Peptide Drug Improvement Using Vitamin B12 and Haptocorrin Binding Substrate Conjugates

The invention involves the coupling of compounds that can be bound by Haptocorrin (R-binder; Transcobalamin I; HC) to a target drug to improve pharmacokinetics, avoid undesirable side effects, and/or modify CNS access and localization. The pharmaceutical effect may be improved by conjugating the drug to haptocorrin binding substrate. This allows the conjugate to become bound to unsaturated haptocorrin in the blood, thereby protecting the drug from metabolism or excretion to increase protein half-life while not interfering with the efficacy of the protein drug. The conjugation may additionally prevent the drug from reaching the central nervous system or modify where the drug localizes and produces undesirable side effects such as nausea or hypophagia. Such a route also would prevent, in all case save for actual vitamin B12, binding by serum transcobalamin II (TCII), and thus not cause B12 deficiency with long term use.