Direct evidence of cell-surface heparan sulfate proteoglycans (HSPG) as diagnostic tools for promoting or preventing tumor progression has been lacking. Others and we have demonstrated that heparanase (Hpa-1) is a key determinant in invasive and metastatic events, and cleaves the HS chains of HSPG at specific intrachain sites. Although Hpa-1 represents the first example of purification and cloning of a mammalian HS degradative enzyme, a gene (hpa-2) related to hpa-1 has been recently cloned, and the gene product named heparanase-2 or Hpa-2. Being in the unique position of having access to newly developed Hpa-2 and Hpa-1 molecular probes, we have been studying mechanisms of heparanases in brain-metastatic melanoma (BMM) models as purified enzymes, antigens, and genes. We have found that Hpa-2 treatment of BMM cells results in opposite effects on brain colonization when compared to a corresponding Hpa-1 exposure. Our central hypothesis is that heparanases/HSPG processing is critical in invasion and metastasis, and targets for anti-cancer therapeutics. Hypotheses for this application are: 1) tumor cell surface HS contain bioactive sequences that impinge on melanoma growth and brain metastasis formation, and 2) HS chains from HSPG act as cryptic inhibitors or promoters of BMM upon their selective degradation by heparanases. The work proposed addresses research priorities raised by the N.C.I. Brain Tumor PRG report for an improved understanding of mechanisms underlying the establishment and spread of brain metastasis. We plan to demonstrate our hypotheses by pursuing the following specific aims: 1. To characterize Hpa-2 expression modalities in brain-metastatic melanoma (BMM) and relate them to Hpa-1 and to patient outcome. 2. To determine mechanisms by which a differential HS degradation specificity by heparanases results in inhibition or promotion of brain metastasis. These studies will assert 1) the relevance of heparanases (in particular Hpa-2) in cancer biology, and 2) the importance of HS chains as promoters or inhibitors of melanoma growth and metastasis, specifically to the brain. They will provide a framework for the development of polysaccharide-based anti-cancer molecules as important prognostic tools and diagnostic screens for metastatic detection, diagnosis and treatment.
