Elevated-c-MYC-expressing Fibrosarcoma Cells With Acquired Gemcitabine Resistance Remain Sensitive to Recombinant Methioninase: A Potential Clinical Strategy for a Recalcitrant Disease

Background/aim: For second-line chemotherapy of soft-tissue sarcoma, gemcitabine is administered in combination with docetaxel. However, more effective treatments are required for advanced soft-tissue sarcoma, where the efficacy is limited. The purpose of the present study was to compare the efficacy of rMETase and gemcitabine against HT1080 human fibrosarcoma cells and Hs27 normal fibroblasts, as well as to identify and effectively treat HT1080 cells that are resistant to gemcitabine associated with elevated c-MYC.

Patients and methods: Cell viability was measured with the WST-8 reagent. Four groups of in vitro tests were conducted involving HT1080 and Hs27 cells: gemcitabine alone, rMETase alone, and a combination of gemcitabine plus rMETase. Gemcitabine resistant cells (GR-HT1080) were established by culturing HT-1080 cells in increasing concentrations of gemcitabine, ranging from 0.016 nM to 16 nM over five months. Western immunoblotting was performed to measure c-MYC levels in HT1080 and GR-HT1080 cells.

Results: Gemcitabine had an IC₅₀ of 12.8 nM against HT1080 cells, 30.8 nM against GR-HT1080 cells, and 4.48 nM against Hs27 cells. The rMETase IC₅₀ value for HT1080 was 0.75 U/ml. The IC₅₀ value of rMETase for GR-HT1080 cells was 0.85 U/ml. The IC₅₀ value for rMETase on Hs27 cells was 0.93 U/ml. Gemcitabine and rMETase demonstrated synergy in killing fibrosarcoma cells, but no synergy was observed on normal fibroblasts. The c-MYC level that was more than 5.1 times higher in GR-HT1080 cells compared to HT-1080 cells. Both the parental HT1080 cells and the GR-HT1080 cells had a similar high sensitivity to rMETase alone.

Conclusion: rMETase may be used as a future clinical strategy to overcome gemcitabine resistance in sarcoma.