Characteristics of the inhibition of human promyelocytic leukaemia HL60 cell growth by S- d-lactoylglutathione in vitro

Abstract

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 ic 50 value was 66 μM (95% C.I. 50–87 μM; n = 18). The inhibition of leukaemia cell growth required exposure of HL60 cells to S- d-lactoylglutathione (and metabolites) for 12 h, with maximum growth inhibition achieved after 24 h. Removal and replacement 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 containing 10% foetal calf serum for 3 h produced no subsequent inhibition of HL60 cell growth. Incubation of HL60 cells in culture medium with low serum content (5% v/v) produced a decreased rate of cell proliferation and a decreased response to S- d-lactoylglutathione. S- d-lactoylglutathione inhibited uptake of 3H-thymidine into DNA in the third hour of culture where the median inhibitory concentration ic 50 value was 74 μM (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 cycle related, mediated by inhibition of DNA synthesis and involve an active metabolite which may be removed and/or inactivated by a change in culture medium.