Cereblon (CRBN) inhibits prostate cancer metastasis by negatively regulating 6-phosphogluconate dehydrogenase (6PGD).

Metastatic Burden in Hormone-Naive Prostate Cancer: A Tale of Two Subgroups

As the third enzyme of the pentose phosphate pathway (PPP), abnormally elevated levels of 6-phosphogluconate dehydrogenase (6PGD) have been documented in various human cancers. We demonstrate that reduced cereblon (CRBN) protein expression is the underlying mechanism of elevated 6PGD expression in metastatic prostate cancer cells. We establish 6PGD as a new endogenous substrate for CRBN by demonstrating that it interacts directly with CRBN and is ubiquitinated by CRL4CRBN. In addition, CRBN negatively regulates prostate cancer cell progression and metastasis, as abnormally high 6PGD, in the absence of sufficient CRBN, enhances the metastatic potential of prostate cancer in vitro and in vivo. Our findings show convincingly that carbohydrate metabolism regulated by 6PGD is linked to prostate cancer metastasis via CRBN. Based on these data, we propose that the 6PGD-CRBN axis may be a suitable target for further research into new therapeutics for mitigating prostate cancer metastasis. Citation Format: Koushik Guchhait, Hyeon Seung Yoon, Seungheon Shin, Hyun-Su An, Hye Seung Nam, Francisco D. Yanqui-Rivera, Samara M. Oña, Miguel Á. Mendez, Seokjae Park, Eun-Kyoung Kim, Jong Yeon Hwang, Jee-Young Han, Doo Yong Chung, Daeho Park, Su-Geun Yang, Chul-Seung Park, Steve K. Cho. Cereblon inhibits prostate cancer progression and metastasis by negatively regulating 6PGD [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 LB157.

Prostate cancer is the second most commonly diagnosed cancer in men, with 1 in 8 men being diagnosed with prostate cancer in his lifetime. AR is a hormone-activated transcription factor that promotes cell growth and survival in the normal prostate, and AR signaling is a key driver of cell proliferation in prostate cancer. Inhibition of AR signaling is a mainstay of current prostate cancer treatment, however, patients often develop resistance to these therapies through mechanisms that retain dependency on AR signaling. GDC-2992 (also known as RO7656594) is a potent, orally bioavailable, heterobifunctional molecule that inhibits AR signaling by binding to both AR and the E3 ubiquitin ligase cereblon (CRBN), resulting in ubiquitination and subsequent degradation of AR. GDC-2992 inhibits AR signaling in the context of wild-type AR and AR proteins with mutations associated with resistance to standard-of-care AR signaling inhibitors (ARSIs). Unlike ARSIs, GDC-2992 does not display evidence of agonism against any AR variants evaluated. Co-treatment of GDC-2992 with the CRBN ligand pomalidomide prevents AR degradation mediated by GDC-2992 in vitro, supporting the role of CRBN in GDC-2992-mediated AR degradation. Importantly however, anti-proliferative potential of GDC-2992 is maintained even when degradation is attenuated, suggesting that the mechanism of GDC-2992 includes competitive AR antagonism in addition to degradation. In vivo, GDC-2992 decreases circulating PSA and inhibits prostate tumor growth in a dose responsive manner. The totality of in vitro and in vivo preclinical data supports that GDC-2992 represents a compelling advance over standard-of-care ARSIs. An ongoing Phase I dose-escalation and expansion study will assess the safety, tolerability, pharmacokinetics, and preliminary anti-tumor activity of GDC-2992 in patients with advanced or metastatic prostate cancer who have previously received AR-targeted therapy [NCT05800665]. By providing more complete and sustained AR inhibition, GDC-2992 has the potential to reduce the occurrence of treatment-resistance and disease relapse in prostate cancer. Citation Format: Ciara Metcalfe, Wei Zhou, Darlene Dela Cruz, Thomas Hunsaker, Pablo Saenz-Lopez Larrocha, Elizabeth Levy, Bu-Er Wang, Tonia Hafner, Nayan Chaudhary, Marc Hafner, Kalpit Shah, Elisia Villemure, Yuxiang Zheng, Jodie Pang, Udi Segal. GDC-2992: A heterobifunctional Androgen Receptor (AR) antagonist and degrader for the treatment of AR wild-type and mutant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr ND02.

Background: Rates of prostate cancer incidence and advanced-stage diagnoses are increasing. Despite curative-intent therapies, nearly all patients with advanced disease progress to metastatic castration-resistant prostate cancer (mCRPC), a lethal form of the disease. There is an urgent unmet need to understand the mechanisms driving prostate cancer progression and identify alternative therapies for patients with mCRPC. It is well-established that cancer-associated fibroblasts (CAF) in the tumor microenvironment secrete factors that enable cancer cells to establish metastases. Asporin (ASPN) is an extracellular protein secreted by a subset of CAF and is associated with worse oncologic outcomes, yet the mechanisms remain poorly understood. In this study, we sought to identify the molecular interactions between the CAF-secreted ASPN and metastatic prostate cancer cells. Methods: ASPN-induced HER2/HER3 activation and downstream signaling was identified by RNA-sequencing and then confirmed by immunoblotting in multiple human metastatic prostate cancer cell lines. Binding interactions were assessed computationally by AlphaFOld2 with Rosetta refinement and substantiated by co-immunoprecipitation assays. CRISPR-cas9 targeting of HER2 and HER3 and therapeutic inhibition of HER2 with Tucatinib were used to determine the role of HER2/HER3 in ASPN-induced signaling and migration. The efficacy of Tucatinib and antibody-drug conjugates (ADC) targeting HER2 (Trastuzumab-deruxtecan) and HER3 (Patritumab-deruxtecan) were assessed in multiple metastatic prostate cancer cell lines in vitro. Trastuzumab-deruxtecan was assessed in PC3 xenografts in vivo. Prostate cancer metastases from 33 patients were assessed by IHC for HER2 and HER3 and by RNAscope for ASPN. Results: We report that ASPN is a novel ligand of HER3 and induces HER3 heterodimerization with its preferred dimerization partner, HER2. ASPN activates established ErbB-associated pathways including Phosphoinositide 3-kinase (PI3K), Mitogen-activated protein kinase (MAPK), and calcium signaling, in multiple metastatic prostate cancer cell lines to promote cell migration. Genetic and molecular inhibition of HER2/HER3 mitigates ASPN-induced signaling and cell migration, suggesting these receptors are required for paracrine activation by ASPN. Importantly, small molecule and ADC therapies targeting HER2/HER3 significantly diminished prostate cancer cell growth in vitro, with enzalutamide-resistant cells showing increased sensitivity. Trastuzumab-deruxtecan nearly resolved tumors in an in vivo xenograft model. Lastly, ASPN+ CAF in the TME of HER2/HER3-expressing metastatic prostate cancer is frequently observed in patient samples, supporting the clinical relevance of these findings. Conclusions: Collectively, these findings indicate ASPN functions as a HER3 ligand to induce cellular migration, and inhibition with anti-HER2/HER3 therapies highlights potential clinical utility for patients with HER2-expressing metastatic prostate cancer. Citation Format: Amanda B. Hesterberg, Hong Yuen Wong, Jorgen Jackson, Monika Antunovic, Brenda L. Rios, Evan Watkins, Riley E. Bergman, Brad A. Davidson, Sarah E. Ginther, Diana Graves, Elliott F. Nahmias, Jared A. Googel, Lillian B. Martin, Violeta Sanchez, Paula Gonzalez Ericsson, Quanhu Sheng, Benjamin P. Brown, Jens Meiler, Ben H. Park, Kerry R. Schaffer, Jennifer B. Gordetsky, Paula J. Hurley. Identification of Asporin as a HER3 ligand exposes a therapeutic vulnerability in metastatic prostate cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr B007.

Prediction of Survival of Metastatic Prostate Cancer Based on Early Serial Measurements of Prostate Specific Antigen and Alkaline Phosphatase

Background: Metastasis is the most common cause of death of prostate cancer patients. Identification of key regulators in prostate cancer metastasis is essential for improved management of the disease. Accumulation of evidence suggests that miRNAs play important roles in cancer metastasis. Here, we investigated the role of miR-451 in prostate cancer progression and metastasis. Methods: In this study, we performed reverse transcription-quantitative PCR analysis to examine the expression of miR-451 in clinical prostate cancer samples and cell lines. TargetScan Release 7.0 programs, luciferase reporter assay, and a rescue experiment were used to validate the direct target of miR-451. The protein expression of the miR-451 target was detected by Western blot. MTS cell viability assay, transwell migration assay, and modified Boyden chamber invasion assay were used to demonstrate the effects of increased miR-451 expression on prostate cancer cell growth, migration and invasiveness. Results: We identified the decreased expression of miR-451 in clinical metastatic prostate cancer compared to localized primary prostate cancer and benign prostate. Consistently, we also observed the decreased expression of miR-451 in highly metastatic prostate cancer cell lines (C4-2 and PC3M) compared to their low metastatic counterparts (LNCaP and PC3). Furthermore, we confirmed the macrophage migration inhibitory factor (MIF) is a direct target of miR-451 in prostate cancer and demonstrated a negative correlation between miR-451 and MIF expression in clinical prostate cancer samples. Functional studies showed increased miR-451 expression significantly suppressed cell growth, migration and invasiveness via targeting MIF. The effect of increased miR-451 expression can be reversed by overexpressing MIF in prostate cancer cells. Conclusions: These findings suggest that miR-451 suppresses prostate cancer cell growth, migration and metastasis, which provides insight into the development of novel therapeutic approaches for prostate cancer treatment.

The transcriptional activity of androgen receptor (AR) is modulated by coregulators that have a significant influence on a number of functional properties of AR, including the ligand specificity as well as the DNA binding capacity. Because androgens and AR have pivotal roles in the development and

Raf kinase inhibitor protein (RKIP) is a small, cytosolic protein named for its ability to block Raf-mediated activation of MAPK and ERK. It also block G-protein signaling and NF-κB activation. An in vitro screen to identify genes that regulate prostate cancer (PCa) metastasis revealed that expression of RKIP was decreased in high versus low metastatic PCa cells. Modulation of RKIP expression revealed that it inhibited invasion and loss of RKIP promoted in vitro invasion. Animal studies were used to demonstrate that RKIP could inhibit PCa metastasis from orthotopically injected tumor cells without an effect on primary tumor growth. Taken together, these results indicated RKIP acted as a PCa metastasis suppressor gene. Evaluation of RKIP expression in clinical cases of PCa revealed that RKIP expression was moderate to high in non-neoplastic prostate, low in 50% of primary prostate cancers, and absent to low in the majority of metastases. Furthermore, low RKIP expression in primary prostate tumors was predictive of early tumor recurrence. Loss of RKIP was shown to induce resistance to radiation in PCa cells in vitro and in an in vivo murine model. Taken together, these studies indicate that RKIP plays multiple roles in PCa pathophysiology, suggesting that a method to increase RKIP expression in PCa may have therapeutic benefits.

MicroRNAs (miRNAs) are short, non-coding RNAs that regulate gene expression and are aberrantly expressed in human cancer. The ERBB-2 tyrosine kinase receptor is frequently overexpressed in prostate cancer and is associated with disease progression and poor survival. We have identified two specific miR-331-3p target sites within the ERBB-2 mRNA 3'-untranslated region and show that miR-331-3p expression is decreased in prostate cancer tissue relative to normal adjacent prostate tissue. Transfection of multiple prostate cancer cell lines with miR-331-3p reduced ERBB-2 mRNA and protein expression and blocked downstream phosphatidylinositol 3-kinase/AKT signaling. Furthermore, miR-331-3p transfection blocked the androgen receptor signaling pathway in prostate cancer cells, reducing activity of an androgen-stimulated prostate-specific antigen promoter and blocking prostate-specific antigen expression. Our findings provide insight into the regulation of ERBB-2 expression in cancer and suggest that miR-331-3p has the capacity to regulate signaling pathways critical to the development and progression of prostate cancer cells.

PIK3CG Is a Potential Therapeutic Target in Androgen Receptor–Indifferent Metastatic Prostate Cancer

Androgen receptor (AR), an androgen‐activated transcription factor, belongs to the nuclear receptor superfamily. AR plays an important role in the development and progression of prostate cancer (PCa). However, the role of AR in PCa metastasis is not fully understood. To investigate the role of AR in PCa metastasis, we examined AR expression level in primary and metastatic PCa by analyzing gene array data of 378 primary prostate tumors and 120 metastatic prostate tumors from Oncomine, as well as carrying out immunohistochemical (IHC) staining of 56 prostate cancer samples. Expression of mRNA and protein of AR as well as its target gene prostate‐specific antigen (PSA) was much higher in metastatic prostate tumors than in primary prostate tumors. Knockdown of AR with siRNA or treating with anti‐androgen Casodex reduced migration and invasion ability of C4‐2B PCa cells. Knockdown of AR increased protein expression of E‐cadherin and AR coregulator KAT5 but reduced expression of epithelial‐mesenchymal transition (EMT) marker proteins Slug, Snail, MMP‐2, vimentin, and β‐catenin. Knockdown of KAT5 increased migration of C4‐2B cells, whereas overexpression of KAT5 suppressed cell migration. KAT5 knockdown rescues the suppressive effect of AR knockdown on migration of C4‐2B cells. Gene expression level of AR and KAT5 showed a negative correlation. PCa patients with higher AR expression or lower KAT5 expression correlated with shorter recurrence‐free survival. Our study suggested that elevation of AR expression and AR signaling in prostate tumors promotes PCa metastasis by induction of EMT and reduction of KAT5.

Dietary Fiber Intake and Risk of Advanced and Aggressive Forms of Prostate Cancer: A Pooled Analysis of 15 Prospective Cohort Studies

For patients with metastatic prostate cancer, treatment is primarily palliative, relying mainly on the suppression of systemic androgen hormone levels. To help document the achievement of palliation and to characterize positive and negative effects of treatment, we evaluated quality-of-life (QOL) parameters in patients with metastatic prostate cancer who were randomly assigned to two methods of androgen deprivation. Patients (n = 739) with stage M1 (bone or soft tissue metastasis) prostate cancer were enrolled in a QOL protocol that was a companion to Southwest Oncology Group INT-0105, a randomized double-blind trial comparing treatment with bilateral orchiectomy (surgical castration) plus either flutamide or placebo. Patients completed a comprehensive battery of QOL questionnaires at random assignment to treatment and at 1, 3, and 6 months later. Data were collected on three treatment-specific symptoms (diarrhea, gas pain, and body image), on physical functioning, and on emotional functioning. All P values are two-sided. Questionnaire return rates for this study never dropped below 80%; only 2% of the patients did not submit baseline QOL assessments. Cross-sectional analyses (corrected for multiple testing) identified statistically significant differences that favored orchiectomy plus placebo for two of the five primary QOL parameters as follows: patients receiving flutamide reported more diarrhea at 3 months (P = .001) and worse emotional functioning at 3 and 6 months (both P<.003). Longitudinal analyses replicated these findings. Other analyzed QOL parameters favored the group receiving placebo but were not statistically significant after adjustment for multiple testing. We found a consistent pattern of better QOL outcomes at each follow-up assessment during the first 6 months of treatment for orchiectomized patients with metastatic prostate cancer who received placebo versus flutamide. Improvement over time was evident in both treatment groups but more so for patients receiving placebo.

Author(s): Moinpour, CM; Savage, MJ; Troxel, A; Lovato, LC; Eisenberger, M; Veith, RW; Higgins, B; Skeel, R; Yee, M; Blumenstein, BA; Crawford, ED; Meyskens, FL | Abstract: BackgroundFor patients with metastatic prostate cancer, treatment is primarily palliative, relying mainly on the suppression of systemic androgen hormone levels. To help document the achievement of palliation and to characterize positive and negative effects of treatment, we evaluated quality-of-life (QOL) parameters in patients with metastatic prostate cancer who were randomly assigned to two methods of androgen deprivation.MethodsPatients (n = 739) with stage M1 (bone or soft tissue metastasis) prostate cancer were enrolled in a QOL protocol that was a companion to Southwest Oncology Group INT-0105, a randomized double-blind trial comparing treatment with bilateral orchiectomy (surgical castration) plus either flutamide or placebo. Patients completed a comprehensive battery of QOL questionnaires at random assignment to treatment and at 1, 3, and 6 months later. Data were collected on three treatment-specific symptoms (diarrhea, gas pain, and body image), on physical functioning, and on emotional functioning. All P values are two-sided.ResultsQuestionnaire return rates for this study never dropped below 80%; only 2% of the patients did not submit baseline QOL assessments. Cross-sectional analyses (corrected for multiple testing) identified statistically significant differences that favored orchiectomy plus placebo for two of the five primary QOL parameters as follows: patients receiving flutamide reported more diarrhea at 3 months (P = .001) and worse emotional functioning at 3 and 6 months (both Pl.003). Longitudinal analyses replicated these findings. Other analyzed QOL parameters favored the group receiving placebo but were not statistically significant after adjustment for multiple testing.ConclusionsWe found a consistent pattern of better QOL outcomes at each follow-up assessment during the first 6 months of treatment for orchiectomized patients with metastatic prostate cancer who received placebo versus flutamide. Improvement over time was evident in both treatment groups but more so for patients receiving placebo.

Luteolin, ellagic acid and punicic acid are natural products that inhibit prostate cancer metastasis.