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Charles Caldwell Jr
MA 05 - Immuno-Oncology: Novel Biomarker Candidates (ID 658)
- Event: WCLC 2017
- Type: Mini Oral
- Track: Immunology and Immunotherapy
- Presentations: 1
MA 05.14 - Differential Expression of IFN-Stimulating DNA Sensors STING and cGAS in Lung Cancer Subtypes (ID 9578)
15:45 - 17:30 | Presenting Author(s): Charles Caldwell Jr
STING is a protein that promotes type I IFN production (IFNα/β) essential for activation of dendritic cells and antigen presentation and priming of T-cells. The cytoplasmic DNA sensor cGAS (cGAMP Synthase) is able to detect tumor DNA, and in response will synthesize cGAMP. cGAMP binds STING specifically, resulting in production of type I IFN. STING is therefore referred to as an adaptor protein essential for immune signaling following detection of tumor DNA. Analysis of the TCGA database indicates decreased survival in lung adenocarcinoma patients lacking STING expression. STING expression is decreased in tumor tissues and can be lost as the tumor progresses. One reported mechanism of loss of STING or cGAS in tumors is due to hypermethylation, a common occurrence in lung cancer. Agonists of STING show potent immune response and are currently in clinical trials. Importantly, recent studies show that expression of STING and cGAS proteins are essential for response to PD-1:PD-L1 blockade.
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We analyzed 55 NSCLC and 39 SCLC cell lines, and 317 NSCLC and 78 SCLC tissues for STING and cGAS expression using immunohistochemistry. 14/55 (25.45%) NSCLC cell lines and 25/39 (64.10%) SCLC cell lines showed no STING expression. Separated in to adenocarcinoma (AC) and squamous cell carcinoma (SCC) subsets, STING expression in AC shows loss of STING as tumor stage increases (Positive: 70% Stage I, 65% Stage II, 52% Stage III, 40% Stage IV, 71% total; n=156) while STING expression is low at all stages of SCC (Positive: 29% Stage I, 18% Stage II, 36% Stage III, 13% Stage IV, 27% total; n=161). SCLC tissues stained showed widespread loss of STING (Positive: 40% Stage I, 27% Stage II, 31% Stage III, 100% Stage IV, 37.18% total, n=78). Expression of cGAS was higher in AC (94%) than SCC (75%) and showed no correlation with stage. TCGA analysis of STING methylation shows hypermethylation in AC (0.15- ± 0.13 tumor vs 0.05 ± 0.02 normal, n=422) and SCC (0.23 ± 0.16 tumor vs 0.04 ± 0.03 normal, n=359). cGAS shows slight methylation in AC (0.05 ± 0.07 tumor vs 0.05 ± 0.01 normal, n=422) but a large increase in SCC (0.19 ± 0.24 tumor vs 0.04 ± 0.01 normal, n=359).
This study indicates drastic differences in STING and cGAS expression in AC, SCC, and SCLC. Differential expression of these proteins could impact the efficacy of STING agonists, radiation therapy, and immunotherapy in lung cancer.
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