Selective androgen receptor modulators activate the canonical prostate cancer androgen receptor program and repress cancer growth.

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.

Combined TP53 and RB1 Loss Promotes Prostate Cancer Resistance to a Spectrum of Therapeutics and Confers Vulnerability to Replication Stress.

Prostate cancers (PCs) with loss of the potent tumor suppressors TP53 and RB1 exhibit poor outcomes. TP53 and RB1 also influence cell plasticity and are frequently lost in PCs with neuroendocrine (NE) differentiation. Therapeutic strategies that address these aggressive variant PCs are urgently needed. Using deep genomic profiling of 410 metastatic biopsies, we determine the relationships between combined TP53 and RB1 loss and PC phenotypes. Notably, 40% of TP53/RB1-deficient tumors are classified as AR-active adenocarcinomas, indicating that NE differentiation is not an obligate consequence of TP53/RB1 inactivation. A gene expression signature reflecting TP53/RB1 loss is associated with diminished responses to AR antagonists and reduced survival. These tumors exhibit high proliferation rates and evidence of elevated DNA repair processes. While tumor cells lacking TP53/RB1 are highly resistant to all single-agent therapeutics tested, the combination of PARP and ATR inhibition is found to produce significant responses, reflecting a clinically exploitable vulnerability resulting from replication stress.

MYC Dysregulates Mitosis, Revealing Cancer Vulnerabilities.

Tumors that overexpress the MYC oncogene are frequently aneuploid, a state associated with highly aggressive cancers and tumor evolution. However, how MYC causes aneuploidy is not well understood. Here, we show that MYC overexpression induces mitotic spindle assembly defects and chromosomal instability (CIN) through effects on microtubule nucleation and organization. Attenuating MYC expression reverses mitotic defects, even in established tumor cell lines, indicating an ongoing role for MYC in CIN. MYC reprograms mitotic gene expression, and we identify TPX2 to be permissive for spindle assembly in MYC-high cells. TPX2 depletion blocks mitotic progression, induces cell death, and prevents tumor growth. Further elevating TPX2 expression reduces mitotic defects in MYC-high cells. MYC and TPX2 expression may be useful biomarkers to stratify patients for anti-mitotic therapies. Our studies implicate MYC as a regulator of mitosis and suggest that blocking MYC activity can attenuate the emergence of CIN and tumor evolution.

Identification of Therapeutic Vulnerabilities in Small-cell Neuroendocrine Prostate Cancer.

PURPOSE: Small-cell neuroendocrine prostate cancer (SCNPC) exhibits an aggressive clinical course and incidence rates seem to be increasing following resistance to potent androgen receptor (AR) antagonists. Currently, treatment options are limited and few model systems are available to identify new approaches for treatment. We sought to evaluate commonalities between SCNPC and other aggressive neuroendocrine carcinomas to identify therapeutic targets. EXPERIMENTAL DESIGN: We generated whole transcriptome RNA-sequencing data from AR-active prostate cancers (ARPCs) and SCNPCs from tumors collected at rapid autopsy and two other neuroendocrine carcinomas, Merkel cell carcinoma (MCC), and small-cell lung cancer. We performed cross-tumor comparisons to identify conserved patterns of expression of druggable targets. We tested inhibitors to highly upregulated drug targets in a panel of prostate cancer cell lines and in vivo patient-derived xenograft (PDX) models. RESULTS: We identified BCL2 as highly upregulated in SCNPC compared with ARPC. Inhibitors targeting BCL2 induced apoptotic cell death in SCNPC cell lines at nanomolar concentrations while ARPC cell lines were resistant. Treatment with the BCL2 inhibitor navitoclax leads to a reduction of growth of SCNPC PDX tumors in vivo, whereas ARPC PDX models were more resistant. We identified Wee1 as a second druggable target upregulated in SCNPC. Treatment with the combination of navitoclax and the Wee1 inhibitor AZD-1775 repressed the growth of SCNPC PDX resistant to single-agent BCL2 inhibitors. CONCLUSIONS: The combination of BCL2 and Wee1 inhibition presents a novel therapeutic strategy for the treatment of SCNPC.

Molecular determinants of response to high-dose androgen therapy in prostate cancer.

Clinical trials of high-dose androgen (HDA) therapy for prostate cancer (PC) have shown promising efficacy but are limited by lack of criteria to identify likely responders. To elucidate factors that govern the growth-repressive effects of HDAs, we applied an unbiased integrative approach using genetic screens and transcriptional profiling of PC cells with or without demonstrated phenotypic sensitivity to androgen-mediated growth repression. Through this comprehensive analysis, we identified genetic events and related signaling networks that determine the response to both HDA and androgen withdrawal. We applied these findings to develop a gene signature that may serve as an early indicator of treatment response and identify men with tumors that are amenable to HDA therapy.

Androgen Receptor Pathway-Independent Prostate Cancer Is Sustained through FGF Signaling.

Androgen receptor (AR) signaling is a distinctive feature of prostate carcinoma (PC) and represents the major therapeutic target for treating metastatic prostate cancer (mPC). Though highly effective, AR antagonism can produce tumors that bypass a functional requirement for AR, often through neuroendocrine (NE) transdifferentiation. Through the molecular assessment of mPCs over two decades, we find a phenotypic shift has occurred in mPC with the emergence of an AR-null NE-null phenotype. These "double-negative" PCs are notable for elevated FGF and MAPK pathway activity, which can bypass AR dependence. Pharmacological inhibitors of MAPK or FGFR repressed the growth of double-negative PCs in vitro and in vivo. Our results indicate that FGF/MAPK blockade may be particularly efficacious against mPCs with an AR-null phenotype.

Exploiting AR-Regulated Drug Transport to Induce Sensitivity to the Survivin Inhibitor YM155.

Androgen receptor (AR) signaling is fundamental to prostate cancer and is the dominant therapeutic target in metastatic disease. However, stringent androgen deprivation therapy regimens decrease quality of life and have been largely unsuccessful in curtailing mortality. Recent clinical and preclinical studies have taken advantage of the dichotomous ability of AR signaling to elicit growth-suppressive and differentiating effects by administering hyperphysiologic levels of testosterone. In this study, high-throughput drug screening identified a potent synergy between high-androgen therapy and YM155, a transcriptional inhibitor of survivin (BIRC5). This interaction was mediated by the direct transcriptional upregulation of the YM155 transporter SLC35F2 by the AR. Androgen-mediated YM155-induced cell death was completely blocked by the overexpression of multidrug resistance transporter ABCB1. SLC35F2 expression was significantly correlated with intratumor androgen levels in four distinct patient-derived xenograft models, and with AR activity score in a large gene expression dataset of castration-resistant metastases. A subset of tumors had significantly elevated SLC35F2 expression and, therefore, may identify patients who are highly responsive to YM155 treatment. IMPLICATIONS: The combination of androgen therapy with YM155 represents a novel drug synergy, and SLC35F2 may serve as a clinical biomarker of response to YM155.

PIM1 kinase inhibition as a targeted therapy against triple-negative breast tumors with elevated MYC expression.

Triple-negative breast cancer (TNBC), in which cells lack expression of the estrogen receptor (ER), the progesterone receptor (PR) and the ERBB2 (also known as HER2) receptor, is the breast cancer subtype with the poorest outcome. No targeted therapy is available against this subtype of cancer owing to a lack of validated molecular targets. We previously reported that signaling involving MYC-an essential, pleiotropic transcription factor that regulates the expression of hundreds of genes-is disproportionally higher in triple-negative (TN) tumors than in receptor-positive (RP) tumors. Direct inhibition of the oncogenic transcriptional activity of MYC has been challenging to achieve. Here, by conducting a shRNA screen targeting the kinome, we identified PIM1, a non-essential serine-threonine kinase, in a synthetic lethal interaction with MYC. PIM1 expression was higher in TN tumors than in RP tumors and was associated with poor prognosis in patients with hormone- and HER2-negative tumors. Small-molecule PIM kinase inhibitors halted the growth of human TN tumors with elevated MYC expression in patient-derived tumor xenograft (PDX) and MYC-driven transgenic mouse models of breast cancer by inhibiting the oncogenic transcriptional activity of MYC and restoring the function of the endogenous cell cycle inhibitor, p27. Our findings warrant clinical evaluation of PIM kinase inhibitors in patients with TN tumors that have elevated MYC expression.

Direct and indirect targeting of MYC to treat acute myeloid leukemia.

PURPOSE: Acute myeloid leukemia (AML) is the most common acute leukemia in adults and is often resistant to conventional therapies. The MYC oncogene is commonly overexpressed in AML but has remained an elusive target. We aimed to examine the consequences of targeting MYC both directly and indirectly in AML overexpressing MYC/Myc due to trisomy 8/15 (human/mouse), FLT3-ITD mutation, or gene amplification. METHODS: We performed in vivo knockdown of Myc (shRNAs) and both in vitro and in vivo experiments using four drugs with indirect anti-MYC activity: VX-680, GDC-0941, artemisinin, and JQ1. RESULTS: shRNA knockdown of Myc in mice prolonged survival, regardless of the mechanism underlying MYC overexpression. VX-680, an aurora kinase inhibitor, demonstrated in vitro efficacy against human MYC-overexpressing AMLs regardless of the mechanism of MYC overexpression, but was weakest against a MYC-amplified cell line. GDC-0941, a PI3-kinase inhibitor, demonstrated efficacy against several MYC-overexpressing AMLs, although only in vitro. Artemisinin, an antimalarial, did not demonstrate consistent efficacy against any of the human AMLs tested. JQ1, a bromodomain and extra-terminal bromodomain inhibitor, demonstrated both in vitro and in vivo efficacy against several MYC-overexpressing AMLs. We also confirmed a decrease in MYC levels at growth inhibitory doses for JQ1, and importantly, sensitivity of AML cell lines to JQ1 appeared independent of the mechanism of MYC overexpression. CONCLUSIONS: Our data support growing evidence that JQ1 and related compounds may have clinical efficacy in AML treatment regardless of the genetic abnormalities underlying MYC deregulation.

Linking tumor mutations to drug responses via a quantitative chemical-genetic interaction map.

UNLABELLED: There is an urgent need in oncology to link molecular aberrations in tumors with therapeutics that can be administered in a personalized fashion. One approach identifies synthetic-lethal genetic interactions or dependencies that cancer cells acquire in the presence of specific mutations. Using engineered isogenic cells, we generated a systematic and quantitative chemical-genetic interaction map that charts the influence of 51 aberrant cancer genes on 90 drug responses. The dataset strongly predicts drug responses found in cancer cell line collections, indicating that isogenic cells can model complex cellular contexts. Applying this dataset to triple-negative breast cancer, we report clinically actionable interactions with the MYC oncogene, including resistance to AKT-PI3K pathway inhibitors and an unexpected sensitivity to dasatinib through LYN inhibition in a synthetic lethal manner, providing new drug and biomarker pairs for clinical investigation. This scalable approach enables the prediction of drug responses from patient data and can accelerate the development of new genotype-directed therapies. SIGNIFICANCE: Determining how the plethora of genomic abnormalities that exist within a given tumor cell affects drug responses remains a major challenge in oncology. Here, we develop a new mapping approach to connect cancer genotypes to drug responses using engineered isogenic cell lines and demonstrate how the resulting dataset can guide clinical interrogation.