Lymphocyte surface poisons: Disulfides and thiolsulfonates

Abstract

Eight disulfides (I–VIII) and a thiolsulfonate (IX) were promising blocking agents of lymphocytes in graft-versus-host reactions (GvHR) without commensurate intracellular effects. The blocking effects were assayed through inhibition of the local GvHR after parental lymphocytes had been incubated with agents at suitable concentrations and then inoculated into F 1 hybrid offspring. The intracellular effects were assessed beforehand by measuring the inhibition of [6- 3H] thymidine incorporation by lymphocytes in the presence of a wide range of concentrations of agents. Concentration levels which induced no greater than approx. 50% inhibition of the [6- 3H] thymidine incorporation were considered to reflect sufficiently small intracellular effects and were used for the subsequent GvHR comparisons. Cellular survival always was 90% or more for the GvHR tests (unless stated otherwise), even when inhibition of thymidine incorporation was as high as 50%; hence the thymidine data are useful not only as guides for dose levels in the GvHR but also as leads to new agents that may show immunosuppressive or antileukemic activity through intracellular effects. Structural specificity of the active compounds as cell-surface poisons is evidenced by little or no activity (< 30% inhibition of GvHR) of 28 other disulfides, 2 trisulfides, 2 Bunte salts, and 8 other thiolsulfonates. Active agents may owe this function to replacement of the H of SH in cell-surface thiol receptors by an SR group. Glutathione did not significantly inactivate agents, probably because the products of reaction also are active disulfides. When two agents (III, IX) were given orally or intraperitoneally to F 1 hybrid recipients of untreated parental cells, doses of 10–15 mg/kg produced a GvHR inhibition of 17–53%.