Protein CK2 has gained much interest as an anti-cancer drug target in the last decade. We had previously described the identification of a new allosteric site on the catalytic α-subunit, along with first small molecule ligands based on the 4-(4-phenylthiazol-2-ylamino) benzoic acid scaffold. In the present work, structure optimizations guided by a binding model led to the identification of the lead compound 2-hydroxy-4-((4-(naphthalen-2-yl)thiazol-2yl)amino)benzoic acid (27), showing a submicromolar potency against purified CK2α (IC 50 = 0.6 µM). Furthermore, 27 induced apoptosis and cell death in 786-O renal cell carcinoma cells (EC 50 = 5 µM) and inhibited STAT3 activation even more potently than the ATPcompetitive drug candidate CX-4945 (EC 50 s: 1.6 µM vs. 5.3 µM). Notably, the potencies of our allosteric ligands to inhibit CK2 varied depending on the individual substrate. Altogether, the novel allosteric pocket was proved a druggable site, offering an excellent perspective to develop efficient and selective allosteric CK2 inhibitors. Recently, we identified 2-aminothiazole derivatives as novel allosteric inhibitors of CK2α; 20 exemplarily shown are compounds 1-4 (Figure 1). Using complementary methods, it was demonstrated that compound 3 binds in an allosteric pocket adjacent to the ATP binding site, between the glycine-rich loop and the αC-helix. A preliminary hit optimization led to compound 4, exhibiting an IC 50 of 3.4 µM. However, it had yet to be shown that the new CK2 modulator class can be developed further into more potent drugs, which is often a limitation with allosteric target sites that were not evolutionary designed for high-affinity interactions with small molecules. 21, 22 Therefore, we carried out a compound optimization guided by a binding model, as will be described below. The cellular effects of the allosteric CK2