Galectins are b-galactoside binding, Ca2+-independent lectins.1,2 In normal cells, galectins regulate cell growth, adhesion, differentiation, and death.3,4 In cancer biology, galectins play an important role in processes including tumor angiogenesis, cancer cell aggregation and migration.5,6,7 Galectin-3 is a chimera galectin with one carbohydrate-binding domain that binds to galactose, lactose, and N-acetyllactosamine (LacNAc) ligands and a proline/glycine-rich, collagen-like domain (Figure 1).8,9Galectin-3 is a monomeric, 31 kDa lectin that oligomerizes both at high concentrations and upon binding to carbohydrate arrays.10,11 Galectin-3 interactions with the extracellular matrix (ECM) may be more significant for cancer cells than for normal cells because of the aberrant glycosylation patterns that are present on cancer cells. The roles of external galectin-3 in cancer include mediation of processes such as angiogenesis, cellular aggregation, tumor invasion and metastasis.12,13 Recombinant human galectin-3 is grown from E. coli cells and purified in our labs using technology provided to us from Dr. Avraham Raz. Dr. Raz (Karmanos Cancer Institute, Wayne State University) continues to perform collaborative experiments with us to study galectin-3 mediated pathways.

galectin

Figure 1. The carbohydrate recognition domain of galectin-3.9

We have synthesized galactose, N-acetylgalactosamine (GalNAc), and lactose functionalized dendrimers for binding to galectin-3. We have also synthesized heterogeneously-functionalized dendrimers bearing Gal/GalNAc and Gal/Lac mixtures in varying ratios (Figure 2). Inhibition ELLAs (enzyme linked lectin assays) in which the glycodendrimers were attached to polystyrene plates and binding of galectin-3 to the glycodendrimer-functionalized surfaces was inhibited by lactose were performed. Galectin-3 recruitment was highest for dendrimers bearing the most lactose (the higher affinity monomer) and was lowest for dendrimers bearing galactose (the lower affinity monomer). Overall, our results indicate that varying the display of low and high affinity ligands alters galectin binding in predictable ways.

glycodendrimer

Figure 2. Gal/Lac functionalized dendrimers. Values for a and b range from 0% to 100% carbohydrate incorporation.

To discern the degree to which these results translate into measurable cellular behavior, we are currently performing a variety of cell based assays using the glycodendrimers with cancer cells.  We are evaluating the effect of the glycodendrimers on cancer cellular aggregation and migration.  These studies are ongoing.

References

  1. Klyosov, A. A.; Witczak, Z. J.; Platt, D., Galectins. Wiley: Hoboken, 2008.
  2. Barondes, S. H.; Castronovo, V.; Cooper, D. N. W.; Cummings, R. D.; Drickamer, K.; Feizi, T.; Gitt, M. A.; Hirabayashi, J.; Hughes, C.; Kasai, K.; Leffler, H.; Liu, F. T.; Lotan, R.; Mercurio, A. M.; Monsigny, M.; Pillai, S.; Poirer, F.; Raz, A.; Rigby, P. W. J.; Rini, J. M.; Wang, J. L., Galectins-A Family of Animal Beta-Galactoside-Binding Lectins. Cell 1994, 76 (4), 597-598.
  3. Cooper, D. N. W., Galectinomics: finding themes in complexity. Biochimica Et Biophysica Acta-General Subjects 2002,1572 (2-3), 209-231.
  4. Ilarregui, J. M.; Bianco, G. A.; Toscano, M. A.; Rabinovich, G. A., The coming of age of galectins as immunomodulatory agents: impact of these carbohydrate binding proteins in T cell physiology and chronic inflammatory disorders. Annals of the Rheumatic Diseases 2005, 64, 96-103.
  5. Le Mercier, M.; Fortin, S.; Mathieu, V.; Kiss, R.; Lefranc, F., Galectins and Gliomas. Brain Pathology 2010, 20 (1), 17-27.
  6. Liu, F. T.; Rabinovich, G. A., Galectins as modulators of tumour progression. Nature Reviews Cancer 2005, 5 (1), 29-41.
  7. Lahm, H.; Andre, S.; Hoeflich, A.; Kaltner, H.; Siebert, H. C.; Sordat, B.; von der Lieth, C. W.; Wolf, E.; Gabius, H. J., Tumor galectinology: Insights into the complex network of a family of endogenous lectins. Glycoconjugate Journal 2003, 20 (4), 227-238.
  8. Dumic, J.; Dabelic, S.; Flogel, M., Galectin-3: An open-ended story. Biochimica Et Biophysica Acta-General Subjects2006, 1760 (4), 616-635.
  9. Sorme, P.; Arnoux, P.; Kahl-Knutsson, B.; Leffler, H.; Rini, J. M.; Nilsson, U. J., Structural and thermodynamic studies on cation - II interactions in lectin-ligand complexes: High-affinity galectin-3 inhibitors through fine-tuning of an arginine-arene interaction. Journal of the American Chemical Society 2005, 127 (6), 1737-1743.
  10. Hsu, D. K.; Kuwabara, I.; Liu, F. T., Galectin-3 and regulation of cell function. Transfusion Medicine and Hemotherapy2005, 32 (2), 83-96.
  11. Ochieng, J.; Furtak, V.; Lukyanov, P., Extracellular functions of galectin-3. Glycoconjugate Journal 2002, 19 (7-9), 527-535.
  12. Nangia-Makker, P.; Balan, V.; Raz, A., Regulation of Tumor Progression by Extracellular Galectin-3. Cancer Microenvironment 2008, 1, 43-51.
  13. Califice, S.; Castronovo, V.; Van Den Brule, F., Galectin-3 and cancer. International Journal of Oncology 2004, 25 (4), 983-992.