tyrphostin AG 1478 [ 4-(3-chloroanilino)-6,7-dimethoxyquinazoline,AG 1478,AG-1478,AG1478,RTKI cpd,tyrphostin AG 1478 monohydrochloride,tyrphostin AG 1478-mesylate,tyrphostin-AG1478 ] preferentially inhibits human glioma cells expressing truncated rather than wild-type epidermal growth factor receptors