Identification of novel small molecule inhibitors of Aurora B kinase

Abstract

Aurora kinases (A, B and C) are frequently amplified and overexpressed in a wide variety of cancers, and their up-regulation often correlates with poor prognosis. The potential role of these kinases in tumorigenesis indicates that they could be appealing target for molecular therapy. Although extensive efforts have been done to develop Aurora kinases inhibitors (AKIs), selective for A, B or both kinases, so far, none of them have yet been approved by FDA due to their severe toxicity. The aim of this study has been to identify novel and powerful AKIs, Aurora B kinase inhibitors. In living cells, we tested the inhibition of Aurora B kinase by 7 potential novel AKIs, called MK1-7, which share a common molecular scaffold, by evaluating Serine 10 phosphorylation of Histone H3, a bona fide downstream target of the kinase in HeLa cells. We selected 4 compounds (MK1, 2, 6 and 7), that were able to reduce phosphorylation of Histone H3 at 10 nM dose. Then, we evaluated the effect of each inhibitor on: cell cycle progression, spindle assembly checkpoint (SAC) escape, cell proliferation and viability. Although with different efficacy, these 4 MKs perturb cell cycle progression inducing polyploidy. In addition, cells treated with the 4 MKs escape from mitosis overtaking the SAC checkpoint. These MKs blocked cell growth with an IC50 ranging from 0.37 to 2.27 nM (MK1 IC50=1,2 nM; MK2 IC50=2,27 nM; MK6 IC50=0,44 nM; MK7 IC50=0,37 nM). Based on MK7 most powerful efficacy, its effect on cell division and viability was more extensively investigated. HeLa cells treated with MK7 were positive for apoptotic Annexin V and propidium iodide staining and showed an increase in caspase 3 and PARP cleavages, indicating induction of apoptosis. Additionally, MK7 treatment caused alteration in mitotic spindle formation, chromosome segregation and cytokinesis. Finally, we observed that MK7 is able to inhibit growth of A2780 (human ovarian carcinoma), HL-60 (human promyelocytic leukemia), HCT116 (human colorectal carcinoma) and 8505-C (human undifferentiated thyroid carcinoma) cell lines. In conclusion, our in vitro data have identified in MK7 a powerful compound which could be widely used to inhibit Aurora B kinase in different cancer types.