Stability of the disulfide bond in an avidin-biotin linked chimeric peptide during in vivo transcytosis through brain endothelial cells

Drug delivery of potential neuropharmaceuticals with poor intrinsic permeab ility through the blood-brain barrier (BBB). such as peptides, is facilitat ed by coupling to a vector that undergoes receptor-mediated transcytosis th rough the endothelial cells of brain microvessels. When cleavable disulfide linkers are used in the synthesis of such "chimeric peptides", it is cruci al that the S-S-bridge is stable during transcytosis. Cleavage within endot helial cells could result in sequestration of the drug moiety instead of pa ssage through the BBB. In the present study the metabolically stable opioid peptide [H-3]DALDA ([H-3]Tyr-DArg-Phe-Lys-NH2) was used as a model drug. I t was monobiotinylated with the cleavable biotin reagent sulfosuccinimidyl 2-(biotinamido)ethyl-1,3'-dithiopropionate (NHS-SS-biotin) to obtain bio-[H -3]DALDA. The biotinylated peptide was then bound to a vector for brain del ivery after intravenous injection in rats, a covalent conjugate of streptav idin and the transferrin receptor monoclonal antibody, OX26. Compared to pe ptide without vector, brain uptake of bio-[H-3]DALDA after was increased 18 -fold to reach 0.12% of the injected dose per g tissue. Transcranial microd ialysis was performed for 60 min after an intravenous bolus of chimeric pep tide. followed by reverse phase HPLC of dialysate. Stability of the chimeri c peptide during transport through the BBB into brain extracellular fluid w as concluded from the absence of a peptide peak generated by disulfide clea vage.