Design, synthesis, characterization and in-vivo activity of a novel salmon calcitonin conjugate containing a novel PEG-lipid moiety

Abstract

OBJECTIVES: The aim of the study was to explore (1) the synthesis of a novel poly(ethylene glycol) modified lipid (PEG-lipid, PL) containing a chemically active tri-block linker, epsilon-maleimido lysine (Mal), and its conjugation with salmon calcitonin (sCT), and (2) the biophysical properties and activity of the resulting conjugate, Mal-PL-sCT, relative to the control, 2PEG-Mal-sCT, which comprises sCT conjugated with alpha-palmitoyl-N-epsilon-maleimido-L-lysine at cysteine 1 and cysteine 7, and PEG moieties at lysine 11 and lysine 18 via a conventional stepwise method. METHODS: The PEG-lipid was obtained by condensing palmitic acid derivative of epsilon-maleimido lysine with methoxy poly(ethylene glycol) amine. Under reductive conditions, the PEG-lipid readily reacted with sCT to yield the resultant compound, Mal-PL-sCT. KEY FINDINGS: Dynamic light scattering analyses suggested that Mal-PL-sCT and 2PEG-Mal-sCT exhibited robust helical structures with a high tendency to aggregate in water. Both compounds were more stable against intestinal degradation than sCT, although Mal-PL-sCT was less stable than 2PEG-Mal-sCT. However, 2PEG-Mal-sCT did not possess hypocalcaemic activity while Mal-PL-sCT retained the hypocalcaemic activity of sCT when it was subcutaneously injected in the rat model. Multiple functional groups may be conjugated to a peptide via a tri-block linker without the risk of obliterating the intrinsic bioactivity of the peptide. CONCLUSIONS: The resultant novel PEG-lipid has a potential role to optimize protein and peptide delivery.