Highly Synergistic Eradication of 143B Osteosarcoma Cells In Vitro by the Combination of Recombinant Methioninase, Chloroquine, and Rapamycin Targeting Methionine Addiction, Autophagy, and mTOR, Respectively.

Abstract

Background/aim: Drug-resistant osteosarcoma is a highly aggressive malignancy with limited therapeutic options. Recombinant methioninase (rMETase) targets the methionine addiction of cancer and acts synergistically with many cancer-chemotherapy agents. The present study investigated the synergistic efficacy of the combination of rMETase, chloroquine (CQ) which targets autophagy, and rapamycin (RAPA) which targets mTOR, on human 143B osteosarcoma cells in vitro.

Materials and methods: 143B human osteosarcoma cells. 143B cells were treated under eight conditions at the IC₃₀ of each agent: untreated control; rMETase alone (0.31 U/ml); CQ alone (61.9 μM); RAPA alone (30.9 μM); rMETase (0.31 U/ml) + CQ (61.9 μM); rMETase (0.31 U/ml) + RAPA (30.9 μM); CQ (61.9 μM) + RAPA (30.9 μM); and rMETase (0.31 U/ml) + CQ (61.9 μM) + RAPA (30.9 μM). Cell viability was measured with the WST-8 reagent.

Results: Each of the single-agents, rMETase, CQ, and RAPA demonstrated moderate cytotoxicity when administered alone to 143B cells. The dual combination of CQ plus RAPA had the highest efficacy compared to single agents and compared to rMETase plus CQ and rMETase plus RAPA, which had moderate efficacy. In contrast, the triple combination of rMETase, CQ, plus RAPA exhibited strong synergistic efficacy, eradicating 143B cells.

Conclusion: The triple combination of rMETase, CQ, and RAPA demonstrated strong synergy and effectively eradicated 143B osteosarcoma cells. Therefore, the triple treatment with rMETase, CQ, and RAPA has potential as a novel, effective therapeutic approach for osteosarcoma.