Discovery and development of aurora kinase inhibitors as anticancer agents

MK-5108, a highly selective Aurora-A kinase inhibitor, shows antitumor activity alone and in combination with docetaxel

Aurora-A kinase is a one of the key regulators during mitosis progression. Aurora-A kinase is a potential target for anticancer therapies because overexpression of Aurora-A, which is frequently observed in some human cancers, results in aberrant mitosis leading to chromosomal instability and possibly tumorigenesis. MK-5108 is a novel small molecule with potent inhibitory activity against Aurora-A kinase. Although most of the Aurora-kinase inhibitors target both Aurora-A and Aurora-B, MK-5108 specifically inhibited Aurora-A kinase in a panel of protein kinase assays. Inhibition of Aurora-A by MK-5108 in cultured cells induced cell cycle arrest at the G(2)-M phase in flow cytometry analysis. The effect was confirmed by the accumulation of cells with expression of phosphorylated Histone H3 and inhibition of Aurora-A autophosphorylation by immunostaining assays. MK-5108 also induced phosphorylated Histone H3 in skin and xenograft tumor tissues in a nude rat xenograft model. MK-5108 inhibited growth of human tumor cell lines in culture and in different xenograft models. Furthermore, the combination of MK-5108 and docetaxel showed enhanced antitumor activities compared with control and docetaxel alone-treated animals without exacerbating the adverse effects of docetaxel. MK-5108 is currently tested in clinical trials and offers a new therapeutic approach to combat human cancers as a single agent or in combination with existing taxane therapies.

A novel roscovitine derivative potently induces G1-phase arrest in platelet-derived growth factor-BB-activated vascular smooth muscle cells

Abnormal vascular smooth muscle cell (VSMC) proliferation contributes to the pathogenesis of restenosis. Thus, drugs interfering with cell cycle progression in VSMC are promising candidates for an antirestenotic therapy. In this study, we pharmacologically characterize N-5-(2-aminocyclohexyl)-N-7-benzyl-3-isopropyl-1(2)H-pyrazolo[4,3-d]pyrimidine-5,7-di-amine (LGR1406), a novel derivative of the cyclin-dependent kinase (CDK) inhibitor roscovitine (ROSC), in PDGF-BB-activated VSMC. Cell proliferation was quantified measuring DNA synthesis via 5-bromo-2'-deoxyuridine incorporation. Analysis of cell cycle distribution was done by flow cytometry using propidium iodide-stained nuclei. Key regulators of the cell cycle and relevant signaling pathways were dissected by Western blot analyses. In addition, in vitro kinase assays and in silico studies regarding the pharmacokinetic profile of both compounds were performed. LGR1406 shows a stronger (IC(50) = 3.0 muM) antiproliferative activity than ROSC (IC(50) = 16.9 muM), halting VSMCs in G(0)/G(1) phase of the cell cycle, whereas ROSC does not arrest but rather delays cell cycle progression. Neither of the compounds interferes with early PDGF-BB-induced signaling pathways (p38, extracellular signal-regulated kinase 1/2, c-Jun NH(2)-terminal kinase, Akt, signal transducer and activator of transcription 3), and both inhibit CDKs, with LGR1406 exerting a slightly higher potency against CDK1/2 and 4 than ROSC. Expression of cyclins A and E as well as hyperphosphorylation of the pocket proteins retinoblastoma protein and p107 are negatively affected by both compounds, although to a different extent. In silico calculations predicted a much higher metabolic stability for LGR1406 compared with ROSC. Altogether, ROSC derivatives, such as LGR1406 seem to be promising compounds for further development in antirestenotic therapy.