Abstract 3839: Nuclear export (karyopherin) inhibitors: A novel therapeutic strategy for treating Philadelphia-positive (Ph+) acute leukemias

Tyrosine kinase inhibitor (TKI)-based therapies do not induce long-term response in myeloid or lymphoid blast crisis (BC) chronic myelogenous leukemia (CML) and Ph+ acute lymphoblastic leukemia (ALL). Increased expression/activity of nucleocytoplasmic-shuttling heterogeneous nuclear ribonucleoproteins (hnRNPs) A1, E2 and K, are critical for the expression of factors (e.g. SET/PP2A, C/EBPβ/miR-328, and c-Myc) regulating proliferation and survival of Ph+ progenitors. Because the karyopherin CRM1 controls nuclear export of hnRNPs, we assessed the therapeutic potential of CRM1 inhibitors in CML-BC and Ph+ ALL models. Thus, myeloid 32D-p210BCR-ABL1 and lymphoid Baf3-p190BCR-ABL1 progenitors were exposed to the CRM1 selective & potent inhibitors of nuclear export (SINE) KPT-185 and KPT-207. MTT viability assays revealed that KPT-185 and KPT-207 decreased cell viability by ∼80% at concentrations ranging from 150-350 nM. The KPT-SINE not only induced killing, but also affected cytokine-independent growth of BCR-ABL1+ cells: proliferation was inhibited 89% and 81% by KPT-185 and KPT-207, respectively. Notably, growth and survival of non-transformed 32Dcl3 and BaF3 cells was not affected (70-100% viable cells) by KPT-SINE. As expected, treatment (1 μM; 48h) with these inhibitors altered the nuclear/cytoplasmic ratio of hnRNPs important for BCR-ABL1 leukemogenesis. As a result, treatment of BCR-ABL1+ cells with KPT-185 and KPT-207 (1 μM; 48h) resulted in 75% and 50% suppression of BCR-ABL1 expression and kinase activity, respectively. Furthermore, KPT-207 also reduced Myc expression in 32D-p210BCR-ABL1 cells; this is consistent with the potential interference of KPT-207 with the proliferation/survival signals triggered by the BCR-ABL1/MAPK/hnRNP K/Myc pathway in CML-BC progenitors. Because both KPT-185 and KPT-207 significantly alter hnRNP A1 localization, which is important for regulation of the PP2A inhibitor SET and, therefore, for BCR-ABL1 leukemogenesis, we assessed whether KPT-207 and KPT-185 negatively regulate PP2A activity. Indeed, treatment with KPT-207 and KPT-185 (250 nM; 48h) restored PP2A activity in 32D-p210BCR-ABL1 cells to levels similar to those detected in non-transformed 32Dcl3 cells. Although further investigation of KPT-207 and KPT-185 mechanism of action and assessment of their biologic/therapeutic effects in CML-BC and Ph+ ALL mouse models and primary leukemic and normal progenitors is currently ongoing, it is safe to conclude that selective n