Zaidi, Samir

Abstract Prostate cancer requires continual escape from immune surveillance, but mechanisms underlying this escape in the transition from androgen sensitivity to resistance and metastasis remain incompletely understood. Androgen-deprivation therapy (ADT)—the treatment backbone—induces tumor cell apoptosis but also remodels the tumor microenvironment (TME). We have assembled a single-cell RNA-seq atlas from >800,000 cells across 68 patients treated at Columbia University and Memorial Sloan Kettering. The resource includes 33 primary tumors (16 treatment-naïve, 17 post-ADT) annotated with time to PSA recurrence, and 31 metastases, including longitudinal pre- and post-ADT data in 14 castration-sensitive tumors (CSPC), 17 castration-resistant tumors (CRPC), and 4 neuroendocrine tumors (NEPC). This dataset spans the spectrum of prostate cancer disease progression.Using ARACNe and VIPER to infer activity of transcriptional regulatory and signaling proteins, we detect conserved cell state programs while minimizing batch effects. Several significant features emerged. Immune infiltration—both lymphoid and myeloid—is significantly higher in CSPC metastases than in primary or CRPC tumors and increases further after ADT. T cells constitute ∼15% of cells in primary tumors versus 30% in treatment-naive CSPC (40% post-ADT), falling to 13% in CRPC and <1% in NEPC (p<1e-32), consistent with an initially "hot" CSPC TME that progressively excludes T cells with disease progression.Among ∼350,000 epithelial/tumor cells, trajectory analysis reveals two differentiation pathways from normal epithelium. Pathway 1—dominant in primary tumors—shows androgen receptor (AR) activity with three sub-phenotypes (T1-T3): T1 exclusive to primary tumors; T2 shared by primary and CSPC; and T3 restricted to CRPC, with high ERG expression, and very strong AR activity. Pathway 2 (clusters T4-T6), present in NEPC and a subset of CRPC, lacks AR activity and displays SOX2, FOXA2, PRKD1. These aggressive states uniformly overexpress AURKA, RET, and TOP2A, suggesting druggable targets for combination therapy.We further define five cancer-associated fibroblast (CAF) subtypes. CAF1-3 track with advanced, treatment-resistant disease—enriched in NEPC versus CRPC (25% vs 18% of CAFs) and in CRPC versus CSPC (18% vs 11%)—while CAF4-5 predominate in primary tumors. We identify druggable proteins and receptor-ligand interactions linking CAF1-3 with T4-T6 tumor states; in vivo perturbations are underway.This atlas provides a resource profiling tumor and immune ecosystems across prostate cancer progression. It highlights MR programs and stromal-tumor-immune interactions that underlie immune evasion and ADT resistance, yielding actionable targets and combination-therapy hypotheses for aggressive disease. Citation Format: Aleksandar Obradovic, Kwangmin Yoo, Chang Liu, Patrick McCann, Casey R. Ager, Matthew C. Dallos, Samir Zaidi. Comprehensive profiling of primary and metastatic prostate tumors reveals distinct tumor and fibroblast cell states associated with androgen resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 7419.

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.