An ongoing area of interest is in the development of agents that either block heparan sulfate-protein interactions or that exploit heparan sulfate proteoglycans as portals of entry for delivery of high molecular weight cargo into cells and tissues. In collaboration with Yitzhak Tor's group at UCSD, we have tested guanidinoglycosides as carriers. Guanidinoneomycin can carry large (>300 kDa) bioactive molecules across cell membranes. Delivery occurs at nanomolar transporter concentrations and under these conditions depends entirely on cell surface heparan sulfate proteoglycans. Conjugation of guanidinoneomycin to the plant toxin saporin, a ribosome-inactivating agent, results in proteoglycan-dependent cell toxicity. Conjugation of gunidinoneomycin to lysosomal enzymes allows reconstitution of lysosomal function in fibroblasts derived from patients with mucopolysaccharidoses (MPS). Recent work has shown that conjugation facilitates delivery to the brain, opening up the possibility of developing tools for treating various brain disorders.
Hereditary Multiple Exostosis (HME) is a dominant disorder characterized by the appearance of osteochondromas along the growth plate of endochondral bones. The disease arises from heterozygous mutations in Ext1 or Ext2, which encodie subunits of the copolymerase complex responsible for the formation of heparan sulfate. We have an ongoing project in collaboration with the Conrad Prebys High Content Screening Center to discover potential drugs for altering the expression of heparan sulfate as a therapeutic approach for treating HME. Drug-like agents have been found that modulate heparan sulfate formation. Current studies focus on their mechanism of action and optimization.
Sarrazin S., Wilson B., Sly W.S., Tor Y., Esko J.D. (2010) Guanidinylated neomycin mediates heparan sulfate-dependent transport of active enzymes to lysosomes. Mol. Therapy 18:1268-1274
Schuksz, M., Fuster, M.M., Brown, J.R., Crawford, B.E., Ditto, D.P., Lawrence, R., Glass, C.A., Wang, L., Tor, Y., and Esko, J.D. (2008) Surfen, a small molecule antagonist of heparan sulfate. Proc. Natl. Acad. Sci. 105:13075-13080
Zak, B.M.*, Schuksz, M.*, Koyama, E., Mundy, C., Wells, D.E., Yamaguchi, Y., Pacifici, M., Esko, J.D. (2011) Compound heterozygous loss of Ext1 and Ext2 is sufficient for formation of multiple exostoses in mouse ribs and long bones. Bone 48:979-987