Decoding the role of HSPGs in tumor onset and progression through use of branched peptide probe

Heparan sulfate Proteoglycans (HSPGs) play a number of signaling and structural roles in tumor progression and metastasis spread. The biological function of HSPGs resides in their ability of interaction with many different types of ligands like growth factors, morphogens, chemokines and proteins of extracellular matrix (ECM). These bindings activate signaling pathways that modulate major transformations of cancer cells, leading to tumor growth, migration, invasion and metastasis. HSPGs are over-expressed on cancer cell membranes. The tetra-branched peptide NT4 binds with high selectivity to different human cancer cells and tissues. Its ability to discriminate between tumor and healthy tissues resides in the high-affinity binding to HSPGs and can be exploited by conjugating NT4 with different functional units, like chemotherapeutical drugs and tracers for cancer cell imaging and therapy. In this work, we test NT4 ability to interfere with processes mediated by HSPGs in tumor cell adhesion, migration and matrix invasiveness. Since HSPGs modulate also neo-angiogenesis, because of their expression by endothelial cells of microvessels that generate new vasculature, we focus also on NT4 role in endothelial cell proliferation, migration and tube formation, in the presence of Fibroblast Growth Factor-2 (FGF-2). Since the internalization and trafficking behaviour of HSPGs seems to reveal a clathrin and caveolin- independent, but dynamin-dependent endocytic pathway, we investigate the pathway used by NT4 to enter cells. Last, but not least, we radiolabel NT4 with 18F in order to measure tumor uptake and whole-body biodistribution in a mouse model of breast cancer, using in vivo PET imaging. NT4-HSPG interactions and consequent modulation of signaling pathways can prove the importance of NT4 peptide as a specific tool to enlighten the role of HSPG in tumor onset and progression.