Abstract A045: Imaging ferroptosis-mediated TME remodeling that sensitize cold tumors for immunotherapy

Abstract Background: Immune checkpoint inhibitors (ICIs) harness the power of the immune system to fight against systemic cancers. Despite being one of the most promising current therapeutic strategies, response rates remain heterogeneous. Immunologically cold tumors, such as triple-negative breast cancer (TNBC), are among those that do not respond well to checkpoint inhibition. Ferroptosis-related therapies are emerging as a new class of therapeutics for chemo-resistant and metastatic cancers, as they exploit the antioxidant dependence of cancer cells, circumventing most resistance mechanisms. However, the relationship between ferroptosis and the tumor microenvironment (TME) is not well characterized. Here, we leverage ferroptosis-inducing therapies as an adjuvant for immunotherapy and monitor the myeloid dynamics in response with immuno-Positron Emission Tomography (immuno-PET). Methods: A myeloid-heavy TNBC model was used to study myeloid dynamics in response to ferroptosis therapy. The immunogenicity of ferroptotic cancer cells was investigated through in vitro quantification of damage-associated molecular patterns (DAMPs). The impact of ferroptosis therapies on macrophages was also evaluated. Furthermore, the synergy of ferroptosis-inducing therapy (using IKE) and ICB (with aPD-1) was assessed in vivo, and immune infiltration changes were quantified via flow cytometry and tissue staining. To facilitate this investigation, a pan-myeloid radioimmunoconjugate, 89Zr-DFO-CD11b, was developed as an immunoPET agent to quantitatively monitor spatiotemporal dynamics of tumor myeloid cells during ferroptosis-based therapy. Results: TNBC cells undergoing ferroptosis exhibit an immunogenic phenotype, characterized by increased DAMP production, which can contribute to TME reprogramming. Macrophages exposed to cells undergoing ferroptosis were polarized to an anti-tumor phenotype, exhibited increased tumor spheroid infiltration, and increased phagocytosis signaling. In vivo combination of IKE with aPD-1 suppressed tumor growth. The combination therapy increased tumor infiltration of lymphocyte populations, particularly CD8+ T cells, as well as anti-tumor macrophages, into the tumor core. After confirming 89Zr-DFO-CD11b showed high radiochemical conversion, stability in serum, and specific binding to myeloid cells both in vitro and in vivo, 89Zr-DFO-CD11b was injected IV into tumor-bearing mice receiving therapy. Tumor uptake was significantly less in the combination therapy group, with a distinct pocket of myeloid cells in the center of treated tumors, compared to control tumors with myeloid cells around the tumor periphery. Conclusions: This study underscores the potential of ferroptosis as an adjuvant to immunotherapy, with spatiotemporal immune cell dynamics highlighted by 89Zr-DFO-CD11b myeloid imaging. Future studies will multiplex PET imaging with T cell and ferroptosis markers to further elucidate TME dynamics. Citation Format: Elana Apfelbaum, Nermin Mostafa, Edwin C Pratt, Jan Grimm. Imaging ferroptosis-mediated TME remodeling that sensitize cold tumors for immunotherapy [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr A045.