Aggressive Variant Prostate Cancer Research Articles

A Modular Trial of Androgen Signaling Inhibitor Combinations Testing a Risk-Adapted Strategy in Patients with Metastatic Castration-Resistant Prostate Cancer.

To determine the efficacy and safety of risk-adapted combinations of androgen signaling inhibitors and inform disease classifiers for metastatic castration-resistant prostate cancers (mCRPC). In a modular, randomized phase II trial, 192 men were treated with 8 weeks of abiraterone acetate, prednisone and apalutamide (AAPA; Module 1), then allocated to Modules 2 or 3 based on Satisfactory (≥50% PSA decline from baseline and <5 CTC/7.5 mL) versus Unsatisfactory status. Men in the former were randomized to continue AAPA alone (Module 2A) or with ipilimumab (Module 2B). Men in the latter had carboplatin+cabazitaxel added to AAPA (Module 3). Optional baseline biopsies were subject to correlative studies. Median overall survival (from allocation) was 46.4 (95% CI 39.2, 68.2), 41.4 (95% CI 33.3, 49.9) and 18.7 (95% CI 14.3, 26.3) months in Modules 2A (n=64), 2B (n=64) and 3 (n=59) respectively. Toxicities were within expectations. Of 192 eligible patients, 154 (80.2%) underwent pre-treatment metastatic biopsies. The aggressive variant prostate cancer molecular profile (defects in ≥2 of p53, RB1, and PTEN) was associated with Unsatisfactory status. Exploratory analyses suggested SPP1+ and IGFBP2+ macrophages, druggable myeloid cell markers, and germline pathogenic mutations were enriched in the Unsatisfactory group. Adding ipilimumab to AAPA did not improve outcomes in men with androgen responsive mCRPC. Despite the addition of carboplatin+cabazitaxel, men in the Unsatisfactory group had shortened survivals. Adaptive designs can enrich for biologically and clinically relevant disease subgroups, to contribute to the development of marker-informed, risk-adapted therapy strategies in men with prostate cancer.

Abstract LB161: Discovery of an oral, potent, and selective CDK9 molecular glue degrader SLX-3065 active in aggressive variant prostate cancers (AVPC)

Abstract Background: The use of new potent targeted therapies in prostate cancers has led to the resistance and development of highly aggressive variant prostate cancers (AVPC), including neuroendocrine prostate cancers (NEPC). N-MYC and C-MYC oncogenes overexpress in all aggressive prostate cancers (PCa). This overexpression is highly prevalent in these lethal subtypes of cancers, detected in 2% of all Prostate Cancers and over 10-17% of mCRPC patients. Transcriptional targets of CDK9 are MYCs, which act as an oncogenic driver, sufficient to transform human-derived prostate cancer cells to take on AVPC and NEPC phenotypic changes. Additionally, N-MYC and C-MYC play key roles in tumor drug resistance, and their downregulation, through CDK9 inhibition or degradation lowers tumor growth. Our efforts have demonstrated that targeting drivers of NEPC and mCRPC with highly selective CDK9 molecular glue degraders SLX-3064 SLX-3065 was designed from reversible SLX-3039 for therapeutic intervention of mCRPC, AVPC, and NEPCs. Materials and Methods: We employed our MolecuLernTM-trained molecular glue library design strategies and in vitro CDK9 kinase binding assays. Other experiments include cellular efficacies of single-agent Molecular Glue degraders and their effect in combination experiments on 22Rv1, LASCPC-01, C4-2, and C4-2B MYC expressed PCa cells. Kinase selectivity, Nano BRET, ADME-Tox, in vitro safety, secondary pharmacological assays, Cell engraftment mouse tumor mode, and PK studies were performed. Results: We designed and synthesized a series of novel small molecule CDK9 Molecular Glue degraders based on our initial CDK9 inhibitor lead SLX-3030 and SLX-3039. The SLX-3064 and SLX-3065 reversibly bind to CDK9 with an IC50 of 9 and 7 nM in kinase binding, in target engagement assays, elicit pharmacological responses in N-MYC, C-MYC, driven prostate cancer cells in vitro in LASCPC-01 (21, 35 nM), 22Rv1 (108, 236 nM), C4-2B (15, 12 nM), C4-2 (2.7, 1.5 nM) and VCap (86, 73 nM) cell lines. SLX-3064 and SLX-3065 exhibited potent activity degrading total, pCDK9, MYCs, Mcl-1, and its downstream RNA Pol II, Ser 2, 5, 7, and pAR Ser-81 in a dose-dependent manner. Additionally, we performed in vitro ADME-Tox, hERG, P450, safety panel screen, and in vivo PK experiments in rodent and beagle dog species. Conclusion: In summary, both SLX-3064 and SLX-3065 molecular glues display complete degradation of CDK9 and its downstream markers, and these degraders possess ideal developable criteria as oral agents. With these characteristics, SLX-3065 was selected as a candidate that had the appropriate developable properties and our plans for conducting additional IND-enabling studies and future clinical trial plans will also be discussed. Citation Format: Chenyu Lin, Zhaoliang Li, Kyle Medley, David J. Bearss, Hariprasad Vankayalapati. Discovery of an oral, potent, and selective CDK9 molecular glue degrader SLX-3065 active in aggressive variant prostate cancers (AVPC) [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 LB161.

Abstract 2756: Single cell analysis reveals treatment response-associated plastic cell state and lineage switching in aggressive variant prostate cancer

Abstract Prostate cancer (PCa) is a common malignancy in men over 65, ranking as the second leading cause of cancer-related deaths among men in the United States. While most prostate cancers respond to androgen receptor (AR) targeting therapies, Aggressive Variant Prostate Cancers (AVPCs), characterized by RB1, Tp53, and/or PTEN alterations, do not. AVPCs exhibit lineage plasticity in preclinical models, enabling the expression of non-prostate epithelial lineage markers to adapt to therapeutic pressures. However, a measurable definition of lineage plasticity as a potential therapeutic target for clinical trials is currently lacking. To arrive at said definition, we perform single-nuclei RNA sequencing (snRNA-seq) on lymph node metastases from twelve AVPC patients with matched sample pairs of both pre- and post-treatment. Additionally, we include snRNA-seq data from eight non-AVPC patients as a baseline. Expanding upon our prior establishment of tumor-specific total mRNA expression (TmS) as an indicator of tumor cell lineage plasticity (Nature Biotechnology, PMID: 35697807), we employ unique molecular identifier (UMI) counts from individual cells to quantify this plasticity. We reveal a distinct cluster of tumor cells with notably high UMI counts in resistant samples, indicative of a less differentiated state and increased transcriptional diversity. This high-UMI cluster is marked by significant enrichment in pathways associated with epithelial-mesenchymal transition (EMT), stemness, one-carbon metabolism, and arginine metabolism pathways. Concurrently, there is a reduction in activity within the androgen receptor (AR) and DNA damage repair pathways. These characteristics suggest an enhanced capacity for lineage switching in AVPC tumor cells, potentially contributing to evasion from targeted therapies. Moreover, immune components within resistant samples consistently display lower UMI counts, indicating a diminished propensity for lineage plasticity. In conclusion, we present a better understanding of lineage switching in therapeutic resistance in AVPCs, paving the way for novel treatment strategies in PCa management. Citation Format: Shuai Guo, Elavarasan Subramani, Daniel E. Frigo, Patrick G. Pilié, Sangeeta Goswami, Rama Soundararajan, Ana Aparicio, Wenyi Wang. Single cell analysis reveals treatment response-associated plastic cell state and lineage switching in aggressive variant 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 2756.

Abstract 4649: BLX-3030, a potent, selective, orally available small molecule CDK9 inhibitor for aggressive variant prostate cancers

Abstract Background: The use of novel, potent targeted therapies in prostate cancers has led to the development of highly aggressive variant cancers, including neuroendocrine prostate cancer (NEPC). Gene amplification of N-MYC and C-MYC oncogenes leads to its overexpression in NEPC and mCRPC patients, highly prevalent in these lethal subtypes of cancers detected in 2% of all Prostate Cancers (PCa) and over 10-17% of mCRPC patients. N-MYC is a transcriptional target of CDK9, which acts as an oncogenic driver sufficient to transform human-derived prostate cancer to take on NEPC phenotypic changes resulting in a more aggressive disease identified in late-stage human PCa patients. Additionally, N-MYC and C-MYC are required for tumor drug resistance, and their downregulation through CDK9 inhibition lowers tumor growth. Our efforts have demonstrated that targeting both N-MYC and C-MYC as a driver of NEPC and mCRPC with highly selective CDK9 inhibitor BLX-3030 is a viable approach for therapeutic intervention of mCRPC and NEPC. Materials and Methods: Our empirical data-driven AI/ML MolecuLernTM fragment library, workflows, LigEdit design strategies, and hit2-lead optimization methods are employed. In vitro experiments include kinase glo, cell titer glo, selectivity profiler, ADME-Tox, FACS/apoptosis, cell migration, live cell imaging, immunofluorescent, western blot, combination studies and in vivo experiments including PK, prostate tumor models, 7-day tox, BLX-3030 non (GMP) scaleup and safety pharmacology experiments conducted. Results: We synthesized a series of novel small molecule CDK9 inhibitors that reversibly bind to CDK9, competitively block the ATP site with an IC50 of 1.06 nM, and elicit pharmacological responses in N-MYC, C-MYC, and other prostate cancer cells in vitro and in vivo. We studied the CDK9 N-MYC expression detected in PC-3, DU-145, LNCaP, and in LASCPC-01, NCI-H660, and 22RV1 cell lines. BLX-3030 exhibited potent cellular efficacy with an IC50 of 22 to 590 nM in PC cell lines and in N-MYC expressed cells had an activity of 76, 470, and 132 nM respectively, and reduced pCDK9, C-MYC, Mcl-1, N-MYC and its downstream RNA Pol II (Ser-2) and pAR (Ser-81) dose-dependently. BLX-3030 exhibits in vivo antitumor activity in LASCPC-01, 22RV1, and C4-2 prostate cancer mouse models. Several ADME-Tox, MTD, dose range finding, hERG and other in vivo safety pharmacology experiments have advanced BLX-3030 to the IND enabling studies. Conclusions: BLX-3030 is currently being investigated in non-clinical toxicology, toxicokinetic, and core battery of safety pharmacology studies including the assessment of effects on cardiovascular, central nervous, and respiratory systems. Citation Format: Zhaoang li, Chenyu Lin, Kyle Medley, Hariprasad Vankayalapati, David J. Bearss. BLX-3030, a potent, selective, orally available small molecule CDK9 inhibitor for aggressive variant prostate cancers [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 4649.

Tissue-Based Diagnostic Biomarkers of Aggressive Variant Prostate Cancer: A Narrative Review.

Prostate cancer (PC) is a common malignancy among elderly men, characterized by great heterogeneity in its clinical course, ranging from an indolent to a highly aggressive disease. The aggressive variant of prostate cancer (AVPC) clinically shows an atypical pattern of disease progression, similar to that of small cell PC (SCPC), and also shares the chemo-responsiveness of SCPC. The term AVPC does not describe a specific histologic subtype of PC but rather the group of tumors that, irrespective of morphology, show an aggressive clinical course, dictated by androgen receptor (AR) indifference. AR indifference represents an adaptive response to androgen deprivation therapy (ADT), driven by epithelial plasticity, an inherent ability of tumor cells to adapt to their environment by changing their phenotypic characteristics in a bi-directional way. The molecular profile of AVPC entails combined alterations in the tumor suppressor genes retinoblastoma protein 1 (RB1), tumor protein 53 (TP53), and phosphatase and tensin homolog (PTEN). The understanding of the biologic heterogeneity of castration-resistant PC (CRPC) and the need to identify the subset of patients that would potentially benefit from specific therapies necessitate the development of prognostic and predictive biomarkers. This review aims to discuss the possible pathophysiologic mechanisms of AVPC development and the potential use of emerging tissue-based biomarkers in clinical practice.

Unraveling the Global Proteome and Phosphoproteome of Prostate Cancer Patient-Derived Xenografts.

Overall, our study highlights the importance of protein-based identification when compared with RNA and provides a rich resource of new and feasible targets for clinical assay development and in understanding the underlying biology of these tumors.

Letter to the editor: Aggressive variant prostate cancer: An exemplary case study and comprehensive literature survey.

This article enthusiastically explores the study of highly aggressive variant prostate cancer (AVPC), acknowledging its relatively rare yet highly menacing presence within the realm of prostate cancer. The paper delves into the pathological characteristics of AVPC, diagnostic and therapeutic challenges, and the potential applications of precision medicine and molecular imaging in the future.

Evaluation of the Aggressive-Variant Prostate Cancer Molecular Signature in Clinical Laboratory Improvement Amendments (CLIA) Environments.

Aggressive-variant prostate cancers (AVPCs) are a subset of metastatic castrate-resistant prostate cancers (mCRPCs) characterized by defects in ≥ two of three of TP53, RB1, and PTEN (AVPCm), a profile linked to lineage plasticity, androgen indifference, and platinum sensitivity. Men with mCRPC undergoing biopsies for progression were assessed for AVPCm using immunohistochemistry (IHC), next-generation sequencing (NGS) of solid tumor DNA (stDNA), and NGS of circulating tumor DNA (ctDNA) assays in CLIA-certified labs. Biopsy characteristics, turnaround times, inter-reader concordance, and inter-assay concordance were assessed. AVPCm was detected in 13 (27%) patients via IHC, two (6%) based on stDNA, and seven (39%) based on ctDNA. The concordance of the IHC reads between pathologists was variable. IHC had a higher detection rate of AVPCm+ tumors with the shortest turnaround times. stDNA had challenges with copy number loss detection, limiting its detection rate. ctDNA detected the greatest proportion of AVPCm+ tumors but had a low tumor content in two thirds of patients. These data show the operational characteristics of AVPCm detection using various assays, and inform trial design using AVPCm as a criterion for patient selection or stratification.

Concordance and Clinical Significance of Genomic Alterations in Progressive Tumor Tissue and Matched Circulating Tumor DNA in Aggressive-Variant Prostate Cancer.

Sequencing of ctDNA is a minimally invasive approach to reveal the genomic alterations of cancer, however, its comparison with sequencing of tumor tissue has not been well documented in real-world patients with aggressive-variant prostate cancer (AVPC). Concordance of genomic alterations was assessed between progressive tumor tissue and matched ctDNA by next-generation sequencing for 63 AVPC patients. Associations of genomic alterations with progression-free survival (PFS) and overall survival (OS) were investigated using Kaplan-Meier and Cox regression analyses. A total of 161 somatic mutations (SMs) and 84 copy number variants (CNVs) were detected in tumors, of which 97 were also found in ctDNA, giving concordance of 39.6% (97/245) across all SMs and CNVs, 49.7% for SMs only and 20.2% for CNVs only. Across all AVPC patients, chemotherapy was associated with significantly longer median PFS (6 vs. 0.75 mo., P=0.001) and OS (11 vs. 8 mo., P < 0.001) than next-generation hormonal therapy (NHT). Among types of chemotherapy, additional platinum-based chemotherapy was associated with significantly longer median PFS and OS than docetaxel only in patients with TP53, RB1 or PTEN alterations, and in those with ctDNA% ≥ 13.5%. The concordance analysis first provides evidence for combining the sequencing of ctDNA and tumor tissue in real-world AVPC patients. Chemotherapy is associated with significantly better survival than NHT, and the benefit of additional platinum-based chemotherapy may depend on the presence of alterations in TP53, RB1 or PTEN and on a sufficiently high proportion of ctDNA in AVPC patients.

Circulating Tumour DNA Biomarkers Associated with Outcomes in Metastatic Prostate Cancer Treated with Lutetium-177-PSMA-617

BackgroundLutetium-177-prostate-specific membrane antigen- 617 (Lu-PSMA) is an effective therapy for metastatic castration-resistant prostate cancer (mCRPC). However, treatment responses are heterogeneous despite stringent positron emission tomography (PET)-based imaging selection criteria. Molecularly based biomarkers have potential to refine patient selection and optimise outcomes. ObjectiveTo identify circulating tumour DNA (ctDNA) features associated with treatment outcomes for men treated with Lu-PSMA. Design, setting, and participantsctDNA from men treated with Lu-PSMA in combination with idronoxil for progressive mCRPC were analysed using an 85-gene customised sequencing assay. ctDNA fractions, molecular profiles, and the presence of alterations in aggressive-variant prostate cancer (AVPC) genes were analysed at baseline, cycle 3 and at disease progression. InterventionMen received Lu-PSMA with idronoxil every 6 wk for up to six cycles. Outcome measurements and statistical analysisBaseline and exit PSMA and fluorodeoxyglucose PET/computed tomography (CT) imaging was conducted at baseline and study exit. Single-photon emission CT (SPECT) scans were performed 24 h after Lu-PSMA. Blood samples were collected at baseline,cycle 3 and at disease progression. Cox proportional-hazards models were used to assess associations and derive hazard ratios (HRs) and confidence intervals (CIs) for associations between molecular factors, imaging features, and clinical outcomes. Results and limitationsSixty samples from 32 men were sequenced (32 at baseline, 24 at cycle 3, four from patients with disease progression); two samples (baseline, on-treatment) from one individual were excluded from analysis owing to poor quality of the baseline sequencing data. Alterations in AVPC genes were associated with shorter prostate-specific antigen (PSA) progression-free survival (PFS) and overall survival (OS) in univariate (HR 3.4, 95% CI 1.5–7.7; p = 0.0036; and HR 3.3, 95% CI 1.4–7.7; p = 0.0063, respectively) and multivariate analyses (HR 4.8, 95% CI 1.8–13; p = 0.0014; and HR 4.1, 95% CI 1.6–11; p = 0.004). ConclusionsctDNA alterations in AVPC genes were associated with shorter PSA PFS and OS among men treated with Lu-PSMA and intermittent idronoxil. These candidate molecular biomarkers warrant further study to determine whether they have predictive value and potential to guide synergistic combination strategies to enhance outcomes for men treated with Lu-PSMA for mCRPC. Patient summaryCertain DNA/gene changes detected in the blood of men with advanced prostate cancer were associated with shorter benefit from lutetium PSMA, a targeted radioactive therapy. This information may be useful in determining which men may benefit most from this treatment, but additional research is needed.

Suppression of Tumor Cell Lactate-generating Signaling Pathways Eradicates Murine PTEN/p53-deficient Aggressive-variant Prostate Cancer via Macrophage Phagocytosis.

Phosphatase and tensin homolog (PTEN) loss-of-function/PI3K pathway hyperactivation is associated with poor therapeutic outcomes and immune checkpoint inhibitor resistance across multiple malignancies. Our prior studies in Pb-Cre;PTENfl/flTrp53fl/fl genetically engineered mice (GEM) with aggressive-variant prostate cancer (AVPC) demonstrated tumor growth control in 60% mice following androgen deprivation therapy/PI3K inhibitor (PI3Ki)/programmed cell death protein 1 (PD-1) antibody combination, via abrogating lactate cross-talk between cancer cells and tumor-associated macrophages (TAM), and suppression of histone lactylation (H3K18lac)/phagocytic activation within TAM. Here, we targeted immunometabolic mechanism(s) of PI3Ki resistance, with the goal of durable tumor control in AVPC. Pb-Cre;PTENfl/flTrp53fl/fl GEM were treated with PI3Ki (copanlisib), MEK inhibitor (trametinib) or Porcupine inhibitor (LGK'974) singly or their combinations. MRI was used to monitor tumor kinetics and immune/proteomic profiling/ex vivo coculture mechanistic studies were performed on GEM tumors or corresponding tumor-derived cell lines. Given our proteomic profiling showing persistent MEK signaling within tumors of PI3Ki-resistant GEM, we tested whether addition of trametinib to copanlisib enhances tumor control in GEM, and we observed 80% overall response rate via additive suppression of lactate within TME and H3K18lac within TAM, relative to copanlisib (37.5%) monotherapy. The 20% resistant mice demonstrated feedback Wnt/β-catenin activation, resulting in restoration of lactate secretion by tumor cells and H3K18lac within TAM. Cotargeting Wnt/β-catenin signaling with LGK'974 in combination with PI3Ki/MEKi, demonstrated durable tumor control in 100% mice via H3K18lac suppression and complete TAM activation. Abrogation of lactate-mediated cross-talk between cancer cells and TAM results in durable ADT-independent tumor control in PTEN/p53-deficient AVPC, and warrants further investigation in clinical trials.

Current Trends in Chemotherapy in the Treatment of Metastatic Prostate Cancer.

Prostate cancer is the second most common cancer among men. Despite advances in diagnosis and management, prostate cancer led to more than 300,000 deaths globally in 2020. Chemotherapy is a cornerstone of therapy for advanced prostate cancer and can prolong survival of patients with both castration-sensitive and castration-resistant disease. Herein, we present a comprehensive review of the data supporting implementation of chemotherapy in the modern treatment of advanced prostate cancer, with special attention to the use of chemotherapy for aggressive variant prostate cancer (e.g., neuroendocrine prostate cancer) and the combination of chemotherapy with androgen signaling inhibitors. As the field of prostate cancer research continues to rapidly evolve yielding novel agents and treatment modalities, chemotherapy continues to play an essential role in prolonging the survival of patients with advanced and metastatic prostate cancer.

Metronomic Administration of Topotecan Alone and in Combination with Docetaxel Inhibits Epithelial-mesenchymal Transition in Aggressive Variant Prostate Cancers.

The utilization of metronomic-like dosing regimens of topotecan alone and in combination with DTX resulted in the suppression of makers associated with EMT and stem-like cell populations in AVPC models. The identification of molecular signatures and their potential to serve as novel biomarkers for monitoring treatment efficacy and disease progression response to treatment efficacy and disease progression were achieved using bulk RNA-seq and single-cell-omics methodologies.

Case Series of Men with the Germline APC I1307K variant and Treatment-Emergent Neuroendocrine Prostate Cancer

Introduction: Somatic mutations in the Wnt signaling gene Adenomatous Polyposis Coli (APC) promote metastatic prostate cancer (PCa) progression. Less is known regarding the impact of germline APC mutations on PCa outcomes. We sought to investigate the prevalence of aggressive variant PCa (AVPC) and treatment-emergent neuroendocrine PCa (t-NEPC) in patients with the germline APC I1307K variant, an alteration found in 7% of Ashkenazi Jewish men. Materials and MethodsWe report a retrospective cohort study comparing patients with PCa and either APC I1307K germline mutation, APC somatic mutations, or unselected patients. Proportions of patients with AVPC among all the cases were estimated along with 95% Clopper-Pearson exact confidence intervals (CI). Odds ratios with 95% CI were provided for the prevalence of t-NEPC and AVPC in patients with germline APC I1307K compared to patients with frameshift alterations in APC. ResultsFrom 2016-2022, 18 patients with PCa at 3 institutions with the germline APC (I1307K) mutation were identified. Clinically-defined AVPC was found in 8 of the 15 cases with metastatic disease (53%; 95% CI: 26%-79%). Combined somatic alterations in two or more of RB1, TP53 or PTEN (molecularly-defined AVPC) were found in 5/18 cases (28%; 95% CI: 10%-54%). When compared to 20 patients with APC somatic frameshift mutations, patients with the germline APC I1307K variant had a significantly increased risk of AVPC (OR 7.2; 95% CI 1.27, 40.68). ConclusionPCa that develops in the presence of the germline APC I1307K mutation appear to be enriched for clinically-defined and molecularly-defined AVPC and in particular, for t-NEPC.

Abstract B070: Global proteomics and phosphoproteomics profiling of prostate cancer patient derived xenografts tumors from the LuCaP series

Abstract Castration Resistant Prostate Cancer (CRPC) is a form of prostate cancer (PCa) that is resistant to androgen deprivation therapies. Resistance to these therapies leads to metastatic CRPC of adenocarcinoma (AD) origin and can transform to emergent aggressive variant prostate cancer (AVPC) which has genetic aberration features similar to neuroendocrine (NE) phenotypes. Understanding and identifying the underlying mechanisms of resistance and genetic transformations leading to protein alterations will enable us to develop novel therapeutic methods to counteract this resistance and improve outcomes for men with lethal metastatic prostate cancer. To this end, we used patient-derived xenografts (PDXs), an in-vivo clinically relevant model from advanced prostate cancer (PC) patients, to investigate the biology, identify novel protein targets and evaluate new treatment modalities. We aimed to identify known and novel protein kinase targets that might be phospho-regulated unique between CRPC, in AD and AVPC in NE. To pursue this, we applied a mass spectrometry base phosphoproteomics analysis. We processed 48 PDX samples, which included 15 non-castrated (NCR), 18 castration resistant (CR), which are the AD samples and 15 AVPC, the NE tumors. To enrich for global phosphorylated residues, we used sequential metal oxide affinity chromatography. We sequenced peptides from each sample using liquid chromatography in tandem with Orbitrap Eclipse Tribid MS and FAIMS technology for 2 hour gradients. To normalize and calibrate the LC method and to compare across all 48 runs, we spiked-in 400 femtomol of internal standards (iRT) to each sample. For peptide sequence and search analysis, we used Maxquant search algorithm. Using a &amp;gt; 0.75 probability phospho-residue cut-off and 5% FDR, we identified more than 9,700 phospho-residues. We identified RET, ASCL1, CHGA and SYP in NEPC and Androgen Receptor (AR), FOXA1, HOXB13, NKX3.1 and TACSTD2 in the adenocarcinoma PDX LuCap tumor samples, which confirms that our approach detected specific proteins already previously established. We subsequently performed a kinase substrate enrichment analysis and identified GSK-3, ERK1, ERK2, CDK5 kinases to be significantly enriched in the NE tumors while ATM kinase and PKC alpha and beta were enriched in the AD PDX tumor samples. Hierarchical clustering analysis across NE versus AD tumor samples indicated that samples within each group clustered uniquely where we observed intra and inter sample variability. We generated pathway enrichment and GSEA analysis, identified novel targets for therapeutic treatments and novel surface proteins. In conclusion, we have performed a global mass spectrometry based proteomic analysis and created an important first global phosphoproteomics and proteomics database that provides insights into the differentially regulated protein and phosphoproteins between AD and NE PDX tumors and provide a protein database source to develop new hypothesis. Citation Format: Zoi E. Sychev, Gabbrianne E. Larson, Hannah E. Bergom, Abderrahman E. Day, Megan E. Ludwig, Atef E. Ali, Eva Corey, Stephen R. Plymate, Justin E. Hwang, Justin M. Drake. Global proteomics and phosphoproteomics profiling of prostate cancer patient derived xenografts tumors from the LuCaP series [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 B070.

Platinum-based chemotherapy in patients with castration-resistant prostate cancer and hepatic metastases.

e17063 Background: Patients with metastatic castration-resistant prostate cancer (mCRPC) and hepatic metastases face a dismal prognosis. In fact, the majority of phase 3 trials show no benefit of novel treatment modalities including Lutetium PSMA radioligand therapy (LuPSMA-RLT) in comparison with standard therapies for the subgroup of visceral metastases. In aggressive variant prostate cancer, the addition of platinum resulted in a clinically relevant improvement of progression free survival (PFS) and overall survival (OS). Whether adding platinum is also beneficial in unselected mCRPC patients with hepatic metastasis is unclear. Methods: We retrospectively analyzed mCRPC patients diagnosed with hepatic metastasis and treated with platinum-based chemotherapy or LuPSMA-RLT in three German centers (Hamburg, Essen, Munich). Patients with pure neuroendocrine prostate cancer were excluded. Survival rates and 95% confidence intervals (CI) were compared using the Kaplan Meier method and the logRank test. Results: A total of 84 mCRPC patients with hepatic metastasis who had received at least one platinum-based therapy and 32 patients treated with LuPSMA-RLT were evaluated. Median age at treatment initiation was 67 and 73 years. Patients had undergone a median of three treatment lines (83% ≥ 1 new hormonal agent (NHA); 87% ≥ 1 taxane based chemotherapy) before initiation of platinum based chemotherapy and a median of 4 treatment lines before LuPSMA-RLT. Median time to initiation of 1st platinum-based chemotherapy after diagnosis of liver metastases was 55 days. In total, 37% received carboplatin/cabazitaxel, 26% cisplatin or carboplatin/ etoposide, 11% carboplatin/docetaxel, and 26% other platinum-based combination therapies. In the platinum-treated group, 52.6% and 27% of the patients did not show progression at 3 and 6 months after treatment initiation as compared to 44.1% and 19.3% of the patients who received LuPSMA-RLT with a median PFS of 3.1 and 2.4 months, respectively. At 6 months 71.3% of the platinum-treated patients and 56.6% of the LuPSMA-RLT were alive. Overall, BRCA1/2 status was available for 53 of the platinum-treated patients, 15% of whom had a pathogenic alteration in either gene. This small subgroup was found to have a similar OS compared to the overall cohort. Conclusions: Platinum-based chemotherapy showed promising activity in mCRPC patients with hepatic metastasis. Given the high unmet medical need, platinum-based combination therapies should be further evaluated prospectively. [Table: see text]

Abstract 3406: GATA2 a novel potential therapeutic target for treatment of neuroendocrine prostate cancer

Abstract Neuroendocrine Prostate Cancer (NEPC) is a lethal and aggressive variant of prostate cancer (PC), arises from prostate adenocarcinoma, mainly as a treatment resistant mechanism to Androgen Receptor (AR) signaling inhibitors like enzalutamide. It is independent of AR signaling and characterized by upregulation of neuroendocrine markers like CHGA, SYP, EZH2, MYCN, and CD56. Despite of therapeutic advances, this lethal subtype of PC remains undruggable and has a shorter survival period. Our lab, as well as others, have previously reported several critical functions of GATA2 in AR signaling in PC progression, but the role of GATA2 in NEPC, remained unclear. Here we investigated the role of GATA2 in NEPC using our Patient Derived Xenografts (PDXs), 3D organoid, and 2D cell line models and characterized the pharmacological potency of K-11706, a small molecule inhibitor (SMI) for GATA2 against those NEPC models. To overcome the absence of suitable in vitro models for NEPC, first, we developed 3D organoid and 2D cell line models from NEPC PDX models generated and shared by Dr. Nora Navone at MDACC (mdpc 155-2 and mdpc 144-13). Molecular and histological characterization of these newly developed models showed retention of parent molecular and histological features of their corresponding PDXs. Immunohistochemical characterization of NEPC patient samples and PDXs shows a strong expression of GATA2 protein. Similarly, enzalutamide sensitive cells (16DCRPC cells) showed a significant upregulation of GATA2 mRNA along with neuroendocrine marker genes upon treatment with enzalutamide suggesting upregulation of GATA2 during progression from Castration Resistant Prostate Cancer (CRPC) to NEPC. Pharmacological inhibition of GATA2 by a previously reported SMI, K-11706, efficiently reduced 3D organoid growth and cell viability in vitro, suggesting GATA2 as a potential therapeutic target for NEPC. Gene set enrichment analysis (GSEA) involving our RNA seq data from NEPC cell lines after both K-11706 treatment as well as silencing GATA2 using siRNA (siGATA2) shows a high enrichment score with respect to EZH2 inhibition in curated datasets involving EZH2 inhibition. MTT assay involving a combination of K-11706 and EPZ6438 (EZH2 inhibitor) reduced NEPC cell viability more efficiently than used alone, suggesting a combinational strategy for the treatment of this lethal aggressive PC. NEPC cell line transcriptional profiling and functional pathway analysis of the K-11706 and siGATA2 transcriptomic footprint against curated databases delineated a biological network composed of genes involved in the epithelial mesenchymal transition, hypoxia, genes regulated by NF-kB in response to TNF and KRAS signaling. Based on these results, we propose GATA2 as an actionable therapeutic target for the treatment of NEPC, and pharmacological inhibition of both GATA2 and EZH2 by small molecule inhibitors is effective in NEPC models in vitro. Citation Format: Amit K. Dash, Maria Elisa Ruiz Echartea, Darlene Skapura, Karen Berman de Ruiz, Jenny Jianmin Deng, Cristian Coarfa, Salma Kaochar. GATA2 a novel potential therapeutic target for treatment of neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3406.

Abstract 3688: Exploring metabolic vulnerabilities of metastatic prostate cancer to bone

Abstract Currently, limited knowledge is available on subtype-specific metabolic features and their implications for treatment. Here, we investigated the metabolic determinants of the two major subtypes of castration-resistant prostate cancer (androgen receptor-expressing prostate cancer, ARPC; and aggressive variant prostate cancer, AVPC). Transcriptomic analyses revealed enrichment of gene sets involved in oxidative phosphorylation in ARPC tumor samples compared to AVPC. Unbiased screening of metabolic signaling pathways in PDX models by proteomic analyses further supported an enrichment of oxidative phosphorylation in ARPC compared to AVPC, and a skewing toward glycolysis by AVPC. Metabolic in vitro analyses showed that C4-2B cells depended on aerobic respiration, while PC3 cells relied more heavily on glycolysis, as further confirmed by pharmacological interference using IACS-010759, a clinical grade inhibitor of oxidative phosphorylation tested in patients. In vivo studies confirmed a significant reduction by IACS-010759 in C4-2B tumors implanted subcutaneously or in bone, and no effect in subcutaneous PC3 tumors. Unexpectedly, PC3 tumors in bone responded to IACS-010759, indicating a microenvironment-induced metabolic reprogramming. These results suggest that castration-resistant ARPC and AVPC exhibit different metabolic dependencies with aerobic respiration being a major driver of ARPC, while AVPC depends on glycolysis, but can undergo metabolic reprogramming in bone. Such metabolic vulnerabilities may be exploited to either introduce further lines of treatments or in combination with the existing therapies. These findings also underscore the important role that the tumor microenvironment can play in reprogramming prostate cancer metabolism and thus, influence the efficacy of metabolically targeted therapies. Citation Format: Federica Mossa, Daniele Robesti, Christopher Vellano, Mark Titus, Joe Marszalek, Daniel Frigo, Christopher Logothetis, Taranjit Gujral, Eleonora Dondossola. Exploring metabolic vulnerabilities of metastatic prostate cancer to bone. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3688.

Abstract 1447: Retinoic acid-induced 2 driven polymerization of c-terminal binding proteins sustains epithelial differentiation in castration-resistant prostate cancer

Abstract Previously, we found that increased Retinoic acid-induced 2 (RAI2) protein concentration in primary tumors predicts early biochemical relapse of prostate cancer patients and described a co-repressor function of RAI2 related to androgen receptor activity (1). The presence of a non-canonical tandem ALDLS motif on RAI2 protein prompted the present investigation on a possible role of a dual interaction of RAI2 with C-terminal binding proteins (CtBPs) in relation to prostate cancer progression. We analyzed RAI2 gene expression as well as CtBP1 protein localization and constitution in circulating tumors cells (CTCs) isolated from metastatic prostate cancer patients by semi-quantitative PCR analysis and immune-fluorescence staining. We employed an integrated structural biology approach combining biophysical techniques like isothermal calorimetry, circular dichroism, size exclusion chromatography with high-resolution structural biology techniques including X-ray crystallography and single particle cryo-electron microscopy. We established RAI2-depleted VCaP cells and used this model for validation of the obtained results. RAI2 gene expression is significantly increased in CTCs isolated from patients with castration-resistant disease in comparison to CTCs isolated from patients with hormone-sensitive, aggressive or neuroendocrine variant prostate cancer. We detected CtBP1 protein foci in the nuclei of individual CTCs. We show that RAI2 induces CtBP polymerization. Using single particle cryo-electron microscopy, we obtained crucial insights into the structural organization of this filament. RAI2 inactivation in VCaP cells caused a significant reduction of both CtBP proteins, which is accompanied by the disappearance of CtBP protein aggregates in nuclei. In addition, we observed the induction of neuroendocrine features, marked by the induction of Synaptophysin and Chromogranin A, a higher nucleus to cytoplasm ratio and smaller cell size of RAI2-depleted cells. In summary, we report tandem motifs-induced polymerization of CtBP’s for the first time. We found that elevated RAI2 gene expression is a characteristic of castration-resistant prostate cancer. Because RAI2 depletion resulted in loss of CtBP aggregates and the induction of neuroendocrine traits, we conclude that RAI2-driven CtBP polymerization sustains epithelial differentiation in castration-resistant prostate cancer. These findings holds potential for the diagnosis of castration-resistant disease and inhibiting the progression from castration-resistant to neuroendocrine prostate cancer. 1. Besler K, Weglarz A, Keller L, von Amsberg G, Bednarz-Knoll N, Offermann A, et al. Expression Patterns and Corepressor Function of Retinoic Acid-induced 2 in Prostate Cancer. Clin Chem 2022;68:973-83 Citation Format: Stefan Werner, Nishit Goradia, Edukondalu Mullapudi, Lina Merkens, Sarah Greimeier, Aleksandra Węglarz, Gunhild von Amsberg, Harriet Wikman, Klaus Pantel, Matthias Wilmanns. Retinoic acid-induced 2 driven polymerization of c-terminal binding proteins sustains epithelial differentiation in castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1447.

Germline APC (I1307K) mutation and clinical outcomes in prostate cancer.

139 Background: The germline I1307K mutation in the adenomatous polyposis coli (APC) gene is a well-known alteration identified in approximately 6% of the Ashkenazi Jewish population. This mutation confers an increased risk of developing colorectal and other cancers. We previously reported high prevalence of aggressive variant prostate cancer (AVPC) in patients with the germline APC (I1307K) mutation. Herein, we report a larger case control analysis evaluating the hypothesis that AVPC is enriched in these patients. Methods: We reviewed records from New York University, Johns Hopkins University and Sheba Medical Center to identify patients with the APC (I1307K) mutation. Eligibility criteria included the identification of the mutation either on germline or somatic tissue testing (when germline testing was not available). AVPC was defined using previously established criteria. Combined somatic alterations in two or more of following genes were assessed: RB1, TP53, PTEN. These somatic alterations have been previously associated with AVPC. We compared cases with 21 controls with APC frameshift mutations. For categorical variables, the odds ratios (OR) for cases compared to controls are provided with 95% confidence intervals (CI). Continuous variables were summarized with descriptive statistics and compared between the case and control groups using 2-sided nonparametric Wilcoxon Rank Sum tests. Results: From 2016-2022, 18 patients at 3 institutions with the germline APC (I1307K) mutation and 21 controls at NYU with frameshift APC mutations were identified. Median ages did not differ between cases (73.5 years) and controls (71 years). At the time of analysis 13 cases (72%) and 18 (86%) controls were alive (OR: 0.43, 95% CI: 0.09, 1.24). The odds of metastatic disease among cases is 2.03 times that of controls (95% CI: 0.56, 7.32). Median PSA at diagnosis was 8 ng/mL (0.4-780) in cases and 12 ng/mL (4.7-1500) in controls. The odds of small cell histology (either on initial or subsequent biopsy) was 18 times greater than in controls (5 cases; 28% and 1 control; 5%). The odds of clinically-defined AVPC was 9.5 times greater in cases than in controls (9 cases; 50% and 2 controls; 10%, 95% CI: 1.69-53.3). In patients with metastatic disease at diagnosis 7/10 cases (70%) vs 0/9 controls had AVPC. The odds of combined somatic alterations in two or more of RB1, TP53 or PTEN was 5.1 times greater in cases than in controls (4 cases; 22% and 1 control; 5%, 95% CI: 0.58, 56.73). Conclusions: Prostate cancers that develop in the presence of the germline APC (I1307K) mutation appear to be enriched for clinically-defined and molecularly-defined AVPC compared to patients with frameshift APC mutations. The odds of combined somatic alterations in two or more of RB1, TP53 and PTEN were more common in cases than in the controls. Larger studies to identify the impact of germline APC (I1307K) mutation in the somatic genomic and epigenomic landscape of prostate cancer are ongoing.