Identification of gene expression determinants of radiosensitivity in bladder cancer (BCa) cell lines.

470 Background: Trimodality therapy with TURBT followed by concurrent chemoradiation is an alternative to cystectomy in selected patients with muscle invasive BCa. Identifying genetic determinants of radiation response may help select patient for organ-sparing treatments with curative intent. Methods: Molecular characterization of 20 cell lines was previously performed, including mutation analysis, CNA (high density SNP arrays) and gene expression (RNAseq). Cell line identity was authenticated by genomic fingerprinting. We performed colony forming assays (CFA) and cumulative survival was quantified using the area under the cell survival curve (AUC, range 0-8Gy) to create a radiosensitivity index. Pre and post-radiation proliferative capacity was determined by cell titer glo (CTG) assay. Gene (R v3.5.1) and network (Ingenuity Pathyway Analysis) level expression differences were determined as a function of AUC to identify biologically relevant associations with radiation response. Results: Of 20 cell lines (7 basal, 13 luminal subtype), both CFA and CTG data was successfully obtained for 13 cell lines (6 basal, 7 luminal) treated with high dose rate (HDR) radiation. AUCs for the colony forming assay (CFA) survival curves ranged 1.79-3.27. RNAseq identified 18,634 unique transcripts mapping to distinct loci and 196 genes were identified with AUC correlation p values <0.01 (FDR <0.5, mean FPKM>0.5). These genes were strongly enriched for membership in the peroxisome proliferator (PPAR) pathway (IPA, p = 9.40E-03) and STAT3 pathway (IPA, p = 1.56E-3). Validation studies confirmed PPARγ, ICAM2, JAK3, IL1B, OAS1 and OAS2 genes to be associated with differential response to radiation, with expression upregulated in radio-resistant cells. A basal subtype was strongly associated with a radiosensitive phenotype (Chi-Squared χ2 p=0.0083). Conclusions: BCa radio-sensitivity was associated with baseline gene expression differences in vitro. The basal subtype and repression of either the PPAR or STAT3 pathways predicted increased radiosensitivity. This study nominates candidate biomarkers for mechanistic studies and clinical validation in BCa.