Chie Kojima

Preparation and cytotoxic activity of poly(ethylene glycol)-modified poly(amidoamine) dendrimers bearing adriamycin

We have developed poly(amidoamine) (PAMAM) dendrimers that have poly(ethylene glycol) (PEG) grafts at all dendrimer chain ends. To obtain PEG-modified dendrimers with sites for conjugation of anticancer drugs for this study, we prepared PAMAM G4 dendrimers that have a glutamic acid (Glu) residue at every chain end of dendrimer; PEG chains were attached to amino groups of Glu residues. We then combined the anticancer drug adriamycin to side chains of the Glu residues using an amide bond, [PEG-Glu(ADR)-G4], or hydrazone bond, [PEG-Glu(NHN-ADR)-G4]. For the dendrimers bearing adriamycin through amide linkage, adriamycin was released only slightly at pH 7.4 and 5.5. Although a negligible level of release occurred at pH 7.4 for dendrimers with adriamycin via hydrazone linkage, a remarkable extent of adriamycin release was induced at pH 5.5, which corresponds to the pH of late endosome. These adriamycin-bearing dendrimers showed much lower toxicity to HeLa cells than did free adriamycin. However, compared to PEG-Glu(ADR)-G4, PEG-Glu(NHN-ADR)-G4 exhibited 7 times higher cytotoxicity, suggesting the importance of pH-sensitive hydrazone linkage for high cytotoxicity. Furthermore, the PEG-modified dendrimers exhibited an equivalent level of toxicity to that of adriamycin-resistant SBC-3/ADR100 cells and their parent adriamycin-sensitive SBC-3 cells.

Highly temperature-sensitive liposomes based on a thermosensitive block copolymer for tumor-specific chemotherapy.

Recently, we showed that incorporation of poly[2-(2-ethoxy)ethoxyethyl vinyl ether (EOEOVE)], which exhibits a lower critical solution temperature around 40 degrees C, provides temperature-sensitive properties to stable liposomes. In this study, we applied this thermosensitive polymer for preparation of temperature-sensitive liposomes for tumor-specific chemotherapy with doxorubicin (DOX). We prepared liposomes consisting of PEG-lipid, egg yolk phosphatidylcholine, cholesterol and copoly(EOEOVE-block-octadecyl vinyl ether), which was synthesized as poly(EOEOVE) having anchors for fixation onto liposome membrane. The copolymer-incorporated liposomes were stable and retained DOX in their inside below physiological temperatures. However, they exhibited a significant release of encapsulated DOX above 40 degrees C and released DOX almost completely within 1 min at 45 degrees C. The copolymer-modified liposomes exhibited a long circulating property and biodistribution similar to that of PEG-modified liposomes. The copolymer-modified liposomes loaded with DOX were injected intravenously into tumor-bearing mice. Tumor growth was strongly suppressed when the tumor site was heated to 45 degrees C for 10 min at 6-12 h after injection. However, injection of the liposomes exhibited only slight tumor-suppressive effects as long as mild heating was not applied to the target site. The highly temperature-sensitive properties of the copolymer-incorporated liposomes might contribute to establishment of tumor-selective and effective chemotherapy.

X-ray computed tomography contrast agents prepared by seeded growth of gold nanoparticles in PEGylated dendrimer

Gold nanoparticles (Au NPs) are a potential x-ray computed tomography (CT) contrast agent. A biocompatible and bioinactive surface is necessary for application of gold nanoparticle to CT imaging. Polyethylene glycol (PEG)-attached dendrimers have been used as a drug carrier with long blood circulation. In this study, the Au NPs were grown in the PEGylated dendrimer to produce a CT contrast agent. The Au NPs were grown by adding gold ions and ascorbic acid at various equivalents to the Au NP-encapsulated dendrimer solution. Both size and surface plasmon absorption of the grown Au NPs increased with adding a large number of gold ions. The x-ray attenuation of the Au NPs also increased after the seeded growth. The Au NPs grown in the PEG-attached dendrimer at the maximum under our conditions exhibited a similar CT value to a commercial iodine agent, iopamidol, in vitro. The Au NP-loaded PEGylated dendrimer and iopamidol were injected into mice and CT images were obtained at different times. The Au NP-loaded PEGylated dendrimer achieved a blood pool imaging, which was greater than a commercial iodine agent. Even though iopamidol was excreted rapidly, the PEGylated dendrimer loading the grown Au NP was accumulated in the liver.

Multi-functional liposomes having temperature-triggered release and magnetic resonance imaging for tumor-specific chemotherapy.

For development of tumor-specific chemotherapy, we designed liposomes with temperature-triggered drug release and magnetic resonance imaging (MRI) functions. We prepared multi-functional liposomes by incorporating thermosensitive poly(2-ethoxy(ethoxyethyl)vinyl ether) chains with a lower critical solution temperatures around 40 °C and polyamidoamine G3 dendron-based lipids having Gd(3+) chelate residues into pegylated liposomes. These stable doxorubicin (DOX)-loaded liposomes retained DOX in their interior below physiological temperature but released DOX immediately at temperatures greater than 40 °C. They exhibited excellent ability to shorten the longitudinal proton relaxation time. When administered intravenously into colon 26 tumor-bearing mice, accumulated liposomes in tumors increased with time, reaching a constant level 8 h after administration by following T(1)-weighted MRI signal intensity in tumors. Liposome size affected the liposome accumulation efficiency in tumors: liposomes of about 100 nm diameter were accumulated more efficiently than those with about 50 nm diameter. Tumor size also affected accumulation: more efficient accumulation occurred in larger tumors. Tumor growth was strongly suppressed when liposomes loaded with DOX were administered intravenously into tumor-bearing mice and the tumor was heated mildly at 44 °C for 10 min at 8 h after administration. Multi-functional liposomes having temperature-triggered drug release and MRI functions might engender personalized chemotherapy, providing efficient patient-optimized chemotherapy.

pH-Sensitive fusogenic polymer-modified liposomes as a carrier of antigenic proteins for activation of cellular immunity

By modification of liposomes with poly(glycidol) derivatives such as succinylated poly(glycidol) and 3-methylglutarylated poly(glycidol), we have developed functional liposomes that generate fusion ability at mildly acidic pH. We investigated the feasibility of these polymer-modified liposomes as a carrier of antigenic proteins for induction of cellular immunity. These pH-sensitive fusogenic liposomes encapsulating ovalbumin (OVA) were applied to DC2.4 cells, a murine dendritic cell line. Observation with confocal laser scanning microscopy showed that these polymer-modified liposomes were taken up efficiently by the cells, thereafter delivering their contents into the cytosol, probably through fusion with endosomal membranes. Murine bone marrow-derived dendritic cells treated with polymer-modified liposomes encapsulating OVA stimulated CD8-OVA1.3 cells more strongly than OT4H.1D5 cells, indicating that the liposomes induced MHC class I-restricted presentation. Furthermore, administration of the polymer-modified, OVA-loaded liposomes from nasal cavities of mice induced stronger cellular immune responses than the OVA-loaded plain liposomes. Because the ability of the polymer-modified liposomes to activate cellular immunity was comparable to that of Freunds complete adjuvant, which is a widely used adjuvant, they potentially have use in production of efficient vaccines for immunotherapy.

A Collagen-Mimic Dendrimer Capable of Controlled Release

A collagen model peptide-attached dendrimer was synthesized as a potential functional collagen material. The peptides that clustered at the surface of the dendrimer formed a thermally reversible collagen-like triple helix. This dendrimer worked as a drug carrier with thermosensitive release capabilities, although it did not exhibit a lower critical solution temperature. From this dendrimer, the hydrogel could be made at low temperature.

Influence of dendrimer generation and polyethylene glycol length on the biodistribution of PEGylated dendrimers.

Dendrimers are a potential drug carrier. Because modification with polyethylene glycol (PEG) is known to improve the blood retention, PEGylated dendrimers have been studied as a useful drug carrier. In this study, three types of PEGylated L-lysine-bearing polyamidoamine dendrimers (PEG2k-Lys-PAMAM (G4), PEG5k-Lys-PAMAM (G4), PEG2k-Lys-PAMAM (G5)) were synthesized, which are composed of a dendrimer of different generations (generations 4 and 5) and PEG chains with different molecular weights (2k and 5k). An acetylated L-lysine-bearing dendrimer was also synthesized as a non-PEGylated dendrimer. Bifunctional diethylenetriaminepentaacetic acid (pSCN-benzyl-DTPA) was bound to the epsilon -amino group of lysine in a dendrimer, to be labeled with radioactive indium-111. These PEGylayed dendrimers showed longer blood retention and lower accumulation in other normal organs such as the kidneys than the non-PEGylated dendrimer. The PEGylated dendrimers with the higher generation and the longer PEG led the greater blood retention.

Design of stimuli-responsive dendrimers

Importance of the field: Dendrimers are synthetic macromolecules with well-defined structures, many terminal functional groups, and an inner space to hold small molecules. These properties make them potential drug carriers. Recently, stimuli-responsive drug delivery systems have become attractive because of the reduction of side effects and maximum expression of drug action. Areas covered in this review: This paper reviews dendrimer nanoparticles that are sensitive to temperature, light, pH and redox state. What the reader will gain: Strategies to design these dendritic polymers are provided in this review. Take home message: By adding stimuli-responsive properties to the dendrimers, dendritic polymers capable of controlled release can be produced. These stimuli-responsive dendrimers are a potential next generation drug carrier.

Dendrimer-based MRI contrast agents: the effects of PEGylation on relaxivity and pharmacokinetics

UNLABELLED Polyethylene glycol (PEG) surface modification can make nanomaterials highly hydrophilic, reducing their sequestration in the reticuloendothelial system. In this study, polyamidoamine (PAMAM) dendrimers bearing gadolinium (Gd) chelates were PEGylated with different PEG-chain lengths, and the effects on paramagnetic and pharmacokinetic properties were evaluated. Specifically, Gd chelate-bearing PAMAM dendrimers (generations 4 and 5; G4 and G5) were conjugated with two different PEG chains (2 kDa and 5 kDa; 2k and 5k). Long PEG chains (5k) on the smaller (G4) dendrimer resulted in reduced relaxivity compared to non-PEGylated dendrimers, whereas short PEG chains (2k) on a larger (G5) dendrimer produced relaxivities comparable to non-PEGylated G4 dendrimers. The relaxivity of all PEGylated or lysine-conjugated dendrimers increased at higher temperature, whereas that of intact G4 Gd-PAMAM dendrimer decreased. All PEGylated dendrimers had minimal liver and kidney uptake and remained in circulation for at least 1 hour. Thus, surface-PEGylated Gd-PAMAM dendrimers showed decreased plasma clearance and prolonged retention in the blood pool. Shorter PEG, higher generation conjugates led to higher relaxivity. FROM THE CLINICAL EDITOR In this study, polyamidoamine dendrimers bearing gadolinium (Gd) chelates were PEGylated with different PEG-chain lengths, and the effects on paramagnetic and pharmacokinetic properties were evaluated.

Synthesis and Characterization of Hyperbranched Poly(glycidol) Modified with pH- and Temperature-Sensitive Groups

Hyperbranched poly(glycidol)s with varying degrees of polymerization were modified by reaction with succinic anhydride and isopropylamine to obtain novel pH- and thermosensitive polymers. These polymers exhibited phase transitions in response to decreasing pH and/or increasing temperature, depending on the degree of polymerization and the ratio of succinyl group to N-isopropylamide. It was possible to harvest a bioactive molecule, rose bengal, from solution using the phase transition of thermosensitive hyperbranched poly(glycidol).