ASPECTS OF GLUTAMINE-METABOLISM IN HUMAN TUMOR-CELLS

The importance of the non-essential amino acid, glutamine, to the prol iferation of human tumour cells was investigated. All of the cells stu died had a high activity of phosphate-dependent glutaminase and were f ound to utilise glutamine from the culture medium during long term cul ture. The rate of cell proliferation, determined by [6-H-3]-thymidine incorporation, was dependent on glutamine concentration with the excep tion of Hs578T and MOLT 4 cells. The glutamine concentration giving ha lf maximal growth (ED(50)) ranged from 0.02-0.24mM. The glutamine anal ogue, acivicin [ L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5 aci d], markedly inhibited cell proliferation in the absence of glutamine. However, in the presence of glutamine acivicin only caused inhibition of proliferation in certain cell lines. Replacement of glutamine in t he culture medium by glutamate resulted in an increase in the rate of cell proliferation when compared with rates in the absence of glutamin e with no glutamate supplement. In addition, cells grown in the presen ce of the glutamine synthetase inhibitor, methionine sulphoximine, sho wed a marked decrease in proliferation. These data suggested the prese nce of glutamine synthetase in human tumour cells, which was confirmed by radiochemical assay of maximal glutamine synthetase activity. The breast tumour cells Hs578T, with high glutamine synthetase activity, w ere able to proliferate at rates similar to that in the presence of gl utamine, when glutamine-deficient medium was supplemented with purine nucleosides. However, the breast tumour cells MCF7, with low glutamine synthetase activity, were unable to proliferate at comparable rates i n the presence of either purine or pyrimidine nucleoside supplements.