Tan, Winston

Abstract Metastatic castration-resistant prostate cancer (mCRPC) is an aggressive malignancy with poor outcomes. To investigate novel therapeutic strategies, we characterized three new metastatic prostate cancer patient derived-tumor xenograft (PDTX) models and developed 3D spheroids from each to investigate molecular targeted therapy combinations including CDK4/6 inhibitors (CDK4/6i) with AKT inhibitors (ATKi). Metastatic prostate cancer tissue was collected and three PDTX models were established and characterized using whole-exome sequencing. PDTX 3D spheroids were developed from these three PDTXs to show resistance patterns and test novel molecular-targeted therapies. CDK4/6i's were combined with AKTi's to assess synergistic antitumor response to prove our hypothesis that blockade of AKT overcomes drug resistance to CDK4/6i. This combination was evaluated in PDTX three-dimensional (3D) spheroids and in vivo experiments with responses measured by tumor volumes, PSA, and Ga-68 PSMA-11 PET-CT imaging. We demonstrated CDK4/6i's with AKTi's possess synergistic antitumor activity in three mCRPC PDTX models. These models have multiple unique pathogenic and deleterious genomic alterations with resistance to single-agent CDK4/6i's. Despite this, combination therapy with AKTi's was able to overcome resistance mechanisms. The IHC and Western blot analysis confirmed on target effects, whereas tumor volume, serum PSA ELISA, and radionuclide imaging demonstrated response to therapy with statistically significant SUV differences seen with Ga-68 PSMA-11 PET-CT. These preclinical data demonstrating antitumor synergy by overcoming single-agent CDK 4/6i as well as AKTi drug resistance provide the rational for a clinical trial combining a CDK4/6i with an AKTi in patients with mCRPC whose tumor expresses wild-type retinoblastoma 1.

Abstract Background The efficacy of pembrolizumab monotherapy in metastatic castration-resistant prostate cancer patients when stratified by MSI-H and/or TMB-H is poorly defined. Additionally, outcomes based on sequencing source (i.e., tissue or liquid biopsy) have not been well described. We sought to assess outcomes of pembrolizumab monotherapy in patients with mCRPC and compare efficacy based on MSI-H and/or TMB-H when identified by tissue or liquid biopsy. Methods A retrospective analysis was performed of mCRPC patients treated at Mayo Clinic with pembrolizumab monotherapy between 2018 and 2023. Objective response rates (ORR), median progression-free survival (mPFS), and overall survival (mOS), were determined by RECIST v1.1 criteria. Results Twenty-two patients with mCRPC received pembrolizumab monotherapy for at least 3 cycles for an MSI-H or TMB-H indication. All patients had next generation sequencing (NGS) performed via tissue (n = 11) or liquid (n = 10) biopsy source. The ORR was 50% (27.3% complete response and 22.7% had partial response). The mPFS for TMB 10-14.9 mut/Mb (n = 4), TMB 15-24.9 mut/Mb (n = 6), and TMB ≥ 25 mut/Mb (n = 10) was 2.1, not reached (NR), and NR, respectively (p = 0.0003). The mOS for these same groups was 5.1 months, 20.5 months, and not reached, respectively. Among patients with TMB-H without co-occurring MSI-H or CDK12 (n = 6), none experienced a response and only one patient had stable disease compared to patients with MSI-H (n = 12) for whom the ORR was 75%. Immunotherapy responsive alterations such as ATRX and PTCH1 mutations were frequently noticed among patients who had complete response (CR). Conclusions Our study highlights that MSI-H drives the efficacy of pembrolizumab in mCRPC with better survival outcomes as TMB increases. Clinicians should consider alternative treatment strategies for advanced prostate cancer when TMB-H is present without co-occurring MSI-H or CDK12. This study further demonstrates the utility of liquid biopsy NGS for identifying MSI-H and/or TMB-H disease.

ASCO Rapid Recommendations Updates highlight revisions to select ASCO guideline recommendations as a response to the emergence of new and practice-changing data. The rapid updates are supported by an evidence review and follow the guideline development processes outlined in the ASCO Guideline Methodology Manual . The goal of these articles is to disseminate updated recommendations, in a timely manner, to better inform health practitioners and the public on the best available cancer care options. See the Appendix for disclaimers and other important information ( Appendix 1 and Appendix 2 , online only).

Abstract Defects in the homologous recombination (HR) pathway, particularly in BRCA2, are of particular therapeutic relevance in mCRPC as they confer sensitivity to PARP inhibitors (PARPi). Nevertheless, durable responses to PARPi remain elusive and primary resistance is an additional major challenge. As a result, dissecting therapeutic vulnerabilities in HR-aberrant patients is crucial and may reveal novel PARPi-based combinations for evaluation in future clinical trials.In this multi-institutional study, we used the CLIA-certified PredicineCARE™ cell-free DNA (cfDNA) assay that assesses 152 genes to profile plasma from 375 mCRPC patients from Australia and the USA. Reportable alterations included pathogenic single-nucleotide (somatic and germline) and copy number variants. Association between alterations and clinical outcomes were assessed using log rank, cox proportional, and chi-squared analyses.Overall, 65 patients (17%) had evidence of a pathogenic BRCA2 aberration, which were commonly hemizygous (78% vs 22% homozygous deletions), monoallelic (70% vs 30% bi-allelic), somatic (87% vs 13% germline), and clonal (83% vs 17% subclonal) in nature. There was no significant difference in plasma tumour fraction in patients with single vs two-copy loss of BRCA2, and BRCA2 zygosity did not have differing effects on outcomes, with both being similarly associated with shorter overall survival (HR 0.48, p<0.002, and HR 0.45, p=0.003, respectively). Pathogenic BRCA1 aberrations were present in 10 patients (3%). PSA response rates to androgen-receptor pathway inhibitors (ARPI) were significantly lower in patients with a BRCA1 and/or a BRCA2 aberration (32% vs 60%, p=0.02), and we observed this BRCA-defective subgroup to be enriched for AR aberrations (71% had >1 AR aberration vs 38% in BRCA-intact patients, p=0.001). BRCA-defective cancers were also significantly enriched for aberrations in key neuroendocrine markers TP53 (62% vs 28%), RB1 (60% vs 17%), and MYC (27% vs 9%), as well as for PI3K pathway aberrations (PTEN 63% vs 25% and PIK3CA 37% vs 14%). In summary, we show that BRCA alterations are associated with worse prognosis in mCRPC and reduced benefit from ARPI, and that the prognostic and predictive utility of cfDNA-detected BRCA2 may be independent of zygosity state, potentially due to constraints with copy number loss identification in samples with low tumour DNA. Additionally, on top of a high proportion of AR alterations, BRCA-defective cancers were also enriched in a number of potentially actionable targets and neuroendocrine markers. Clinical trials that leverage rational co-targeting strategies will provide an opportunity to enhance the efficacy of PARPi in mCRPC. Citation Format: Heidi Fettke, Chao Dai, Edmond M. Kwan, Tiantian Zheng, Winston Tan, P Du, Nicole Ng, Patricia Bukszynska, Maria Docanto, L K. Graham, Kate Mahon, Lisa G. Horvath, Shidong Jia, Manish Kohli, Arun A. Azad. Adverse clinical outcomes and distinct genomic phenotype of BRCA-deficient metastatic castration-resistant prostate cancer (mCRPC) [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 2303.

e17009 Background: Decreased circulating levels of ether lipids (glycerophospholipids with an ether-linked fatty alcohol, e.g. plasmalogens) have been observed in obesity, diabetes and cardiovascular disease. In vitro and in vivo studies suggest that ether lipids are anti-inflammatory and protective against obesity. A recent landmark study revealed that ether lipids can kill cancer cells through ferroptosis. However, the role of ether lipids in prostate cancer has not been thoroughly investigated despite the known association of dysregulated lipid metabolism with poorer clinical outcomes. The aim of this study was to assess the relationship between the circulating profiles of ether lipids and clinical outcomes in localised and metastatic prostate cancer. Methods: The profiles of ~150 ether lipids (8 lipid classes) in plasma lipidomic data from localised prostate cancer (389 men in Australia) and metastatic castration-resistant prostate cancer (mCRPC)(2 cohorts –147 men in USA, 128 men in Australia) were analysed for associations with disease progression or overall survival (OS). Open-access genomic data of mCRPC tumours (108 men, CbioPortal) were analysed for aberrations in genes associated with ether lipid metabolism in relation to clinical outcome. Results: Previously in these study cohorts, we had identified men with poorer prognosis based on their plasma lipidome and our validated sphingolipid signature. These men with poorer prognosis have lower plasma levels of ether lipids than those with better prognosis (t-test p < 0.05, localised disease – 110 ether lipids, mCRPC – 54 ether lipids). Decreased plasma levels of up to 46 ether lipid species were associated with higher rates of clinical relapse in localised disease (hazard ratio (HR) range 0.37-0.73, p-value range 0.006-0.049), shorter radiological progression-free survival in mCRPC (HR range 0.35-0.73, p-value range 0.00009-0.049), and shorter OS in mCRPC (HR range 0.33-0.79, p-value range 0.000004-0.0497). Chromosomal loss of tumour GNPAT, an essential gene in ether lipid synthesis, was associated with shorter OS in mCRPC (HR = 1.36, 95% CI 1.02-1.81, p = 0.03). Conclusions: Lower circulating levels of ether lipids were associated with worse prognosis in localised and metastatic prostate cancer, suggesting that these lipids are protective against disease progression. Further research is required to understand the role of ether lipids in disease progression, and to determine if modulation of ether lipid levels through supplementation is beneficial.

AbstractObjectiveElevated serum chromogranin A (CGA) is associated with intrinsic or treatment‐related neuroendocrine differentiation (NED) in men with metastatic castration‐resistant prostate cancer (mCRPC). Fluctuations in serum CGA during treatment of mCRPC have had conflicting results. We analyzed the impact of (i) rising serum CGA and (ii) baseline CGA/PSA ratio during treatment to identify associations with abiraterone acetate (AA) therapy.MethodsBetween June 2013 and August 2015, 92 men with mCRPC were enrolled in a prospective trial with uniform serum CGA processing performed before initiating abiraterone acetate/prednisone (AA/P) and serially after 12 weeks of AA/P treatments. Serum CGA was measured using a homogenous automated immunofluorescent assay. Patients receiving proton pump inhibitors or with abnormal renal function were excluded due to possible false elevations of serum CGA (n = 21 excluded), therefore 71 patients were analyzed. All patients underwent a composite response assessment at 12‐weeks. Kaplan–Meier estimates and Cox Regression models were used to calculate the association with time‐to‐treatment failure analyses and overall survival.ResultsAn increase in chromogranin was associated with a lower risk of treatment failure (hazard ratio [HR]: 0.52, p = 0.0181). The median CGA/PSA ratio was 7.8 (2.6–16.0) and an elevated pretreatment CGA/PSA ratio above the median was associated with a lower risk of treatment failure (HR: 0.54 p value = 0.0185). An increase in CGA was not found to be associated with OS (HR: 0.71, 95% CI: 0.42–1.21, p = 0.207). An elevated baseline CGA/PSA ratio was not associated with OS (HR: 0.62, 95% CI: 0.37–1.03, p = 0.062). An increase in PSA after 12 weeks of treatment was associated with an increased risk of treatment failure (HR: 4.14, CI: 2.21–7.73, p = < 0.0001) and worse OS (HR: 2.93, CI: 1.57–4.45, p = < 0.0001).ConclusionsWe show that an increasing chromogranin on AA/P and an elevated baseline CGA/PSA in patients with mCRPC were associated with a favorable response to AA/P with no changes in survival. There may be limited clinical utility in serum CGA testing to evaluate for lethal NED as AA/P did not induce lethal NED in this cohort. This highlights that not all patients with an increasing CGA have a worse OS.

201 Background: Previous studies have evaluated peripheral whole blood mRNA to identify prognostic biomarkers in metastatic prostate cancer, with no consistent genes of prognostic significance between studies and sample collection done at various points of therapy. We aim to identify the prognostic value of 20 previously identified genes in patients mCRPC from a prospective clinical trial. Methods: Between June 2013 and August 2015, whole blood was prospectively collected in PAXgene RNA tubes from 92 men with mCRPC (NCT01953640). Gene expression from samples with RIN > 4.0 were quantified using a customized NanoString CodeSet of 20 candidate genes (C1QA, MCM2, STOM, GABARAPL2, R10K3, HMBS, TFDP1, CDKN1A, ITGAL, TMCC2, TERF2IP, MMP9, SNCA, TIMP1, SLC4A1, SELENBP1, TMEM66, SEMA4D, PROS1, CD22). The raw data from the nCounter Analysis system were normalized to the positive controls and log2 transformed. Univariable Cox proportional hazards models were performed on each target gene sufficiently above negative control (5 times the maximum value of the negative control) to evaluate associations with overall survival (OS). For each gene we considered a linear, quadratic, or categorical model with quantile cutpoints. Categorical models with cutpoints at the 25th percentile for the genes CD22, GABARAPL2, R10K3, and STOM were used as there was a nonlinear relationship between gene expression and death hazard. The remaining genes were modeled with a linear model. Findings were considered statistically significant based on p-values adjusted using the Holm-Bonferroni correction. Results: 18/20 genes were identified and passed quality control (QC) measures, which excluded C1QA and MCM2. 72/92 men had an evaluable pretreatment specimen that passed QC. The median age was 72 years. The study cohort was evenly balanced in terms of Gleason score ( < = 7 v. > 7) and 60% had high volume disease. The median follow-up time was 5.73 years (IQR: 5.39, 6.49) and 58 patients had died. Of the 18 genes evaluated, STOM (Stomatin) [hazard ratio (HR) 3.00, adjusted p = 0.007] and GABARAPL2 (GABA Type A Receptor Associated Protein Like 2) [HR 2.62, adjusted p = 0.033] were significantly associated with overall survival in univariate analysis. In multivariate analysis, after adjusting for volume of metastatic disease and Gleason score, STOM [HR 2.89, adjusted p = 0.014] was significantly associated with overall survival. Conclusions: Elevated whole blood mRNA expression of STOM is adversely associated with OS in mCRPC. Further studies investigating elucidating the molecular significance of STOM in mCRPC are planned. Clinical trial information: NCT01953640 .

Abstract Survival rates of patients with metastatic castration-resistant prostate cancer (mCRPC) are low due to lack of response or acquired resistance to available therapies, such as abiraterone (Abi). A better understanding of the underlying molecular mechanisms is needed to identify effective targets to overcome resistance. Given the complexity of the transcriptional dynamics in cells, differential gene expression analysis of bulk transcriptomics data cannot provide sufficient detailed insights into resistance mechanisms. Incorporating network structures could overcome this limitation to provide a global and functional perspective of Abi resistance in mCRPC. Here, we developed TraRe, a computational method using sparse Bayesian models to examine phenotypically driven transcriptional mechanistic differences at three distinct levels: transcriptional networks, specific regulons, and individual transcription factors (TF). TraRe was applied to transcriptomic data from 46 patients with mCRPC with Abi-response clinical data and uncovered abrogated immune response transcriptional modules that showed strong differential regulation in Abi-responsive compared with Abi-resistant patients. These modules were replicated in an independent mCRPC study. Furthermore, key rewiring predictions and their associated TFs were experimentally validated in two prostate cancer cell lines with different Abi-resistance features. Among them, ELK3, MXD1, and MYB played a differential role in cell survival in Abi-sensitive and Abi-resistant cells. Moreover, ELK3 regulated cell migration capacity, which could have a direct impact on mCRPC. Collectively, these findings shed light on the underlying transcriptional mechanisms driving Abi response, demonstrating that TraRe is a promising tool for generating novel hypotheses based on identified transcriptional network disruptions. Significance: The computational method TraRe built on Bayesian machine learning models for investigating transcriptional network structures shows that disruption of ELK3, MXD1, and MYB signaling cascades impacts abiraterone resistance in prostate cancer.

Prostate cancer (PCa) accounted for more than 34,000 deaths in US males [...]

Abstract We identified resistance mechanisms to abiraterone acetate/prednisone (AA/P) in patients with metastatic castration-resistant prostate cancer (mCRPC) in the Prostate Cancer Medically Optimized Genome-Enhanced Therapy (PROMOTE) study. We analyzed whole-exome sequencing (WES) and RNA-sequencing data from 83 patients with metastatic biopsies before (V1) and after 12 weeks of AA/P treatment (V2). Resistance was determined by time to treatment change (TTTC). At V2, 18 and 11 of 58 patients had either short-term (median 3.6 months; range 1.4–4.5) or long-term (median 29 months; range 23.5–41.7) responses, respectively. Nonresponders had low expression of TGFBR3 and increased activation of the Wnt pathway, cell cycle, upregulation of AR variants, both pre- and posttreatment, with further deletion of AR inhibitor CDK11B posttreatment. Deletion of androgen processing genes, HSD17B11, CYP19A1 were observed in nonresponders posttreatment. Genes involved in cell cycle, DNA repair, Wnt-signaling, and Aurora kinase pathways were differentially expressed between the responder and non-responder at V2. Activation of Wnt signaling in nonresponder and deactivation of MYC or its target genes in responders was detected via SCN loss, somatic mutations, and transcriptomics. Upregulation of genes in the AURKA pathway are consistent with the activation of MYC regulated genes in nonresponders. Several genes in the AKT1 axis had increased mutation rate in nonresponders. We also found evidence of resistance via PDCD1 overexpression in responders. Implications: Finally, we identified candidates drugs to reverse AA/P resistance: topoisomerase inhibitors and drugs targeting the cell cycle via the MYC/AURKA/AURKB/TOP2A and/or PI3K_AKT_MTOR pathways.