A compound of formula (I) or a pharmaceutically acceptable salt, solvate or N-oxide thereof: ** Formula ** wherein: two of Z1, Z2, Z3 and Z4 are independently CR1c or N and the remainder are independently CR1c； or Z3 and Z4 together represent S and one of Z1 and Z2 is CR1c or N and the other is independently CR1c； R1a, R1b and R1c are independently chosen from hydrogen； halogen； cyano； (C1-6) alkyl； (C1-6) alkylthio； trifluoromethyl； trifluoromethoxy； carboxy； hydroxy optionally substituted with (C1-6) alkyl or (C1-6) alkyl substituted with (C1-6) alkoxy； (C1-6) alkyl substituted with (C1-6) alkoxy； hydroxyalkyl (C1-6)； an amino group optionally N-substituted with one or two (C1-6) alkyl, formyl, (C1-6) alkylcarbonyl or (C1-6) alkylsulfonyl groups； or aminocarbonyl where the amino group is optionally substituted with (C1-4) alkyl； or two of R1a, R1b and R1c on adjacent carbon atoms can together form an ethylenedioxy group； R2 is hydrogen or (C1-4) alkyl, or together with R6 form Y as defined below； A is a group (i): ** Formula ** in which: R3 is as defined for R1a, R1b and R1c or is oxo or aminomethyl and n is 1 or 2； or A is a group (ii) ** Formula ** W1, W2 and W3 are CR4R8； or W2 and W3 are CR4R8 and W1 represents a bond between W3 and N； X is O, CR4R8, or NR6； a R4 is as defined for R1a, R1b and R1c and the residue and R8 are hydrogen, or a R4 and R8 are together oxo and the residue are hydrogen； R6 is hydrogen or (C1-6) alkyl； or together with R2 form Y； R7 is hydrogen； halogen； hydroxy optionally substituted with (C1-6) alkyl； or (C1-6) alkyl； Y is CR4R8CH2； CH2CR4R8； (C>； = O)； CR4R8； CR4R8 (C>； = O)； or (C>； = O) CR4R8； or when X is CR4R8, R8 and R7 together represent a bond； U is selected from CO and CH2； and R5 is an optionally substituted heterocyclic bicyclic ring system (B): ** Formula ** containing up to four heteroatoms in each ring, wherein the heterocyclic ring (B) has an aromatic ring (a) that is an optionally pyrimidine ring substituted in w
