Extensive DNA Damage and Loss of Cell Viability Occur Synergistically With the Combination of Recombinant Methioninase and Paclitaxel on Pancreatic Cancer Cells which Report DNA-Damage Response in Real Time.

BACKGROUND/AIM: Methionine restriction selectively arrests cancer cells during the S-phase of the cell cycle. We hypothesized that DNA damage may occur in S-phase in cancer cells during methionine restriction. To determine if this occurs, we used MiaPaCa-2 53BP1-green fluorescent protein (GFP) pancreatic cancer cells, which report GFP fluorescence in real time after DNA-damage response (DDR) in these cells. We also determined whether a chemotherapy drug in combination with methionine restriction increases the rate of DNA damage.

MATERIALS AND METHODS

MiaPaCa-2 53BP1-GFP cells were used for in vitro experiments. The 25% and 50% inhibitory concentrations (IC and IC, respectively) of recombinant methioninase (rMETase) and paclitaxel on MiaPaCa-2 53BP1-GFP pancreatic cancer cells were determined. Cell viability and DDR with rMETase alone, paclitaxel alone, and their combination were measured in MiaPaCa-2 53BP1-GFP cells.

RESULTS

The IC of rMETase on MiaPaCa-2 53BP1-GFP cells was 1.66 U/ml. The IC for paclitaxel on MiaPaCa-2 53BP1-GFP cells was 3.31 nM. The combination of rMETase and paclitaxel synergistically reduced the viability of MiaPaCa-2 53BP1-GFP cells. The IC of paclitacel on MiaPaCa-2 53BP1-GFP cells was 5.1 nM. The IC of rMETase on MiaPaCa-2 53BP1-GFP cells was 2.3 U/ml. The combination of rMETase (IC) plus paclitaxel (IC) on MiaPaCa-2 53BP1-GFP cells also caused more DNA damage than either agent alone.

CONCLUSION

The present study suggests the synergy of methionine restriction and chemotherapy is due, at least in part, to DNA damage of cancer cells.