Highly pleiotropic and constitutively active protein kinase CK2 is a key target in cancer therapy, but only one small-molecule inhibitor has reached clinical trials - CX-4945. In this study we present the indeno[1,2-b]indole derivative 5-isopropyl-4-methoxy-7-methyl-5,6,7,8-tetrahydro-indeno[1,2-b]indole-9,10-dione (5a-2) that decreased the intracellular CK2 activity in A431, A549 and LNCaP tumor cell lines analogous to CX-4945 (>75% inhibition at 20 µM) and similarly blocked CK2-specific Akt phosphorylation in LNCaP cells. Cellular uptake analysis demonstrated higher intracellular concentrations of 5a-2 (408.3 nM) compared to CX-4945 (119.3 nM). This finding clarifies the comparable effects of both compounds on the intracellular CK2 activity despite their different inhibitory potency in vitro [IC$_{50}$ = 25 nM (5a-2) and 3.7 nM (CX-4945)]. Examination of the effects of both CK2 inhibitors on cancer cells using live cell imaging revealed notable differences. Whereas CX-4945 showed a stronger pro-apoptotic effect on tumor cells, 5a-2 was more effective in inhibiting tumor cell migration. Our results showed that 49% of intracellular CX-4945 was localized in the nuclear fraction, whereas 71% of 5a-2 was detectable in the cytoplasm. The different subcellular distribution, and thus the site of CK2 inhibition, provide a possible explanation for the different cellular effects. Our study indicates that investigating CK2-inhibition-mediated cellular effects in relation to the subcellular sites of CK2 inhibition may help to improve our understanding of the preferential roles of CK2 within different cancer cell compartments.