Addition of poly (propylene glycol) to multiblock copolymer to optimize siRNA delivery

Dai, Zhi; Arévalo, Maria T; Li, Junwei; Zeng, Mingtao

The CMC is defined as the concentration of surfactants above which micelles form, and almost all additional surfactants added to the system go to micelles. The CMC of P1, P2, and P3 copolymers were analyzed by fluorescent spectroscopy using pyrene as a probe. From the plot of fluorescence intensity vs. copolymer concentration (Fig. 3) , the CMC of the P1, P2, and P3 obtained in this study are 556, 459, and 264 mg/l, respectively. The CMC of P3 is much less than that of P1 or P2 because of the highly hydrophobic PPG blocks in P3, and this is in agreement with previously reported research. 24 Self-assembly of cationic copolymers with siRNA The water-soluble and cationic P1, P2, and P3 copolymers formed polyplexes with siRNA via electrostatic interactions as shown by agarose gel electrophoresis. In the gel retardation assay, when siRNA is efficiently bound to its carrier and shielded from the environment, migration through the gel is completely retarded. Polyplexes were formed at N/P ratio of 0 (naked siRNA) to 4. Cationic copolymers P1 and P2 condense siRNA at an N/P ratio of 4. However, complete retardation by cationic copolymer P3 was achieved at N/P ratio of 2, indicating that the hydrophobic PPG blocks improve siRNA-binding (data not shown). The increased condensation associated with the PPG blocks of P3 copolymer can be explained by the increased charge density of the polymer.