LSD1 inhibition enhances radiotherapy efficacy in OSCC by attenuating SUMOylation and activating NK cells

Background: Oral squamous cell carcinoma (OSCC) is a prevalent and deadly cancer, with limited treatment success using radiation therapy (RT) alone. This study investigated the role of lysine-specific demethylase 1 (LSD1) in promoting oncogenic signaling, resistance to RT, and immunosuppression in OSCC. We hypothesized that targeting LSD1-specific mechanisms, in combination with RT, could inhibit OSCC growth and immune evasion. Methods: We employed a 4NQO-treated progressive mouse OSCC model to identify the molecular and cellular changes during radiotherapy and LSD1 inhibition (with SP2509) in combination with radiation. To identify these changes, we used RNA-seq for pathway-related changes, flow cytometry for immune regulation, and in vitro cell culture techniques for ChIP, qRT-PCR, and pathway validation. Finally, we treated feline spontaneous OSCC with a combination of SP2509 and radiation to test its efficacy. Results: RT combined with the LSD1 inhibitor SP2509 promoted the infiltration of natural killer (NK) cells and dendritic cell (DC)-mediated antitumor immunity in mouse OSCC preneoplasia. Feline OSCC treated with an LSD1 inhibitor and RT showed reduced tumor growth. In vitro studies have demonstrated that combination therapy induces the activation of IFNgamma+ CD8+ T cells and NK cells. RNA sequencing showed that the combination therapy attenuated the cell cycle and CDK-related pathways. Clinical OSCC samples treated with RT exhibited inhibition of CD8+ T cells, while the combination of an LSD1 inhibitor and RT recovered CD8+ T cell proliferation with a significant increase in NK cell population in mouse OSCC and peripheral blood mononuclear cells co-cultured with human OSCC cells (HSC3). It was also observed that LSD1 inhibition in OSCC, both in vivo and in vitro, attenuated SUMOylation pathways and downregulated the SUMO1 gene while upregulating NKG2DL-related genes such as MICB in humans and their mouse analog RAEgamma. Using ChIP-qPCR, we observed that LSD1 inhibition increased H3K9me2 methylation at the SUMO1 gene locus and decreased H3K4me2 methylation. LSD1 inhibition in combination with radiotherapy in feline OSCC attenuates cancer growth. Conclusion: SP2509 treatment enhances the efficacy of radiation therapy by inhibiting SUMOylation pathways, which increases NK cells by NKG2DL-NKG2D axis activation, thereby inducing anti-tumor immunity.