The growth-stimulating capacity of calf serum (CS) in cell culture reaches a maximum of 10% with Balb 3T3 cells, remains at a plateau to 40% CS, and declines steeply to 100% CS. Growth capacity can be largely restored to the latter by a combination of cystine and glutamine. Glutamine is a conditionally essential amino acid that continues to function at very low concentrations to support the growth of nontransformed cells, but transformed cells require much larger concentrations to survive. These different requirements hold true over a 10-fold variation in background concentrations of CS and amino acids. The high requirement of glutamine for transformed cells applies to the development of neoplastically transformed foci. These observations have given rise to a novel protocol for cancer therapy based on the large difference in the need for glutamine between nontransformed and transformed cells. This protocol would stop the cumulative growth and survival of the transformed cells without reducing the growth rate of the nontransformed cells. The results call for studies of glutamine deprivation as a treatment for experimental cancer in rodents and clinical trials in humans.
Keywords: glutamine regulation; nontransformed cells; transformed cells.