PEG-PAsp

PEG-PAsp (4-phenyl-1-butanol substituted Paclitaxel Passive Colon 26 tumor-bearing CDFl mice ... 

Fig. 2 A first generation of drug-loading micelles, a Schematic illustration of the formation of polymeric micelle of Dox-conjugated PEG-PAsp block copolymer. Additional Dox can be physically entrapped in the micelle, b Chemical structures of PEG-PAsp block copolymer and Dox...

We introduced CDDP into the micelle system where CDDP was complexed with carboxyl groups on PEG-PAsp to form a metal complex micelle (Fig. 3a). The complex spontaneously forms a micelle with a very narrow size distribution having an average diameter of 20 nm [57]. The PEG-PAsp(CDDP) micelles showed an environment responsive drug release behavior. They are stable in distilled water at room temperature, yet in contrast, an exchange between the chloride ion and cisplatin occurred in 150 mM NaCl, resulting in the sustained release of the drug for over 50 h [58]. 

Thus, extension of the blood circulation time of the micelles as well as a regulated release rate of the CDDP from the micelle was concluded to be necessary to achieve a more effective anti-tumor activity. This was eventually achieved using PEG-PGlu instead of PEG-PAsp. Here, CDDP was loaded in the micelle in a similar manner to the PEG-PAsp metal complexation with the ligand substitution reaction between CDDP and the carboxylic group of PEG-PGlu (Fig. 3b) [60]. The formed micelle had a very narrow size distribution with an approximately 30 nm diameter. The PEG-PGlu(CDDP) micelle showed a more sustained release of CDDP (half-value period > 90 h) than... 

Fig. 3 Polymeric micelle formation of PEG-PAsp/CDDP (a), and PEG-PGlu/CDDP (b), where carboxylic groups and Pt are linked through coordination bonds, c Effect of free CDDP (left hand side) and PEG-PGlu(CDDP) micelles (right hand side) on the growth of C26 colon adenocarcinoma subcutaneously transplanted in CDFl mice (n = 10). Each drug was administrated by i. v. route five times at 2 day intervals (arrow) at the dose of 4 mg/kg CDDP eq. The molecular ratio of CDDP to the block copolymer in the micelles was calculated to be 27, and the dose of the injected polymer was 6.3 mg/kg...

In a pH-sensitive micellar system, Dox was conjugated to the core-forming PAsp segment of the PEG-PAsp through the hydrazone hnker [61] that is stable under physiological conditions but cleavable under the acidic intracellular environments of endosomes and lysosomes (Fig. 4a). 

Fig. 4 A second generation of the drug loading micelle with a pH-sensitive drug releasing property, a Formation of pH-sensitive polymeric micelles from PEG-(PAsp-Hyd-Dox) block copolymers. Antitumor drugs (Dox), conjugated through acid-labile hydrazone linkers, are released in lower pH conditions, b Time- and pH-dependent Dox release profile from the micelles. The micelles selectively release Dox under the pH condition of region B, which corresponds to the intracellular environment. The amount of loaded Dox in the micelles was calculated from the released Dox at pH 3.0 where all of the loaded drugs were assumed to be released from the micelle...

PEG-PAsp(DPT) was then applied to construct a nanocarrier of short interference RNA (siRNA), with the ability to show effective RNA interference (RNAi) properties [115]. RNA is extremely unstable against nuclease attack, and thus the establishment of an efficient delivery system is crucial for promoting the RNAi therapy. The complexation behavior of PEG-PAsp(DPT) with siRNA was examined through gel electrophoresis and EtBr exclusion assay to confirm the formation of stable complexes. The free siRNA disappeared at the N/P ratio > 2 in a gel electrophoresis analysis, which was consistent with the result of the EtBr assay where a substantial fluorescence quenching of EtBr was observed at N/P > 2. 

Fig. 11 PEG-PAsp(DPT) block copolymer, a Chemical structure of PEG-PAsp(DPT) where dipropylenetriamine is substituted to the benzyl group of PEG-PBLA by aminolysis. b The pH-a(a = [protonated amino groups])/[whole amino groups]) curve of BOC-Asp(DPT)-Pr as model compound for PEG-PAsp(DPT). The pK values, which are defined as pH at a = 0.25 and 0.75, respectively, were determined to be 9.9 and 6.4...

Fig. 12 Evaluation of gene knockdown effect by siRNA complexed with PEG-PAsp(DPT). a GL3 luciferase gene knockdown by siRNA complex with various block copolymers having varying charge ratios, commercially available reagent (RNAiFect), and naked siRNA evaluated in HuH-7 cells ( = 4 SD). GL3 and RL luciferases were pre-transfected by pGL3 and pRL plasmid DNA complexed with LipofectAMlNE. The siRNA complexes (GL3 knockdown) were then applied and evaluated by dual luciferase assay, b Endogenous gene (Lamin A/C) knockdown in the presence or absence of 50% serum evaluated in 293T cells...

The high gene silencing efficiency of the PEG-PAsp(DPT) complex may be attributed to the presence of the secondary amino group with a lower pfCa in the complex that promotes siRNA transport into the cytoplasm by buffering the endosomal cavity, in addition to the increased tolerance against nuclease attack due to complexation. These results, obtained for the engineered block catiomer of PEG-PAsp(DPT), facilitates the clinical use of siRNA for the treatment of various diseases. 

The degree of polymerization of the PAsp(MPA) and PEL segments in the triblock copolymer were set at 36 and 50, respectively. For comparison, diblock copolymers, PEG-PAsp(MPA) with 39 PAsp(MPA) units and PEG-PEE with 48 PEE units, were also synthesized. The plQ values of each diblock copolymer were determined to be 6.2 and 9.4, respectively. 

At the Eys/nucleotide ratio of 2, the triblock copolymer formed a micelle with a size and zeta potential of 90 nm and -i- 7 mV. The interaction between the triblock copolymers and pDNA was evaluated and compared to the diblock copolymers using the EtBr exclusion assay. In the case of PEG-PEE, the fluorescence intensity decreased to 20% of the uncondensed naked pDNA at the N/P ratio of two. In contrast, PEG-PAsp(MPA), which has a cationic segment with a lower pKa value, maintained a relatively high fluorescence (> 90%) over a wide range of N/P ratios, suggesting that PEG-PAsp(MPA) lacks the capacity to condense pDNA based on the EtBr assay result. On the other hand, PEG-PAsp(MPA)-PEE exhibited a 80% decrease in fluorescence... 

Fig. 13 Panel for triblock copolymer PEG-PAsp(MPA)-PLL system, a Chemical structure of PEG-PAsp(MPA)-PLL. b Schematic illustration hypothesizing a three-layered micelle formed from the triblock copolymer and pDNA with spatially regulated structure, c In vitro transfection of the luciferase gene to HeLa cells by the micelles from di- or triblock copolymers and polyplex with PEI. The micelles were prepared at a Lys/nucleotide ratio of 2. HeLa cells were incubated with each micelle in a mediiun containing 10% serinn for 24 h, followed by additional 24 h incnbation withont micelles, d The effects of HCQ and NR on the transfection efficiency of the micelles and polyplex. The PEI polyplex was prepared at a N/P ratio of 10. (Fig. 13d Reprinted with permission from [116])...

Fig. 14 Inorganic-organic hybrid CaP/PEG-PAsp/DNA micelle system, a Schematic representation of organic-inorganic hybrid micelle formation, b Biological activities of siRNA incorporated hybrid nanoparticles formed at various PEG-PAsp concentrations. Ratios of GL3 luciferase to RL luciferase -were normalized to cells treated with nanoparticles formed without siRNA. Grey and white bars indicate the ratios of GL3 to RL in the presence of the nanoparticles loading siRNA targeting GL3 luciferase and non-sUencing siRNA (mock) used as a control, respectively. Stars indicate significant difference, with p<0.01 ( ) ( = 6, SEM)...

Fig. 14 a, b Chemical structures of a poly (ethylene glycol)-Wock-poly(a, P-aspartate) (PEG- -PAsp) and polyethylene glycol)-Wock-poly(a, P-aspartamide) (PEG-b-PAspA), b poly (ethylene oxide)-Wocfc-polystyrene-protoporphyrin IX (PEO- -PS-PPIXZn) and crystal structure of horse radish peroxidase (HRP) the arrow marks the positioning of the cofactor... 

Nishiyama, N. and Kataoka, K. 2003. Polymeric micelle drug carrier systems PEG-PAsp(Dox) and second generation of micellar drugs. Adv. Exp. Med. Biol. 519 155-177. 

---