Differentiation therapy for the treatment of t(8;21) acute myeloid leukemia using histone deacetylase inhibitors

Abstract

Key Points• HDACi-mediated differentiation therapy is a potent and molecularly rational treatment strategy in t(8;21) AML.Epigenetic modifying enzymes such as histone deacetylases (HDACs), p300, and PRMT1 are recruited by AML1/ETO, the pathogenic protein for t(8;21) acute myeloid leukemia (AML), providing a strong molecular rationale for targeting these enzymes to treat this disease. Although early phase clinical assessment indicated that treatment with HDAC inhibitors (HDACis) may be effective in t(8;21) AML patients, rigorous preclinical studies to identify the molecular and biological events that may determine therapeutic responses have not been performed. Using an AML mouse model driven by expression of AML1/ ETO9a (A/E9a), we demonstrated that treatment of mice bearing t(8;21) AML with the HDACi panobinostat caused a robust antileukemic response that did not require functional p53 nor activation of conventional apoptotic pathways. Panobinostat triggered terminal myeloid differentiation via proteasomal degradation of A/E9a. Importantly, conditional A/E9a deletion phenocopied the effects of panobinostat and other HDACis, indicating that destabilization of A/E9a is critical for the antileukemic activity of these agents. (Blood. 2014;123(9):1341-1352

The CDK9 Inhibitor Dinaciclib Exerts Potent Apoptotic and Antitumor Effects in Preclinical Models of MLL-Rearranged Acute Myeloid Leukemia

“…injection. For panobinostat, mice were treated with 25 mg/kg Monday-Friday (M-F) for the first week and then 15 mg/kg M-F thereafter as described previously (20). For dinaciclib, mice were given 30 mg/kg every third day.…”

“…Primary leukemias were generated by the retroviral coexpression of MSCV-MLL-AF9-IRES-VENUS with MSCV-luciferase-IRESNras G12D or MSCV-luciferase-IRES-Cherry expression constructs as described previously (20). Transduced cells were used to reconstitute the hematopoietic compartment of each irradiated 6-to 8-week-old C57BL/6 mice.…”

“…The spleens were then macerated and sifted through a 0.40-mm filter, centrifuged, and resuspended in fetal calf serum (FCS; Invitrogen Life Technologies)/dimethyl sulfoxide (DMSO; Life Technologies) before cryopreservation. For subsequent in vitro assays, thawed primary MLL-AF9 leukemia cells were cultured as described previously (20). Retroviral transduction of MLL-AF9 leukemia cells with the murine stem cell virusinternal ribosomal entry site-GFP (MSCV-I-GFP) Mcl-1 construct was performed as described previously (26).…”

“…Small molecules targeting DOT1L (15,16), BRD4 (8,17), LSD1 (18,19), HDACs (20), and CDK9 (21) have been tested for activity against MLL-FP-driven AML in diverse in vitro and in vivo systems with varying effect. Herein, we have used sophisticated genetically engineered mouse models of MLL-AF9 AML and human leukemias expressing MLL-AF9 and other MLL-FPs to test the sensitivity of these tumors to a range of agents that target the epigenetic and transcriptional regulatory proteins recruited by these oncogenic fusion proteins.…”

Epigenetics in the hematologic malignancies

“…101 Indeed, recent mechanistic insight into the antileukemic activity of HDACi in t(8;21) AML demonstrates the induction of terminal myeloid differentiation following HDACi mediated proteasomal degradation of the AML1/ETO9a fusion protein. 102 Acetylation of lysine residues is primarily recognized by protein-binding motifs named bromodomains. Over 40 bromodomain containing proteins in eight subfamilies with functionally diverse roles such as chromatin remodeling, post-translational histone modification and transcriptional co-activation have been identified.…”