Abstract 6245: Selective HDAC6 inhibition by ITF3756 modifies the landscape of gene and protein expression in human monocytes: Possible identification of a specific biomarker signature

Abstract

Abstract Histone deacetylase 6 (HDAC6) modulates tumor immunogenicity through several pathways, such as the control of PD-L1 expression on tumor and on lymphoid cells. Thus, HDAC6 is a potential pharmacological target for cancer treatment. In humans, HDAC6 inhibition can be monitored by measuring the ratio between tubulin and histone acetylation. However, the identification of biomarkers to be used as a signature for patient stratification that correlates with the treatment efficacy is missing. Since we have previously demonstrated that the activity of the selective HDAC6 inhibitor ITF3756 on myeloid cells plays a role in the antitumor immune response in the TME, we reasoned that an ITF3756-specific signature could be identified in unstimulated monocytes treated with the compound. Monocytes were purified from healthy donors, treated with ITF3756 and RNAseq and proteomic analyses were performed. Gene Ontology analysis shows that ITF3756 has a widespread effect on monocyte transcriptome and proteome. We observed the down-modulation of genes and proteins involved in inflammatory pathways and in transcription regulation. Up-regulation of neutrophil-mediated immunity, metabolic pathways and protein phosphorylation was also identified. Focusing on genes that could be relevant in the tumor context, we selected a panel of genes from the most up- (SCL27A1, ANXA6 and IRF6) and down-modulated (CD84, RANK, CXCL2, CXCL3, STAB-1, CD163, PD-L1, CD206 and ADA). Interestingly, we found among the downmodulated genes markers of M2 macrophages, genes related to the tumor associated macrophages, and STAB-1, whose targeting is currently in clinical trials for cancer immunotherapy. Peripheral Blood Mononuclear Cells (PBMCs) could be a less expensive starting material for biomarker identification to be collected during a clinical trial when compared to purified monocytes. Thus, to ascertain whether the regulation by ITF3756 of our selected genes was detectable also in PBMCs we performed gene expression analysis after ITF3756 treatment and we confirmed that all selected genes were reproducibly modulated. Surface protein expression of M2 macrophages biomarkers in our panel, were determined by flow cytometry and all of them were significantly modulated in PBMCs. These data show how our approach successfully led both to the identification of a biomarker signature that could be used in clinical trials to monitor the pharmacodynamic effect of ITF3756, and to the discovery of previously unknown targets of HDAC6 inhibition. Citation Format: Chiara Ripamonti, Valeria Spadotto, Monica Forino, Christian Steinkuhler, Gianluca Fossati. Selective HDAC6 inhibition by ITF3756 modifies the landscape of gene and protein expression in human monocytes: Possible identification of a specific biomarker signature. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6245.