PEGylation of octreotide: I. Separation of positional isomers and stability against acylation by poly(D,L-lactide-co-glycolide).
OBJECTIVE
To investigate the mechanism by which polyethylene glycol (PEG) conjugation (PEGylation) prevents the acylation of octreotide by poly(d,l-lactide-co-glycolide) (PLGA).


METHODS
Octreotide was chemically modified by reaction with succinimidyl propionate-monomethoxy PEG. Each PEGylated octreotide species with different PEG number and modified position was separated by reversed-phase high-performance liquid chromatography (RP-HPLC) and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with endoproteinase Lys-C digestion. Acylation of octreotide and PEGylated octreotides was observed with hydrophobic and hydrophilic PLGA.


RESULTS
Two mono- and one di-PEGylated octreotides were separated by RP-HPLC. MALDI-TOF MS of the PEGylated products after Lys-C digestion at different pH revealed that the two mono-PEGylated octreotides were modified at the N-terminus and Lys(5) residue, respectively. The interaction of octreotide with PLGA involved an initial adsorption followed by acylation and the subsequent release of octreotide and acylated octreotide. The initial adsorption of octreotide was dependent on the acidity of PLGA. PEGylation of octreotide significantly inhibited the initial adsorption and acylation by PLGA. In particular, the acylation could be completely prevented by mono-PEGylation at the N-terminus of octreotide.


CONCLUSIONS
This study shows that the N-terminus of octreotide is the preferred PEGylation site to prevent acylation in degrading PLGA microspheres. The mono-N-terminally PEGylated octreotide may possibly serve as a new source for somatostatin microsphere formulation.
Na
Dong Hee
DH
College of Pharmacy, Kyungsung University, Busan, South Korea.
DeLuca
Patrick P
PP
D000215:Acylation / Q000187:drug effects*; D000327:Adsorption / Q000187:drug effects; D000595:Amino Acid Sequence / Q000187:drug effects / Q000502:physiology; D002626:Chemistry, Pharmaceutical / Q000379:methods; D002851:Chromatography, High Pressure Liquid; D004347:Drug Interactions; D004355:Drug Stability; D007536:Isomerism; D019344:Lactic Acid / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D015282:Octreotide / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D011092:Polyethylene Glycols / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D011100:Polyglycolic Acid / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D013678:Technology, Pharmaceutical / Q000379:methods
D011108:Polymers; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; D011092:Polyethylene Glycols; D015282:Octreotide