Carboxylesterase-1 assisted targeting of HDAC inhibitors to mononuclear myeloid cells in Inflammatory Bowel Disease

Background and Aims Histone deacetylase inhibitors (HDACi) exert potent anti-inflammatory effects. Because of the ubiquitous expression of HDACs, clinical utility of HDACi is limited by off-target effects. Esterase-sensitive motif (ESM) technology aims to deliver ESM-conjugated compounds to human mononuclear myeloid cells, based on their expression of carboxylesterase 1 (CES1). This study aims to investigate utility of an ESM-tagged HDACi in inflammatory bowel disease (IBD). Methods CES1 expression was assessed in human blood, in vitro differentiated macrophage and dendritic cells and Crohn's disease (CD) colon mucosa by mass cytometry, quantitative PCR and immunofluorescence staining respectively. ESM-HDAC528 intracellular retention was evaluated by mass spectrometry. Clinical efficacy of ESM-HDAC528 was tested in DSS-induced colitis and T cell transfer colitis models using transgenic mice expressing human CES1 under the CD68 promotor. Results CES1 mRNA was highly expressed in human blood CD14 + monocytes, in vitro differentiated and LPS stimulated macrophages and dendritic cells. Specific hydrolysis and intracellular retention of ESM-HDAC528 in CES1 + cells was demonstrated. ESM-HDAC528 inhibited LPS-stimulated IL-6 and TNF-α production 1000 times more potently than its control, HDAC800, in CES1 high monocytes. In healthy donors peripheral blood, CES1 expression was significantly higher in CD14 ++CD16 - monocytes compared to CD14 +CD16 ++ monocytes. In CD inflamed colon, a higher number of mucosal CD68 + macrophages expressed CES1 compared to non-inflamed mucosa. In vivo, ESM-HDAC528 reduced monocyte differentiation in the colon and significantly improved colitis in a T cell transfer model, whilst having limited potential in ameliorating DSS-induced colitis. Conclusions We demonstrate that monocytes and inflammatory macrophages specifically express CES1, and can be preferentially targeted by ESM-HDAC528 to achieve therapeutic benefit in IBD.