Chemical modification of enzyme molecules to improve their characteristics

Effect of Modification Strategies on the Biological Activity of Peptides/Proteins

Covalent attachment of biologically active peptides/proteins with functional moieties is an effective strategy to control their biodistribution, pharmacokinetics, enzymatic digestion, and toxicity. This review focuses on the characteristics of different modification strategies and their effects on the biological activity of peptides/proteins and illustrates their relevant applications and potential.

Biopolymer Molecular Weight Can Modulate the Wound Healing Efficacy of Multivalent Sonic Hedgehog-Hyaluronic Acid Conjugates

There is a clinical need for new therapeutics to improve healing of chronic impaired wounds. Thus, we investigated how biopolymer conjugation could be used to improve the wound healing performance of a key growth factor for tissue regeneration: Sonic hedgehog (Shh). We generated two multivalent Shh conjugates (mvShh) using hyaluronic acid with two different MWs, which exhibited equivalent potency and proteolytic protection in vitro. Using db/db diabetic mice, we showed that mvShh made with smaller HyA MW resulted in more rapid and robust neovascularization compared to mvShh made with larger MW HyA. Further, smaller mvShh conjugates resulted in faster wound resolution compared to the unconjugated Shh. This study is the first to show how the wound healing efficacy of multivalent protein-polymer conjugates is sensitive to the polymer MW, and our findings suggest that this parameter could be used to enhance the efficacy of growth factor conjugates.

Role of tumor vascular architecture in drug delivery

Tumor targeted drug delivery has the potential to improve cancer care by reducing non-target toxicities and increasing the efficacy of a drug. Tumor targeted delivery of a drug from the systemic circulation, however, requires a thorough understanding of tumor pathophysiology. A growing or receding (under the impact of therapy) tumor represents a dynamic environment with changes in its angiogenic status, cell mass, and extracellular matrix composition. An appreciation of the salient characteristics of tumor vascular architecture and the unique biochemical markers that may be used for targeting drug therapy is important to overcome barriers to tumor drug therapy and to facilitate targeted drug delivery. This review discusses the unique aspects of tumor vascular architecture that need to be overcome or exploited for tumor targeted drug delivery.

ATTEMPTS: a heparin/protamine-based triggered release system for the delivery of enzyme drugs without associated side-effects

A prodrug type delivery system based on competitive ionic binding for the conversion of the prodrug to an active drug has been developed for delivery of enzyme drugs without their associated toxic side-effects. This approach, termed "ATTEMPTS" (antibody targeted, triggered, electrically modified prodrug-type strategy), would permit the administration of an inactive drug and then subsequently triggered release of the active drug at the target site. The underlying principle was to modify the enzyme with small cationic species so that it could bind a negatively charged heparin-linked antibody, and the latter would block the activity of the enzyme drug until it reached the target. To provide the enzyme drug with appropriate binding strength to heparin, a cationic poly(Arg)(7) peptide was incorporated onto the enzyme either by the chemical conjugation method using a bifunctional crosslinker or by the biological conjugation method using the recombinant methodology. Methods for drug modification, heparin-antibody conjugation, and the prodrug and triggered release features of the "ATTEMPTS" approach are described in detail in this review article.

Polysialylated asparaginase: preparation, activity and pharmacokinetics

Erwinia carotovora L-asparaginase was coupled covalently to colominic acid, a low molecular mass polysialic acid, by reductive amination. Depending on the molar ratios of colominic acid-asparaginase (50:1, 100:1 and 250:1), polysialylated constructs contained 4.2-8.1 molecules of colominic acid per molecule of enzyme. Such constructs retained most (82-86%) of the initial asparaginase activity and also maintained the Km values of the native enzyme towards the substrate asparagine. On exposure to (mouse) blood plasma at 37 degrees C, polysialylated asparaginase constructs exhibited resistance to proteolysis with 65-83% of the initial enzyme activity still present after 6 h. In contrast, most of the native enzyme was inactivated under the same conditions. In vivo experiments with intravenously injected mice revealed a significant increase in the half-life of the polysialylated asparaginase over that observed with the native enzyme. Such an increase was greatest (250%, about 38 h) for the construct with the highest degree of polysialylation. Results suggest that polysialylation of asparaginase and other proteins may provide an alternative means to improve their effective use in therapeutics.