Effect of Recombinant Methioninase Dose and Timing on the Selective and Precise Elimination of Cancer Cells from Co-Cultured Normal Cells and on Methionine-dependent Rescue of Cancer Cells.

[BACKGROUND/AIM] Methionine addiction is a fundamental and general hallmark of cancer, known as the Hoffman effect. The aim of the present study was to target methionine addiction of cancer cells co-cultured with normal cells with various doses of recombinant (rMETase) to precisely eliminate cancer cells and to determine the timing of rescue of cancer cells by methionine supplementation.

[MATERIALS AND METHODS] HCT116 human colon cancer cells were co-cultured with Hs-27 diploid human normal fibroblasts in 12-well tissue-culture plates containing Dulbecco's Modified Eagle's Medium (DMEM) with 10% fetal bovine serum. rMETase was added to the co-cultures at 0.25, 0.5, or 1.0 U/ml. In attempts to rescue the cancer cells, normal DMEM which contains 0.2 mM of methionine, replaced DMEM containing rMETase on days -2, -4 or -6. Co-cultures were observed for cell viability and proliferation using phase-contrast microscopy.

[RESULTS] The efficacy of rMETase to eliminate cancer cells co-cultured with normal cells was dose-dependent. rMETase at 0.25 U/ml allowed large numbers of cancer cells to remain in the co-cultures by day 12. rMETase at 0.5 U/ml and 1.0 U/ml largely eliminated the cancer cells from the co-cultures by day 12. rMETase at 1.0 U/ml was slightly toxic to the normal cells. However, at each dose of rMETase, even at 1.0 U/ml, DMEM could rescue the cancer cells even when added on day 6.

[CONCLUSION] The ability of rMETase to eliminate cancer cells co-cultured with normal cells is dose-dependent. Even at high effective doses of rMETase, the cancer cells could be rescued by methionine supplementation up to at least day-6, indicating the need for the continuous presence of rMETase to selectively inhibit the cancer cells.