Add time:08/26/2019         Source:sciencedirect.com

In previous reports, our laboratory has described a drug-responsive NADH oxidase activity of the external surface of the plasma membrane of HeLa and other cancer cells, but not from normal cells, that was shed into media conditioned by the growth of cancer cells such as HeLa and also into sera of cancer patients. The sulfonylurea-altered activity was found in sera of a wide variety of cancer patients but the activity was either inhibited or stimulated by 1 μM LY181984. In this report, we demonstrate that one basis for whether or not the activity was stimulated or inhibited may be the redox environment of the protein. If plasma membrane vesicles from HeLa cells were first treated with dithiothreitol (DTT) or with reduced glutathione (GSH) and then assayed for NADH oxidase activity, the sulfonylurea inhibited the activity in a concentration-dependent manner. In contrast, if the plasma membrane vesicles were first treated with diluted hydrogen peroxide or oxidized glutathione (GSSG) and then assayed for NADH oxidase activity, the antitumor sulfonylurea stimulated the activity. Growth experiments were conducted in parallel. LY181984 administered to HeLa cells in the presence of GSH was approximately 2 log orders more effective than LY181984 administered to HeLa cells in the presence of GSSG. Similar results were found in the sera of cancer patients. With sera from normal individuals or with plasma membranes of rat liver, the oxidizing or reducing conditions were without effect. The findings suggest that the response of the cell surface NADH oxidase of HeLa cells to the antitumor sulfonylurea LY181984 is influenced by the redox environment which may determine whether the drug will stimulate or inhibit the activity and that the degree of response may be reflected in the ability of LY181984 to inhibit HeLa cell growth.

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