Abstract 15671: Targeting Chromatin Structure: The Combined Inhibition of Histone Deacetylases and Bromodomain Proteins in Normalizing Persistently Activated Pulmonary Hypertensive Fibroblasts

Abstract

Rationale: The multifactorial nature of pulmonary hypertension (PH) suggests epigenetic changes as potential determinants of vascular remodeling through regulating gene expression (both up-regulated and down-regulated genes) in vascular cells. Changes in the chromatin state (especially histone acetylation) of specific genes can lead to their repression or activation. We and others have demonstrated histone deacetylases inhibitors (HDACi) and histone acetylation readers inhibitors (BRDi) can prevent and ameliorate PH changes by normalizing pathological gene expression. However, the non-histone protein targets and the narrow therapeutic window of currently available HDACi limits their clinical utility. In this study, we evaluated the effect of combination treatments using a new HDACi (OKI-005, US patent) with high potency and selectivity for HDACs (targeting decreased genes) together with BRDi (targeting increased genes), in low doses. Methods and Results: Cultured human pulmonary artery fibroblasts derived from patients with IPAH (PH-Fibs) or from control donors (CO-Fibs) were used as in vitro model system. PH-Fibs exhibit increased pro-inflammatory genes (e.g. CXCL12), proliferation markers (e.g. Mki67) and anti-apoptosis genes (e.g. BCL2) as well as decreased anti-inflammatory genes (e.g. HMOX1), anti-proliferation genes (e.g. P21) and pro-apoptotic genes (e.g. PERP). In PH-Fibs, the increased expressed CXCL2 gene exhibited more opened chromatin structure and BRD4 binding (ChIP-assay), and BRDi (JQ1) can decrease its expression in a dose dependent trend. At the low doses, JQ1 (100 nM) alone is sufficient to normalize most of increased genes, while the new HDACi (OKI-005) was more effective in normalizing decreased genes in PH- Fibs. The combination of low dose of JQ1 (100 nM) and OKI-005 (64 nM) was sufficient to normalize both increased genes and decreased genes thus inhibiting the persistently activated PH-phenotype without deleterious effects on CO-Fibs. Conclusion: Combination of HDACi and BRDi in low doses is effective in normalizing the persistent activation of PH-Fibs without deleterious effects on control cells, offering promise for epigenetic-targeted therapies in PH.