Inhibitors of DNA-PK.

The invention relates to the use of compounds of formula (I) and isomers, salts, solvates, chemically protected forms, and prodrugs thereof, in the preparation of a medicament for inhibiting the activity of DNA-PK, wherein R 1 and R 2 are independently hydrogen, an optionally substituted C 1-7 alkyl group, C 3-20 heterocyclyl group, or C 5-20 aryl group, or may together form, along with the nitrogen atom to which they are attached, an optionally substituted heterocyclic ring having from 4 to 8 ring atoms; X and Y are selected from CR 4 and O, O and CR' 4 and NR'' 4 and N, where the unsaturation is in the appropriate place in the ring, and where one of R 3 and R 4 or R' 4 is an optionally substituted C 3-20 heteroaryl or C 5-20 aryl group, and the other of R 3 and R 4 or R' 4 is H, or R 3 and R 4 or R'' 4 together are -A-B-, which collectively represent a fused optionally substituted aromatic ring. The compounds also selectively inhibit the activity of DNA-PK compared to PI 3-kinase and/or ATM.