**2.1 Biochemical properties**

HA belongs to the glycosaminoglycan group of polysaccharides composed of disaccharide units of a hexose linked to a hexosamine. It consists of repeating units of *N*-acetyl glucosamine and -glucuronic acid (Fig. 2). The native polymer consists of up to 106 to 107 non-branching disaccharide units. The functions of HA within the ECM and cells depend upon its molecular weight, the type of cell, and the HA receptor(s) that target cells express. High molecular weight HA (e.g. >200 kDa) is a major biomechanical factor in ECM, which contributes to tissue hydration and elasticity by providing a template for the assembly of macromolecular complexes. A well known example is the "bottle brush" complex of aggrecan and link proteins, which provides the visco-elastic nature of synovial fluid. HA fragments provide signalling functions and are usually present during the ECM remodelling that is associated with morphogenesis or disease. Regulated synthesis and degradation are key factors in maintaining a delicate balance between structural (homeostatic) and signalling

Conversely, breast tumour cells can be reverted by blocking signalling through ECM receptors, including integrins (Turley *et al*., 2008) and HA receptors such as RHAMM (Hall *et al*., 1995). These and other studies have revealed a key role of ECM in initiating and sustaining breast cancer and introduced the novel concept that transformation can be a plastic rather than irreversible process. Specifically, increased HA accumulation in tumour cells or stroma is associated with poor outcome in Breast Cancer (BCA) (Tammi *et al.*, 2008). These studies predict that HA is an important component of ECM that determines a

HA belongs to the glycosaminoglycan group of polysaccharides composed of disaccharide units of a hexose linked to a hexosamine. It consists of repeating units of *N*-acetyl glucosamine and -glucuronic acid (Fig. 2). The native polymer consists of up to 106 to 107 non-branching disaccharide units. The functions of HA within the ECM and cells depend upon its molecular weight, the type of cell, and the HA receptor(s) that target cells express. High molecular weight HA (e.g. >200 kDa) is a major biomechanical factor in ECM, which contributes to tissue hydration and elasticity by providing a template for the assembly of macromolecular complexes. A well known example is the "bottle brush" complex of aggrecan and link proteins, which provides the visco-elastic nature of synovial fluid. HA fragments provide signalling functions and are usually present during the ECM remodelling that is associated with morphogenesis or disease. Regulated synthesis and degradation are key factors in maintaining a delicate balance between structural (homeostatic) and signalling

Fig. 1. Breast tumour microenvironment

homeostatic vs. tumourigenesis "switch".

**2. HA biology** 

**2.1 Biochemical properties** 

(wound and disease) functions of HA (Itano *et al.*, 2008, Jiang *et al.*, 2007, Veiseh and Turley, 2011). BCA cells are particularly adept at producing and responding to HA fragments. BCA cells produce increased levels of HA by increasing HA synthase expression, rapidly fragmenting HA as a result of increased Reactive Oxygen Species (ROS) production, and increasing hyaluronidase expression and release, and increasing expression and display of HA receptors to elevate the response to these fragments (Simpson and Lokeshwar, 2008, Toole and Slomiany, 2008, Veiseh and Turley, 2011).

Fig. 2. HA structure and molecular weight ranges.
