Lacuna, Kristine Peregrino

382 Background: Androgen receptor signaling drives prostate cancer (PC) progression, and genes involved in androgen production, uptake, and conversion (APUC) are key therapeutic targets. We previously defined a 6-APUC gene set ( HSD3B1, HSD3B2, CYP3A43, CYP11A1, CYP11B1, and CYP17A1 ), that identified metastatic PC with favorable prognosis and predict docetaxel benefit. However, the expression landscape and clinical relevance of APUC genes have not been interrogated in localized PC. Methods: We analyzed the expression of 21 APUC genes in 55,329 radical prostatectomy tumor samples that underwent Decipher prostate genomic classifier (GC) testing (Veracyte Inc) between 2016-2024. Baseline clinical/pathologic factors were retrieved from Decipher GRID database (NCT02609269). Associations between gene expression quartiles with PathoGenomic Risk Factors (PGRF) including Very High Decipher score >0.85 (VHD), Grade Group (GG) 4-5, LNI and SVI were examined. Associations with distant metastatic (DM) outcomes and metastasis free survival (MFS) were evaluated using logistic regression in Mayo545 and Cox regression in Meta855 RP cohorts, respectively. Results: High expression of SRD5A2 was associated with favorable PGRF (lower odds ratio (OR), p<0.0001), lower rate of development of DM (OR 0.36, p<0.05), and longer MFS (Hazard ratio (HR) 0.51, p<0.05). HSD17B6 showed similar results for PGRF (lower OR, p<0.0001), DM (OR 0.58, p<0.05) and longer MFS (HR 0.39, p<0.05) despite being associated with GG4-5 and SVI+ in samples with VHD. In contrast, high expression of SRD5A3 and HSD17B10 had high OR for PGRFs (p<0.0001). High expression of SLCO2B1 , an androgen uptake gene, had the strongest association with GG4-5 and SVI/LNI (p<0.001 for both). We noted that SRD5A2 lacked correlation with SRD5A1 and SRD5A3 , which instead correlated with each other. Compared to all APUC genes, SRD5A2 had limited correlations with almost all APUC genes, including ones that exhibited robust cross correlation with each other . Similar to our prior finding, most APUC genes demonstrated negative correlation with AR expression and AR activity signatures. Key outcomes were validated based on transcriptomic data from 492 samples from TCGA database. Conclusions: Comprehensive analysis of 21 APUC genes in over 55,000 PC identified distinct, context-dependent associations with metastatic outcomes and clinical and molecular risk factors. Notably, high SRD5A2 expression was associated with lower odds of high-risk features and metastatic outcomes, whereas SRD5A1 and SRD5A3 linked to adverse outcomes, suggesting critical yet divergent roles among 5-alpha-reductase family members. These findings underscoring androgen-metabolic heterogeneity and highlighting SRD5A2 as a potential biomarker of indolent biology in localized prostate cancer.

Abstract Purpose: Prostate-specific membrane antigen (PSMA)–directed therapies provide meaningful clinical benefit in metastatic castration-resistant prostate cancer (mCRPC), yet responses remain limited, underscoring the need for additional biomarkers of PSMA expression heterogeneity. In this study, we explored the relationship between PSMA imaging and PSMA expression on circulating tumor cells (CTC) in our early-phase trial using a PSMA-targeted small molecule. Experimental Design: This phase I study investigated EC1169, a small molecule conjugated to a tubulysin analog warhead, and 99mTc–EC0652, a PSMA imaging agent. Part A (dose escalation) identified the recommended phase II dose. Part B (dose expansion) assessed radiographic progression-free survival (rPFS) as its primary endpoint. We enrolled and treated 103 patients with mCRPC. Most part B patients underwent 99mTc–EC0652 PSMA imaging. A CTC assay assessed PSMA-positive CTCs and their association with response and PSMA imaging. Results: 99mTc–EC0652 single-photon emission computed tomography (SPECT) imaging demonstrated increased sensitivity for detecting bone lesions compared with standard scans (computed tomography/bone scans). Using an optimized CTC assay, we observed that patients with a decrease in PSMA+ CTCs at baseline versus C3D1 displayed a longer rPFS (8 vs. 2.9 months; P = 0.04). Importantly, patients with predominantly PSMA-positive disease on 99mTc–EC0652 imaging also harbored PSMA-negative CTCs, with a subset displaying neuroendocrine prostate cancer–like morphology. Conclusions: Although EC1169 showed limited activity, CTC and imaging analyses showed significant heterogeneity in PSMA expression on CTCs in patients with predominantly PSMA-positive lesions on SPECT. Our study highlights the importance of assessing both PSMA-based CTC and imaging assays in future validation trials.

11526 Background: There are no FDA-approved treatments for advanced cCS. Chemotherapy provides limited benefit. IDH1/2 mutations (m) occur in 50% of cCS. Both IDHm and wild-type cCS harbor epigenetic dysregulation. In preclinical models, HDAC + DNMT inhibition (i) suppressed growth by inducing apoptosis, reversing the hypermethylated state, and upregulating expression of interferon (IFN) response genes including PDL1(1). This prompted a phase 2 study of HDACi + DNMTi in cCS, which failed to meet the 1° endpoint of ORR. The majority of pts had a best response of stable disease, with a trend towards improved mPFS in IDHm (2). Here we report correlative analysis of NCI 10330. Methods: NCI 10330 is a single-arm, multicenter, phase 2 study of belinostat with SGI-110 or ASTX727 in advanced cCS. All pts were required to have pre- and on-treatment (tx) biopsies (Cycle 2, Day 3-5). Tissue was evaluated with whole exome sequencing (WES) and RNA sequencing (RNAseq). From RNAseq, Tumor Inflammation Signature Scores (TISS) and Tumor Microenvironment functional Gene Set Enrichment Analysis scores (TME GSEA) were calculated as the mean of the log2 normalized counts of 18 signature genes (Danaher et al. J Imm Can 2018) and pre-defined gene sets (3), respectively. Wilcoxon rank sum test was used to analyze TME GSEA between pre- and on-tx samples. Differential expression was significant if |FC| > 1.33, adjusted P <0.01. Results: 19 pts were treated; all received paired biopsies. WES was adequate in 7/19 (37%) pts, with IDHm identified in 3/7 (43%) pts. All pts were MSI-stable, TMB: 1.01-3.57 mut/Mb. RNAseq was adequate in 7/19 (37%) pts at pre-tx and 5/19 (26%) pts at on-tx. TISS ranges trended higher for pre-tx (8.77-10.14) vs on-tx (7.36-9.51) samples. TME GSEA identified significantly enriched tumor immune infiltration (p < 0.05) in pre- vs on-tx samples. Differential analysis identified several gene sets related to inflammation overexpressed in pre-tx samples only, including IFN response. On-tx samples were enriched in myogenesis and coagulation gene sets. Conclusions: This is the first study to describe transcriptomic changes following epigenetic tx in cCS. Contradictory to our preclinical data, HDACi + DNTMi resulted in low expression of inflammation. Prior studies reported that the immune infiltrate of CS at progression is immunosuppressive; higher immune infiltrate is correlated with worse outcomes (4). Loss of inflammation may have implications for disease stability experienced by most pts on NCI 10330. Further analyses are planned to correlate TME (pro- vs anti-inflammatory infiltrates) and outcomes. Analyses are limited by small sample size, highlighting the challenges in collecting adequate CS specimens. 1. Sheikh, Schwartz et al. Mol Cancer Ther 2021. 2. Lacuna et al. ASCO 2023: #11531. 3. Bagaev et al. Can Cell 2021. 4. Richert et al. J Bone Onc 2020. Clinical trial information: NCT04340843 .

TPS11584 Background: Uterine leiomyosarcoma (uLMS) is an aggressive sarcoma subtype with frequent metastatic relapse. Advanced uLMS is treated with gemcitabine/docetaxel or anthracycline-based regimens. After failure of initial chemotherapy, remaining options provide limited benefit (trabectedin: objective response rate (ORR) 11%, median progression-free survival (mPFS) 4.0 months (mo); pazopanib: ORR 11%, mPFS 3.0 mo; dacarbazine: ORR 9%, mPFS 1.5 mo). 18-23% of uLMS harbor deleterious alterations in homologous recombination (HR) DNA repair genes. HR-deficient cancers are unable to effectively repair double-stranded DNA breaks and may be sensitive to poly ADP-ribose polymerase (PARP) inhibitor-based strategies. In preclinical studies, the combination of temozolomide (T), an alkylating agent, and olaparib (O), a PARP inhibitor, markedly suppressed proliferation of uLMS models. Among 22 uLMS patients with median 3 prior lines, O+T demonstrated mPFS 6.9 mo and ORR 27% (Ingham M. et al. ASCO 2021: #11506). In correlative analysis, alterations in HR genes including PALB2 and RAD51B or absence of RAD51 foci formation by a functional assay were observed in patients with prolonged PFS (Bose S. et al. ASCO 2022: #11509). Based on these results, we designed a randomized phase 2/3 study to further evaluate O+T in advanced, pretreated uLMS. Methods: Alliance for Clinical Trials in Oncology A092104 is a randomized, open-label phase 2/3 clinical trial of O+T versus investigator’s choice in advanced uLMS. Eligible patients have ECOG performance status ≤2, progression on ≥ 2 prior treatment lines and measurable disease. Patients are randomized 1:1 to receive T 75 mg/m2 orally daily + O 200 mg orally twice daily on days 1-7 in 21-day cycles (Arm 1) or investigator’s choice of trabectedin 1.5 mg/m2 over 24 hours every 21 days or pazopanib 400-600 mg orally daily (Arm 2). For phase 2, the primary endpoint is PFS. The design evaluates for an improvement in PFS from 4 mo to 8 mo, requires 70 patients, and yields 90% power and 1-sided alpha 0.10. If phase 2 is positive, phase 3 will enroll. For phase 3, the primary endpoint is overall survival (OS). The design evaluates for an improvement in OS from 13 mo to 23 mo, requires 165 patients (including 70 from phase 2) and yields 90% power with 1-sided alpha 0.025. Secondary endpoints include ORR, duration of response, safety and patient-reported outcomes. Archival tissue will be collected and evaluated with a RAD51 foci formation assay. Genomic sequencing results will be obtained where available. The study opened to accrual in 1/2023. Support: U10CA180821, U10CA180882, U24 CA196171; https://acknowledgments.alliancefound.org . Clinical trial information: NCT05633381 .

11531 Background: Conventional chondrosarcoma (cCS) is the 2nd most common primary bone tumor and is resistant to chemotherapy and radiation. IDH1/2 mutations (m) occur in 50% of cCS. Both IDHm and wild-type (wt) cCS harbor epigenetic dysregulation. In preclinical models of IDHm and wt cCS, combination treatment with HDAC and DNMT inhibitors (i) suppressed growth in vitro and in vivo by reversing the hypermethylated state and inducing tumor suppressors, interferon response genes and apoptosis (Sheikh T, Schwartz G. Mol Cancer Ther 2021;20). Methods: NCI 10330 is a single-arm, multicenter, phase 2 study evaluating the HDACi belinostat (B) with the DNMTi SGI-110 (S) or ASTX727 (A). A replaced S due to drug availability (pts were replaced). Pts had advanced cCS, ECOG PS ≤ 2 and could be treatment naïve. Progression was required for grade 1 cCS. Pts received B 1000mg/m2 IV + S 45mg/m2 SC both days 1-5 or B (same dosing) + A (cedazuridine 100mg/decitabine 35mg) PO both days 1-5, in 28-day cycles. 1° endpoint was objective response. A Simon 2-stage design was used. If ≥ 2/13 responses occurred in stage 1, the study would proceed to full accrual. Design had 85% power with α = 0.05 to test ORR 8% vs 28%. 2° endpoints included safety, PFS and OS. A safety lead-in was performed. Paired biopsies were collected. Results: Stage 1 is complete. 19 pts were treated: 6 on B+S and 13 on B+A. Median age was 50 and 67 years, respectively. All pts had prior surgery. 17% (B+S) and 38% (B+A) had prior radiation. 33% (B+S) and 55% (B+A) were IDHm. 67% (B+S) and 75% (B+A) were histologic grade ≥ 2. There were no objective responses. Best response (at 8 weeks) was stable disease (SD) in 4/6 pts (67%) on B+S and 6/10 pts (60%) on B+A. mPFS was 4.2 mos (95% CI 1.97-NR) for B+S and 3.8 mos (95% CI 2.17-NR) for B+A. mOS has not been reached. For B+A, mPFS for IDHm vs wt pts was 4.7 and 3.1 mos, respectively (p=0.21). One pt with IDHm grade 2 cCS who progressed on FT-2102 (IDH1i) remains on B+A > 1 year. There were no DLTs during either safety lead-in. Grade 3/4 treatment-related adverse events (TRAEs) occurred in 17% (B+S) and 69% (B+A). For B+A, the most common grade 3/4 TRAE was neutropenia (54%) and the most common all-grade TRAEs were nausea (69%), leukopenia (61%), neutropenia (54%), anemia (46%) and fatigue (46%). Paired tumor biopsies are being evaluated with whole exome sequencing, RNAseq, methylation array and multiplex IHC with results forthcoming. Conclusions: Combination HDACi + DNMTi was well-tolerated in advanced cCS. There were no objective responses; however, a subset of pts experienced prolonged SD with a trend towards improved mPFS in IDHm pts. Correlative work is ongoing with a focus on differential effects on IDHm tumors and whether modulation of the immune microenvironment might support combinations with immunotherapy. Support: UM1CA186689. Clinical trial information: NCT04340843 .