Provided is a kinase inhibitor, comprising a compound of formula I, or a pharmaceutically acceptable salt, a solvate, an ester, an acid, a metabolite, or a prodrug thereof. Further provided are a pharmaceutical composition comprising the kinase inhibitor, and a use and a method for using the compound or the composition to inhibit the activity of wild-type FLT3, mutant FLT3-ITD, PDGFRα, and/or PDGFRβ kinases in a cell or a subject, and to prevent or treat a kinase-related disorder in a subject.