Suhong Wu

Biodegradable amphiphilic copolymer containing nucleobase: synthesis, self-assembly in aqueous solutions, and potential use in controlled drug delivery.

Biodegradable nucleobase-grafted amphiphilic copolymer, the methoxyl poly (ethylene glycol)-b-poly (L-lactide-co-2-methyl-2(3-(2,3-dihydroxylpropylthio) propyloxycarbonyl)-propylene carbonate/1-carboxymethylthymine) (mPEG-b- P(LA-co-MPT)), was synthesized. (1)H NMR titration and FT-IR spectroscopy indicated that the hydrogen-bonding could be formed between mPEG-b-P(LA-co-MPT) and 9-hexadecyladenine (A-C16). The hydrophobic microenvironment of the amphiphilic copolymer can protect the complementary multiple hydrogen bonds between mPEG-b-P(LA-co-MPT) and A-C16 from water effectively. The addition of A-C16 not only lowered the critical aggregation concentration (CAC) of mPEG-b-P(LA-co-MPT)/A-C16 nanoparticles (NPs) in aqueous solution but also induced different morphologies, which can be observed by transmission electron microscopy (TEM). Meanwhile, dynamic light scattering (DLS) and turbidometry was utilized to evaluate the effect of temperature and pH change on the stability of mPEG-b-P(LA-co-MPT)/A-C16 NPs. Cytotoxicity evaluation showed good biocompatibility of the mPEG-b-P(LA-co-MPT)/A-C16 NPs. The in vitro drug release profile showed that with the increase of A-C16 content, the doxorubiucin (DOX) release at pH 7.4 decreased, while the faster release rate was observed with the addition of A-C16 with a pH of 5.0. Importantly, DOX-loaded NPs exerted comparable cytotoxicity against MDA-MB-231 cells. This work provided a new method to stabilize NP structure using hydrogen-bonds and would have the potential to be applied in controlled drug delivery.

Reduction-responsive shell-crosslinked micelles prepared from Y-shaped amphiphilic block copolymers as a drug carrier

Biodegradable Y-shaped amphiphilic block copolymer mPEG-b-PLG-b-(PLA)2 was synthesized and characterized by 1H NMR and FTIR. The amphiphilic property of the copolymer with a mPEG-b-PLG segment as the hydrophilic arm and two PLA segments as the hydrophobic arms endows the copolymer with the ability to form core–shell nanoparticles in aqueous solution. Co-assembly of doxorubicin (Dox) and the block copolymer in selective solvent was carried out to prepare Dox-loaded micelles. The inner-shell (PLG) of the micelle was crosslinked through a carbodiimide coupling method with cystamine as the crosslinker. The crosslinked micelles exhibit reduction-responsive release of Dox and the stability in vitro was much better than non-crosslinked micelles. In acidic release condition, the total amount of Dox released could be increased due to the increased solubility of Dox. The blood clearance of Dox in different form of micelles was studied and the results show that Dox loaded in the crosslinked micelles with PEG5K as the outer shell exhibit the longest blood circulation after intravenous injection.

Core-crosslinked amphiphilic biodegradable copolymer based on the complementary multiple hydrogen bonds of nucleobases: synthesis, self-assembly and in vitro drug delivery

Nucleobases (adenine and thymine) were conjugated to the amphiphilic biodegradable copolymers methoxyl poly(ethylene glycol)-b-poly(L-lactide-co-2-methyl-2-allyloxycarbonylpropylene carbonate) (mPEG-b-P(LA-co-MAC)). The hydrogen bonds between adenine (A) and thymine (T) were confirmed by 1H NMR titration experiments and FT-IR. It was found that the incorporation of nucleobases into the hydrophobic segment of the amphiphilic copolymers could be used for core-crosslinking of the formed micelles containing a lowered critical micelle concentration (CMC) via hydrogen bond interaction between A and T in aqueous solution. The anticancer drug doxorubicin (DOX) was encapsulated into the copolymer micelles. The in vitro drug release profile showed that the incorporation of nucleobases significantly restricted DOX release at pH 7.4, because of the compact crosslinking structure of micelles. However, a much faster release rate was observed at pH 5.0, due to the dissociation of hydrogen bonds between nucleobases. This character facilitates drug delivery in the acidic tumor micro-environment inside the endosome. Meanwhile, the DOX-loaded core-cross-linked micelles could be efficiently internalized into cancer cells and exhibit similar anticancer efficacy as free DOX against MDA-MB-231 cells. Therefore, the complementary multiple hydrogen bonds of nucleobases provided a convenient tool to stabilize the micelle structures by forming core-crosslinking, and could be further applied for controlled drug delivery.

Design and delivery of camplatin to overcome cisplatin drug resistance

Camplatin, a prodrug formed via coining camphoric anhydride and cisplatin, was delivered in biodegradable nanoparticles. This camphoric acid and cisplatin co-delivery system exhibited enhanced anticancer activity compared to cisplatin and has successfully overcome cisplatin drug resistance.

Facile preparation of core cross-linked micelles from catechol-containing amphiphilic triblock copolymer

Efficient delivery of anti-cancer drugs into tumor cells for enhancing the intracellular drug concentration is a major challenge for cancer therapy due to the instability of drug-loading vehicle. In this report, we developed a simple method to stabilize the nanostructure of micelles only by bubbling air to crosslink the outer layer of the micelle core. Dopamine was conjugated to a biodegradable triblock copolymer monomethoxy poly(ethylene glycol)-b-poly(2-methyl-2-carboxyl-propylene carbonate)-b-poly(L-lactide) (mPEG-b-PMCC-b-PLA) to obtain dopamine grafted copolymer mPEG-b-P(MCC-g-dopamine)-b-PLA. After self-assembly, the core cross-linked micelles were then prepared by the oxidative self-polymerization of dopamine in the middle hydrophobic phase of the micelles. The cross-linked micelles had smaller sizes and narrower particle size distributions than their uncross-linked precursors. The improved stability was confirmed by critical micelle concentration (CMC) experiments and 1H NMR spectra. The kinetics and processes of oxidative cross-linking of micelles under air flux were monitored by UV-Vis spectroscopy and transmission electron microscopy (TEM). These core cross-linked micelles were able to load doxorubicin (DOX) with superior loading capacity of up to 19.5% (w/w, drug/micelle) with high drug loading efficiency (97.5%). Compared with the uncross-linked ones, drug release efficacy from the cross-linked micelles extremely decreased at pH 7.4. However, a properly sustained release occurred at pH 5.0, which is very favorable for drug delivery in tumor cells. The DOX-loaded micelles had similar cytotoxicity as the free drug and could be effectively internalized into MDA-MB-231 cells. This controllable and convenient approach for preparing core cross-linked micelles will have a pragmatic future in stabilizing the architecture of nanocarriers for drug delivery.

Guanidinated amphiphilic cationic copolymer with enhanced gene delivery efficiency

The lack of safe and effective carriers for RNA interference therapeutics remains a barrier for its wide clinical application. In this study, guanidino groups were incorporated into poly(ethylene glycol)-block-poly(e-caprolactone)-block-poly(L-lysine) (mPEG-b-PCL-b-PLL, AG0) by simple replacement of the amino groups on PLL segments by the guanidino groups to enhance the transfection performance by mimicking the transmembrane function of cell penetrating peptides, such as TAT or other arginine-rich peptides. The guanidinated copolymers (AG1–AG3) displayed similar siRNA-binding capacity to AG0, but less cytotoxicity and higher silencing efficiency than AG0. Typically, AG3 with full replacement of the amino groups by guanidino groups exhibited higher silencing efficiency than PEI-25k and Lipofectamine 2000. Cell uptake and cell imaging experiments showed that the enhanced silencing efficiency of AG3–siRNA complex was due to the enhanced endocytosis cross the cell-membrane and the enhanced escape from the endosomes/lyosomes. The guanidino groups on the polylysine units were responsible for these enhancements although they are attached to the polymer backbone with a spacer of (CH2)4, in comparison with (CH2)3 in polyarginine. In conclusion, guanidination of mPEG-b-PCL-b-PLL resulted in a less toxic and more efficient siRNA vector and contribution of the guanidine groups to cell-membrane penetration and endosome/lyosome-membrane penetration was demonstrated. Therefore, replacement of the amino groups in conventional gene delivery vectors with guanidine groups might be a useful strategy of developing novel gene or drug delivery vectors.

Contribution of cholesterol moieties attached on MPEG-b-PCL-b-PLL to the cell uptake, endosomal escape and gene knockdown of the micelleplexes of siRNA

To further enhance the transfection efficiency of a micelleplex system based on monomethoxy poly(ethylene glycol)-block-poly(ɛ-caprolactone)-block-poly(L-lysine) (MPEG-b-PCL-b-PLL), cholesterol (Chol) moieties are attached to the ɛ-termini of PLL segments to obtain MPEG-b-PCL-b-PLL/Chol. The structure and morphology of the copolymer are studied by 1H-NMR, TEM and DLS (dynamic light scattering). The cytotoxicity, cell uptake, endosomal release and mRNA knockdown are studied by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay, flow cytometry, CLSM (confocal laser scanning microscopy) and RT-PCR (real-time polymerase chain reaction). The results show that compared to their precursor MPEG-b-PCL-b-PLL, the cholesterol-grafted copolymer shows significantly lower toxicity, more rapid cellular endocytosis and endosome escape, and consequently displays enhanced siRNA transfection efficiency even at a lower N/P ratio. These improvements are ascribed to enhanced interaction of the cholesterol moieties with both cellular membrane and endosomal membrane. Moreover, effect of the PLL block length is examined. The final conclusion is that long enough PLL segments and incorporation of proper fraction of cholesterol onto the PLL segments benefit the enhancement of siRNA transfection efficiency.