Abstract 1554: Combining an optimized irinotecan formulation with self-amplyfing RNA to treat an immunosuppressive lung metastasis melanoma model

Abstract Background: Melanoma is an aggressive skin cancer that frequently metastasizes to the lungs in its advanced stages. The tumor microenvironment of melanoma is typically immunosuppressive; lacking immune cells with strong antitumor activity. While interleukin-12 (IL-12) based immunotherapy has shown potential for treating melanoma, its clinical application is limited by significant toxicity. To address this, we are developing a self-amplifying RNA (saRNA)-lipid nanoparticle (LNP) system to produce IL-12 in vivo. The formulation selected is similar to that used for Onpattro, a clinically approved formulation of siRNA designed to deliver RNA to liver hepatocytes. IL-12 saRNA delivery to hepatocytes will increase plasma levels of IL-12 and sustain expression which should stimulate an immune response. This saRNA LNP formulation is being combined with a novel liposomal formulation of irinotecan (Irinosome High C). This formulation can improve the tumor immune microenvironment (TIME)from an immunosuppressive one to an immunosupportive one. We believe that this formulation is ideally suited for combination with IL-12 saRNA-LNPs. Method: The safe and effective (as judged by IL-12 levels on the plasma) dose of saRNA-LNPs was determined in C57BL/6 mice following intravenous (iv) administration. A safe and effective (as judged by assessments of anti-tumor activity) was determined for Irinosome High C following iv administration. These treatments were used alone and in combination to treat a model lung metastasis model where mice were injected iv with B16F10 melanoma cells. Tumor burden in the lungs was determined 18 days after cell injection (6 days after last treatment) and overall survival data was collected along with health status data. As a function of time after treatments splenocytes from mice were isolated and co-cultured with B16F10 cells in vitro and immune mediated cell kill was determined. Results: The combination of IL-12 saRNA-LNP and Irinosome High C significantly improved survival and reduced lung tumor burden in B16 tumor bearing mice compared to those receiving either treatment alone. Splenocyte assays confirmed that IL-12 treatment enhanced levels of key immune cytokines, including IL-12, IL-2, and IFN-γ, indicating a robust antitumor immune response. Conclusion: The combination of Irinosome High C and IL-12 saRNA-LNPs represents a promising new approach for treating lung metastatic disease a life-threatening complication seen in patients with late-stage melanoma. This strategy may offer a safer, more effective treatment option through use of a TIME modulatory agent with IL-12 mediated immune activation. Studies are on going to better understand the underlying mechanisms driving enhanced antitumor responses and the development of strategies to see this approach transition in various tumor models and from the lab to patients. Citation Format: XuXin Sun, Nasim Sarrami, Irafasha C. Casmil, Sijie Zhang, Marcel B. Bally, Anna K. Blakney. Combining an optimized irinotecan formulation with self-amplyfing RNA to treat an immunosuppressive lung metastasis melanoma model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1554.