Abstract 3476: A single intratumoral injection of IL-12 bound to mesoporous silica rods generates effective anti-tumor immune responses and tumor growth control in multiple syngeneic tumor models

Abstract Background: Interleukin-12 (IL-12) is a potent inflammatory cytokine, which demonstrated anti-tumor activity in both experimental model systems and in a number of clinical trials. Unfortunately, the development of IL-12 as a therapeutic is hampered by severe toxicity in the event of significant systemic exposure. Therefore, intralesional IL-12 therapy has been actively pursued for intratumoral therapy. When delivered into the TME, IL-12 increases intratumoral interferon-γ expression leading to conversion of myeloid cells from an immunosuppressive state into an immunogenic one, recruits CXCR3+ NK and effector T cells, upregulates antigen presentation/processing machinery, and generates anti-tumor immunity. Mesoporous silica rods [MSRs] are currently in development as a modular localized therapeutic platform, due to their large payload capacity, slow-release kinetics, high biocompatibility and intrinsic proinflammatory nature. In this study, we evaluated the anti-tumor effect of MSR plus IL-12 [ATT-02] as an “in situ” (“antigen-less”) vaccine and characterized the immune effects of MSR alone and in in combo with IL-12. Methods: Syngeneic mouse models [B16F10, B16-OVA, CT26, and EMT-6] were conducted by challenging the mice with tumor cells on one flank. Tumors were treated one time with ATT-02 i.t. [Murine IL-12, MSR] when tumors reached the target size. Abscopal models were conducted by injecting tumor cells [CT26, B16F10, and B16-OVA] on both flanks at day zero. The tumor on one flank was treated when it reached the target size. Lymph nodes and spleens were collected at day 7 and analyzed by flow cytometry. In vitro work was conducted by co-culturing MSRs with THP-1 cells that had been initially polarized to an “M2” like phenotype. Repolarization (“M2 to M1”) and APC functionality of THP-1 cells were assayed using flow cytometric phenotyping and proliferation of co-cultured antigen-specific T- cells. Results: ATT-02 i.t. generated potent anti-tumor immunity compared to PBS and IL-12 alone in 3 single tumor syngeneic models and 3 abscopal syngeneic models. Complete responses [CRs] were observed in the CT26 and EMT-6 model after a single dose of ATT-02. Upon rechallenge no tumor growth was observed. In the B16-OVA group, SIINFEKL+ T cells and CD86+ macrophages were observed at a higher level than controls in the draining lymph node of ATT-02 treated mice. Interestingly, MSR i.t. alone resulted in delayed tumor progression the B16F10 model. In vitro, we demonstrated that MSR alone results in a repolarization of macrophages to an immunogenic phenotype capable of driving T cell activation. Addition of IL-12 enhances this effect. Conclusions: I.t. injection of ATT-02 (MSR_IL-12) leads to significant anti-tumor immune responses, antigen-specific responses, and tumor growth inhibition in multiple syngeneic tumor models. Citation Format: Fernanda Langellotto, Jessica McDonough, Everton Mandley, Benjamin Seiler, Brena Barra, Edward Doherty, Robert Pierce. A single intratumoral injection of IL-12 bound to mesoporous silica rods generates effective anti-tumor immune responses and tumor growth control in multiple syngeneic tumor models [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 3476.