A compound of formula wherein Y1 = N-R1, Y2 = C and Y3 = C, or Y1 = C-R1, Y2 = N and Y3 = C; Z1 is selected from NH, CH 2, O and S; Z2 is selected from NH, CH 2, O and S; with the proviso that at least one of Z1 and Z2 is CH 2; R1 is selected from the group consisting of hydrogen, linear or branched C 1-4 alkyl and saturated monocyclic C 3-4 cycloalkyl, wherein said linear or branched C 1-4 alkyl and saturated monocyclic C 3-4 cycloalkyl can be optionally substituted with one or more halogen; R2 is selected from the group consisting of linear or branched C 1-6 alkyl, saturated monocyclic C 3-6 cycloalkyl, oxetanyl, tetrahydrofuranyl and tetrahydropyranyl, all of which can optionally be substituted with one or more halogen; R3 is a 5- or 6-membered heteroaryl, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen, or R3 is a 9-membered bicyclic heteroaryl, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen; R4 is a 5- or 6-membered heteroaryl, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen, or R4 is a phenyl, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen, or R4 is a pyridinone, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen; or R4 is a 9-membered bicyclic heteroaryl, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen; or a pharmaceutically acceptable salt thereof. Y1 = N-R1, Y2 = C and Y3 = C, or Y1 = C-R1, Y2 = N and Y3 = C; Z1 is selected from NH, CH 2, O and S; Z2 is selected from NH, CH 2, O and S; with the proviso that at least one of Z1 and Z2 is CH 2; R1 is selected from the group consisting of hydrogen, linear or branched C 1-4 alkyl and saturated monocyclic C 3-4 cycloalkyl, wherein said linear or branched C 1-4 alkyl and saturated monocyclic C 3-4 cycloalkyl can be optionally substituted with one or more halogen; R2 is selected from the group consisting of linear or branched C 1-6 alkyl, saturated monocyclic C 3-6 cycloalkyl, oxetanyl, tetrahydrofuranyl and tetrahydropyranyl, all of which can optionally be substituted with one or more halogen; R3 is a 5- or 6-membered heteroaryl, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen, or R3 is a 9-membered bicyclic heteroaryl, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen; R4 is a 5- or 6-membered heteroaryl, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen, or R4 is a phenyl, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen, or R4 is a pyridinone, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen; or R4 is a 9-membered bicyclic heteroaryl, which can optionally be substituted with one or more substituents selected from linear or branched C 1-4 alkyl, linear or branched C 1-4 alkoxy and halogen, wherein said linear or branched C 1-4 alkyl and linear or branched C 1-4 alkoxy can be optionally substituted with one or more halogen; or a pharmaceutically acceptable salt thereof.