Quinolone antibiotic derivatives as new selective Axl kinase inhibitors

Axl is a new promising molecular target for antineoplastic therapies. A series of quinolone antibiotic derivatives were designed and synthesized as new selective Axl inhibitors. One of the most promising compound 8i bound tightly to Axl with a K_d value of 1.1 nM, and inhibited its kinase activity with an IC₅₀ value of 26 nM. The compound also significantly inhibited the phosphorylation of Axl and dose dependently inhibited cell invasion and migration in TGF-β1 induced MDA-MD-231 breast cancer cells. In addition, 8i demonstrated reasonable pharmacokinetic properties and exhibited extraordinary target selectivity over 468 kinases except for Flt3 (IC₅₀ = 50 nM)), with a S(10) and S(35) value of 0.022 and 0.42 at 1.0 μM, respectively. Compound 8i may serve as a new valuable lead compound for future anticancer drug discovery.