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

Abstract

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^Tet-On 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^Tet-On 53BP1-GFP cells were used for in vitro experiments. The 25% and 50% inhibitory concentrations (IC₂₅ and IC₅₀, respectively) of recombinant methioninase (rMETase) and paclitaxel on MiaPaCa-2^Tet-On 53BP1-GFP pancreatic cancer cells were determined. Cell viability and DDR with rMETase alone, paclitaxel alone, and their combination were measured in MiaPaCa-2^Tet-On 53BP1-GFP cells. Results: The IC₂₅ of rMETase on MiaPaCa-2^Tet-On 53BP1-GFP cells was 1.66 U/ml. The IC₂₅ for paclitaxel on MiaPaCa-2^Tet-On 53BP1-GFP cells was 3.31 nM. The combination of rMETase and paclitaxel synergistically reduced the viability of MiaPaCa-2^Tet-On 53BP1-GFP cells. The IC₅₀ of paclitacel on MiaPaCa-2^Tet-On 53BP1-GFP cells was 5.1 nM. The IC₅₀ of rMETase on MiaPaCa-2^Tet-On 53BP1-GFP cells was 2.3 U/ml. The combination of rMETase (IC₅₀) plus paclitaxel (IC₅₀) on MiaPaCa-2^Tet-On 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.