Olaratumab exerts anti-tumor activity in preclinical models of pediatric bone and soft tissue tumors through inhibition of platelet-derived growth factor receptor {alpha}

Purpose: Platelet-derived growth factor receptor alpha (PDGFRα) is implicated in several adult and pediatric malignancies, where activated signaling in tumor cells and/or cells within the microenvironment drive tumorigenesis and disease progression. Olaratumab (LY3012207/IMC-3G3) is a human monoclonal antibody that exclusively binds to PDGFRα and recently received accelerated FDA approval and conditional EMA approval for treatment of advanced adult sarcoma patients in combination with doxorubicin. In this study, we investigated olaratumab in preclinical models of pediatric bone and soft tissue tumors. Experimental Design: PDGFRα expression was evaluated by qPCR and western blot analysis. Olaratumab was investigated in in vitro cell proliferation and invasion assays using pediatric osteosarcoma and rhabdoid tumor cell lines. In vivo activity of olaratumab was assessed in preclinical mouse models of pediatric osteosarcoma and malignant rhabdoid tumor. Results: In vitro olaratumab treatment of osteosarcoma and rhabdoid tumor cell lines reduced proliferation and inhibited invasion driven by individual PDGFs or serum. Furthermore, olaratumab delayed primary tumor growth in mouse models of pediatric osteosarcoma and malignant rhabdoid tumor and this activity was enhanced by combination with either doxorubicin or cisplatin. Conclusion: Overall, these data indicate that olaratumab, alone and in combination with standard of care, blocks the growth of some preclinical PDGFRα-expressing pediatric bone and soft tissue tumor models.

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