Physicochemical and biological characterisation of an antisense oligonucleotide targeted against the bcl-2 mRNA complexed with cationic-hydrophilic copolymers

The aim of this study was to evaluate the use of cationic-hydrophilic copol ymers for self-assembly with antisense oligonucleotides targeted to the bcl -2 mRNA in order to improve their biocompatibility and modulation of their pharmacokinetics for greater therapeutic usefulness, Examination of the abi lity of poly(trimethylammonioethyl methacrylate chloride)-poly[N-(2-hydroxy propyl)methacrylamide] (pHPMA-b-pTMAEM) block copolymers to condense the ol igonucleotide by fluorescence and electrophoresis techniques showed that co mplexes were formed more efficiently than with copolymers containing poly(e thylene glycol) blocks grafted onto the backbone of poly(L-lysine) (pLL-g-p EG). In addition, the copolymer pTMAEM-b-pHPMA produced oligonucleotide com plexes with the most favourable physicochemical properties appropriate for in vivo applications. The complexes were small (approximately 36 nm in diam eter), with low surface charge as measured by zeta potential, relatively st able to physiological salt conditions and could be formed at a DNA concentr ation of 500 mu g/ml. Complex formation with the copolymer pTMAEM-b-pHPMA o r pLL-g-pEG reduced the urinary clearance of the oligonucleotide after intr avenous injection into mice. However after 30 min, the oligonucleotide comp lexes were cleared from the bloodstream, These results indicate that for th e systemic delivery of oligonucleotides the polymer-derived complexes are n ot stable enough for prolonged circulation. Instead, these complexes may be more suitable for localised in vivo applications. (C) 2000 Elsevier Scienc e B.V, All rights reserved.