Tumor Growth and Disulfide Reduction: Possible Dependence on Protein-Disulfide Reductase,

Abstract

Tumor cells, washed and resuspended in balanced salt solution containing 2–5 mM disodium ethylenediaminetetraacetate (EDTA), lost transplantability after incubation with 1 mM iodoacetate or tri-ethylmaleimide. All 7 ascites and 2 solid murine tumors investigated were inactivated by sulfhydryl (SH)-blocking procedure though their cells were still metabolizing and excluding supravital stains. Projection was conferred by the SH compounds dithiothreitol (DTT), l-cysteine, and reduced glutathione (1 mM). Inactivated cells could be reactivated by further incubation with an SH compound or with native cell-free ascitic fluid. Therefore, loss of transplantability was not attributable to a lethal effect of the blocking agents. Protection with DTT or incubation with it alone resulted in more malignant tumors. Both ascitic fluid and intercellular material of solid tumors protected against inactivation. This protection was overcome when a) the disulfides were converted into reactive SH's before SH blocking, or b) the nucleotide (NADPH)-dependent protein-disulfide reductase (PDR) of the fluid was inhibited by heating 30 minutes at 70° C or by 0.1 mM arsenite. Activity of the NADPH-dependent PDR was much higher in tumor cells than in normal cells. We found no NADPH-dependent PDR activity in normal serum, but detectable activities in cell-free dscitic fluid and in serum of tumor-bearing mice. Pretreatment of the fluid with DTT, EDTA, arsenite, or Heat increased the immunogenicity of SH-blocked ascites tumor. Thus, proliferation and immunogenicity of (murine) tumors appeared to depend on reactive SH's, protein-disulfide reduction, and implicated enzyme(s).