metastatic prostate cancer include the loss of PTEN, translocation of the TMPRSS2 and ERG genes, upregulation of the androgen receptor (AR), and disruption of the DNA homologous repair pathway driven by mutations to BRCA1, BRCA2, and ATM. Many of these mutations can be observed while the cancer is still localized in the prostate. Here, we seek to identify genetic features indicative of therapeutic response and novel drivers of cancer progression to inform clinical practice.

Methods: Using tissue from 33 patients in an intense neoadjuvant anti-androgen clinical trial at the NCI (NCT02430480), we examined genetic features that would predict exceptional or poor response to anti-androgen enzalutamide therapy. Each patient on trial presented with multiple tumor foci, allowing us to investigate the intratumoral heterogeneity across foci within individual patients, as well as investigating the tumor profiles across multiple patients. Several patients exhibited exceptional response with residual tumor burdens less than 0.5cc, while others had substantial treatment-resistant cancers. We developed a panel of 12 immunohistopathological stains and used this panel to guide laser capture microdissection on pre-treatment biopsies and spatially matched post-treatment radical prostatectomy specimens to isolate ultrapure tumor foci from each patient. DNA from these foci was used for whole exome sequencing, as somatic copy number alterations and mutations also confirm their evolutionary relationship. This enabled us to classify baseline specimens as responder or nonresponder, while examining variations in genetic features between the two cohorts.

Results: To date, focal PTEN loss was observed in all nonresponders, while focal ERG staining was absent in 100% of responders and present in 60% of nonresponders. Synaptophysin positivity was rare at baseline but predicted resistance to treatment with 100% sensitivity. Intriguingly, baseline copy number profiles highlight a 6q deletion in 100% of exceptional responders, but not in the non-responders. Together, these data suggest an immunostain panel to assess oncogene and tumor suppressor alterations can predict response to anti-androgen therapy, while also suggesting a novel role of 6q in resistance to anti-androgen hormone therapy. Current studies are examining the role of 6q in response to anti-androgen therapies, which remains an area of active interest in our laboratory.

Conclusions: These findings demonstrate the feasibility in identifying intratumoral heterogeneity based on prostate biomarker status both in pre-treatment and post-treatment specimens. Using these data, comprehensive molecular analysis of prostate cancer at diagnosis may better-enable physicians to predict response to anti-androgen therapy and provide tailored treatment based on gene expression status.

Citation Format: Scott Wilkinson, Huihui Ye, Nicole Carrabba, Rayann Atway, Shana Y. Trostel, Thomas Hennigan, Ross Lake, Stephanie Harmon, Guinevere Chun, Baris Turkbey, Peter A. Pinto, Peter L. Choyke, Fatima Karzai, David J. VanderWeele, Kathleen Kelly, William L. Dahut, Adam G. Sowalsky. Combining genetic and histopathologic features to predict response to anti-androgen therapy in aggressive prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2510.

Localized high-risk prostate cancer harbors an androgen receptor low subpopulation susceptible to HER2 inhibition

Patients diagnosed with localized high-risk prostate cancer have higher rates of recurrence, and the introduction of neoadjuvant intensive hormonal therapies seeks to treat occult micrometastatic disease by their addition to definitive treatment. Sufficient profiling of baseline disease has remained a challenge in enabling the in-depth assessment of phenotypes associated with exceptional vs. poor pathologic responses after treatment. In this study, we report comprehensive and integrative gene expression profiling of 37 locally advanced prostate tumors prior to six months of androgen deprivation therapy (ADT) plus the androgen receptor (AR) inhibitor enzalutamide prior to radical prostatectomy. A robust transcriptional program associated with HER2 activity was positively associated with poor outcome and opposed AR activity, even after adjusting for common genomic alterations in prostate cancer including PTEN loss and expression of the TMPRSS2:ERG fusion. Patients experiencing exceptional pathologic responses demonstrated lower levels of HER2 and phospho-HER2 by immunohistochemistry of biopsy tissues. The inverse correlation of AR and HER2 activity was found to be a universal feature of all aggressive prostate tumors, validated by transcriptional profiling an external cohort of 121 patients and immunostaining of tumors from 84 additional patients. Importantly, the AR activity-low, HER2 activity-high cells that resist ADT are a pre-existing subset of cells that can be targeted by HER2 inhibition alone or in combination with enzalutamide. In summary, we show that prostate tumors adopt an AR activity-low prior to antiandrogen exposure that can be exploited by treatment with HER2 inhibitors.

Low tristetraprolin expression activates phenotypic plasticity and primes transition to lethal prostate cancer in mice

Phenotypic plasticity is a hallmark of cancer and is increasingly realized as a mechanism of resistance to androgen receptor-targeted (AR-targeted) therapy. Now that many prostate cancer (PCa) patients are treated upfront with AR-targeted agents, it is critical to identify actionable mechanisms that drive phenotypic plasticity, to prevent the emergence of resistance. We showed that loss of tristetraprolin (TTP; gene ZFP36) increased NF-κB activation, and was associated with higher rates of aggressive disease and early recurrence in primary PCa. We also examined the clinical and biological impact of ZFP36 loss with co-loss of PTEN, a known driver of PCa. Analysis of multiple independent primary PCa cohorts demonstrated that PTEN and ZFP36 co-loss was associated with increased recurrence risk. Engineering prostate-specific Zfp36 deletion in vivo induced prostatic intraepithelial neoplasia, and, with Pten codeletion, resulted in rapid progression to castration-resistant adenocarcinoma. Zfp36 loss altered the cell state driven by Pten loss, as demonstrated by enrichment of epithelial-mesenchymal transition (EMT), inflammation, TNF-α/NF-κB, and IL-6-JAK/STAT3 gene sets. Additionally, our work revealed that ZFP36 loss also induced enrichment of multiple gene sets involved in mononuclear cell migration, chemotaxis, and proliferation. Use of the NF-κB inhibitor dimethylaminoparthenolide (DMAPT) induced marked therapeutic responses in tumors with PTEN and ZFP36 co-loss and reversed castration resistance.

Radiogenomic profiling of prostate tumors prior to external beam radiotherapy converges on a transcriptomic signature of TGF-β activity driving tumor recurrence

Background

Patients with localized prostate cancer have historically been assigned to clinical risk groups based on local disease extent, serum prostate specific antigen (PSA), and tumor grade. Clinical risk grouping is used to determine the intensity of treatment with external beam radiotherapy (EBRT) and androgen deprivation therapy (ADT), yet a substantial proportion of patients with intermediate and high risk localized prostate cancer will develop biochemical recurrence (BCR) and require salvage therapy. Prospective identification of patients destined to experience BCR would allow treatment intensification or selection of alternative therapeutic strategies.

Methods

Twenty-nine individuals with intermediate or high risk prostate cancer were prospectively recruited to a clinical trial designed to profile the molecular and imaging features of prostate cancer in patients undergoing EBRT and ADT. Whole transcriptome cDNA microarray and whole exome sequencing were performed on pretreatment targeted biopsy of prostate tumors (n=60). All patients underwent pretreatment and 6-month post EBRT multiparametric MRI (mpMRI), and were followed with serial PSA to assess presence or absence of BCR. Genes differentially expressed in the tumor of patients with and without BCR were investigated using pathways analysis tools and were similarly explored in alternative datasets. Differential gene expression and predicted pathway activation were evaluated in relation to tumor response on mpMRI and tumor genomic profile. A novel TGF-β gene signature was developed in the discovery dataset and applied to a validation dataset.

Findings

Baseline MRI lesion volume and PTEN/TP53 status in prostate tumor biopsies correlated with the activation state of TGF-β signaling measured using pathway analysis. All three measures correlated with the risk of BCR after definitive RT. A prostate cancer-specific TGF-β signature discriminated between patients that experienced BCR vs. those that did not. The signature retained prognostic utility in an independent cohort.

Interpretation

TGF-β activity is a dominant feature of intermediate-to-unfavorable risk prostate tumors prone to biochemical failure after EBRT with ADT. TGF-β activity may serve as a prognostic biomarker independent of existing risk factors and clinical decision-making criteria.

Funding

This research was supported by the Prostate Cancer Foundation, the Department of Defense Congressionally Directed Medical Research Program, National Cancer Institute, and the Intramural Research Program of the NIH, National Cancer Institute, Center for Cancer Research.

Multiple primary prostate tumors with differential drug sensitivity

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Background: The differential aggressiveness of potentially independent prostate cancer clones remains largely unknown. Appropriate prostate cancer staging using mpMRI and biopsy tissue can be confounded by sampling error. To date, there has been no understanding of whether clonal variability influences management decisions for localized prostate tumors. We sought to identify the sensitivity and genomic profile of distinct localized tumors from a patient following systemic intense neoadjuvant androgen deprivation therapy (ADT). Methods: A 66-year-old man with high risk prostate cancer enrolled in a Phase 2 study of intense neoadjuvant ADT (goserelin + enzalutamide; inADT). Baseline mpMRI showed a single semi-contiguous lesion encompassing the right apical-mid PZ extending into the left distal apical PZ. MR/US-fusion targeted biopsy was performed before 6 months of inADT. A second mpMRI was performed before radical prostatectomy. Whole exome sequencing on microdissected tumor foci identified somatic mutations and copy number alterations, which were further used with immunohistochemistry to assess tumor clonal architecture and genomic/phenotypic evolution of treatment resistant tumor. Results: We found two clonally independent tumors exhibited intrinsic heterogeneity at baseline which correlated with response or resistance. Biopsies of distinct left- and right-sided tumors showed differing histologies. mpMRI and pathology showed near complete response of the left-sided tumor and substantial resistance of the right-sided tumor, which exhibited a large intraductal component. Histology and whole exome data highlighted a divergence in the status of PTEN and TP53, tumor suppressor genes implicated in prostate cancer progression. Conclusions: These data highlight that even nascent prostate cancer is heterogenous and neoadjuvant therapeutic strategies will need to consider this for clinical optimization. Evolutionary trajectories that resulted in tumor heterogeneity in this case likely contributed to our observation that two independent prostate tumor nodules with distinct genetic alterations responded differently to neoadjuvant intense ADT. Clinical trial information: NCT02430480.

Reproducible preclinical models of androgen receptor driven human prostate cancer bone metastasis

BACKGROUND

Preclinical models recapitulating the metastatic phenotypes are essential for developing the next-generation therapies for metastatic prostate cancer (mPC). We aimed to establish a cohort of clinically relevant mPC models, particularly androgen receptor positive (AR+) bone metastasis models, from LuCaP patient-derived xenografts (PDX) that reflect the heterogeneity and complexity of mPC.

METHODS

PDX tumors were dissociated into single cells, modified to express luciferase, and were inoculated into NSG mice via intracardiac injection. The progression of metastases was monitored by bioluminescent imaging. Histological phenotypes of metastases were characterized by immunohistochemistry and immunofluorescence staining. Castration responses were further investigated in two AR-positive models.

RESULTS

Our PDX-derived metastasis (PDM) model collection comprises three AR+ adenocarcinomas (ARPC) and one AR- neuroendocrine carcinoma (NEPC). All ARPC models developed bone metastases with either an osteoblastic, osteolytic, or mixed phenotype, while the NEPC model mainly developed brain metastasis. Different mechanisms of castration resistance were observed in two AR+ PDM models with distinct genotypes, such as combined loss of TP53 and RB1 in one model and expression of AR splice variant 7 (AR-V7) expression in another model. Intriguingly, the castration-resistant tumors displayed inter- and intra-tumor as well as organ-specific heterogeneity in lineage specification.

CONCLUSION

Genetically diverse PDM models provide a clinically relevant system for biomarker identification and personalized medicine in metastatic castration-resistant prostate cancer.

Androgen Receptor Inhibition Increases MHC Class I Expression and Improves Immune Response in Prostate Cancer

SIGNIFICANCE

Immunotherapy options for immune cold tumors, like prostate cancer, are limited. We show that AR downregulates MHCI expression/antigen presentation and that AR inhibition improves T-cell responses and tumor control. This suggests that treatments combining AR inhibitors and checkpoint blockade may improve tumor immune surveillance and antitumor immunity in patients.