Neurofibromatosis type 1 (NF1) is a common genetic disease with a wide variety of features, which primarily involve the nervous system and related tissues. NF1 is characterized by abnormal cell growth and a high incidence of neurofibroma, a nerve tumor composed predominantly of Schwann cells. Plexiform neurofibromas often grow very large and are debilitating or fatal to NF1 patients. Thus, there is a serious need for better therapies to manage NF1 tumor growth. To this end, we have developed and exploited two animal models of NF1. The first involves a strain of mice in which the Nf1 gene was functionally deleted.

These Nf1 knockout mice are a valuable model for examining the biology of Nf1 tissues both in vivo and in vitro. Second, we have cultured tumor cells from human NF1 tumors. These human cell lines form neurofibroma-like tumors when implanted into the mouse nerve. Using these resources and animal models we can examine the formation of NF1 tumors under controlled conditions. The aims of this proposal are to determine how NF1 tumors induce the formation of new blood vessels and to test therapies to inhibit this process as a means to stop tumor growth.

There is considerable heterogeneity in the vasculature found in different tissue and tumor types. The first aim of this work is to determine whether blood vessel formation might be altered in NF1 patients. For this we will use the Nf1 knockout mouse. Blood vessel cells (endothelial cells) will be cultured from wild-type and Nf1 mouse tissues. The ability of these cells to form blood vessels in response to pro-angiogenic and anti-angiogenic factors will be tested in tissue culture assays. Important differences in the responsiveness of Nf1 endothelial cells will be confirmed using in vivo assays conducted in wild-type and Nf1 knockout mice.

We have established and characterized numerous cell cultures from human NF1 tumors, many of which have been grown as tumor grafts in the nerves of Nf1 mice. We will test the hypothesis that the rate of growth by these NF1 tumor xenografts is associated with the degree of newly formed vasculature. Also, comparisons will be made between xenografts implanted in normal mice and Nf1 mice. In vivo tumor growth and vascularity will be correlated with the expression of angiogenic regulators by the implanted cell lines. These experiments will test the hypothesis that tumor growth and invasion is dependent on the responsiveness of Nf1 endothelial cells and other reactive cells in the nerve that contribute to tumor formation.

There are several anti-angiogenic factors that show excellent promise as potent inhibitors of tumor growth. In this aim, we will test endostatin as an antitumor treatment for peripheral nerve tumors in NF1. This aim will be expanded to include other anti-angiogenic therapies based on discoveries made in the aims described above. Gene therapy using endogenous angiogenic inhibitors, like endostatin, is considered by many to be the most promising approach to bring the anti-angiogenic therapy into the clinic. As a simplified experimental model, we will examine the growth and vascularity of tumor xenografts that are engineered to produce endostatin. Second, using a strategy more relevant to clinic treatment, we will apply an endostatin-viral vector (AAV-endostatin) to NF1 tumors already growing in the mouse. In both treatment models, growth and regression of tumor and neovasculature will be monitored in vivo by noninvasive magnetic resonance imaging (MRI) followed by autopsy examination of the tumor tissues. Our overall goal is to discover effective therapies for the treatment of plexiform neurofibromas by blocking the ability of these aggressive tumors to recruit the blood vessels required for their growth.