Search

Zwitterionic copolymers have exhibited high resistance to nonspecific protein adsorption and have wide applications in drug delivery systems. Herein, a pH-responsive poly(Lysine-alt-N,N'-bis(acryloyl) diaminohexane) was synthesized through the Michael addition polymerization between N, N'-bis(acryloyl) diaminohexane and lysine. Subsequently, nano micelles (NMs) were formed by self-assembly of the copolymer in an aqueous solution. The NMs showed a slightly negative charge in blood environment, but a positively charged surface in extracellular pH of tumor. This feature could be used to enhance permeability and retention effect, and reinforce tumor cell uptake. Vitro release studies revealed that the release of DOX from the DOX-loaded NMs was evidently faster at pH 5.0 than at pH 7.4. MTT assays revealed that NMs were nontoxic. Thus, these smart NMs were feasible candidates and could be potentially used in cancer chemotherapy.

A new kind of biodegradable poly(urethane-urea)s based on poly-lysine oligomer used as the soft segment was synthesized and characterized. In vitro degradation behavior of poly (urethane-urea)s was investigated, and was assessed by (1)H NMR and mass loss. The results indicated that the peptide bonds in poly(urethane-urea)s were effectively cleaved in simulated pancreatic juice containing trypsin, while those in buffer solution without trypsin remained unaffected. The degradability was obviously improved by introducing poly-lysine oligomer into the main chain of poly(urethane-urea)s. The results of cells viability test indicated that the poly (urethane-urea)s showed a good biocompatibility on endothelial cells. The thermostability and hydrophilicity of poly(urethane-urea)s increased with increase in poly-lysine oligomer content.

Overhauser-enhanced magnetic resonance imaging (OMRI), which is a double resonance technique, creates images of free radical distribution in animals by enhancing the water proton signal intensity by the overhauser effect. In this study, we constructed a contrast agent by combining PROXYL groups that have nitroxyl radicals with PEG-modified dendritic poly(l-lysine) that accumulates in the tumor by enhanced permeability and retention (EPR) effect. Addition of the PROXYL groups at the PEG chains' termini on KG6 was advantageous in OMRI, because the ESR signal of the nitroxyl radical was maintained without decay caused by mobility restriction, even if the PROXYL groups were attached at 25 mol% on one molecule. After intramuscular injection of the molecule modified at 25 mol%, that is, PR25-PEG-KG6, a significant OMRI signal was observed at the injected site. However, no signal was detected in the tumor after intravenous injection of PR25-PEG-KG6 to a tumor-bearing mouse, although PR25-PEG-KG6 itself accumulated in the tumor. The reason was that the nitroxyl radicals were immediately reduced in the blood after the injection, suggesting that use of stable nitroxyl radicals will enable detection of tumors by OMRI after intravenous injection.

To deliver anti-cancer drugs to tumors, a hydrophobic cavity was prepared in the dendritic molecule, dendritic poly(L-lysine) of sixth generation (KG6), which was used as a drug carrier. The dendritic molecule was modified with polyethylene glycol (PEG)-linked hydrophobic penta-phenylalanine or penta-alanine. The hydrophobic cavity was formed between the KG6 and PEG chains. The penta-phenylalanine peptide was better in encapsulating doxorubicin (DOX) in the cavity compared with penta-alanine. The loaded DOX was slowly released from the cavity, and it depended on pH. After intravenous injection, the DOX-loaded dendrimers accumulated in the tumor by the enhanced permeability and retention effect, and showed significant suppression of tumor growth without loss of body weight. These results indicate that hydrophobic oligopeptides can be used for forming a hydrophobic cavity in a dendritic molecule for delivery of anti-cancer drugs to tumor sites.

The endosomal membrane has proven to be a challenging barrier for the delivery of therapeutic biomacromolecules, including DNA, siRNA and proteins, which are taken up by endosomes but cannot freely diffuse across lipid bilayers. Anionic polymers that undergo conformational changes and become membrane disruptive in low-pH environments have the potential to assist in the delivery of these biomacromolecules across the endosomal membrane to the cytosol. Such endosomolytic polymers have been synthesized through the grafting of hydrophobic side-chains to a poly(L-lysine iso-phthalamide) backbone. The phenylalanine grafted form of poly(L-lysine iso-phthalamide) has a pH-sensitive membrane disruptive profile corresponding to the pH range of maturing endosomes and, thus, has a favourable endosomolytic profile. In order to understand the influence of hydrophobicity versus pi-pi interactions mediated by aromatic rings, a tyrosine grafted form of poly(L-lysine iso-phthalamide) was synthesized and its aqueous pH-sensitive properties, cytotoxicity and endosomal disruptive capacity were compared to phenylalanine-grafted poly(L-lysine iso-phthalamide). The similarity between these two polymers' properties, despite the large difference in hydrophobicity between their side-chains, supports the conclusion that the aromatic character of sidechains in poly(L-lysine iso-phthalamide) is an important property, as opposed to hydrophobicity alone, in determining the effectiveness of acidic pH triggered endosomolysis.

In order to evaluatet effects of different cationic moieties, such as primary amino and guanidino groups, on interactions between DNAs and cationic comb-type copolymers, comb-type copolymers having guanidino groups were prepared. The copolymers (GPLL-g-Dex) were obtained by guanidination of poly(L-lysine)-graft-dextran copolymers (PLL-g-Dex) using 1-guanyl-3,5-dimethylpyrazole nitrate under weak basic conditions. The resulting copolymers were characterized using NMR spectroscopy and size-exclusion chromatography-multiangle light scattering (SEC-MALS). The primary amino groups of the PLL backbones were thoroughly replaced with guanidino ones without any detectable side reactions, including fragmentation of PLL or Dex chains. The interactions of GPLL-g-Dex and PLL-g-Dex with DNAs were assessed by UV-melting curve measurements. These copolymers diversly affected the melting behavior of double-stranded DNA (dsDNA). GPLL-g-Dex has a lower ability to increase the Tm of dsDNA than PLL-g-Dex and also exhibits a higher affinity for dsDNA. The results suggest that the stability of dsDNA may be affected not only by ionic interaction between the copolymers and DNAs, but also by other modes of interactions, such as hydrogen-bondinginteractions.