Abstract 7206: STING agonist ADU-S100 in combination with vemurafenib induces STING upregulation, immune-stimulatory cytokine modulation and enhancing NK-mediated cytotoxicity in BRAF V600E-mutant melanoma

Abstract Background: Targeting the mitogen-activated protein kinase (MAPK) pathway with BRAF inhibitors, has significantly advanced the treatment of melanoma patients whose tumor harbor a BRAF V600E/K mutation. therapeutic resistance occurs in the majority of patients, highlighting the need for combination strategies to improve treatment outcomes. The activation of the Stimulator of Interferon Genes (STING) pathway has emerged as a promising approach to boost anti-tumor immunity. This study explores the potential efficacy of combining the STING agonist ADU-S100 (ADU) with vemurafenib in human melanoma cell lines harboring the BRAF V600E mutation, focusing on its impact on tumor signaling, cytokine profiles, and NK-cell-mediated cytotoxicity. Methods: Human melanoma cell lines with BRAF V600E mutation—SK-MEL-28, SK-MEL-24-SH4, RPMI7951, and SK-MEL-3—were treated with ADU, vemurafenib, or both in combination. Cell viability was assessed, while changes in total STING were measured by Western blot. Cytokine profiles were analyzed using a multiplex Luminex panel. NK cell-mediated cytotoxicity was assessed through co-culture experiments. Results: Cell viability assays demonstrated treatment with ADU alone did not significantly reduce cell viability. Western blot analysis revealed minimal baseline STING levels in the SH4 cell line, with a marked increase following ADU, vemurafenib, or their combination. The most pronounced upregulation of STING occurred when ADU & vemurafenib were used together. In SK-MEL-28, the combination treatment was the only condition to result in substantial STING upregulation and a corresponding reduction in pERK. Cytokine analysis showed that the combination treatment significantly increased the levels of beta-2 microglobulin (B2M) across all three cell lines, suggesting modulation of immune checkpoint inhibitor resistance. Additionally, the combination treatment led to a marked reduction in CXCL-8, a key mediator of melanoma progression and metastasis, and decreased VEGF levels across all three cell lines. The CXCL5/CXCL13 axis, known to influence responses to targeted immunotherapies, was most favorably modulated under the combination condition. Co-culture with NK cells revealed an increase in tumor cell death in all three cell lines following combination treatment. Conclusion: The combination of STING agonist ADU-S100 and vemurafenib effectively enhances immune-stimulatory cytokine profiles in BRAF V600E-mutant melanoma. Notably, this approach may be used to promote NK cell-mediated cytotoxicity and modulation of key cytokines associated with immune resistance. This strategy shows promise for overcoming resistance and improving outcomes, warranting further clinical investigation. Citation Format: Vida Tajiknia, Matthew Hadfield, Andrea Schmidt, Connor purcell, Claire Lin, wafik El Deiry, Sean Lawler. STING agonist ADU-S100 in combination with vemurafenib induces STING upregulation, immune-stimulatory cytokine modulation and enhancing NK-mediated cytotoxicity in BRAF V600E-mutant melanoma [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 7206.