Patient-derived Hormone-naive Prostate Cancer Xenograft Models Reveal Growth Factor Receptor Bound Protein 10 as an Androgen Receptor-repressed Gene Driving the Development of Castration-resistant Prostate Cancer.

Although androgen deprivation therapy is initially effective in controlling growth of hormone-naive prostate cancers (HNPCs) in patients, currently incurable castration-resistant prostate cancer (CRPC) inevitably develops. To identify CRPC driver genes that may provide new targets to enhance CRPC therapy. Patient-derived xenografts (PDXs) of HNPCs that develop CRPC following host castration were examined for changes in expression of genes at various time points after castration using transcriptome profiling analysis; particular attention was given to pre-CRPC changes in expression indicative of genes acting as potential CRPC drivers. The functionality of a potential CRPC driver was validated via its knockdown in cultured prostate cancer cells; its clinical relevance was established using data from prostate cancer patient databases. Eighty genes were found to be significantly upregulated at the CRPC stage, while seven of them also showed elevated expression prior to CRPC development. Among the latter, growth factor receptor bound protein 10 (GRB10) was the most significantly and consistently upregulated gene. Moreover, elevated GRB10 expression in clinical prostate cancer samples correlated with more aggressive tumor types and poorer patient treatment outcome. GRB10 knockdown markedly reduced prostate cancer cell proliferation and activity of AKT, a well-established CRPC mediator. A positive correlation between AKT activity and GRB10 expression was also found in clinical cohorts. GRB10 acts as a driver of CRPC and sensitizes androgen receptor pathway inhibitors, and hence GRB10 targeting provides a novel therapeutic strategy for the disease. Development of castration-resistant prostate cancer (CRPC) is a major problem in the management of the disease. Using state-of-the-art patient-derived hormone-naive prostate cancer xenograft models, we found and validated the growth factor receptor bound protein 10 gene as a driver of CRPC, indicating that it may be used as a new molecular target to enhance current CRPC therapy.

Hao J ，Ci X ，Xue H ，Wu R ，Dong X ，Choi SYC ，He H ，Wang Y ，Zhang F ，Qu S ，Zhang F ，Haegert AM ，Gout PW ，Zoubeidi A ，Collins C ，Gleave ME ，Lin D ，Wang Y ... -  《-》

GRB10 sustains AR activity by interacting with PP2A in prostate cancer cells.

Prostate cancer (PCa) progression is driven by androgen receptor (AR) signaling. Unfortunately, androgen-deprivation therapy and the use of even more potent AR pathway inhibitors (ARPIs) cannot bring about a cure. ARPI resistance (ie, castration-resistant PCa, CRPC) will inevitably develop. Previously, we demonstrated that GRB10 is an AR transcriptionally repressed gene that functionally contributes to CRPC development and ARPI resistance. GRB10 expression is elevated prior to CRPC development in our patient-derived xenograft models and is significantly upregulated in clinical CRPC samples. Here, we analyzed transcriptomic data from GRB10 knockdown in PCa cells and found that AR signaling is downregulated. While the mRNA expression of AR target genes decreased upon GRB10 knockdown, AR expression was not affected at the mRNA or protein level. We further found that phosphorylation of AR serine 81 (S81), which is critical for AR transcriptional activity, is decreased by GRB10 knockdown and increased by its overexpression. Luciferase assay using GRB10-knockdown cells also indicate reduced AR activity. Immunoprecipitation coupled with mass spectrometry revealed an interaction between GRB10 and the PP2A complex, which is a known phosphatase of AR. Further validations and analyses showed that GRB10 binds to the PP2Ac catalytic subunit with its PH domain. Mechanistically, GRB10 knockdown increased PP2Ac protein stability, which in turn decreased AR S81 phosphorylation and reduced AR activity. Our findings indicate a reciprocal feedback between GRB10 and AR signaling, implying the importance of GRB10 in PCa progression.

Hao J ，Ci X ，Wang Y ，Choi SYC ，Sullivan SE ，Xue H ，Wu R ，Dong X ，Haegert AM ，Collins CC ，Lin D ，Wang Y ... -  《-》

NDRG2 acts as a negative regulator downstream of androgen receptor and inhibits the growth of androgen-dependent and castration-resistant prostate cancer.

Yu C ，Wu G ，Li R ，Gao L ，Yang F ，Zhao Y ，Zhang J ，Zhang R ，Zhang J ，Yao L ，Yuan J ，Li X ... -  《-》

ZRSR2 overexpression is a frequent and early event in castration-resistant prostate cancer development.

Androgen deprivation therapy (ADT) remains the leading systemic therapy for locally advanced and metastatic prostate cancers (PCa). While a majority of PCa patients initially respond to ADT, the durability of response is variable and most patients will eventually develop incurable castration-resistant prostate cancer (CRPC). Our research objective is to identify potential early driver genes responsible for CRPC development. We have developed a unique panel of hormone-naïve PCa (HNPC) patient-derived xenograft (PDX) models at the Living Tumor Laboratory. The PDXs provide a unique platform for driver gene discovery as they allow for the analysis of differentially expressed genes via transcriptomic profiling at various time points after mouse host castration. In the present study, we focused on genes with expression changes shortly after castration but before CRPC has fully developed. These are likely to be potential early drivers of CRPC development. Such genes were further validated for their clinical relevance using data from PCa patient databases. ZRSR2 was identified as a top gene candidate and selected for further functional studies. ZRSR2 is significantly upregulated in our PDX models during the early phases of CRPC development after mouse host castration and remains consistently high in fully developed CRPC PDX models. Moreover, high ZRSR2 expression is also observed in clinical CRPC samples. Importantly, elevated ZRSR2 in PCa samples is correlated with poor patient treatment outcomes. ZRSR2 knockdown reduced PCa cell proliferation and delayed cell cycle progression at least partially through inhibition of the Cyclin D1 (CCND1) pathway. Using our unique HNPC PDX models that develop into CRPC after host castration, we identified ZRSR2 as a potential early driver of CRPC development.

He H ，Hao J ，Dong X ，Wang Y ，Xue H ，Qu S ，Choi SYC ，Ci X ，Wang Y ，Wu R ，Shi M ，Zhao X ，Collins C ，Lin D ，Wang Y ... -  《-》

RGS2 is prognostic for development of castration resistance and cancer-specific survival in castration-resistant prostate cancer.

Regulator of G-protein signaling 2 (RGS2) is a multifaceted protein with a prognostic value in hormone-naïve prostate cancer (PC). It has previously been associated with the development of castration resistance. However, RGS2 expression in clinical specimens of castration-resistant prostate cancer (CRPC) and its clinical relevance has not been explored. In the present study, RGS2 was assessed in CRPC and in relation to the development of castration resistance. In the present study, RGS2 expression was evaluated with immunohistochemistry in patient materials of hormone-naïve and castration-resistant primary tumors, also in matched specimens before and after 3 months of androgen deprivation therapy (ADT). Cox regression and Kaplan-Meier curves were used to evaluate the clinical significance of RGS2 expression. RGS2 expression in association to castration-resistant growth was assessed experimentally in an orthotopic xenograft mouse model of CRPC. In vitro, hormone depletion of LNCaP and enzalutamide treatment of LNCaP, 22Rv1, and VCaP was performed to evaluate the association between RGS2 and the androgen receptor (AR). Stable RGS2 knockdown was used to evaluate the impact of RGS2 in association to PC cell growth under hormone-reduced conditions. Gene and protein expression were evaluated with quantitative polymerase chain reaction and Western blot analysis, respectively. RGS2 expression is increased in CRPC and enriched under ADT. Furthermore, a high RGS2 level is prognostic for poor cancer-specific survival for CRPC patients and significantly reduced failure-free survival (FFS) after an initiated ADT. Additionally, the prognostic value of RGS2 outperforms prostate-specific antigen (PSA) in terms of FFS. The present study furthermore suggests that RGS2 expression is reflective of AR activity. Moreover, low RGS2-expressing cells display hampered growth under hormone-reduced conditions, in line with the poor prognosis associated with high RGS2 expression. High levels of RGS2 are associated with aggressive forms of castration-resistant PC. The results demonstrate that a high level of RGS2 is associated with poor prognosis in association with castration-resistant PC growth. RGS2 alone, or in association with PSA, has the potential to identify patients that require additional treatment at an early stage during ADT.

Linder A ，Larsson K ，Welén K ，Damber JE ... -  《-》