Validating Aurora B as an anti-cancer drug target

Abstract

The Aurora kinases, a family of mitotic regulators, have received much attention as potential targets for novel anti-cancer therapeutics. Several Aurora kinase inhibitors have been described including ZM447439, which prevents chromosome alignment, spindle checkpoint function and cytokinesis. Subsequently, ZM447439-treated cells exit mitosis without dividing and lose viability. Because ZM447439 inhibits both Aurora A and B, we set out to determine which phenotypes are due to inhibition of which kinase. Using molecular genetic approaches, we show that inhibition of Aurora B kinase activity phenocopies ZM447439. Furthermore, a novel ZM compound, which is 100 times more selective for Aurora B over Aurora A in vitro, induces identical phenotypes. Importantly, inhibition of Aurora B kinase activity induces a penetrant anti-proliferative phenotype, indicating that Aurora B is an attractive anti-cancer drug target. Using molecular genetic and chemical-genetic approaches, we also probe the role of Aurora A kinase activity. We show that simultaneous repression of Aurora A plus induction of a catalytic mutant induces a monopolar phenotype. Consistently, another novel ZM-related inhibitor, which is 20 times as potent against Aurora A compared with ZM447439, induces a monopolar phenotype. Expression of a drug-resistant Aurora A mutant reverts this phenotype, demonstrating that Aurora A kinase activity is required for spindle bipolarity in human cells. Because small molecule-mediated inhibition of Aurora A and Aurora B yields distinct phenotypes, our observations indicate that the Auroras may present two avenues for anti-cancer drug discovery.

Mitotic drivers—inhibitors of the Aurora B Kinase

“…The majority of the early inhibitors yielded phenotypes consistent with inhibition of Aurora B (see below) raising the question as to whether it was possible to inhibit Aurora A in cells with a small molecule. However, in 2006 it was it shown using a dual Aurora A/B inhibitor, ZM3 that it was possible to suppress Aurora A kinase activity in cells with a small molecule [30]. Encouragingly, this resulted in a monopolar spindle phenotype, confirming the observations derived from model organisms [25].…”

“…3 A new concept-mitotic drivers 3.1 Inhibition of Aurora B overrides the spindle checkpoint As mentioned above, the initial Aurora inhibitors described, such as ZM447439 and Hesperadin, were relative selective for Aurora B over A [30,[42][43][44]. Even dual Aurora inhibitors, such as VX-680, yielded phenotypes more consistent with Aurora B inhibition [45].…”

“…ZM447439 shows 20-fold selectivity for Aurora B over A and has proved to be a useful tool for probing Aurora B function. Similarly, Hesperadin has been used extensively to probe Aurora B function; note however that the cytokinesis failure induced by Hesperadin may be due to an off-target effect in addition to the inhibition of Aurora B [30]. VX680 is a dual A/B inhibitor but as with the majority of Aurora inhibitors-the exception being MLN8054-the predominant phenotypes in cell based assays arise due to Aurora B inhibition yielding the mitotic driver phenotype described above.…”

Targeted disruption of Aurora A causes abnormal mitotic spindle assembly, chromosome misalignment and embryonic lethality

“…These effects may, in part, be explained by the reported role of Aurora A in facilitating expression and activation of critical mitosis regulators cyclin B and Cdc25B (Mendez et al, 2000;Tay et al, 2000;Dutertre et al, 2004). However, involvement of Aurora A in regulating specific cellular phenotypes still remain uncertain in view of the inherent limitations in assessing the contributions of the endogenous proteins in ex vivo experiments and also due to occasional contradictory results published on the consequence of ablating Aurora A function in cells grown in vitro (Girdler et al, 2006;Hoar et al, 2007).…”

An integrated pharmacokinetic–pharmacodynamic model for an Aurora kinase inhibitor

“…Mad2 can directly interact with Cdc20 and inhibit the activation of APC/C [37]. Treatment of cells with AK-B inhibitors caused chromosome alignment problems, spindle checkpoint override and cytokinesis failure [34,38,39]. From the above observations and following [22], it can therefore be reasonably hypothesised that: (i) AK-A inhibition reduces all net transition rates in the state transition framework in Fig.…”