Elevated hyaluridase 1 expression in an in vivo tumor model predicts the metastatic phenotype. Free

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Hyaluronic Acid, a very high molecular weight glycosaminoglycan, is a major component of the extracellular matrix in both normal and tumor tissues. It is secreted by many cell types, including tumor cells and its concentration in the peri-cellular stroma is controlled by a balance of synthesis by Hyaluron Synthases and degradation by Hyaluronidase enzymes. Elevated levels of Hyaluronidase enzymes, particularly Hyaluronidase 1 have been reported in several cancers, most notably bladder and prostate tumors. It is thought that degradation of the stromal Hyaluronic Acid within the tumor mass may promote extravasation and subsequent seeding of distant metastases. It is also known that the degradation products of Hyaluronic Acid are strongly pro-angiogenic.

We used in vivo bioluminescent imaging to track the pattern of metastasis from implanted MDA MB-435 cells which formed a ‘primary’ tumor in the mammary fat pads of SCID mice. We identified lung, bone, brain and the adrenal glands as the major metastatic sites under these experimental conditions.

Microarray analysis of metastases to bone, brain and lung originating from individual ‘primary’ mammary fat pad tumors showed that the metastases and their ‘primary’ tumors shared an almost completely identical gene profile, despite the very different conditions which would prevail at their sites of growth. The only notable difference in gene expression was in the Hyaluronidase 1 gene, where the level in the cells originating from the ‘primary’ mammary fat pad tumor was significantly lower than the levels seen in all metastases deriving from it. This preferential expression of Hyaluronidase 1 in metastatic foci was noted in several independent experiments. Hyaluronic acid zymography confirmed that the elevated gene expression correlated with the secretion of high levels of biologically active enzyme by the metastatic cells.

Hyaluronidase 1 expression was also found to be elevated in the sera of mice which had metastatic lesions but was not observed in mice whose tumors had not yet metastasized from the orthotopic ‘primary’ site.

These data indicate that serum levels of Hyaluronidase 1 might be predictive of active metastatic disease and we are currently studying this hypothesis in both melanoma and breast cancer patients.