Acetamides-substituted N- (hetero) aryl, 2- (hetero) aryl for use as modulators of Wnt

Compound having the formula (6): ** ** Formula or a pharmaceutically acceptable salt thereof, wherein: wherein X1, X2, X3 and X4 are selected from N and CR7; one of X5, X6, X7 and X8 is N and the others are CH; X9 is selected from N and CH; Z is selected from phenyl, pyrazinyl, pyridinyl, pyridazinyl and piperazinyl; wherein each phenyl, pyrazinyl, pyridinyl, pyridazinyl or piperazinyl Z is optionally substituted with a group R6; R1, R2 and R3 are hydrogen; m is 1; R4 is selected from hydrogen, halogen, difluoromethyl, trifluoromethyl and methyl; R6 is selected from hydrogen, halogen and -C (O) R10; wherein R10 is methyl; and R7 is selected from hydrogen, halogen, cyano, methyl and trifluoromethyl.