The growth and metastasis of tumors depends, to a large extent, on the development of new blood vessels to supply food and oxygen to rapidly growing and dividing cells. Proteins involved in angiogenesis are attractive targets for new cancer therapeutics. One protein in particular, tumor endothelial marker 8 (TEM8), appears to be expressed exclusively, in adults, in the endothelial cells lining tumor blood vessels. A recent report found that a fusion of TEM8 and the Fc portion of IgG (TEM8-Fc) was a potent anti-cancer agent in a mouse model against a range of human tumor types. The overall goal of this Phase I project is to produce, using a rapid and transient plant expression system, forms of TEM8-Fc that will have enhanced binding to certain receptors on immune effector cells. Improvements in receptor binding will be achieved through both glycoform and amino acid engineering of the recombinant protein. We will then test the hypothesis that the anti-tumor activity of TEM8-Fc is related to its ability to mediate antibody dependent cellular cytotoxicity (ADCC) of cells expressing surface TEM8. Comparisons of ADCC activity will be followed by comparisons of anti-tumor activity in a nude mouse xenotransplantation model. Transgenic plants are a promising platform for the large-scale production of antibodies and other therapeutic proteins for treating serious and life-threatening conditions, including cancer. The advantages of using plants, rather than genetically modified animal cells in bioreactors, include very low cost of goods, and safety, due to the inability of plants to be infected with mammalian viruses and prions. Production in tobacco, a plant not used in the human food chain, avoids concerns about adventitious presence of therapeutic proteins in food or feed. In addition, the amount of protein that can be produced per acre with tobacco far exceeds what is possible with a seed crop like corn. Costs of purification, however, are similar to that of proteins produced in mammalian cell culture. The long-term goal is to develop TEM8-Fc into a highly effective, safe and economical treatment for a wide range of metastatic cancers.
New and more effective therapies for cancer are needed. This project would examine the mechanism of action of a novel recombinant protein that inhibits angiogenesis and growth of tumors, and should identify modifications to the protein that will make it even more effective at lower doses. Expression of this protein in plants will allow highly economical, large scale and safe production, making cancer therapy using dosages of a gram or greater of this recombinant protein much more available. ? ? ?
