CHARACTERISTICS OF THE INHIBITION OF HUMAN PROMYELOCYTIC LEUKEMIA HL-60 CELL-GROWTH BY S-D-LACTOYLGLUTATHIONE INVITRO

The mechanism of the inhibition of proliferation of human leukaemia 60 (HL60) cells by S-D-lactoylglutathione in vitro was investigated. The median inhibitory concentration IC50 value was 66 muM (95% C.I. 50-87 muM; n = 18). The inhibition of leukaemia cell growth required exposu re of HL60 cells to S-D-lactoylglutathione (and metabolites) for 12 h, with maximum growth inhibition achieved after 24 h. Removal and repla cement of culture medium within the initial 12 h of culture prevented inhibition of growth and toxicity. S-D-lactoylglutathione was consumed within the initial 3 h of culture. Pretreatment of culture medium con taining 10% foetal calf serum for 3 h produced no subsequent inhibitio n of HL60 cell growth. Incubation of HL60 cells in culture medium with low serum content (5% v/v) produced a decreased rate of cell prolifer ation and a decreased response to S-D-lactoylglutathione. S-D-lactoylg lutathione inhibited uptake of H-3-thymidine into DNA in the third hou r of culture where the median inhibitory concentration IC50 value, was 74 muM (95% C.I. 51-102; n = 10). The mechanism of inhibition of HL60 cell growth by S-D-lactoylglutathione is unknown but may be cell cycl e related, mediated by inhibition of DNA synthesis and involve an acti ve metabolite which may be removed and/or inactivated by a change in c ulture medium.