Synergistic Activity with NOTCH Inhibition and Androgen Ablation in ERG-Positive Prostate Cancer Cells

Anti-NOTCH1 therapy with OMP-52 M51 inhibits salivary adenoid cystic carcinoma by depressing epithelial-mesenchymal transition (EMT) process and inducing ferroptosis

Salivary adenoid cystic carcinoma (ACC) is a common type of salivary gland cancer, and the mechanisms underlying its progression still remain poorly understood without efficient therapies. NOTCH1, an evolutionally conserved cell-cell signaling pathway, is involved in the progression of ACC. In our study, we attempted to explore whether NOTCH1 suppression using the monoclonal anti-NOTCH1 antibody OMP-52 M51 could be of potential for ACC treatment. Here, we identified NOTCH1 elevation in human ACC tissues compared with the matched normal samples. Patients with metastasis expressed much higher NOTCH1. We then found that OMP-52 M51 markedly reduced the expression of NOTCH1 and its intracellular active form NICD1 (NOTCH1 intracellular domain). Importantly, OMP-52 M51 markedly reduced the proliferation, migration and invasion of ACC cells. RNA-Seq and in vitro studies further showed that OMP-52 M51 significantly induced ferroptosis in ACC cells, indicated by the increased cellular malondialdehyde (MDA), iron contents and lipid ROS production, and decreased glutathione (GSH) levels. Further, remarkable glutathione peroxidase 4 (GPX4) reduction was detected in ACC cells with OMP-52 M51 treatment. However, promoting NOTCH1 expression markedly abolished the function of OMP-52 M51 to induce ferroptosis. Intriguingly, low-dose OMP-52 M51 strongly facilitated the capacity of ferroptosis inducer erastin to trigger ferroptotic cell death, revealing that OMP-52 M51 could improve the sensitivity of ACC cells to ferroptosis. In vivo, OMP-52 M51 administration suppressed tumor growth and induced ferroptosis in the constructed ACC xenograft mouse model. Collectively, our findings demonstrated that NOTCH1 inhibition by OMP-52 M51 represses the proliferation and epithelial-mesenchymal transition (EMT) in ACCs, and promotes ferroptosis, revealing the potential therapeutical application of OMP-52 M51 in ACC.

Knocking down SOX2 overcomes the resistance of prostate cancer to castration via notch signaling

BACKGROUND

Castration-resistant prostate cancer (CRPC) is a terminal type of advanced cancer resistant to androgen deprivation therapy (ADT). Due to the poor therapeutic response of CRPC, novel treatment strategies are urgently required. This study aimed to clarify the regulatory roles of the SOX2/Notch axis in CRPC.

METHODS

For the evaluation of the SOX2, Notch, and Hey1 expression in the prostate cancer (PCa) and CRPC tissues, we conducted immunohistochemistry (IHC) analyses. RT-PCR, Western blotting, and immunofluorescence were performed to evaluate SOX2 and Notch expression in enzalutamide-resistant LNCaP cells (Enza-R). CCK-8, Transwell, Wound healing, and Western blotting assays were used to assess the viability, invasion, migration, cell cycle, and drug-resistant in Enza-R cells.

RESULTS

Compared to the PCa tissues, CRPC tissues exhibited significantly elevated SOX2, Notch1, and Hey1 expression. SOX2-positive patients were more likely to develop bone metastases than SOX2-negative ones. Significant activation of the signaling associated with SOX2 and Notch was detected in Enza-R cells. The suppression of SOX2 clearly inactivated the Notch signaling and inhibited malignant behaviors, including proliferation, invasion, migration, and drug resistance in Enza-R cells. Theγsecretase inhibitor, GSI-IX, abrogated the enzalutamide resistance by inhibiting Notch signaling in vitro in vitro. Also, GSI-IX alone had a significant anti-tumor effect in Enza-R cells.

CONCLUSION

We demonstrated that SOX2/Notch signaling was responsible for Enzalutamide resistance in CRPC. Targeting SOX2/Notch signaling might represent a new choice for the treatment and therapy of CRPC.

Prostate Cancer Stem Cells: Biology and Treatment Implications

Stem cells differentiate into mature organ/tissue-specific cells at a steady pace under normal conditions, but their growth can be accelerated during the process of tissue healing or in the context of certain diseases. It is postulated that the proliferation and growth of carcinomas are sustained by the presence of a vital cellular compartment resembling stem cells residing in normal tissues: 'stem-like cancer cells' or cancer stem cells (CSCs). Mutations in prostate stem cells can lead to the formation of prostate cancer. Prostate CSCs (PCSCs) have been identified and partially characterized. These express surface markers include CD44, CD133, integrin α2β1, and pluripotency factors like OCT4, NANOG, and SOX2. Several signaling pathways are also over-activated, including Notch, PTEN/Akt/PI3K, RAS-RAF-MEK-ERK and HH. Moreover, PCSCs appear to induce resistance to radiotherapy and chemotherapy, while their presence has been linked to aggressive cancer behavior and higher relapse rates. The development of treatment policies to target PCSCs in tumors is appealing as radiotherapy and chemotherapy, through cancer cell killing, trigger tumor repopulation via activated stem cells. Thus, blocking this reactive stem cell mobilization may facilitate a positive outcome through cytotoxic treatment.

The roles of proteases in prostate cancer

Since the proposition of the pro-invasive activity of proteolytic enzymes over 70 years ago, several roles for proteases in cancer progression have been established. About half of the 473 active human proteases are expressed in the prostate and many of the most well-characterized members of this enzyme family are regulated by androgens, hormones essential for development of prostate cancer. Most notably, several kallikrein-related peptidases, including KLK3 (prostate-specific antigen, PSA), the most well-known prostate cancer marker, and type II transmembrane serine proteases, such as TMPRSS2 and matriptase, have been extensively studied and found to promote prostate cancer progression. Recent findings also suggest a critical role for proteases in the development of advanced and aggressive castration-resistant prostate cancer (CRPC). Perhaps the most intriguing evidence for this role comes from studies showing that the protease-activated transmembrane proteins, Notch and CDCP1, are associated with the development of CRPC. Here, we review the roles of proteases in prostate cancer, with a special focus on their regulation by androgens.

Anti-Cancer Stem-Cell-Targeted Therapies in Prostate Cancer

Prostate cancer (PCa) is the second-most commonly diagnosed cancer in men around the world. It is treated using a risk stratification approach in accordance with the National Comprehensive Cancer Network (NCCN) in the United States. The main treatment options for early PCa include external beam radiation therapy (EBRT), brachytherapy, radical prostatectomy, active surveillance, or a combination approach. In those with advanced disease, androgen deprivation therapy (ADT) is considered as a first-line therapy. However, the majority of cases eventually progress while receiving ADT, leading to castration-resistant prostate cancer (CRPC). The near inevitable progression to CRPC has spurred the recent development of many novel medical treatments using targeted therapies. In this review, we outline the current landscape of stem-cell-targeted therapies for PCa, summarize their mechanisms of action, and discuss avenues of future development.

SOX8 Knockdown Overcomes Enzalutamide Resistance in Castration-Resistant Prostate Cancer by Inhibiting the Notch Signaling Pathway

Castration-resistant prostate cancer (CRPC) is still challenging to treat. Dissatisfaction with androgen signal-targeted therapy forces people to look for other treatment strategies. Therefore, this study is aimed at exploring the role of SOX8/Notch signaling in CRPC. The upregulation of SOX8, Notch4, and Hes5 indicated a poor progression-free survival (PFS) in CRPC patients. The expression of these proteins was also upregulated in enzalutamide-resistant LNCaP cells (Enza-R). Moreover, knocking down SOX8 inhibited malignant biological behaviors and decreased the activation of Notch signaling in Enza-R cells. Importantly, knocking down SOX8 obviously reversed the enzalutamide resistance in Enza-R cells, while RO0429097 (a γ secretase inhibitor inactivates Notch signaling) exerted similar effects. At last, we found that both SOX8 knockdown and/or RO0429097 suppressed tumor growth and bone metastasis in vivo. Altogether, our study indicated that the SOX8/Notch signaling is involved in CRPC and that these enzymes are possible targets to develop novel treatment for CRPC.

Interplay of Developmental Hippo-Notch Signaling Pathways with the DNA Damage Response in Prostate Cancer

Prostate cancer belongs in the class of hormone-dependent cancers, representing a major cause of cancer incidence in men worldwide. Since upon disease onset almost all prostate cancers are androgen-dependent and require active androgen receptor (AR) signaling for their survival, the primary treatment approach has for decades relied on inhibition of the AR pathway via androgen deprivation therapy (ADT). However, following this line of treatment, cancer cell pools often become resistant to therapy, contributing to disease progression towards the significantly more aggressive castration-resistant prostate cancer (CRPC) form, characterized by poor prognosis. It is, therefore, of critical importance to elucidate the molecular mechanisms and signaling pathways underlying the progression of early-stage prostate cancer towards CRPC. In this review, we aim to shed light on the role of major signaling pathways including the DNA damage response (DDR) and the developmental Hippo and Notch pathways in prostate tumorigenesis. We recapitulate key evidence demonstrating the crosstalk of those pathways as well as with pivotal prostate cancer-related 'hubs' such as AR signaling, and evaluate the clinical impact of those interactions. Moreover, we attempt to identify molecules of the complex DDR-Hippo-Notch interplay comprising potentially novel therapeutic targets in the battle against prostate tumorigenesis.

AL101, a gamma-secretase inhibitor, has potent antitumor activity against adenoid cystic carcinoma with activated NOTCH signaling

Adenoid cystic carcinoma (ACC) is an aggressive salivary gland malignancy with limited treatment options for recurrent or metastatic disease. Due to chemotherapy resistance and lack of targeted therapeutic approaches, current treatment options for the localized disease are limited to surgery and radiation, which fails to prevent locoregional recurrences and distant metastases in over 50% of patients. Approximately 20% of patients with ACC carry NOTCH-activating mutations that are associated with a distinct phenotype, aggressive disease, and poor prognosis. Given the role of NOTCH signaling in regulating tumor cell behavior, NOTCH inhibitors represent an attractive potential therapeutic strategy for this subset of ACC. AL101 (osugacestat) is a potent γ-secretase inhibitor that prevents activation of all four NOTCH receptors. While this investigational new drug has demonstrated antineoplastic activity in several preclinical cancer models and in patients with advanced solid malignancies, we are the first to study the therapeutic benefit of AL101 in ACC. Here, we describe the antitumor activity of AL101 using ACC cell lines, organoids, and patient-derived xenograft models. Specifically, we find that AL101 has potent antitumor effects in in vitro and in vivo models of ACC with activating NOTCH1 mutations and constitutively upregulated NOTCH signaling pathway, providing a strong rationale for evaluation of AL101 in clinical trials for patients with NOTCH-driven relapsed/refractory ACC.

Molecular mechanisms and genetic alterations in prostate cancer: From diagnosis to targeted therapy

Prostate cancer remains one of the most lethal malignancies among men worldwide. Although the primary tumor can be successfully managed by surgery and radiotherapy, advanced metastatic carcinoma requires better therapeutic approaches. In this context, a deeper understanding of the molecular mechanisms that underlie the initiation and progression of this disease is urgently needed, leading to the identification of new diagnostic/prognostic markers and the development of more effective treatments. Herein, the current state of knowledge of prostate cancer genetic alterations is discussed, with a focus on their potential in tumor detection and staging as well as in the screening of novel therapeutics.

Past, Current, and Future Strategies to Target ERG Fusion-Positive Prostate Cancer

Simple Summary

In addition to its role in development and in the vascular and hematopoietic systems, ERG plays a central role in prostate cancer. Approximately 40–50% of prostate cancer cases are characterized by ERG gene fusions, which lead to ERG overexpression. Importantly, inhibition of ERG activity in prostate cancer cells decreases their viability. Therefore, inhibiting ERG might represent an important step to improve treatment efficacy for patients with ERG-positive prostate tumors. Here, we summarize the attempts made over the past years to repress ERG activity, the current use of ERG fusion detection and the strategies that might be utilized in the future to treat ERG fusion-positive tumors.

Abstract

The ETS family member ERG is a transcription factor with physiological roles during development and in the vascular and hematopoietic systems. ERG oncogenic activity characterizes several malignancies, including Ewing’s sarcoma, leukemia and prostate cancer (PCa). In PCa, ERG rearrangements with androgen-regulated genes—mostly TMPRSS2—characterize a large subset of patients across disease progression and result in androgen receptor (AR)-mediated overexpression of ERG in the prostate cells. Importantly, PCa cells overexpressing ERG are dependent on ERG activity for survival, further highlighting its therapeutic potential. Here, we review the current understanding of the role of ERG and its partners in PCa. We discuss the strategies developed in recent years to inhibit ERG activity, the current therapeutic utility of ERG fusion detection in PCa patients, and the possible future approaches to target ERG fusion-positive tumors.

New Selective Inhibitors of ERG Positive Prostate Cancer: ERGi-USU-6 Salt Derivatives

Prostate cancer is among the leading causes of cancer related death of men in the United States. The ERG gene fusion leading to overexpression of near full-length ERG transcript and protein represents most prevalent (50–65%) prostate cancer driver gene alterations. The ERG oncoprotein overexpression persists in approximately 35% of metastatic castration resistant prostate cancers. Due to the emergence of eventual refractoriness to second- and third-generation androgen axis-based inhibitors, there remains a pressing need to develop drugs targeting other validated prostate cancer drivers such as ERG. Here we report the new and more potent ERG inhibitor ERGi-USU-6 developed by structure–activity studies from the parental ERGi-USU. We have developed an improved procedure for the synthesis of ERGi-USU-6 and identified a salt formulation that further improves its activity in biological assays for selective targeting of ERG harboring prostate cancer cells.

Systematic Evaluation for the Influences of the SOX17/Notch Receptor Family Members on Reversing Enzalutamide Resistance in Castration-Resistant Prostate Cancer Cells

The treatment of castration-resistant prostate cancer (CRPC) remains challenging due to the failure of androgen deprivation therapy (ADT); hence the search for other molecular therapeutic targets besides androgen receptor signaling is ongoing. This study systematically investigated the expression of SOX17 and Notch receptors in CRPC tissues and cells in vitro, showing that consistent clinical CRPC, SOX17/Notch1, and Notch4 were responsible for enzalutamide resistance in CRPC cells. The γ secretase inhibitors, BMS-708163, GSI-IX, PF-3084014, and RO4929097 abrogated the enzalutamide resistance by inhibiting Notch1 or/and Notch4 in vitro, with GSI-IX and RO4929097 being more effective than BMS-708163 and PF-3084014 in reliving bone metastasis in vivo. In conclusion, the Notch1 and Notch4 inhibitors GSI-IX and RO4929097 are promising therapeutic agents for the treatment of CRPC.

Targeting treatment options for castration-resistant prostate cancer

Prostate cancer (PCa) is the most commonly diagnosed solid tumor and the second leading cause of cancer-related deaths in U.S. men in 2020. Androgen-deprivation therapy (ADT) is the standard of care for metastatic PCa. Unfortunately, PCa relapse often occurs one to two years after initiation of ADT, resulting in the development of castration-resistant PCa (CRPCa), a lethal disease. While several anticancer agents such as docetaxel, abiraterone acetate, and enzalutamide are currently utilized to extend a patient's life after development of CRPCa, patients will eventually succumb to the disease. Hence, while targeting androgen signaling and utilization of docetaxel remain the most crucial agents for many of these combinations, many studies are attempting to exploit other vulnerabilities of PCa cells, such as inhibition of key survival proteins, anti-angiogenesis agents, and immunotherapies. This review will focus on discussing recent advances on targeting therapy. Several novel small molecules will also be discussed.

TERF1 downregulation promotes the migration and invasion of the PC3 prostate cancer cell line as a target of miR‑155

Telomeric repeat binding factor 1 (TERF1) has been identified as a tumor suppressor gene in numerous types of human cancer. However, the expression of TERF1 and its mechanism in prostate cancer (PCa) remains unclear. The present study aimed to explore the expression and functions of TERF1 in PCa. The UALCAN database was used to analyze the differential expression of TERF1 between normal prostate tissue and primary PCa tissue. Cell apoptosis was analyzed by Annexin V/propidium iodide staining, and wound healing and Transwell assays were used to detect the cell migration and invasion abilities, respectively. The cell viability was analyzed using an MTT assay. Reverse transcription-quantitative PCR and western blotting were used to analyze the mRNA and protein expression levels, respectively, of epithelial-mesenchymal transition (EMT) markers following TERF1 knockdown in the PC3 cell line. A dual luciferase reporter assay was used to verify the association between TERF1 and microRNA (miR)-155 predicted by bioinformatics analysis. Rescue experiments were performed to determine the role of the miR-155/TERF1 axis in regulating the cellular behaviors of PCa. The results demonstrated that the expression levels of TERF1 in the primary prostate tumors were significantly downregulated compared with in prostate normal tissue. TERF1 silencing was discovered to significantly promote cell viability, migration and invasion, while suppressing cell apoptosis. The impact of TERF1 on PC3 cells was suggested to occur through the EMT pathway. TERF1 was confirmed to be the direct target of miR-155. The overexpression of miR-155 promoted the viability, migration and invasion, while suppressing the apoptosis of the PC3 cell line, while the knockdown of miR-155 in PC3 cells achieved the opposite trends. In addition, TERF1 overexpression reversed the promotive effects of upregulated miR-155 expression levels on the migration and apoptosis of PC3 cells. On the contrary, the knockdown of TERF1 reversed the migration and apoptosis abilities of the downregulated miR-155 expression levels on the cellular behaviors of PC3 cells. In conclusion, TERF1, as a direct target of miR-155, was discovered to be significantly downregulated in PCa, which was suggested to promote the migration and invasion of PCa via the EMT pathway.

Top Notch Targeting Strategies in Cancer: A Detailed Overview of Recent Insights and Current Perspectives

Evolutionarily conserved Notch plays a critical role in embryonic development and cellular self-renewal. It has both tumour suppressor and oncogenic activity, the latter of which is widely described. Notch-activating mutations are associated with haematological malignancies and several solid tumours including breast, lung and adenoid cystic carcinoma. Moreover, upregulation of Notch receptors and ligands and aberrant Notch signalling is frequently observed in cancer. It is involved in cancer hallmarks including proliferation, survival, migration, angiogenesis, cancer stem cell renewal, metastasis and drug resistance. It is a key component of cell-to-cell interactions between cancer cells and cells of the tumour microenvironment, such as endothelial cells, immune cells and fibroblasts. Notch displays diverse crosstalk with many other oncogenic signalling pathways, and may drive acquired resistance to targeted therapies as well as resistance to standard chemo/radiation therapy. The past 10 years have seen the emergence of different classes of drugs therapeutically targeting Notch including receptor/ligand antibodies, gamma secretase inhibitors (GSI) and most recently, the development of Notch transcription complex inhibitors. It is an exciting time for Notch research with over 70 cancer clinical trials registered and the first-ever Phase III trial of a Notch GSI, nirogacestat, currently at the recruitment stage.

Notch signalling is a potential resistance mechanism of progenitor cells within patient-derived prostate cultures following ROS-inducing treatments

Low Temperature Plasma (LTP) generates reactive oxygen and nitrogen species, causing cell death, similarly to radiation. Radiation resistance results in tumour recurrence, however mechanisms of LTP resistance are unknown. LTP was applied to patient-derived prostate epithelial cells and gene expression assessed. A typical global oxidative response (AP-1 and Nrf2 signalling) was induced, whereas Notch signalling was activated exclusively in progenitor cells. Notch inhibition induced expression of prostatic acid phosphatase (PAP), a marker of prostate epithelial cell differentiation, whilst reducing colony forming ability and preventing tumour formation. Therefore, if LTP is to be progressed as a novel treatment for prostate cancer, combination treatments should be considered in the context of cellular heterogeneity and existence of cell type-specific resistance mechanisms.

Second-Generation Antiandrogens: From Discovery to Standard of Care in Castration Resistant Prostate Cancer

Prostate cancer is the most commonly diagnosed cancer affecting men in the United States. The prostate is a hormone-dependent gland in which androgen hormones testosterone and dihydrotestosterone bind to and activate the androgen receptor, initiating nuclear translocation of androgen receptor and a subsequent signaling cascade. Due to the androgen dependency of the prostate, androgen deprivation therapies have emerged as first line treatment for aggressive prostate cancer. Such therapies are effective until the point at which prostate cancer, through a variety of mechanisms including but not limited to generation of ligand-independent androgen receptor splice variants, or intratumoral androgen production, overcome hormone deprivation. These cancers are androgen ablation resistant, clinically termed castration resistant prostate cancer (CRPC) and remain incurable. First-generation antiandrogens established androgen receptor blockade as a therapeutic strategy, but these therapies do not completely block androgen receptor activity. Efficacy and potency have been improved by the development of second-generation antiandrogen therapies, which remain the standard of care for patients with CRPC. Four second-generation anti-androgens are currently approved by the Food and Drug Administration (FDA); abiraterone acetate, enzalutamide, and recently approved apalutamide and darolutamide. This review is intended to provide a thorough overview of FDA approved second-generation antiandrogen discovery, treatment application, strategies for combination therapy to overcome resistance, and an insight for the potential future approaches for therapeutic inhibition of androgen receptor.

Cellular and Molecular Mechanisms Underlying Prostate Cancer Development: Therapeutic Implications

Prostate cancer is the most frequent nonskin cancer and second most common cause of cancer-related deaths in man. Prostate cancer is a clinically heterogeneous disease with many patients exhibiting an aggressive disease with progression, metastasis, and other patients showing an indolent disease with low tendency to progression. Three stages of development of human prostate tumors have been identified: intraepithelial neoplasia, adenocarcinoma androgen-dependent, and adenocarcinoma androgen-independent or castration-resistant. Advances in molecular technologies have provided a very rapid progress in our understanding of the genomic events responsible for the initial development and progression of prostate cancer. These studies have shown that prostate cancer genome displays a relatively low mutation rate compared with other cancers and few chromosomal loss or gains. The ensemble of these molecular studies has led to suggest the existence of two main molecular groups of prostate cancers: one characterized by the presence of ERG rearrangements (~50% of prostate cancers harbor recurrent gene fusions involving ETS transcription factors, fusing the 5' untranslated region of the androgen-regulated gene TMPRSS2 to nearly the coding sequence of the ETS family transcription factor ERG) and features of chemoplexy (complex gene rearrangements developing from a coordinated and simultaneous molecular event), and a second one characterized by the absence of ERG rearrangements and by the frequent mutations in the E3 ubiquitin ligase adapter SPOP and/or deletion of CDH1, a chromatin remodeling factor, and interchromosomal rearrangements and SPOP mutations are early events during prostate cancer development. During disease progression, genomic and epigenomic abnormalities accrued and converged on prostate cancer pathways, leading to a highly heterogeneous transcriptomic landscape, characterized by a hyperactive androgen receptor signaling axis.

Clonal Evolution and Epithelial Plasticity in the Emergence of AR-Independent Prostate Carcinoma

In spite of an initial clinical response to androgen deprivation therapy (ADT), the majority of prostate cancer patients eventually develop castration-resistant prostate cancer (CRPC). Recent studies have highlighted the role of epithelial plasticity, including transdifferentiation and epithelial-to-mesenchymal transition (EMT), in the development of AR pathway-negative CRPC, a form of the disease that has increased in incidence after the introduction of potent AR inhibitors. In this review, we will discuss the switches between different cell fates that occur in response to AR blockade or acquisition of specific oncogenic mutations, such as those in TP53 and RB1, during the evolution to CRPC. We highlight the urgent need to dissect the mechanistic underpinnings of these transitions and identify novel vulnerabilities that can be targeted therapeutically.

ERG Tumor Type is Less Frequent in High Grade and High Stage Prostate Cancers of Chinese Men

Background: The incidence of prostatic adenocarcinoma has been rapidly increasing among Chinese men. This alarming trend prompted evaluations of early causal genomic alterations known to drive prostate tumorigenesis. Recurrent activation of the ETS-Related Gene (ERG) by genomic rearrangements is the most recognized early event in prostate cancer. Following the initial detection of ERG rearrangement at gene expression and genomic and levels, development of diagnostic quality antibodies against ERG oncoprotein have streamlined the rapid assessment of ERG frequencies world-wide. Unexpectedly, these studies revealed highest frequencies of ERG among Caucasian descents, lower frequencies among African Americans and even lower prevalence of ERG among Asian men.

Objective: To asses in a prospective study ERG frequencies, clinico-pathological and prognostic associations of ERG among prostate cancer patients of the Dalian region of Northeast China, by an established immunohistochemical procedure that have been used in studies world-wide.

Methods: Formalin fixed paraffin embedded specimens donated by patients (N=50) diagnosed with prostatic adenocarcinoma who underwent transurethral resection of the prostate (TURP) between 2007 and 2012 were evaluated for ERG by immunohistochemistry.

Results: Of the 50 cases, 13/50 (26.0%) tumors were positive for ERG. In all cases, normal prostatic epithelial were ERG negative. ERG was more frequently detected in the lower Gleason score (≤7) and low T-stage. Consistent with reports from Asian countries the results of our study shows lower overall frequencies of ERG positive tumors when compared to reports from Western countries.

Conclusion: The intriguing association of even lower ERG frequencies with high Gleason scores and higher T-stages provides impetus for current driver gene discoveries focused on the predominantly ERG negative prostate cancers of Asian men.

Targeted Notch1 inhibition with a Notch1 antibody, OMP-A2G1, decreases tumor growth in two murine models of prostate cancer in association with differing patterns of DNA damage response gene expression

Notch plays a protumorigenic role in many cancers including prostate cancer (PCa). Global notch inhibition of multiple Notch family members using γ-secretase inhibitors has shown efficacy in suppressing PCa growth in murine models. However, global Notch inhibition is associated with marked toxicity due to the widespread function of many different Notch family members in normal cell physiology. Accordingly, in the current study, we explored if specific inhibition of Notch1 would effectively inhibit PCa growth in a murine model. The androgen-dependent VCaP and androgen-independent DU145 cell lines were injected subcutaneously into mice. The mice were treated with either control antibody 1B7.11, anti-Notch1 antibody (OMP-A2G1), docetaxel or the combination of OMP-A2G1 and docetaxel. Tumor growth was measured using calipers. At the end of the study, tumors were assessed for proliferative response, apoptotic response, Notch target gene expression, and DNA damage response (DDR) expression. OMP-A2G1 alone inhibited tumor growth of both PCa cell lines to a greater extent than docetaxel alone. There was no additive or synergistic effect of OMP-A2G1 and docetaxel. The primary toxicity was weight loss that was controlled with dietary supplementation. Proliferation and apoptosis were affected differentially in the two cell lines. OMP-A2G1 increased expression of the DDR gene GADD45α in VCaP cells but downregulated GADD45α in Du145 cells. Taken together, these data show that Notch1 inhibition decreases PCa xenograft growth but does so through different mechanisms in the androgen-dependent VCaP cell line vs the androgen-independent DU145 cell line. These results provide a rationale for further exploration of targeted Notch inhibition for therapy of PCa.

Transcriptional Reprogramming and Novel Therapeutic Approaches for Targeting Prostate Cancer Stem Cells

Prostate cancer is the most common malignancy in men and the second cause of cancer-related deaths in western countries. Despite the progress in the treatment of localized prostate cancer, there is still lack of effective therapies for the advanced forms of the disease. Most patients with advanced prostate cancer become resistant to androgen deprivation therapy (ADT), which remains the main therapeutic option in this setting, and progress to lethal metastatic castration-resistant prostate cancer (mCRPC). Current therapies for prostate cancer preferentially target proliferating, partially differentiated, and AR-dependent cancer cells that constitute the bulk of the tumor mass. However, the subpopulation of tumor-initiating or tumor-propagating stem-like cancer cells is virtually resistant to the standard treatments causing tumor relapse at the primary or metastatic sites. Understanding the pathways controlling the establishment, expansion and maintenance of the cancer stem cell (CSC) subpopulation is an important step toward the development of more effective treatment for prostate cancer, which might enable ablation or exhaustion of CSCs and prevent treatment resistance and disease recurrence. In this review, we focus on the impact of transcriptional regulators on phenotypic reprogramming of prostate CSCs and provide examples supporting the possibility of inhibiting maintenance and expansion of the CSC pool in human prostate cancer along with the currently available methodological approaches. Transcription factors are key elements for instructing specific transcriptional programs and inducing CSC-associated phenotypic changes implicated in disease progression and treatment resistance. Recent studies have shown that interfering with these processes causes exhaustion of CSCs with loss of self-renewal and tumorigenic capability in prostate cancer models. Targeting key transcriptional regulators in prostate CSCs is a valid therapeutic strategy waiting to be tested in clinical trials.

Loss of Notch1 Activity Inhibits Prostate Cancer Growth and Metastasis and Sensitizes Prostate Cancer Cells to Antiandrogen Therapies

Prostate cancer remains among the leading causes of cancer-related deaths in men. Patients with aggressive disease typically undergo hormone deprivation therapy. Although treatment is initially very successful, these men commonly progress to lethal, castration-resistant prostate cancer (CRPC) in 2 to 3 years. Standard therapies for CRPC include second-generation antiandrogens, which prolong patient lifespan by only several months. It is imperative to advance our understanding of the mechanisms leading to resistance to identify new therapies for aggressive prostate cancer. This study identifies Notch1 as a therapeutic target in prostate cancer. Loss of NOTCH1 in aggressive prostate cancer cells decreases proliferation, invasion, and tumorsphere formation. Therapeutic inhibition of Notch1 activity with gamma secretase inhibitors RO4929097 or DAPT in prostate cancer cells further results in decreased proliferative abilities. Loss of NOTCH1 and treatment of immunocompromised mice bearing prostate cancer xenografts with RO4929097 display significantly impaired tumor growth. Loss of NOTCH1 additionally decreased metastatic potential of prostate cancer cells in invasion assays in vitro as well as in vivo experiments. Moreover, treatment with gamma secretase inhibitors or NOTCH1 gene deletion synergized with antiandrogen therapies, enzalutamide or abiraterone, to decrease the growth of prostate cancer cells. Combination of gamma secretase inhibitors with abiraterone significantly inhibited cell migration and invasion, while combination with enzalutamide reversed enzalutamide-induced migration and invasion. These collective findings suggest loss of NOTCH1 delays growth of CRPC and inhibits metastasis, and inhibition of Notch1 activation in conjunction with second-generation antiandrogen therapies could delay growth and progression of prostate cancer.

NOTCH signaling is activated in and contributes to resistance in enzalutamide-resistant prostate cancer cells

Prostate cancer is the second leading cause of cancer death among men in the United States. The androgen receptor (AR) antagonist enzalutamide is a Food and Drug Administration-approved drug for treatment of patients with late-stage prostate cancer and is currently under clinical study for early-stage prostate cancer treatment. After a short positive response period, tumors will develop drug resistance. In this study using RNA-Seq and bioinformatics analyses, we observed that NOTCH signaling is a deregulated pathway in enzalutamide-resistant cells. NOTCH2 and c-MYC gene expression positively correlated with AR expression in samples from patient with hormone refractory disease in which AR expression levels correspond to those typically observed in enzalutamide resistance. Cleaved NOTCH1, HES1 (Hes family BHLH transcription factor 1), and c-MYC protein expression levels are elevated in two enzalutamide-resistant cell lines, MR49F and C4-2R, indicating NOTCH signaling activation. Moreover, inhibition of the overexpressed ADAM metallopeptidase domain 10 (ADAM10) in the resistant cells induces an exclusive reduction in cleaved NOTCH1 expression. Furthermore, exposure of enzalutamide-resistant cells to both PF-03084014 and enzalutamide increased cell death, decreased colony formation ability, and resensitized cells to enzalutamide. Knockdown of NOTCH1 in C4-2R increased enzalutamide sensitivity by decreasing cell proliferation and increasing cleaved PARP expression. In a 22RV1 xenograft model, PF-03084014 and enzalutamide decreased tumor growth through reducing cell proliferation and increasing apoptosis. These results indicate that NOTCH1 signaling may contribute to enzalutamide resistance in prostate cancer, and inhibition of NOTCH signaling can resensitize resistant cells to enzalutamide.

Recent advances in prostate cancer research: large-scale genomic analyses reveal novel driver mutations and DNA repair defects

Prostate cancer (PCa) is a disease of mutated and misregulated genes. However, primary prostate tumors have relatively few mutations, and only three genes ( ERG, PTEN, and SPOP) are recurrently mutated in more than 10% of primary tumors. On the other hand, metastatic castration-resistant tumors have more mutations, but, with the exception of the androgen receptor gene ( AR), no single gene is altered in more than half of tumors. Structural genomic rearrangements are common, including ERG fusions, copy gains involving the MYC locus, and copy losses containing PTEN. Overall, instead of being associated with a single dominant driver event, prostate tumors display various combinations of modifications in oncogenes and tumor suppressors. This review takes a broad look at the recent advances in PCa research, including understanding the genetic alterations that drive the disease and how specific mutations can sensitize tumors to potential therapies. We begin with an overview of the genomic landscape of primary and metastatic PCa, enabled by recent large-scale sequencing efforts. Advances in three-dimensional cell culture techniques and mouse models for PCa are also discussed, and particular emphasis is placed on the benefits of patient-derived xenograft models. We also review research into understanding how ETS fusions (in particular, TMPRSS2-ERG) and SPOP mutations contribute to tumor initiation. Next, we examine the recent findings on the prevalence of germline DNA repair mutations in about 12% of patients with metastatic disease and their potential benefit from the use of poly(ADP-ribose) polymerase (PARP) inhibitors and immune modulation. Lastly, we discuss the recent increased prevalence of AR-negative tumors (neuroendocrine and double-negative) and the current state of immunotherapy in PCa. AR remains the primary clinical target for PCa therapies; however, it does not act alone, and better understanding of supporting mutations may help guide the development of novel therapeutic strategies.

Identification of a Small Molecule That Selectively Inhibits ERG-Positive Cancer Cell Growth

Oncogenic activation of the ETS-related gene (ERG) by recurrent gene fusions (predominantly TMPRSS2-ERG) is one of the most validated and prevalent genomic alterations present in early stages of prostate cancer. In this study, we screened small-molecule libraries for inhibition of ERG protein in TMPRSS2-ERG harboring VCaP prostate cancer cells using an In-Cell Western Assay with the highly specific ERG-MAb (9FY). Among a subset of promising candidates, 1-[2-Thiazolylazo]-2-naphthol (NSC139021, hereafter ERGi-USU) was identified and further characterized. ERGi-USU selectively inhibited growth of ERG-positive cancer cell lines with minimal effect on normal prostate or endothelial cells or ERG-negative tumor cell lines. Combination of ERGi-USU with enzalutamide showed additive effects in inhibiting growth of VCaP cells. A screen of kinases revealed that ERGi-USU directly bound the ribosomal biogenesis regulator atypical kinase RIOK2 and induced ribosomal stress signature. In vivo, ERGi-USU treatment inhibited growth of ERG-positive VCaP tumor xenografts with no apparent toxicity. Structure-activity-based derivatives of ERGi-USU recapitulated the ERG-selective activity of the parental compound. Taken together, ERGi-USU acts as a highly selective inhibitor for the growth of ERG-positive cancer cells and has potential for further development of ERG-targeted therapy of prostate cancer and other malignancies.Significance: A highly selective small-molecule inhibitor of ERG, a critical driver of early stages of prostate cancer, will be imperative for prostate cancer therapy. Cancer Res; 78(13); 3659-71. ©2018 AACR.

Oncogenic fusion proteins adopt the insulin-like growth factor signaling pathway

The insulin-like growth factor-1 receptor (IGF1R) has been identified as a potent anti-apoptotic, pro-survival tyrosine kinase-containing receptor. Overexpression of the IGF1R gene constitutes a typical feature of most human cancers. Consistent with these biological roles, cells expressing high levels of IGF1R are expected not to die, a quintessential feature of cancer cells. Tumor specific chromosomal translocations that disrupt the architecture of transcription factors are a common theme in carcinogenesis. Increasing evidence gathered over the past fifteen years demonstrate that this type of genomic rearrangements is common not only among pediatric and hematological malignancies, as classically thought, but may also provide a molecular and cytogenetic foundation for an ever-increasing portion of adult epithelial tumors. In this review article we provide evidence that the mechanism of action of oncogenic fusion proteins associated with both pediatric and adult malignancies involves transactivation of the IGF1R gene, with ensuing increases in IGF1R levels and ligand-mediated receptor phosphorylation. Disrupted transcription factors adopt the IGF1R signaling pathway and elicit their oncogenic activities via activation of this critical regulatory network. Combined targeting of oncogenic fusion proteins along with the IGF1R may constitute a promising therapeutic approach.

Ethnicity and ERG frequency in prostate cancer

Emerging observations emphasize a distinct biology of prostate cancer among men of different ethnicities and races, as demonstrated by remarkable differences in the frequency of ERG oncogenic activation, one of the most common and widely studied prostate cancer driver genes. Worldwide assessment of ERG alterations frequencies show consistent trends, with men of European ancestry having the highest rates of alteration and men of African or Asian ancestries having considerably lower alteration rates. However, data must be interpreted cautiously, owing to variations in assay platforms and specimen types, as well as ethnic and geographical classifications. Many opportunities and challenges remain in assessing cancer-associated molecular alterations at a global level, and these need to be addressed in order to realize the true potential of precision medicine for all cancer patients.