P5-07-04: Is a-L-Fucose Overexpressed on Cells of Aggressive Human Breast Cancers?

Abstract Enzymatic removal of a-L-fucose (fucose) was shown over 20 years ago to abolish metastases in vivo in a rat model of mammary adenocarcinoma [J Cell Biochem 1988; 37: 49–59]. Since that time, evidence has accumulated to indicate that fucose is a functional effector in human breast cancer; essential for construction of the invasive and metastatic phenotypes. In light of these findings, the role of fucose in aggressive breast cancers is worthy of further investigation. Our group has modified the method of Wright et al. in order to selectively remove cell surface fucose from viable human breast cancer cells in vitro. In our experience, a 30 min incubation of breast cancer cells with α-L-fucosidase (3.2.1.51) leads to a loss of transformative abilities including decreased cancer cell adhesion to select extracellular matrix components, decreased invasion into complex extracellular matrices, decreased binding by relevant antibodies and lectins, and decreased adhesion of cells (rolling) to model endothelium under shear stress flow conditions. From this work we postulated that decisive differences in phenotypic and functional properties between treated and control human breast cancer cells should be obtainable with currently available models of aggressive disease. To that end, we and others have subsequently shown that human breast cancer cells express cell surface CD44 which carries fucosylated ligands and that its’ defucosylation altered its’ malignant phenotype.. Based on these precedents, it is reasonable to hypothesize that CD44-enriched breast cancer stem cell populations require fucose in order to exert their aggressive behavior. Assays to assess the role of fucose in these stem cells are apparent and include a battery of tests involving stem cell invasion into extracellular matrices, cell binding of antibodies or fucolectins, stem cell aggregation into spheroids, colony formation in soft agar, assessment of stem cell rolling/adhesion to endothelial cells or purified E-selectin under both static or physiological flow conditions and the ability to initiate tumors upon inoculation into animal models. We believe that new insights into aggressive breast cancer cell behaviors can be gained through the depletion of cell surface fucose from breast cancer cells. Knowledge gained from these studies should yield new insights when using current models of human breast cancer in vitro and in vivo. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-07-04.</jats:p

P2-18-06: Conventional Trastuzumab Is an Antagonist of Natural Killer Cells: Making the Case for Fucose-Depleted Trastuzumab.

Abstract The discovery of the HER2 receptor and later the development of trastuzumab (an anti-HER2 antibody) were major advances leading toward the treatment of a significant proportion of human breast cancers. Trastuzumab (Herceptin®) is a humanized monoclonal IgG1 whose discrete antitumor effects are exerted through the 2 main components of the antibody. Trastuzumab's FAB portion binds to the HER2 extracellular domain, interrupting HER2 signaling. The FC portion then engages the activating receptor (FcγRIIIa) on an effector cell, usually a natural killer (NK) cell and instigates a lytic attack via antibody-dependent cellular cytotoxicity (ADCC). The value of trastuzumab in breast cancer therapy is well established, but, there are limitations to the drug's effectiveness. These include: (1) unresponsive tumors with low or equivocal HER2 expression; (2) de novo (primary) resistance to therapy in over 50% of patients with HER2−positive tumors; (3) frequent emergence of secondary resistance often after short exposure periods; (4) competition of plasma IgG proteins with antibodies for binding to the activating FC receptors on NK cells; and (5) the high cost of trastuzumab treatment, raising concerns for the economic sustainability of this form of therapy. Trastuzumab and other therapeutic antibodies share a structural feature that is critical to their effectiveness: a specific oligosaccharide which is covalently linked to the FC region at asparagine 297 (Asn297) in each of the 2 heavy chains. This oligosaccharide, a mannosyl-chitobiose core, is “core-fucosylated” with a single α-L-fucose (fucose) sugar attached via an α(1,6) linkage. In 2002, Shields et al. developed a novel form of trastuzumab which lacked core fucose in the Fc region [J Biol Chem 2002; 277: 26733–40]. When compared to conventional trastuzumab, the fucose-depleted trastuzumab was 43-fold more potent in provoking ADCC against HER2−expressing human breast cancer cells in vitro. Subsequent studies with several monoclonal antibodies have elucidated the role of core fucose in inhibiting ADCC, by reducing the affinity of trastuzumab's Fc portion for the activating FC receptors located on effector cells. The superior ADCC effect of fucose-depleted trastuzumab has now been demonstrated in vivo [Junttila TT et al., Cancer Res 2010; 70: 4481–4489]. We review both in vitro and in vivo evidence from multiple laboratories (working with trastuzumab, rituximab and other therapeutic antibodies) to argue that fucose-depleted trastuzumab offers several potential advantages over conventional trastuzumab. Such advantages in clinical use, we postulate, include (1) treatment of patients with trastuzumab-resistant tumors, (2) treatment of patients with equivocal or low expression of HER2, and (3) decreased cost of treatment. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-18-06.</jats:p