HT1080 Fibrosarcoma With Acquired Trabectedin Resistance: Increased Malignancy But Sustained Sensitivity to...

Trabectedin is a DNA-binding agent that has shown moderate efficacy for soft-tissue sarcomas. We have previously shown that methionine restriction enhances trabectedin efficacy on both parental and trabectedin-resistant HT1080 (TR-HT1080) cells in vitro The aim of the present study was to determine whether fibrosarcoma cells that acquire trabectedin resistance become more malignant but maintain sensitivity to methionine restriction in vivoMaterials and Methods: TR-HT1080 was established by culturing HT1080 cells in stepwise increasing concentrations of trabectedin. An in vitro wound-healing invasion assay was used to compare malignancy of HT1080 and TR-HT1080. In vivo, six groups were established: G1-G4 (TR-HT1080): G1, untreated control; G2, trabectedin treatment; G3, methionine-restricted diet; G4, methionine-restricted diet combined with trabectedin; G5, untreated control of parental HT1080; and G6, trabectedin treatment of parental HT1080.

The IC₅₀ of trabectedin was previously determined to be 3.3 nM for the parental HT1080 cells and 42.9 nM for trabectedin-resistant HT1080 cells, representing a 13-fold increase. Wound-healing invasion assays in vitro showed a more rapid wound-closure ratio in TR-HT1080 cells than in parental cells, suggesting increased malignancy compared to the parental cells. The volume of untreated TR-HT1080 tumors grew more rapidly than that of HT1080 tumors, indicating a higher malignancy of TR-HT1080 tumors. The IC₅₀ of recombinant methioninase was previously determined as 0.75 U/ml for HT1080 and 0.93 U/ml for TR-HT1080 cells. Methionine restriction was highly effective on TR-HT1080 tumors, decreasing tumor growth by 4-fold.

TR-HT1080 cells acquired high malignancy by in vitro selection for trabectedin resistance. However, methionine restriction overcame trabectedin resistance in vivo, strongly inhibiting tumor growth, which should be further investigated in the clinic.