A compound of Formula I: or a tautomer or pharmaceutically acceptable salt thereof, wherein X 1, X 2, X 3, and X 4 are each independently C(R 7) or N, wherein 0 to 2 of X 1, X 2, X 3, and X 4 are N; R 1 is -H, -CN, -OR a, C 1-6 haloalkyl or halogen; R 2 is -H, -NR b R c, -SR a, -OR a or C 1-6 alkyl, wherein C 1-6 alkyl is optionally substituted with 1, 2, 3, 4 or 5 R 8 groups, which may be the same or different; R 3 and R 4 are each independently -H, -OR a, halogen, -NR b R c, -C OR a, -CN, - C NR b R c, -NHC NR b R c, -OC NR b R c, CH 2 C NR b R c, C 1-6 alkyl or C 1-6 heteroalkyl, wherein each C 1-6 alkyl or C 1-6 heteroalkyl is optionally substituted with 1, 2, 3, 4 or 5 R 8 groups, which may be the same or different; R 5 and R 6 are each independently halogen, -OR a or C 1-6 alkyl, wherein each C 1-6 alkyl is optionally substituted with 1, 2, 3, 4 or 5 R 8 groups, which may be the same or different; each R 7 is independently -H, halogen, -OR a or C 1-6 alkyl, wherein each C 1-6 alkyl is optionally substituted with 1, 2, 3, 4 or 5 R 8 groups, which may be the same or different; each R 8 is independently C 1-6 alkyl, C 1-6 heteroalkyl, aryl, heteroaryl, halogen, -OR a, -C R a, -C OR a, -C NR b R c, -OC NR b R c, -NR b C OR a, -SR a, - S 1-2 R a, -S 2 F, -S 2 NR b R c, -NR b S 2 R a, -N 3, -CN or -NO 2, wherein each C 1-6 alkyl, C 1-6 heteroalkyl, aryl or heteroaryl is optionally substituted with 1, 2, 3, 4 or 5 halogen, -OR a, -C R a, -C OR a, -C NR b R c, - OC NR b R c, -NR b C OR a, -SR a, -S 1-2 R a, -S 2 F, -S 2 NR b R c, - NR b S 2 R a, -N 3, -CN or -NO 2 groups, which may be the same or different; each R a is independently -H, C 1-6 alkyl, C 1-6 haloalkyl, C 1-6 heteroalkyl, aryl or heteroaryl, wherein each aryl or heteroaryl is optionally substituted with 1, 2, 3, 4 or 5 R 21 groups, which may be the same or different; R b and R c are each independently -H, -NH 2, C 1-6 alkyl, C 1-6 heteroalkyl, aryl or heteroaryl, wherein each C 1-6 alkyl, C 1-6 heteroalkyl, aryl or heteroaryl is optionally substituted with 1, 2, 3, 4 or 5 R 21 groups; or R b and R c together with the atoms to which they are attached form a C 1-10 heterocycloalkyl; R 21 is C 1-6 alkyl, -CN, aryl, heteroaryl or halogen. X 1, X 2, X 3, and X 4 are each independently C(R 7) or N, wherein 0 to 2 of X 1, X 2, X 3, and X 4 are N; R 1 is -H, -CN, -OR a, C 1-6 haloalkyl or halogen; R 2 is -H, -NR b R c, -SR a, -OR a or C 1-6 alkyl, wherein C 1-6 alkyl is optionally substituted with 1, 2, 3, 4 or 5 R 8 groups, which may be the same or different; R 3 and R 4 are each independently -H, -OR a, halogen, -NR b R c, -C OR a, -CN, - C NR b R c, -NHC NR b R c, -OC NR b R c, CH 2 C NR b R c, C 1-6 alkyl or C 1-6 heteroalkyl, wherein each C 1-6 alkyl or C 1-6 heteroalkyl is optionally substituted with 1, 2, 3, 4 or 5 R 8 groups, which may be the same or different; R 5 and R 6 are each independently halogen, -OR a or C 1-6 alkyl, wherein each C 1-6 alkyl is optionally substituted with 1, 2, 3, 4 or 5 R 8 groups, which may be the same or different; each R 7 is independently -H, halogen, -OR a or C 1-6 alkyl, wherein each C 1-6 alkyl is optionally substituted with 1, 2, 3, 4 or 5 R 8 groups, which may be the same or different; each R 8 is independently C 1-6 alkyl, C 1-6 heteroalkyl, aryl, heteroaryl, halogen, -OR a, -C R a, -C OR a, -C NR b R c, -OC NR b R c, -NR b C OR a, -SR a, - S 1-2 R a, -S 2 F, -S 2 NR b R c, -NR b S 2 R a, -N 3, -CN or -NO 2, wherein each C 1-6 alkyl, C 1-6 heteroalkyl, aryl or heteroaryl is optionally substituted with 1, 2, 3, 4 or 5 halogen, -OR a, -C R a, -C OR a, -C NR b R c, - OC NR b R c, -NR b C OR a, -SR a, -S 1-2 R a, -S 2 F, -S 2 NR b R c, - NR b S 2 R a, -N 3, -CN or -NO 2 groups, which may be the same or different; each R a is independently -H, C 1-6 alkyl, C 1-6 haloalkyl, C 1-6 heteroalkyl, aryl or heteroaryl, wherein each aryl or heteroaryl is optionally substituted with 1, 2, 3, 4 or 5 R 21 groups, which may be the same or different; R b and R c are each independently -H, -NH 2, C 1-6 alkyl, C 1-6 heteroalkyl, aryl or heteroaryl, wherein each C 1-6 alkyl, C 1-6 heteroalkyl, aryl or heteroaryl is optionally substituted with 1, 2, 3, 4 or 5 R 21 groups; or R b and R c together with the atoms to which they are attached form a C 1-10 heterocycloalkyl; R 21 is C 1-6 alkyl, -CN, aryl, heteroaryl or halogen.