Largazole, a Novel Cyclic Peptide Histone Deacetylase Inhibitor, Demonstrates Anti-MM Effects Alone and Increases the Anti-MM Effects of Bortezomib.

Abstract 4925

Multiple myeloma (MM) remains an incurable malignancy. Therefore, there is a need for the development of new agents to improve the survival for these patients. Histone acetylation, which is controlled by the balanced activities between histone acetyltransferase (HAT) and histone deacetylase (HDAC), is a major epigenetic modification that contributes to tumorigenesis. Through inhibition of HDAC activity, HDAC inhibitors (HDACis) increase acetylation levels of histones as well as other tumor suppressor gene products; and, therefore, are potential anti-cancer agents. Based on the structures, currently available HDAC inhibitors can be divided into four groups, including hydroxamates, cyclic peptides, aliphatic acids, and benzamides. Largazole is a novel member of the cyclic peptide family of HDACis some of which have shown anti-cancer effects in preclinical studies and early clinical trials including for patients with MM especially when used in combination with the proteasome inhibitor bortezomib. In this study, we have explored the potential anti-MM activity of largazole alone and in combination with bortezomib in preclinical in vitro studies. As demonstrated using the MTS assay, this HDACi inhibits the growth of cells from the MM cell lines RPMI8226, U266 and MM1S with an IC₅₀ of approximately 0.2 μM in all three cell lines. In addition, largazole also induces apoptotic death of MM cells as determined with Annexin V staining followed by flow cytometric analysis. Largazole was also shown to induce histone acetylation in MM cells as determined with Western blot analysis using an antibody against acetyl-histone H4. Furthermore, the combination of this HDACi and bortezomib demonstrated synergistic anti-MM effects in these cell lines. Importantly, treatment of mice with largazole shows excellent tolerability at doses that produce concentrations in vivo that are higher than those shown to produce anti-MM effects in our in vitro studies. Thus, largazole may be a potential new agent for the treatment of MM alone and in combination with bortezomib. Currently, we are evaluating the cytotoxic effects of largazole on normal peripheral blood and bone marrow mononuclear cells in vitro and in vivo using our severe combined immunodeficiency mouse models of human myeloma alone as well as in combination with several other drugs including bortezomib used in the treatment of MM. Updated results from these ongoing studies will be presented at the meeting.