Primary Prostate Cancer Research Articles

Quantifying Y chromosome loss in primary and metastatic prostate cancer by chromosome painting.

Somatic Y chromosome loss in hematopoietic cells is associated with higher mortality in men. However, the status of the Y chromosome in cancer tissue is not fully known due to technical limitations, such as difficulties in labelling and sequencing DNA from the Y chromosome. We have developed a system to quantify Y chromosome gain or loss in patient-derived prostate cancer organoids. Using our system, we observed Y chromosome loss in 4 of the 13 (31%) patient-derived metastatic castration-resistant prostate cancer (mCRPC) organoids; interestingly, loss of Yq (long arm of the Y chromosome) was seen in 38% of patient-derived organoids. Additionally, potential associations were observed between mCRPC and Y chromosome nullisomy. The prevalence of Y chromosome loss was similar in primary and metastatic tissue, suggesting that Y chromosome loss is an early event in prostate cancer evolution and may not a result of drug resistance or organoid derivation. This study reports quantification of Y chromosome loss and gain in primary and metastatic prostate cancer tissue and lays the groundwork for further studies investigating the clinical relevance of Y chromosome loss or gain in mCRPC.

Assessment of PSMA Expression of Healthy Organs in Different Stages of Prostate Cancer Using [68Ga]Ga-PSMA-11-PET Examinations.

The efficacy of radioligand therapy (RLT) targeting prostate-specific membrane antigen (PSMA) is currently being investigated for its application in patients with early-stage prostate cancer (PCa). However, little is known about PSMA expression in healthy organs in this cohort. Collectively, 202 [68Ga]Ga-PSMA-11 positron emission tomography (PET) scans from 152 patients were studied. Of these, 102 PET scans were from patients with primary PCa and hormone-sensitive biochemically recurrent PCa and 50 PET scans were from patients with metastatic castration-resistant PCa (mCRPC) before and after three cycles of [177Lu]Lu-PSMA-RLT. PSMA-standardized uptake values (SUV) were measured in multiple organs and PSMA-total tumor volume (PSMA-TTV) was determined in all cohorts. The measured PET parameters of the different cohorts were normalized to the bloodpool and compared using t- or Mann-Whitney U tests. Patients with early-stage PCa had lower PSMA-TTVs (10.39 mL vs. 462.42 mL, p < 0.001) and showed different SUVs in the thyroid, submandibular glands, heart, liver, kidneys, intestine, testes and bone marrow compared to patients with advanced CRPC, with all tests showing p < 0.05. Despite the differences in the PSMA-TTV of patients with mCRPC before and after [177Lu]Lu-PSMA-RLT (462.42 mL vs. 276.29 mL, p = 0.023), no significant organ differences in PET parameters were detected. These suggest different degrees of PSMA-ligand binding among patients with different stages of PCa that could influence radiotoxicity during earlier stages of disease in different organs when PSMA-RLT is administered.

Abstract LB319: Klf5 acetylation remodels tumor microenvironment to constrain PTEN-deficient prostate tumor growth

Abstract Prostate cancer is the most common cancer and the second leading cause of cancer-related death in men in the United States. PTEN deficiency is prevalent in patients with prostate cancer. As a tumor suppressor, PTEN is mutated in approximately 20% of primary prostate cancers, and up to 50% of metastatic castration resistant prostate cancer. PTEN inactivation results in high-grade adenocarcinoma with a long latency. The limited tumor progression induced by PTEN deficiency suggests that additional molecular events are activated to constrain tumor progression, and second hits are required. Understanding these secondary genetic hits will provide the rationale for combined therapies in prostate cancer treatment. In this study, we employed a unique genetically knockin mouse model and found that PTEN deficiency induces a KLF5 K369 acetylation-dependent barrier that attenuates FGFR1 signaling and constrains prostate tumor growth. More importantly, we discovered novel microenvironmental crosstalk between prostate cancer cells and cancer associated fibroblasts (CAFs). As suggested by RNA-seq and bioinformatic analyses and further validated by molecular and cellular experiments, we found that interruption of KLF5 acetylation in cancer cells stimulates CAFs to release FGF9 via TNF-α, and FGF9 activating FGFR1 signaling in cancer cells. In addition to this paracrine crosstalk, deacetylated KLF5 induces CX3CR1 and facilitates FGFR1 activation. Our findings provide a proof of concept for posttranslational modifications as essential molecular events induced by PTEN inactivation to stall prostate cancer progression and demonstrate KLF5 acetylation as a key component in a negative feedback loop by which FGFR1 was suppressed by AKT activation. This study reveals a paracrine reciprocal communication between cancer cells and fibroblasts and provides a clinical rationale for combined therapies using FGFR1 inhibitors (or CX3CR1 inhibitors) and p-AKT inhibitors in PTEN-deficient prostate cancer. Citation Format: Baotong Zhang, Mingcheng Liu, Fengyi Mai, Siyuan Xia, Jin-Tang Dong. Klf5 acetylation remodels tumor microenvironment to constrain PTEN-deficient prostate tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB319.

Detection of Adenocarcinoma of the Colon on 18 F-Fluciclovine PET/CT.

An 85-year-old man with prostate cancer and de novo bone metastases was treated with hormonal therapy with resolution of bone lesions, improved primary disease, and improved serum tumor markers. Although on hormonal therapy, biochemical recurrence prompted performance of 18 F-fluciclovine PET/CT. Fluciclovine PET/CT revealed primary prostate cancer progression with incidental note of avid foci in the colon for which colonoscopy was recommended. Colonoscopy with biopsy was performed with pathology revealing primary colon adenocarcinoma. Before reinitiation of prostate cancer therapy, segmental colon resection was performed with pathology positive for additional sites of colon cancer.

Identification of an anaplastic subtype of prostate cancer amenable to therapies targeting SP1 or translation elongation.

Histopathological heterogeneity is a hallmark of prostate cancer (PCa). Using spatial and parallel single-nucleus transcriptomics, we report an androgen receptor (AR)-positive but neuroendocrine-null primary PCa subtype with morphologic and molecular characteristics of small cell carcinoma. Such small cell-like PCa (SCLPC) is clinically aggressive with low AR, but high stemness and proliferation, activity. Molecular characterization prioritizes protein translation, represented by up-regulation of many ribosomal protein genes, and SP1, a transcriptional factor that drives SCLPC phenotype and overexpresses in castration-resistant PCa (CRPC), as two potential therapeutic targets in AR-indifferent CRPC. An SP1-specific inhibitor, plicamycin, effectively suppresses CRPC growth in vivo. Homoharringtonine, a Food And Drug Administration-approved translation elongation inhibitor, impedes CRPC progression in preclinical models and patients with CRPC. We construct an SCLPC-specific signature capable of stratifying patients for drug selectivity. Our studies reveal the existence of SCLPC in admixed PCa pathology, which may mediate tumor relapse, and establish SP1 and translation elongation as actionable therapeutic targets for CRPC.

Radioguided surgery for lymph node metastases in prostate cancer.

This review highlights recent advancements in radioguided surgery (RGS) for prostate cancer. Our objective is to provide expert insights into the state of research, as reflected in the selected articles, and to offer perspectives on the clinical implications and future directions that emerge from this rapidly evolving domain. Key findings include the potential of PSMA-RGS surgery to improve the detection of lymph node invasion in primary prostate cancer, to guide successful removal of metastatic lesions in oligorecurrent patients with acceptable complications, and the feasibility of robot-assisted PSMA-RGS using a miniaturized gamma probe. Additionally, the development of novel PSMA ligands and the integration of fluorescence imaging offer promising improvements in imaging and surgical guidance. PSMA-RGS is an emerging approach that shows promise for improving lymph node assessment and treatment outcomes in prostate cancer. However, its effect on cancer-specific as well as overall survival are still being investigated, and PSMA-targeted surgery remains an area of active research.

Clinical implications of AGR2 in primary prostate cancer: Results from a large-scale study.

Human anterior gradient-2 (AGR2) has been implicated in carcinogenesis of various solid tumours, but the expression data in prostate cancer are contradictory regarding its prognostic value. The objective of this study is to evaluate the expression of AGR2 in a large prostate cancer cohort and to correlate it with clinicopathological data. AGR2 protein expression was analysed immunohistochemically in 1023 well-characterized prostate cancer samples with a validated antibody. AGR2 expression levels in carcinomas were compared with matched tissue samples of adjacent normal glands. AGR2 expression levels were dichotomized and tested for statistical significance. Increased AGR2 expression was found in 93.5% of prostate cancer cases. AGR2 levels were significantly higher in prostate cancer compared with normal prostate tissue. A gradual loss of AGR2 expression was associated with increasing tumour grade (ISUP), and AGR2 expression is inversely related to patient survival, however, multivariable significance is not achieved. AGR2 is clearly upregulated in the majority of prostate cancer cases, yet a true diagnostic value appears unlikely. In spite of the negative correlation of AGR2 expression with increasing tumour grade, no independent prognostic significance was found in this large-scale study.

Deficiency in DNA Damage Repair Proteins Promotes Prostate Cancer Cell Migration through Oxidative Stress

Introduction: DNA damage repair gene deficiency defines a subgroup of prostate cancer patients with early metastatic progression and unfavorable disease outcome. Whether deficiency in DNA damage repair genes directly promotes metastatic dissemination is not completely understood. Methods: The migratory behavior of prostate cancer cells was analyzed after siRNA-mediated knockdown of DNA damage repair and checkpoint proteins, including BRCA2, ATM, and others, using transwell migration assays, scratch assays and staining for F-actin to ascertain cell circularity. Cells deficient in BRCA2 or ATM were tested for oxidative stress by measuring reactive oxygen species (ROS). The effects of ROS inhibition on cell migration were analyzed using the antioxidant N-acetylcysteine (NAC). The correlation between BRCA2 deficiency and oxidative stress was ascertained via immunohistochemistry for methylglyoxal (MG)-modified proteins in 15 genetically defined primary prostate cancers. Results: Prostate cancer cells showed a significantly increased migratory activity after the knockdown of BRCA2 or ATM. There was a significant increase in ROS production in LNCaP cells after BRCA2 knockdown and in PC-3 cells after BRCA2 or ATM knockdown. Remarkably, the ROS scavenger NAC abolished the enhanced motility of prostate cancer cells after the knockdown of BRCA2 or ATM. Primary prostate cancers harboring genetic alterations in BRCA2 showed a significant increase in MG-modified proteins, indicating enhanced oxidative stress in vivo. Conclusions: Our results indicate that DNA damage repair gene deficiency may contribute to the metastatic dissemination of prostate cancer through enhanced tumor cell migration involving oxidative stress.

Diagnostic value of dual-time point 68Ga-PSMA PET/CT image for benign and malignant lesions in patients with prostate cancer.

This study aimed to ascertain the diagnostic efficacy of routine 68Ga-PSMA imaging conducted 1h post-injection, in conjunction with delayed imaging performed 3h post-injection, for differentiating between benign and malignant lesions in prostate cancer (PCa) patients. A retrospective assessment was undertaken on 44 prostate cancer patients who had undergone both routine and delayed 68Ga-PSMA PET/CT scans. Variations in SUVmax and SUVmean values in normal organs, primary prostate cancer sites, metastatic sites, and benign lesions were analyzed. Pathological examination and extended follow-ups were used to confirm all lesions. The study encompassed 44 patients, presenting 35 primary prostate cancer lesions, 44 metastatic lesions, and 30 benign lesions. Delayed imaging (3h post-injection) demonstrated a decreasing trend in the SUVmax and SUVmean for the liver, blood, and spleen. Conversely, an increasing trend was observed for the parotid, lacrimal, and submandibular glands. For primary lesions, the SUVmax and SUVmean values were 17.63 ± 9.61 and 9.77 ± 5.18 during routine imaging, and 25.09 ± 15.11 and 14.05 ± 8.02 (P < 0.001) during delayed imaging. A comparable increase in SUVmax and SUVmean was seen in the delayed images for metastatic lesions when juxtaposed with routine images. Nevertheless, benign lesions displayed a decrease in SUVmax and SUVmean during delayed imaging when set against routine imaging (SUVmax: 3.56 ± 1.49 vs 2.93 ± 1.47, P = 0.001; SUVmean: 1.99 ± 0.87 vs 1.65 ± 0.87, P = 0.003). Imaging using 68Ga-PSMA PET/CT at 3h post-injection manifested a higher uptake and target-to-background uptake in most malignant prostate cancer lesions, but a diminished uptake in benign lesions. This observation can assist clinicians in distinguishing non-specific PSMA uptake in prostate cancer patients based on PSMA PET/CT image.

RNA m6a Methylation Regulator Expression in Castration-Resistant Prostate Cancer Progression and Its Genetic Associations.

N6-methyladenosine (m6A) methylation, a prevalent epitranscriptomic modification, plays a crucial role in regulating mRNA expression, stability, and translation in mammals. M6A regulators have gained attention for their potential implications in tumorigenesis and clinical applications, such as cancer diagnosis and therapeutics. The existing literature predominantly addresses m6A regulators in the context of primary prostate cancer (PCa). However, a notable gap in the knowledge emerges regarding the dynamic expression patterns of these regulators as PCa progresses towards the castration-resistant stage (CRPC). Employing sequential window acquisition of all theoretical mass spectra (SWATH-MS) and RNAseq analysis, we comprehensively profiled the expression of 27 m6A regulators in hormone/androgen-dependent and -independent PCa cell lines, revealing distinct clustering between tumor and adjacent normal prostate tissues. High-grade PCa tumors demonstrated the upregulation of METTL3, RBM15B, and HNRNAPA2B1 and the downregulation of ZC3H13, NUDT21, and FTO. Notably, we identified six m6A regulators associated with PCa survival. Additionally, association analysis of the PCa-associated risk loci in the cancer genome atlas program (TCGA) data unveiled genetic variations near the WTAP, HNRNPA2B1, and FTO genes as significant expression quantitative trait loci. In summary, our study unraveled abnormalities in m6A regulator expression in PCa progression, elucidating their association with PCa risk loci. Considering the heterogeneity within the PCa phenotypes and treatment responses, our findings suggest that prognostic stratification based on m6A regulator expression could enhance PCa diagnosis and prognosis.

Quantification and molecular correlates of tertiary lymphoid structures in primary prostate cancer.

To morphologically describe tertiary lymphoid structures (TLS) in prostatectomy specimens and correlate them with clinical and transcriptomic features. A total of 72 consecutive cases of entirely submitted radical prostatectomy (RP) patients tested with the Decipher Genomic Classifier were included in the study. Images were manually annotated using QuPath tools to denote tumor regions and each cluster of TLS. Clusters of lymphocytes that were surrounded on all four sides by tumor were defined as intra-tumor TLS (IT-TLS). Clusters of lymphocytes at the leading edge of carcinoma with either the prostatic pseudocapsule or benign parenchyma at one end were defined as peri-tumor TLS (PT-TLS). A classification algorithm to distinguish lymphocytes from non-lymphocytic cells using a supervised machine learning model was used. The associations between TLS formation and 265 gene expression-based signatures were examined. The magnitude of total TLS correlations with primary tumor gene expression signatures was moderate (~0.35-0.5) with several HLA, T-cell and B-cell Cluster signatures, showing positive correlation with various metrics for quantification of TLS. On the other hand, immune suppressive signatures (Treg, MDSC) were negatively correlated. While signatures for macrophages, NK cells and other immune cell types were uncorrelated for the most part. PT-TLS was associated with MHC signatures while IT TLS correlated with MHC andT-cell signatures. Clusters of inflammatory cells in the RP specimen can be divided spatially into PT TLS and IT-TLS, each with its unique molecular correlates of tumor immune microenvironment. The presence of TLS is positively correlated with MHC signatures, T- cell and B-cell cluster signatures but, negatively correlated with immune suppressive signatures. A subset of prostate cancer demonstrate a robust inflammatory response, and warrant further characterization in larger cohorts.

Abstract 1175: Differential patterns of immune infiltration in the tumor immune microenvironment associate with therapeutic response in primary prostate cancer following chemohormonal therapy

Abstract There is a critical need to develop novel therapeutic strategies and diagnostic tools to precisely deliver treatments to improve survival for men with prostate cancer. To support this development, improved strategies are needed to better understand heterogenous tumor microenvironments and tumor biology that associate with variable treatment responses. We hypothesized that the tumor immune microenvironment (TIME) plays a critical role in treatment resistance. In this study we aimed to evaluate TIME signatures of treatment response and resistance utilizing a novel, integrated technological tool to identify response patterns and enable precision sampling for comparative cellular and molecular analysis. 30 patients with newly diagnosed, locally advanced, high-risk, primary prostate cancer underwent 18F-DCFPyL PSMA PET/MRI with multiparametric MRI scans followed by 3 cycles of chemohormonal therapy (NCT03358563). Repeat PSMA PET/MRI was performed prior to prostatectomy and scans were used to categorize lesions as complete response (CR), partial response (PR), no response (NR) or normal tissue. MRI scans were used to print a 3D mold of the prostate to allow microdissection of regions of interest from the resected prostate. Cellular infiltrates were analyzed by flow cytometry in 3 to 5 tissue specimens per patient. Statistical analysis was performed with One-way ANOVA with Tukey-correction. The frequency of CD8+ T cells in the total CD45+ infiltrate was highest in normal and CR areas and was significantly reduced in PR vs CR (p&amp;lt;0.01). CXCR3+CD8+ and CD103+CD8+ T cell frequencies were also reduced in PR vs CR foci (p&amp;lt;0.01, p&amp;lt;0.05, respectively). Meanwhile, the frequency of CXCR3+CD8+ T cells was highest and significantly elevated in CR vs normal tissue. A tendency of reduced CCR6+, CXCR5+, and CCR4+CD8+ T cells was observed in PR vs CR foci, while those frequencies remained higher in normal and CR areas. An increase in total CD8+ and CD103+CD8+ T cells associated with longer progression-free survival. Additionally, the analysis of EpCAM+ cells showed a significant increase in B7H3 expression in PR vs CR lesions (p&amp;lt;0.05) and a tendency of reduced HLA I expression in foci that associated with treatment resistance. We are currently integrating analysis of myeloid cells and transcriptomic analysis of sorted CD4+, CD8+ and CD11b/CD14+ cells to further dissect patterns of therapeutic response in our study cohort. In conclusion, PSMA/PET MRI based precision sampling of tumor tissue associated with differential therapeutic response patterns captured differences in the TIME infiltrates and these observations may provide hypothesis to test biological mechanisms to expedite discovery of targetable mechanisms to improve tumor stratification and targeting in high-risk prostate cancer. Citation Format: Erika Heninger, Jamie M. Sperger, Kristin Weinstein, Brian P. Johnson, Peter G. Geiger, Shane Wells, Steve Y. Cho, Wei Huang, Philippos Tsourkas, Sean McIlwain, Irene M. Ong, Sheena C. Kerr, David F. Jarrard, David J. Beebe, Joshua M. Lang. Differential patterns of immune infiltration in the tumor immune microenvironment associate with therapeutic response in primary prostate cancer following chemohormonal therapy [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 1175.

Abstract 5199: Protease-activated CDCP1 as a marker for aggressive primary prostate cancer and castration resistance

Abstract CUB domain-containing protein 1 (CDCP1) is a type 1 transmembrane protein overexpressed in many cancers, including prostate cancer. CDCP1 has been associated with tumor progression, metastasis, drug resistance and poor prognosis in prostate cancer, making it a potential prognostic biomarker and therapeutic target. It has been shown to be overexpressed in a subset of castration resistant prostate cancers (CRPC) and cooperate with the loss of tumor suppressor PTEN to promote metastatic dissemination. Extracellular serine proteases activate CDCP1 by cleaving it into an N-terminal and C-terminal fragments. Proteolytic cleavage has been associated with the tumor-promoting functions of CDCP1. We studied the expression of full-length and cleaved form of CDCP1 in grade group 2-4 primary prostate cancer tissues and CRPCs using immunohistochemistry. Total CDCP1 staining was observed in 60% of primary prostate cancer samples, while the staining of cleaved CDCP1 was somewhat less frequently observed (45%). The results will be further analyzed regarding the PTEN status and for association with survival of the patients. In conclusion, so far, our results have indicated that cleaved CDCP1, which likely represents activated CDCP1, is detectable in GG 2-4 prostate cancers. Citation Format: Ruusu-Maaria Merivirta, Timo-Pekka Lehto, Antti Rannikko, Tuomas Mirtti, Hannu Koistinen. Protease-activated CDCP1 as a marker for aggressive primary prostate cancer and castration resistance [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 5199.

Abstract 2745: Sequential tracking of PD-L1 expression on circulating epithelial tumor cells (CETCs) in men with primary non-metastatic prostate cancer

Abstract Background: Radiotherapy (RT) is an essential component of multimodality therapy in the primary or postoperative treatment of prostate cancer with curative intent by preventing local recurrence and distant metastases, indicating its impact on residual occult tumor, such as circulating tumor cells. Immunogenic changes in cancer cells induced by RT can lead to adaptive up-regulation of PD-L1 expression. As immune checkpoint inhibition plays an increasingly important role in prostate cancer, radiogenic PD-L1 upregulation may be of therapeutic importance. The aim of this study was to determine PD-L1 status on CETCs before and during RT. Methods: Peripheral blood samples were collected from 52 primary non-metastatic prostate cancer patients. CETCs were enumerated and analyzed for PDL-L1 expression prior to (baseline), 3 and 6 weeks after the start of RT using fluorescence scanning microscopy. Results: PD-L1 expression was detectable in CETCs and localized in the membrane and/or cytoplasm. We found a correlation between PD-L1 status in CETCs and aggressiveness of cancer disease prior to RT. The frequency of PD-L1 positive CETCs depended on the grading and Gleason score of the primary tumor. Patients with a high Gleason score and G3 tumors had significantly more PD-L1 positive CETCs compared to patients with a low Gleason Score and G1 tumors. Moreover, patients in stage I/II had significantly less PD-L1 positive CETCs compared to patients in stage III/IV (mean 54.25 vs. mean 69.65; p&amp;lt;0.05). A higher number of PD-L1 positive CETCs were detected in patients who had radical prostatectomy before start of RT than in those who had no surgical intervention (mean 66.24 vs. mean 47.46; p&amp;lt;0.01). Interestingly, the fraction of PD-L1 positive CETCs decreased significantly during RT only in patients with G3 tumors and a high Gleason Score. Conclusion: Our results indicated that PD-L1 in CETCs is closely related to the aggressiveness of the primary tumor and may be a co-factor associated with the progression of prostate cancer. PD-1/PD-L1 blockade combined with RT represents a novel and promising treatment strategy that could contribute to improve the treatment efficacy of prostate cancer. Citation Format: Dorothea Schott, Monika Pizon, Ulrich Pachmann, Katharina Pachmann, Matthias Mäurer. Sequential tracking of PD-L1 expression on circulating epithelial tumor cells (CETCs) in men with primary non-metastatic 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 2745.

Abstract 371: Hypoxia-induced centrosome loss as a driver of chromosomal instability in prostate cancer

Abstract PURPOSE: This study aims to identify a causal mechanism of centrosome loss previously observed in primary prostate cancer. Prostate cancer progression is accompanied by bursts of chromosomal instability (CIN), including chromosomal translocations, oncogene amplifications, and chromothripsis. While high CIN correlates with most metrics of aggressive disease, we lack a mechanistic understanding of how CIN originates in prostate cancer. Recently, we discovered that cells in primary prostate tumors lack centrosomes, cytoplasmic organelles that ensure the fidelity of chromosome segregation by organizing the shape of the mitotic spindle. Experimental elimination of centrosomes in immortalized, non-tumorigenic prostate cell lines was sufficient to generate extensive CIN, resulting in oncogenic transformation of these lines when sub-cutaneously injected into NSG mice. Because we identified centrosome loss as a potential driver of CIN, we sought to understand mechanisms that can trigger centrosome loss in the prostate. Although centrosome loss naturally occurs during the development of some tissues, for example centrosome elimination during oogenesis, the mechanisms that trigger loss are not known. Therefore, we first investigated microenvironmental changes in early prostate cancer as a potential cause. Hypoxia, pathologically low oxygen concentration, is common in the aging prostate due to loss of vasculature and is associated with poor prostate cancer prognosis and high CIN. Therefore, we hypothesized that hypoxic exposure induces centrosome loss in prostate cells. Indeed, we found that exposure to 1% oxygen concentrations leads to progressive centrosome loss in non-tumorigenic, immortalized prostate epithelial cell lines. Using immunofluorescence of centrosomes in cultured cells, we found that hypoxia-induced centrosome loss is independent of HIF transcription but requires activation of the confluence-dependent Hippo signaling pathway. Mechanistically, we found that centrosome disassembly begins with the removal of the pericentriolar material (PCM), the outer shell of the centrosome that nucleates microtubules. We were able to block centrosome disassembly by over-expressing a constitutively-active mutant of Polo-like Kinase 1, which normally strengthens the PCM during mitosis to promote centrosome maturation. Furthermore, centrosome loss was prevented by treatment with the Protein Phosphatase 2A (PP2A) inhibitor Okadaic Acid. Using RNAseq, we have identified potential PP2A regulatory subunits that are up-regulated in cells undergoing hypoxia-induced centrosome loss. Our model is that hypoxia induces dephosphorylation of the PCM, mechanically weakening the centrosome and leaving it vulnerable to disassembly. Together with previous findings, we conclude that hypoxia-induced centrosome disassembly is a plausible driver of CIN in early prostate cancer. Citation Format: John M. Ryniawec, Gregory C. Rogers, Anne E. Cress. Hypoxia-induced centrosome loss as a driver of chromosomal instability 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 371.

Abstract 3440: Etiology of prostate cancer with the TMPRSS2:ERG fusion: A systematic review of risk factors

Abstract Background: The TMPRSS2:ERG gene fusion is the most common somatic alteration in primary prostate cancer and an early event in carcinogenesis. There are emerging data highlighting etiologic differences in prostate cancer by TMPRSS2:ERG status. This systematic review synthesized evidence from epidemiologic studies on prostate cancer risk factors for tumors with and without the TMPRSS2:ERG fusion. Methods: A systematic literature search was performed in Ovid MEDLINE, EMBASE, and Web of Science without language restriction for studies published by September 27, 2022. Studies that assessed associations between epidemiologic and genetic factors and prostate cancer risk by tumor TMPRSS2:ERG (ERG) fusion status in human populations were included. Results: Of 3,071 records identified, 20 publications comprising prospective cohort and case-control studies from five study populations (published 2009-2022) were included. Risk factors included germline genetic variants, circulating hormones, diet, lifestyle factors, and medications. The included studies suggested that taller height and higher total and free circulating testosterone levels tended to be associated with higher risk of ERG-positive, but not ERG-negative prostate cancer. CAG repeat length in the androgen receptor (AR) gene, related inversely to transcriptional activity, appeared to be associated with a lower risk of ERG-positive, but not ERG-negative prostate cancer. There was statistical evidence for etiologic differences for several germline single nucleotide polymorphisms (SNPs) by ERG status. Excess body weight, greater vigorous physical activity, greater lycopene intake, and calcium channel blocker use appeared to specifically be associated with a lower risk of ERG-positive tumors. Associations of other potential etiologic factors, including diabetes mellitus, baldness, aspirin use, circulating antioxidant levels, and sex hormones other than testosterone, with ERG-positive prostate cancer were null or inconclusive. Most associations had low precision, and the results were based on few distinct study populations, highlighting a need for replication. Conclusions: Prostate cancer with the TMPRSS2:ERG fusion may be an etiologically distinct subtype impacted by certain modifiable and hormonally-acting risk factors that align with the established mechanistic role of this gene fusion in androgen, insulin, and growth factor pathways. The findings suggest a potentially distinct genetic predisposition to prostate cancer with or without the TMPRSS2:ERG fusion. More broadly, these findings suggest that considering molecular subtypes of prostate cancer, beyond TMPRSS2:ERG, may strengthen etiologic understanding of prostate cancer and evidence for prevention. Citation Format: Colleen B. McGrath, Alaina H. Shreves, Megan R. Shanahan, Hannah E. Guard, Manelisi V. Nhliziyo, Kathryn L. Penney, Tamara L. Lotan, Michelangelo Fiorentino, Konrad H. Stopsack, Lorelei A. Mucci. Etiology of prostate cancer with the TMPRSS2:ERG fusion: A systematic review of risk factors [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 3440.

Abstract 7320: Expression of circadian rhythm genes and lethal prostate cancer

Abstract Background: The circadian rhythm regulates diverse physiological and oncologic processes. We have previously shown in epidemiology studies that disruption of the circadian rhythm may be associated with increased risk of aggressive prostate cancer, including germline polymorphisms in certain circadian rhythm genes. This study sought to investigate the relationship between tumor circadian rhythm gene expression and lethal prostate cancer. Methods: We studied patients with primary prostate cancer in the Health Professionals Follow-up Study (HPFS) and Physicians’ Health Study (PHS). We created a composite score of mRNA expression using principal components that incorporated 11 circadian rhythm genes: AANAT, ARNTL, CLOCK, CRY1, CSNK1E, MTNR1A, MTNR1B, NPAS2, PER1, PER2, PER3. An age-stratified analysis was performed, and the mean differences of the score both by Gleason score and compared to normal tissue were calculated. The relationship between the score in prostate tumor tissue and lethal prostate cancer (metastases/prostate cancer-specific death) vs. indolent disease (no metastases after &amp;gt;8 years of follow-up) was assessed using logistic regression. The contribution of each gene was evaluated by leave-one-out analysis, generating scores leaving out one gene and assessing the relationship between the modified score and lethal disease. Results: Among 404 cancer patients in HPFS/PHS, there were 119 lethal events over 30 years of follow-up (median: 17 years). The circadian rhythm gene score was lower in tumor tissue compared to tumor-adjacent, histologically normal tissue (mean difference in units of standard deviation [SD] of gene score: -0.31, 95% confidence interval [CI]: -0.48 to -0.15). In addition, the score was lower in Gleason 9-10 compared to Gleason 6 tumors (mean difference in SD units: -1.05, 95% CI: -1.55 to -0.54). The three PER genes were the most strongly correlated with each other and with the score (Spearman correlation coefficients from 0.52-0.88 for the score and 0.31-0.63 between PER genes). Higher circadian rhythm gene scores were inversely associated with lethal prostate cancer (odds ratio [OR] for highest vs. lowest quartile: 0.43, 95% CI: 0.20 to 0.90) in a dose-response fashion and after adjusting for clinical and pathologic factors. The association appeared to be stronger in patients aged ≥65 years (OR for highest vs. lowest quartile: 0.21, 95% CI: 0.08 to 0.47) compared to &amp;lt;65 years at diagnosis (OR: 0.78, 95% CI: 0.29, 2.17). Results were consistent in the leave-one-out analysis for all genes except PER2 (OR for highest vs. lowest quartile: 1.00, 95% CI: 0.55 to 1.83) and PER1 (OR: 0.55, 95% CI: 0.30 to 1). Conclusion: This study examining intratumoral circadian rhythm gene expression contributes further evidence in support of the relationship between circadian rhythm disruption and aggressive prostate cancer. Tumor expression of PER1 and PER2 may be a predominant factor in the association. Citation Format: Jane Bailey Vaselkiv, Sarah C. Markt, Hannah E. Guard, Anqi Wang, Kathryn L. Penney, Konrad H. Stopsack, Lorelei A. Mucci. Expression of circadian rhythm genes and lethal 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 7320.

Abstract 448: Alterations in glycolytic pathway enzymes and metabolic plasticity in prostate cancer progression

Abstract Background: Although oxidative phosphorylation (OXPHOS) is the main ATP source in primary prostate cancer, as the tumor progresses to castration resistance and/or metastatic disease, glycolysis becomes increasingly prevalent. Dependence on glycolysis can further increase under hypoxic conditions found in advanced cancers. We previously demonstrated that a novel small molecule, BKIDC-1553, inhibits proliferation and tumor growth of prostate cancer cell lines and xenografts through a hexokinase-2 (HK2) dependent inhibition of glycolysis. HK2 is a glucose 6-phosphorylating enzyme that works in conjunction with glucose transporter-1 (GLUT1) to drive glycolysis in cells. While our previous work suggests that BKIDC-1553 works primarily through a HK2 dependent mechanism, the objective of this current project is to further examine how expression and function of HK2 and GLUT1 are altered in response to BKIDC-1553 treatment. Methods: Hypoxic conditions are common in late-stage prostate cancer. Effects of hypoxia on cell proliferation and expression levels of HK1, HK2, and GLUT1 were examined with and without BKIDC-1553 treatment. To examine role of HK1, HK2, and GLUT1 in response to BKIDC-1553 treatment, we created CRISPR knockouts and shRNA knockdowns of HK1 and HK2 in the LNCaP prostate cancer cell line. GLUT1 was inhibited using a commercially available inhibitor, BAY-876. PCR and Western blots were used to confirm expression levels of HK1, HK2, and GLUT1. MTS proliferation assays were used to examine effect of KO and KD on response to BKIDC-1553 and BAY-876. Results: GLUT1 levels, but not HK1 or 2, increased at 72 hrs under hypoxic conditions. HK1, HK2, and GLUT1 levels all increased in cells in response to 144 hrs of BKIDC-1553 compared with 72 hrs treatment in both normoxic and hypoxic conditions. The KO and KD studies were all conducted in normoxic conditions. Westerns blots demonstrated that HK2 KO, but not HK1 KO, results in increased levels of GLUT1. HK1 or HK2 KD, however, did not alter GLUT1 levels. HK2 KD cells, with GLUT1 levels remaining the same, displayed less growth inhibition than control cells in response to BKIDC-1553 treatment, while HK2 KO cells, with increased levels of GLUT1, remained sensitive to BKIDC-1553. Because GLUT1 levels increase in response to HK2 KO, we wanted to see if inhibiting GLUT1 in these cells could decrease their proliferation. We found that KO cells were indeed more sensitive to growth inhibition of BAY-876. Conclusion/Summary: These studies indicate that KO of HK2 increases levels of GLUT1. These cells remain sensitive to BKIDC-1553 treatment, which could in part be due to the cells' continued reliance on glycolysis through increased GLUT1. A continued reliance on glycolysis allows BKIDC-1553 to continue to inhibit cell growth. Future studies examining how combination treatment with BKIDC-1553 and BAY-876 affects growth of advanced prostate cancer cells is underway. Citation Format: Cynthia Sprenger, Mika Munari, Shihua Sun, Kathryn Soriano Epilepsia, Stephen Plymate. Alterations in glycolytic pathway enzymes and metabolic plasticity in prostate cancer progression [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 448.

Abstract 253: Investigating key molecular players in putative stem cell subpopulations of prostate cancer

Abstract Background: Androgen deprivation therapy is the standard treatment for prostate cancer (PCa). Nevertheless, despite initial effectiveness, pre-existing cancer stem cell (CSC) populations invariably lead to incurable castration-resistant prostate cancer. CSCs are a subset of cancer cells possessing self-renewal properties, driving tumor progression and regrowth. CD44+ PCa cells exhibit more stemness features and are enriched in tumorigenic and metastatic progenitor cells. Here, we aim to explore different subpopulations in tumors based on levels of CD44 expression and investigate whether they have distinct molecular properties and functional characteristics. Material and Method: The number of CD44+ cells was evaluated in a tissue microarray from primary prostate cancer patient samples (EMPACT cohort) with clinical follow-up. Flow cytometry sorted the CRPC model LAPC9 tumor into CD44 high (CD44-H) and CD44 low (CD44-L) cells. RNA sequencing was performed on these subpopulations to explore their transcriptomic profiles. CD44 expression was validated at the cDNA and protein levels using qPCR and Western blot (WB) analysis. Sorted cells were maintained as organoids in vitro. To trace the dynamics of CD44-H and CD44-L subpopulations in vivo, LAPC9 tumor was labeled by fluorescent and luciferent markers. The CD44 status was determined by flow cytometry when tumor growth. Results: Patients with elevated expression of CD44 (higher number of CD44+ cells) at the time of surgery exhibited a greater propensity for clinic progression (5-year progression-free survival: 75% vs 95%, P=0.03). Furthermore, CD44-H cell ratio increased in the LAPC9 after castration, indicating that CD44-H cells can survive after treatment. Subsequent WB analysis confirmed that CD44 was highly expressed in sorted CD44-H cells, validating the flow cytometry results. Analysis of the CD44 RNA-seq data showed CD44 transcript variants CD44v10 (CD44-201) and CD44v7-10 (CD44-209) were notably upregulated in CD44-H cells. In organoid culture, sorted CD44-H cells displayed enhanced formation, indicating they possessed higher proliferative capacity and clonogenicity than CD44-L cells. Furthermore, when GFP-labeled CD44-H cells and RFP-labeled CD44-L cells were recombined in vivo, CD44-H cells exhibited robust proliferation, while CD44-L cells transitioned to a CD44hi state to facilitate tumor growth. Moreover, those GFP and RFP subpopulations displayed the same CD44hi cell ratio at the endpoint. Conclusion: Elevated CD44 expression is related to an increased risk in primary PCa. In addition, CD44-H cells exhibit high tumorigenicity in vitro and in vivo and can convert to each other. Moreover, the ratio of CD44-H cells in tumor at endpoint is consistent despite the starting CD44 expression status. Furthermore, the upregulation of CD44v10 and v7-10 in the CD44-H subpopulation may promote tumor formation and metastasis. Citation Format: Wanli Cheng, Marta De Menna, Francesco Bonollo, Panagiotis Chouvardas, George N. Thalmann, Sofia Karkampouna, Marianna Kruithof Julio. Investigating key molecular players in putative stem cell subpopulations of 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 253.

Abstract 5539: PRDM16 is an intrinsic regulator of dormancy in bone disseminated prostate cancer cells

Abstract Metastatic prostate cancer (PCa) frequently occurs in the bone and can remain inactive for extended periods after primary tumor treatment. Understanding the intricate molecular mechanisms that govern this phenomenon could open the door to novel therapies, potentially reducing mortality rates. To address this, we developed a novel protocol to induce cellular dormancy in PCa cell lines (RM1, 22Rv1, LAPC4) in vitro. We noted that dormant cells exhibited distinctive clustering and could be reactivated when exposed to serum even after 21 days of stasis. The dormancy program was validated by multiple assays including cell cycle analysis, membrane dye retention, and Edu+ incorporation. RNASeq analysis showed significant transcriptional changes during dormancy induction, with 8 genes commonly upregulated across multiple human and mouse PCa cell lines, of which the transcription factor, PRDM16. We focused on PRDM16 since, 1) it is a known regulator of hematopoietic stem cell quiescence, 2) our emerging data points to bone morphogenetic protein-7 (BMP7), a well-known exogenous mediator of dormancy as an inducer of PRDM16 expression and 3) clinically, PRDM16 is suppressed in primary PCa and active metastases. First, we validated the upregulation of PRDM16 during dormancy in vitro. Silencing PRDM16 led to impaired dormancy phenotype and cell death, while its overexpression significantly mitigated proliferation rates and promoted survival. In vivo, we employed an intra-iliac immunocompetent model (RM1 &amp; C57BL6J) and demonstrated that overexpressing PRDM16 in active RM1 cells resulted in significant reduction of metastasis formation and Ki67 expression concurrent with extended survival when injected in vivo compared to control cells. Prostate cancer cells with PRDM16 over-expression were detected in bone sections as solitary or small clusters (&amp;lt;20 cells) demonstrating an inverse relationship between PRDM16 expression and metastatic outbreak. In defining the targets via which PRDM16 controls dormancy entry, we focused on RAR related orphan receptor C (RORC) based on bioinformatic analysis and publicly available PRDM16 ChIP-Seq. Our data demonstrate that pharmacological inhibition of RORC using GSK805 promoted the apoptosis of dormant PCa cells specifically when compared to their actively growing counterparts. In conclusion, our studies have revealed the critical role of PRDM16 in promoting PCa cell dormancy, in part via upregulating RORC. Translationally, clinically approved RORC inhibitors for non-cancerous conditions (psoriasis) have been developed. We expect, based on our results, that these inhibitors could be repurposed for the eradication of dormant PCa cells in patients with advanced disease. Citation Format: Mostafa M. Nasr, Tao Li, Ryan T. Bishop, Jeremy S. Frieling, Conor C. Lynch. PRDM16 is an intrinsic regulator of dormancy in bone disseminated prostate cancer cells [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 5539.