Use of glu-tubulin as a biomarker to predict the response to a compound, in which the compound is a compound of general formula I, ** Formula ** wherein R represents phenyl, thienyl or pyridinyl, where phenyl is optionally substituted with one or two substituents independently selected from alkyl, halo-lower alkyl, hydroxy-lower alkyl, lower alkoxy-lower alkyl, acyloxy-lower alkyl, phenyl, hydroxy, lower alkoxy, hydroxy-lower alkoxy, lower alkoxy-lower alkoxy, phenyl - lower alkoxy, lower alkylcarbonyloxy, amino, monoalkylamino, dialkylamino, lower alkoxycarbonylamino, lower alkylcarbonylamino, substituted amino, where the two nitrogen substituents form, together with the nitrogen, heterocyclyl, lower alkylcarbonyl, carboxy , lower alkoxycarbonyl, cyano, halogen and nitro； and wherein two adjacent substituents are methylenedioxy； and wherein pyridinyl is optionally substituted with lower alkoxy, amino or halogen； X represents a group C>； = Y, where Y represents oxygen or nitrogen substituted with hydroxy or lower alkoxy； R1 represents hydrogen, lower alkyl-carbonyl, hydroxy-lower alkyl or cyano-lower alkyl； R2, R3 and R6 represent hydrogen； R4 and R5, independently of each other, represent hydrogen, lower alkyl or lower alkoxy； or R4 and R5 together represent methylenedioxy； and pharmaceutically acceptable derivatives thereof, wherein the pharmaceutically acceptable derivatives are selected from the group consisting of a salt, solvate, ester or an in vivo hydrolysable amide of said compound, salt of such an in vivo hydrolysable ester or amide, and polymorph of said compound, or wherein R represents phenyl or pyridinyl, wherein phenyl is optionally substituted with one or two substituents independently selected from alkyl, halo-lower alkyl, hydroxy-lower alkyl, lower alkoxy-lower alkyl, acyloxy-lower alkyl, phenyl, hydroxy, lower alkoxy, lower hydroxy-alkoxy, lower alkoxy-lower alkoxy, phenyl-lower alkoxy, lower alkyl-carbonyloxy, amino, monoalkylamino, dialkylamin
