Ullrich found some of the most important evidence in research on animals, conducted with colleagues Birgit Millauer and the late Werner Risau, formerly of the Max Planck Institute of Neurobiology. There is a receptor specific to VEGF, called Flk-1/VEGFR2, found only in endothelial cells which are the building stones of new blood vessels. When Flk-1/VEGFR2 is made inoperative, this blocks the development of tumours. If no blood vessels are created in tumour tissue, the tumour fails to grow. This discovery led to the invention of what are called angiogenesis inhibitors (angiogenesis is the process of blood vessel formation).
Ullrich and the Max Planck Society, in co-operation with New York University, founded SUGEN, Inc. in California in 1991. SUGEN is the first biotechnology company with roots in the Max Planck Society. The firm developed chemical substances which block Flk-1/VEGFR2 in endothelial cells. At the end of the 1990s SUGEN was taken over by Pharmacia, which itself was bought by Pfizer in 2003. Development of the project continued at Pfizer. SUTENT® (active ingredient Sunitinib) has now reached the market as a multi-targeted tyrosine kinase inhibitor, which blocks both the building of blood vessels in tumours as well as other illness-related enzymes in tumour cell signalling networks.
Clinical studies with GIST patients looked into their ability to tolerate Sunitinib, as well as its effectiveness on them. Some of these patients had already been treated with Imatinib, but their tumours continued to develop. Others were not able to tolerate Imatinib at all. Still other patients had advanced renal cell carcinoma with failed available treatment. In the case of the GIST patients, it took four times longer for tumours to renew growth when