Abstract B055: Targeting LSD1 for anti-PD1 therapy resistance mechanism in Head and Neck Cancer for future therapy
Head and Neck Squamous cell carcinoma (HNSCC) frequently exhibits resistance to anti–PD-1 immune checkpoint blockade. We asked whether dysregulated major histocompatibility complex class I (MHC-I) is a determinant of anti–PD-1 resistance, and whether targeting Lysine-specific demethylase 1 (LSD1/KDM1A) is an effective strategy. LSD1 promotes phospho-CDK7– and STAT3-mediated tumor growth and immunosuppression, whereas it promotes dendritic cells and CD8+ T cell-mediated antitumor immunity. Effects of SP2509 ± anti–PD-1 (pembrolizumab) were evaluated in (1) a humanized orthotopic NCG model bearing MHC-I–deficient HNSCC stem-cell tumors and (2) an MHC-I-sufficient 4NQO-induced HNSCC model. Immune phenotypes were assessed by flow cytometry and immunohistology. Mechanistic studies included gene expression analyses (Batf3, Cxcl9, Cxcr3), TCGA correlations between KDM1A and immune-infiltration signatures, and PBMC co-culture assays using HNSCC lines engineered for MHC-I gain- or loss-of-function. In the humanized MHC-I–deficient model, pembrolizumab did not reduce primary tongue tumor burden by gross or histopathologic assessment; instead, it decreased tumor-infiltrating human immune populations (CD45+, CD3+, CD4+, CD8+ subsets, and DCs), consistent with immune exclusion, and was associated with increased metastatic liver lesions. In contrast, in the MHC-I-sufficient 4NQO model, anti–PD-1 reduced tumor burden and increased CD45+ leukocyte infiltration, DC accumulation, and CD69+CD8+ T cells. SP2509 attenuated tumor growth in humanized HNSCC mice, improved tumor histopathology, and remodeled the tumor immune microenvironment with minimal change in total CD45+ frequency. MHC-I loss coupled with insufficient DC and CD8+ T-cell activity drives anti–PD-1 resistance and can paradoxically exacerbate tumor progression and metastasis. SP2509 increased infiltration of CD3+, CD4+, CD8+ T cells, NKT, and NK cells and enhanced activation of CD8+, NKT, and NK populations. Mechanistically, LSD1 inhibition upregulated Batf3, Cxcl9, and Cxcr3, consistent with enhanced DC-associated antigen presentation and effector lymphocyte recruitment. TCGA analysis revealed inverse correlations between KDM1A expression and immune-infiltration genes (PTPRC/CD45, CD4, CD8A/B, ITGAX/CD11c, XCR1, CXCL9, CXCR3, IFNG). In PBMC co-culture assays, SP2509 plus anti–PD-1 induced immune activation in an MHC-I–dependent manner: MHC-I overexpression rescued immune activation in MHC-I–deficient stem cells, while MHC-I knockout reduced activation in MHC-I-sufficient HSC3 cells. Overall, LSD1 inhibition attenuated tumor growth in both MHC-I-sufficient and -deficient tumors. Pre-treatment assessment of tumor MHC-I status may predict non-responder and immune-related adverse outcomes to anti–PD-1 therapy. LSD1 inhibition promotes MHC-I–dependent antigen presentation, Batf3/DC-linked signaling, and effector lymphocyte activation, providing a rational strategy to overcome MHC-I–associated resistance to anti–PD-1 therapy in HNSCC/OSCC. Amit Chakraborty, Rajnikant Raut, Chumki Choudhury, Bikash Sahay, Manish V. Bais. Targeting LSD1 for anti-PD1 therapy resistance mechanism in Head and Neck Cancer for future therapy [abstract]. In: Proceedings of AACR Drug Discovery and Development (AACR D3) Conference; 2026 Jul 21-24; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(14_Suppl):Abstract nr B055.