Abstract
Drug/polymer interactions occur during in situ polymerization of poly(alkylcyanoacrylate) (PACA) formulations. We have used MALDI ionization coupled tandem time-of-flight (TOF) mass spectrometry as an accurate method to characterize covalent peptide/polymer interactions of PACA nanoparticles with the bioactives D-Lys6-GnRH, insulin, [Asn1-Val5]-angiotensin II, and fragments of insulin-like growth factor 1 (IGF-1 (1-3)) and human adrenocorticotropic hormone (h-ACTH, (18-39)) at the molecular level. Covalent interactions forming peptide/PACA co-polymers were identified for D-Lys6-GnRH, [Asn1- Val5]-angiotensin II and IGF-1 (1-3). D-Lys6-GnRH and [Asn1-Val5]-angiotensin II were modified at their histidine side chain within the peptide, whilst IGF-1 (1-3) was modified at the C-terminal glutamic acid residue. The more complex protein insulin did not co-polymerize despite the presence of 2 histidine residues. This might be explained by the engagement of histidine residues in the folding and sterical arrangement of insulin under polymerization conditions. As expected, h-ACTH (18-39) that does not contain histidine residues did not co- polymerize. Lowering the pH did not prevent the co-polymerization of PACA with D-Lys6- GnRH or IGF-1 (1-3). Conclusively, protein and peptide bioactives are potentially reactive towards PACA nanoparticles via various mechanisms with limited interference of pH. Histidines and C-terminal glutamic acid residues have been identified as potential sites of interaction. The likelihood of their engagement in co-polymerization, however, seems dependant on their sterical availability. The potential for co-polymerization should be considered when designing a PACA delivery system for protein and peptide biopharmaceuticals.