A method for treating drug-resistant cancer, includes: administering to a patient in need thereof, a compound of formula I, a tautomer of the compound, a salt of the compound, a salt of the tautomer, a mixture thereof, or a pharmaceutical composition comprising the compound, the tautomer, the salt of the compound, the salt of the tautomer, or the mixture, wherein the patient is a cancer patient with drug-resistant cancer, wherein the compound of Formula I is as defined in the application.
