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.