Copolymers of covalently crosslinked linear and branched polyethylenimines as efficient nucleic acid carriers.

The present study describes the formation of copolymers of linear and branched PEIs (25 kDa each). These polyethylenimines (bPEI and IPEI) were crosslinked with each other to obtain branched-linear (BL) PEI copolymers using epichlorohydrin as a crosslinker in two steps. First, IPEI was reacted with epichlorohydrin to form IPEI-chlorohydrin (CHL) and subsequently, bPEI was grafted onto CHL in basic medium by in situ generation of epoxy functionalities. The two PEIs were crosslinked by varying the weight ratio of bPEI while keeping the amount of IPEI fixed. The ratio of two PEIs (1:1, 2:1, 3:1, 4:1 and 5:1) and crosslinking percentage of epichlorohydrin (5, 10, 15 and 20%) appeared as the main parameters to have affected the transfection efficiency. The lead conjugate/DNA complex was tested for in vivo transgene expression in Balb/c mice and was found to show maximum expression in the spleen.