3151 - Palmitoylation of Sting Promotes Immune Activation and Reformulates Antitumor Immunity following Radiation
Presenter(s)
B. Wang1, and L. Zhao2; 1State Key Laboratory of Holistic Integrative Management of Gastrointestinal Cancers and Department of Radiation Oncology, Xijing Hospital, Fourth Military Medical University, Xi'an, China, 2StateKey Laboratory of Holisticntegrative Managementof Gastrointestinal Cancersand Department of RadiationOncology,Xijing Hospital,Fourth Military MedicalUniversity, Xi'an, China
Purpose/Objective(s): The standard treatment for Esophageal cancer (EC) includes a multimodal approach combining surgery, radiation therapy (RT), and chemotherapy. Despite, only a limited proportion of EC patients achieve a complete pathological response following neoadjuvant chemoradiation therapy. Additionally, biochemical changes in the tumor and its surroundings have been associated to RT resistance. Agonists targeting the stimulator of interferon genes (STING) pathway have been explored in clinical trials due to their potential antitumor effects. Nevertheless, the precise cell populations that mediate the antitumor immune response triggered by STING activation following radiation remain incompletely characterized in EC. This study aimed to elucidate the anti-tumor effects and underlying mechanisms associated with STING palmitoylation in response to radiation, and offer theoretical foundations and insights to support clinical treatment.
Materials/Methods: EC cell line KYSE410 and EC109 were injected in the left flanks of C57BL/6 mice models for efficacy and survival studies. Mice were randomized into four groups, including vehicle, STING?RT(8Gy*3F)?STING+RT. Mice were euthanized when tumor volumes reached 1500-2000 mm3. A comparison of treatment groups was performed using the log-rank test with p<0.05 considered significant. Immune cell makers were stained by antibodies and then analyzed by flow cytometry. In vitro, Flow cytometry fluorescence quantitative analysis, and immunofluorescence was used to detect the expression of STING. Protein palmitoylation in cultured EC cell was detected by immunoprecipitation and acyl-biotin exchange (ABE). The liquid chromatography-mass spectrometry technology, is used to identify the specific palmitoylation sites of STING. Immune cell makers were stained by antibodies and then analyzed by flow cytometry.
Results: When the defined tumor volume endpoint was reached, the STING+RT group delayed tumor volume and improved the survival of the mouse model more than other groups. Furthermore, flowcytometry and immunofluorescence suggested that RT upregulated the expression of STING on EC cells. This explained the anti-tumor capacity of radiotherapy combined with STING agonists. In addition, immunoprecipitation and acyl-biotin exchange (ABE) show that the catalytic activity of ZDHHC20 is essential for the palmitoylation of STING in EC. The results of LC-MS technology indicated that the cysteine residues at positions c106 of the mouse sting protein were successfully identified as key sites for palmitoylation modification.
Conclusion: These findings demonstrate that palmitoylation of STING catalyzed by ZDHHC20 promotes its stability, resulting in immune activation and repaired antitumor immunity. This study proposes that combination therapy can potentially enhance treatment efficacy in radiation resistance EC and provides insights into STING agonists and radiotherapy can influence tumor micro-environment.