Hyaluronan (HA) is a high molecular weight anionic polysaccharide that is elevated in primary prostate tumors. Metastatic prostate cancer cells synthesize and assemble HA into a pericellular matrix that is important for anchorage-independent tumor growth in vitro and tumor growth/angiogenesis in vivo. Prostate tumor cells that express elevated hyaluronan synthases also adhere more readily to microvessel (e.g. bone marrow) endothelial cells in vitro than controls implicating pericellular hyaluronan in the homing of metastatic prostate tumor cells to bone and other organs in vivo. Indeed, we have proposed that an ability to assemble an HA-rich pericellular matrix may offer metastasizing prostate tumor cells a selective advantage by providing them with an adhesive, growth factor-rich protective microenvironment as they adjust and colonize distinct tissues such as bone. Metastatic, androgen independent human prostate carcinoma cell lines express high levels of two HA receptors: CD44 and cell surface RHAMM (gene name is HMMR, also designated CD168), which we have shown to co-associate and which functionally collaborate to promote motility and invasion, particularly through Ras-transformation pathways. Inhibiting endogenous expression of CD44 and/or Rhamm with RNA interference of either receptor significantly reduces anchorage-independent growth in vitro, which is reversed by the addition of exogenous HA. Collectively, these and other studies have led us to propose that prostate cancer progression is hyaluronan-driven. Preliminary data show that RHAMM, HA and Hyaluronidase 1 (HYal1) are elevated in human prostate cancer and in particular RHAMM protein expression increases with increasing Gleason scores. In contrast, CD44 protein expression is significantly decreased in prostate cancer compared to normal or benign hyperplastic tissue. In addition to its role in proliferation and migration/invasion, CD44 is an endocytic receptor that internalizes and targets HA for lysosomal destruction. Therefore the increased HA observed in prostate cancer is at least partly due to decreased CD44 protein expression. Both the decreased CD44 levels and elevated HYal 1 are expected to promote HA/HA fragment accumulation producing a tumor-supporting microenvironment. Conversely, because abundant RHAMM and HA/HA fragments are present in an environment of low CD44, the stoichiometry favors RHAMM-HA-CD44 interactions. Data indicate that cell surface RHAMM maintains CD44 on the cell surface, negating its endocytic function and promoting its signaling function, """"""""hyper-activating"""""""" the remaining CD44 resulting in increased aggressiveness of the tumor. The working model for this proposal is that as an HA matrix is synthesized, assembled and then fragmented by the expanding prostate tumor, it creates a microenvironment which facilitates tumor cell survival, growth and invasion by interacting with RHAMM/HA/CD44 complexes on the surface of tumor cells. We propose that selective interference with the HA/tumor cell interaction is a viable neoadjuvant therapeutic approach in patients to enhance the effectiveness of current therapies.
Prostate cancer is the second leading cause of cancer deaths in men in the United States. The projects proposed will study tumor associated changes in the molecular composition of prostate tumor microenvironments which are linked to malignant progression. The focus of this proposal is to determine the mechanisms by which these changes contribute to progression and to use compounds (specific synthetic peptides) that disrupt these mechanisms to inhibit tumor growth, invasion and metastasis.
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