Abstract B006: GSTT2 modulates immune activation and impacts response to BCG immunotherapy in bladder cancer
Authors: Patwardhan Mugdha Vijay , Toh Kane , Chiong Edmund , Mahendran Ratha 
Published: May 2024

Whilst M. bovis Bacillus Calmette-Guérin (BCG) therapy is the gold-standard for treating high risk non-muscle invasive bladder cancer (NMIBC), 30-40% of patients fail therapy, resulting in disease recurrence and progression. Loss of glutathione-S-transferase theta 2 (GSTT2) expression resulting from a promoter deletion, has been associated with modulation of intracellular ROS and BCG survival in BC cells. Retrospective analysis of NMIBC patients revealed that patients with the promoter deletion responded better to fewer instillations of BCG. To understand these responses, wildtype (WT) and GSTT2-knockout (KO) mice were implanted with MB49-PSA BC cells, either subcutaneously or orthotopically, and treated with weekly BCG instillations. Subcutaneous tumors were harvested after 3 BCG instillations for flow cytometry analysis, or after 4 BCG instillations for immunofluorescence (IF) imaging and gene expression analysis. Bladders (orthotopic model) were harvested after 4 BCG instillations for single-cell RNA sequencing. Splenocytes from WT and KO male mice were also stimulated in-vitro with TLR agonists, for 48h, to assess immune responses. In the subcutaneous model, in male mice, the cure rate was higher in WT mice (57%) compared to KO mice (0%). Flow cytometry analysis showed significantly higher numbers of tumor-associated CD8+ T-cells in BCG-treated KO males compared to WT males; however, IF imaging revealed higher penetration of CD8+ T-cells in tumors from WT males. In female mice, the cure rate was similar in WT (25%) and GSTT2-KO (38%) mice. IF imaging showed higher penetration of CD8+ T-cells in KO females. Quantitative real-time PCR (q-PCR) analysis of BCG-treated subcutaneous tumors from female mice revealed lower expression of the immune exhaustion markers, PD-L1 and CTLA-4, in KO mice compared to WT mice. Similarly, in the orthotopic model (female mice), q-PCR analysis of bladders also showed lower expression of PD-L1 and CTLA-4 in KO mice compared to WT mice. Single-cell RNA sequencing of bladders from BCG-treated mice revealed differences in the expression of genes such as Peak1, Hmga2, Scl2a1, Kras, Ahank, Gsta4, Mecom and Sh3gl2, of which Gsta4, Mecom, Sh3gl2, Hmga2 and Peak1 were validated using q-PCR. In-vitro analysis of splenocytes from male mice revealed higher levels of IL-6, IL-1β and IFN-α, after stimulation with TLR7/8 and TLR9 agonists, in KO splenocytes relative to WT splenocytes. Despite the higher levels of cytokine production by splenocytes and higher proportion of tumor-associated CD8+ T-cells in KO male mice, these mice fared poorly, which could be explained by immune exhaustion or lack of immune penetration into the tumor. In females, lower expression of immune exhaustion markers in KO mice did not yield better responses; however, single-cell data showed differences in expression of genes associated with pro- and anti-tumorigenic pathways, which could influence response. Thus, loss of GSTT2 may influence the response to BCG therapy, through modulating downstream signaling pathways and immune responses.

Citation Format: Mugdha Vijay Patwardhan, Kane Toh, Edmund Chiong, Ratha Mahendran. GSTT2 modulates immune activation and impacts response to BCG immunotherapy 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 B006.