Design, Synthesis, and Evaluation of Brain-Penetrant PACAP-Derived Glycopeptides for the Treatment of Neurodegeneration and Neuroinflammation

Abstract

Neurodegenerative disorders negatively impact the health of millions of people worldwide each year, and current therapeutic strategies only alleviate symptoms and exhibit little to no curative potential. Peptides comprise an important class of biological regulatory molecules that may be able to meet these concerns. Many endogenous peptides act as hormones, neuromodulators, secretagogues, and regulators of the inflammatory response. Furthermore, peptides are highly selective for their target receptors, leading to reduced side effect profiles, and they are regarded as non-toxic due to their metabolism yielding innocuous amino acids. However, progress in developing peptide drugs is hampered by their poor in vivo pharmacokinetic profiles, limited membrane permeability, and low oral bioavailability. Several chemical strategies including cyclization, N-methylation, lipidation, PEGylation, and incorporation of unnatural amino acids have been largely successful in improving the stability of peptides, but generally don’t elicit membrane penetration. One such chemical modification that can address the membrane permeability problem is glycosylation. Glycosylation has been demonstrated to improve water solubility and in vivo stability of peptides, and dramatically enhance penetration across biological membranes, most notably the blood-brain barrier (BBB). We have applied our glycosylation methodology to a variety of endogenous peptides, and this work summarizes the glycosylation of PACAP, a potential candidate for treating neurodegenerative disorders. Overall, we found that our PACAP glycopeptides exhibited superior stability in vitro and in vivo compared to their non-glycosylated counterparts while maintaining the intrinsic efficacy and potency of native PACAP. Most importantly, we found that our PACAP glycopeptides were able to penetrate the BBB in physiologically relevant concentrations and elicit neuroprotective and anti-inflammatory activities in animal models of Parkinson’s disease, stroke, and traumatic brain injury.