Abstract B031: Proteomic profiling of oligometastatic castration-sensitive prostate cancer treated with stereotactic ablative radiotherapy
Authors: Wang Jarey H. , Shetty Amol , Song Yang , Radwan Noura , Bazyar Soha , Shi Xiaolei , DeWeese Theodore L. , Song Daniel Y. , Phillips Ryan M. , Deek Matthew P. , Sutera Philip , Kiess Ana P. , Tran Phuoc T. 
Published: January 2025

Abstract
Background: The trajectory of metastatic castration-sensitive prostate cancer varies based on disease presentation and biology. While proteomic profiling studies of primary prostate tissue have linked protein expression with metastatic progression and prognosis, few studies have explored biological changes after treatment and their associations with response. Therefore, we conducted proteomic profiling of patients with oligometastatic castration-sensitive prostate cancer (omCSPC) treated with stereotactic ablative radiotherapy (SABR) or observation in the ORIOLE phase 2 randomized clinical trial (RCT). Methods Plasma from omCSPC patients in the ORIOLE trial was collected at baseline (day 1), day 90, and day 180. Protein abundance was quantified using the Olink Explore Assay. Differential expression from baseline to day 90 or 180 in each treatment arm was analyzed using a 2-sided t-test with Benjamini-Hochberg correction. Changes in protein expression at day 90 and 180 were compared with a Pearson correlation. Pathway enrichment was performed via gene set enrichment analysis (GSEA) using Reactome, KEGG, and Hallmark gene sets. Associations with progression-free survival (PFS) were analyzed using Kaplan-Meier and log-rank tests. Results In total, 1,472 proteins were assayed across 130 samples from 46 patients over 3 time points. Significant changes in expression post-SABR were noted at day 90 and 180 compared to baseline (using adjusted p-value cutoff of 0.05). At day 90, four proteins (FCRL1, CD22, TCL1A, FCER2) were downregulated; at day 180, only FCRL1, a Fc receptor-like gene family preferentially expressed in B cells, remained downregulated. No significant expression changes were found in the observation arm. Differential expression of proteins during follow-up were associated with PFS. In particular, LTO1, a maturation factor of ABCE1 important for ribosomal biogenesis and translation, was overexpressed at both day 90 and 180 post-SABR, and overexpression was associated with improved PFS at day 90 (median 24.5 mo vs 6 mo; p=0.017) and day 180 (median 33 mo vs 6 mo; p=0.043). These associations were absent in the observation arm. For proteins differentially expressed in the SABR arm at day 90, several signaling pathways were significantly enriched for patients with prolonged PFS, including positive enrichment of unfolded protein response (UPR) (p=0.008) and IL-4/IL-13 (p=0.009). At 180 days, several pathways were enriched for patients with prolonged PFS including negative enrichment of CTLA4 inhibitory signaling (p=0.005) and CD28 co-stimulation (p=0.008). Conclusion Proteomic analysis in omCSPC patients from the ORIOLE trial reveals significant expression changes at days 90 and 180 after SABR. B-cell signaling proteins were selectively downregulated in the SABR arm, and pathways associated with protein translation and immune response were enriched post-SABR for patients with prolonged PFS. Further research will explore connections to genomic and transcriptomic changes, with additional validation needed.
Citation Format: Jarey H. Wang, Amol Shetty, Yang Song, Noura Radwan, Soha Bazyar, Xiaolei Shi, Theodore L. DeWeese, Daniel Y. Song, Ryan M. Phillips, Matthew P. Deek, Philip Sutera, Ana P. Kiess, Phuoc T. Tran. Proteomic profiling of oligometastatic castration-sensitive prostate cancer treated with stereotactic ablative radiotherapy. [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Targeted Therapies in Combination with Radiotherapy; 2025 Jan 26-29; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(2_Suppl):Abstract nr B031.