Complex formation between cationic polymethacrylates and oligonucleotides

With regard to the development of pharmaceutical carriers for oligonucleoti des, the interactions between a cationic polymer, poly(2-dimethylamino)ethy l methacrylate (pDMAEMA), and rhodamine-labeled 25-mer phosphodiester oligo nucleotides (Rh-ONs) were studied. The composition of the pDMAEMA/Rh-ON com plexes was investigated as a function of the charge ratio (phi; +/-) by inc reasing the pDMAEMA concentration and keeping the Rh-ON concentration const ant. Gel electrophoresis revealed that at phi < 1 only a fraction of the sh ort Rh-ONs bind the longer pDMAEMA chains. Dynamic light scattering and zet a potential (<zeta>) indicated that at phi < 1 only a fraction of the phosp hate anions on the Rh-ONs are involved in complex formation which results i n "dangling" of the Rh-ONs. Moreover, from fluorescence measurements, multi molecular complexes (i.e., several Rh-ONs per pDMAEMA chain) were revealed. At 1 < phi < 3, <zeta> approximated zero. This led to a clustering of indi vidual complexes. At phi > 3, all the Rh-ONs were bound while, compared to complexes at phi < 1, the average number of Rh-ONs bound to one pDMAEMA cha in was decreased. The presence of multimolecular complexes was confirmed fr om fluorescence correlation spectroscopy (FCS) measurements. The multimolec ular complexes were observed as highly intense fluorescent particles upon t heir diffusion through the confocal volume of the FCS instrument. Also, the decrease in the average number of Rh-ONs bound to one pDMAEMA chain, upon increasing <phi>, was confirmed by FCS.