Background/Aim: Osteosarcoma is a recalcitrant neoplasm which occurs predominantly in adolescents and young adults. Recently, using a patient-derived orthotopic xenograft (PDOX) model of malignant soft-tissue sarcoma (STS), we showed that oral recombinant methioninase (o-rMETase), in combination with caffeine, was more efficacious than o-rMETase alone in inhibiting STS tumor growth. In the present report, we determined the efficacy of o-rMETase combined with oral caffeine on a cisplatinum (CDDP)resistant osteosarcoma PDOX model. Materials and Methods: Osteosarcoma PDOX models were randomly divided into seven treatment groups (6 mice in each group): untreated control; CDDP alone; o-rMETase alone; o-rMETase with caffeine; CDDP plus o-rMETase; CDDP plus caffeine; and CDDP plus o-rMETase with caffeine. Tumor size and body weight were measured throughout the treatment. Results: Tumors regressed after treatment with CDDP plus o-rMETase with caffeine. Tumors treated with CDDP plus o-rMETase with caffeine also had the most necrosis. Conclusion: The combination of o-rMETase and caffeine together with first-line chemotherapy was efficacious for drug-resistant osteosarcoma and has clinical potential in the treatment of this highly-resistant neoplasm.
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