Effect of multifold charge groups and imidazole-4-carboxaldehyde on physicochemical characteristics and transfection of cationic polyphosphazenes/DNA complexes

To understand the dual influence of multifold charge groups and conjugation of imidazole moiety on the physicochemical characteristics and the transfection activity of polymer complexes, a series of cationic polyphosphazenes based on poly(2-(2-aminoethyoxy)ethoxy) phosphazene (PAEP) with different components of multifold charge groups was synthesized by means of introducing imidazole-4-carboxaldehyde (IC) into PAEP through the formation of Schiff base. Though the polymers with primary amino groups (1°) alone or with abundant primary amino groups could bind DNA more efficiently than the ones with mainly or totally secondary (2°) and tertiary (3°) amino groups, all of the polymers could condense DNA into small particles within 100 nm at the N/P ratio of 24. The cell viability of complexes and the pH buffering capacity of polymers increased with substitution degree of IC increasing. Among all the PAEP-based polymers, the highest transfection activity was found for poly(2-(2-aminoethyoxy)ethoxy/IC)phosphazene (PAEIC) 18 complexes containing 1°, 2° and 3° amines at a ratio of 3.5:1:1 with 18% substitution degree of IC, which indicated that either the coexistence of 1°, 2° and 3° amines or the conjugation of imidazole moiety played an important role in transfection activity. These results suggested that the most efficient gene carrier could be these polymers with 1°, 2° and 3° amines at an appropriate ratio, together with the presence of imidazole moiety in a small fraction.