Inhibits Prostate Tumor Growth Research Articles

Manzamine A reduces androgen receptor transcription and synthesis by blocking E2F8-DNA interactions and effectively inhibits prostate tumor growth in mice.

The androgen receptor (AR) is the main driver in the development of castration-resistant prostate cancer, where the emergence of AR splice variants leads to treatment-resistant disease. Through detailed molecular studies of the marine alkaloid manzamine A (MA), we identified transcription factor E2F8 as a previously unknown regulator of AR transcription that prevents AR synthesis in prostate cancer cells. MA significantly inhibited the growth of various prostate cancer cell lines and was highly effective in inhibiting xenograft tumor growth in mice without any pathophysiological perturbations in major organs. MA suppressed the full-length AR (AR-FL), its spliced variant AR-V7, and the AR-regulated prostate-specific antigen (PSA; also known as KLK3) and human kallikrein 2 (hK2; also known as KLK2) genes. RNA sequencing (RNA-seq) analysis and protein modeling studies revealed E2F8 interactions with DNA as a potential novel target of MA, suppressing AR transcription and its synthesis. This novel mechanism of blocking AR biogenesis via E2F8 may provide an opportunity to control therapy-resistant prostate cancer over the currently used AR antagonists designed to target different parts of the AR gene.

Abstract 5359: Targeted engineering mRNA 3′UTR length enhances immunotherapy response in prostate cancer

Abstract Background: Global mRNA 3′untranslated region (3′UTR) shortening through alternative polyadenylation (APA) has been widely observed in most cancers; however, it has not been demonstrated whether targeted interference of specific oncogenic mRNA 3′UTR lengths can inhibit tumor growth and potentiate immunotherapy response in prostate cancer. Methods: DaPars algorithm was applied for de novo identification of dynamic alternative polyadenylation (APA) during prostate cancer progression to the lethal phase; 3′UTR polyadenylation site (PAS) locations and usages were identified by Poly(A)-ClickSeq (PAC-seq) and 3′RACE; APA transcripts were quantified by RHAPA assay; a 3′UTR CRISPR/dCas13 Engineering System (3′UTRCES) was developed to manipulate the length of desired 3′UTRs; RIP-qPCR and PAR-CLIP-qPCR assays were used to determine the mechanistic basis of 3′UTRCES in APA editing; RNA-seq was utilized to evaluate the off-target effects; TT3 Lipid-like nanoparticles (LLN) were applied for intratumoral delivery of 3′UTRCES RNA molecules for targeted 3′UTR therapy. Quantitative proteomics and immunoprecipitation assays were conducted to investigate how major histocompatibility complex class I (MHC-I) substrates were recognized by SPSB1-containing ubiquitin ligase complex for degradation; Flow cytometry and T cell cytotoxicity assays were performed to evaluate MHC-I level and killing of tumor cells by antigen-stimulated CD8+ T cells. Results: 3′UTR globally shortens during prostate cancer progression to castration-resistance. Through blocking the proximal PASs, 3′UTRCES efficiently and specifically reverses the 3′UTR shortening of novel APA-linked, clinically-relevant prostate cancer oncogenic mRNAs, such as SPSB1, leading to reduced SPSB1 mRNA translation and prostate cancer cell proliferation. Intratumoral injection of TT3 LLN encapsulating 3′UTRCES RNA molecules effectively and safely inhibits prostate tumor growth in engrafted and transgenic mouse models. Notably, downregulation of SPSB1 protein by 3′UTRCES disrupts the interactions of SPSB1-containing ubiquitin ligase complex, leading to compromised ubiquitination-mediated MHC-I degradation and increased stability and abundance of MHC-I protein. Consistently, 3′UTRCES enhances MHC-I-regulated antigen presentation and thereby augments CD8+ T cell-mediated cytotoxicity, which suggest the potentials of 3′UTRCES to sensitize prostate cancer to immune checkpoint therapies. Importantly, 3′UTR shortening of SPSB1 mRNA is significantly associated with decreased MHC-I expression, reduced cytotoxic T-cell infiltration and activation in castration resistant prostate cancer patients. Conclusions: Our results establish the concept of “3′UTR targeted therapy” for treatment of prostate cancer with broad applications to other cancers and other 3′UTR-related diseases. Citation Format: Furong Huang, Fuwen Yuan, Ya Cui, Lei Li, Kexin Li, Zhifen Cui, Jingyue Yan, Qiang Chen, Christopher Nicchitta, Wenbin Ye, Yuebao Zhang, William Hankey, Jeffrey Everitt, Ming Chen, Jiaoti Huang, Hongyan Wang, Xin Lu, Eric Wagner, Yizhou Dong, Wei Li, Qianben Wang. Targeted engineering mRNA 3′UTR length enhances immunotherapy response in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5359.

DNA Methyltransferase 1 Targeting Using Guadecitabine Inhibits Prostate Cancer Growth by an Apoptosis-Independent Pathway.

Epigenetic alterations such as DNA methylation and histone modifications are implicated in repressing several tumor suppressor genes in prostate cancer progression. In this study, we determined the anti-prostate cancer effect of a small molecule drug guadecitabine (gDEC) that inhibits/depletes the DNA methylation writer DNA methyltransferase 1 (DNMT1). gDEC inhibited prostate cancer cell growth and proliferation in vitro without activating the apoptotic cascade. Molecular studies confirmed DNMT1 depletion and modulated epithelial-mesenchymal transition markers E-cadherin and β-catenin in several prostate cancer cell lines (LNCaP, 22Rv1, and MDA PCa 2b). gDEC treatment also significantly inhibited prostate tumor growth in vivo in mice (22Rv1, MDA PCa 2b, and PC-3 xenografts) without any observed toxicities. gDEC did not impact the expression of androgen receptor (AR) or AR-variant 7 (AR-V7) nor sensitize the prostate cancer cells to the anti-androgen enzalutamide in vitro. In further investigating the mechanism of cytoreduction by gDEC, a PCR array analyses of 84 chromatin modifying enzymes demonstrated upregulation of several lysine-specific methyltransferases (KMTs: KMT2A, KMT2C, KMT2E, KMT2H, KMT5A), confirmed by additional expression analyses in vitro and of harvested xenografts. Moreover, gDEC treatment increased global histone 3 lysine 4 mono-and di-methylation (H3K4me1 and H3K4me2). In sum, gDEC, in addition to directly depleting the corepressor DNMT1, upregulated KMT activating epigenetic enzymes, activating terminal epithelial program activation, and prostate cancer cell cycling exits independent of apoptosis.

Abstract 4246: Synergistic inhibition of prostate tumor growth and progression by the combination of curcumin and ursolic acid in HiMyc mice

Abstract Prostate cancer (PCa) is the second leading cause of cancer death among men in the United States. According to the World Health Organization, approximately one-third of all cancer deaths could be prevented through an increased consumption of natural compounds. Through the use of a two-tiered screening method in PCa cells (depletion of cellular ATP level followed by glutamine uptake) of a phytochemical library, curcumin and ursolic acid were selected for further investigation. Twenty-four hour treatment of LNCaP, 22Rv1 and HMVP2 cells with the combination resulted in significant decreases in expression of members of the miR-17-92 and miR-106b-25 clusters, which are upregulated in PCa and have been shown to be involved in tumorigenesis, cell survival, and metastasis. In the HiMyc mouse model, where mice spontaneously develop primary PCa, supplementing diets with the combination of curcumin (1%) and ursolic acid (0.2%) resulted in significant inhibition of tumor growth and progression compared to diets containing either compound alone. There were no differences in body weight or food consumption in any of the diet groups during the tumor experiment. The current data suggests that the combination of curcumin and ursolic acid synergistically inhibits PCa growth and progression in HiMyc mice, which may be in part due to their effects on microRNA expression. Ongoing studies are further examining the role of specific miRNAs as well as oncogenic signaling pathways potentially involved in the mechanism of synergistic chemopreventive action of this combination. The current data suggest that this novel combination could be a valuable therapeutic option for prevention and/or treatment of PCa. Funding: This work was supported by NIH Grant CA228404. Citation Format: Chelsea A. Friedman, Achinto Saha, John DiGiovanni. Synergistic inhibition of prostate tumor growth and progression by the combination of curcumin and ursolic acid in HiMyc mice. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4246.

CYCLONE 3: A phase 3, randomized, double-blind, placebo-controlled study of abemaciclib in combination with abiraterone plus prednisone in men with high-risk, metastatic, hormone-sensitive prostate cancer (mHSPC).

TPS289 Background: Landmark trials have established a survival benefit for novel hormonal agents (NHA) added to androgen deprivation therapy (ADT) for mHSPC. Yet, there is a significant medical need to expand therapeutic options, especially for pts with high-risk mHSPC who experience poorer outcomes. Abemaciclib is an oral selective inhibitor of cyclin-dependent kinase 4 and 6 (CDK4 & 6) dosed on a continuous schedule, approved for the treatment of node-positive high-risk early-stage and advanced or metastatic HR+, HER2- breast cancer. Analogous to the estrogen receptor signaling pathway in breast cancer, there is evidence that the androgen receptor axis activates CDK4 & 6 to sustain prostate cancer cell proliferation, and upregulation of cyclin D1 is a potential mechanism of resistance to NHA therapy. In preclinical models, abemaciclib induces cell cycle arrest and inhibition of prostate tumor growth. Methods: CYCLONE 3 (NCT05288166) is a global, randomized, double-blind, placebo-controlled study evaluating the addition of abemaciclib to abiraterone+prednisone (AP) in pts with high-risk mHSPC. Approximately 900 pts with high-risk mHSPC defined by ≥4 bone metastasis and/or visceral disease will be randomised in a 1:1 ratio to the AP + abemaciclib or AP + placebo arm. Up to 3 months of ADT prior to randomization is permitted; prior D for mHSPC will be excluded per planned protocol amendment. Pts who have not undergone orchiectomy will continue ADT. Stratification factors are de novo mHSPC and visceral metastases. Primary endpoint is investigator-assessed radiographic progression-free survival (rPFS). Key secondary endpoints include rPFS assessed by blinded independent central review, castration-resistant prostate cancer-free survival, overall survival, time to pain progression, safety and pharmacokinetics. Enrollment is open at approximately 270 sites across 25 countries. Clinical trial information: NCT05288166 .

Targeting KDM1B-dependent miR-215-AR-AGR2-axis promotes sensitivity to enzalutamide-resistant prostate cancer.

Post-translational modifications of histones by histone demethylases plays an important role in the regulation of gene transcription and are implicated in cancers. Castrate resistant prostate cancer (CRPC) is often driven by constitutively active androgen receptor and commonly becomes resistant to established hormonal therapy strategies such as enzalutamide as a result. However, the role of KDM1B involved in next generation anti-enzalutamide resistance and the mechanisms of KDM1B regulation are poorly defined. Here, we show that KDM1B is upregulated and correlated with prostate cancer progression and poor prognosis. Downregulation of miR-215 is correlated with overexpression of KDM1B in enzalutamide-resistant prostate cancer cells, which promotes AR-dependent AGR2 transcription and regulates the sensitivity to next generation AR-targeted therapy. Inhibition of KDM1B significantly inhibits prostate tumor growth and improves enzalutamide treatments through AGR2 suppression. Our studies demonstrate inhibition of KDM1B can offer a viable therapeutic option to overcome enzalutamide resistance in tumors with deregulated miR-215-KDM1B-AR-AGR2 signaling axis.

The Dual Androgen Receptor and Glucocorticoid Receptor Antagonist CB-03-10 as Potential Treatment for Tumors that have Acquired GR-mediated Resistance to AR Blockade.

CB-03-10 (cortexolone 17α-valerate-21-propionate) is a synthetic steroidal compound derived from cortexolone (11-deoxycortisone), an intermediate in cortisol biosynthesis. Characterization of the activity of CB-03-10 and its main related compound CB-03-05 (cortexolone 17α-valerate) included in vitro binding to the androgen and glucocorticoid receptors (AR and GR), antagonism of AR and GR transcriptional activities, and screening for antitumor activity across a selected panel of human prostate and in triple-negative breast cancer cell lines. CB-03-10 cytotoxic activity in these cancer cell lines was in the low micromolar range and was primarily associated with induction of the apoptotic cascade via activation of caspases. The compound's potential for antitumor activity was verified in a murine xenograft model utilizing the AR-positive LNCaP prostate cancer cell line as well as in an orthotopic model utilizing AR-negative/GR-positive MDA-MB-231 breast cancer cell line. Orally administered CB-03-10 inhibited prostate tumor growth and orthotopically implanted breast tumor growth in these mice and maintained body weight, as compared with vehicle-treated mice. On the basis of AR/GR binding affinities, antagonism of androgen and glucocorticoid-dependent transcriptional activities, and AR/GR mRNA and protein expression, the mechanism of tumor growth suppression is related to AR and GR antagonist activities. Importantly, these compounds lack biologically relevant AR/GR agonist activities. Overall, these preclinical findings support the selection of CB-03-10 for further development as an anticancer agent in cases where resistance to AR-targeted therapy or chemotherapy, via upregulation of GR activity, continues to limit the efficacy and duration of clinical benefit with these interventions.

An Aptamer for Broad Cancer Targeting and Therapy.

Simple SummaryRecent efforts to improve chemotherapy’s antitumor effects have increasingly focused on targeted therapies, where the drug is modified with an agent able to specifically deliver it to the tumor while limiting its accumulation in normal tissue. Aptamers, comprised of short pieces of RNA or DNA, are ideal for this type of drug targeting due in part to their ease of chemical synthesis. The E3 aptamer was previously conjugated to highly toxic chemotherapeutics and shown to target and treat prostate tumors. Here, we show that E3 is not limited to prostate cancer targeting but appears to broadly target cancer cells. E3 highly toxic drug conjugates also efficiently kill a broad range of cancer types, and E3 targets tumors that closely model patient tumors. Thus, the E3 aptamer appears to be a general agent for specific delivery of chemotherapy to tumors and should improve antitumor treatment while reducing unwanted toxicities in other tissues. Recent advances in chemotherapy treatments are increasingly targeted therapies, with the drug conjugated to an antibody able to deliver it directly to the tumor. As high-affinity chemical ligands that are much smaller in size, aptamers are ideal for this type of drug targeting. Aptamer-highly toxic drug conjugates (ApTDCs) based on the E3 aptamer, selected on prostate cancer cells, target and inhibit prostate tumor growth in vivo. Here, we observe that E3 also broadly targets numerous other cancer types, apparently representing a universal aptamer for cancer targeting. Accordingly, ApTDCs formed by conjugation of E3 to the drugs monomethyl auristatin E (MMAE) or monomethyl auristatin F (MMAF) efficiently target and kill a range of different cancer cells. Notably, this targeting extends to both patient-derived explant (PDX) cancer cell lines and tumors, with the E3 MMAE and MMAF conjugates inhibiting PDX cell growth in vitro and with the E3 aptamer targeting PDX colorectal tumors in vivo.

Neuronal calcitonin gene-related peptide promotes prostate tumor growth in the bone microenvironment

Advanced stage of prostate cancer cells preferentially metastasizes to varying bones of prostate cancer patients, resulting in incurable disease with poor prognosis and limited therapeutical treatment options. Calcitonin gene-related peptide (CGRP), a neuropeptide produced by prostate gland, is known to play a pivotal role in facilitating tumor growth and metastasis of numerous human cancers. In this study, we aim to investigate the clinical relevance of CGRP in prostate cancer patients and the effects of CGRP and CGRP antagonists on prostate tumor growth in the mouse model. The prostate tumor-bearing mice were received either CGRP or CGRP antagonist treatment, and the tumor growth was monitored by quantification of luminescence intensities. We found that the CGRP+ nerve fiber density and serum CGRP levels were substantially upregulated in the bone or serum specimens from advanced prostate cancer patients as well as in prostate tumor-bearing mice. Administration of CGRP promoted, whereas treatment of CGRP antagonists inhibited prostate tumor growth in the femurs of mice. In addition, CGRP treatment activated extracellular signal-regulated kinases (ERKs)/ Signal transducer and activator of transcription 3 (STAT3) signaling in prostate cancer cells. Targeting CGRP may serve as a potential therapeutic strategy for advanced prostate cancer patients.

‘MUSCADINE GRAPE SKIN EXTRACT INHIBITS ANDROGEN‐INDEPENDENT PROSTATE CANCER CELL GROWTH, INDUCING CELL‐CYCLE ARREST, AND DECREASING MIGRATION BY TARGETING HEAT SHOCK PROTEIN 40

Previously we demonstrated that muscadine grape skin extract (MSKE), a natural product, significantly inhibited androgen‐responsive prostate cancer cell growth by inducing apoptosis through the targeting of survival pathways. However, the therapeutic effect of MSKE on more aggressive androgen‐independent prostate cancer remains unknown. This study examined the effects of MSKE treatment in metastatic prostate cancer using complementary PC‐3 cells and xenograft model. MSKE significantly inhibited PC‐3 human prostate cancer cell tumor growth in vitro and in vivo. The growth‐inhibitory effect of MSKE appeared to be through the induction of cell‐cycle arrest. This induction was accompanied by a reduction in the protein expression of Hsp40 and cell‐cycle regulation proteins, cyclin D1 and NF‐kBp65. In addition, MSKE induced p21 expression independent of wild‐type p53 induced protein expression. Moreover, we demonstrate that MSKE significantly inhibited cell migration in PC‐3 prostate cancer cells. Overall, these results demonstrate that MSKE inhibits prostate tumor growth and migration, and induces cell‐cycle arrest by targeting Hsp40 and proteins involved in cell‐cycle regulation and proliferation. This suggests that MSKE may also be explored either as a neo‐adjuvant or therapeutic for castration resistant prostate cancer.

Arctigenin inhibits prostate tumor growth in high-fat diet fed mice through dual actions on adipose tissue and tumor

This study investigated the inhibitory effect of arctigenin, a novel anti-inflammatory lignan, on prostate cancer in obese conditions both in vitro and in vivo. In vitro obese models were established by co-culture of mouse adipocytes 3T3-L1 with androgen-sensitive LNCaP human prostate cancer cells, or by culturing LNCaP cells in adipocytes-conditioned medium. Arctigenin significantly inhibited LNCaP proliferation, along with decreased androgen receptor (AR) and increased Nkx3.1 cellular expression. Male severe combined immunodeficiency mice were subcutaneously implanted with human prostate cancer LAPC-4 xenograft tumors for in vivo study. Mice were fed high-fat (HF) diet and orally given arctigenin at 50 mg/kg body weight daily or vehicle control for 6 weeks. Tumor bearing HF control mice showed a significant increase in serum free fatty acids (FFAs) and decrease in subcutaneous/peritoneal fat depots compared to non-tumor bearing control mice. Arctigenin intervention significantly reduced tumor growth by 45%, associated with decreased circulating FFAs and adipokines/cytokines including IGF-1, VEGF, and MCP-1, along with decreased AR, Ki67, and microvessel density and increased Nkx3.1 expression in tumors. These results indicate the strong ability of arctigenin to co-target obesity and tumor itself in inhibition of prostate tumor growth at a lower concentration compared to most phytochemicals.

MiRNA-29b Inhibits Prostate Tumor Growth and Induces Apoptosis by Increasing Bim Expression

Prostate cancer is one of the most common cancers among men. Currently available therapies improve patient survival against local prostate cancer but have shown severe side effects. Advanced prostate cancer is still incurable. Studies have suggested the involvement of non-coding RNAs, especially micro-RNAs (miRNAs), in the regulation of multiple cellular events in cancer and thus several clinical trials are ongoing using miRNAs mimics or inhibitors. We previously demonstrated that miRNA-29b-3p (miR-29b) was downregulated in prostate cancer and that the overexpression of miR-29b limited prostate cancer metastasis. However, the therapeutic potential of the miR-29b against prostate cancer remains unknown. Here, we evaluated the therapeutic role of miR-29b in in vivo prostate tumors in a mouse model. Intratumoral injection of mimic miR-29b significantly inhibited prostate cancer xenograft tumor growth in nude mice. Subsequent study demonstrated that the overexpression of miR-29b reduced prostate cancer cell PC3 proliferation in a time dependent manner and induced cell death. Mechanistic study using a cancer pathway specific transcriptomic array revealed a significant overexpression of the pro-apoptotic gene BCL2L11 (Bim) in the miR-29b overexpressed PC3 cells, which was further verified in PC3 cells overexpressing miR-29b. We also observed a significant induction of Bim protein in miR-29b treated xenograft tumors. The induction of cytosolic accumulation of cytochrome C and PARP cleavage in miR-29b overexpressed PC3 cells was observed. Thus, our results suggest that miR-29b can be used as a potential molecule for prostate cancer therapy.

Mechanosensitive ion channel Piezo1 promotes prostate cancer development through the activation of the Akt/mTOR pathway and acceleration of cell cycle.

Prostate cancer is one of the most common types of cancer affecting men worldwide; however, its etiology and pathological mechanisms remain poorly understood. Mechanical stimulation plays a key role in prostate cancer development. Piezo type mechanosensitive ion channel component 1 (Piezo1), which functions as a cell sensor and transducer of mechanical stimuli, may have a crucial role in the development of prostate cancer. In the present study, the expression of the Piezo1 channel was demonstrated to be significantly elevated in prostate cancer cell lines and in human prostate malignant tumor tissues. Downregulation of Piezo1 significantly suppressed the viability, proliferation and migration of prostate cancer cells in vitro, and inhibited prostate tumor growth in vivo. The activation of the Akt/mTOR pathway or acceleration of cell cycle progression from G0/G1 to S phase may downstream consequences of Piezo 1 signal pathway activation. Downregulation of Piezo1 considerably suppressed Ca2+ signal increments, inhibited the phosphorylation of Akt and mTOR and arrested the cell cycle of prostate cancer cells at G0/G1 phase in while inhibiting the activation of CDK4 and cyclin D1. Taken together, these findings suggest that Piezo1 channels have a crucial role in prostate cancer development and may, therefore, be a novel therapeutic target in the treatment of prostate cancer.

Abstract 4391: Disruption of the translation initiation complex by eIF4A mutant inhibits prostate tumor growth in vivo

Abstract Translation initiation in cancer cells is the rate-limiting step of oncogenic mRNAs translation/protein synthesis and is primarily mediated by the eukaryotic translation initiation factor 4 F (eIF4F) complex that consists of three subunits: eIF4E, which binds the cap of mRNA; eIF4A, an RNA helicase implicated in unwinding mRNA structure; and a scaffold protein eIF4G. Our prior crystal structure determination of human eIF4A in complex with Heat 1 domain of eIF4GI (722-999) revealed that eIF4G interacts with both N- and C-terminal domains of human eIF4A (eIF4A1-NTD and eIF4A1-CTD). Utilizing structural information gained from this complex, we generated a series of eIF4A mutants (eIF4A1-NTD: E41K, R45D, Y48A and eIF4A1-CTD: T271A, R324D, D296A/T298A) in order to identify the crucial site(s) of interaction with eIF4G Heat 1 domain. Using in vitro binding studies, we demonstrated that amongst various mutants tested, eIF4A-CTD (eIF4A1R324D) mutant disrupted the eIF4A/eIF4G Heat 1 complex formation, mirroring the binding residue E809K mutant of eIF4G that also interrupted eIF4A/eIF4G Heat 1 interaction. Given that eIF4G has an additional eIF4A-binding site named Heat 2 domain, we further investigated whether eIF4A1R324D mutant is able to disrupt binding to full-length eIF4G protein in vivo. Surprisingly, overexpression of Flag-tagged eIF4A1R324D in prostate cancer cell line blocked interaction with exogenous eIF4G as well as endogenous eIF4G. Taken together, these results strongly suggest that eIF4A1R324 residue plays a crucial role in mediating eIF4A/eIF4G complex formation in vivo. Furthermore, overexpression of eIF4A1R324D mutant significantly blocked oncogene c-myc and Bcl-2 mRNA translation thereby inhibiting prostate tumor growth in vivo. To conclude, our studies provide a previously unexplored strategy to identify small-molecule compounds disrupting eIF4A-eIF4G complex by targeting the pocket spanning eIF4AR324 and its binding site residues on eIF4G for cancer therapy. Citation Format: Puja Singh, Hanyong Chen, Hanxuan Li, Young-In Chi, Bin Liu, Junxuan Lu, Wei Li, Zigang Dong, Yibin Deng. Disruption of the translation initiation complex by eIF4A mutant inhibits prostate tumor growth in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4391.

Abstract 2134: Niraparib combined with abiraterone acetate inhibits the growth of BRCA2wt prostate tumors

Abstract Patients with metastatic prostate cancer may initially respond well to first- and second-generation androgen receptor (AR)-targeted therapies, but many will experience disease progression, indicating a need for alternative therapies. A subset of these patients bears prostate tumors that harbor deleterious mutations in DNA damage repair (DDR) pathway genes, such as BRCA2. These DDR mutations render the tumors sensitive to drugs that inhibit poly (ADP-ribose) [PAR] polymerase-1 (PARP1), inducing synthetic lethality. Studies indicate that there are interactions between AR signaling pathways and DDR pathways in prostate cancer cells, supporting the hypothesis that dual AR/PARP inhibition could inhibit prostate tumor growth more potently than single agents, regardless of the DDR status of the tumor. This hypothesis was tested using well-known human and mouse prostate tumor models that are sensitive to androgen deprivation. Genotyping of the models confirmed that none of them carried homozygous pathogenic mutations in DDR genes, including BRCA1, BRCA2, and ATM. When the cell lines were incubated in vitro with niraparib, a potent and highly selective PARP1/2 inhibitor, PAR formation was significantly inhibited, and there was induction of γH2AX in treated cells, indicating the drug induced DNA double-stranded breaks. In addition, the cytotoxicity IC50 values for niraparib were in the range of 1-10 µM, as expected for cells that are DDRwt. In vivo efficacy studies demonstrated that the VCaP and Myc-CaP tumor models were insensitive or modestly sensitive to single agent treatment with niraparib or abiraterone acetate (AA). In contrast, the combination treatment of niraparib plus AA significantly reduced tumor growth and increased survival (p<0.05) as compared with control or single agent arms. Studies are ongoing to understand the mechanisms of tumor growth control mediated by the combination of these two agents. The results support the hypothesis that prostate tumors may respond to a combination treatment with niraparib, a PARP inhibitor, and AA, an androgen synthesis inhibitor, even in the absence of DDR anomalies. A Phase 3 study is planned to evaluate this hypothesis and the safety and efficacy of this combination in humans. Citation Format: Rajendra N. Damle, Rebecca Hawkins, Jennifer Hosbach, Georges Habineza Ndikuyeze, Jenny Driscoll, Natalie L. Fulton, David Derosa, Anna Hughes, Gerald Chu, Karl Calara-Nielsen, Denis Smirnov, Dong Shen, Linda A. Snyder. Niraparib combined with abiraterone acetate inhibits the growth of BRCA2wt prostate tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2134.

The dark side of IL-1: role in prostate cancer progression

Abstract IL-1 is a pro-inflammatory cytokine essential for host defense against pathogens, but its role in cancer progression remains understudied. Recently our lab identified the IL-1 pathway as a molecular mechanism responsible for myeloid-driven prostate cancer development. Here, we report that IL-1 signaling in tumor cells drives prostate cancer progression. To identify the contribution of IL-1 signaling in prostate cancer progression, we downregulated expression of IL1R1 (the only known functional receptor for IL-1α/β) using shRNA or Crisr/Cas9 in androgen-sensitive (LNCaP) and androgen-independent (PC-3M) prostate cancer cell lines. We found that IL-1α inhibited expression of androgen receptor in LNCaP while suppression of IL-1 signaling abrogated this effect. The expression of neuron-specific enolase which was shown to be a prognostic marker associated with poor survival outcome was significantly reduced in PC-3M cells lacking IL1R1. Downregulation of IL-1 signaling in cancer cells resulted in significant inhibition of prostate tumor growth while no effect on cell proliferation was detected. We established this phenomenon and found several possible mechanisms underlying it. We found that knocking down of IL1R1 in cancer cells resulted in suppression of mTOR and ACC signaling in tumors. TUNEL staining revealed increased number of apoptotic cells in shIL1R1-PC-3M tumors. Tumors lacking IL1R1 were characterized by impaired vascularization which was accompanied by reduced COX-2, VEGF-A and IL-8 expression. Taken together, our findings indicate that downregulation of IL-1 signaling modifies prostate cancer cell phenotype and suppresses tumor growth.

Muscadine grape skin extract inhibits prostate cancer cells by inducing cell-cycle arrest, and decreasing migration through heat shock protein 40

Previously we demonstrated that muscadine grape skin extract (MSKE), a natural product, significantly inhibited androgen-responsive prostate cancer cell growth by inducing apoptosis through the targeting of survival pathways. However, the therapeutic effect of MSKE on more aggressive androgen-independent prostate cancer remains unknown. This study examined the effects of MSKE treatment in metastatic prostate cancer using complementary PC-3 cells and xenograft model. MSKE significantly inhibited PC-3 human prostate cancer cell tumor growth in vitro and in vivo. The growth-inhibitory effect of MSKE appeared to be through the induction of cell-cycle arrest. This induction was accompanied by a reduction in the protein expression of Hsp40 and cell-cycle regulation proteins, cyclin D1 and NF-kBp65. In addition, MSKE induced p21 expression independent of wild-type p53 induced protein expression. Moreover, we demonstrate that MSKE significantly inhibited cell migration in PC-3 prostate cancer cells. Overall, these results demonstrate that MSKE inhibits prostate tumor growth and migration, and induces cell-cycle arrest by targeting Hsp40 and proteins involved in cell-cycle regulation and proliferation. This suggests that MSKE may also be explored either as a neo-adjuvant or therapeutic for castration resistant prostate cancer.

Proteostasis by STUB1/HSP70 complex controls sensitivity to androgen receptor targeted therapy in advanced prostate cancer

Protein homeostasis (proteostasis) is a potential mechanism that contributes to cancer cell survival and drug resistance. Constitutively active androgen receptor (AR) variants confer anti-androgen resistance in advanced prostate cancer. However, the role of proteostasis involved in next generation anti-androgen resistance and the mechanisms of AR variant regulation are poorly defined. Here we show that the ubiquitin-proteasome-system (UPS) is suppressed in enzalutamide/abiraterone resistant prostate cancer. AR/AR-V7 proteostasis requires the interaction of E3 ubiquitin ligase STUB1 and HSP70 complex. STUB1 disassociates AR/AR-V7 from HSP70, leading to AR/AR-V7 ubiquitination and degradation. Inhibition of HSP70 significantly inhibits prostate tumor growth and improves enzalutamide/abiraterone treatments through AR/AR-V7 suppression. Clinically, HSP70 expression is upregulated and correlated with AR/AR-V7 levels in high Gleason score prostate tumors. Our results reveal a novel mechanism of anti-androgen resistance via UPS alteration which could be targeted through inhibition of HSP70 to reduce AR-V7 expression and overcome resistance to AR-targeted therapies.

Abstract 5777: Ormeloxifene augments the therapeutic response of enzalutamide via targeting androgen receptor splice variant 7

Abstract Enzalutamide (ENZ) is a second generation anti-androgen drug in clinical use for the treatment of advanced prostate cancer (PrCa). Use of ENZ has some limitations because of its toxic side effect and developing chemoresistance. It has been shown that expression of androgen receptor splice variant 7 (ARV7) in advanced PrCa is involved in ENZ therapy resistance. It is noteworthy that ENZ does not target AR splice variants because these lack the ligand binding domain of AR. Thus, identification of non-toxic agents which can target ARV7 can improve the enzalutamide therapy response and could be used for the management of advanced stage PrCa. Herein, we identified a clinically approved selective estrogen receptor modulator ormeloxifene (ORM), which augments ENZ therapy response via suppression of ARV7 expression in PrCa cells. We used androgen-independent human prostate cancer cells (22Rv1), which express ARV7 as a model system to study the effect of ORM alone or in combination with ENZ. ORM treatment showed a more potent effect in 22Rv1 cells as compared to ENZ alone. ORM treatment also sensitized the effects of ENZ in 22Rv1 cells. ORM treatment effectively inhibited colony formation ability of 22Rv1 cells; this effect was additive in combination with ENZ. We next performed Western blot analysis of ARV7 in control and ORM treated 22Rv1 cells. ORM effectively inhibited the protein level of AR V7 at 12 hrs post-treatment in 22Rv1 cells; however, no effect was observed with the treatment of ENZ. ORM treatment also inhibited the promoter activity of the AR target gene PSA as determined by luciferase assay. To translate these finding to an in vivo model system, we investigated the chemo-sensitization potential of ORM in a 22Rv1 cell-derived xenograft mouse model. ORM treatment (200 µg/mouse three times a week for 8 consecutive weeks) significantly (P<0.01) inhibited prostate tumor growth. However, we did not observe any significant tumor growth inhibition with oral administration of ENZ (10 mg/kg body weight). ORM treatment improved the therapeutic response of ENZ in 22Rv1 cells derived xenograft mouse model as monitored by significant (P<0.01) decreases in both tumor volume and tumor weight as compared to ENZ treatment alone. Our findings indicate that ORM alone or in combination with ENZ could be an effective therapeutic approach for the treatment of advanced PrCa. Citation Format: Bilal B. Hafeez, Andrew E. Massey, Vivek K. Kashyap, Mohammed Sikander, Advit Shetty, Mehdi Chaib, Hassan Mandil, Shabnam Malik, Mohan M. Yallapu, Meena Jaggi, Subhash C. Chauhan. Ormeloxifene augments the therapeutic response of enzalutamide via targeting androgen receptor splice variant 7 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5777.

CRISPR-Mediated Reactivation of DKK3 Expression Attenuates TGF-β Signaling in Prostate Cancer.

The DKK3 gene encodes a secreted protein, Dkk-3, that inhibits prostate tumor growth and metastasis. DKK3 is downregulated by promoter methylation in many types of cancer, including prostate cancer. Gene silencing studies have shown that Dkk-3 maintains normal prostate epithelial cell homeostasis by limiting TGF-β/Smad signaling. While ectopic expression of Dkk-3 leads to prostate cancer cell apoptosis, it is unclear if Dkk-3 has a physiological role in cancer cells. Here, we show that treatment of PC3 prostate cancer cells with the DNA methyltransferase (DNMT) inhibitor decitabine demethylates the DKK3 promoter, induces DKK3 expression, and inhibits TGF-β/Smad-dependent transcriptional activity. Direct induction of DKK3 expression using CRISPR-dCas9-VPR also inhibited TGF-β/Smad-dependent transcription and attenuated PC3 cell migration and proliferation. These effects were not observed in C4-2B cells, which do not respond to TGF-β. TGF-β signals can regulate gene expression directly via SMAD proteins and indirectly by increasing DNMT expression, leading to promoter methylation. Analysis of genes downregulated by promoter methylation and predicted to be regulated by TGF-β found that DKK3 induction increased expression of PTGS2, which encodes cyclooxygenase-2. Together, these observations provide support for using CRISPR-mediated induction of DKK3 as a potential therapeutic approach for prostate cancer and highlight complexities in Dkk-3 regulation of TGF-β signaling.