Investigational NEDD8-Activating Enzyme (NAE) Inhibitor, MLN4924, Demonstrates Activity Against Primary AML Blast, Progenitor and Stem Cell Populations

Abstract 1414

Acute myelogenous leukemia (AML) has a poor prognosis. Most patients die of either primary refractory or relapsed disease. It has been proposed that relapse may result from ineffective ablation of leukemia stem cells (LSCs) by chemotherapy. Therefore, in order to improve therapy, it is imperative to identify agents that eliminate leukemic progenitor and stem cell populations in addition to blasts. We have previously demonstrated that proteasome inhibition can result in selective ablation of LSCs, without harming normal hematopoietic stem cells (HSCs). Thus, we sought to investigate the activity of a more specific inhibitor of the ubiquitin-proteasome pathway, an investigational NEDD8-Activating Enzyme (NAE) inhibitor MLN4924. Treatment of primary human AML and blast crisis CML samples with MLN4924 resulted in a dose-dependent decrease in the total viability of the blast-cell populations, with an average LD50 of 0.367 μM (0.203–0.530 95% CI; N=17). The average LD50 for phenotypically described LSCs was 0.645μM (0.304–0.986; 95%CI; N=12). Interestingly, when performing progenitor/stem functional assays, we observed a 64% and 86% decrease in colony formation after treatment with 0.25μM and 1 μM of MLN4924 (p< 0.001; N=5; p< 0.001 N=8 respectively). Furthermore, MLN4924 had little to no effect on colony formation of normal hematopoietic cells. Thus, MLN4924 may impair the activity of AML stem/progenitor cells, but not normal cells, in vitro. Importantly, primary AML samples that were resistant to standard chemotherapeutics such as cytarabine in vitro were sensitive to MLN4924. Treatment of primary AML samples with MLN4924 showed increased γH2AX foci, indicating activation of stress responses. Together, these data suggest that MLN4924 can eliminate AML blasts, progenitor and stem cell populations in vitro.