The anti-leukemic effect and molecular mechanisms of novel hydroxamate and benzamide histone deacetylase inhibitors with 5-aza-cytidine

Abstract

Abstract. Histone deacetylase inhibitors (HDACi) demonstrate considerable in vitro and in vivo activity and clinical efficacy in the treatment of hematological malignancies. Pre-clinical and early phase clinical trials identify therapeutic activity using a combination of HDACi and demethylating agents which may be more efficacious than single agent treatment. Our studies aimed to determine the effects and molecular mechanisms of action of novel hydroxamate (MCT-3) and benzamide [MGCD0103 (MG)] HDACi's in the HL-60 cell line alone and in combination with the demethylating agent 5-aza-cytidine (AZA). MG, MCT-3 and AZA treatment significantly inhibited HL-60 cell growth in vitro with MG being the most potent agent. MG in combination with AZA demonstrated no significant increase in inhibition of cell growth over MG treatment alone whilst MCT-3 in combination with AZA demonstrated increased inhibition of cell growth over either agent alone although no more significant than MG alone. MG alone or MCT-3 in combination with AZA significantly increased p15 and caspase-3 expression. MG and MCT-3 significantly attenuated AZA-induced MMP-9 mRNA expression and proteolytic activity. Interestingly, MCT-3, MG and AZA alone and in combination increased expression of the novel tumour suppressor gene Nur77, important in leukemogenesis, with MG a more potent inducer as a single agent. These observations suggest the enhanced anti-leukemia activity of the combination of AZA and HDACi may only reside with certain HDACi classes and may be in-part explained by regulation of genes associated with cell cycle arrest, apoptosis and tumour suppression. IntroductionHistone deacetylase inhibitors (HDACi) represent a novel, structurally heterogeneous class of compounds. The four chemical classes of HDACi, include the benzamides (e.g., MGCD0103), the hydroxamates (e.g., MCT-3, SAHA), the short-chain fatty acids (e.g., valproic acid), and the cyclic tetrapeptides (e.g., Depsipeptide/FK228) (1-4). The hydroxamates are frequently referred to as 'broad-spectrum' or 'pan'-HDACi resulting from inhibition of several HDAC isoforms). The remaining chemical classes of HDACi selectively inhibit class I HDACs (3,4). HDACi have recently been described to have significant therapeutic activity in the treatment of hematological malignancies including cutaneous T-cell lymphoma, Hodgkin's lymphoma, myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) (5). In vitro HDACi have been shown to up-regulate the expression of p15INK4b , p21 WAF1/CIP1 , caspase-3 and the inducible orphan nuclear receptor Nur-77, whose expression is important in the induction of apoptosis and has recently been demonstrated to be abrogated in acute myeloid leukemia, whilst also down regulating Bcl-XL and MMPs in cell lines (6)(7)(8)(9)(10)(11)(12)(13)(14).Numerous in vitro studies together with recent pre-clinical and early phase clinical studies identify significant antileukemic activity of a combination of HDACi with demethylating agents with greater inhibition of growth and DNA...

Mocetinostat (MGCD0103): a review of an isotype-specific histone deacetylase inhibitor

“…Indeed, future studies should include predictive biomarkers, for instance serum TARC levels, in patients treated with MGCD0103, to determine which subset of patients would get the most benefit from this compound. Recent in vitro data with MGCD0103 indicate that it synergizes with proteasomal inhibitors in lymphoma [20] as well as demethylating agents [48], BCL-2 antagonists [22] and inhibitors of antioxidant pathway [16] in leukemic cells. Further development of clinical trials of MGCD0103 in combination with these agents is therefore warranted.…”