Phenotypic and Functional Effects of Novel HDAC Inhibitor LBH589 On Human Lymphocyte Populations.

Abstract Abstract 3681 Poster Board III-617 LBH589 is a novel pan-HDAC inhibitor belonging to the cinnamic hydroxamic acid class. Preclinical studies have shown that LBH589 has potent antitumor activity. It induces hyperacetylation of core histone proteins, resulting in modulation of protein expression, leading to cell cycle arrest in the G2/M phase and apoptosis. Currently, LBH589 is undergoing phase I/II clinical evaluation in multiple myeloma and other hematologic malignancies. Although the role of HDAC inhibition by LBH589 has been widely studied, its effects on immune function have not yet been defined. In this study, we investigated the effects of LBH589 on the phenotype and function of human lymphocyte populations including T cells, Th17 cells and NK cells. The effect of LBH589 at clinically relevant concentrations from 2.5 nM to 20nM on phenotypes of T cells purified from peripheral blood mononuclear cells (PBMCs) by negative selection was analyzed by flow cytometry. We observed that LBH589 treatment at 48 hours led to a dose-dependent downregulation of a series of important surface molecules, including CD3, CD4, CD8 and CD28. To evaluate the LBH589 effects on the T cell function, anti-CD2/CD3/CD28 activated- T cells were treated with or without LBH589 for 48 hours and the IFN-γ production was measured by ELISA. The significant inhibition of INF-γ production was observed upon LBH589 treatment (141 pg/ml (LBH10nM), 53pg/ml (LBH20nM) vs 605pg/ml (control)). Moreover, we investigated the LBH589 effects on the activity of Th17 cells, which were induced from CD4+ T cells culturing in the presence of IL-1β, IL-6 and IL-23. Our data demonstrated that LBH589 treatment resulted in the significant repression of IL-17 production (438 pg/ml (LBH10nM) vs 706 pg/ml (control) at 24 hours; 541pg/ml (LBH10nM) vs 898 pg/ml (control) at 48 hours)). We next investigate the effects of LBH589 on NK cells, which were enriched from healthy donor PBMCs. LBH589 treatment had no effect on the phenotype of resting NK cells (NKp30, NKp44, NKp46, NKG2D and KIR). However, it significantly decreased expression of activation molecule NKp44 on IL-2 and IL-12-activated NK cells. In addition, the IFN-γ production by IL-2 and IL-12- induced NK cells was significantly inhibited following 24 hour-LBH589 treatment (609 pg/m (LBH1nM), 359pg/ml (LBH2.5nM), 107pg/ml (LBH10nM) and 44pg/ml (LBH20nM) vs. 1756 pg/ml (control)). Moreover, we observed significant decreased cytotoxicities by NK cells treated with LBH589 against the U266 myeloma cell line (13% (LBH10nM), 4% (LBH20nM) vs. 51% (control) (E: T=10:1) and 8% (LBH10nM), 2% (LBH20nM) vs 36% (control) (E: T=5:1) respectively) at 24 hours. Taken together, we demonstrate that HDAC inhibition by LBH589 significantly affects phenotype and function of human T cells, Th17 cells and NK cells. Our pre-clinical data therefore indicates the need to monitor immune functions in patients under the HDAC inhibitor treatment as well as it provides a preclinical basis to evaluate its activity for the treatment of autoimmune diseases. Disclosures: No relevant conflicts of interest to declare.