**6. Conclusion**

98 Biomedicine

line/animal

NIH-3T3, HeLa, HCT116,

COS-7, HEK293

HEK293, HT1080

HEK293, HeLa, NIH3T3, C2C12, HUVECs

pEGFP A549 4-fold higher than

pLuc, pEGFP 293T, HeLa 5-10 times higher

pLuc, pEGFP 293T, HeLa Comparable (293T)

murine brain capillary endothelial bEnd.3 cells

MCF-7, MCF-7/ADR

Table 1. A summary of bioreducible cationic polymers and their transfection efficiencies in

Transfection Ref.

(Lee et al., 2007)

(Breunig et al., 2007)

(Peng et al., 2008)

(Choi & Lee, 2008)

(Sun et al., 2008)

(Son et al., 2010)

(Koo et al., 2010)

(Jere et al., 2009)

(J. Liu et al., 2010)

(Xue et al., 2010)

(Gao et al., 2010)

(Zhang & Vinogradov, 2010)

ExGen 500 (25kDa *l*-

5-7 times higher than Lipofectamine 2000, JetPEI, FuGENE6, 40-70 eGFP+%

25- kDa PEI (HeLa), 3-fold higher eGFP+% (293T)

8-fold higher (HeLa) than 25 kDa PEI

100-fold higher than that of 1.2kDa-BPEI

1000-fold higher than 6-kDa *l*-PEI, but comparable to 25-

kDa BPEI

25-kDa PEI

than 25-kDa PEI

or a little higher (HeLa) than 25-kDa

2.3-4.9 fold higher than ExGen500

Comparable to 25kDa- BPEI

BPEI

PEI)

HeLa, 293T 10-fold higher than

HEK293 Comparable to 25 kDa PEI

293T, HeLa Comparable (293T),

Plasmid Cell

pCMV-Luc, pCMV-EGFP

pCMV-NGVL3 (both GFP and

pCMV-Luc and

Luciferase gene

pCN-Luc or pEGFP

qWIZ-Luc (6.7 kb), qWIZ-GFP

iMDR1-pDNA,

(5.7 kb)

pEGFP

Luc)

pEGFP

pDNA

Linear SS-PEI pCMV-Luc HepG2, HeLa comparable to

pCMV-EGFP CHO, HepG2,

Disulfide-based polymers

DTSP-Crosslinked linear PEI (2-4kDa)

PEI-SS(x) from thiolated 800-kDa

listeriolysinOconjugated reducible 25kDa-PEI (LLO-SS-

SS-PEI in the presence

BPEI-SS-PEG-cNGR (cNGR: cyclic NRG (CNGRCK) peptide)

poly(ethylenimine sulde) (b-PEIS)

CBA-crosslinked reductable polyspermine

Reducible PEI (PEI-SS-CLs) via "click" chemistry

Linear PAA grafted

polyamidoamines

linear disulfide-based "click" polymer (RCP)

different types of cell lines.

CBA-crosslined reducible polyamines (pLPEI/pTETA/pSPE)

with

PEI)

of RGD

branched

Cationic polymers with multiple functionalities are promising as non-viral vectors for gene transfection. Since more and more extracellular and intracellular gene delivery barriers are identified that seriously hamper efficient gene transfection, a number of cationic polymers have been designed that are capable of overcoming one or more gene delivery barriers, thus leading to detectable gene transfection efficiency. From those conventional non-degradable cationic polymers to current bioreducible cationic polymers, peoples have more and more reached virus-like, safe and potent polymeric gene delivery vectors. Further understanding on structure-activity relationships of cationic polymers and their intracellular fate should be indispensable, in order to achieve polymer systems that can exhibit multiple gene delivery properties for highly efficient gene transfection.
