Abstract B051: GSTT2 modulates the bladder tumor environment and response to BCG Immunotherapy
Authors: Mahendran Ratha , Patwardhan Mugdha Vijay , Toh Qin Kane , Chiong Edmund 
Published: December 2023

The purpose of this study was to elucidate the impact of Glutathione -S-transferase Theta 2 (GSTT2) loss on the response of bladder tumors to Mycobacterium Bovis, Bacillus Calmette Guerin (BCG) immunotherapy. GSTT2 gene expression is controlled by a promoter deletion that occurs frequently in 25-29% of Asians and 41% of Caucasians. The GSTT2 promoter deletion correlated with better response to BCG therapy in a retrospective analysis of patients who received less BCG therapy. To understand this response, we generated GSTT2 knockout mice to elucidate the role of GSTT2 in BCG immunotherapy. Female C57BL/6J mice from GSTT2 wildtype (WT) and KO backgrounds were orthotopically implanted with MB49-PSA cells (murine MB49 cells secreting human PSA). To view the impact of GSTT2 loss on BCG immunotherapy, mice were treated with only 4 instillations of BCG Tokyo. This therapeutic schedule would not result in a high cure rate and but was chosen as we expected it to provide insights into the anti-tumor response. Mice were treated weekly with intravesical BCG Tokyo instillations and tumor growth was monitored by urinary PSA secretion. Final tumor presence was confirmed by real-time PCR analysis of PSA gene expression. One day after the last instillation the bladders (n=7) were harvested for single cell RNA sequencing (Parse Biosciences). Cell clusters were identified by their gene expression profiles. The response to BCG in terms of the cure rate was similar in KO and WT mice (cure rate of 18-20%) but several genes were differentially expressed. Genes with a Log2FC value of +1.5 in KO mice (Peak1, Rpph1, Gphn and Gm19551) and -1.5 in KO (Rora, Tshz2, Sh3gl2, Ankfn1, Rbms3, Naaladl2, Prkn, Mecom, Fmo5, Saa3, Tmprss2, C3, Gm10800 and Gm10801) relative to WT mice were examined. Based on the literature, these genes either block tumor progression (Rora, Tshz2, Sh3gl2 and Gphn); promote tumor progression (Ankfn1, Rbms3, Naaladl2, Prkn, Mecom, Fmo5, Tmprss2, Saa3, C3, Peak1, Rpph1) or modulate immune cells (C3, Saa3 and Rpph1). The majority of these genes were not previously associated with bladder cancer. Interrogation of the TCGA database showed that high expression of Gphn, Peak1 and GSTT2 correlated with poorer outcomes in bladder cancer patients in terms of disease-free survival (HR=1.9 log rank p=0.00038). While expression of the genes downregulated in KO mice and GSTT2 resulted in better outcomes with lower expression of all the genes (HR=1.4, log rank p=0.042). This data indicates that the loss of GSTT2 expression impacts the response of tumors to BCG immunotherapy, primarily by modulating the expression of genes associated with cancer progression and the expression of genes in multiple cell types. Given the common loss of GSTT2 expression in man this gene may be a parameter that should be evaluated in further detail in patients receiving BCG immunotherapy.

Citation Format: Ratha Mahendran, Mugdha Vijay Patwardhan, Qin Kane Toh, Edmund Chiong. GSTT2 modulates the bladder tumor environment and response to BCG Immunotherapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr B051.