The mortality associated with most solid tumors is the direct result of regional and systemic metastases. Enzymatic destruction of basement membranes (BM) is thought to be important in the invasion and metastasis of tumors to distant organ sites. The brain is one of the predominant target organs for secondary involvement by malignant neoplasms, in particular malignant melanoma. Melanoma has been a long-standing focus of both clinical and laboratory-based research because of its grave prognosis and its propensity to affect young adults. The role of growth factor networks in regulating the progression of human melanocytes towards tumorigenicity and ultimately the malignant phenotype is poorly understood. In particular, the autocrine and paracrine influences that modulate cellular invasion and extracellular matrix degradative enzymes of melanoma cells remain undefined at the molecular level. We have found that biologically active 2.5S Nerve Growth Factor (NGF) treatment of early passage human and murine metastatic cells resulted in a) delayed density-dependent inhibition of melanoma cell growth, b) increased """"""""in vitro"""""""" invasion through a reconstituted basement membrane (Matrigel), c) time- and dose-dependent induction of heparanase, a heparan sulfate specific endo-beta-D-glucuronidase associated with human melanoma metastasis and d) increased cellular invasion in a chemoinvasion assay performed with filters coated with purified heparan sulfate proteoglycan (HSPG). These NGF effects were most dramatic in the brain colonizing sublines (human 70W and murine B16B15b. We will assess whether the observed """"""""in vitro"""""""" metastatic capability of melanoma cells in response to NGF treatment compare with presence both """"""""in vitro"""""""" and """"""""in vivo"""""""" of the newly discovered neurotrophic factors related in structure/function to NGF and collectively called the neurotrophins (NT). We will determine presence and expression of several members of trk family of tyrosine kinase receptors as biologically relevant NT receptors and NT stimulation in relation to invasive processes. We will continue mechanistic studies to define the role of NT in production of heparanase and NT involvement in Matrigel/heparan sulfate proteoglycan (HSPG) degradation/cellular secretion following NT exposure. We have started and continue to pursue clinically related studies to define the levels of NT receptors and their expression in malignant melanoma at various stages of tumor progression to the metastatic phenotype and study brain metastasis site preference in relation to sites of synthesis and function of NT in the brain. The role of the various neurotrophins in human melanoma will be assessed, a novel undertaking. The results of these studies will extend our understanding of NT functionality in those regions targets of melanoma metastasis and may provide the basis for therapeutic exploitation of NT biological effects occurring during progression to advanced stages of malignancy.
