Efficacy of novel histone deacetylase inhibitor, AR42, in a mouse model of, human T-lymphotropic virus type 1 adult T cell lymphoma.

Human T-lymphotropic virus type 1 (HTLV-1) causes a variety of forms of adult T-cell leukemia/lymphoma (ATL), a refractory CD4+/CD25+ T-cell malignancy. Novel approaches to treat ATL patients are required due to the resistance of ATL to conventional chemotherapies. Histone deacetylase inhibitors (HDACi), which induce histone hyperacetylation leading to chromatin remodeling and reactivation of transcriptionally repressed genes have shown efficacy against a variety of cancers. Herein, we tested if valproic acid and the novel orally bioavailable HDACi, AR-42 reduced the proliferation of ATL cell lines by promoting apoptosis and histone hyperacetylation. Both compounds were cytotoxic and elicited a dose dependent increase in cytochrome C and cleaved Poly (ADP-ribose) polymerase (PARP) indicating the induction of cell death by apoptosis and promoted acetylation of histone H3 in both MT-2 and C8166 cell lines. We then evaluated the effects of AR-42, for survival in an ATL NOD/SCID mouse model. A dietary formulation of AR-42 prolonged survival of ATL engrafted mice compared to controls. Our data provide new directions for the treatment of ATL and support the further development of AR-42 against HTLV-1-associated lymphoid malignancies.