A first aspect of the invention relates to a compound of formula (I), or a pharmaceutically acceptable salt or ester thereof, (Formula (I)) wherein: R1 is -(CH2)nNR3R4, -OR5 or -(CH2)n-heterocycloalkyl, wherein said heterocycloalkyl group is optionally substituted by one or more R7 groups R2 is selected from aryl, heteroaryl, fused aryl-heterocycloalkyl and fused hetero aryl-heterocycloalkyl each of which is substituted by at least one R8 group R3 is H or alkyl R4 is: (i) cycloalkyl optionally substituted by one or more -NR11R12 or NHCOR11 groups or (ii) -(CH2)n-heterocycloalkyl, wherein said heterocycloalkyl is a 4, 5 or 6-membered nitrogen-containing group optionally containing one or more CO groups, wherein said heterocycloalkyl is optionally substituted by one or more one or more (CH2)nR7 groups or (iii) alkyl substituted by one or more -NR11R12groups or R3 and R4 are linked together with the nitrogen to which they are attached to form a 4, 5, 6 or 7-membered monocyclic heterocycloalkyl group or a bicyclic heterocyclic group, each of which optionally contains one or two further groups selected from CO, O, N and S, and which is optionally further substituted by one or more R7 groups R5 is selected from alkyl, -(CH2)n-heteroaryl and - (CH2)n-heterocycloalkyl, wherein said heteroaryl and heterocycloalkyl groups are each optionally substituted by one or more R7 groups each R8 is independently selected from - NR16R17, -OR17 and -(CH2)nR17 where each R16 is H and each R17 is independently - (CHR10)n-heteroaryl, wherein said heteroaryl group is in turn optionally substituted by one or more R7 groups each R10, R11 and R12 is independently H or alkyl or in the case of an - NR11R12 group, R11 and R12 may be linked together with the nitrogen to which they are attached to form a 4, 5, 6 or 7-membered monocyclic or bicyclic heterocycloalkyl group optionally containing one or two further groups selected from CO, O, N and S, and which is optionally further substituted by one o
