Abstract 3539: Targeting levels and oligomerization of mutant nucleophosmin induces differentiation and loss of survival of human AML cells with mutant NPM1

Abstract

Abstract NPM1 is an oligomeric, nucleolar phosphoprotein that functions as a molecular chaperone for both proteins and nucleic acids. NPM1 plays multiple roles in cell growth and proliferation by participating in diverse biological processes, including ribosome biogenesis and transport, centrosome duplication, DNA repair, transcriptional regulation and histone chaperoning. NPM1 has an N-terminal conserved, hydrophobic, oligomerization domain (residues, 1-110), which is common to all isoforms of NPM1 and critical for its chaperone activity. Recently, NSC348884 was identified as a small molecule inhibitor that disrupts NPM1 dimer/oligomer formation, inducing apoptosis of cancer cells. NPM1 is mutated in approximately one-third of patients with AML. The mutant NPM1c+ contains a 4-base insert that results in extra C-terminal residues encoding a nuclear export signal (NES), which causes NPM1c+ to be aberrantly localized in the cytoplasm. Here, we determined the effects of targeting NPM1 in cultured and primary AML cells. Treatment with siRNA to NPM1, which depleted both NPM1c+ and un-mutated NPM1, significantly induced p21, decreased the % of cells in S-phase of the cell cycle, as well as induced differentiation of the AML OCI-AML3 cells that express both NPMc+ and un-mutated NPM1. This was associated with up-regulation of C/EBPα but attenuation of the levels of HOXA9 and MEIS1. Notably, treatment with NPM1 siRNA sensitized OCI-AML3 more than HL-60 cells (expressing only wild-type NPM1) to all-trans retinoic acid (ATRA) and cytarabine. Moreover, inhibition of NPM1 oligomerization by NSC348884-induced apoptosis and sensitized OCI-AML3 and primary AML cells expressing NPM1c+, but not AML or normal CD34+ progenitor cells expressing wild-type NPM1, to ATRA and cytarbine. NSC348884 was also able to sensitize primary AML cells that expressed NPM1c+ as well as FLT3-ITD to ATRA and cytarbine. Addtionally, co-treatment with NSC384884 sensitized these primary AML cells to the lethal effects of the FLT3 kinase inhibitor PKC412 (Novartis Pharma). These results show that attenuating levels or oligomerization of NPM1 selectively induces apoptosis and sensitizes AML cells expressing NPM1c+ alone or with FLT3-ITD to treatment with ATRA, cytarabine and FLT3 kinase inhibitor. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3539. doi:10.1158/1538-7445.AM2011-3539