Targeting Aurora Kinases in Acute Lymphoblastic Leukemia

Despite improved treatment outcome in acute lymphoblastic leukemia (ALL), drug resistance and disease recurrence remain major obstacles in specific subgroups. Thus, there is an urgent need to identify new targets for therapy. Several studies showed that Aurora kinases were therapeutic targets in cancer therapy, including solid tumors and hematological malignancies. Here we describe preclinical testing of Aurora kinase inhibitors in ALL and the molecular mechanism of different drug activity.

Quantitative RT-PCR and Western blot were used to assess the expressions of Aurora kinases and their activators in ALL. RT-PCR was used to detect the expression of MDR-1. To test activity against Aurora kinases, different ALL cell lines were treated with various concentrations of Aurora kinase inhibitors “VE-465 and VX-680”. The effects of Aurora kinase inhibitors on the cell cycle were evaluated by flow cytometry. Gene expression profiling was performed to identify the candidate targets which regulate the different drug sensitivity. Transient knockdown and overexpression of candidate genes in ALL cell lines were also employed in this study.

Nine ALL cell lines treated with Aurora kinase inhibitors (VE-465 and VX-680) exhibited different drug sensitivity. Five ALL cell lines were sensitive to drug treatment with IC₅₀ around 10–40 nM, including MLL-AF4-positive and BCR-ABL-positive cell lines. However, RPMI-8402 was one of the three cell lines which were resistant to VE-465 and VX-680 with IC₅₀ more than 10 μM. Among these sensitive ALL cell lines, treatment of Aurora kinase inhibitors resulted in an increased G2/M and sub-G1 populations. In contrast, drug-resistant ALL cell lines showed increased polyploidy status after exposure to Aurora kinase inhibitors. The different treatment efficacy was not related to the expression of Aurora kinases, their activators or MDR-1. In order to elucidate the molecular mechanism to regulate the different drug sensitivity, microarray study was performed. It showed that treatment of Aurora kinase inhibitors resulted in differential expressions of genes (75 up-regulated and 90 down-regulated genes) and CDKN1Awas one of the potential molecules which regulated the treatment diversity. RT-PCR and Western blot confirmed the cDNA microarray data: CDKN1A was up-regulated after treatment with Aurora kinase inhibitors in the drug-sensitive cell lines, but no change in the level of CDKN1A in the drug-resistance cell lines. Knockdown of CDKN1A in drug-sensitive cell lines impaired the treatment activity. Over-expression of CDKN1A in drug-resistant cell lines increased the anti-leukemia effect of Aurora kinase inhibitors.

These data suggest that treatment with Aurora kinase inhibitors may be a novel and effective therapy in specific subgroups of ALL, including MLL-AF4-positive ALL. These data show that status of Aurora kinases, their activators or MDR-1 does not correlate with the drug susceptibility in ALL cell lines. The susceptibility to Aurora kinase inhibitors in ALL depends on the activation status of CDKN1A.

No relevant conflicts of interest to declare.