MAP3K7 Loss Drives Enhanced Androgen Signaling and Independently Confers Risk of Recurrence in Prostate Cancer with Joint Loss of CHD1

Prostate cancer genomic subtypes that stratify aggressive disease and inform treatment decisions at the primary stage are currently limited. Previously, we functionally validated an aggressive subtype present in 15% of prostate cancer characterized by dual deletion of MAP3K7 and CHD1. Recent studies in the field have focused on deletion of CHD1 and its role in androgen receptor (AR) chromatin distribution and resistance to AR-targeted therapy; however, CHD1 is rarely lost without codeletion of MAP3K7. Here, we show that in the clinically relevant context of co-loss of MAP3K7 and CHD1 there are significant, collective changes to aspects of AR signaling. Although CHD1 loss mainly impacts the expansion of the AR cistrome, loss of MAP3K7 drives increased AR target gene expression. Prostate cancer cell line models engineered to cosuppress MAP3K7 and CHD1 also demonstrated increased AR-v7 expression and resistance to the AR-targeting drug enzalutamide. Furthermore, we determined that low protein expression of both genes is significantly associated with biochemical recurrence (BCR) in a clinical cohort of radical prostatectomy specimens. Low MAP3K7 expression, however, was the strongest independent predictor for risk of BCR over all other tested clinicopathologic factors including CHD1 expression. Collectively, these findings illustrate the importance of MAP3K7 loss in a molecular subtype of prostate cancer that poses challenges to conventional therapeutic approaches. IMPLICATIONS: These findings strongly implicate MAP3K7 loss as a biomarker for aggressive prostate cancer with significant risk for recurrence that poses challenges for conventional androgen receptor-targeted therapies.

Loss of MAP3K7 Sensitizes Prostate Cancer Cells to CDK1/2 Inhibition and DNA Damage by Disrupting Homologous Recombination

The combined loss of CHD1 and MAP3K7 promotes aggressive prostate cancer by unknown mechanisms. Because both of these genes are lost genetically in prostate cancer, they cannot be directly targeted. We applied an established computational systems pharmacology approach (TRAP) to identify altered signaling pathways and associated druggable targets. We compared gene expression profiles of prostate cancer with coloss of CHD1 and MAP3K7 with prostate cancer diploid for these genes using The Cancer Genome Atlas patient samples. This analysis prioritized druggable target genes that included CDK1 and CDK2. We validated that inhibitors of these druggable target genes, including the CDK1/CDK2 inhibitor dinaciclib, had antiproliferative and cytotoxic effects selectively on mouse prostate cells with knockdown of Chd1 and Map3k7. Dinaciclib had stronger effects on prostate cells with suppression of Map3k7 independent of Chd1 and also compared with cells without loss of Map3k7. Dinaciclib treatment reduced expression of homologous recombination (HR) repair genes such as ATM, ATR, BRCA2, and RAD51, blocked BRCA1 phosphorylation, reduced RAD51 foci formation, and increased γH2AX foci selectively in prostate cells with suppression of Map3k7, thus inhibiting HR repair of chromosomal double-strand breaks. Dinaciclib-induced HR disruption was also observed in human prostate cells with knockdown of MAP3K7. Cotreatment of dinaciclib with DNA-damaging agents or PARP inhibitor resulted in a stronger cytotoxic effect on prostate cells with suppression of MAP3K7 compared with those without loss of MAP3K7, or to each single agent. IMPLICATIONS: These findings demonstrate that loss of MAP3K7 is a main contributing factor to drug response through disruption of HR in prostate cancer.

Abstract 1580: Combined neuroendocrine differentiation and androgen receptor hyperactivity in MAP37 and CHD1 null prostate cancer

We recently functionally validated a clinically aggressive subtype of prostate cancer characterized by dual deletion of MAP3K7 and CHD1. This subtype accounts for up to 25% of prostate cancer deaths. Androgen signaling is a critical component of prostate tumorigenesis and disease progression, which is exploited in treatment of prostate cancer with androgen deprivation and anti-androgen therapies. Neuroendocrine differentiation is thought to provide a selective growth advantage of prostate cancer in androgen-depleted conditions such as surgical or chemical castration. REST is a transcriptional repressor of neuronal gene expression and has been implicated in neuroendocrine differentiation of prostate cancer. The impact of combined MAP3K7 and CHD1 loss on androgen signaling and neuroendocrine differentiation has not been determined. Here, we demonstrate that dual loss of MAP3K7 and CHD1 simultaneously stimulates enhanced androgen signaling and enhanced neuronal differentiation correlated with enhanced growth in both androgen-depleted and androgen-replete conditions. These changes occur via increased androgen receptor chromatin binding, loss of CHD1 chromatin binding, loss of REST expression, and reduced chromatin binding by REST. Suppression of CHD1 and MAP3K7 attenuates the antiproliferative activity of the anti-androgen Enzalutamide. Furthermore, we translate these findings to clinical samples and show that decreased expression of CHD1, MAP3K7, and REST is associated with previous therapeutic intervention, castrate-resistant disease, and progression to a neuroendocrine phenotype. Overall, patients with low expression of all three have poorer disease-free survival. Together these data support the lineage plasticity of prostate tumors with loss of CHD1 and MAP3K7 exhibiting both androgen-dependent and -independent phenotypes leading to poor clinical outcome, which poses challenges to conventional therapeutic approaches.

Citation Format: Leah C. Rider, Lindsey U. Rodrigues, Anis Karimpour-Fard, Lina Romero, Claire Gillette, James C. Costello, Scott D. Cramer. Combined neuroendocrine differentiation and androgen receptor hyperactivity in MAP37 and CHD1 null prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1580. doi:10.1158/1538-7445.AM2017-1580

Influence of stromal-epithelial interactions on androgen action

Androgen receptor (AR) signaling is vital to the development and function of the prostate and is a key pathway in prostate cancer. AR is differentially expressed in the stroma and epithelium, with both paracrine and autocrine control throughout the prostate. Stromal-epithelial interactions within the prostate are commonly dependent on AR signaling and expression. Alterations in these pathways can promote tumorigenesis. AR is also expressed in normal and malignant mammary tissues. Emerging data indicate a role for AR in certain subtypes of breast cancer that has the potential to be exploited therapeutically. The aim of this review is to highlight the importance of these interactions in normal development and tumorigenesis, with a focus on the prostate and breast.