Michael Klagsbrun has made major contributions to the field of growth factors and their receptors, particularly those that regulate the vascular system. He is credited with the first purifications of basic fibroblast growth factor (FGF-2), a potent angiogenesis factor, and of heparin-binding EGF-like growth factor (HB-EGF), a potent smooth muscle mitogen.

More recently, Dr. Klagsbrun's laboratory has purified vascular growth factor receptors. One of these, neuropilin, is a novel receptor for the angiogenesis factor, VEGF. Neuropilin was originally described as a receptor for semaphorin, a protein involved in regulating axon guidance. These studies have suggested that similar molecular mechanisms regulate angiogenesis and neuronal guidance, both of which are networking processes.

The Klagsbrun lab has demonstrated that Semaphorin 3F (SEMA3F) is a potent inhibitor of tumor angiogenesis, tumor progression and metastasis. The mechanism of SEMA3F inhibition involves rapid collapse of the F-actin cytoskeleton due to inactivation of RhoA, a small GTPase that regulates stress fiber formation. As a consequence of the cytoskeletal collapse, cell migration, a hallmark of tumor progression and metastasis, is inhibited.

Tumor-associated endothelial cells (EC) are the actual targets for anti-angiogenesis therapy. They were originally thought to be normal diploid cells. However, it is now apparent that EC are heterogenous cell types with different functions in different organs. The Klagsbrun lab has isolated mouse EC from human tumor xenografts in mice. Unexpectedly, some tumor EC are cytogenetically abnormal and are more drug-resistant. In addition, tumor EC isolated from the TRAMP mouse model of prostate carcinoma are multi-potent and stem cell-like. They can differentiate into cartilage and bone and express EC cartilage and bone markers. In human patient samples, tumor EC are associated with calcification. Taken together, these results indicate that it may be more difficult to successfully target tumor blood vessels than originally thought.