Abstract A119: Liposomal doxorubicin improves response to immune checkpoint blockade by enhancing innate immunity in a murine model of oral cavity squamous cell carcinoma

Abstract Despite advances in the treatment of head and neck cancer, squamous cell carcinoma of the oral cavity remains primarily a surgical disease with few effective systemic therapies. Oral cavity tumors harbor both innate and acquired resistance mechanisms to cytotoxic chemotherapy. Additionally, the tumor microenvironment (TME) has limited immune cell infiltration, resulting in low response rates to immune checkpoint inhibitors. Given the need for novel systemic therapies for oral cavity squamous cell carcinoma, we investigated the role of liposomal doxorubicin (Doxil®) as both a cytotoxic agent and an immunomodulatory agent. We utilized the MOC2 syngeneic murine model of oral cavity squamous cell carcinoma, an aggressive tumor model with resistance to immune checkpoint blockade. We demonstrated that Doxil has moderate activity as a single agent in vivo for C57BL/6J mice harboring MOC2 flank tumors. We next performed flow cytometric analysis to characterize the changes in immune cell populations in the TME after treatment with Doxil. We found significantly increased numbers of innate immune cells including NK cells and myeloid cells. Multiplex immunofluorescence was also used to confirm the increase in myeloid cell tumor infiltration upon Doxil treatment. Given the changes seen in the tumor immune microenvironment, we hypothesized Doxil may improve response to immune checkpoint blockade. Therefore, we treated C57BL/6J mice inoculated with MOC2 flank tumors with Doxil alone or in combination with radiation therapy (RT) and/or anti-CTLA-4 therapy. While RT or anti-CTLA-4 alone had modest anti-tumor activity, combining either RT or anti-CTLA-4 with Doxil significantly reduced tumor growth. Moreover, the triple combination therapy of Doxil, RT, and anti-CTLA-4 had an increased effect compared to the dual therapy of Doxil and anti-CTLA-4. This included several complete responses, which resulted in a significant improvement in survival. Triple combination therapy also reduced both local and distant metastatic burden compared to single agent and dual combination therapy. Next, we selectively inhibited CD8+ T cells, myeloid cells, or NK cells to determine which immune cell populations contribute to the immunomodulatory activity of Doxil. We observed that inhibition of NK cells resulted in increased tumor growth as well as decreased survival, suggesting that Doxil-mediated infiltration of NK cells into the TME contributes to response to anti-CTLA-4 therapy. Taken together, these data provide a rationale for combining liposomal doxorubicin with anti-CTLA-4 therapy for the treatment of oral cavity squamous cell carcinoma. Citation Format: Jennifer L Anderson, Fabio H Brasil Da Costa, Allison Nipper, Laxman Devkota, Rohan Bhavane, Ratna Veeramachaneni, Sofia Cortes, Neeraja Dharmaraj, Sarah Latka, Andrew Badachhape, Renuka TR Menon, Prajwal Bhandari, Ketankumar Ghaghada, Simon Young, Ananth Annapragada, Andrew Sikora. Liposomal doxorubicin improves response to immune checkpoint blockade by enhancing innate immunity in a murine model of oral cavity squamous cell carcinoma [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 A119.