The inhibitory effect of phenothiazines on NK-mediated cytolysis of tumor cells.
Non-toxic concentrations of fluphenazine caused a marked (90%) inhibition of NK-mediated cytolysis of YAC-1 tumor cells. The biologically inactive sulphoxide derivative was not inhibitory and the efficacy of inhibition of other compounds was directly correlated (r = -0.96, p less than 0.02) with their reported affinities for calmodulin. Fluphenazine may act on the earliest stages of the target-effector interaction since conjugate formation between CBA effectors and YAC target cells decreased from 20% to 6% (p less than 0.02) upon pre-treatment with fluphenazine. However, fluphenazine was not selective for NK cells since cytotoxic T lymphocytes, derived from both mixed lymphocyte culture and by concanavalin A stimulation, revealed depressed cytolytic activity against P815 tumor targets after fluphenazine treatment. Tumoricidal activity by activated macrophages and effectors of antibody-dependent cell-mediated cytotoxicity was also blocked. Fluphenazine inhibition was reversible, since addition of 1.25-5 micrograms/ml of the calcium ionophore A23187 to fluphenazine-treated effectors restored NK binding and cytolytic functions to normal levels. Calmodulin was isolated from NK-enriched populations by affinity chromatography on sepharose-fluphenazine columns. Pre-treatment of effector cells with [3H]fluphenazine and isolation of calmodulin by immunoprecipitation and SDS-polyacrylamide gel electrophoresis showed that fluphenazine entered the cells and bound a calmodulin-like molecule. These data are compatible with the suggestion that fluphenazine inhibits NK function by inactivating the calcium-calmodulin complex and thereby altering binding events in the target-effector interaction. Other actions of the phenothiazines are also possible.
D000818:Animals; D002460:Cell Line; D002846:Chromatography, Affinity; D003602:Cytotoxicity, Immunologic / Q000187:drug effects*; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005476:Fluphenazine / Q000494:pharmacology; D007694:Killer Cells, Natural / Q000187:drug effects / Q000276:immunology*; D007700:Kinetics; D008264:Macrophages / Q000187:drug effects / Q000276:immunology; D008297:Male; D051379:Mice; D008808:Mice, Inbred CBA; D008811:Mice, Inbred DBA; D009374:Neoplasms, Experimental / Q000276:immunology*; D010640:Phenothiazines / Q000494:pharmacology*
D010640:Phenothiazines; D005476:Fluphenazine