Abstract 6131: Temozolomide induces innate immune responses via the production of double-stranded RNAs in glioblastoma cells

Immunotherapy using immune checkpoint inhibitors (ICIs) has revolutionized cancer treatment by enhancing T cell-mediated anti-tumor immunity. However, its efficacy in glioblastoma (GBM) remains limited, as demonstrated by unsuccessful clinical trials. The primary challenge is the low abundance of tumor-infiltrating lymphocytes (TILs) within the GBM tumor microenvironment (TME), which fosters an "immune-cold" or "immune-suppressive" state, rendering the tumor resistant to immunotherapy. The first-line treatment for GBM is temozolomide (TMZ), and several studies have examined whether TMZ improves patient outcomes when combined with ICIs. However, one such trial, Ipi-Glio, did not demonstrate improved outcomes with the addition of ipilimumab to TMZ. In contrast, the MAYA study in metastatic colon cancer patients showed clinical benefits when patients were treated with TMZ followed by low-dose ICIs. As a result, it remains unclear whether TMZ has synergistic effects with ICIs in GBM treatment. To address this question, we consider the following: Does TMZ increase the abundance of TILs within the GBM TME? The recruitment and activation of TILs depend on pro-inflammatory cytokines, including type I interferons (IFN-I), which bridge innate and acquired immunity. Thus, we further investigate: Does TMZ stimulate IFN-I production to enhance TIL infiltration?When the U251 GBM cell line was treated with TMZ, the cells expressed IFNB1, a type of IFN-I, as well as interferon-stimulated genes (ISGs). We also aimed to clarify the pathway through which IFN-I is induced. Several pathways are known to activate IFN-I, so we knocked down the expression of key intermediates in these pathways and treated the cells with TMZ. As a result, the upregulation of IFNB1 and ISGs induced by TMZ was diminished when RIG-I was knocked down. RIG-I is a pattern recognition receptor that detects double-stranded RNA (dsRNA). This finding suggests that the IFN-I induction observed in TMZ-treated GBM cells is linked to the presence of dsRNA within the tumor cells. In this presentation, we will discuss the origins of the dsRNAs and whether TMZ-induced IFN-I is sufficiently strong to transform the "immune-cold" or "immune-suppressive" GBM TME into an "immune-hot" state. Citation Format: Natsuki Koide, Tatsunori Nishimura, Miho Suzuki, Keiko Shinjo, Yutaka Kondo. Temozolomide induces innate immune responses via the production of double-stranded RNAs in glioblastoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6131.