RESPONSE OF A CELL-SURFACE NADH OXIDASE TO THE ANTITUMOR SULFONYLUREALPHENYLSULFONYL)-N'-(4-CHLOROPHENYLUREA)(LY181984) MODULATED BY REDOX

In previous reports, our laboratory has described a drug-responsive NA DH 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 w as found in sera of a wide variety of cancer patients but the activity was either inhibited or stimulated by 1 mu M LY181984. In this report , we demonstrate that one basis for whether or not the activity was st imulated or inhibited may be the redox environment of the protein. If plasma membrane vesicles from HeLa cells were first treated with dithi othreitol (DTT) or with reduced glutathione (GSH) and then assayed for NADH oxidase activity, the sulfonylurea inhibited the activity in a c oncentration-dependent manner. In contrast, if the plasma membrane ves icles were first treated with diluted hydrogen peroxide or oxidized gl utathione (GSSG) and then assayed for NADH oxidase activity, the antit umor sulfonylurea stimulated the activity. Growth experiments were con ducted in parallel. LY181984 administered to HeLa cells in the presenc e of GSH was approximately 2 log orders more effective then LY181984 a dministered to HeLa cells in the presence of GSSG. Similar results wer e found in the sera of cancer patients. With sera from normal individu als or with plasma membranes of rat liver, the oxidizing or reducing c onditions were without effect. The findings su est that the response o f the cell surface NADH oxidase of HeLa cells to the antitumor sulfony lurea LY181984 is influenced by the redox environment which may determ ine whether the drug will stimulate or inhibit the activity and that t he degree of response may be reflected in the ability of LY181984 to I nhibit HeLa cell growth. (C) 1998 Elsevier Science B.V.