Ex vivo use of BUBR1 as a biomarker to predict response to a compound, where the compound is a compound of general formula I, ** Formula ** where 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 alkyl-carbonyloxy, amino, monoalkylamino, dialkylamino, lower alkoxy-carbonylamino, lower alkyl-carbonylamino, substituted amino, wherein the two substituents on nitrogen form, together with the nitrogen, heterocyclyl, lower alkyl-carbonyl, carboxy , lower alkoxy-carbonyl, 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 an in vivo hydrolyzable salt, solvate, ester or amide of said compound, in vivo hydrolyzable ester or ester salt, 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, hydroxy-lower alkoxy, lower alkoxy-lower alkoxy, phenyl-lower alkoxy, lower alkyl-carbonyloxy, amino, monoalkylamino, dialkylamino, lower