Background: To eradicate HIV-infection, the reservoir of latently infected resting T-cells must be depleted. We investigated the potential for disrupting HIV-latency and the effect on T-cell activation of LBH589, a novel highly potent histone deacetylase inhibitor (HDACi) currently used in clinical trials, and compared this with other HDACi in clinical use.

Methods: The latently infected T-cell line ACH2 and the monocytic cell line U1 were treated with the HDACi LBH589 (panobinostat), ITF2357 (givinostat), PXD101 (belinostat), SAHA (vorinostat), and valproic acid (VPA) across a broad range of concentrations, including the levels obtained with clinical use. We estimated viral replication by p24 production in culture supernatant using enzyme linked immunosorbent assay (ELISA). The potency of reversing HIV-latency was defined as p24 fold-increase above background. To investigate the effect on primary T-cells, we treated peripheral blood mononuclear cells (PBMCs) from healthy donors with ITF2357, PXD101, SAHA (all 62.5-500nM), LBH589 (15.6-500nM), and VPA (0.5mM). The expression of T-cell phenotype and activation markers as well as HIV co-receptors was measured using flow cytometry.

Results: The various HDACi displayed significant differences in potency when stimulating HIV-1 expression from the latently infected cell lines with LBH589 >ITF2357 and PXD101 >SAHA >VPA. LBH589 was significantly more potent than all other HDACi and showed great potential for reversing latency even in the very low concentration range. Compared to untreated cells, LBH589 increased p24 levels 26.1-fold and 73.4-fold at 15.6nM and 31.1nM in ACH2 cells and 10.6-fold and 11.9-fold in U1 cells, respectively. This was significantly higher compared to SAHA in the clinically relevant concentration of 250nM (P=0.021 for ACH2 cells and P <0.001 for U1 cells). The proportion of primary T-cells expressing the early activation marker CD69 increased in HDACi-treated cells compared to untreated cells with LBH589 >ITF2357 and PXD101 >SAHA >VPA. HDACi-treatment decreased expression of the HIV co-receptor CCR5 on monocytes and, to a lesser degree, CXCR4 on CD4+ T-cells.

Conclusions: At physiological concentrations, LBH589, ITF2357 and PXD101 stimulate HIV-1 expression from latently infected cell lines more efficiently than SAHA. Given the high potency of LBH589 in reversing HIV-latency, this HDACi may be an attractive candidate for purging HIV-1 from the latent reservoir.