Abstract 3280: TTFields induces immunogenic cell death and STING pathway activation through cytoplasmic double-stranded DNA in glioblastoma cells

Abstract

Abstract Glioblastoma (GBM) is the most common and deadliest malignant brain cancer in adults despite aggressive chemoradiotherapy. Tumor Treating Fields (TTFields) was recently approved in combination with adjuvant temozolomide chemotherapy for newly diagnosed GBM patients. The addition of TTFields resulted in a significant improvement in overall survival. TTFields are low-intensity alternating electric fields that are thought to disturb mitotic macromolecules’ assembly, leading to disrupted chromosomal segregation, integrity and stability. In many patients, a transient stage of increased peritumoral edema is often observed early in the course of TTFields treatment followed subsequently by objective radiographic responses, suggesting that a major component of therapeutic efficacy by TTFields may be an immune mediated process. However, the mechanism underlying these observations remains unclear. Here we report results on a panel of GBM cell lines treated with TTFields at the clinically approved frequency of 200 kHz using an in vitro TTFields system. Our data showed 24 hrs TTFields-treated GBM cells had a significantly higher rate (19.9% vs. 4.3%, p=0.0032) of micronuclei structures released into the cytoplasm as a result of TTFields-induced chromosomal instability. Nearly 40% of these micronuclei were co-localized with two upstream dsDNA sensors: absent in melanoma 2 (AIM2)andInterferon (IFN)-inducible proteinCyclic GMP-AMP synthase (cGAS), compared to absence of co-localization in untreated cells. TTFields-activated micronuclei-dsDNA sensor complexes led to i) induction of pyroptotic cell death, as measured by a specific LDH release assay, and through AIM2-recruited caspase1 and cleavage of pyroptosis-specific Gasdermin D; and ii) activation of STING pathway components including Type I IFNs and pro-inflammatory cytokines downstream of the NFκB pathway. GBM cell-specific shRNA depletion of either AIM2 or STING or both in a co-culture experiment of bone marrow cells or splenocytes with supernanants obtained from knockdown GBM cells was able to reverse the inducement of immune cells. These results provide compelling evidence that TTFields function as an activator of the immune system in GBM cells, and a strong rationale for combining TTFields with immunotherapy aimed at augmenting an anti-tumor immune response such as immune checkpoint inhibitors. Note: This abstract was not presented at the meeting. Citation Format: Dongjiang Chen, Nagheme Thomas, David D. Tran. TTFields induces immunogenic cell death and STING pathway activation through cytoplasmic double-stranded DNA in glioblastoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3280.