Six transmembrane epithelial antigen of the prostate 1 (STEAP1) is a cell surface antigen for therapeutic targeting in prostate cancer. Here, we report broad expression of STEAP1 relative to ...prostate-specific membrane antigen (PSMA) in lethal metastatic prostate cancers and the development of a STEAP1-directed chimeric antigen receptor (CAR) T cell therapy. STEAP1 CAR T cells demonstrate reactivity in low antigen density, antitumor activity across metastatic prostate cancer models, and safety in a human STEAP1 knock-in mouse model. STEAP1 antigen escape is a recurrent mechanism of treatment resistance and is associated with diminished tumor antigen processing and presentation. The application of tumor-localized interleukin-12 (IL-12) therapy in the form of a collagen binding domain (CBD)-IL-12 fusion protein combined with STEAP1 CAR T cell therapy enhances antitumor efficacy by remodeling the immunologically cold tumor microenvironment of prostate cancer and combating STEAP1 antigen escape through the engagement of host immunity and epitope spreading.
The androgen receptor (AR) pathway regulates key cell survival programs in prostate epithelium. The AR represents a near-universal driver and therapeutic vulnerability in metastatic prostate cancer, ...and targeting AR has a remarkable therapeutic index. Though most approaches directed toward AR focus on inhibiting AR signaling, laboratory and now clinical data have shown that high dose, supraphysiological androgen treatment (SPA) results in growth repression and improved outcomes in subsets of prostate cancer patients. A better understanding of the mechanisms contributing to SPA response and resistance could help guide patient selection and combination therapies to improve efficacy. To characterize SPA signaling, we integrated metrics of gene expression changes induced by SPA together with cistrome data and protein-interactomes. These analyses indicated that the Dimerization partner, RB-like, E2F and Multi-vulval class B (DREAM) complex mediates growth repression and downregulation of E2F targets in response to SPA. Notably, prostate cancers with complete genomic loss of RB1 responded to SPA treatment whereas loss of DREAM complex components such as RBL1/2 promoted resistance. Overexpression of MYC resulted in complete resistance to SPA and attenuated the SPA/AR-mediated repression of E2F target genes. These findings support a model of SPA-mediated growth repression that relies on the negative regulation of MYC by AR leading to repression of E2F1 signaling via the DREAM complex. The integrity of MYC signaling and DREAM complex assembly may consequently serve as determinants of SPA responses and as pathways mediating SPA resistance.
To catalog protein-altering mutations that may drive the development of prostate cancers and their progression to metastatic disease systematically, we performed whole-exome sequencing of 23 prostate ...cancers derived from 16 different lethal metastatic tumors and three high-grade primary carcinomas. All tumors were propagated in mice as xenografts, designated the LuCaP series, to model phenotypic variation, such as responses to cancer-directed therapeutics. Although corresponding normal tissue was not available for most tumors, we were able to take advantage of increasingly deep catalogs of human genetic variation to remove most germline variants. On average, each tumor genome contained ∼200 novel nonsynonymous variants, of which the vast majority was specific to individual carcinomas. A subset of genes was recurrently altered across tumors derived from different individuals, including TP53, DLK2, GPC6, and SDF4. Unexpectedly, three prostate cancer genomes exhibited substantially higher mutation frequencies, with 2,000–4,000 novel coding variants per exome. A comparison of castration-resistant and castration-sensitive pairs of tumor lines derived from the same prostate cancer highlights mutations in the Wnt pathway as potentially contributing to the development of castration resistance. Collectively, our results indicate that point mutations arising in coding regions of advanced prostate cancers are common but, with notable exceptions, very few genes are mutated in a substantial fraction of tumors. We also report a previously undescribed subtype of prostate cancers exhibiting "hypermutated" genomes, with potential implications for resistance to cancer therapeutics. Our results also suggest that increasingly deep catalogs of human germline variation may challenge the necessity of sequencing matched tumor-normal pairs.
Retinoblastoma (RB; encoded by RB1) is a tumor suppressor that is frequently disrupted in tumorigenesis and acts in multiple cell types to suppress cell cycle progression. The role of RB in tumor ...progression, however, is poorly defined. Here, we have identified a critical role for RB in protecting against tumor progression through regulation of targets distinct from cell cycle control. In analyses of human prostate cancer samples, RB loss was infrequently observed in primary disease and was predominantly associated with transition to the incurable, castration-resistant state. Further analyses revealed that loss of the RB1 locus may be a major mechanism of RB disruption and that loss of RB function was associated with poor clinical outcome. Modeling of RB dysfunction in vitro and in vivo revealed that RB controlled nuclear receptor networks critical for tumor progression and that it did so via E2F transcription factor 1-mediated regulation of androgen receptor (AR) expression and output. Through this pathway, RB depletion induced unchecked AR activity that underpinned therapeutic bypass and tumor progression. In agreement with these findings, disruption of the RB/E2F/nuclear receptor axis was frequently observed in the transition to therapy resistance in human disease. Together, these data reveal what we believe to be a new paradigm for RB function in controlling prostate tumor progression and lethal tumor phenotypes.
Prostate cancer (PC) is driven by androgen receptor (AR) activity, a master regulator of prostate development and homeostasis. Frontline therapies for metastatic PC deprive the AR of the activating ...ligands testosterone (T) and dihydrotestosterone (DHT) by limiting their biosynthesis or blocking AR binding. Notably, AR signaling is dichotomous, inducing growth at lower activity levels, while suppressing growth at higher levels. Recent clinical studies have exploited this effect by administration of supraphysiological concentrations of T, resulting in clinical responses and improvements in quality of life. However, the use of T as a therapeutic agent in oncology is limited by poor drug-like properties as well as rapid and variable metabolism. Here, we investigated the antitumor effects of selective AR modulators (SARMs), which are small-molecule nonsteroidal AR agonists developed to treat muscle wasting and cachexia. Several orally administered SARMs activated the AR program in PC models. AR cistromes regulated by steroidal androgens and SARMs were superimposable. Coregulatory proteins including HOXB13 and GRHL2 comprised AR complexes assembled by both androgens and SARMs. At bioavailable concentrations, SARMs repressed MYC oncoprotein expression and inhibited the growth of castration-sensitive and castration-resistant PC in vitro and in vivo. These results support further clinical investigation of SARMs for treating advanced PC.
The significance of ERG in human prostate cancer is unclear because mouse prostate is resistant to ERG-mediated transformation. We determined that ERG activates the transcriptional program regulated ...by YAP1 of the Hippo signaling pathway and found that prostate-specific activation of either ERG or YAP1 in mice induces similar transcriptional changes and results in age-related prostate tumors. ERG binds to chromatin regions occupied by TEAD/YAP1 and transactivates Hippo target genes. In addition, in human luminal-type prostate cancer cells, ERG binds to the promoter of YAP1 and is necessary for YAP1 expression. These results provide direct genetic evidence of a causal role for ERG in prostate cancer and reveal a connection between ERG and the Hippo signaling pathway.
•Upregulation of ERG is sufficient to cause age-dependent prostate tumors in mice•ERG transcriptional output is similar to the output of YAP1 of the Hippo pathway•ERG is necessary for YAP1 expression in luminal-type human prostate cancer cells•Activation of YAP1 is sufficient to cause age-dependent prostate tumors in mice
Nguyen et al. show that ERG activates YAP1-regulated transcriptional output and that activation of ERG or YAP1 in mouse prostate induces similar transcriptional changes and age-related prostate tumors. Moreover, pharmacological inhibition of YAP1 suppresses growth of ERG-positive human prostate tumor xenografts.
The incidence of prostate cancer is directly linked to age, but age-associated changes that facilitate prostate cancer development and progression are poorly understood. This study investigated ...age-related changes in the prostate microenvironment for their influence on prostate cancer behavior. Prostate cancer cells implanted orthotopically into the prostate demonstrated accelerated tumor growth in aged compared with young mice. Metastatic lesions following intravenous injection were also more numerous in aged mice. Tumors from young and aged mice showed no significant differences concerning their proliferation index, apoptosis, or angiogenesis. However, analysis of tumor-infiltrating immune cells by IHC and RNA sequencing (RNA-seq) revealed elevated numbers of macrophages in prostates from aged mice, which are quickly polarized towards a phenotype resembling protumorigenic tumor-associated macrophages upon tumor cell engraftment. Older patients with prostate cancer (>60 years old) in The Cancer Genome Atlas Prostate Adenocarcinoma (TCGA-PRAD) dataset displayed higher expression of macrophage markers (CD163 and VSIG4) which associated with higher rates of biochemical relapse. Remodeling of the collagenous extracellular matrix (ECM) was associated with prostate cancer growth and invasion in the aged microenvironment. Moreover, the collagen matrix extracted from aged mice enhanced the invasiveness and proliferation of prostate cancer cells
. Together, these results demonstrate that the aged prostatic microenvironment can regulate the growth and metastasis of malignant prostate cells, highlighting the role of resident macrophages and their polarization towards a protumorigenic phenotype, along with remodeling of the ECM. IMPLICATIONS: These findings demonstrate the importance of age-associated tumor microenvironment alterations in regulating key aspects of prostate cancer progression.
The androgen receptor (AR) is a driver of cellular differentiation and prostate cancer development. An extensive body of work has linked these normal and aberrant cellular processes to mRNA ...transcription; however, the extent to which AR regulates posttranscriptional gene regulation remains unknown. Here, we demonstrate that AR uses the translation machinery to shape the cellular proteome. We show that AR is a negative regulator of protein synthesis and identify an unexpected relationship between AR and the process of translation initiation in vivo. This is mediated through direct transcriptional control of the translation inhibitor 4EBP1. We demonstrate that lowering AR abundance increases the assembly of the eIF4F translation initiation complex, which drives enhanced tumor cell proliferation. Furthermore, we uncover a network of pro-proliferation mRNAs characterized by a guanine-rich cis-regulatory element that is particularly sensitive to eIF4F hyperactivity. Using both genetic and pharmacologic methods, we demonstrate that dissociation of the eIF4F complex reverses the proliferation program, resulting in decreased tumor growth and improved survival in preclinical models. Our findings reveal a druggable nexus that functionally links the processes of mRNA transcription and translation initiation in an emerging class of lethal AR-deficient prostate cancer.
•Four fusion-detection NGS tests compared.•Fusion partners and breakpoints known vs. unknown impacts detectability.•OCAv3 and FusionPlex selected for further clinical validation.•Check percent fusion ...read over total read count for reportability of low-level calls.
As fusion detection NGS techniques are adopted by clinical labs, assay performance comparison is urgently needed. We compared four fusion-detection assay platforms on a pilot cohort of 24 prostate cancer samples: (1) Oncomine Comprehensive panel v3; (2) AmpliSeq comprehensive panel v3; (3) The solid tumor panel of FusionPlex; and (4) The human oncology panel of QIAseq. The assays were compared for the detection of different types of fusion based on whether the partner gene or the breakpoints are known. All assays detected fusion with known gene partners and known breakpoint, represented by TMPRSS2-ERG. A fusion with known partners but unknown breakpoint, TMPRSS2-ETV4, was reported by OCAv3 and FusionPlex, but not by AICv3 because the specific breakpoint was not in the manifest, nor by QIAseq since the panel did not target the exact exons involved. For fusion with unknown partners, FusionPlex identified the largest number of ETV1 fusions because it had the highest exon coverage for ETV1. Among these, SNRPN-ETV1 and MALAT1-ETV1, were novel findings. To determine reportability of low-level calls of highly prevalent fusions, such as TMPRSS2-ERG, we propose the use of percent fusion reads over total number of reads per sample instead of the fusion read count.
A significant proportion of human prostate cancers carry a chromosomal rearrangement resulting in the overexpression of the ETS transcription factor, ERG; however, the functional significance of this ...event is poorly understood. We report here that up-regulation of ERG transcript is sufficient for the initiation of prostate neoplasia. In agreement with measurements of ERG transcripts, we found that ERG protein is expressed in neoplastic human prostate epithelium. Overexpression of ERG in prostate cell lines increased cell invasion. Moreover, targeted expression of this transcript in vivo in luminal prostate epithelial cells of transgenic mice results in initiation of prostate neoplasia observed as the development of focal precancerous prostatic intraepithelial neoplasia (PIN). Similar to human cancers, luminal epithelial cells in these PIN lesions displace diminishing in numbers basal epithelial cells and establish direct contact with the stromal cell compartment. Loss of basal cells is considered to be one of the critical hallmarks of human prostate cancer; however, the mechanisms responsible for this event were unknown. We propose that up-regulation of ERG in human prostate cancer activates cell invasion programs that subsequently displace basal cells by neoplastic epithelium. Our data demonstrate that ERG plays an important causal role in the transformation of prostate epithelium and should be considered as a target for prevention or early therapeutic intervention.
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