Delivering Molecules to the Brain using Blood-Brain Barrier Modulators: Mechanism of Action and Activity of Cyclic and Linear Peptides from E-cadherin.

摘要

The goals of this work are to (a) compare the blood-brain barrier (BBB) modulatory activities of cyclic cHAVc3 (cyclo(1,6)Ac-CSHAVC-NH2) and linear HAV4 (Ac-SHAVAS-NH2) peptides, (b) compare the rat plasma stability of HAV4 and cHAVc3, and (c) probe the mechanism of binding of HAV peptides (i.e., HAV6, cHAVc3) and ADT peptides (i.e., ADTc5, ADTc7, ADTc9) to the EC1 domain of E-cadherin. The cyclic and linear HAV and ADT peptides were derived from the EC1 domain of human E-cadherin. Cyclic cHAVc3 was more effective than linear HAV4 in modulating MDCK cell monolayers and in improving in vivo brain delivery of Gd-DTPA upon i.v. administration in Balb/c mice. In vivo, the duration of the BBB modulation was longer for cyclic cHAVc3 (2--4 h) than for linear HAV4 (<1 h). Both HAV4 and cHAVc3 peptides also enhanced the in vivo brain delivery of IRdye800cw-PEG (25 kDa) as detected by near IR imaging. Cyclic cHAVc3 (t1/2 = 12.95 h) has better plasma stability compared to linear HAV4 (t1/2 = 2.4 h). Using 2D 1H,- 15N-HSQC NMR, molecular dynamics, and molecular docking simulations, cyclic cHAVc3 peptide was shown to bind at residues Y36, S37, I38, I53, F77, S78, H79, and I94 on the EC1 domain of human E-cadherin. Using chemical shift perturbations of several residues, the dissociation constants (Kd values) of cHAVc3 peptide to EC1 were estimated to be between 0.5 x 10-5 and 7.0 x 10-5 M. In summary, cyclic cHAVc3 peptide has better plasma stability and in vitro and in vivo activities to modulate BBB than linear HAV4 peptide. The proposed mechanism of modulatory activity of HAV and ADT peptides is due to binding to the EC1 domain of E-cadherin. Using NMR and molecular docking techniques, HAV and ADT peptides were found to bind to the EC1 domain and the binding site of HAV peptides in EC1 was different from ADT peptides. The ADT and HAV peptides bind to the EC1 domain with different affinities. ADTc5 and ADTc7 peptides showed lower dissociation constants (Kd ~ 10 muM) than ADTc9 peptide that showed a higher Kd values (Kd ~ 190 muM). HAV6 peptide showed similar binding site for cHAVc3 peptide on the EC1 domain with higher Kd values (Kd ~ 190 muM) in comparison to cHAVc3 peptide (Kd ~ 5 muM).