Target In Advanced Prostate Cancer Research Articles

Abstract 470: AR-induced miRNA124-3p.2 suppresses the metastasis-promoting factor CCL2

Abstract Objective: The standard treatment for advanced prostate cancer is androgen deprivation therapy that blocks androgen receptor (AR) signaling, but this therapy becomes ineffective within a few years, resulting in castration-resistant prostate cancer. We have previously shown that blockade of AR signaling induces CCL2 and activates cancer cells through an autocrine mechanism, but why AR blockade induces CCL2 secretion has not been elucidated. Micro RNAs (miRs) are endogenous non-coding RNAs that regulate the translation of various proteins. In this study, we investigated whether miRs are involved in CCL2 induction. Subjects and Methods: We used miRNA PCR Plate Array and Target Scan (https://www.targetscan.org) to search for miRs that are controlled by AR and bind to and repress the CCL2 gene. We knocked down the AR of human prostate cancer cell lines LNCaP and C4-2B with siRNA (siAR) and examined the expression of target miRs and CCL2. siAR-transfected LNCaP and C4-2B were transfected with target miR mimic and CCL2 expression was examined. siAR-transfected LNCaP, C4-2B, and C4-2B were transfected with target miR mimic and CCL2 expression was examined. siAR-transfected LNCaP and C4-2B were transfected with target miR mimic and CCL2 expression was examined. The target miR mimic was introduced into them, and the changes in migration ability were evaluated. Results: miR-124-3p.2 was extracted as a candidate from miRNA PCR Plate Array and Target Scan. miR-124-3p.2 expression was upregulated in both LNCaP and C4-2B when DHT was added and downregulated when CCL2 was added. In siAR LNCaP and C4-2B, the expression of CCL2 was decreased when miR-124-3p.2 mimic was introduced. Furthermore, in siAR-transfected LNCaP, C4-2B, the introduction of miR-124-3p.2 mimic suppressed the migration. Conclusion: AR suppresses CCL2 via miR124-3p.2. miR124-3p.2-mediated regulation of CCL2 may be a new therapeutic target for advanced prostate cancer. Citation Format: Shuhei Aoyama, Kouji Izumi, Atsushi Mizokami. AR-induced miRNA124-3p.2 suppresses the metastasis-promoting factor CCL2 [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 470.

DHODH inhibition represents a therapeutic strategy and improves abiraterone treatment in castration-resistant prostate cancer.

Castration-resistant prostate cancer (CRPC) is an aggressive disease with poor prognosis, and there is an urgent need for more effective therapeutic targets to address this challenge. Here, we showed that dihydroorotate dehydrogenase (DHODH), an enzyme crucial in the pyrimidine biosynthesis pathway, is a promising therapeutic target for CRPC. The transcript levels of DHODH were significantly elevated in prostate tumors and were negatively correlated with the prognosis of patients with prostate cancer. DHODH inhibition effectively suppressed CRPC progression by blocking cell cycle progression and inducing apoptosis. Notably, treatment with DHODH inhibitor BAY2402234 activated androgen biosynthesis signaling in CRPC cells. However, the combination treatment with BAY2402234 and abiraterone decreased intratumoral testosterone levels and induced apoptosis, which inhibited the growth of CWR22Rv1 xenograft tumors and patient-derived xenograft organoids. Taken together, these results establish DHODH as a key player in CRPC and as a potential therapeutic target for advanced prostate cancer.

The β-Secretase 1 Enzyme as a Novel Therapeutic Target for Prostate Cancer.

Recent studies have demonstrated the association of APP and Aβ with cancer, suggesting that BACE1 may play an important role in carcinogenesis. In the present study, we assessed BACE1's usefulness as a therapeutic target in prostate cancer (PCa). BACE1 expression was observed in human PCa tissue samples, patient-derived xenografts (PDX), human PCa xenograft tissue in nude mice, and transgenic adenocarcinoma of the mouse prostate (TRAMP) tissues by immunohistochemistry (IHC) analysis. Additionally, the downstream product of BACE1 activity, i.e., Aβ1-42 expression, was also observed in these PCa tissues by IHC as well as by PET imaging in TRAMP mice. Furthermore, BACE1 gene expression and activity was confirmed in several established PCa cell lines (LNCaP, C4-2B-enzalutamide sensitive [S], C4-2B-enzalutamide resistant [R], 22Rv1-S, 22Rv1-R, PC3, DU145, and TRAMP-C1) by real-time PCR and fluorometric assay, respectively. Treatment with a pharmacological inhibitor of BACE1 (MK-8931) strongly reduced the proliferation of PCa cells in in vitro and in vivo models, analyzed by multiple assays (MTT, clonogenic, and trypan blue exclusion assays and IHC). Cell cycle analyses revealed an increase in the sub-G1 population and a significant modulation in other cell cycle stages (G1/S/G2/M) following MK-8931 treatment. Most importantly, in vivo administration of MK-8931 intraperitoneal (30 mg/kg) strongly inhibited TRAMP-C1 allograft growth in immunocompetent C57BL/6 mice (approximately 81% decrease, p = 0.019). Furthermore, analysis of tumor tissue using the prostate cancer-specific pathway array revealed the alteration of several genes involved in PCa growth and progression including Forkhead O1 (FOXO1). All together, these findings suggest BACE1 as a novel therapeutic target in advanced PCa.

Adipose Triglyceride Lipase Is a Therapeutic Target in Advanced Prostate Cancer That Promotes Metabolic Plasticity.

ATGL promotes prostate cancer metabolic plasticity and progression through both lipase-dependent and lipase-independent activity, informing strategies to target ATGL and lipid metabolism for cancer treatment.

Abstract B066: Genome-wide CRISPR screens identify PTGES3 as a druggable AR modulator

Abstract BACKGROUND The androgen receptor (AR) is the central therapeutic target in advanced prostate cancer (PCa). While treatments that directly target AR are effective in prolonging patient survival, aggressive prostate cancers invariably find a way to evade these therapies. Frequently, evasion mechanisms reestablish AR expression and therefore AR-driven oncogenic pathways are restored. Comprehensively understanding the protein regulation machinery of AR and identifying alternative therapeutic targets are crucial for effective treatment of this disease. METHODS To study regulators of AR, we utilized CRISPR-Cas9 technology to knock-in a split neon green fluorescent protein onto AR in prostate cancer cells. We evaluated the AR expression and activity in these AR reporter cell lines by multiple approaches including ARE-luciferase assay, ChIP, and RNA-seq. We further built a unique loss-of-function CRISPRi screening system in this AR reporter cell line where we performed a genome-wide fluorescence-activated cell sorting based screen and functionally interrogated hits that modulate AR protein levels. RESULTS We established the first prostate cancer cell line models harboring an endogenous AR reporter. Extensive genotypic and phenotypic characterization of this system demonstrated that the reporter is effective and does not alter AR activity. These models have enabled us to precisely measure the dynamic endogenous AR protein levels by its fluorescence signal. By utilizing a genome-wide CRISPRi screening method in this system, we identified classic AR regulators such as HOXB13, GATA2 and GRHL2, as well as many novel genes that have not been characterized in the context of prostate cancer. Among these novel hits, Prostaglandin E synthase 3 (PTGES3) is the highest ranked druggable target. We validated this finding by establishing PTGES3 knockdown cell lines and demonstrated that loss of PTGES3 downregulated AR and its downstream genes. Follow-up studies show that beyond the canonical chaperone function, PTGES3 physically interacts with AR in the nucleus, where it promotes AR activity. PTGES3 is required for cell proliferation in vitro and in vivo in multiple AR-driven PCa models but not in AR-independent PCa models, such as PC3 cells. From our preliminary data, this unique interaction further suggests that high tumor PTGES3 expression is associated with resistance to first-line androgen deprivation therapies in a retrospective clinical cohort. These results collectively confirm that PTGES3 regulates AR activity and is a potential therapeutic target. Lastly, using a disulfide tethering fragment screen, we developed a PTGES3 inhibitor that blocks the PTGES3/AR interaction and represses AR signaling in PCa cells. We aim to further optimize this PTGES3-specific inhibitor as a therapeutic alternative for patients with aggressive prostate cancer. CONCLUSIONS Together, these genetic, biochemical and chemical biology experiments point to a new class of AR-directed PTGES3 inhibitor therapies that may overcome known mechanisms of ARSI resistance in mCRPC. Citation Format: Haolong Li, James E. Melnyk, Becky Xu Hua Fu, Siyu Feng, Martin Sjöström, Raunak Shrestha, Meng Zhang, Lisa N. Chesner, Hyun Jin Shin, Marsha Calvert, Jonathan Chou, Rajdeep Das, Emily A. Egusa, Aidan Winters, Jun Zhu, Ashutosh Maheshwari, Junjie T. Hua, Mohammed Alshalalfa, William S. Chen, Bradley A. Stohr, Javed Siddiqui, Bo Huang, Eric J. Small, David A. Quigley, Kevan M. Shokat, Luke A. Gilbert, Felix Y. Feng. Genome-wide CRISPR screens identify PTGES3 as a druggable AR modulator [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B066.

Abstract B072: Induction of PARP7 creates a vulnerability for growth inhibition by RBN2397 in prostate cancer cells

Abstract The ADP-ribosyltransferase PARP7 modulates protein function by conjugating ADP-ribose to the side chains of acceptor amino acids. PARP7 has been shown to affect gene expression in prostate cancer cells and certain other cell types by mechanisms that include transcription factor ADP-ribosylation. Here, we use a recently developed catalytic inhibitor to PARP7, RBN2397 (NCT04053673), to study the effects of PARP7 inhibition in androgen receptor-positive (AR+) and androgen receptor-negative (AR-) prostate cancer cells. Ribon Therapeutics developed RBN2397 as a first-in-class mono-ADP-ribosyltransferase inhibitor, and showed that it blocks PARP7 negative regulation of TBK1 [1]. We find that RBN2397 has nanomolar potency for inhibiting androgen-induced ADP-ribosylation of the androgen receptor. RBN2397 inhibits the growth of prostate cancer cells in culture when cells are treated with ligands that activate the androgen receptor (PC3-AR, VCaP, CWR22Rv1), or the aryl hydrocarbon receptor (PC3, DU145, NCI-H660), and induce PARP7 expression. We show that the growth inhibitory effects of RBN2397 are distinct from its enhancement of interferon signaling recently shown to promote tumor immunogenicity in lung cancer models [1]. Chemical inhibitors to PARP1 exert effects on cells by blocking enzyme function, but also via cytotoxic effects attributed to stabilizing PARP1-chromatin interactions in a process termed trapping [2]. Drug-induced trapping of PARP1 can be detected biochemically by immunoblotting the detergent-resistant chromatin fraction. We found that RBN2397 treatment of AR+ and AR- prostate cancer cells induces biochemical trapping of PARP7 within the nucleus, which was also detected by confocal microscopy. Potential therapeutic benefits of RBN2397 are likely to depend on the level of PARP7 expression, given its induction is necessary for growth inhibitory effects of RBN2397 in cell culture. As a first step towards evaluating whether PARP7 levels in human prostate cancer may be actionable with RBN2397, we used computational methods to analyze PARP7 gene expression data from primary prostate tumors and metastatic AR+ and AR- prostate tumors. To assess PARP7 mRNA levels, we used data from the online resource recount3, which uniformly reprocesses publicly available RNA-seq datasets using a Monorail analysis pipeline. Using the level of PARP7 expression in VCaP cells that confers sensitivity to RBN2397 as a threshold, 50% of primary tumors, 41% of metastatic AR- and 11% of AR+ tumors are predicted to have PARP7 expression levels that are sufficient for a response to RBN2397. Because RBN2397 can inhibit the growth of castration-resistant and neuroendocrine prostate cancer cells, PARP7 may be an actionable target in advanced prostate cancer. 1. Gozgit, J.M., et al., PARP7 negatively regulates the Type I interferon response in cancer cells and its inhibition triggers antitumor immunity. Cancer Cell, 2021. 39(9): p. 1214-1226 e10 2. Murai, J., et al., Trapping of PARP1 and PARP2 by Clinical PARP Inhibitors. Cancer Res, 2012. 72(21): p. 5588-99. Citation Format: Chunsong Yang, Krzysztof Wierbilowicz, Natalia M. Dworak, Song Yi Bae, Sachi B. Tengse, Nicki Abianeh, Justin M. Drake, Tarek Abbas, Aakrosh Ratan, David Wotton, Bryce M. Paschal. Induction of PARP7 creates a vulnerability for growth inhibition by RBN2397 in prostate cancer cells [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B072.

Abstract CT159: CYCLONE 1: abemaciclib in men with heavily pretreated metastatic castration-resistant prostate cancer (mCRPC)

Abstract Background: Treatment options for patients (pts) with heavily pretreated mCRPC are limited. Augmenting endocrine therapy by targeting CDK4/6 with abemaciclib has dramatically improved outcomes in HR+ breast cancer. Similar to ER, AR signaling activates CDK4 & 6 and abemaciclib showed preclinical anti-tumor activity in prostate cancer (PC). This signal seeking single arm Phase 2 study evaluated the safety and clinical activity of abemaciclib monotherapy in pts with heavily pretreated poor prognosis mCRPC who progressed after both a novel hormonal agent (NHA) and two taxanes. Methods: Eligible pts had progressive mCRPC, measurable disease by RECIST1.1, and previously received ≥1 NHA, docetaxel, and cabazitaxel for metastatic PC. Abemaciclib was administered at 200 mg BID on a continuous 28-day dosing schedule. The primary endpoint was investigator-assessed objective response rate without concurrent bone progression (ORR). A target ORR of ≥12.5% was deemed suitable to support further evaluation of abemaciclib monotherapy in this refractory mCRPC setting. Key secondary endpoints included disease control rate (DCR), time to PSA progression, radiographic progression-free survival (rPFS), overall survival (OS), and safety. Results: Forty-four pts (median age 68 yrs; 75% ECOG PS 1, median PSA of 96 ng/mL) were enrolled. In total, 46.5% had visceral metastasis, including 27.9% with liver metastases. Median time from development of mCRPC to study entry was 2.1 yrs and the median number of prior systemic regimens for mCRPC was 3. Median number of treatment cycles was 3 (1-13). Five pts (11.8%) had soft tissue response. The ORR without concurrent bone progression was 6.8%. Eighteen pts (40.9%) had stable disease, of which 6 (13.6%) lasted ≥6 months (mos); DCR was 47.7%. Median rPFS was 2.7 mos (95% CI 1.9, 3.7); 6-mos rPFS rate was 24.9% (95% CI 12.4, 39.5); median time to PSA progression was 6.5 mos. Median OS was 7.6 mos (95% CI 5.6, NE). Any grade (G) TRAEs experienced by ≥50% of pts were diarrhea (79.5%), decreased appetite (52.3%) and fatigue (50%); majority were G1/2. G3 TRAEs in ≥ 5% of pts were neutropenia (22.7%), anemia (6.8%), fatigue (6.8%) and diarrhea (6.8%). There were no G4 or G5 TRAEs. Discontinuation rate due to AE was 13.6%. Conclusions: Abemaciclib demonstrated modest but objective single-agent clinical activity in pts with very heavily pretreated progressive mCRPC. The safety profile of abemaciclib was consistent with the experience in breast cancer. Although the primary endpoint was not formally met, the single agent activity observed in this late line mCRPC setting validates CDK4/6 as a therapeutic target in advanced PC. The CYCLONE 2 and CYCLONE 3 studies are currently evaluating abemaciclib in combination with abiraterone/prednisone to leverage synergy of combined CDK4/6 and hormonal inhibition in first line mCRPC and mHSPC settings, respectively. Citation Format: Neeraj Agarwal, Daniel Castellano Guana, Teresa A. Gordoa, Jose A. Arija, Emeline Colomba, Gwenaelle Gravis, Loic Mourey, Stephanie Oudard, Aude Flechon, Macarena Gonzalez, Pablo Maroto-Rey, Michael Schweizer, Enrique Gallardo, Karim Nacerddine, Adams K. Appiach, Arjun Balar, Erica Johnston, José M. Piulats. CYCLONE 1: abemaciclib in men with heavily pretreated metastatic castration-resistant prostate cancer (mCRPC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT159.

MP20-04 ARHGEF2 REGULATES LINEAGE PLASTICITY PROMOTING NEUROENDOCRINE DIFFERENTIATION AND TREATMENT RESISTANCE IN ADVANCED PROSTATE CANCER

You have accessJournal of UrologyCME1 Apr 2023MP20-04 ARHGEF2 REGULATES LINEAGE PLASTICITY PROMOTING NEUROENDOCRINE DIFFERENTIATION AND TREATMENT RESISTANCE IN ADVANCED PROSTATE CANCER Shu Ning, Wei Lou, Alan Lombard, Masuda Sharifi, Zachary Schaaf, Christopher Evans, and Allen Gao Shu NingShu Ning More articles by this author , Wei LouWei Lou More articles by this author , Alan LombardAlan Lombard More articles by this author , Masuda SharifiMasuda Sharifi More articles by this author , Zachary SchaafZachary Schaaf More articles by this author , Christopher EvansChristopher Evans More articles by this author , and Allen GaoAllen Gao More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003245.04AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Treatment-emergent neuroendocrine prostate cancer (NEPC) after androgen receptor (AR) targeted therapies has been an aggressive variant of prostate cancer with unfavorable prognosis and limited therapeutic options. This study aims to identify potential neural lineage signature genes and evaluate whether they could serve as early biomarkers to stratify patients for optimal treatment and potential therapeutic targets in advanced prostate cancer. METHODS: We performed transcriptomic analysis on the enzalutamide-resistant prostate cancer cell lines and advanced prostate cancer patient databases to identify neural lineage signature (NLS) genes including ARHGEF2. The correlation of NLS genes with clinicopathologic features was determined. RNA sequencing analysis and viability of tumor organoids were performed on C4-2B MDVR and H660 cells with ARHGEF2 knocking down and gene set enrichment was analyzed. RESULTS: We identified a 95-gene NLS representing the molecular landscape of neural precursor cell proliferation, embryonic stem cell pluripotency and neural stem cell differentiation, which may indicate a spectrum of early and intermediate stages of neuroendocrine differentiation. These NLS genes positively correlate with conventional neuroendocrine (NE) markers such as chromogranin and synaptophysin, and negatively correlate with AR and AR target genes. Differentially expressed NLS genes stratify small cell NEPC from prostate adenocarcinoma, which is closely associated with higher Gleason Score and metastasis status. Higher ARHGEF2 levels correlate with a shortened survival time in NEPC patients. ARHGEF2 regulates neuron differentiation and neural precursor cell proliferation which are significantly enriched in treatment-emergent NEPC patients and H660 cells. Upregulation of ARHGEF2 in both patient and experimental models positively correlates with NE markers. ARHGEF2 knocking down inhibited tumor organoids viability and NE markers in enzalutamide-resistant and NEPC cells. CONCLUSIONS: Our studies suggest that ARHGEF2 activation promotes neural lineage plasticity contributing to the survival and proliferation of enzalutamide-resistance and NEPC cells. ARHGEF2 could serve as a biomarker to stratify advanced prostate cancer patients for better treatment options and a potential therapeutic target in advanced prostate cancer. Source of Funding: NIH CA253605, CA 225836, CA250082, DOD PC180180 © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e276 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Shu Ning More articles by this author Wei Lou More articles by this author Alan Lombard More articles by this author Masuda Sharifi More articles by this author Zachary Schaaf More articles by this author Christopher Evans More articles by this author Allen Gao More articles by this author Expand All Advertisement PDF downloadLoading ...

CXCR7 as a novel therapeutic target for advanced prostate cancer.

Chemokines and their cognate receptors comprise an intricate signaling network that becomes high-jacked by cancer cells for uncontrollable tumor growth and dissemination. ACKR3 (Atypical Chemokine Receptor 3), traditionally called CXCR7, is up-regulated in many cancers, including advanced prostate cancer, and represents promising targets for therapeutic intervention. Unlike typical G protein-coupled receptors such as CXCR4, CXCR7, once bound by its cognate ligand CXCL12, initiates the recruitment of β-arrestin instead of G proteins, and results in rapid internalization and degradation of CXCL12, functioning as a scavenger receptor. However, recent evidence suggests that CXCR7 may be more than a scavenger or auxiliary receptor of CXCR4 and that it may play essential roles in regulating cancer progression, some of which are independent of CXCR4 and its ligands, such as CXCL12. Constitutively active CXCR7 binds to β-arrestin. This protein complex internalizes to form a scaffold for assembling and activating various cytoplasmic kinases necessary for cell survival and tumor growth. Here we review and discuss the up-to-date knowledge on CXCR7 regulation and function and how this new understanding guides the development of CXCR7 inhibitors, focusing on prostate cancer.

B7-H3 as a Therapeutic Target in Advanced Prostate Cancer

BackgroundB7-H3 is a cell surface immunomodulatory glycoprotein overexpressed in prostate cancers (PCs). Understanding its longitudinal expression at emergence of castration resistance and association with tumour genomics are critical to the development of and patient selection for B7-H3 targeted therapies. ObjectiveTo characterise B7-H3 expression in same-patient hormone-sensitive (HSPC) and castration-resistant (CRPC) PC biopsies, associating this with PC genomics, and to evaluate the antitumour activity of an anti–B7-H3 antibody-drug conjugate (ADC) in human CRPC in vitro and in vivo. Design, setting, and participantsWe performed immunohistochemistry and next-generation sequencing on a cohort of 98 clinically annotated CRPC biopsies, including 72 patients who also had HSPC biopsies for analyses. We analysed two CRPC transcriptome and exome datasets, and PC scRNASeq datasets. PC organoids (patient-derived xenograft [PDX]-derived organoids [PDX-Os]) were derived from PDXs generated from human CRPC biopsies. Outcome measurements and statistical analysisWe evaluated B7-H3 mRNA expression in relation to a panel of 770 immune-related genes, compared B7-H3 protein expression between same-patient HSPC and CRPC biopsies, determined associations with PC genomic alterations, and evaluated the antitumour activity of DS-7300a, a topoisomerase-1 inhibitor payload anti–B7-H3 ADC, in human PC cell lines, organoids (PDX-Os), and xenografts (PDXs) of different histologies, B7-H3 expressions, and genomics. Results and limitationsB7-H3 was among the most highly expressed immunomodulatory genes in CRPCs. Most CRPCs (93%) expressed B7-H3, and in patients who developed CRPC, B7-H3 expression was frequently expressed at the time of HSPC diagnosis (97%). Conversion from B7-H3 positive to negative, or vice versa, during progression from HSPC to CRPC was uncommon. CRPC with neuroendocrine features were more likely to be B7-H3 negative (28%) than adenocarcinomas. B7-H3 is overexpressed in tumours with defective DNA repair gene (ATM and BRCA2) alterations and is associated with ERG expression, androgen receptor (AR) expression, and AR activity signature. DS7300a had antitumour activity against B7-H3 expressing human PC models including cell lines, PDX-Os, and PDXs of adenocarcinoma and neuroendocrine histology. ConclusionsThe frequent overexpression of B7-H3 in CRPC compared with normal tissue and other B7 family members implicates it as a highly relevant therapeutic target in these diseases. Mechanisms driving differences in B7-H3 expression across genomic subsets warrant investigation for understanding the role of B7-H3 in cancer growth and for the clinical development of B7-H3 targeted therapies. Patient summaryB7-H3, a protein expressed on the surface of the most lethal prostate cancers, in particular those with specific mutations, can be targeted using drugs that bind B7-H3. These findings are relevant for the development of such drugs and for deciding which patients to treat with these new drugs.

PSMA as a Target for Advanced Prostate Cancer: A Systematic Review

ObjectiveProstate-specific membrane antigen (PSMA) is a cell-surface protein widely expressed on most prostate cancer cells that has rapidly emerging clinical utility in the realm of prostate cancer. This systematic review aims to evaluate the efficacy as well as cost-effectiveness of PSMA in the roles of diagnosis and treatment in prostate cancer management.BackgroundThe use of PSMA in the initial staging of patients, early detection of recurrence, and response monitoring are critical to improving prostate cancer treatment. We performed a systematic review of the role of Gallium-68 (68Ga)-PSMA in the initial detection of prostate cancer and detection of biochemical recurrence (BCR) as well as the role of Lutium-177 (177Lu)-PSMA in theranostics. We also investigated the cost-effectiveness of both ligands in comparison to the current standard of care.MethodsIn February 2022 we performed a systematic and comprehensive review of the existing literature. We identified and screened articles published from 1983 up to January 2022 through PubMed. Only 1 study was included prior to 2011. We included articles that investigated the efficacy or cost-effectiveness of PSMA in prostate cancer detection and therapy. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRSIMA) guidelines eligible articles were selected, and relevant information was extracted from the original articles.ResultsA total of 26 articles were included in the analysis of this systematic review. These studies were heterogeneous and were comprised of five prospective studies including 336 patients, three retrospective analyses including 540 patients, one phase III trial, one survival analysis, one randomized control trial, three systematic reviews, three meta-analyses, two in-vivo studies, three reviews, and four cost analyses.ConclusionThe diagnostic and therapeutic role of PSMA appears more efficacious and potentially less expensive than the standard treatment for patients with BCR of prostate cancer. Current evidence suggests PSMA will also fill an unmet need in initial diagnostics of prostate cancer and ligand therapy. However, a consensus has not yet been reached on cost-effectiveness of PSMA and further prospective studies are needed.

Elevated NF-κB/SHh/GLI1 Signature Denotes a Worse Prognosis and Represent a Novel Potential Therapeutic Target in Advanced Prostate Cancer

Prostate cancer (PCa) is the second most frequent cancer in men worldwide. NF-κB seems to play a key role in cell survival, proliferation and invasion, sustaining the heterogeneous multifocal nature of PCa. In recent years, the Hedgehog (Hh) signaling pathway has attracted attention as a therapeutic target due to its implication in tumorigenesis and metastasis in several types of cancer, including PCa. Although it is well-known that Sonic Hedgehog (SHh) is a transcriptional target of NF-κB(p65), and that GLI1 is the effector of this crosstalk, the precise role played by this axis in PCa is still not completely clear. Here, we set out to explore the correlation between NF-κB activation and SHh pathways in PCa, investigating if the interplay between NF-κB(p65) and SHh-GLI1 in advanced PCa could be a prospective therapeutic target. Our findings demonstrate that a NF-κB-SHh-GLI1 gene signature is enriched in PCa patients featuring a higher Gleason score. Moreover, elevated levels of this signature are associated with worse prognosis, thus suggesting that this axis could provide a route to treat aggressive PCa.

Abstract 2807: HER3 is an actionable target in advanced prostate cancer

Abstract Background: ERBB signaling is implicated in castration resistant prostate cancer (CRPC), but so far clinical trials of ERBB targeting drugs failed to demonstrate antitumor activity. We elected to re-investigate ERBB receptors in endocrine treatment-resistant lethal PC, hypothesizing that targeting ERBB receptors merits further evaluation in metastatic CRPC (mCRPC). Design: We analyzed matching, same-patient, formalin-fixed paraffin-embedded (FFPE) treatment-naïve, castration-sensitive PC (CSPC) samples (n=88), and mCRPC biopsies (n=51), from patients treated at The Royal Marsden Hospital, UK. Samples were stained for HER2 and HER3 protein, by immunohistochemistry (IHC), data was generated through digital image analysis and results were analyzed against clinical characteristics and outcome data. Moreover, we treated HER3 high (CP50) and low (CP142) expressing patient derived xenograft (PDX) models with anti-HER3 antibody-drug conjugate (HER3-ADC) U3-1402 (10mg/Kg), IgG-ADC (MAAA-9289, 10mg/Kg), anti-HER3 antibody Patritumab (U3-1287, 10mg/Kg) and 10mM acetate buffer-5% sorbitol-pH 5.5 as vehicle control, in vitro and in vivo. In vitro cell growth inhibitory activity was monitored for 7-days with endpoint assay luminescence. In vivo efficacy was evaluated comparing tumor volumes, measured every 2-3 days. Statistical significance was analyzed using ANOVA with Dunnett’s multiple comparisons correction test. Results: Membranous HER2 (mHER2) and HER3 (mHER3) proteins were detectable in both CSPC and mCRPC biopsies, with HER3 being highly expressed in many tumors. The median optical density (OD) for mHER3 expression at diagnosis was 2958.0; PC with high mHER3 expression (> median OD; n=44) had a significantly shorter median time to CRPC (20.3 vs 14.2 months; p=0.016) and worse overall survival (OS) (79.0 vs 48.8 months; p=0.04) compared to CSPC with low mHER3 (≤ median; n=44). mHER2 staining did not associate with outcome. U3-1402 demonstrated in vivo potent and sustained antitumor activity in CP50, without inducing any body weight loss or apparent toxicity. Additionally, no tumor regrowth was observed up to 60-days following the end of dosing. This anti-HER3-ADC had minimal antitumor activity in CP142, highlighting the relevance of high HER3 expression as a functional therapeutic target. Conclusion: HER3 is commonly expressed in advanced PC and has clinical relevance in this setting. Our data indicate that HER3 is a valid target for clinical trials for men suffering from high HER3 expressing advanced PC. Citation Format: Susana Miranda, Veronica Gil, Ruth Riisnaes, Bora Gurel, Mariantonietta D’Ambrosio, Alessandro Vasciaveo, Mateus Crespo, Ana Ferreira, Daniela Brina, Martina Troiani, Adam Sharp, Beshara Sheehan, Rossitza Christova, George Seed, Ines Figueiredo, Maryou Lambros, David Dolling, Jan Rekowski, Abdullah Alajati, Matthew Clarke, Rita Pereira, Penny Flohr, Gemma Fowler, Gunther Boysen, Semini Sumanasuriya, Diletta Bianchini, Pasquale Rescigno, Caterina Aversa, Nina Tunariu, Christina Guo, Alec Paschalis, Claudia Bertan, Lorenzo Buroni, Jian Ning, Suzanne Carreira, Paul Workman, Amanda Swain, Andrea Califano, Michael M. Shen, Andrea Alimonti, Antje Neeb, SU2C/PCF International Prostate Cancer Dream Team, Jonathan Welti, Wei Yuan, Johann de Bono. HER3 is an actionable target in advanced prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2807.

Regulation and role of CAMKK2 in prostate cancer

In 2011, CAMKK2, the gene encoding calcium/calmodulin-dependent kinase kinase 2 (CAMKK2), was demonstrated to be a direct target of the androgen receptor and a driver of prostate cancer progression. Results from multiple independent studies have confirmed these findings and demonstrated the potential role of CAMKK2 as a clinical biomarker and therapeutic target in advanced prostate cancer using a variety of preclinical models. Drug development efforts targeting CAMKK2 have begun accordingly. CAMKK2 regulation can vary across disease stages, which might have important implications in the use of CAMKK2 as a biomarker. Moreover, new non-cell-autonomous roles for CAMKK2 that could affect tumorigenesis, metastasis and possible comorbidities linked to disease and treatment have emerged and could present novel treatment opportunities for prostate cancer.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

HER3 Is an Actionable Target in Advanced Prostate Cancer.

It has been recognized for decades that ERBB signaling is important in prostate cancer, but targeting ERBB receptors as a therapeutic strategy for prostate cancer has been ineffective clinically. However, we show here that membranous HER3 protein is commonly highly expressed in lethal prostate cancer, associating with reduced time to castration resistance (CR) and survival. Multiplex immunofluorescence indicated that the HER3 ligand NRG1 is detectable primarily in tumor-infiltrating myelomonocytic cells in human prostate cancer; this observation was confirmed using single-cell RNA sequencing of human prostate cancer biopsies and murine transgenic prostate cancer models. In castration-resistant prostate cancer (CRPC) patient-derived xenograft organoids with high HER3 expression as well as mouse prostate cancer organoids, recombinant NRG1 enhanced proliferation and survival. Supernatant from murine bone marrow-derived macrophages and myeloid-derived suppressor cells promoted murine prostate cancer organoid growth in vitro, which could be reversed by a neutralizing anti-NRG1 antibody and ERBB inhibition. Targeting HER3, especially with the HER3-directed antibody-drug conjugate U3-1402, exhibited antitumor activity against HER3-expressing prostate cancer. Overall, these data indicate that HER3 is commonly overexpressed in lethal prostate cancer and can be activated by NRG1 secreted by myelomonocytic cells in the tumor microenvironment, supporting HER3-targeted therapeutic strategies for treating HER3-expressing advanced CRPC. SIGNIFICANCE: HER3 is an actionable target in prostate cancer, especially with anti-HER3 immunoconjugates, and targeting HER3 warrants clinical evaluation in prospective trials.

A Suite of Activity-Based Probes To Dissect the KLK Activome in Drug-Resistant Prostate Cancer.

Kallikrein-related peptidases (KLKs) are a family of secreted serine proteases, which form a network (the KLK activome) with an important role in proteolysis and signaling. In prostate cancer (PCa), increased KLK activity promotes tumor growth and metastasis through multiple biochemical pathways, and specific quantification and tracking of changes in the KLK activome could contribute to validation of KLKs as potential drug targets. Herein we report a technology platform based on novel activity-based probes (ABPs) and inhibitors enabling simultaneous orthogonal analysis of KLK2, KLK3, and KLK14 activity in hormone-responsive PCa cell lines and tumor homogenates. Importantly, we identifed a significant decoupling of KLK activity and abundance and suggest that KLK proteolysis should be considered as an additional parameter, along with the PSA blood test, for accurate PCa diagnosis and monitoring. Using selective inhibitors and multiplexed fluorescent activity-based protein profiling (ABPP), we dissect the KLK activome in PCa cells and show that increased KLK14 activity leads to a migratory phenotype. Furthermore, using biotinylated ABPs, we show that active KLK molecules are secreted into the bone microenvironment by PCa cells following stimulation by osteoblasts suggesting KLK-mediated signaling mechanisms could contribute to PCa metastasis to bone. Together our findings show that ABPP is a powerful approach to dissect dysregulation of the KLK activome as a promising and previously underappreciated therapeutic target in advanced PCa.

Upregulation of ATP Binding Cassette Subfamily C Member 5 facilitates Prostate Cancer progression and Enzalutamide resistance via the CDK1-mediated AR Ser81 Phosphorylation Pathway.

The treatment of advanced prostate cancer, castration-resistant prostate cancer, remains challenging. The mechanisms of action of ATP binding cassette subfamily C member 5 (ABCC5) in prostate cancer and its relationship with drug resistance are still unclear. Expression and prognostic analyses of ABCC5 were performed through bioinformatic methods and immunohistochemistry analyses in multiple public databases as well as in our own prostate cancer cohort. The biological function of ABCC5 in prostate cancer cells was evaluated by in vitro and in vivo cell proliferation and migration and invasion assays. The regulation of CDK1 by ABCC5 was determined via RT-qPCR, western blots, and immunofluorescence. ABCC5 was significantly overexpressed in prostate cancer and positively associated with unfavorable clinicopathological features and prognosis. Upregulation of ABCC5 could enhance the cell proliferation, migration, and invasion of prostate cancer in vitro and in vivo. Mechanistically, ABCC5 exerts a protumor effect by binding to and inhibiting the protein degradation of CDK1, which promotes the phosphorylation of AR at Ser81 by CDK1 and activates the transcriptional activity of AR on target genes. Moreover, the addition of a CDK1 inhibitor or knockdown of CDK1 significantly improved the efficacy of enzalutamide on prostate cancer cells. The ABCC5-CDK1-AR regulatory pathway could be a potential therapeutic target for advanced prostate cancer, especially castration-resistant prostate cancer (CRPC), to enhance the therapeutic effect of enzalutamide.

Steroid Sulfatase Stimulates Intracrine Androgen Synthesis and is a Therapeutic Target for Advanced Prostate Cancer.

Most patients with prostate cancer receiving enzalutamide or abiraterone develop resistance. Clinical evidence indicates that serum levels of dehydroepiandrosterone sulfate (DHEAS) and biologically active DHEA remain in the high range despite antiandrogen treatment. The conversion of DHEAS into DHEA by steroid sulfatase (STS) may contribute to sustained intracrine androgen synthesis. Here, we determine the contribution of STS to treatment resistance and explore the potential of targeting STS to overcome resistance in prostate cancer. STS expression was examined in patients and cell lines. In vitro, STS activity and expression were modulated using STS-specific siRNA or novel STS inhibitors (STSi). Cell growth, colony formation, androgen production, and gene expression were examined. RNA-sequencing analysis was conducted on VCaP cells treated with STSi. Mice were treated with STSis with or without enzalutamide to determine their effects in vivo. STS is overexpressed in patients with castration-resistant prostate cancer (CRPC) and resistant cells. STS overexpression increases intracrine androgen synthesis, cell proliferation, and confers resistance to enzalutamide and abiraterone. Inhibition of STS using siRNA suppresses prostate cancer cell growth. Targeting STS activity using STSi inhibits STS activity, suppresses androgen receptor transcriptional activity, and reduces the growth of resistant C4-2B and VCaP prostate cancer cells. STSis significantly suppress resistant VCaP tumor growth, decrease serum PSA levels, and enhance enzalutamide treatment in vitro and in vivo. These studies suggest that STS drives intracrine androgen synthesis and prostate cancer proliferation. Targeting STS represents a therapeutic strategy to treat CRPC and improve second-generation antiandrogen therapy.

Recent Discoveries in the Androgen Receptor Pathway in Castration-Resistant Prostate Cancer.

The androgen receptor (AR) is the main therapeutic target in advanced prostate cancer, because it regulates the growth and progression of prostate cancer cells. Patients may undergo multiple lines of AR-directed treatments, including androgen-deprivation therapy, AR signaling inhibitors (abiraterone acetate, enzalutamide, apalutamide, or darolutamide), or combinations of these therapies. Yet, tumors inevitably develop resistance to the successive lines of treatment. The diverse mechanisms of resistance include reactivation of the AR and dysregulation of AR cofactors and collaborative transcription factors (TFs). Further elucidating the nexus between the AR and collaborative TFs may reveal new strategies targeting the AR directly or indirectly, such as targeting BET proteins or OCT1. However, appropriate preclinical models will be required to test the efficacy of these approaches. Fortunately, an increasing variety of patient-derived models, such as xenografts and organoids, are being developed for discovery-based research and preclinical drug screening. Here we review the mechanisms of drug resistance in the AR signaling pathway, the intersection with collaborative TFs, and the use of patient-derived models for novel drug discovery.