The Potential of Aurora Kinases A and B As Therapeutic Targets in Pediatric Acute Leukemia

Abstract 1465

Aurora kinases (AURK) A and B play distinct and important roles during mitosis, and many human cancer types are characterized by upregulated AURK expression. Several small-molecule inhibitors targeting AURKA, B or both, are in development and have shown promising anti-tumour activity in vitro and in vivo. However, most studies address the efficacy of these small-molecule inhibitors in adult cancer. Of all childhood cancers, acute leukemia is the most common type and there is a great medical need to improve outcome and side-effects of current treatment strategies. We therefore analyzed the effects of targeting AURKA and B in pediatric acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML).

Affymetrix microarray analysis of pediatric ALL (n=297) and AML cases (n=237), and normal bone marrow (nBM) samples (n=8), showed that AURKA and B gene expression was low in all patients. AURK protein expression was determined by western blot and reverse phase protein array. Protein levels of both kinases were significantly elevated in ALL and AML compared to nBM (p<0.0002), especially in patients with an E2A-PBX1 translocation (p<0.002). We used short hairpin RNAs and LNA-based mRNA antagonists to silence AURKA and B expression in three ALL and three AML cell lines of different genetic subtypes. Silencing of AURKA caused no or only minor growth delay, whereas AURKB knockdown resulted in proliferation arrest and apoptosis, as indicated by reduced cell counts and the presence of cleaved PARP. This suggests a pivotal role for AURKB in the survival and proliferation of leukemic cells. A panel of leukemic cell lines was exposed to several AURK-inhibitors, and cell viability was determined with an MTS assay. Comparable sensitivity in the low- to mid-nanomolar range was observed for the pan-Aurora inhibitor VX-680, AURKA-selective inhibitor MLN8237 and AURKB-selective inhibitor Barasertib-HQPA (AZD1152-HQPA), whereas cell lines were relatively resistant to the pan-Aurora inhibitor Danusertib. Since silencing experiments suggested that AURKB would be a suitable target, we tested the efficacy of Barasertib-HQPA in primary ALL cells. ALL patient cells with a high AURKB protein expression, especially E2A-PBX1-positive cases, were more sensitive to Barasertib-HQPA than those with a low expression (p<0.05), whereas nBM cells were resistant up to a concentration of 20μM.

In conclusion, inhibition of AURKB, more than AURKA, has an anti-proliferative and pro-apoptotic effect on ALL and AML cells, suggesting that particularly targeting AURKB may be of benefit in the treatment of pediatric acute leukemia. Moreover, this study shows the potential of both LNA-containing mRNA antagonists and Barasertib, for which clear responses have been observed in adult AML early clinical trials, in the treatment of children with ALL and AML.