Poster abstracts

Poster number 73 submitted by Christopher Walker

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

Christopher J Walker (OSU, CCC), Joshua J Oaks (OSU CCC), Ramasamy Santhanam (OSU CCC), Paolo Neviani (OSU CCC), Jason G Harb (OSU CCC), Guido Marcucci (OSU CCC)

Abstract:
TKI-based therapies do not induce long-term response in myeloid or lymphoid blast crisis (CML) and Ph+ ALL. Increased expression/activity of nucleocytoplasmic-shuttling hnRNPs A1, E2 and K, are critical for the expression of factors (e.g. SET/PP2A, C/EBPa/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 uM; 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 uM; 48h) resulted in ~75% suppression of BCR-ABL1 expression and kinase activity. Furthermore, KPT-207 also reduced Myc expression in 32D-p210BCR-ABL1 cells; this is consistent with the potential interference of KPT-207 with 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 is currently ongoing, it is safe to conclude that these SINEs represent potentially powerful therapeutic tools that, if used alone or in combination with TKIs, might lead to sustained complete molecular remission in CML-BC and Ph+ ALL patients.

Keywords: CML, CRM1, PP2A