Human fibrosarcoma cells selected for very-high doxorubicin resistance, acquire trabectedin and eribulin cross-resistance, remain sensitive to recombinant methioninase, and have increased c-MYC expression

Doxorubicin is first-line chemotherapy for soft tissue sarcoma; however, the development of drug resistance limits its efficacy. The purpose of the present study was to select very-high doxorubicin-resistant (VHDR) HT1080 fibrosarcoma cells, determine cross-resistance to second-line chemotherapy drugs, determine maintenance of sensitivity to recombinant methioninase (r-METase) alone and in combination with doxorubicin, and measure the level of c-MYC expression. VHDR-HT1080 cells were generated by cultivating HT-1080 cells in a series of step-wise progressively higher concentrations of doxorubicin, ranging from 8 nM to 15 µM, an 1875-fold increase, over a five-month period. The WST-8 reagent was used to assess cell viability. Four groups of in vitro drug-sensitivity tests were conducted, which involved both parental HT1080 and VHDR-HT1080 cells: 1) doxorubicin alone; 2) rMETase alone; 3) a combination of doxorubicin and rMETase; and 4) untreated control. The cross-resistance of VHDR-HT1080 cells to eribulin, trabectedin, gemcitabine and docetaxel was determined. The c-MYC levels in HT1080 and VHDR-HT1080 cells were measured using Western blotting. Doxorubicin had an IC ₅₀ of 3.3 µM against HT1080 cells and 38.2 µM against VHDR-HT1080 cells an 11.6-fold increase. The rMETase IC ₅₀ value for HT1080 was 0.75 U/ml and 0.59 U/ml for VHDR-HT1080. rMETase sensitized VHDR-HT1080 cells to doxorubicin. VHDR-HT1080 cells were cross-resistant to trabectedin 8.9-fold and cross-resistant to eribulin 1.87-fold compared to parental HT1080 cells. c-MYC expression was 8.4 times higher in VHDR-HT1080 cells compared to HT-1080 cells. The present results suggest rMETase may be used as a future clinical strategy to overcome super-doxorubicin resistance in soft tissue sarcoma.