The present invention provides a pyridofuropyrimidine derivative of formula (I): wherein G1 represents a group selected from -CR6R7- and -O- wherein R6 and R7 independently represent hydrogen atoms or C1-4 alkyl groups; R1 and R2 are independently selected from hydrogen atoms and C1-4 alkyl groups; R3 represents a group selected from C1-4 alkyl, C1-4 alkoxy, amino, hydroxy, mono- C1-4 alkylamino, di- C1-4 alkylamino, C3-8 cycloalkylamino, aryl, heteroaryl and saturated N-containing heterocyclyl groups which are bound to the pyridine ring through their nitrogen atom, all of them being optionally substituted by one or more substituents selected from the group consisting of halogen atoms and hydroxy, C1-4 alkyl, C1-4 alkoxy- C1-4 alkyl, aryl-C1-4 4alkyl, -O(CO)O R8, C1-4 alkoxy, -(CO)NR8R9, -CN, -CF3, -NR8R9, -SR8 and -SO2NH2 groups wherein R8 and R9 each independently represent a hydrogen atom or a C1-4 alkyl group; R4 and R5 are independently selected from the group consisting of hydrogen atoms, C1-4 alkyl groups, hydroxyl- C1-4 alkyl groups and groups of formula (II): wherein p and q are integers selected from 0, 1 , 2 and 3; A is either a direct bond or a group selected from -CONR14-, -NR14CO-, -0-, -COO-, -OCO-, -S-, -SO- and -SO2-, wherein each R10, R11, R12, R13 and R14 independently represents a hydrogen atom or a C1-4 alkyl group and G2 is a group selected from aryl, heteroaryl or heterocyclyl groups; wherein the group G2 is optionally substituted by one or more substituents selected from group consisting of halogen atoms and C1-4 alkyl, hydroxy, oxo, C1-4 alkoxy- C1-4 alkyl, aryl- C1-4 alkyl, -(CO)OR16, C1-4 alkoxy, -(CO)NR16R17, -CN, -CF3, -NR16R17, -SR16 and -SO2NH2 groups; wherein R16 and R17 each independently represent a hydrogen atom or a C1-4 alkyl group and the pharmaceutically acceptable salts and N-oxides thereof.