Chemotherapy of methioninase-synchronized S/G2 phase-blocked cancer cells identified by cell cycle-specific fluorescent reporters.

Abstract

1063 Background: Cancer cells of all types have a generally elevated requirement for methionine compared to normal cells. This phenomenon is termed methionine-dependence and may be due to excessive methylation reactions in cancer cells, since methionine is the global source of cellular methyl groups (Biochim. Biophys. Acta, Reviews on Cancer 738, 49-87, 1984). Deprivation of methionine selectively arrests cancer cells during late S-phase (Proc. Natl. Acad. Sci. USA 77, 7306-7310, 1980), where they are highly sensitive to chemotherapy drugs which damage DNA (J. Natl. Cancer Inst. 76, 629-639, 1986). Methods: Cancer cells, transformed to express different color fluorescent reporters during specific phases of the cell cycle (Cell 132, 487-498, 2008), were used to monitor the onset of the S/G2-phase block due to methionine deprivation effected by recombinant methioninase (rMETase). The S/G2-phase blocked cancer cells fluoresced yellow or green in contrast to cancer cells in G1 which fluoresced red. Cancer cells, including MKN45 stromal cancer and MCF-7 breast cancer, synchronously blocked in S/G2-phase by rMETase, were identified by their yellow-green fluorescence and allowed to accumulate to the maximum extent. At the point of maximum yellow/green cells in the culture, the cells were administered chemotherapy drugs which interact with DNA or block DNA synthesis such as doxorubicin, cisplatin or 5-fluorouracil. We termed this procedure color-coded chemotherapy (CCC). Results: CCC was highly effective against the cancer cells (90% cell kill). In contrast, treatment of cancer cells with drugs only, and without rMETase-effected S/G2-phase synchrony, led to the majority of the cancer cell population being blocked in G1 phase (red fluorescent) where they were resistant to the drugs (40% cell kill). Conclusions: CCC, which identifies, by fluorescent color, when cancer cells are blocked in S/G2-phase by a unique cell-cycle-blocking agent, rMETase, demonstrates the potential of cell-synchronization-based chemotherapy.