Receptor-mediated delivery of foreign genes to hepatocytes

Development of Novel Galactosylated PLGA Nanoparticles for Hepatocyte Targeting Using Molecular Modelling

Doxorubicin-loaded PLGA nanoparticles conjugated with a new galactose-based ligand for the specific recognition by human hepatoma cellular carcinoma cells (Hep G2) were successfully produced. The new targeting compound was selected using molecular docking combined with quantum chemical calculations for modelling and comparing molecular interactions among the H1 subunit of the asialoglycoprotein receptor containing the carbohydrate recognition domain and the ligand. The ligand, bis(1-O-ethyl-β-D-galactopyranosyl)amine, was synthetized, characterized, and subsequently linked to PLGA. Unloaded (PLGA-di-GAL NP) and doxorubicin-loaded (DOX-PLGA-di-GAL NP) nanoparticles were prepared using an emulsion method and characterized. The produced DOX-PLGA-di-GAL NP are spherical in shape with a size of 258 ± 47 nm, a zeta potential of -62.3 mV, and a drug encapsulation efficiency of 83%. The in vitro drug release results obtained show a three-phase release profile. In vitro cell studies confirmed the interaction between Hep G2 cells and PLGA-di-GAL NP. Cell cytotoxicity tests showed that unloaded NP are nontoxic and that DOX-PLGA-di-GAL NP caused a decrease of around 80% in cellular viability. The strategy used in this work to design new targeting compounds represents a promising tool to develop effective hepatocyte targeting drug delivery systems and can be applied to other tissues/organs.

Surface-modified PLGA nanoparticles with PEG/LA-chitosan for targeted delivery of arsenic trioxide for liver cancer treatment: Inhibition effects enhanced and side effects reduced

Arsenic trioxide (As₂O₃), an effective drug for leukemia, is limited to be used for solid tumor treatment due to its high side effects. In this study, polyethylene glycol (PEG) and lactobionic acid (LA) modified chitosan (PLC) was synthesized and was used to coat poly(lactide-co-glycolide) (PLGA) nanoparticles for encapsulation and targeted release of As₂O₃ in liver cancer treatment. The As₂O₃-loaded PLGA/PLC nanoparticles (As₂O₃-PLGA/PLC NPs) were fabricated through double emulsion-solvent evaporation method and were optimized by orthogonal tests. As₂O₃-PLGA/PLC NPs presented suitable physical stability, positive charge, high encapsulation efficiency and drug loading, and good biocompatibility. As expected, the NPs can quickly release enough dose of As₂O₃ in a short time and then sustain the drug concentration. The As₂O₃-PLGA/PLC NPs showed effective inhibition of SMMC-7721 cells while having lower cytotoxicity against normal human liver cells (LO2 cells). Furthermore, In vivo study showed that the NPs did not present toxic effects on kidney and liver, but showed relatively high growth inhibition effect on liver tumor. Therefore, this PLGA/PLC NPs could be an effective and safe drug delivery system for liver cancer chemotherapy.

Combination therapy with doxorubicin-loaded galactosylated poly(ethyleneglycol)-lithocholic acid to suppress the tumor growth in an orthotopic mouse model of liver cancer

Despite advances in technology, neither conventional anti-cancer drugs nor current nanoparticle (NP) drugs have gained substantial success in cancer treatment. While conventional chemotherapy drugs have several limitations such as low potency, poor in vivo stability and limited bioavailability, non-specific targeting of NP drugs diminishes their potency at actual target sites. In addition, the development of drug resistance to anti-cancer drugs is another challenging problem. To overcome these limitations, we aimed to develop a polymer-drug conjugate, which functions as an active NP drug and drug carrier both, to deliver a chemotherapeutic drug for combination therapy. Accordingly, we made targeting NP carrier of lithocholic acid-poly(ethylene glycol)-lactobionic acid (LPL) loading doxorubicin (Dox) to produce Dox/LPL NPs. The cellular uptake of Dox/LPL NPs was relatively higher in human liver cancer cell line (SK-HEP-1) due to galactose ligand-asialoglycoprotein receptor interaction. Consequently, the cellular uptake of Dox/LPL NPs led to massive cell death of SK-HEP-1 cells by two different mechanisms, particularly apoptotic activity by LPL and mitotic catastrophe by Dox. Most importantly, Dox/LPL NPs, when administered to orthotopic xenograft model of liver cancer, greatly reduced proliferation, invasion, migration, and angiogenesis of liver tumor in vivo. Thus, this study exemplifies the superiority of combination therapy over individual NP drug or conventional small molecule drug for cancer therapy. Overall, we present a promising approach of combinatorial therapy to inhibit the hepatic tumor growth and metastasis in the orthotopic xenograft model mice, thus representing an effective weapon for cancer treatment.

Galactosylated poly(ethyleneglycol)-lithocholic Acid selectively kills hepatoma cells, while sparing normal liver cells

Delivering drugs selectively to cancer cells but not to nearby normal cells is a major obstacle in drug therapy. In this study, lithocholic acid (LCA), a potent anti-cancer drug, is converted to two forms of poly(ethyleneglycol) (PEG) conjugates, viz., PEG-LCA (PL) and lactobionic acid (LBA) conjugated PEG-LCA (LPL). The latter form contains a galactose ligand in LBA to target the hepatocytes. Both forms are self-assembled to form nanoparticle formulation, and they have high potency than LCA to kill HepG2 cancer cells, sparing normal LO2 cells. Besides, LPL has high specificity to mouse liver cells in vivo. Western blot results confirm that the cell death is occurred through apoptosis induced by LPL nanoparticles. In conclusion, the induction of apoptosis and cell death is much more efficient with LPL nanoparticles than LCA molecules.

Efficient intracellular delivery and multiple-target gene silencing triggered by tripodal RNA based nanoparticles: a promising approach in liver-specific RNAi delivery

RNA interference (RNAi) triggering oligonucleotides in unconventional structural format can offer advantages over conventional small interfering RNA (siRNA), enhanced cellular delivery and improved target gene silencing. With this concept, we present a well-defined tripodal-interfering RNA (tiRNA) structure that can induce simultaneous silencing of multiple target genes with improved potency. The tiRNA structure, formed by the complementary association of three single-stranded RNA units, was optimized for improved gene silencing efficacy. When combined with cationic polymers such as linear polyethyleneimine (PEI), tiRNA assembled to form a stable nano-structured complex through electrostatic interactions and induced stronger RNAi response over conventional siRNA-PEI complex. In combination with a liver-targeting delivery system, tripodal nucleic acid structure demonstrated enhanced fluorescent accumulation in mouse liver compared to standard duplex nucleic acid format. Tripodal RNA structure complexed with galactose-modified PEI could generate effective RNAi-mediated gene silencing effect on experimental mice models. Our studies demonstrate that optimized tiRNA structural format with appropriate polymeric carriers have immense potential to become an RNAi-based platform suitable for multi-target gene silencing.

Glucose-containing diblock polycations exhibit molecular weight, charge, and cell-type dependence for pDNA delivery

A series of diblock glycopolycations were created by polymerizing 2-deoxy-2-methacrylamido glucopyranose (MAG) with either a tertiary amine-containing monomer, N-[3-(N,N-dimethylamino) propyl] methacrylamide (DMAPMA), or a primary amine-containing unit, N-(2-aminoethyl) methacrylamide (AEMA). Seven structures were synthesized via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization that varied in the block lengths of MAG, DMAPMA, and AEMA along with two homopolymer controls of DMAPMA and AEMA that lacked a MAG block. The polymers were all able to complex plasmid DNA into polyplex structures and to prevent colloidal aggregation of polyplexes in physiological salt conditions. In vitro transfection experiments were performed in both HeLa (human cervix adenocarcinoma) cells and HepG2 (human liver hepatocellular carcinoma) cells to examine the role of charge type, block length, and cell type on transfection efficiency and toxicity. The glycopolycation vehicles with primary amine blocks and PAEMA homopolymers revealed much higher transfection efficiency and lower toxicity when compared to analogs created with DMAPMA. Block length was also shown to influence cellular delivery and toxicity; as the block length of DMAPMA increased in the glycopolycation-based polyplexes, toxicity increased while transfection decreased. While the charge block played a major role in delivery, the MAG block length did not affect these cellular parameters. Lastly, cell type played a major role in efficiency. These glycopolymers revealed higher cellular uptake and transfection efficiency in HepG2 cells than in HeLa cells, while homopolycations (PAEMA and PDMAPMA) lacking the MAG blocks exhibited the opposite trend, signifying that the MAG block could aid in hepatocyte transfection.

A targetable acid-responsive micellar system for signal activation based high performance surgical resolution of tumors

High-performance illumination of subcutaneous tumor and liver tumor foci at sub-millimeter levels was achieved with lectin-targeted glyco-micelles which become fluorescent upon internalization into tumor lysosomes.

Preliminary Study on Hepatocyte-Targeted Phosphorus-31 MRS Using ATP-Loaded Galactosylated Chitosan Oligosaccharide Nanoparticles

Background. The clinical applications of hepatic phosphorus-31 magnetic resonance spectroscopy (31P MRS) remain to be difficult because the changes of phosphates between normal hepatic tissues and pathological tissues are not so obvious, and furthermore, up to now there is few literature on hepatocyte-targeted 31P MRS. Materials and Methods. The ATP-loaded Gal-CSO (Gal-CSO/ATP) nanoparticles were prepared and the special cellular uptake of them as evaluated by using HepG-2 tumor cells and A549 tumor cells, respectively. Two kinds of cells were incubated with the nanoparticles suspension, respectively. Then were prepared the cell samples and the enhancement efficiency of ATP peaks detected by 31P MRS was evaluated. Results. The cellular uptake rate of Gal-CSO/ATP nanoparticles in HepG-2 cells was higher than that in A549 cells. Furthermore, the enlarged ATP peaks of Gal-CSO/ATP nanoparticles in HepG-2 cells were higher than those in A549 cells in vitro detected by 31P MRS. Conclusions. Gal-CSO/ATP nanoparticles have significant targeting efficiency in hepatic cells in vitro and enhancement efficiency of ATP peaks in HepG-2 cells. Furthermore, 31P MRS could be applied in the research of hepatic molecular imaging.

Targeted doxorubicin delivery by chitosan-galactosylated modified polymer microbubbles to hepatocarcinoma cells

Targeted drug delivery is a main issue in cancer treatment. Taking advantage of recently developed polyvinyl alcohol (PVA)-based microbubbles, which are characterized by chemical versatility of the polymeric surface thereby allowing coating with different ligands, we set up a strategy for the targeted delivery of the anticancer agent doxorubicin to hepatocarcinoma cells. Such microbubbles are exceptionally efficient ultrasound scatterers and thus represent also an option as potential ultrasound contrast agents. Moreover, the oscillation of microbubbles induced by ultrasound could contribute to favor the release of drugs allocated on shell. Specifically, PVA-based microbubbles were reacted with a galactosylated chitosan complex and loaded with doxorubicin to enable the localization and drug delivery to HepG2 hepatocarcinoma cells overexpressing asialoglycoprotein receptors. We demonstrated selectivity and greater bioadhesive properties of the functionalized microbubbles for tumor cells than to normal fibroblasts, which were influenced by the degree of galactosylation. The presence of galactosylated chitosan did not modify the rate of doxorubicin release from microbubbles, whichwas almost complete within 48h. Cellular uptake of doxorubicin loaded on functionalized microbubbles was higher in HepG2 than in normal fibroblasts, which do not over express the asialoglycoprotein receptors. In addition, doxorubicin loaded onto functionalized microbubbles fully retained its cytotoxic activity. Cells were also irradiated with ultrasound, immediately after exposure to microbubbles. An early enhancement of doxorubicin release and cellular drug uptake associated to a concomitant increase in cytotoxicity was observed in HepG2 cells. Overall, results of the study indicate that galactosylated chitosan microbubbles represent promising devices for the targeted delivery of antitumor agents to liver cancer cells.

Hepatocyte-targeting single galactose-appended naphthalimide: a tool for intracellular thiol imaging in vivo

We present the design, synthesis, spectroscopic properties, and biological evaluation of a single galactose-appended naphthalimide (1). Probe 1 is a multifunctional molecule that incorporates a thiol-specific cleavable disulfide bond, a masked phthalamide fluorophore, and a single galactose moiety as a hepatocyte-targeting unit. It constitutes a new type of targetable ligand for hepatic thiol imaging in living cells and animals. Confocal microscopic imaging experiments reveal that 1, but not the galactose-free control system 2, is preferentially taken up by HepG2 cells through galactose-targeted, ASGP-R-mediated endocytosis. Probe 1 displays a fluorescence emission feature at 540 nm that is induced by exposure to free endogenous thiols, most notably GSH. The liver-specificity of 1 was confirmed in vivo via use of a rat model. The potential utility of this probe in indicating pathogenic states and as a possible screening tool for agents that can manipulate oxidative stress was demonstrated in experiments wherein palmitate was used to induce lipotoxicity in HepG2 cells.

Suppression of tumor growth in H-ras12V liver cancer mice by delivery of programmed cell death protein 4 using galactosylated poly(ethylene glycol)-chitosan-graft-spermine

Non-viral gene delivery systems based on polyethyleneimine (PEI) are efficient due to their proton-sponge effect within endosomes, but they have poor physical characteristics such as slow dissociation, cytotoxicity, and non targeted gene delivery. To overcome many of the problems associated with PEI, we synthesized a galactosylated poly(ethylene glycol)-chitosan-graft-spermine (GPCS) copolymer with low cytotoxicity and optimal gene delivery to hepatocytes using an amide bond between galactosylated poly(ethylene glycol) and chitosan-graft-spermine. The GPCS copolymer formed complexes with plasmid DNA, and the GPCS/DNA complexes had well-formed spherical shapes. The GPCS/DNA complexes were nanoscale size with homogenous size distribution and a positive zeta potential by dynamic light scattering (DLS). The GPCS copolymer had lower cytotoxicity than that of PEI 25K in HepG2, HeLa, and A549 cell lines at various concentrations and showed good hepatocyte-targeting ability. Furthermore, GPCS/DNA complexes showed higher levels of GFP expression in the liver in model mice after intravenous injection than naked DNA and metoxy-poly(ethylene glycol)-chitosan-graft-spermine as controls without remarkable fibrosis, inflammation, lipidosis, or necrosis. In a tumor suppression study, an intravenous injection of the GPCS/Pdcd4 complexes significantly suppressed tumor growth, activated apoptosis, and suppressed proliferation and angiogenesis in liver tumor-bearing H-ras12V mice. Our results indicate that the GPCS copolymer has potential as a hepatocyte-targeting gene carrier.

Smart siRNA delivery systems based on polymeric nanoassemblies and nanoparticles

RNA interference is a post-transcriptional gene-silencing pathway induced by double-stranded small interfering RNA (siRNA). The potential use of siRNA as a therapeutic agent has attracted great attention as a novel approach to the treatment of several intractable diseases. Despite the rapid progress in the therapeutic use of siRNA, systemic application is still controversial due to the limitations of siRNA, such as low enzymatic tolerability, cellular internalization and body distribution after systemic administration. This review describes the recent progress and strategies of siRNA delivery systems based on polyion complexes. Numerous siRNA-containing polyion complex systems bound together through electrostatic interactions between the negatively charged siRNA and positively charged components, including synthetic polymers, biopolymers and nanoparticles, have been developed for the therapeutic application of siRNA. Additionally, stimulus-sensitive smart siRNA carrier systems, including bioreducible polycations and hydrophilic polymer-siRNA conjugates, have been developed to enhance the gene-silencing efficacy of siRNAs.

Engineered nanoscaled polyplex gene delivery systems

Improving the transfection efficiencies of nonviral gene delivery requires properly engineered nanoscaled delivery carriers that can overcome the multiple barriers associated with the delivery of oligonucleotides from the site of administration to the nucleus or cytoplasm of the target cell. This article reviews the current advantages and limitation of polyplex nonviral delivery systems, including the apparent barriers that limit gene expression efficiency compared to physical methods such as hydrodynamic dosing and electroporation. An emphasis is placed on engineered nanoscaled polyplexes (NSPs) of modular design that both self-assemble and systematically disassemble at the desired stage of delivery. It is suggested that NSPs of increasingly sophisticated designs are necessary to improve the efficiency of the rate limiting steps in gene delivery.

Enhanced growth inhibition of hepatic multicellular tumor spheroids by lactosylated poly(ethylene glycol)-siRNA conjugate formulated in PEGylated polyplexes

PEGylated polyplexes (lac-PEGylated polyplexes) composed of poly(L-lysine) and lactosylated poly(ethylene glycol)-small interfering RNA conjugate, which inhibits the RecQL1 gene product, were revealed to show an appreciable growth inhibition of multicellular HuH-7 spheroids (human hepatocarcinoma cell lines) for up to 21 days (IC(50)=6 nM); this system used as an in vitro three-dimensional (3D) model mimicking the in vivo biology of tumors. The PEGylated polyplexes thus prepared had a size of approximately 110 nm with clustered lactose moieties on their periphery as targeting ligands for the asialoglycoprotein-receptor-expressing HuH-7 cells. In contrast, OligofectAMINE/siRNA (cationic lipoplex) was observed to have almost no growth-inhibitory effect against HuH-7 spheroids, even though the lipoplex showed a stronger growth-inhibitory effect than the lac-PEGylated polyplexes on conventional monolayer-cultured HuH-7 cells. The FITC-tagged conjugate in the lac-PEGylated polyplexes showed smooth penetration into the HuH-7 spheroids compared with that in the lipoplexes, as observed by confocal fluorescence-scanning microscopy. This indicates that the small size of approximately 100 nm and the reduced nonspecific interaction due to the nonionic and hydrophilic lactosylated PEG layer contributes to the smooth penetration of the PEGylated polyplexes into the spheroid interior, eventually facilitating their uptake into the cells composing the spheroids. Cellular apoptosis indicating programmed cell death was also observed in the HuH-7 spheroids treated with the PEGylated polyplexes, revealing that the observed growth inhibition was indeed induced by the RNAi of the RecQL1 siRNA. These data suggest that the smart PEGylated polyplexes can indeed penetrate into the multiple cell layers of 3D tumor masses in vivo, exerting therapeutic effects through the RNAi.

Galactosylated poly(ethylene glycol)-chitosan-graft-polyethylenimine as a gene carrier for hepatocyte-targeting

Chitosan and chitosan derivatives have been proposed as alternative and biocompatible cationic polymers for non-viral gene delivery. However, the low transfection efficiency and low specificity of chitosan is an aspect of this approach that must be addressed prior to any clinical applications. In the present study a chitosan derivative, galactosylated poly(ethylene glycol)-chitosan-graft-polyethylenimine (Gal-PEG-CHI-g-PEI), was investigated as a potential hepatocyte-targeting gene carrier. The composition of Gal-PEG-CHI-g-PEI was characterized using (1)H nuclear magnetic resonance ((1)H NMR), and the particle size and zeta potential of Gal-PEG-CHI-g-PEI/DNA complexes were measured using dynamic light scattering (DLS). The Gal-PEG-CHI-g-PEI exhibited lower cytotoxicity compared to PEI 25K as a control. Likewise, Gal-PEG-CHI-g-PEI/DNA complexes showed good hepatocyte specificity. Furthermore, Gal-PEG-CHI-g-PEI/DNA complexes transfected liver cells more effectively than PEI 25K in vivo after intravenous (i.v.) administration. Together, these results suggest that Gal-PEG-CHI-g-PEI, which has improved transfection efficiency and hepatocyte specificity both in vitro and in vivo, may be useful for gene therapy.

Liver target delivery of small interfering RNA to the HCV gene by lactosylated cationic liposome

BACKGROUND/AIMS

RNA interference has considerable therapeutic potential, particularly for anti-viral therapy. We previously reported that hepatitis C virus (HCV)-directed small interfering RNA (siRNA; siE) efficiently inhibits HCV replication, using HCV replicon cells. To employ the siRNA as a therapeutic strategy, we attempted in vivo silencing of intrahepatic HCV gene expression by siE using a novel cationic liposome.

METHODS

The liposomes consisted of conjugated lactose residues, based on the speculation that lactose residues would effectively deliver siRNA to the liver via a liver specific receptor. The lactosylated cationic liposome 5 (CL-LA5) that contained the most lactose residues introduced the most siRNA into a human hepatoma cell line, which then inhibited replication of HCV replicons.

RESULTS

In mice, the siRNA/CL-LA5 complexes accumulated primarily in the liver and were widespread throughout the hepatic parenchymal cells. Moreover, siE/CL-LA5 specifically and dose-dependently suppressed intrahepatic HCV expression in transgenic mice without an interferon response.

CONCLUSIONS

The present results indicate that the CL-LA5 we developed is a good vehicle to lead siRNA to the liver. Hence, CL-LA5 will be helpful for siRNA therapy targeting liver diseases, especially hepatitis C.

Therapeutic application of RNA interference for hepatitis C virus

RNA interference (RNAi) is a sequence-specific post-transcriptional gene silencing by double-stranded RNA. Because the phenomenon is conserved and ubiquitous in mammalian cells, RNAi has considerable therapeutic potential for human pathogenic gene products. Recent studies have demonstrated the clinical potential of logically designed small interfering RNA (siRNA). However, there are still obstacles in using RNAi as an antiviral therapy, particularly for hepatitis C virus (HCV) that displays a high rate of mutation. Furthermore, delivery is also an important obstacle for siRNA based gene therapy. This paper presents the potential applications and the hurdles facing anti-HCV siRNA drugs. The present review provides insight into the feasible therapeutic strategies of siRNA technology, and its potential for silencing genes associated with HCV disease.

Receptor-mediated gene delivery using chemically modified chitosan

Chitosan has been investigated as a non-viral vector because it has several advantages such as biocompatibility, biodegradability and low toxicity with high cationic potential. However, the low specificity and low transfection efficiency of chitosan need to be solved prior to clinical application. In this paper, we focused on the galactose or mannose ligand modification of chitosan for enhancement of cell specificity and transfection efficiency via receptor-mediated endocytosis in vitro and in vivo.

Galactosylated chitosan-graft-polyethylenimine as a gene carrier for hepatocyte targeting

Chitosans have been proposed as alternative, biocompatible cationic polymers for nonviral gene delivery. However, the low transfection efficiency and low specificity of chitosan need to be addressed before clinical application. We prepared galactosylated chitosan-graft-polyethylenimine (GC-g-PEI) copolymer by an imine reaction between periodate-oxidized GC and low-molecular-weight PEI. The molecular weight and composition were characterized using gel permeation chromatography column with multi-angle laser scattering and (1)H nuclear magnetic resonance, respectively. The copolymer was complexed with plasmid DNA in various copolymer/DNA (N/P) charge ratios, and the complexes were characterized. GC-g-PEI showed good DNA-binding ability and superior protection of DNA from nuclease attack and had low cytotoxicity compared to PEI 25K. GC-g-PEI/DNA complexes showed higher transfection efficiency than PEI 25K in both HepG2 and HeLa cell lines. Transfection efficiency into HepG2, which has asialoglycoprotein receptors, was higher than that into HeLa, which does not. GC-g-PEI/DNA complexes also transfected liver cells in vivo after intraperitoneal (i.p.) administration more effectively than PEI 25K. These results suggest that GC-g-PEI can be used in gene therapy to improve transfection efficiency and hepatocyte specificity in vitro and in vivo.

Galactosylated Chitosan/Carbonate Apatite Nanohybridization for Cell Specificity and High Transfection Efficiency as a DNA Carrier

The strategies developed for gene delivery are generally classified into two categories of viral and non-viral vectors. The limitation of viral vectors, which have problems including toxicity, immunogenicity and inflammatory response has led to the development of a novel, synthetic vectors based on non-viral vectors. Chitosan, one of non-viral vectors, has been a good candidate in gene delivery field. Moreover, galactosylated chitosan (GC) had the specific recognition of hepatocytes by galactose in the GC. Also, carbonate apatite increased the rate of DNA endocytosis and the efficiency of gene transfer. We describe here a new concept for improving cell specificity and transfection efficiency by hybridization of carbonate apatite (CAp) with GC. The complex formation was confirmed by agarose gel electrophoresis. The complex optimized through controlling calcium ion and charge ratio was evaluated on the cell specificity and transfection efficiency.

Receptor-Mediated Gene Delivery Using Chitosan Derivatives In Vitro and In Vivo

The key strategy for the advancement of gene therapy is the development of an efficient targeted gene delivery system into cells. The targeted gene delivery system is especially important in non-viral gene transfer which shows the relatively low transfection efficiency. It also opens the possibility of selective delivery of therapeutic plasmids to specific tissues. Chitosan has been considered to be a good candidate for gene delivery system, since it is already known as a biocompatible, biodegradable, and low toxic material with high cationic potential. However, low specificity and low transfection efficiency of chitosan need to be overcome prior to clinical trial. In this study, we focused on the chemical modification of chitosan for enhancement of cell specificity and transfection efficiency. Also, the potential of clinical application was investigated.

Targeting specificity and pharmacokinetics of asialoorosomucoid, a specific ligand for asialglycoprotein receptor on hepatocyte

OBJECTIVE

To testify that the asialoorosomucoid (ASOR) prepared by us has liver-targeting specificity and to investigate its pharmacokinetic characteristics.

METHODS

The distribution of 125I-ASOR in vivo was determined by single photon emission computed tomography (SPECT) and immunohistochemical technique after 125I-ASOR was injected into Sprague-Dawley (S-D) rats through their caudal veins. In vitro, different doses of pEGFP-N1 plasmid were transfected into both HepG2 cells and HT1080 cells with the use of ASOR-poly-L-lysine. At 24 and 48 h after transfection, the expression of green fluorescent protein (GFP) was determined under fluorescent microscope. Pharmacokinetic parameters were calculated according to two-compartment open system model with first-order kinetics.

RESULTS

SPECT images showed that 125I-ASOR was located only in liver/stomach and root of caudal vein/bladder at 10 min after injection. The 125I-ASOR radioactivities of organs taken out from S-D rats were different at different times, and about 63% of 125I-ASOR was located in the liver at 10 min after injection. At 30 min after injection a peak of radioactivity was seen in stomach. The times of these two radioactivity peaks were different. Immunohistochemical study of liver frozen sections showed that ASOR was combined mainly with hepatocyte membrane, especially in areas with rich blood flow. In vitro study showed that ASOR targeted specifically cells with asialoglycoprotein receptor (ASGr). GFP expression was detected in HepG2 cells but not in HT1080 cells. Furthermore, the more quantity of pEGFP-N1 transfected and the longer expression time, the higher GFP expression level was in HepG2 cells. The 125I-ASOR pharmacokinetics equation for liver was Ct=662216e-3.362t+8896e-2343t. 125I-ASOR was excreted from liver slowly after an initial rapid decrease. The pharmacokinetic equation for stomach was Ct=-114815e-1.7t+1148153e-15t and the half-life of 125I-ASOR in stomach was 4.62 h.

CONCLUSIONS

ASOR prepared by us could be an efficient gene transfer vector, ASOR was distributed mainly in the liver and stomach and had high targeting specificity to hepatocytes or hepatic originating cells.

Receptor-Mediated Gene Delivery Using Chitosan Derivatives In Vitro and In Vivo

The development of an efficient targeted gene delivery system into cells is an important strategy for the advancement of gene therapy. The targeted gene delivery system is especially important in non-viral gene transfer which shows the relative low transfection efficiency. And it also opens the possibility of selective delivery of therapeutic plasmids to specific tissues. Chitosan has been considered to be a good candidate for gene delivery system, since it is already known as a biocompatible, biodegradable, and low toxic material with high cationic potential. However, low specificity and low transfection efficiency of chitosan need to be overcome prior to clinical trial. In this study, we focused on the chemical modification of chitosan for enhancement of cell specificity and transfection efficiency.

Synergistic effect of poly(ethylenimine) on the transfection efficiency of galactosylated chitosan/DNA complexes

The use of chitosan for gene delivery is limited due to the low transfection efficiency and difficulty in transfecting into a variety of cell types, especially the hepatoma cells. In order to solve this problem, lactobionic acid (LA) bearing galactose group was coupled with water-soluble chitosan (WSC) for liver specificity and poly(ethylenimine) (PEI) was combined to galactosylated chitosan (GC)/DNA complexes to enhance the transfection efficiency. For initial study, the effect of PEI on the transfection efficiency of WSC/DNA complex was studied in HeLa, A549 and 293 T cells, and bafilomycin A1 was used to ascertain the mechanism of synergistic effect. Transfection efficiency, cytotoxicity, and physicochemical properties of GC/DNA complex combined with PEI were investigated to determine the potential for the hepatocyte-targeting. The combination of PEI with WSC/DNA and GC/DNA complex dramatically increased the luciferase expression 10- to 1000-fold in various cell lines, and the synergistic effect was proved to be induced by proton sponge effect of PEI. The transfection of GC/DNA complex in HepG2 was much higher than that of WSC/DNA even after combination with PEI, and was highly inhibited in the presence of galactose. Cytotoxicity of PEI was much decreased by combination with GC/DNA complex. And PEI was proved to be coated on the surface of GC/DNA complex through the ionic interaction.

Smart polyion complex micelles for targeted intracellular delivery of PEGylated antisense oligonucleotides containing acid-labile linkages

A novel pH-sensitive and targetable antisense ODN delivery system based on multimolecular assembly into polyion complex (PIC) micelles of poly(L-lysine) (PLL) and a lactosylated poly(ethylene glycol)-antisense ODN conjugate (Lac-PEG-ODN) containing an acid-labile linkage (beta-propionate) between the PEG and ODN segments has been developed. The PIC micelles thus prepared had clustered lactose moieties on their peripheries and achieved a significant antisense effect against luciferase gene expression in HuH-7 cells (hepatoma cells), far more efficiently than that produced by the nonmicelle systems (ODN and Lac-PEG-ODN) alone, as well as by the lactose-free PIC micelle. In line with this pronounced antisense effect, the lactosylated PIC micelles showed better uptake than the lactose-free PIC micelles into HuH-7 cells; this suggested the involvement of an asialoglycoprotein (ASGP) receptor-mediated endocytosis process. Furthermore, a significant decrease in the antisense effect (27 % inhibition) was observed for a lactosylated PIC micelle without an acid-labile linkage (thiomaleimide linkage); this suggested the release of the active (free) antisense ODN molecules into the cellular interior in response to the pH decrease in the endosomal compartment is a key process in the antisense effect. Use of branched poly(ethylenimine) (B-PEI) instead of the PLL for PIC micellization led to a substantial decrease in the antisense effect, probably due to the buffer effect of the B-PEI in the endosome compartment, preventing the cleavage of the acid-labile linkage in the conjugate. The approach reported here is expected to be useful for the construction of smart intracellular delivery systems for antisense ODNs with therapeutic value.

Chitosan Derivatives as Gene Carriers

Chitosan has been considered to be a good candidate for gene delivery system, since it is already known as a biocompatible, biodegradable, and low toxic material with high cationic potential. However, low specificity and low transfection efficiency of chitosan need to be overcome prior to clinical trial. In this review paper, chemical modification of chitosan for enhancement of cell specificity and transfection efficiency was explained. Also, chemical modification of chitosan for the stability of chitosan/DNA complexes was reviewed.

Lactosylated poly(ethylene glycol)-siRNA conjugate through acid-labile beta-thiopropionate linkage to construct pH-sensitive polyion complex micelles achieving enhanced gene silencing in hepatoma cells

The remarkably enhanced gene silencing in hepatoma cells was achieved by assembling lactosylated-PEG-siRNA conjugates bearing acid-labile beta-thiopropionate linkages into polyion complex (PIC) micelles through the mixing with poly(l-lysine). The PIC micelles with clustered lactose moieties on the periphery were successfully transported into hepatoma cells in a receptor-mediated manner, releasing hundreds of active siRNA molecules into the cellular interior responding to the pH decrease in the endosomal compartment. Eventually, almost 100 times enhancement in gene silencing activity compared to that of the free conjugate was achieved for the micelle system, facilitating the practical utility of siRNA therapeutics.

Feasibility on systemic delivery of asialoorosomucoid complex to hepatic origin cells mediated by asialoglycoprotein receptor

Receptor mediated gene delivery is a new gene transfer strategy. Asialoglycoprotein receptor (ASGP-R), the receptor of asialoorosomucoid (Asor), is specially expressed on the surface of hepatocyte. In this paper, the nuclide 131I was combined with Asor to form a kind of soluble nuclide-protein complex, which can be specifically endocytosed into hepatocyte by ASGP-R. After in travenous injection of the complex into experimental animals, the deposition of Asor in vivo and the targeting quality of hepatocyte was detected by ECT. This research testified the feasibility of targeting Asor complex delivery to hepatocyte mediated by ASGP-R in vivo, and provided foundation for the genetic diagnosis and gene therapy of hepatic cell-related diseases.

Galactosylated chitosan/DNA nanoparticles prepared using water-soluble chitosan as a gene carrier

Water-soluble chitosan (WSC) was used to increase the stability of chitosan in water and decrease the cytotoxicity induced by acetic acid. Lactobionic acid (LA) bearing galactose group was coupled with WSC for hepatocytes specificity. The composition of galactose in galactosylated chitosan (GC) was determined by NMR spectroscopy. The GC was complexed with plasmid DNA in various GC/DNA (N/P) charge ratios and the resulting complex was characterized by dynamic light scattering, gel retardation, and turbidity to determine the particle sizes, complex formation, and complex stability, respectively. Cytotoxicity and transfection efficiency of GC were also studied in cultured HepG2 human hepatoblastoma cell line and HeLa human cervix epithelial carcinoma cells. The complete GC/DNA complex was formed at the charge ratio of 5 and the GC/DNA complex to DNase I resistance was obtained. Particle sizes decreased with increasing charge ratio of GC to DNA and had a minimum value around 120 nm at the charge ratio of 5. And no significant difference in particle sizes from the charge ratio of 5-20 was found. The suspension of GC/DNA complexes exhibited no significant change in turbidity at the charge ratios of 10, indicating the complete shielding of DNA charge. Cytotoxicity study showed that GC prepared by the water-soluble chitosan had no cytotoxic effects on cells. And transfection efficiency into HepG2, which has asialoglycoprotein receptors (ASGP-R), was higher than that into HeLa without ASGP-R.

Hepatocyte targeting of 111In-labeled oligo-DNA with avidin or avidin-dendrimer complex

To establish an effective nonviral gene transfer vector to hepatocytes, various oligo-carrier complexes were developed employing dendrimer (G4) and avidin-biotin systems (Av-bt), and their biodistribution were evaluated. In-111-labeled-oligo, without any carriers, showed low uptake in normal organs other than the kidney (21.48% ID/g at 15 min, 18.48% ID/g at 60 min). In contrast, 111In-oligo coupled with avidin through biotin (111In-oligo-bt-Av) showed very high accumulation in the liver (50.95% at 15 min, 47.88% at 60 min). 111In-oligo complexed with G4 showed high uptake in the kidney and spleen, but its hepatic uptake was relatively low (13.12% at 15 min, 10.67% at 60 min). When both G4 and Av-bt systems were employed, 111In-oligo/G4-bt-Av showed extremely high uptake in the lung (182.33% at 15 min, 125.54% at 60 min), probably due to the formation of large molecular weight complex and aggregates which are trapped in the lung, and its hepatic uptake was lower than 111In-oligo-bt-Av. 111In-oligo-bt-Av, which exhibited the highest hepatic uptake in vivo, also showed high and rapid internalization into hepatocytes. The avidin-biotin system seems to have potential as a carrier of oligo-DNA to the liver.

A cationic peptide consists of ornithine and histidine repeats augments gene transfer in dendritic cells

Condensing the plasmid with high molecular weight cationic polymers such as poly-L-lysine (PLL) and poly-L-ornithine (PLO) can enhance antigen-specific immunity generated from genetic vaccination with naked DNA encoding antigens. While these high molecular weight polymers are clearly effective in transfection experiments, clinical applications are limited by their physical heterogeneity and toxicity. Three chemically defined low molecular weight cationic peptides, K(16), K(10)H(6), and O(10)H(6), were examined in the context of DNA binding, toxicity, and efficiency of gene transfer in dendritic cells (DC). The results showed that while all three peptides can bind to a plasmid encoding a reporter gene with similar efficiency, in vitro transfection with DNA complexed with O(10)H(6) complexed resulted in the highest level of gene expression. Moreover, free O(10)H(6) was not toxic to DC, while the lysine-based peptides caused significant cell death in DC cultures. We also showed that DC transfected ex vivo with DNA complexed with O(10)H(6) was capable of eliciting antigen-specific INFgamma production in vivo. Taken together, these results indicate ornithine and histidine repeats are suitable building blocks of non-viral gene transfer vector for DC.

Study on relationship between expression level and molecular conformations of gene drugs targeting to hepatoma cells in vitro

AIM: To increase exogenous gene expression level by modulating molecular conformations of targeting gene drugs.

METHODS: The full length cDNAs of both P₄₀ and P₃₅ subunits of human interleukin 12 were amplified through polymerase chain reaction (PCR) and cloned into eukaryotic expressing vectors pcDNA3.1 (±) to construct plasmids of P (+)/IL-12, P (+)/P₄₀ and P (-)/P₃₅. These plasmids were combined with ASOR-PLL to form two targeting gene drugs [ASOR-PLL-P (+)/IL-12 and ASOR-PLL-P (+)/P₄₀ + ASOR-PLL-P (-)/P₃₅] in optimal ratios. The conformations of these two drugs at various concentrations adjuvant were examined under electron microscope (EM) and the drugs were transfected into HepG2 (ASGr+) cells. Semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) was performed with total RNA extracted from the transfected cells to determine the hIL12 mRNA transcript level. The hIL12 protein in the cultured supernatant was measured with enzyme-linked immunosorbent assay (ELISA) 48 hours after transfection.

RESULTS: Targeting gene drugs, whose structures were granular and circle-like and diameters ranged from 25 nm to 150 nm, had the highest hIL-12 expression level. The hIL-12 expression level in the group co-transfected with ASOR-PLL-P (+)/P₄₀ and ASOR-PLL-P (-)/P₃₅ was higher than that of ASOR-PLL-P (+)/IL-12 transfected group.

CONCLUSION: The molecular conformations of targeting gene drugs play an important role in exogenous gene expression level, the best structures are granular and circle-like and their diameters range from 25 nm to 150 nm. The sizes and linking styles of exogenous genes also have some effects on their expression level.

Barriers to nonviral gene delivery

The use of various synthetic lipids and polymers to deliver DNA for gene therapy applications has been the subject of intense examination for the last 15 years. Our understanding of the processes involved in the delivery of DNA, although still limited, can be described in terms of specific physical and chemical barriers encountered along the delivery pathway. Successful engagement of this pathway involves avoiding inactivation in the extracellular compartment and initial favorable interactions with the cell surface. Internalization of the delivery system by endocytosis results in a poorly defined endosomal trafficking process which, if not escaped, leads to degradation of the therapeutic DNA in lysosomes. For the small fraction of material that is able to escape this vesicular trafficking pathway, the cytosol provides additional physical and metabolic barriers to further trafficking to the nucleus. Finally, nuclear uptake has been demonstrated to be a significant barrier to gene delivery. In this review, we outline in greater detail the various processes involved in each step and describe various formulation variables that have been explored to overcome these delivery barriers to nonviral gene delivery.

Synthesis of galactosyl compounds for targeted gene delivery

Cell-specific DNA delivery offers a great potential for targeted gene therapy. Toward this end, we have synthesized a series of compounds carrying galactose residues as a targeting ligand for asialoglycoprotein receptors of hepatocytes and primary amine groups as a functional domain for DNA binding. Biological activity of these galactosyl compounds in DNA delivery was evaluated in HepG2 and BL-6 cells and compared with respect to the number of galactose residues as well as primary amine groups in each molecule. Transfection experiments using a firefly luciferase gene as a reporter revealed that compounds with multivalent binding properties were more active in DNA delivery. An optimal transfection activity in HepG2 cells requires seven primary amine groups and a minimum of two galactose residues in each molecule. The transfection activity of compounds carrying multi-galactose residues can be inhibited by asialofetuin, a natural substrate for asialoglycoprotein receptors of hepatocytes, suggesting that gene transfer by these galactosyl compounds is asialoglycoprotein receptor-mediated. These results provide direct evidence in support of our new strategy for the use of small and synthetic compounds for cell specific and targeted gene delivery.

Determination of the upper size limit for uptake and processing of ligands by the asialoglycoprotein receptor on hepatocytes in vitro and in vivo

The asialoglycoprotein receptor (ASGPr) on hepatocytes plays a role in the clearance of desialylated proteins from the serum. Although its sugar preference (N-acetylgalactosamine (GalNAc) >> galactose) and the effects of ligand valency (tetraantennary > triantennary >> diantennary >> monoantennary) and sugar spacing (20 A 10 A 4 A) are well documented, the effect of particle size on recognition and uptake of ligands by the receptor is poorly defined. In the present study, we assessed the maximum ligand size that still allows effective processing by the ASGPr of mouse hepatocytes in vivo and in vitro. Here too, we synthesized a novel glycolipid, which possesses a highly hydrophobic steroid moiety for stable incorporation into liposomes, and a triantennary GalNAc(3)-terminated cluster glycoside with a high nanomolar affinity (2 nm) for the ASGPr. Incorporation of the glycolipid into small (30 nm) [(3)H]cholesteryl oleate-labeled long circulating liposomes (1-50%, w/w) caused a concentration-dependent increase in particle clearance that was liver-specific (reaching 85 +/- 7% of the injected dose at 30 min after injection) and mediated by the ASGPr on hepatocytes, as shown by competition studies with asialoorosomucoid in vivo. By using glycolipid-laden liposomes of various sizes between 30 and 90 nm, it was demonstrated that particles with a diameter of >70 nm could no longer be recognized and processed by the ASGPr in vivo. This threshold size for effective uptake was not related to the physical barrier raised by the fenestrated sinusoidal endothelium, which shields hepatocytes from the circulation, because similar results were obtained by studying the uptake of liposomes on isolated mouse hepatocytes in vitro. From these data we conclude that in addition to the species, valency, and orientation of sugar residues, size is also an important determinant for effective recognition and processing of substrates by the ASGPr. Therefore, these data have important implications for the design of ASGPr-specific carriers that are aimed at hepatocyte-directed delivery of drugs and genes.

Endogenous carriers and ligands in non-immunogenic site-specific drug delivery

Targeted drug delivery has gained recognition in modern therapeutics and attempts are being made to explore the potentials and possibilities of cell biology related bioevents in the development of specific, programmed and target oriented systems. The components which have been recognized to be tools include receptors and ligands, where the receptors act as molecular targets or portals, and ligands, with receptor specificity and selectivity, are trafficked en route to the target site. Although ligands of exogenous or synthetic origin contribute to the selectivity component of carrier constructs, they may impose immunological manifestations of different magnitudes. The latter may entail a continual quest for bio-compatible, non-immunogenic and target orientated delivery. Endogenous serum, cellular and extracellular bio-ligands interact with the colloidal carrier constructs and influence their bio-fate. However, these endogenous bio-ligands can themselves serve as targeting modules either in their native form or engineered as carrier cargo. Bio-regulatory, nutrient and immune ligands are sensitive, specific and effective site directing handles which add to targeted drug delivery. The present review provides an exhaustive account of the identified bio-ligands, which are not only non-immunogenic in nature but also site-specific. The cell-related bioevents which are instrumental in negotiating the uptake of bio-ligands are discussed. Further, a brief account of ligand-receptor interactions and the set of biological events which ensures ligand-driven trafficking of the ligand-receptor complex to the cellular interior is also presented. Since ligand-receptor interaction is a critical pre-requisite for negotiating cellular uptake of endogenous ligands and anchored carrier cargo, an attempt has been made to identify differential expression of receptors and bio-ligands under normal and etiological conditions. Studies which judiciously utilized bio-ligands or their analogs in negotiating site-specific drug delivery have been reviewed and presented. Targeted delivery of bioactives using endogenous bio-ligands offers enormous options and opportunities through carrier construct engineering and could become a future reality in clinical practice.