A review of the developments of characteristics of PEI derivatives for gene delivery applications

Redox-active stimuli have gained a great deal of interest as an indicating factor for designing bioresponsive matrices in gene delivery. Hence, a wide range of gene carriers has been designed incorporating the redox-stimuli characteristics. The most important type of gene carriers is the class of redox responsive polymers. Among them, disulfide incorporated redox-responsive polyethyleneimine (PEI) and its derivatives, as a result of their outstanding DNA entrapping characteristics and their intrinsic endosomolytic activity, have attracted considerable attention in recent studies. The review presents the main developments of the characteristics of PEI derivatives and their applications in gene delivery. It is found that despite the uniquely stated characteristics, the noncleavable structure of conventional PEI (high molecular weight PEI: 25k), which makes it a nondegradable material, as well as the frequent inclusion of positively charged amino groups, which reduces its blood circulation period, render conventional PEI a very toxic material for gene-delivery applications. The extremely high cellular toxicity of conventional PEI has restricted its administration for real in-vivo physiological media. Recent studies have shown that employing low molecular weight PEI cross-linked by disulfide linkages (SS-PEI) and assembling low molecular weight disulfide linkages PEI (LMW SS-PEI) with bio-detachable anionic groups were two successful approaches for increasing bioavailability of the PEI-based gene carriers, while keeping outstanding cellular transfection. VC 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42096.