pH-Responsive Oligodeoxynucleotide (ODN)−Poly(Ethylene Glycol) Conjugate through Acid-Labile β-Thiopropionate Linkage:  Preparation and Polyion Complex Micelle Formation

Abstract

An oligodeoxynucleotide (ODN) conjugated to poly(ethylene glycol) (PEG) through a pH-responsive ester linkage (PEG-ODN conjugate) was successfully synthesized by the Michael reaction of 3'-thiol-modified ODN with a heterobifunctional PEG bearing an acetal group at the alpha-end and an acrylate group at the omega-end (acetal-PEG-acrylate), aimed at the development of a novel ODN delivery system. The prepared PEG-ODN conjugate and linear-poy(ethyleneimine) (L-PEI) spontaneously associated to form a polyion complex (PIC) micelle whose diameter and polydispersity index micro(2)/Gamma(2)) were 102.5 nm and 0.096 as determined by DLS measurements, respectively. Both the PEG-ODN conjugate and PIC micelle showed cleavage of the ester linkage at the endosomal pH (=5.5), suggesting that the PIC micelle is anticipated to release the ODN in the intracellular compartment. Furthermore, the PEG-ODN conjugate in the PIC micelle was stable against deoxyribonuclase (DNase I) digestion and has no interaction with the serum component because of the steric stabilization of the highly dense PEG corona surrounding the PIC core. These characteristics of the PIC micelles entrapping the PEG-ODN conjugate are promising for their utility as a novel ODN delivery system.

Site-Specific Delivery of Oligonucleotides to Hepatocytes after Systemic Administration

“…In contrast, this conjugate was fairly stable in rat serum for at least 4 h. The result suggests that the conjugate was fairly stable in serum, but its acid labile ester linkage can be cleaved at acidic pH. Our study also confirmed the previous report about this kind of conjugates by Oishi et al (23).…”

“…Therefore, we synthesized Gal-PEG and conjugated to ODN by β-thiopropionate, an acid-labile linkage which is easily cleaved at acidic pH, leading to endosomal release of ODNs after endocytosis (23). Following synthesis and characterization, we determined the biodistribution at whole body, organ (liver) and cellular (liver cells) levels after systemic administration of Gal-PEG-33 P-ODN in rats.…”

Theranostic pH-sensitive nanoparticles for highly efficient targeted delivery of doxorubicin for breast tumor treatment

“…30,31 The protonated tertiary amine groups of the aminoester segments and PEG segments, and other low MW segments, were water soluble and easily metabolized.…”

Design of Lipid and Polymeric Carriers for Nucleic Acid Delivery

“…Therefore, we synthesized Gal-PEG and conjugated to ODN by β-thiopropionate, an acid-labile linkage which is easily cleaved at acidic pH, leading to endosomal release of ODNs after endocytosis (196). Following synthesis and characterization, we determined the biodistribution at whole body, organ (liver) and cellular (liver cells) levels after systemic administration of Gal-PEG-33 P-ODN in rats.…”

“…However, these PEG-ODN conjugates were less effective, since PEG could not be cleaved early from the ODNs in the cytoplasm. Therefore, Oishi et al conjugated ODN to acrylated or lactosylated PEG through a pH-responsive ester (139,196). However, these authors did not determine the biodistribution of Lac-PEG-ODN and used in conjunction with a cationic polymer like linear polyethyleneimine (PEI), which is likely to promote nonspecific interaction with plasmaproteins and uptake by phagocytic cells.…”