BACKGROUND:TP53, PTEN, and RB1 tumor suppressor genes (TSGs) are recurrently altered in treatment-resistant prostate cancer. Cooperative loss of two or more TSGs may drive more aggressive disease. OBJECTIVE:To determine clinical outcomes of single and compound TSG alterations across the spectrum of prostate cancer. DESIGN, SETTING, AND PARTICIPANTS:Massively parallel targeted sequencing using castration-sensitive prostate cancer (CSPC; localized [L] and metastatic [M1]) and castration-resistant prostate cancer (CRPC) specimens (n=285). TSG altered (TSG-alt) was any copy number loss or deleterious mutation of one or more TSGs (TP53, PTEN, and RB1). OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS:For L-CSPC, event-free survival (EFS) and time to CRPC were estimated. For M1-CSPC and M1-CRPC, overall survival (OS) was estimated. Cox regression models assessed the association between cumulative TSG hits (zero hits vs one hit vs two to three hits) and outcomes with multivariable analyses adjusted for clinicopathological factors. RESULTS AND LIMITATIONS:TSG variants increased with advanced disease (L-CSPC: 39%; M1-CSPC: 63%, M1-CRPC: 92%). TSG-alt L-CSPC had shorter EFS (median 2.6yr, hazard ratio [HR] 1.95, 95% confidence interval [CI] 1.22-3.13) and time to CRPC (median 9.5mo, HR 3.36, 95% CI 1.01-11.16). Cumulative gene hits led to an incremental risk of relapse (EFS: one gene, HR 1.69, 95% CI 0.99-2.87; two to three genes, HR 2.70, 95% CI 1.43-5.08; both versus zero genes, p=0.004). There was evidence of inferior OS with increasing TSG hits in the metastatic cohorts. Only four (8%) patients in the M1-CRPC cohort were TSG-neg, one of whom died after 5.2yr. Multivariable analyses adjusting for mutational and copy number burden did not demonstrate a significant independent association of increasing gene hits and poorer outcomes. CONCLUSIONS:Deleterious TSG variants are associated with an increased risk of relapse (L) and death (M1) in CSPC. Poorer outcomes are seen with compound gene hits in both early and advanced disease, and this may in part reflect increasing global genomic instability. PATIENT SUMMARY:Men with prostate tumors with compound tumor suppressor gene mutations have poorer outcomes. These findings help identify patients with aggressive features who may benefit from intensified treatment.

The mechanisms by which prostate cancer shifts from an indolent castration-sensitive phenotype to lethal castration-resistant prostate cancer (CRPC) are poorly understood. Identification of clinically relevant genetic alterations leading to CRPC may reveal potential vulnerabilities for cancer therapy. Here we find that CUB domain-containing protein 1 (CDCP1), a transmembrane protein that acts as a substrate for SRC family kinases (SFKs), is overexpressed in a subset of CRPC. Notably, CDCP1 cooperates with the loss of the tumor suppressor gene PTEN to promote the emergence of metastatic prostate cancer. Mechanistically, we find that androgens suppress CDCP1 expression and that androgen deprivation in combination with loss of PTEN promotes the upregulation of CDCP1 and the subsequent activation of the SRC/MAPK pathway. Moreover, we demonstrate that anti-CDCP1 immunoliposomes (anti-CDCP1 ILs) loaded with chemotherapy suppress prostate cancer growth when administered in combination with enzalutamide. Thus, our study identifies CDCP1 as a powerful driver of prostate cancer progression and uncovers different potential therapeutic strategies for the treatment of metastatic prostate tumors.

Histologic transformation to small cell neuroendocrine prostate cancer occurs in a subset of patients with advanced prostate cancer as a mechanism of treatment resistance. Rovalpituzumab tesirine (SC16LD6.5) is an antibody-drug conjugate that targets delta-like protein 3 (DLL3) and was initially developed for small cell lung cancer. We found that DLL3 is expressed in most of the castration-resistant neuroendocrine prostate cancer (CRPC-NE) (36 of 47, 76.6%) and in a subset of castration-resistant prostate adenocarcinomas (7 of 56, 12.5%). It shows minimal to no expression in localized prostate cancer (1 of 194) and benign prostate (0 of 103). DLL3 expression correlates with neuroendocrine marker expression, loss, and aggressive clinical features. DLL3 in circulating tumor cells was concordant with matched metastatic biopsy (87%). Treatment of DLL3-expressing prostate cancer xenografts with a single dose of SC16LD6.5 resulted in complete and durable responses, whereas DLL3-negative models were insensitive. We highlight a patient with neuroendocrine prostate cancer with a meaningful clinical and radiologic response to SC16LD6.5 when treated on a phase 1 trial. Overall, our findings indicate that DLL3 is preferentially expressed in CRPC-NE and provide rationale for targeting DLL3 in patients with DLL3-positive metastatic prostate cancer.

The transition from castration-resistant prostate adenocarcinoma (CRPC) to neuroendocrine prostate cancer (NEPC) has emerged as an important mechanism of treatment resistance. NEPC is associated with overexpression and gene amplification of MYCN (encoding N-Myc). N-Myc is an established oncogene in several rare pediatric tumors, but its role in prostate cancer progression is not well established. Integrating a genetically engineered mouse model and human prostate cancer transcriptome data, we show that N-Myc overexpression leads to the development of poorly differentiated, invasive prostate cancer that is molecularly similar to human NEPC. This includes an abrogation of androgen receptor signaling and induction of Polycomb Repressive Complex 2 signaling. Altogether, our data establishes N-Myc as an oncogenic driver of NEPC.

Metastases account for most cancer-related deaths, yet the mechanisms underlying metastatic spread remain poorly understood. Recent evidence demonstrates that senescent cells, while initially restricting tumorigenesis, can induce tumor progression. Here, we identify the metalloproteinase inhibitor TIMP1 as a molecular switch that determines the effects of senescence in prostate cancer. Senescence driven either by PTEN deficiency or chemotherapy limits the progression of prostate cancer in mice. TIMP1 deletion allows senescence to promote metastasis, and elimination of senescent cells with a senolytic BCL-2 inhibitor impairs metastasis. Mechanistically, TIMP1 loss reprograms the senescence-associated secretory phenotype (SASP) of senescent tumor cells through activation of matrix metalloproteinases (MMPs). Loss of PTEN and TIMP1 in prostate cancer is frequent and correlates with resistance to docetaxel and worst clinical outcomes in patients treated in an adjuvant setting. Altogether, these findings provide insights into the dual roles of tumor-associated senescence and can potentially impact the treatment of prostate cancer.

BACKGROUND:Interleukin-6 (IL-6) is a mediator of inflammation that can facilitate prostate cancer progression. We previously demonstrated that IL-6 is present in the prostate tumor microenvironment and is restricted almost exclusively to the stromal compartment. The present study examined the influence of paracrine IL-6 signaling on prostate tumor growth using allograft models of mouse prostate cancer (TRAMP-C2), colon cancer (MC38), and melanoma (B16) cell lines in wildtype (WT) and IL-6 knockout (IL-6 ) mice. METHODS:Cells were implanted into WT or IL-6 mice and tumor sizes were measured at a 3 to 4 day interval. Serum, tumors, and other organs were collected for IL-6 analysis by ELISA and RNA in situ hybridization (RISH). RESULTS:There was a significant reduction in TRAMP-C2 and B16 tumor size grown in IL-6 mice versus WT mice (P = 0.0006 and P = 0.02, respectively). This trend was not observed for the MC38 cell line. RISH analysis of TRAMP-C2 tumors grown in WT mice showed that cells present in the tumor microenvironment were the primary source of IL-6 mRNA, not the TRAMP-C2 cells. Serum IL-6 ELISA analyses showed an increase in the circulating levels of IL-6 in WT mice bearing TRAMP-C2 tumors. Similar phospho-STAT3 expression and tumor vascularization were observed in TRAMP-C2 tumors grown in WT and IL-6 mice. CONCLUSIONS:Our results are consistent with previous studies in prostate cancer patients demonstrating that paracrine IL-6 production in the tumor microenvironment may influence tumor growth. Additionally, these data provide evidence that elevated systemic IL-6 levels may be involved in tumor growth regulation in prostate cancer, and are not simply caused by or indicative of tumor burden.

Despite the development of second-generation antiandrogens, acquired resistance to hormone therapy remains a major challenge in treating advanced prostate cancer. We find that cancer-associated fibroblasts (CAFs) can promote antiandrogen resistance in mouse models and in prostate organoid cultures. We identify neuregulin 1 (NRG1) in CAF supernatant, which promotes resistance in tumor cells through activation of HER3. Pharmacological blockade of the NRG1/HER3 axis using clinical-grade blocking antibodies re-sensitizes tumors to hormone deprivation in vitro and in vivo. Furthermore, patients with castration-resistant prostate cancer with increased tumor NRG1 activity have an inferior response to second-generation antiandrogen therapy. This work reveals a paracrine mechanism of antiandrogen resistance in prostate cancer amenable to clinical testing using available targeted therapies.

Prostate cancer (PCa) is one of the most common malignant cancers in male and docetaxel is commonly used as an effective chemotherapeutic drug for PCa patients. However, docetaxel resistance inhibits the therapeutic effect of this agent, thus investigating the mechanism of chemoresistance to docetaxel of PCa may help to improve the prognosis of PCa patients. In our present study, we found that miR-223-3p was up-regulated in PCa cell lines (C4-2, LNCap, PC3, DU-145). Transfection with miR-223-3p inhibitor increased chemo-sensitivity to docetaxel and cell apoptosis rate in PCa cells compared with docetaxel + miR-223-3p mock group, especially in DU-145 cells which were more resistant to docetaxel. Bioinformatics study and luciferase reporter assay indicated that FOXO3 was a target of miR-223-3p and the results from western blot suggested that FOXO3 was negatively regulated by miR-223-3p. Further study revealed that up-regulation of FOXO3 by transfection with pCMV-FOXO3 decreased the IC values of docetaxel and increased cell apoptosis rate compared with docetaxel + pCMV-vector group, suggesting that overexpressed FOXO3 suppressed cell survival and sensitized PCa cells to docetaxel. Moreover, siRNA-mediated knockdown of FOXO3 abolished the effects of miR-223-3p inhibitor on chemo-sensitivity and apoptosis in PCa cells by increasing chemoresistance and decreasing cell apoptosis rate. Finally, the in vivo experiments showed that miR-223-3p inhibitor sensitized prostatic cancer mouse model to docetaxel by increasing the expression of FOXO3. In conclusion, our present study indicated that miR-223-3p regulated cell chemo-sensitivity by targeting FOXO3 in prostatic cancer both in vitro and in vivo, providing new potential therapeutic strategy for PCa treatment.