Table 2.

Inhibition of human CK2 holoenzyme and comparison with ABCG2

Indenoindoles	CK2 inhibition		AGCG2/CK2d
	% at 10 µMa	IC50 (µM)
Ketonic reference
4c	59	7.0b	16
Phenolic derivatives
5a	72	2.0b	<1
5b	20	∼25c	∼4
5c	57	7.5b	47
5d	27	∼20c	∼31
5e	48	∼10.5c	∼1
5f	42	∼12c	∼75
5g	45	∼11c	∼22
5h	78	1.3b	9
5i	44	∼11.5c	∼31
5j	38	∼14c	∼70
p-Quinonic derivatives
6a	60	5.5b	<1
6b	70	2.2b	<1
6c	40	∼13c	<1
6d	60	6.4b	<1
6e	40	∼13c	<1
6f	65	4.1b	5
6g	44	∼11.5c	∼27

Notes:

^aThe percentage inhibition of CK2 activity was determined, for each compound, at 10 μM.

^bFor the best compounds, producing at least 50% inhibition at 10 μM, the concentration was varied in order to precisely determine the IC₅₀ values.

^cFor the other, less potent compounds, a rough estimation was obtained from the experimental inhibition produced at 10 μM.

^dThe ABCG2/CK2 ratio, indicating the inhibitory efficiency of compounds toward ABCG2 relatively to CK2, was calculated by dividing the IC₅₀ (CK2) values with the IC₅₀ (ABCG2) values of Table 1.

Abbreviations: CK2, casein kinase II; IC₅₀, half-maximal inhibitory concentration.