**1. Introduction**

434 Breast Cancer – Focusing Tumor Microenvironment, Stem Cells and Metastasis

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Breast cancer is the most common cancer diagnosis among women worldwide (Jemal et al., 2011). Significant numbers of women present with advanced metastatic breast cancer despite major improvements in population screening and health awareness (Breast Cancer Facts & Figures 2009-2010, 2009; Autier et al., 2011). Metastatic spread leads to the poor prognosis and incurring low survival rates of patients presenting with advanced stage breast cancer or tumor recurrence. Therefore, effective therapies targeting metastatic spread should be designed to prevent the devastating consequences of breast cancer progression. In this regard, novel pro-metastatic molecules must be identified and their functional roles in the progression of the disease need to be addressed.

Cell–cell and cell–matrix adhesions have a profound role in the hematogenous phase of cancer metastasis. Tumor-associated glycans participate in these cell–cell and cell–matrix adhesions and their expression is associated with the metastatic potential of tumor cells and the prognosis of cancer patients (Hakomori, 1996; Couldrey and Green, 2000; Gorelik et al., 2001; Kawaguchi, 2005; Korourian et al., 2008).

We have been studying the role carbohydrates play in breast cancer metastasis (Monzavi-Karbassi et al., 2005; Carcel-Trullols et al., 2006; Monzavi-Karbassi et al., 2007). A large body of evidence indicates that P-selectin expressed on endothelial cells and platelets plays a crucial role during hematogenous metastasis (Borsig et al., 2001; Kohler et al., 2010). In a murine model of breast cancer we observed that the expression of carbohydrates that react with the P-selectin receptor plays a major role in metastasis (Monzavi-Karbassi et al., 2005). This evidence indicates that P-selectin-mediated interaction of breast cancer cells with platelets is a relevant cellular adhesion mechanism that participates in establishing distant metastases. A novel finding in our work is the observation that chondroitin sulfate glycosaminoglycans (CS-GAGs) can serve as P-selectin ligands on breast cancer cells. This observation links CS-GAGs to P-selectin binding in defining the metastatic phenotype dependent on the interaction of cancer cells with platelets (Monzavi-Karbassi et al., 2007). Therefore, CS-GAGs can be targeted for development of novel anti-metastatic therapies.

On the Role of Cell Surface Chondroitin Sulfates and

Disaccharide repeat

3GalNAc(4S)]

3GalNAc(4S)]

3GalNAc(6S)]

3GalNAc(6S)]

3GalNAc(4S,6S)]

3GalNAc(4S,6S)]

Chondroitin

A [GlcUA1-

C [GlcUA1-

D [GlcUA(2S)1-

E [GlcUA1-

iE [IdoUAα1-

Table 1. Chondroitin sulfate types

surface CS glycans is highly significant

**2.1 Biological functions of CS/DS chains** 

B [IdoUA(2s)α1-

type

Their Core Proteins in Breast Cancer Metastasis 437

The Chondroitin chain backbone consists of repetitive disaccharide units containing Dglucuronic acid (GlcUA) and *N*-acetyl-D-galactosamine (GalNAc) residues. They further differentiate into variable chains with distinct structures and functions after various modifications. Sulfation and epimerization will further generate CS/DS isomers (**Table 1**). DS or CS-B is a stereoisomeric variant of CS with varying proportions of L-iduronic acid (IdoUA) in place of GlcUA, which forms by epimerization of GlcUA to IdoUA (**Table 1**).

Modifying enzymes

CHST12 and CHST13)

14 (CHST14)

sulfotransferase)

The monosulfated disaccharide A-unit [GlcUA-GalNAc(4S)] and C-unit [GlcUA-GalNAc(6S)] are common and major components of mammalian CS chains. Disulfated disaccharide D-unit [GlcUA(2S)-GalNAc(6S)] and E-unit [GlcUA-GalNAc(4S,6S)] also exist

CS/DS chains that often found as CS/DS hybrid structures have the potential to display an enormous structural diversity by embedding multiple overlapping sequences constructed with distinct disaccharide blocks modified by different patterns of sulfation (Kusche-Gullberg and Kjellen, 2003; Sugahara et al., 2003). Given the complexity of these structures, the expression of modifying enzymes may correlate better with an aggressive tumor phenotype. Therefore, linking the expression of these enzymes with a functional role of cell

CS/DS chains specifically interact with heparin binding proteins. The interaction of DS chains with fibroblast growth factor (FGF) activates FGF-2 to signal cell proliferation (Penc et al., 1998). DS also acts as a cofactor for FGF-7 (Trowbridge et al., 2002). In addition, DS has been shown to bind and activate hepatocyte growth factor/scatter factor (HGF/SF), a

that are based on further sulfation of monosulfated C and A units, respectively.

Carbohydrate (chondroitin-4)

Carbohydrate (chondroitin 6) sulfotransferase 3 (CHST3 ) and

sulfotransferase 7 (CHST7)

sulfotransferase 11, 12 and 13 (CHST11,

Uronyl-2-O-sulfotransferase (UST) and CHST11, CHST12 and Carbohydrate (Nacetylgalactosamine 4-O) Sulfotransferase

Carbohydrate (N-acetylglucosamine 6-O)

CHST11, CHST12, CHST13 and CHST15 (N-acetylgalactosamine 4-sulfate 6-O-

UST, CHST3 and CHST7 -

CHST11, CHST12, CHST14 and CHST15 Dermatan-

Sulfotransferase Epimerase




sulfate 5-epimerase

Dermatansulfate 5-epimerase

Large variation exists in CS-GAG sequences and in proteoglycans (PGs) presenting them. The prevalence of a presenting core protein may predict the functional outcomes of Pselectin-mediated adhesion of tumor cells. To use these molecules as targets for diagnostic or therapeutic purposes, a thorough understanding of their presentation and expression is necessary. This chapter reviews the biological roles of chondroitin sulfates (CS) in tumor development and metastasis and the role of different types of CS and the core protein carrying these polysaccharides.
