Selective ATM inhibition augments radiation-induced inflammatory signaling and cancer cell death

Abstract

Over half of all cancer patients undergo radiation therapy but there is an unmet need for more efficacious combination strategies with molecular targeted drugs. DNA damage response has emerged as an important intervention point for improving anti-tumor effects of radiation and several inhibitors are currently in development. Ataxia telangiectasia mutated (ATM) kinase is a key regulator of cellular response to DNA double strand breaks and a potential target for radiosensitization. We recently reported two new potent and selective ATM inhibitors, M3541 and M4076, that effectively sensitize cancer cells to radiation and regress human xenografts in clinically relevant animal models. Here, we dive deeper into the cellular events in irradiated cancer cells exposed to ATM inhibitors. Suppression of ATM activity inhibited radiation-induced ATM signaling and abrogated G1 checkpoint activation resulting in enhanced cell death. Our data indicated that entry into mitosis with gross structural abnormalities in multiple chromosomes is the main mechanism behind the increased cell killing. Misalignment and mis-segregation led to formation of multiple micronuclei and robust activation of the interferon response and inflammatory signaling via the cGAS/STING/TBK1 pathway. Cancer cells exposed to radiation in the presence of M3541 were more susceptible to killing in co-culture with NK cells from healthy donors. In addition, strong upregulation of PD-L1 expression was observed in the surviving irradiated cancer cells exposed to M3541. Simultaneous activation of the STING pathway and PD-L1 suggested that combination of radiation, ATM inhibitors and PD-L1 targeted therapy may offer a novel approach to radio-immunotherapy of locally advanced tumors.

The mechanism and clinical application of DNA damage repair inhibitors combined with immune checkpoint inhibitors in the treatment of urologic cancer

“…DDR inhibitors accelerate the production of micronuclei in the nucleus, which is an important factor in dsDNA production. The production of dsDNA activates the cGAS-STING-TBK1-IRF3 signaling pathway and promotes the release of type I IFN ( Chiu et al, 2023 ). Meanwhile, DDR-related inhibitors promote the SUMO-ization of SHP1 at lysine 127, inhibiting the TRAF6-STING-p65 signaling pathway and activating the nonclassical STING signaling pathway.…”

“…Many preclinical trials have been conducted to explore the mechanism of the combined application of ATM inhibitors and ICIs to enhance the efficacy of immunotherapy. The application of ATM inhibitors to tumor cells blocks ATM signaling in tumor cells, leading to the inability to activate the G1/S cell cycle checkpoint and massive tumor cell death ( Chiu et al, 2023 ). ATM inhibitors lead to defective DNA damage repair, which in turn induces chromosomal instability and abnormal division, forming micronuclei.…”

“…ATM inhibitors lead to defective DNA damage repair, which in turn induces chromosomal instability and abnormal division, forming micronuclei. Micronuclei contain unrepaired DNA breaks or circular DNA that can be recognized by cGAS in the cytoplasm and activate the STING/TBK1 signaling pathway, thereby upregulating type I IFN expression and enhancing inflammatory signaling ( Chiu et al, 2023 ). In addition, ATM inhibitors affect mitochondrial function and number and downregulate transcription factors such as TFAM.…”

Emerging mechanisms and implications of cGAS-STING signaling in cancer immunotherapy strategies

“…These findings highlight the complex interplay of chemotherapy with the cGAS-STING pathway 96 . Additionally, ATM kinase, a regulator of DNA damage responses, plays a major role in cGAS-STING activation, and ATM inhibitors have shown potential in enhancing cancer cell sensitivity to radiation and promoting interferon responses via the cGAS-STING/TBK1 pathway 30 , 97 .…”

ATM inhibition augments type I interferon response and antitumor T-cell immunity when combined with radiation therapy in murine tumor models

“… 23 In addition, ATM inhibition on irradiated tumor cells showed mitotic disruption, STING pathway activation, and programmed death-ligand 1 (PD-L1) expression in tumors. 24 Furthermore, another group reported that combined radiation and ATM inhibition showed increased CD8+T cell infiltration, decreased CD4+T cell infiltration, and PD-L1 induction in tumor-associated macrophages. 25 These previous reports suggest a capacity for ATM inhibition to modulate the immunogenic effects of radiation within the tumor microenvironment, however further investigation is needed to clarify the mechanisms of this interaction.…”