Oral-recombinant Methioninase Converts an Osteosarcoma from Docetaxel-resistant to -Sensitive in a Clinically-relevant Patient-derived Orthotopic-xenograft (PDOX) Mouse Model

Background/Aim: Osteosarcoma is the most frequent malignant bone tumor. Failure of first-line therapy results in poor prognosis of osteosarcoma. In the present report, we examined the efficacy of the combination of oral recombinant methioninase (o-rMETase) and docetaxel (DOC) on an osteosarcoma patient-derived orthotopic xenograft (PDOX) mouse model. Materials and Methods: Osteosarcoma-PDOX models were established by tumor insertion within the tibia of nude mice. The osteosarcoma PDOX models were randomized into four groups (4-5 mice per group): control; o-rMETae alone; DOC alone; o- rMETase combined with DOC. The treatment period was 3 weeks. Results: The combination of o-rMETase and DOC showed significant efficacy compared to the control group (p=0.03). In contrast, there was no significant efficacy of o-rMETase alone or DOC alone (p=0.65, 0.60, respectively). Conclusion: o-rMETase converted an osteosarcoma PDOX from DOC-resistant to -sensitive. This combination therapy may be effective against recalcitrant osteosarcoma and other recalcitrant cancers.