The proteasome inhibitor ixazomib targets epigenetic chromatin modification enzymes upregulated by m2c macrophage polarisation in lung cancer*

Abstract

Background and Aims: Poor prognosis in lung cancer is associated with tumor-associated macrophages (TAMs) that exhibit M2clike behaviours that support multiple pathways in the tumour microenvironment. The interplay between epigenetic modifications and the ubiquitin-proteasome pathway involves three key mechanisms: regulation of epigenetic enzymes by ubiquitin, interaction between ubiquitin and epigenetic modifiers, and epigenetic silencing of critical genes involved in cellular processes. Therefore, we investigated the effects of ixazomib, a proteasome inhibitor, on gene expression changes in epigenetic chromatin modification enzymes in a co-culture of M2c macrophages and A549 lung cancer cells. Methods: The IC50 50 concentration of ixazomib was determined to be 2.19 mu M using a real-time cell analyser. THP-1 monocytes were polarised into M0 macrophages with 100 ng/mL phorbol 12-myristate 13-acetate (PMA), rested, and then exposed to 1 mM hydrocortisone to become M2c macrophages. A549 cells were seeded in the lower chamber of a co-culture plate. M2c macrophages were then co-cultured with A549 cells for 24 h with or without 2.19 mu M ixazomib. After being isolated, mRNA was converted to cDNA and analysed using a gene panel with RT-PCR. Results: The findings showed that 56 genes had exceptionally high expression levels (up to 1848-fold. Ixazomib downregulated these overexpressed genes. Conclusion: Ixazomib effectively modulates the expression of genes involved in epigenetic chromatin modification in the lung cancer microenvironment, indicating its utility in lung cancer therapy. Further studies are needed to explore the combined use of epigenetic drugs and proteasome inhibitors.