Direct comparison of serine restriction on the viability of normal and cancer cells demonstrates that methionine restriction is more cancer specific.

BACKGROUND/AIM: Many studies in the present century have stated that restriction of serine is a cancer-specific vulnerability. The present study aimed to determine whether restriction of serine, compared to restriction of methionine, distinguishes cancer and normal cells. MATERIALS AND METHODS: 143B-RFP osteosarcoma cells, HT1080-RFP fibrosarcoma cells, HCT116-GFP colon-cancer cells, and Hs27 normal fibroblasts were used in the present study. All cells are of human origin. Cancer and normal cells were cultured in RPMI-1640 medium without serine and glycine for serine/glycine restriction, and in Dulbecco's modified Eagle's medium without methionine for methionine restriction, each supplemented with 10% dialyzed fetal bovine serum. Cancer and normal cells were cultured in 96-well plates at 2 × 103 cells/well. Serine, glycine, and methionine were added back as controls. Cell viability was measured with the WST-8 cell-viability reagent to establish dose-response curves for serine (with or without glycine) and for methionine in cancer and normal cells. Each cancer cell line was also co-cultured with Hs27 normal fibroblasts in 12-well plates. Each cell type was evaluated by phase-contrast and GFP/RFP fluorescence microscopy to determine the effects of serine/glycine restriction or methionine restriction. RESULTS: Serine restriction alone did not distinguish cancer and normal cells. Both 143B osteosarcoma and Hs27 normal fibroblasts maintained approximately 100% viability without serine in glycine-containing medium. The HT1080-RFP and HCT116-GFP cancer cells lost approximately 40% of their viability without serine and showed increasing viability with increasing serine concentration. When both serine and glycine were restricted, Hs27 fibroblasts lost approximately 20% viability, whereas all cancer cells lost about 40% viability. Neither serine restriction nor serine/glycine restriction could lower the viability of cancer cells to 50% of control. In co-culture, the removal of serine and glycine still left many cancer cells viable. In contrast, methionine removal caused a much greater reduction in cancer-cell viability than removal of serine/glycine. Hs27 normal fibroblasts survived well under both serine/glycine and methionine restriction. CONCLUSION: Serine restriction and serine/glycine restriction are not as cancer-specific as methionine restriction.