Direct polymer conjugation at peptide tyrosine residues
is described.
In this study Tyr residues of both leucine enkephalin and salmon calcitonin
(sCT) were targeted using appropriate diazonium salt-terminated linear
monomethoxy poly(ethylene glycol)s (mPEGs) and poly(mPEG) methacrylate
prepared by atom transfer radical polymerization. Judicious choice
of the reaction conditionspH, stoichiometry, and chemical
structure of diazonium saltled to a high degree of site-specificity
in the conjugation reaction, even in the presence of competitive peptide
amino acid targets such as histidine, lysines, and N-terminal amine. In vitro studies showed
that conjugation of mPEG2000 to sCT did not affect the
peptide’s ability to increase intracellular cAMP induced in
T47D human breast cancer cells bearing sCT receptors. Preliminary in vivo investigation showed preserved ability to reduce
[Ca2+] plasma levels by mPEG2000-sCT conjugate
in rat animal models.