R428, a potent and selective small-molecule inhibitor, blocks the catalytic and procancerous activities of Axl. R428 inhibits Axl with low nanomolar activity and blocked Axl-dependent events, including Akt phosphorylation, breast cancer cell invasion, and proinflammatory cytokine production. In a recent study, the Axl inhibitor R428 shows a mean IC50 dose of ? 2.0μM for the primary CLL B cells after 24 hours of treatment and normal B-, T-, and natural killer (NK) cells show no significant amount of cell death at this dose of R428 (2.5 μM) under similar experimental conditions. R428 inhibits angiogenesis in corneal micropocket and tumor models.