Molecular and functional immunogenicity induced by LSD1 inhibition. A, Immunoblot analysis of RP-48OVA-LLO190 cells treated with bomedemstat (1 μM, BOM) or DMSO for a total of 10 days, with or without interferon gamma (IFN-g, 10 ng/mL) for the final 48 hours. B, Immunoblot analysis of RP-48OVA-LLO190 cells transduced with a CRISPR knockout vector encoding a non-targeting (control) or LSD1-targeting sgRNA. C, Immunoblot analysis of H510 cells and, D, H146 cells treated with bomedemstat (1 μM) or DMSO for a total of 96 hours. E, Percent of CD8+ T cells positive for CD107a cytotoxic degranulation marker following 24h co-culture with RP-48OVA-LLO190 cells that were pre-treated with bomedemstat (1 μM) or DMSO for a total of 72h with or without IFN-ɣ (10 ng/mL) from 48-72h, shown for nonspecific bulk CD8 T cells (red) or antigen-specific OT-I CD8+ T cells (blue). PI, PMA+ionomycin. One-way ANOVA with Dunnett’s test performed on OT-I populations excluding PI and media, *P<0.05, **P<0.01, ****P<0.0001. F, Relative RP-48OVA-LLO190 cell survival following exposure to bomedemstat, IFN-g, and co-culture with OVA-specific OT-I or non-specific CD8+ T cells. Cells were treated with bomedemstat (1 μM) or DMSO for 72h, IFN-ɣ at 0 or 10 ng/mL for 24h prior to co-culture, and then co-cultured with OT-I or non-specific CD8+ T cells for 24h (2:1 effector:target ratio). Percent of cells surviving was calculated as the number of viable SCLC cells in co-culture with OT-I T cells relative to the number of viable SCLC cells in co-culture with non-specific CD8+ T cells multiplied by 100, as determined by flow cytometric quantification with counting bead spike-in (mean±SEM of 6 technical replicates performed in two groups of three at separate timepoints). Multiple unpaired t-tests with unequal variance and Sidak’s correction for multiple testing *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001. G, Schematic of molecular targets and associated direct mechanisms, subsequent tumor cell-autonomous effects, and eventual multicellular phenotype of LSD1 inhibition in combination with PD1/PDL1 axis blockade. H, Schematic of an upcoming clinical trial of bomedemstat in combination with maintenance atezolizumab for patients with ES-SCLC who do not experience disease progression during four cycles of standard of care (SOC) induction platinum, etoposide, and anti-PDL1 antibody systemic therapy.