Regulation and Pharmacology of the Mitotic Kinesin Kif15

Abstract

The mitotic spindle is the microtubule (MT)-based machine that segregates a replicated set of chromosomes during cell division. Many chemotherapeutics target the mitotic spindle by altering or disrupting microtubules, the polymer that form the mitotic spindle. While these drugs are efficacious, microtubules are a major component of all cells and their disruption can have deleterious effects on cell types with dynamic microtubules, such as neurons. Microtubule-dependent molecular motors that function during mitosis are logical alternative mitotic targets for drug development. Eg5 (Kinesin-5) and Kif15 (Kinesin-12), in particular, are an attractive pair of motor proteins, as they work in concert to drive centrosome separation and promote spindle bipolarity. Furthermore, we hypothesize that the clinical failure of Eg5 inhibitors may be (in part) due to compensation by Kif15. While the biochemical properties of the Eg5-driven spindle assembly pathway are well-established, knowledge of Kif15 biochemical properties and regulation is only just emerging. Similarly, while dozens of Eg5 inhibitors are available, small molecule tools with which to validate Kif15 as a cancer drug target do not exist. To address these deficiencies, we have studied how the cell regulates Kif15 activity under normal conditions through auto-inhibitory and binding partner mechanisms and also established a small molecule screening protocol for the discovery of Kif15 inhibitors. We screened a small library of kinase inhibitors and identified GW108X, an oxindole that inhibits Kif15 in vitro. We show that GW108X has a distinct mechanism of action compared with a commercially available Kif15 inhibitor called Kif15-IN-1. Since these GW108X and Kif15-IN-1 differ in their inhibitory mechanisms, they each may serve as unique leads with which to further develop Kif15 inhibitors as clinically relevant agents.