(0635) Differential mTOR Inhibition in TP53-Mutant Head and Neck Squamous Cell Carcinomas: Dissecting Immune Cold and Hot Microenvironments

Introduction: TP53 mutant head and neck squamous cell carcinoma (HNSCC) presents a therapeutic challenge due to the complex interplay within its tumor microenvironment (TME). This study aims to elucidate the effect of mammalian target of rapamycin inhibitor (mTORi) and its downstream effector hypoxia-inducible factor 1-alpha (HIF-1a) on HNSCC, focusing on the distinction between immune cold (ROC1) and immune hot (4MOSC) phenotypes. The immune cold phenotype is typified by minimal T-cell infiltration, rendering it less responsive to immunotherapy, whereas the immune hot phenotype exhibits substantial immune cell presence, potentially increasing immunotherapy efficacy.

Methods: Using the ROC1 and 4MOSC cell lines as models for immune cold and hot HNSCC, respectively, we assessed the impact of mTORi in vitro and in vivo using a tumor-cell orthotopic model. ROC1 line represents a TME with limited immune cell infiltration, and the 4MOSC line represents a TME with active immune engagement. We evaluated the growth inhibitory effects of Everolimus and investigated the underlying molecular mechanisms via HIF-1α pathway analysis, PD-L1 expression, and VEGF modulation.

Results: Treatment with Everolimus demonstrated consistent growth inhibition in both ROC1 and 4MOSC cell lines in vitro as well in tumor cell orthotopic model in vivo. In the ROC1 cells, inhibition mechanism was primarily via immune sensitization, evidenced by HIF-1α-driven PD-L1 upregulation suggesting a potential for mTORi to enhance immune cell infiltration and activity in these tumors. In contrast, the 4MOSC line exhibited an inhibition mechanism focused on direct modulation of tumor cell intrinsic properties via HIF-1α-mediated VEGF modulation.

Conclusions: Our research highlights the diverse responses of TP53-mutant HNSCC to mTORi, influenced by the tumor's immune environment. mTORi may help overcome immunotherapy resistance in immune cold HNSCC, while in immune hot HNSCC, it impacts tumor growth and angiogenesis. These findings underscore the importance of customized therapies in HNSCC, taking into account the complex interactions within the TME.