Table 2.

Apparent in situ and in vitro kinetic parameters for physiological and synthetic inhibitors of human AKR1C2

Inhibitor	Monkey kidney cells (COS-1)		In vitro
	Fluorimetric, IC50, μM (Ki,app, μM)	Radiometric, IC50, μM (Ki,app, μM)	Fluorimetric, IC50, μM (Ki, μM)
Natural inhibitor
Ursodeoxycholate	0.24 ± 0.03 (0.11)	0.14 ± 0.03 (0.070)	0.049 ± 0.005 (0.012)
NSAIDs
Naproxen	9.4 ± 0.9	16 ± 2	2.7 ± 0.2
Flufenamic acid	4.0 ± 0.6 (2.2)	—	0.31 ± 0.03 (0.11)
Ibuprofen	17 ± 2	—	9 ± 1
Celecoxib	>50*	—	50 ± 10

The fluorimetric method based on the novel metabolic probe 1 was validated by the standard radiochemical assay (see Fig. 4). Data shown are the average ± SD of three independent experiments run in triplicate.

*Concentrations of celecoxib >50 μM resulted in noticeable cell detachment.