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 methioninase (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.