Abstract 2791: mTOR inhibitor and VEGFR inhibitor combination therapy regress a doxorubicin resistant osteosarcoma in a patient-derived orthotopic xenograft model and in vivo angiogenesis assay model
Authors: Oshiro Hiromichi , Tome Yasunori , Hoffman Robert M. , Nishida Kotaro 
Published: September 2020

Abstract
Introduction: The efficacy of the combination therapy of mTOR inhibitor and VEGFR inhibitor was reported in advanced renal cell cancer with anti-angiogenesis. However, none of the reports have been published in osteosarcoma (OS). A tumor from 16-year-old patient who failed doxorubicin (DOX) was previously implanted orthotopically into the lateral condyle of distal femur of nude mice to establish a patient-derived orthotopic xenograft (PDOX) model in our laboratory at AntiCancer Inc. We previously found that the OS PDOX model was resistant to DOX matching the clinical setting. We also previously established in vivo angiogenesis assay model using OS cell line with nestin green fluorescent protein (GFP) mouse and reported that OS cells have highly angiogenesis. In the present study, we evaluated the efficacy of everolimus (EVE, a mTOR inhibitor), pazopanib (PAZ, a VEGFR inhibitor) and the combination of EVE and PAZ on the DOX resistant OS PDOX model and in vivo angiogenesis assay model using OS patient derived cells (PDCs).
Methods: The OS PDOX model was randomized into five groups of seven mice. An OS PDC was established from a patient-derived OS tumor fragment. After several passages, OS-PDCs were established and were transplanted into the back of nestin GFP mice to make in vivo angiogenesis assay model. For the angiogenesis study, In vivo angiogenesis assay models were randomized into five groups of eight fields: Group 1, Control (Ctrl) treated with PBS, i.p.; Group 2, DOX, 2.4 mg/kg, i.p., weekly; Group 3, EVE, 5 mg/kg, oral gavage, daily; Group 4, PAZ, 50 mg/kg, oral gavage, daily; Group 5,the combination of EVE and PAZ. Treatment was performed for 2 weeks in each model. In the OS PDOX model, treatment efficacy was evaluated on tumor volume ratio and histopathology. Adverse event was evaluated on body weight ratio. In the in vivo angiogenesis assay model, treatment efficacy was evaluated on vascular length ratio. Treatment efficacy and adverse event were evaluated after 2 weeks treatment.
Results: Tumor volume ratios in OS PDOX model were the Ctrl group: 4.70 ± 0.58, DOX group: 3.97 ± 0.53, EVE group: 3.89 ± 0.80, PAZ group: 4.16 ± 1.01 and combination group: 1.70 ± 0.30, respectively. Vascular length ratios in vivo angiogenesis assay model were the Ctrl group: 1.44 ± 0.50, DOX group: 1.22 ± 0.30, EVE group: 0.97 ± 0.31, PAZ group: 0.80 ± 0.12 and combination group: 0.58 ± 0.08, respectively. EVE and PAZ combination group regress tumor volume ratio and vascular length ratio with significant difference compared to all groups. In H&E-staining, partial necrosis was detected only in OS PDOX tumors treated with combination of EVE and PAZ. Body weight ratio was no significant difference among all groups.
Conclusion: The combination therapy of EVE and PAZ was the most effective in the OS PDOX mouse model and in vivo angiogenesis assay model due to suppress angiogenesis strongly. This study demonstrates that the combination therapy of mTOR inhibitor and VEGFR inhibitor has possibility to be therapeutic strategy for DOX resistant osteosarcoma.
Citation Format: Hiromichi Oshiro, Yasunori Tome, Robert M. Hoffman, Kotaro Nishida. mTOR inhibitor and VEGFR inhibitor combination therapy regress a doxorubicin resistant osteosarcoma in a patient-derived orthotopic xenograft model and in vivo angiogenesis assay model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2791.