Myristoylation is required for biological activity of >200 intracellular proteins. N-myristoyltransferases (NMTs) transfer the fatty acid myristate to N-terminal glycine residue; there are two isoforms, NMT1 and 2. In acute myeloid leukemia (AML), upregulation of Lyn and Src, important myristoylated proteins, contribute to cell survival and proliferation. The specific roles of NMT1 and NMT2 are unknown in this context. The relationships among NMT1/NMT2 expression and acute AML patient outcomes were studied using RNA-sequencing and microarray cohorts with over 350 patients. We found that high NMT1 and low NMT2 expression were associated with reduced overall and event-free survival in adult AML, which was independent of other prognostic markers on multivariate analysis. High NMT1, but not NMT2, expression was associated with proliferative gene sets in AML cell lines, indicating potential for distinct isozyme substrates. Given these results, we examined NMT1 and NMT2 levels in AML cell lines and AML patient blast cells using Western blotting and flow cytometry. We determined that NMT2 expression varied greatly among patients, but was markedly reduced in most cases, while NMT1 expression was relatively preserved. A potent small molecule NMT inhibitor, PCLX-001, preferentially induced apoptosis and reduced viability in NMT2-deficient AML cell lines cultured in vitro compared with normal lymphocytes and peripheral blood mononuclear cells. PCLX-001 also killed freshly isolated human AML blasts ex vivo with an IC50 of ~170nM regardless of their mutational background. In a murine AML xenograft model, subcutaneously delivered PCLX-001 monotherapy demonstrated dose-dependent anticancer activity and produced complete remissions after five daily 50 mg/kg doses. NMT expression provides independent prognostic information to refine existing clinical stratification, and NMT inhibition is a promising novel therapeutic strategy for AML.
Citation Format: John R. Mackey, Aishwarya Iyer, Megan C. Yap, Zoulika Zak, Krista Vincent, Erwan Beauchamp, Lynne M. Postovit, Joseph Brandwein, Luc G. Berthiaume. Examination of NMT1 and NMT2 as independent prognostic markers and novel drug targets in adult acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3043.