Selective Synergy of Recombinant Methioninase Plus Docetaxel Against Docetaxel-resistant and -sensitive Fibrosarcoma Cells Compared to Normal Fibroblasts.

Abstract

Background/aim: Docetaxel combined with gemcitabine is a second-line treatment for soft-tissue sarcoma; however, its effectiveness is limited because of docetaxel resistance. The objective of the present study was to determine the potential of recombinant methioninase (rMETase) to enhance the efficacy of docetaxel on high-docetaxel-resistant human fibrosarcoma cells in vitro.

Materials and methods: Docetaxel-resistant HT1080 (DTR-HT1080) human fibrosarcoma cells were established by culturing them in by progressively increasing concentrations of docetaxel from 0.02 to 9 nM in vitro. The IC₅₀ values for docetaxel and rMETase, as well as the efficacy of their combination, in inhibiting HT1080 human fibrosarcoma cells, DTR-HT1080 cells, and Hs27 normal human fibroblasts were determined. Four experimental groups were examined in vitro: control group without treatment; docetaxel alone; rMETase alone; docetaxel combined with rMETase.

Results: The IC₅₀ of docetaxel for DTR-HT1080 cells was 7.57 nM, compared to the parental HT1080 cells with an IC₅₀ of 1.68 nM, a 4.5-fold increase. The IC₅₀ of docetaxel on Hs27 fibroblasts was 4.46 nM. The IC₅₀ of rMETase on HT1080 cells was 0.75 U/ml (data from [6]). The IC₅₀ of rMETase on DTR-HT1080 cells was 0.55 U/ml. The IC₅₀ of rMETase on Hs27 fibroblasts was 0.93 U/ml (data from [6]). Docetaxel (1.68 nM [IC₅₀]) plus rMETase (0.75 U/ml [IC₅₀]) synergistically reduced the viability of HT1080 cells (p<0.05). In contrast, docetaxel (4.46 nM) plus rMETase (0.93 U/ml) did not reduce the viability of Hs27 fibroblasts, compared to either agent alone. The combination of rMETase (0.55 U/ml [IC₅₀]) and docetaxel (1.68 nM [IC₅₀ of the parental cells]) overcame docetaxel resistance of DTR-HT1080 cells, resulting in an inhibition of 48.1% compared to docetaxel alone (6.8%) or rMETase alone (37.5%) (p<0.05). rMETase thus increased the efficacy of docetaxel 7-fold on docetaxel-resistant human fibrosarcoma cells.

Conclusion: The combination of docetaxel and rMETase was synergistic on HT1080 fibrosarcoma cells, but not normal fibroblasts. rMETase plus docetaxel synergistically reduced the high docetaxel resistance of DTR-HT1080 cells. The present results indicate the clinical potential of rMETase to reduce docetaxel resistance in soft-tissue sarcoma patients in the future.