Effects of targeting CTMP on immunogenicity of MSI-L colon adenocarcinoma cells by metabolism and cell cycle modulation.

Abstract

246 Background: Regimen of metastatic colon cancer (mCOAD) is moving towards combination of immune checkpoint inhibitors (ICBs) and targeted therapy, however ICBs are rarely effective in MSI-L metastatic colon cancers, limiting options for backline treatments, new targeted therapy is on demand to improve immunogenicity of MSI-L mCOAD. As targeting fatty acid metabolism or cell cycle has shown potential in improving the efficacy of ICBs, our team focused on CTMP, a thioesterase (ACOT) family member, mainly modulates fatty acid β oxidation, meanwhile it binds to phosphorylation sites of AKT thus intervenes cell cycle, currently its role on immunogenicity of COAD is not clear. Methods: Correlation between CTMP and OS in MSI-L colon cancer patients was assessed by KM plotter in GEO database.11 Clinical samples of MSI-L colon cancer, who received a third-line treatment regimen of anti-PD-1 and fruquintinib, were collected then applied in immunofluorescence and western blot analyses to evaluate CTMP and MHC-I expression. In vitro, Lentiviral transfection of targeted genes were stably established,then applied in RNA-seq and metabolic assays. Proteomic analysis and co-IP were applied to explore CTMP-modulating pathway. In vitro, IFNγ was intratumorally injected. Results: KM curve showed CTMP was negatively correlated with OS in MSI-L COAD in GEO database. In clinical samples, lower CTMP expression and higher MHC-I expression were observed in partial response (PR) than progressive disease (PD) group. In vitro, CTMP-OE reduced MHC-I, increased AKT phosphorylation and immune checkpoints (PD-L1, IDO-1), promoted clone formation. Seahorse assay showed increased capacity of glycolysis and oxidative phosphorylation in CTMP-OE than vector. RNA-seq showed CTMP-OE reduced MHC-I augmentation under IFN-γ treatment, meanwhile glucose metabolism genes, ACOT family ,immune checkpoints were also up-regulated, indicating ACOT family related metabolism promotion and immunogenicity suppression of COAD. Proteomic analysis and co-IP assay indicated CTMP interacts REV7, a key mitotic regulatory protein. Enzyme activity assay showed REV7 negatively regulates CDK1. Furthermore, REV7-OE alone is capable to induce MHC I augmentation and G2 arrest, accordingly CTMP-KD enhanced REV7's negative modulation on CDK1,contributing to G2 arrest, that also augmented MHC I . In homologous mice tumor-bearing model, tumor shrinkage was observed in CTMP-KD/ REV7-OE group. CTMP-KD/ REV7-OE increases MHC I expression,CD8+ T cell infiltration under IFN γ intra-tumoral injection. Conclusions: In summary, our studies suggested that CTMP regulates the metabolism of colorectal cancer and intervenes MHC-I molecules expression, and targeting CTMP is potential in suppressing tumor cell cycle and promoting immunogenicity through its modulation on REV7.