132 - Inhibition of Cellular Proliferation by the Representative Organic Arsenical Phenylarsine Oxide: Possible Selective Targeting of Glycolysis

Abstract

Inorganic and organic arsenicals have received recent attention as proven and potential anti-cancer agents. While trivalent arsenic can bind with high affinity to closely-spaced (vicinal) thiols on proteins, proposed mechanisms by which arsenicals kill cancer cells vary. Upregulation of glycolysis, necessary to support rapid cellular growth, occurs in most cancer cells and is a potential target of anticancer therapeutics. We have begun to investigate the hypothesis that trivalent organic arsenicals may inhibit cellular proliferation by selectively targeting glycolytic enzymes containing reactive thiols either directly or following secondary elevations in reactive oxygen species (ROS). We report here the effects of the representative organic arsenical phenylarsine oxide (PAO) on the growth and metabolism of the yeast Saccharomyces cerevisiae which reproduces many of the metabolic features of human cancer cells. Our findings demonstrate that high micromolar concentrations of PAO abolished cellular proliferation and inhibited the uptake and metabolic reduction of the cationic probe 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) by mechanisms that appear to be independent of any secondary production of ROS. Moreover, we identified, by combined immobilized PAO-affinity chromatography and LC-MS/MS, key metabolic enzymes necessary for the support of glycolysis as potential mediators of the cytotoxic actions of PAO. Among these enzymes were glyceraldehyde-3-phosphate dehydrogenase, pyruvate kinases, alcohol dehydrogenases, and the vacuolar-ATPase which helps to maintain a cytosolic pH optimal for glycolysis. Work aimed at establishing which of these enzymes may be inhibited by PAO is underway. In addition, preliminary results are consistent with the possibility that hydrogen peroxide may inhibit cellular proliferation by a pathway similar to PAO, a result which has implications for targeting highly proliferating cancer cells by redox-active therapeutics.