Liver cell-targeted delivery of therapeutic molecules.

The liver is the largest internal organ in mammals and is involved in metabolism, detoxification, synthesis of proteins and lipids, secretion of cytokines and growth factors and immune/inflammatory responses. Hepatitis, alcoholic or non-alcoholic liver disease, hepatocellular carcinoma, hepatic veno-occlusive disease, and liver fibrosis and cirrhosis are the most common liver diseases. Safe and efficient delivery of therapeutic molecules (drugs, genes or proteins) into the liver is very important to increase the clinical efficacy of these molecules and to reduce their side effects in other organs. Several liver cell-targeted delivery systems have been developed and tested in vivo or ex vivo/in vitro. In this review, we discuss the literature concerning liver cell-targeted delivery systems, with a particular emphasis on the results of in vivo studies.

Releasable, Immune-Instructive, Bioinspired Multilayer Coating Resists Implant-Induced Fibrosis while Accelerating Tissue Repair.

Implantable biomaterials trigger foreign body reactions (FBRs), which reduces the functional life of medical devices and prevents effective tissue regeneration. Although existing therapeutic approaches can circumvent collagen-rich fibrotic encapsulation secondary to FBRs, they disrupt native tissue repair. Herein, a new surface engineering strategy in which an apoptotic-mimetic, immunomodulatory, phosphatidylserine liposome (PSL) is released from an implant coating to induce the formation of a macrophage phenotype that mitigates FBRs and improves tissue healing is described. PSL-multilayers constructed on implant surfaces via the layer-by-layer method release PSLs over a 1-month period. In rat muscles, poly(etheretherketone) (PEEK), a nondegradable polymer implant model, induces FBRs with dense fibrotic scarring under an aberrant cellular profile that recruits high levels of inflammatory infiltrates, foreign body giant cells (FBGCs), scar-forming myofibroblasts, and inflammatory M1-like macrophages but negligible amounts of anti-inflammatory M2-like phenotypes. However, the PSL-multilayer coating markedly diminishes these detrimental signatures by shifting the macrophage phenotype. Unlike other therapeutics, PSL-multilayered coatings also stimulate muscle regeneration. This study demonstrates that PSL-multilayered coatings are effective in eliminating FBRs and promoting regeneration, hence offering potent and broad applications for implantable biomaterials.

Development of human hepatocellular carcinoma cell-targeted protein cages.

We described herein a human hepatocellular carcinoma (HCC) cell-targeted protein cage for which the HCC-binding peptide termed SP94 was modified at the surface of a naturally occurred heat shock protein (Hsp) cage. Six types of HCC-targeted Hsp cages were chemically synthesized using two types of heterobifunctional linker (SM(PEG)(n)) with different lengths and two types of SP94 peptide, which contained a unique Cys residue at the N- or C-terminus of the peptide. These Hsp cages were characterized using matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-ToF MS) analyses, sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses, and dynamic light scattering (DLS) measurement. Fluorescence microscopic observations revealed that all the engineered protein cages bind selectively to HCC cells but not to the other cell lines tested (including normal liver cell). Moreover, the number of SP94 peptides on Hsp cages, conjugation site of SP94 peptide, and linker length between a Hsp cage and a SP94 peptide had important effects upon the binding of engineered Hsp cages to HCC cells. An engineered Hsp cage conjugated to the N-terminus of SP94 peptide via a longer linker molecule and containing high SP94 peptide levels showed greater binding toward HCC cells. Surprisingly, through optimization of these three factors, up to 10-fold greater affinity toward HCC cells was achieved. These results are critically important not only for the development of HCC cell-targeting devices using SP94 peptide, but also to create other cell-targeting materials that utilize other peptide ligands.

Phosphatidylserine liposome multilayers mediate the M1-to-M2 macrophage polarization to enhance bone tissue regeneration.

An appropriate immune microenvironment, governed by macrophages, is essential for rapid tissue regeneration after biomaterial implantation. The macrophage phenotypes, M1 (inflammatory) and M2 (anti-inflammatory/healing), exert opposing effects on the repair of various tissues. In this study, a new strategy to promote tissue repair and tissue-to-biomaterial integration by M1-to-M2 macrophage transition using artificial apoptotic cell mimetics (phosphatidylserine liposomes; PSLs) was developed using bone as a model tissue. Titanium was also selected as a model substrate material because it is widely used for dental and orthopedic implants. Titanium implants were functionalized with multilayers via layer-by-layer assembly of cationic protamine and negatively charged PSLs that were chemically stabilized to prevent disruption of lipid bilayers. Samples carrying PSL multilayers could drive M1-type macrophages into M2-biased phenotypes, resulting in a dramatic change in macrophage secretion for tissue regeneration. In a rat femur implantation model, the PSL-multilayer-coated implant displayed augmented de novo bone formation and bone-to-implant integration, associated with an increased M1-to-M2-like phenotypic transition. This triggered the proper generation and activation of bone-forming osteoblasts and bone-resorbing osteoclasts relative to their uncoated counterparts. This study demonstrates the benefit of local M1-to-M2 macrophage polarization induced by PSL-multilayers constructed on implants for potent bone regeneration and bone-to-implant integration. The results of this study may help in the design of new immunomodulatory biomaterials. STATEMENT OF SIGNIFICANCE: Effective strategies for tissue regeneration are essential in the clinical practice. The macrophage phenotypes, M1 (inflammatory) and M2 (anti-inflammatory/healing), exert opposing effects on the repair of various tissues. Artificially produced phosphatidylserine-containing liposomes (PSLs) can induce M2 macrophage polarization by mimicking the inverted plasma membranes of apoptotic cells. This study demonstrates the advantages of local M1-to-M2 macrophage polarization induced by PSL-multilayers constructed on implants for effective bone regeneration and osseointegration (bone-to-implant integration). Mechanistically, M2 macrophages promote osteogenesis but inhibit osteoclastogenesis, and M1 macrophages vice versa. We believe that our study makes a significant contribution to the design of new immunomodulatory biomaterials for regenerative medicine because it is the first to validate the benefit of PSLs for tissue regeneration.

Fluorescent nanoparticles consisting of lipopeptides and fluorescein-modified polyanions for monitoring of protein kinase activity.

Protein kinase (PK)-responsive nanoparticles (NPs) comprising a hydrophobically modified peptide substrate for PKs and a fluorescein-labeled polyanion (pA-F) were reported for monitoring PK activity via fluorescence intensity measurements. In this system, the formation of NPs by mixing lipopeptides and pA-Fs results in fluorescence quenching, while the quenched fluorescence recovered following dissociation of the NPs owing to the phosphorylation reaction of PKs. Eleven lipopeptides with different hydrophobic moieties (hydrocarbon and lithocholic acid) and four pA-Fs having main chains with differing flexibilities and fluorescein contents were synthesized and used to fabricate a series of twenty-four PK-responsive NP probes. The responses of the PK-responsive NP probes to PKs were evaluated to screen the most suitable NP probes. The assay system was then used to determine the IC(50) values for five inhibitors, the results of which were very similar to those previously reported. Thus, PK-responsive NPs are useful tools for high-throughput screening (HTS) of PK inhibitors.

Protein Kinase C α-Responsive Gene Carrier for Cancer-Specific Transgene Expression and Cancer Therapy.

The presence of intracellular signal transduction and its abnormal activities in many cancers has potential for medical and pharmaceutical applications. We recently developed a protein kinase C α (PKCα)-responsive gene carrier for cancer-specific gene delivery. Here, we demonstrate an in-depth analysis of cellular signal-responsive gene carrier and the impact of its selective transgene expression in response to malfunctioning intracellular signaling in cancer cells. We prepared a novel gene carrier consisting of a linear polyethylenimine (LPEI) main chain grafted to a cationic PKCα-specific substrate (FKKQGSFAKKK-NH2). The LPEI-peptide conjugate formed a nanosized polyplex with pDNA and mediated efficient cellular uptake and endosomal escape. This polyplex also led to successful transgene expression which responded to the target PKCα in various cancer cells and exhibited a 10-100-fold higher efficiency compared to the control group. In xenograft tumor models, the LPEI-peptide conjugate promoted transgene expression showing a clear-cut response to PKCα. Furthermore, when a plasmid containing a therapeutic gene, human caspase-8 (pcDNA-hcasp8), was used, the LPEI-peptide conjugate had significant cancer-suppressive effects and extended animal survival. Collectively, these results reveal that our method has great potential for cancer-specific gene delivery and therapy.

Liver-targeted siRNA delivery by polyethylenimine (PEI)-pullulan carrier.

Recently, small interfering RNA (siRNA)-based therapeutics have been used to treat diseases. Efficient and stable siRNA delivery into disease cells is important in the use of this agent for treatment. In the present study, pullulan was introduced into polyethylenimine (PEI) for liver targeting. PEI/siRNA or pullulan-containing PEI/siRNA complexes were delivered into mice through the tail vein either by a hydrodynamics- or non-hydrodynamics-based injection. The incidence of mortality was found to increase with an increase in the nitrogen/phosphorus (N/P) ratio of PEI/siRNA complexes. Moreover, the hydrodynamics-based injection increased mice mortality. Introduction of pullulan into PEI dramatically reduced mouse death after systemic injection. After systemic injection, the PEI/fluorescein-labeled siRNA complex increased the level of fluorescence in the lung and the PEI-pullulan/siRNA complex led to an increased fluorescence level in the liver. These results suggest that the PEI-pullulan polymer may be a useful, low toxic means for efficient delivery of siRNA into the liver.

Unique cellular interaction of macrophage-targeted liposomes potentiates anti-inflammatory activity.

Nanomedicines that suppress macrophage-mediated chronic inflammation are important therapeutics for many inflammatory diseases. The small-sized (<100 nm) apoptotic-cell-mimetic macrophage-targeted liposomes served as a long-lasting immunosuppressive agent through preferential association with CD300a receptor, unlike larger liposomes, enabling the amelioration of hepatic inflammation in mice.

Protein kinase Calpha-responsive polymeric carrier: its application for gene delivery into human cancers.

For cancer-targeting gene delivery, we applied a protein kinase C (PKC)alpha-responsive polymeric carrier to human cancers (U-87 MG [human glioblastoma-astrocytoma, epithelial-like cell line] and A549 [human lung adenocarcinoma epithelial cell line]). Two polymers, one a PKCalpha-responsive polymer (PPC[S]) containing the phosphorylation site serine, and the other a negative control polymer (PPC[A]), in which the serine was substituted with alanine, were synthesized. No cytotoxicity of the polymer was identified. When the complexes were transfected into cancer cells or tissues in which PKCalpha was hyper-activated, the luciferase expression from the PPC(S)/plasmid (pDNA) complex was higher than that from the PPC(A)/pDNA complex. These results show that the phosphorylation of complex by PKCalpha in cancer cells leads to high gene expression and that our system can be used as a human cancer cell-targeting gene delivery system.

Rapid and continuous accumulation of nitric oxide-releasing liposomes in tumors to augment the enhanced permeability and retention (EPR) effect.

The modulation of blood flow to tumors is a prominent strategy for improving the tumor accumulation of nanomedicines, resulting from the enhanced permeability and retention (EPR) effect. We previously reported a promising EPR enhancer-a nitric oxide (NO) donor-containing liposome (NO-LP)-which showed enhanced accumulation in tumor tissue. Herein, we study NO-LP in greater detail to clarify its practical use as an EPR enhancer. NO-LP was found to have advantages as a NO donor, including the ability to maintain NO donation over long periods of time, and a constant rate of NO-release irrespective of the environmental pH. NO-LP showed rapid accumulation in tumor tissue after injection (1 h), and then accumulation was continuously enhanced until 48 h. Enhanced NO-LP accumulation was observed specifically in tumor, while the accumulation in other organs remained relatively unchanged. The results obtained show the promising features of NO-LP as an EPR enhancer.

Effective delivery of DNA into tumor cells and tissues by electroporation of polymer-DNA complex.

Electroporation is a useful means for non-viral gene delivery. Here, we investigated the use of electroporation to deliver polymer-DNA complexes into living cells using a protein kinase C (PKC)alpha-responsive polymer. The polymer was complexed with a luciferase-encoding DNA and electroporated into B16 melanoma cells. Gene expression from polymer-DNA complexes was 3- to 5-fold higher than from naked DNA. Moreover, after introduction of the polymer-DNA complex into tissues, luciferase levels were >2-fold higher in B16 melanoma tumors than in normal skin tissue. These results suggest that the combination of our polymer and electroporation is useful for the effective delivery of DNA into tumors.

Macrophage Uptake Behavior and Anti-inflammatory Response of Bovine Brain- or Soybean-derived Phosphatidylserine Liposomes.

Phosphatidylserine (PtdSer) is mainly derived from the bovine brain cortex or soybean lecithin. We investigated macrophage uptake behavior and the anti-inflammatory response induced by liposomes containing bovine brain- (B-PSL) or soybean-derived PtdSer (S-PSL). The size of B-PSL and S-PSL was very similar. There were no significant differences in the uptake of B-PSL and S-PSL by Raw 264.7 macrophage cells. Addition of B-PSL or S-PSL decreased the production of the inflammatory cytokines, IL-1α, IL-6 and TNF-α, in lipopolysaccharide-treated Raw 264.7 cells, but there were no differences between them. These results suggest that S-PSL may be used as an anti-inflammatory agent.

Efficient delivery of signal-responsive gene carriers for disease-specific gene expression via bubble liposomes and sonoporation.

Sonoporation is a promising method to intracellularly deliver synthetic gene carriers that have lower endocytotic uptake than viral carriers. Here, we applied sonoporation to deliver genes via polyethylene glycol (PEG)-grafted polymeric carriers that specifically respond to hyperactivated protein kinase A (PKA). PEG-grafted polymeric carrier/DNA polyplexes were not efficiently delivered into cells via the endocytotic pathway because of the hydrophilic PEG layer surrounding the polyplexes. However, the delivery of polyplexes into cells was significantly increased by sonoporation. The delivered polyplexes exhibited PKA-responsive transgene expression in PKA-overexpressing cells, but not in cells with low PKA activation. These results show that the sonoporation-mediated delivery of PEG-modified PKA-responsive polyplexes is a promising approach for safely applying gene therapy to abnormal cells with hyperactivated PKA.

An intracellular kinase signal-responsive gene carrier for disordered cell-specific gene therapy.

We have previously reported artificial gene-regulation systems responding to cyclic AMP-dependent protein kinase (PKA) using cationic polymer. This cationic polymer (PAK) was a graft-type polymer with an oligopeptide that is a substrate for PKA and could regulate gene-expression in a cell-free system. In the present study, we carried out a detailed characterization of the PAK-DNA complex (AFM observation and DLS measurement) and tried to apply this polymer to living cells. In the unstimulated NIH 3T3 cells, transfection of the PAK-DNA complex showed no expression of the delivered gene. This means that PAK formed a stable complex with DNA in the normal cells to totally suppress gene expression. In contrast, significant expression was seen when the PAK-DNA complex was delivered to forskolin-treated cells. Thus, activated PKA disintegrates the complexes even in living cells, resulting in gene expression. Our results indicate that this type of intracellular signal-responsive polymer will be useful for the cell-specific release of genes.

Anti-obesity and anti-inflammatory effects of macrophage-targeted interleukin-10-conjugated liposomes in obese mice.

Obesity is associated with chronic inflammation and is known as a major risk factor for several diseases including chronic kidney disease, diabetes, and cardiovascular diseases. Macrophages play a critical role in the development of obesity-induced inflammation. Efficient delivery of therapeutic anti-inflammatory molecules, such as interleukin (IL)-10, to macrophages can dramatically improve therapeutic efficacy of obesity treatments. We used liposomes containing the 'eat-me' signal phosphatidylserine (PS) (PS-containing liposomes; PSL), which have macrophage targeting ability and anti-inflammatory functions, as a biomaterial carrier for the delivery of IL-10 to macrophages. The IL-10-conjugated PSL (PSL-IL10) showed high affinity for macrophages. In obese mice, PSL-IL10 treatment exhibited significant anti-obesity and anti-inflammatory effects, such as reduced serum total cholesterol, adipocyte size, crown-like structures, proinflammatory cytokine secretion (IL-6 and tumor necrosis factor α) in adipose tissue, liver injury, hepatic steatosis, and inflammation foci, while treatment with IL-10 or PSL alone did not. These findings suggest that the PSL-IL10 has macrophage targeting ability and enhanced anti-inflammatory effect due to the synergistic anti-inflammatory effects of IL-10 and PSL, and can be used as a macrophage-targeted therapeutic material for inflammation-related diseases, including obesity.

Effect of peptide content on the regulation of transgene expression by protein kinase Cα-responsive linear polyethylenimine-peptide conjugates.

We examined a series of linear polyethylenimine (LPEI)-based nanocarriers that activate transgene expression in response to cancer-specific protein kinase Cα (PKCα). Eight types of LPEI-peptide conjugate differing in peptide content and number were synthesized using click chemistry. The conjugates could form polyplexes with pDNA through electrostatic interaction, but the degree of pDNA condensation, sizes, and surface charges of the resulting polyplexes depended on the pendant-peptide content and number. None of the polyplexes showed significant cytotoxicity toward human hepatoma cells (HepG2). Furthermore, pendant peptide content and number markedly affected transgene activation in response to PKCα. To achieve an all-or-none response to PKCα, we determined the optimum peptide content and number in LPEI-peptide conjugates as ≈6 mol% and ≈40 peptides/conjugate.

Stabilization of cancer-specific gene carrier via hydrophobic interaction for a clear-cut response to cancer signaling.

Here, we developed a new gene carrier, comprising a linear polyethylenimine (LPEI) grafted with a hydrophobically modified cationic peptide containing a long alkyl chain, for use in cancer-specific gene delivery. The cationic peptide is a substrate of protein kinase Cα (PKCα), which is known to be activated specifically in cancer cells. The hydrophobically modified LPEI-peptide conjugate (LPEI-C10-peptide) could form a polyplex with DNA through electrostatic and hydrophobic interactions between the anionic DNA strands and the cationic peptide substrate. The hydrophobic modification of the peptide did not affect the reactivity of the peptide toward PKCα, while the polyplex showed improved intracellular uptake. Because of the efficient endosomal escape and enhanced stability, the polyplex significantly improved the transgene regulation responding to intracellular PKCα activity.

Efficient reduction of serum cholesterol by combining a liver-targeted gene delivery system with chemically modified apolipoprotein B siRNA.

Apolipoprotein B (Apo B) is a key amphipathic glycoprotein compound in the metabolism of plasma lipoproteins (mainly very low-density lipoprotein (VLDL) and LDL). Inhibition of Apo B synthesis by short interfering RNA (siRNA) targeting Apo B (Apo B siRNA) is very efficient for serum LDL reduction. In the present study, the chemically modified Apo B siRNA (Apo B-siBNA) with the increased enzymatic stability was selected. We developed a cationic conjugate for efficient delivery of Apo B-siBNA into the liver by introducing pullulan with different molecular weights (MWs) (5900 and 107,000) into polyethylenimine (PEI). Introduction of pullulan into PEI dramatically decreased mortality and lung damage after systemic injection of the conjugate/Apo B-siBNA complexes into mice. The PEI-pullulan carrier prepared with high MW pullulan (107,000) was more stable in the blood stream and showed higher fluorescence levels in the liver for a longer time than the carrier prepared with low MW pullulan (5900). Moreover, efficient reduction of serum LDL and Apo B mRNA in the liver was observed in mice injected with PEI-pullulan (MW, 107,000)/Apo B-siBNA, whereas there was no or little change in serum LDL and Apo B mRNA in livers of mice treated with Apo B-siBNA alone, PEI/Apo B-siBNA, and PEI-pullulan (MW, 5900)/Apo B-siBNA. These results suggest that combining a liver-targeted gene delivery system with chemically modified Apo B siRNA efficiently reduces the level of serum LDL and Apo B mRNA in the liver.

Improvement in the colloidal stability of protein kinase-responsive polyplexes by PEG modification.

We have reported a disease-cell specific gene expression system that is responsive to intracellular signaling proteins (e.g., protein kinases and proteases) hyperactivated in diseased cells. For this system, cationic peptide-grafted polymers were synthesized for polyplex formation with genes. Here, we modified poly(ethylene glycol) (PEG) to a protein kinase A (PKA)-responsive polymer to improve polyplex stability. PEG modification neutralized the surface charge of the polyplex and successfully increased polyplex stability at physiological conditions. However, PEG modification (PEG contents, 0.6 and 3.3 mol %) showed almost negligible effects on the reactivity of grafted peptides to PKA and the promotion of gene expression responding to PKA activity. Excessive modification of PEG (PEG contents, 6.8 mol %) inhibited polyplex formation. These results indicate that moderate modification of PEG to the enzyme-responsive polymer improves polyplex stability without inhibiting the reaction with enzymes.

Transgene regulation system responding to Rho associated coiled-coil kinase (ROCK) activation.

Recently, we have proposed a new system of gene regulation called 'drug or gene delivery system responding to cellular signals' (D-RECS). In this system, transgene expression is activated in response to intracellular target protein kinases or proteases for safe, cell-specific gene delivery by using peptide-polymer conjugates. Here we applied this system to an intracellular Rho-associated coiled-coil kinase (ROCK) signal, which is activated abnormally in cardiovascular diseases. A ROCK responsive polymer consisting of neutral polymers in main chain and cationic ROCK substrate peptides in side chains was prepared and could form the complex with plasmid DNA. The complex was transferred into NIH3T3 cells with or without L-α-lysophosphatidic acid (LPA) that increases ROCK activity. At an N/P ratio of 2.0, a significant increase of the gene expression was identified in LPA-treated NIH3T3 cells, but was disappeared in NIH3T3 cells treated with ROCK specific inhibitor, Y-27632. These results suggest that the ROCK responsive polymer can regulate gene expression in response to ROCK activity.