The present invention relates to compounds of formula (I), combinations and uses thereof for disease therapy, wherein R1 represents heteroaryl, -carbocyclyl-heteroaryl, -alkenylheteroaryl or -alkylheteroaryl; R2 represents alkyl; carbocyclyl which may optionally be substituted by alkyl; alkenyl; alkynyl, provided a triple bond is not adjacent to X; -alkyl-aryl; -alkyl-heteroaryl; -alkyl-heterocyclyl in which heterocyclyl may optionally be substituted by alkyl; -alkyl-carbocyclyl in which carbocyclyl may optionally be substituted by alkyl; aryl; heteroaryl; or H; X represents S or NR3; R3 represents H or C1-4 alkyl.