Abstract B019: Identification of gene signatures predictive of response to Ad-IFNα/Syn3 in bladder cancer

Abstract Introduction: Interferon α gene therapy (Ad-IFNα/Syn3) is FDA approved for treatment of BCG-unresponsive non-muscle invasive bladder cancer. Ad-IFNα/Syn3 is a non-replicating adenovirus that when transduced into target tissues, produces IFNa2b protein with anti-tumor activity. In the phase 3 multicenter trial, 45.5% of patients with carcinoma-in-situ and 60% of those with Ta/T1 disease who had a complete response to Ad-IFNα/Syn3 at 3 months remained recurrence free at 12 months. Targeting mechanisms of resistance and identifying predictive biomarkers to improve patient selection and overall response rates is a top priority. Towards this, we treated 29 human bladder cancer cell lines with Ad-IFNα/Syn3 and assessed their responses to therapy. We identified sensitive and resistant cell lines and gene signatures predictive of response. Methods: Human bladder cancer cell lines were grown in MEM supplemented with 10% FBS in 96-well plate. After overnight attachment, these were treated with Ad-IFNα/Syn3 (MOI 1000) and cell titre glow assay was performed 72h post-treatment. Cells were also seeded in 6-well plates. and after 24h cell-free supernatants were collected for ELISA and cells were collected for RNA isolation using RNAqueous Total RNA Isolation kit (Thermo Fisher). RNA quality was assessed using Tapestation. RNAseq analysis was carried out using Ion proton Sequencer. Ingenuity pathway analysis (IPA) and gene set enrichment were performed on the sequencing data for the cell lines. ELISA was used to measure IFNα and IL6 protein levels in cell free supernatants. We also tested organoids developed from bladder cancer patients to test drug efficacy and identify gene signatures. Results: Out of the 29 cell lines, we identified that sensitivity to Ad-IFNα/Syn3 was pronounced in luminal cells (8/13 luminal cell lines). Most basal cells were either resistant (>70% viability) or only moderately sensitive to Ad-IFNα/Syn3 (between 70-40% viability) when compared to control. We selected 7 cell lines for sequencing and ELISA measurements: luminal cell lines BV, UC6, Rt4V6 and UC5, and basal cell lines ScaBER, HT1197, and T24. All cell lines mentioned above could be successfully transduced by the adenoviral vector as measured by increased expression of IFNα protein in the cell-free supernatants. Ad-IFNα/Syn3-sensitive luminal cell lines at baseline had lower IFNα and IFNγ scores when compared to resistant basal cell lines. We identified several cell-death pathways enriched in treated cells that were sensitive to Ad-IFNα/Syn3. IL6 measurements in cell free supernatants revealed increased expression of IL6 after treatment in sensitive cells. However, in resistant cells IL6 expression was either high at baseline (ScaBER) or both undetectable at baseline and after treatment (UC5). Conclusion: Our results suggest that the luminal cell lines are more sensitive to Ad-IFNα/Syn3 and that high baseline expression of IFNα and IFNγ in basal cell lines contributes to resistance. IL6 levels are also predictive of response to Ad-IFNα/Syn3. Citation Format: Morgan E. Pierce, Alexis R. Steinmetz, Aruna Nannapaneni, Tanner S. Miest, David J. McConkey, Sharada Mokkapati, Colin P.N. Dinney. Identification of gene signatures predictive of response to Ad-IFNα/Syn3 in bladder cancer [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr B019.