Paul A. Konowicz

Drug Delivery and Medical Applications of Chemically Modified Hyaluronan

Publisher Summary Hyaluronan (HA) is a linear naturally occurring polyanionic polysaccharide that is ubiquitous in nature and is produced virtually by every tissue in higher organisms and some bacteria. HA has excellent biocompatibility and is readily catabolized and cleared in vivo. For these reasons, there has been a significant commercial focus on the development of products either from HA or from chemically modified derivatives of HA. HA and HA plus chemically cross-linked HA preparations are the principal components in several viscosupplements for patients with early-stage osteoarthritis of the knee. Conjugation of drugs to HA holds great promise for the generation of a new class of polymer-based therapeutics. These polymer-based systems can serve not only a biomaterials-based function, such as the separation or bulking of tissue, but also as concomitant drug delivery systems for the local delivery of therapeutics. Drugs conjugated to HA could also serve to target the drug to cells or tissues in the body that are rich in HA-binding receptors, such as CD44, RHAMM, TLR2, and TLR4. One of the most promising uses of chemically modified HA is in the area of tissue engineering. HA is found in the extracellular matrix of virtually all tissues so its use as a cell delivery vehicle is obvious. The combination of cell delivery and drug attachment to HA offers a very versatile material for the development of sophisticated products to address complex and unmet medical needs.

Glycan Structure Determinants for Cation-Independent Mannose 6-Phosphate Receptor Binding and Cellular Uptake of a Recombinant Protein

The cation-independent mannose 6-phosphate receptor (CI-MPR) plays a critical role in intracellular transport of lysosomal enzymes as well as the uptake of recombinant proteins. To define the minimal glycan structure determinants necessary for receptor binding and cellular uptake, we synthesized a series of glycans containing mono-, di-, tri-, tetra-, and hexamannoses terminated with either one or two phosphates for conjugating to a model protein, recombinant human acid α-glucosidase. A high affinity interaction with the CI-MPR can be achieved for the enzyme conjugated to a dimannose glycan with a single phosphate. However, tightest binding to a CI-MPR affinity column was observed with a hexamannose structure containing two phosphates. Moreover, maximal cellular uptake and a 5-fold improvement in in vivo potency were achieved when the bisphosphorylated hexamannose glycan is conjugated to the protein by a β linker. Nevertheless, even a monophosphorylated dimannose glycan conjugate showed stronger binding to the receptor affinity column, higher cellular uptake, and significantly greater in vivo efficacy compared to the unconjugated protein which contains a low level of high affinity glycan structure. These results demonstrate that the phosphorylated dimannose moiety appears to be the minimal structure determinant for enhanced CI-MPR binding and that the orientation of the glycan is critical for maximum receptor interaction. In summary, we have improved the understanding of the mechanism of CI-MPR binding and developed a simple alternative for CI-MPR targeting.