Abstract 2953: Selective activity of XPO1 inhibitors in TET2-mutant myeloid malignancies
Authors: Prutsch Nicole , Jing Chang-Bin , Etchin Julia , Berezovskaya Alla , Tiv Hong , Poitras Michael J. , Gokhale Prafulla , Landesman Yosef , Look A. Thomas 
Published: August 2019

Abstract
TET2 is among the most frequently mutated genes in hematopoietic malignancies. Inactivating mutations in TET2 are found in ∼30% of patients with myelodysplastic syndrome (MDS), ∼19% with de novo acute myeloid leukemia (AML), and ~15% with myeloproliferative neoplasm (MPN). TET2 mutations are also identified in a subset of individuals over 50 years of age with clonal hematopoiesis of indeterminate potential (CHIP), a condition that predisposes affected individuals to progression to myeloid malignancy and atherosclerotic heart disease with heart attack or stroke. TET2 mutations represent an early genetic lesion in hematopoietic stem and progenitor cells (HSPCs), inducing a premalignant state of clonal dominance that predisposes to the acquisition of additional mutations. Thus, effective therapy for patients with TET2 mutations in HSPCs will require identifying drugs that are selectively lethal to TET2 mutant HSPCs but spare normal HSPCs, a property analogous to the widely studied genetic relationship called “synthetic lethality”. Using a tet2-mutant zebrafish model created in our laboratory, we screened for drugs from libraries of FDA-approved compounds and drugs in Phase I/II testing. We found that nuclear exporter XPO1 inhibitors, selinexor (KPT-330) and eltanexor (KPT-8602), were among the most promising, in that they are selectively lethal to HSPCs in tet2-mutant compared to wild-type fish. Moreover, we treated HSPCs of wild-type and Tet2-deficient mice with both selinexor and eltanexor in a methylcellulose colony formation assay. WT HSPCs lose their replating capacity at passage 3 (P3), while Tet2-mutant clones demonstrate aberrant sustained self-renewal capacity over multiple replatings. We found that both drugs selectively kill primary Tet2-mutant murine HSPCs and also block the aberrant self-renewal of these cells. By transplanting WT and Tet2-mutant CD45.2 donor cells into CD45.1 recipient mice, we monitored peripheral blood cells before and after treatment with selinexor or eltanexor to explore synthetic lethality of these drugs in vivo. Moreover, the human AML cell line K562 with TET2 homozygous mutations generated with CRISPR-Cas9, was more sensitive to selinexor and eltanexor than the parental cell line. To elucidate the mechanism behind the selective targeting of Tet2-mutant blood stem cells, we will use PRO-Seq and START-Seq methods to identify transcriptional elongation and initiation sites at single-nucleotide resolution. These preclinical studies must be done to show a therapeutic efficacy and mechanism of action of these new drugs before they can be translated to improve therapy of patients who have TET2 inactivating mutations.
Citation Format: Nicole Prutsch, Chang-Bin Jing, Julia Etchin, Alla Berezovskaya, Hong Tiv, Michael J. Poitras, Prafulla Gokhale, Yosef Landesman, A. Thomas Look. Selective activity of XPO1 inhibitors in TET2-mutant myeloid malignancies [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 2953.