Selective benzopyranone and pyrimido[2,1-α]isoquinolin-4-one inhibitors of DNA-dependent protein kinase:: Synthesis, structure-activity studies, and radiosensitization of a human tumor cell line in vitro

A diverse range of chromen-2-one, chromen-4-one and pyrimidoisoquinolin-4-one derivatives was synthesized and evaluated for inhibitory activity against the DNA repair enzyme DNA-dependent protein kinase (DNA-PK), with a view to elucidating structure-activity relationships for potency and kinase selectivity. DNA-PK inhibitory activity varied widely over the series of compounds evaluated IC50 values ranged from 0.19 to > 10 muM), with excellent activity being observed for the 7, 8-benzochromen-4-one and pyrimido[2.1-a]isoquinolin-4-one templates. By contrast, inhibitors based on the benzochromen-2-one (coumarin) or 2-aryl-1-7,8-benzochromen-4-one (flavone) scaffolds were less potent. Crucially, these studies revealed a very constrained structure -activity relationship at the 2-position of the benzopyranone and pyrimido[2.1-a]-isoquinolin-4-one pharmacophore, with only a 2-morpholino, or 2-(2'-methylmorpholino) group being tolerated at this position. More detailed biological studies conducted with the most potent inhibitor NU7163 (48; IC50 = 0.19 muM) demonstrated ATP-competitive DNA-PK inhibition, with a K-i value of 24 nM, and 48 exhibited selectivity for DNA-PK compared with the related enzymes ATM, ATR, mTOR, and PI 3-K (p110alpha). Compound 48 sensitized the HeLa human tumor cell line to the cytotoxic effects of ionizing radiation in vitro. a doze modification factor of 2.3 at 10% survival being observed with an inhibitor concentration of 5 PM. This study identified these structural classes as novel DNA-PK inhibitors and delineated initial structure activity relationships against DNA-PK.