Shigeto Fukushima

Doxorubicin-loaded poly(ethylene glycol)-poly(β-benzyl-L-aspartate) copolymer micelles : Their pharmaceutical characteristics and biological significance

Doxorubicin (DOX) was physically loaded into micelles prepared from poly(ethylene glycol)-poly(beta-benzyl-L-aspartate) block copolymer (PEG-PBLA) by an o/w emulsion method with a substantial drug loading level (15 to 20 w/w%). DOX-loaded micelles were narrowly distributed in size with diameters of approximately 50-70 nm. Dimer derivatives of DOX as well as DOX itself were revealed to be entrapped in the micelle, the former seems to improve micelle stability due to its low water solubility and possible interaction with benzyl residues of PBLA segments through pi-pi stacking. Release of DOX compounds from the micelles proceeded in two stages: an initial rapid release was followed by a stage of slow and long-lasting release of DOX. Acceleration of DOX release can be obtained by lowering the surrounding pH from 7.4 to 5.0, suggesting a pH-sensitive release of DOX from the micelles. A remarkable improvement in blood circulation of DOX was achieved by use of PEG-PBLA micelle as a carrier presumably due to the reduced reticuloendothelial system uptake of the micelles through a steric stabilization mechanism. Finally, DOX loaded in the micelle showed a considerably higher antitumor activity compared to free DOX against mouse C26 tumor by i.v. injection, indicating a promising feature for PEG-PBLA micelle as a long-circulating carrier system useful in modulated drug delivery.

Development of the polymer micelle carrier system for doxorubicin

We show the result of pre-clinical study of NK911, a polymeric micelle carrier system for doxorubicin (DOX). The NK911 micelle carrier consists of polyethyleneglycol and conjugated doxorubicin-polyaspartic acid. It has high hydrophobic inner core, and therefore can entrap the sufficient amount of DOX. NK911 has a small particle size of about 40 nm in diameter that accumulates in tumor tissue by EPR effect showing much stronger activity than the free DOX. We plan to perform a clinical trial at National Cancer Center Hospital, Japan from 2001.

Characterization of physical entrapment and chemical conjugation of adriamycin in polymeric micelles and their design for in vivo delivery to a solid tumor

An anticancer drug adriamycin (ADR) was incorporated into polymeric micelles forming from poly(ethylene glycol)-poly(aspartic acid) block copolymer by chemical conjugation and physical entrapment. Structural stability of the polymeric micelles was found to be dependent on both the contents of chemically conjugated and physically entrapped ADR. The polymeric micelle with high contents of the chemically conjugated ADR and the physically entrapped ADR expressed very high in vivo antitumor activity against murine C 26 tumor, while the polymeric micelle with only the chemically conjugated ADR showed negligible in vivo activity. This indicates that the physically entrapped ADR played a major role in antitumor activity in vivo. For the polymeric micelle with the high ADR contents, it was found that a dimer of adriamycin molecules formed and that this dimer was physically entrapped in the inner core of the micelle as well as intact ADR.

Polyplexes from poly(aspartamide) bearing 1,2-diaminoethane side chains induce pH-selective, endosomal membrane destabilization with amplified transfection and negligible cytotoxicity

Polyplexes assembled from poly(aspartamide) derivatives bearing 1,2-diaminoethane side chains, [PAsp(DET)] display amplified in vitro and in vivo transfection activity with minimal cytotoxicity. To elucidate the molecular mechanisms involved in this unique function of PAsp(DET) polyplexes, the physicochemical and biological properties of PAsp(DET) were thoroughly evaluated with a control bearing 1,3-diaminopropane side chains, PAsp(DPT). Between PAsp(DET) and PAsp(DPT) polyplexes, we observed negligible physicochemical differences in particle size and zeta-potential. However, the one methylene variation between 1,2-diaminoethane and 1,3-diaminopropane drastically altered the transfection profiles. In sharp contrast to the constantly high transfection efficacy of PAsp(DET) polyplexes, even in regions of excess polycation to plasmid DNA (pDNA) (high N/P ratio), PAsp(DPT) polyplexes showed a significant drop in the transfection efficacy at high N/P ratios due to the progressively increased cytotoxicity with N/P ratio. The high cytotoxicity of PAsp(DPT) was closely correlated to its strong destabilization effect on cellular membrane estimated by hemolysis, leakage assay of cytoplasmic enzyme (LDH assay), and confocal laser scanning microscopic observation. Interestingly, PAsp(DET) revealed minimal membrane destabilization at physiological pH, yet there was significant enhancement in the membrane destabilization at the acidic pH mimicking the late endosomal compartment (pH approximately 5). Apparently, the pH-selective membrane destabilization profile of PAsp(DET) corresponded to a protonation change in the flanking diamine unit, i.e., the monoprotonated gauche form at physiological pH and diprotonated anti form at acidic pH. These significant results suggest that the protonated charge state of 1,2-diaminoethane may play a substantial role in the endosomal disruption. Moreover, this novel approach for endosomal disruption neither perturbs the membranes of cytoplasmic vesicles nor organelles at physiological pH. Thus, PAsp(DET) polyplexes, residing in late endosomal or lysosomal states, smoothly exit into the cytoplasm for successful transfection without compromising cell viability.

A PEG‐Based Biocompatible Block Catiomer with High Buffering Capacity for the Construction of Polyplex Micelles Showing Efficient Gene Transfer toward Primary Cells

Nonviral gene vectors from synthetic catiomers (polyplexes) are a promising alternative to viral vectors. In particular, many recent efforts have been devoted to the construction of biocompatible polyplexes for in vivo nonviral gene therapy. A promising approach in this regard is the use of poly(ethylene glycol) (PEG)‐based block catiomers, which form a nanoscaled core–shell polyplex with biocompatible PEG palisades. In this study, a series of PEG‐based block catiomers with different amine functionalities were newly prepared by a simple and affordable synthetic procedure based on an aminolysis reaction, and their utility as gene carriers was investigated. This study revealed that the block catiomers carrying the ethylenediamine unit at the side chain are capable of efficient and less toxic transfection even toward primary cells, highlighting critical structural factors of the cationic units in the construction of polyplex‐type gene vectors. Moreover, the availability of the polyplex micelle for transfection with primary osteoblasts will facilitate its use for bone regeneration in vivo mediated by nonviral gene transfection.

Targeted polymeric micelles for siRNA treatment of experimental cancer by intravenous injection

Small interfering ribonucleic acid (siRNA) cancer therapies administered by intravenous injection require a delivery system for transport from the bloodstream into the cytoplasm of diseased cells to perform the function of gene silencing. Here we describe nanosized polymeric micelles that deliver siRNA to solid tumors and elicit a therapeutic effect. Stable multifunctional micelle structures on the order of 45 nm in size formed by spontaneous self-assembly of block copolymers with siRNA. Block copolymers used for micelle formation were designed and synthesized to contain three main features: a siRNA binding segment containing thiols, a hydrophilic nonbinding segment, and a cell-surface binding peptide. Specifically, poly(ethylene glycol)-block-poly(L-lysine) (PEG-b-PLL) comprising lysine amines modified with 2-iminothiolane (2IT) and the cyclo-Arg-Gly-Asp (cRGD) peptide on the PEG terminus was used. Modification of PEG-b-PLL with 2IT led to improved control of micelle formation and also increased stability in the blood compartment, while installation of the cRGD peptide improved biological activity. Incorporation of siRNA into stable micelle structures containing the cRGD peptide resulted in increased gene silencing ability, improved cell uptake, and broader subcellular distribution in vitro and also improved accumulation in both the tumor mass and tumor-associated blood vessels following intravenous injection into mice. Furthermore, stable and targeted micelles inhibited the growth of subcutaneous HeLa tumor models and demonstrated gene silencing in the tumor mass following treatment with antiangiogenic siRNAs. This new micellar nanomedicine could potentially expand the utility of siRNA-based therapies for cancer treatments that require intravenous injection.

Enhanced photodynamic cancer treatment by supramolecular nanocarriers charged with dendrimer phthalocyanine.

Photodynamic therapy (PDT) is a promising method for the localized treatment of solid tumors. In order to enhance the efficacy of PDT, we have recently developed a novel class of photosensitizer formulation, i.e., the dendrimer phthalocyanine (DPc)-encapsulated polymeric micelle (DPc/m). The DPc/m induced efficient and unprecedentedly rapid cell death accompanied by characteristic morphological changes such as blebbing of cell membranes, when the cells were photoirradiated using a low power halogen lamp or a high power diode laser. The fluorescent microscopic observation using organelle-specific dyes demonstrated that DPc/m might accumulate in the endo-/lysosomes; however, upon photoirradiation, DPc/m might be promptly released into the cytoplasm and photodamage the mitochondria, which may account for the enhanced photocytotoxicity of DPc/m. This study also demonstrated that DPc/m showed significantly higher in vivo PDT efficacy than clinically used Photofrin (polyhematoporphyrin esters, PHE) in mice bearing human lung adenocarcinoma A549 cells. Furthermore, the DPc/m-treated mice did not show skin phototoxiciy, which was apparently observed for the PHE-treated mice, under the tested conditions. These results strongly suggest the usefulness of DPc/m in clinical PDT.

Three-layered polyplex micelle as a multifunctional nanocarrier platform for light-induced systemic gene transfer

Nanocarriers responding to light have great potential for pinpoint therapy, and recent studies have revealed promising in vivo activity. However, light-selective gene transfer still remains challenging in the systemic application. Here we report systemic light-responsive nanocarriers for gene delivery developed through the sequential self-assembly of ABC-type triblock copolymer/DNA/dendrimeric photosensitizer, forming polyplex micelles with three-layered functional nanocompartments. The DNA-packaged core is covered by the photosensitizer-incorporated intermediate layer, which is encompassed by an outer shielding shell. This three-layered structure permits multistep photosensitizer and DNA delivery into a solid tumour by a systemic route: the shielding layer minimizes unfavourable interactions with blood components, and the photosensitizer is delivered to endo-/lysosomal membranes to facilitate light-selective cytoplasmic translocation of the micelles, accomplishing DNA delivery into the nucleus to exert gene expression. The polyplex micelles display >100-fold photoenhanced gene expression in cultured cells and exhibit light-induced in vivo gene transfer in solid tumours following systemic administration.

In situ quantitative monitoring of polyplexes and polyplex micelles in the blood circulation using intravital real-time confocal laser scanning microscopy.

Surface modification using poly(ethylene glycol) (PEG) is a widely used strategy to improve the biocompatibility of cationic polymer-based nonviral gene vectors (polyplexes). A novel method based on intravital real-time confocal laser scanning microscopy (IVRTCLSM) was applied to quantify the dynamic states of polyplexes in the bloodstream, thereby demonstrating the efficacy of PEGylation to prevent their agglomeration. Blood flow in the earlobe blood vessels of experimental animals was monitored in a noninvasive manner to directly observe polyplexes in the circulation. Polyplexes formed distinct aggregates immediately after intravenous injection, followed by interaction with platelets. To quantify aggregate formation and platelet interaction, the coefficient of variation and Pearsons correlation coefficient were adopted. In contrast, polyplex micelles prepared through self-assembly of plasmid DNA with PEG-based block catiomers had dense PEG palisades, revealing no formation of aggregates without visible interaction with platelets during circulation. This is the first report of in situ monitoring and quantification of the availability of PEGylation to prevent polyplexes from agglomeration over time in the blood circulation. This shows the high utility of IVRTCLSM in drug and gene delivery research.

Biocompatible micellar nanovectors achieve efficient gene transfer to vascular lesions without cytotoxicity and thrombus formation.

Gene therapy, a promising treatment for vascular disease, requires appropriate gene vectors with high gene transfer efficiency, good biocompatibility and low cytotoxicity. To satisfy these requirements from the approach of nonviral vectors, a novel block copolymer, poly(ethylene glycol) (PEG)-block-polycation, carrying ethylenediamine units in the side chain (PEG-b-P[Asp(DET)]) was prepared. PEG-b-P[Asp(DET)] formed a polyplex micelle through polyion complex formation with plasmid DNA (pDNA). The PEG-b-P[Asp(DET)] polyplex micelle showed efficient gene expression with low cytotoxicity against vascular smooth muscle cells in vitro. It also showed reduced interactions with blood components, offering its feasibility of gene delivery via the vessel lumen. To evaluate in vivo gene transfer efficiency for vascular lesions, PEG-b-P[Asp(DET)] micelle was instilled into rabbit carotid artery with neointima by an intravascular method, and expression of the reporter gene in vascular lesions was assessed. Polyplexes from homopolymer P[Asp(DET)] and branched polyethyleneimine (BPEI) were used as controls. Ultimately, only the polyplex micelle showed appreciable gene transfer into vascular lesions without any vessel occlusion by thrombus, which was in strong contrast to BPEI and P[Asp(DET)] polyplexes which frequently showed occlusion with thrombus. These findings suggest that the PEG-b-P[Asp(DET)] polyplex micelle may have promising potential as a nonviral vector for the treatment of vascular diseases.