High Efficacy of Pazopanib on an Undifferentiated Spindle-Cell Sarcoma Resistant to First-Line Therapy Is Identified With a Patient-Derived Orthotopic Xenograft (PDOX) Nude Mouse Model

Undifferentiated spindle-cell sarcoma (USCS) is a recalcitrant ­cancer. Our laboratory pioneered the patient-derived orthotopic xenograft (PDOX) nude mouse model with the technique of surgical orthotopic implantation (SOI). In the present study, we evaluated the efficacy of standard first-line chemistry of doxorubicin (DOX), gemcitabine (GEM) combined with docetaxel (DOC), compared to pazopanib (PAZ), a multi-targeting tyrosine-kinase inhibitor, in an USCS PDOX model. A high-grade USCS from a striated muscle of the patients was grown orthotopically in the right biceps femoris muscle of nude mice to establish the PDOX model. The PDOX models were randomized into the following groups when tumor volume reached 100 mm³: G1, control without treatment; G2, DOX (3 mg/kg, intraperitoneal (i.p.) injection, weekly, for 2 weeks); G3, GEM (100 mg/kg, i.p., weekly, for 2 weeks) combined with DOC (20 mg/kg, i.p., once); G4, PAZ (100 mg/kg, p.o., daily, for 14 days). All treatments except DOX significantly inhibited tumor growth compared to untreated control on day 14 after treatment initiation. Tumor sizes were as fallows: control (G1): 332.0 ± 58.7 mm³; DOX (G2): 316.9 ± 55.9 mm³, P = 0.605; GEM + DOC (G3): 228.9 ± 39.8 mm³, P = 0.001; PAZ (G4): 173.8 ± 23.3 mm³, P < 0.0001. PAZ showed significantly more efficacy compared to other therapies evaluated: DOX (P < 0.0001), GEM + DOC (P = 0.006). There were no animal deaths in any group and body weight of treated mice was not significantly different in each group. The present results demonstrate that the PDOX model of USCS can identify a promising novel agent with significantly greater efficacy than first-line therapy for this recalcitrant disease. J. Cell. Biochem. 118: 2739–2743, 2017.