Inhibition of Yeast Hexokinase by Acyl Glucosides of Phloretin and its Implication in the Warburg Effect

Contrary to differentiated cells, cancer cells predominantly convert glucose to lactate even under conditions of adequate oxygen supply (“Warburg effect”). The initial enzyme implicated in this route is hexokinase, which transforms D-glucose into D-glucose-6-phosphate. We proposed the use of different polyphenols (resveratrol, epigallocatechin gallate, pterostilbene, phloretin) and their derivatives (α-glucosides and acylated α-glucosides) to inhibit this enzyme. For this study, we used Saccharomyces cerevisiae hexokinase, whose two isoforms show high resemblance at the active site with human hexokinase HK2. To monitor the reactions, a method of anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) was developed. Remarkably, most of the assayed compounds inhibited the enzyme more than 50 % in the standard assay. Among them, phloretin 4’-O-(6’’-O-octanoyl)-α-D-glucopyranoside showed the highest inhibition and was studied in depth to determine the inhibition pattern and inhibition constant. The Ki for glucose was calculated to be 22.1±0.4 μM. Computational models of inhibition were carried out with the three molecules displaying the highest inhibition, and correlated adequately with the observed inhibitory effects on the enzyme. The inhibitory effect of several of the assayed polyphenols on hexokinase and their lack of toxicity renders them promising candidates as adjuvant drugs for cancer therapy.