PO-220 Defining the role of heparanase in breast cancer progression using the PyMT-MMTV mouse model

Introduction Heparanase (HPSE) is a beta-d-endoglucuronidase and the only mammalian enzyme that cleaves heparan sulphate (HS), a major structural and regulatory component of the extracellular matrix (ECM) and the vascular basement membrane (BM). The expression of HPSE is tightly controlled and under physiological conditions is limited to immune cells, endothelial cells, placental trophoblasts and keratinocytes. However, during pathological conditions such as cancer, HPSE expression is dysregulated and high expression often correlates with poor patient survival. The cleavage of HS by HPSE expressing tumours degrades the ECM/BM and releases HS bound growth factors and cytokines, promoting cellular signalling in a positive feed-back mechanism. This in turn leads to enhanced primary tumour growth, metastasis, angiogenesis and inflammation. HPSE is therefore a critical promoter of the hallmarks of cancer and has generated significant interest as an anti-cancer drug target. However, despite decades of research, the precise mechanistic role of HPSE in the tumour microenvironment remains poorly defined. Breast cancer is the most prevalent malignancy in women worldwide. Clinical data reveals that the expression of HPSE in mammary tumours results in poor patient survival. Material and methods We recently generated a HPSE-deficient C57Bl/6 mouse strain (C57Bl/6xHPSE -/- ) that were crossed with spontaneous mammary tumour developing PyMT-MMTV mice to generate the PyMT-MMTVxHPSE -/- strain, providing us with a valuable in vivo model to characterise the role of HPSE in early mammary tumour development, tumour progression and metastasis. Results and discussions Our data indicate that although HPSE promoted tumour angiogenesis, overall tumour development and metastasis between PyMT-MMTV and PyMT-MMTVxHPSE -/- mice remained comparable. By examination of the tumour microenvironment, we also demonstrate that the tumour stroma positively contributes to mammary tumour HPSE activity, promoting tumour angiogenesis. In contrast, HPSE expressed in the tumour-bearing host appeared to play no significant role in tumour growth and metastasis. These data suggest that in the PyMT-MMTV model and indeed, in certain cancer settings such as breast cancer, HPSE may not play as significant a role to what has been proposed over the last two decades. Conclusion These findings may have important implications for the ongoing development and application of HPSE inhibitors in the treatment of cancer.