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Sixteen novel cationic click polymers (CPs) were parallelly synthesized via the conjugation of four alkyne-functionalized monomers to four azide-functionalized monomers by "click chemistry". The biocompatibility of CPs was evaluated by in vitro cytotoxicity (MTT assay, Hoechst/PI apoptosis/necrosis assay, and cell cycle analysis) and blood compatibility tests (hemolysis and erythrocyte aggregation). The experimental results showed that the kind of amine groups, charge density, and number of methylene or ethylene glycol groups brought about the effect on toxicity of CPs. Among all polymers, two polymers (B1 and B2) showed good biocompatibility, inducing neither apoptosis nor necrosis at the test concentration and low hemolysis ratio and erythrocyte aggregation. In particular, B1 and B2 exhibited the comparable transfection efficiency compared with PEI (25 kDa) but much lower cytotoxicity. These results suggested that the novel cationic CPs could be promising carriers for gene delivery.

To achieve efficient gene delivery to the tumor after intravenous administration, biodegradable poly(2-(2-aminoethyoxy)ethoxy)phosphazene (PAEP) was modified by lactobionic acid, bearing a galactose group as a targeting ligand. Galactosylated poly(2-(2-aminoethyoxy)ethoxy)phosphazene (Gal-PAEP) with 4.9% substitution degree of galactose could condense pDNA into nanoparticles with a size around 130 nm at the polymer/DNA ratio (N/P) of 2-40. For BEL-7402 cells, the in vitro transfection efficiency of gal-PAEP/DNA complex nanoparticles (gal-PACNs) was much higher than that of the PAEP/DNA complex nanoparticles (PACNs). MTT assay indicated that the cytotoxicity of PACNs significantly decreased after conjugating with the galactose moiety. Gal-PACNs displayed the selective gene expression in the tumor and liver with relatively low gene expression in the lung or other organs compared with PACNs. These results suggested that gal-PACNs could be a promising targeting gene carrier to deliver a therapeutic gene in future.

The selective introduction of a trimethylammonium cationic group into the C-6 position of chitosan (Cs) was successfully performed by "click chemistry" for the first time, and the 6-N,N,N-trimethyltriazole-Cs (TCs) showed good solubility in water. TCs showed strong DNA binding ability and high protection of DNA against nuclease degradation assessed by gel electrophoresis assay. TCNs showed lower degree of flocculation than Cs/DNA self-assembled nanoparticles (CsNs) in the presence of medium containing serum within 60 min. The introduction of trimethyltriazole group led to significantly increased cellular uptake compared with unmodified Cs, which resulted in higher transfection efficiency in HEK 293 and MDA-MB-468 cells. TCs were noncytotoxic, and viability of cells exposure to TCNs for 24 h was over 80% even at 50 microg/mL of polymer. These results suggested that TCs could be an efficient and safe material for gene delivery.

For efficient reversal of multidrug resistance (MDR) in chemotherapy for breast cancer, multifunctional self-assembled nanoparticles (MSN) based on a new amphiphilic copolymer consisting of bioreducible poly[bis(2-hydroxylethyl)-disulfide-diacrylate-β-tetraethylenepentamine] and polycaprolactone (PBD-PCL) were constructed and characterized. shRNA targeting the apoptosis-inhibiting gene, Survivin, was incorporated into the nanoparticles with high RNA interference efficiency. PBD-PCL significantly inhibited the activity of P-glycoprotein, one of the most well-described drug-efflux pumps, and glutathione S-transferase, an important detoxification enzyme. MSN achieved colocalization of RNA and doxorubicin in tumors after intravenous administration and showed remarkable antitumor efficacy in MDR tumor-bearing mice with less side-effect than drug combination therapy. This was a new attempt to overcome MDR against three different mechanisms of MDR simutaneously: overexpression of drug efflux protein, activation of detoxification system, and blockage of apoptosis. These results indicated that the PBD-PCL-based MSN had obvious potential for therapy of breast cancer.

The conception of a modular designed and viruslike nonviral vector has been presented for gene delivery. Recently, we constructed a new smart nanoassembly (SNA) with multifunctional components that was composed of a condensed core of pDNA with protamine sulfate (PS) and a dioleoyl phosphatidylethanolamine (DOPE)-based lipid envelope containing poly(ethylene glycol)--vinyl ether--DOPE (PVD). SNAs with mPEG 2000 (SNAs1) or mPEG 5000 (SNAs2) loading PS/DNA were prepared by the lipid film hydration technique. The particle size was about 160 nm for SNAs1 and 240 nm for SNAs2 loading PS/DNA (10:1 w/w), and the zeta potential was about 4 mV for two SNAs. The in vitro release experiment indicated that PVD possessed a good ability for self-dePEGylation, which could result in the recovery of an excellent fusogenic capacity of DOPE at low pH. SNAs showed a higher transfection efficiency and much lower cytotoxicity than did Lipofectamine 2000 on HEK 293, HeLa, and COS-7 cells. The cellular uptake and subcellular localization demonstrated that the superior transfection efficiency of SNAs could result from the fact that the DOPE-based lipid envelope containing PVD increased PS/DNA in the cytoplasm, and protamine enhanced the nuclear delivery or overcame the nuclear membrane barrier. These results implied that the PVD-based nanoassembly loading PS/DNA could be a promising gene delivery system.