Dual-Color Imaging of Angiogenesis and Its Inhibition in Bone and Soft Tissue Sarcoma

Background. Angiogenesis is a critical step in tumor growth, progression, and metastasis. Soft tissue and bone sarcoma are resistant to most therapeutic ap-proaches. Angiogenesis of these tumors may be an ef-fective target. We hypothesized that we could inhibit tumor growth by targeting angiogenesis in a mouse model of sarcoma. We demonstrate in this report, using powerful color-coded fluorescent imageable tumor-host models, the onset of angiogenesis of these sarcomas and its inhibition. Materials and methods. Transgenic mice were used as the host in which green fluorescent protein (GFP) is driven by a regulatory element of the stem cell marker nestin (ND-GFP). Nascent blood vessels express ND-GFP in this model. We visualized, by dual-color fluo-rescence imaging, angiogenesis of sarcoma formed by the HT-1080 human fibrosarcoma cell line expressing red fluorescent protein (RFP) in the ND-GFP mice. Tumor cells were injected into either the muscle or the bone. Results. Nestin was highly expressed in proliferat-ing endothelial cells and nascent blood vessels in the growing tumors, including the surrounding tissues. Immunohistochemical staining showed that CD31 co-localized in ND-GFP-expressing nascent blood vessels. The density of nascent blood vessels in the tumor was readily quantitated. The mice were given daily i.p. injections of 5mg/kg of doxorubicin after implantation of tumor cells. Doxorubicin significantly decreased the mean nascent blood vessel density in the tumors as well as decreased tumor volume. Conclusion. The dual-color model of the ND-GFP nude mouse and RFP sarcoma cells is useful for the visualization and quantitation of bone and soft tissue tumor angiogenesis and evaluation of angiogenic in-hibitors for such tumors. These data suggest targeting angiogenesis of sarcomas as a promising clinica