Structure–activity relationship study of 4-(thiazol-5-yl)benzoic acid derivatives as potent protein kinase CK2 inhibitors

Two classes of modified analogs of 4-(thiazol-5-yl)benzoic acid-type CK2 inhibitors were designed. The azabenzene analogs, pyridine- and pyridazine-carboxylic acid derivatives, showed potent protein kinase CK2 inhibitory activities [IC50 (CK2α)=0.014–0.017μM; IC50 (CK2α′)=0.0046–0.010μM]. Introduction of a 2-halo- or 2-methoxy-benzyloxy group at the 3-position of the benzoic acid moiety maintained the potent CK2 inhibitory activities [IC50 (CK2α)=0.014–0.016μM; IC50 (CK2α′)=0.0088–0.014μM] and led to antiproliferative activities [CC50 (A549)=1.5–3.3μM] three to six times higher than those of the parent compound.