Abstract 589: Targeting of metastatic osteosarcoma with F8-TNF-alpha in an orthotopic mouse model
Authors: Robl Bernhard , Botter Sander Martijn , Boro Aleksandar , Neri Dario , Fuchs Bruno 
Published: July 2016

Osteosarcoma (OS) is a malignancy of bone and five-year survival rates are still at a low 20% if metastatic disease is present. Metastatic OSs most frequently metastasize to the lung. TNF-α is a powerful cytokine already shown to be active against many cancers. Nevertheless, TNF-α is highly toxic at clinically relevant concentrations. To overcome this limitation, targeted forms of TNF-α can be used. In this study, targeting is achieved through linking TNF-α to the antibody fragment F8, targeting the EDA-domain of fibronectin. To test the efficacy of F8-TNF-α against OS, we sought to investigate the effects of F8-TNF-α in an orthotopic syngeneic OS model. In addition to evaluating compound efficacy, we also tested whether the route of administration (systemic versus local application) can even further increase treatment efficacy. Ultimately, we aimed at measuring treatment success by assessing different stages of OS progression, especially metastatic disease.

To show clinical relevance, we performed immunofluorescence (IF) of EDA on primary human OS samples. In a second step, we evaluated drug efficacy in a syngeneic OS mouse model. K7M2L2 OS cells, stably infected to express the marker proteins lacZ and mCherry, were orthotopically injected into the tibia of mice. Once primary tumors were detectable, the mice were treated with either PBS or F8-TNF-α. The compound was given either systemically (intravenously (i.v.), tail vein) or locally (intraarterial (i.a.), femoral artery). Four days after the last treatment, all mice were sacrificed, terminal blood sampling was performed and blood samples were analyzed for the presence of circulating tumor cells (CTCs) via FACS/mCherry fluorescence. Following X-gal staining, metastases on the surface of lungs were counted. EDA and infiltration of immune cells (CD4+, CD8+, natural killer (NK) cells, CD19+) were assessed histologically.

Using IF, we detected strong expression of EDA in primary tumors as well as bone and lung metastases from human OS patients. Preliminary results from our treatment study showed a significant decrease in the number of lung metastases as well as the number of CTCs in mice treated with i.a. F8-TNF-α while the treatment was well tolerated by the mice. The reduction of lung metastases could, at least in part, be explained by a strong expression of EDA in the lung metastases. In addition, significant increases in lung-infiltrating immune cells were observed after administration of F8-TNF-α (i.v. F8- TNF-α: increased CD4+ T-cells; i.a. F8-TNF-α: increased NK cells). Although significant reductions in numbers of metastases and CTCs were detected, F8-TNF-α did not significantly impair the growth of the primary tumors.

In conclusion, our study demonstrates a reduction of CTCs as well as lung metastases after administration of F8-TNF-α and thus, provides a rationale for further studying the anti-metastatic effects of this compound in a clinically relevant model of OS.

Citation Format: Bernhard Robl, Sander Martijn Botter, Aleksandar Boro, Dario Neri, Bruno Fuchs. Targeting of metastatic osteosarcoma with F8-TNF-alpha in an orthotopic mouse model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 589.