AKR1C3 inhibition by curcumin, demethoxycurcumin, and bisdemethoxycurcumin: an investigation

Abstract

Background: Aldo-keto reductase 1C3 (AKR1C3) has been shown to be overexpressed in cancers due to its regulatory roles in cell proliferation and differentiation. Curcumin, known to have anti-tumour properties, and its analogues demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC) were studied to determine their inhibitory effects on the AKR1C3 enzyme. Methods: AKR1C3 was purified and analysed to determine its protein concentration in transformed Escherichia coli (E. coli) cells. Enzyme assays equaling 1 mL contained 2.82 mg/mL AKR1C3, 50 μM of 3 mM NADPH, and varying volumes of potassium phosphate (50 mM, pH 6.5), 9,10-phenanthrenequinone (PQ), and inhibitors were measured at 340 nm. The Vmax, Km, KI, and 2 of AKR1C3 in the presence and absence of inhibitors were determined using a non- linear regression analysis on Fig.P Software. Results: PQ alone found Vmax = 0.47 IU/mg, Km = .435 μM, Ki = 6.29 μM, and 2 = 0.946. Inhibitor potency was BDMC > DMC > curcumin in the presence of 1 μM PQ. Further analysis of BDMC indicated mixed inhibition (Vmax = 0.46 IU/mg, Km = .406 μM, Ki = 1.59 μM, and 2 = 0.970). Further analysis of PQ at higher concentrations found a divergence from Michaelis-Menten kinetics, with a decrease in AKR1C3 activity after Vmax was reached. Conclusions: BDMC was the more potent inhibitor of AKR1C3 in transformed E. coli compared to DMC and curcumin. The results suggest mixed inhibition of AKR1C3 in the presence of BDMC. Additional analysis of PQ at higher concentrations saw a loss of Michaelis-Menten kinetics as the activity of AKR1C3 decreased after reaching Vmax. This requires further examination.