Development of targeted delivery systems for nucleic acid drugs

Role of pharmacokinetic consideration for the development of drug delivery systems: A historical overview

Drug delivery system is defined as a system or technology to achieve optimum therapeutic effects of drugs through precise control of their movements in the body. In order to optimize function of drug delivery systems aiming at targeting, their whole-body distribution profiles should be systematically evaluated and analyzed, where pharmacokinetic analysis based on the clearance concepts plays important role. Organ perfusion experiments combined with statistical moment analysis further supply detailed information on drug disposition at organ and cellular levels. Based on general relationship between physicochemical properties and distribution profile, macromolecular prodrugs or polymer conjugates of proteins are rationally designed and further introduction of ligand structure brings cell-specific delivery for them. These approaches are also applicable for particulate carriers such as liposomes and offer various opportunities for biological drugs such as nucleic acid drugs for their delivery. Mechanistic approach for dermal absorption analysis based on physiological skin model offers another opportunity in rational design of drug delivery. Potential of drug delivery technology in future medicines such as cell therapy and nanomaterial platform application is further discussed in relation to pharmacokinetic consideration.

Pharmacokinetic evaluation of liposomal nanoparticle-encapsulated nucleic acid drug: A combined study of dynamic PET imaging and LC/MS/MS analysis

In vivo biodistribution analyses, especially in tumors, of nucleic acids delivered with nanoparticles are important to develop drug delivery technologies for medical use. We previously developed wrapsome® (WS), an ~100 nm liposomal nanoparticle that can encapsulate siRNA, and reported that WS accumulates in tumors in vivo and inhibits their growth by an enhanced permeability and retention effect. In the present study, we evaluated the pharmacokinetics of nucleic acid-containing nanoparticles by combining dynamic positron emission tomography (PET) imaging and liquid chromatography-tandem mass spectrometry (LC/MS/MS) analysis. An 18-mer phosphorothioate oligodeoxynucleotide (ODN), trabedersen, was used as a model drug and was encapsulated in WS. Dynamic PET imaging and time-activity curve analysis of WS-encapsulated ⁶⁴Cu-labeled ODNs administered to mice with MIA PaCa-2 subcutaneous xenograft tumors showed tumor accumulation (~3% injected dose per gram (%ID/g)) and liver accumulation (~30 %ID/g) at 24 h. Under these conditions, LC/MS/MS analysis showed that the level of intact ODNs was 1.62 %ID/g in the tumor and 1.70 %ID/g in the liver. From these pharmacokinetic data, the intact/accumulated ODN ratios were calculated using the following equation: intact/accumulated ODN ratio (%) = %ID/g _{LC/MS/MS, tissue, mean}/%ID/g _{PET, tissue, mean} × 100. Interestingly, the ratios for the tumor and kidney were maintained at 20-50% over 48 h after administration of the WS-encapsulated form. In contrast, the ratio for the liver rapidly decreased at 24 h, showing the same pattern as that for naked ODN. These different patterns indicate that WS effectively protected the ODN in the tumor and kidney, but protected it less efficiently in the liver. A combined approach of dynamic PET imaging and LC/MS/MS analysis will assist the development of nanoparticle-encapsulated nucleic acid drugs, such as those using WSs, to determine their detailed pharmacokinetics.

Quantitative evaluation of the improvement in the pharmacokinetics of a nucleic acid drug delivery system by dynamic PET imaging with (18)F-incorporated oligodeoxynucleotides

Recently, we demonstrated the utility of positron emission tomography (PET) imaging-based pharmacokinetic evaluation studies for preclinical experiments and microdose clinical trials, mainly focused on low molecular weight compounds. In order to investigate the pharmacokinetics of nucleic acid drugs and their drug delivery systems (DDSs) in vivo by using PET imaging, we developed a novel and efficient method for radiolabeling oligodeoxynucleotides with the positron-emitting radionuclide (18)F (stoichiometry-focused Huisgen-type (18)F labeling). By using this method, we succeeded in synthesizing a variety of (18)F-labeled oligodeoxynucleotides with not only phosphodiesters (PO) in natural forms, but also phosphorothioate (PS) and bridged nucleic acid (BNA) in artificial forms, and then performed PET studies and radioactive metabolite analyses of these (18)F-labeled oligodeoxynucleotides. The tissue-distribution and dynamic changes in radioactivity showed significantly different profiles between these antisense oligodeoxynucleotides. The radioactivity of (18)F-labeled PO-DNA and PO-BNA rapidly accumulated in the kidneys and liver and then moved to the renal medulla, ureter, bladder, and intestine. However, the radioactivity of (18)F-labeled PS-DNA and PS-BNA, possessing PS backbone structures, was retained in the blood for relatively long periods and then gradually accumulated in the liver and kidneys. The metabolite analysis showed that (18)F-labeled PO-DNA rapidly degraded by 5min and (18)F-labeled PO-BNA gradually degraded over time by 60min. Conversely, (18)F-labeled PS-DNA and PS-BNA were shown to be much more stable. To demonstrate the usefulness of the PET imaging technique for evaluating the improved targeting potential of the DDS, we designed and synthesized a cholesterol-modified oligodeoxynucleotide, that we developed as an antisense nucleic acid drug against proprotein convertase subtilisin/kexin type 9 (PCSK9) for hypercholesterolemia therapy, and evaluated its pharmacokinetics using PET imaging. As expected, the (18)F-labeled cholesterol-modified PS-BNA-type oligodeoxynucleotide showed much higher and more rapid accumulation in the delivery target organ, that is, the liver, which encourages us to develop this drug. These results suggest that dynamic PET studies using (18)F-incorporated oligodeoxynucleotide synthesized by stoichiometry-focused Huisgen-type labeling is useful for quantitative pharmacokinetic evaluation of nucleic acid drugs and their delivery systems.

Functional RNA delivery targeted to dendritic cells by synthetic nanoparticles

Dendritic cells (DCs) are essential to many aspects of immune defense development and regulation. They provide important targets for prophylactic and therapeutic delivery. While protein delivery has had considerable success, RNA delivery is still expanding. Delivering RNA molecules for RNAi has shown particular success and there are reports on successful delivery of mRNA. Central, therein, is the application of cationic entities. Following endocytosis of the delivery vehicle for the RNA, cationic entities should promote vesicular membrane perturbation, facilitating cytosolic release. The present review explains the diversity of DC function in immune response development and control. Promotion of delivered RNA cytosolic release is discussed, relating to immunoprophylactic and therapeutic potential, and DC endocytic machinery is reviewed, showing how DC endocytic pathways influence the handling of internalized material. The potential advantages for application of replicating RNA are presented and discussed, in consideration of their value and development in the near future.

Localized delivery of antisense oligonucleotides by cationic hydrogel suppresses TNF-α expression and endotoxin-induced osteolysis

PURPOSE

To investigate the possibility of using localized nucleic drug delivery methods for the treatment of osteolysis-related bone disease.

METHODS

A bio-degradable cationic hydrogel composed of gelatin and chitosan was used to deliver an antisense oligonucleotide (ASO) targeting murine TNF-α for the treatment of endotoxin-induced osteolysis.

RESULTS

ASO combined with this hydrogel was released when it was digested by adhering cells. The released ASO was efficiently delivered into contacted cells and tissues in vitro and in vivo. When tested in animal models of edotoxin-induced bone resorption, ASO delivered by such means effectively suppressed the expression of TNF-α and subsequently the osteoclastogenesis in vivo. Osteolysis in the edotoxin-induced bone resorption animal models was blocked by the treatment.

CONCLUSION

This is a successful attempt to apply localized gene delivery method to treat inflammatory diseases in vivo.

Biodistribution of antisense nanoparticles in mammary carcinoma rat model

Efficient and specific delivery of antisenses (ASs) and protection of the sequences from degradation are critical factors for effective therapy. Sustained release nanoparticles (NP) offer increased resistance to nuclease degradation, increased amounts of AS uptake, and the possibility of control in dosing and sustained duration of AS administration. The biodegradable and biocompatible poly(D,L-lactic-co-glycolic acid) copolymer (PLGA) was utilized to encapsulate AS directed against osteopontin (OPN), which is a promising therapeutic target in mammary carcinoma. Whole body biodistribution of OPN AS NP was evaluated in comparison to naked AS, in intact and mammary carcinoma metastasis model bearing rats. Naked and NP encapsulated AS exhibited different biodistribution profiles. AS NP, in contrast to naked AS, tended to accumulate mostly in the spleen, liver, and at the tumor inoculation site. Drug levels in intact organs were negligible. The elimination of naked AS was faster, due to rapid degradation of the unprotected sequence. It is concluded that AS NP protect the AS from degradation, provide efficient AS delivery to the tumor tissue, and minimize AS accumulation in intact organs due to the AS sustained release profile as well as the favorable NP physicochemical properties.

DNA-based nano-sized systems for pharmaceutical and biomedical applications

DNA is one of the most important components for all living organisms and many species, including humans, use DNA to store and transmit genetic information to new generations. Recent advances in the handling of DNA have made it possible to use DNA as a building block of nano-sized materials with precisely designed architectures. Although various approaches have been proposed to obtain DNA assemblies with designed architecture in the nano- to micrometer range, there is little information about their interaction with biological components, including target molecules. Understanding the interaction between DNA assemblies and the body is highly important for successful pharmaceutical and biomedical applications. Here, we first review the basic aspects of externally administered DNA molecules, including the stability, permeability and delivery issues. Then, we discuss the unique responses observed in the interaction of structured DNA assemblies and cells expressing Toll-like receptor-9, the receptor responsible for the recognition of unmethylated CpG dinucleotides that are abundant in the DNA of invading pathogens, such as bacteria and viruses.

Sustained delivery and efficacy of polymeric nanoparticles containing osteopontin and bone sialoprotein antisenses in rats with breast cancer bone metastasis

Poor prognosis in mammary carcinoma is associated with a certain expression profile of a defined set of genes including osteopontin and bone sialoprotein. Efficient and specific delivery of antisenses (AS) and a protection of the sequences from degradation are the crucial conditions for AS therapeutic efficiency. We hypothesized that effective and safe AS delivery direceted against these genes could be achieved by polymeric nanoparticles (NP) fabricated from a biocompatible polymer. Due to their nano-size range and small negative charge, AS-NP can overcome the absorption barrier offering increased resistance to nuclease degradation, sustained duration of AS administration, and consequently, prolonged antisense action. The ASs designed against OPN and BSP-II were successfully encapsulated in NP composed of the biodegradable and biocompatible polylactide-co-glycolide polymer (PLGA), exhibiting sustained release and stability of the ASs. The therapeutic efficacy of the AS-NP delivery system was examined in vitro, and in a breast cancer bone metastasis animal model of MDA-MB-231 human breast cancer cells in nude rats. Treatment with OPN-AS or BSP-AS loaded NP in comparison with osmotic mini-pumps (locoregional injection and SC implants, respectively) resulted in a significant decrease in both, tumor bone metastasis incidence and in the size of the lesions in rats with metastases. Despite its smaller dose, AS-NP exhibited a better therapeutic efficacy than osmotic mini-pumps in terms of lesion ratio at later time periods (8-12 weeks). It may be concluded that AS delivery by NP is a promising therapeutic modality providing stability of the encapsulated AS and a sustained release.

[Development of nucleic acid transfection technology to the kidney]

The kidney is one of the most important organs that play a crucial role in homeostasis and, therefore, congenital or acquired renal dysfunction causes refractory diseases, i.e., Alport's syndrome, Fabry's disease, diabetic nephropathy, IgA nephropathy, kidney cancer, transplant glomerulopathy. Nucleic acid transfection technology to the kidney is indispensable for the progress of biomedical research and the realization of gene therapy and nucleic acid drug for renal diseases. Control of renal nucleic acid transfection was difficult because of the structural complexity; however, the study of recombinant virus, synthetic carrier and physical force-mediated nucleic acid transfection to the kidney has advanced. Recombinant virus and synthetic carrier-mediated methods require long-term block of the blood or urinary flow for efficient transfection of nucleic acid because of the rich blood flow of the kidney. In contrast, physical force-mediated methods that transfect with nucleic acid via transient membrane permeability do not apprehend ischemia-reperfusion injury and, therefore, may be beneficial for nucleic acid transfection to the kidney. In this article, we collect the information of therapeutic gene, target molecule of the nucleic acid drug and target cells for renal diseases and structural property of the kidney from the point of view of nucleic acid transfection. Additively, current status of nucleic acid transfection technology to the kidney is reviewed.

Gene Transfer Mediated by Sphingosine/ Dioleoylphosphatidylethanolamine Liposomes in the Presence of Poloxamer 188

A cationic liposome system consisting of sphingosine (SP) and dioleoylphosphatidylethanolamine (DOPE) was developed for in vitro and in vivo gene transfer. A nonionic surface active agent of poloxamer 188 was incorporated in the formulations to stabilize the DNA/liposome complex. Comparison of the results obtained from systems with and without the effect of poloxamer 188 was made to investigate the efficiency of gene expression. In vitro transfection study of the DNA/liposome complex showed that with the effect of poloxamer 188, gene transfer into some cell lines was enhanced. In vivo systemic delivery of the DNA/liposome complex with poloxamer 188 demonstrated gene expression with improved luciferase activity in all major organs including lung, spleen, heart, liver, and kidney. High level transgene activity was found in lung and spleen with prolonged gene expression. This was attributed to poloxamer 188 that stabilized the liposome system and produced homogeneous DNA/liposome complex for enhancement of gene delivery.

Nonviral approaches for targeted delivery of plasmid DNA and oligonucleotide

Successful gene therapy depends on the development of efficient delivery systems. Although pDNA and ODN are novel candidates for nonviral gene therapy, their clinical applications are generally limited owing to their rapid degradation by nucleases in serum and rapid clearance. A great deal of effort had been devoted to developing gene delivery systems, including physical methods and carrier-mediated methods. Both methods could improve transfection efficacy and achieve high gene expression in vitro and in vivo. As for carrier-mediated delivery in vivo, since gene expression depends on the particle size, charge ratio, and interaction with blood components, these factors must be optimized. Furthermore, a lack of cell-selectivity limits the wide application to gene therapy; therefore, the use of ligand-modified carriers is a promising strategy to achieve well-controlled gene expression in target cells. In this review, we will focus on the in vivo targeted delivery of pDNA and ODN using nonviral carriers.

Firefly luciferase enzyme fragment complementation for imaging in cells and living animals

We identified different fragments of the firefly luciferase gene based on the crystal structure of firefly luciferase. These split reporter genes which encode for protein fragments, unlike the fragments currently used for studying protein-protein interactions, can self-complement and provide luciferase enzyme activity in different cell lines in culture and in living mice. The comparison of the fragment complementation associated recovery of firefly luciferase enzyme activity with intact firefly luciferase was estimated for different fragment combinations and ranged from 0.01 to 4% of the full firefly luciferase activity. Using a cooled optical charge-coupled device camera, the analysis of firefly luciferase fragment complementation in transiently transfected subcutaneous 293T cell implants in living mice showed significant detectable enzyme activity upon injecting d-luciferin, especially from the combinations of fragments identified (Nfluc and Cfluc are the N and C fragments of the firefly luciferase gene, respectively): Nfluc (1-475)/Cfluc (245-550), Nfluc (1-475)/Cfluc (265-550), and Nfluc (1-475)/Cfluc (300-550). The Cfluc (265-550) fragment, upon expression with the nuclear localization signal (NLS) peptide of SV40, shows reduced enzyme activity when the cells are cotransfected with the Nfluc (1-475) fragment expressed without NLS. We also proved in this study that the complementing fragments could be efficiently used for screening macromolecule delivery vehicles by delivering TAT-Cfluc (265-550) to cells stably expressing Nfluc (1-475) and recovering signal. These complementing fragments should be useful for many reporter-based assays including intracellular localization of proteins, studying cellular macromolecule delivery vehicles, studying cell-cell fusions, and also developing intracellular phosphorylation sensors based on fragment complementation.

Modulation of gene expression by antisense and antigene oligodeoxynucleotides and small interfering RNA

Antisense oligodeoxynucleotides, triplex-forming oligodeoxynucleotides and double-stranded small interfering RNAs have great potential for the treatment of many severe and debilitating diseases. Concerted efforts from both industry and academia have made significant progress in turning these nucleic acid drugs into therapeutics, and there is already one FDA-approved antisense drug in the clinic. Despite the success of one product and several other ongoing clinical trials, challenges still exist in their stability, cellular uptake, disposition, site-specific delivery and therapeutic efficacy. The principles, strategies and delivery consideration of these nucleic acids are reviewed. Furthermore, the ways to overcome the biological barriers are also discussed so that therapeutic concentrations at their target sites can be maintained for a desired period.

Oligonucleotide-Based Therapeutic Options against Hepatitis C Virus Infection

The hepatitis C virus (HCV) is the cause of a silent pandemic that, due to the chronic nature of the disease and the absence of curative therapy, continues to claim an ever-increasing number of lives. Current antiviral regimens have proven largely unsatisfactory for patients with HCV drug-resistant genotypes. It is therefore important to explore alternative therapeutic stratagems whose mode of action allows them to bypass viral resistance. Antisense oligonucleotides, ribozymes, small interfering RNAs, aptamers and deoxyribozymes constitute classes of oligonucleotide-based compounds designed to target highly conserved or functionally crucial regions contained within the HCV genome. The therapeutic expectation for such compounds is the elimination of HCV from infected individuals. Progress in oligonucleotide-based HCV antivirals towards clinical application depends on development of nucleotide designs that bolster efficacy while minimizing toxicity, improvement in liver-targeting delivery systems, and refinement of small-animal models for preclinical testing.

Cytosolic delivery of antisense oligonucleotides by listeriolysin O-containing liposomes

Antisense oligodeoxynucleotides (ODNs) possess great potential as sequence-specific therapeutic agents. Sufficient concentrations of intact ODN must bypass membrane barriers and access the cytosol and nucleus, for ODNs to be therapeutically effective. A cytosolic delivery strategy was designed to improve the efficiency of ODN delivery in bone-marrow-derived macrophages. This liposome-based formulation utilizes listeriolysin O (LLO), the endosomolytic hemolysin from Listeria monocytogenes, to mediate the escape of ODN from endocytic compartments into the cytosol. To monitor the cytosolic delivery of ODN, subcellular trafficking of fluorescently labeled ODNs was visualized using epifluorescence microscopy. The expression of target protein and mRNA after delivery was measured using flow cytometry and Northern blot analysis, respectively. ODN specific for murine intercellular adhesion molecule-1 (ICAM-1) encapsulated in LLO-liposomes was released to the cytosol and trafficked to the nucleus, efficiently and specifically suppressing activation-induced expression of ICAM-1 at both protein and mRNA levels. Delivery without LLO resulted in sequestration of ODN in vesicular compartments leading to little inhibition of ICAM-1 expression, which supports the requirement of LLO for efficient cytosolic delivery using this system. The data clearly demonstrate that LLO-mediated escape of ODN from intracellular vesicles is an effective approach to achieve full therapeutic antisense activity in cultured macrophages.

Synthesis of structurally identical fluorine-18 and iodine isotope labeling compounds for comparative imaging

The synthesis of a benzophenone-based labeling compound designed for comparative imaging studies with both in vivo positron emission tomograph (PET) and single-photon computed tomography (SPECT) and ex vivo autoradiography is described. The new compound can be labeled with either F-18 or iodine radioisotopes to give two different radioisotopmers: N-[2-fluoro-5-(3-[I-131]iodobenzoyl)benzyl]-2-bromoacetamide (1) and N-[2-[F-18]fluoro-5-(3-iodobenzoyl)benzyl]-2-bromoacetamide (2). Compound 1 and 2 have a 2-bromoacetyl group, which can be used to conjugate with biomolecules through a nucleophilic substitution reaction. Compound 1 was synthesized from the corresponding tributyltin derivatives via an oxidative destannylation reaction, and compound 2 was prepared via a four-step radiosynthesis (nucleophilic aromatic substitution, reduction, oxidation, and alkylation) starting from 4-(N,N,N-trimethylammonio)-3-cyano-3'-iodobenzophenone triflate. A remarkably high radiochemical yield (>90%) was achieved for the F-18 nucleophilic aromatic substitution under mild conditions (room temperature in less than 10 min), indicating the structural advantage of the designed molecule to facilitate the F-18 for trimethylammonium substitution in the presence of two electron-withdrawing groups (nitrile and carbonyl). The overall radiosynthesis time for compound 2 is less than 3 h after end of bombardment (EOB) with an unoptimized radiochemical yield of about 2% (not decay corrected) and specific activity of 0.8 Ci/micromol at EOB. The radiolabeling precursors for compound 1 and 2 were synthesized via a carbon-carbon bond-forming reaction between 2-substituted-5-lithiobenzonitrile and 3-substituted benzaldehyde derivatives. Compounds 1 and 2 should allow us to label biomolecules with F-18 or iodine isotopes and gives structurally identical products, which are expected to have identical biological properties and should be useful for comparative imaging studies.

Novel PDGFbetaR antisense encapsulated in polymeric nanospheres for the treatment of restenosis

Nanospheres composed of the biocompatible and biodegradable polymer, poly-DL-lactide/glycolide and containing platelet-derived growth factor beta-receptor antisense (PDGFbetaR-AS) have been formulated and examined in vitro and in vivo in balloon-injured rat restenosis model. The nanospheres (approximately 300 nm) of homogenous size distribution exhibited high encapsulation efficiency (81%), and a sustained release of PDGFbetaR-AS (phosphorothioated). Cell internalization was visualized, and the inhibitory effect on SMC was observed. Partially phosphorothioated antisense sequences were found to be more specific than the fully phosphorothioated analogs. A significant antirestenotic effect of the naked AS sequence and the AS-NP (nanoparticles) was observed in the rat carotid in vivo model. The extent of mean neointimal formation 14 days after injection of AS-NP, measured as a percentage of luminal stenosis, was 32.21 +/- 4.75% in comparison to 54.89 +/- 8.84 and 53.84 +/- 5.58% in the blank-NP and SC-NP groups, respectively. It is concluded that PLGA nanospheres containing phosphorothioated oligodeoxynucleotide antisense could serve as an effective gene delivery systems for the treatment of restenosis.

Liver targeting of plasmid DNA by pullulan conjugation based on metal coordination

Liver targeting of plasmid DNA was achieved through conjugation of pullulan derivatives with chelate residues based on metal coordination. Triethylenetetramine (Ti), diethylenetriamine pentaacetic acid (DTPA), and spermine (Sm) were chemically introduced to pullulan, a polysaccharide with an inherent affinity for the liver, to obtain various pullulan-Ti, pullulan-DTPA, and pullulan-Sm derivatives. Irrespective of the type of pullulan derivatives, intravenous injection of the pullulan derivatives-plasmid DNA conjugates with Zn2+ coordination significantly enhanced the level of gene expression only in the liver to a significant greater extent than that of free plasmid DNA. The enhanced gene expression by the pullulan-DTPA-plasmid DNA conjugate was specific to the liver and the level was significantly higher than that of the pullulan-DTPA-plasmid DNA mixture. The level of gene expression depended on the percentage of chelate residue introduced, the mixing ratio of the plasmid DNA-DTPA residue in conjugate preparation, and the plasmid DNA dose. The gene expression induced by the conjugate lasted over 12 days after injection. A fluorescent-microscopic study revealed that the plasmid DNA was localized at the liver after injection of the pullulan-DTPA-plasmid DNA conjugate with Zn2+ coordination. Pre-injection of both arabinogalactan and galactosylated albumin suppressed significantly the liver level of gene expression, in contrast to that of mannosylated albumin, indicating that the plasmid DNA in the conjugate was transfected at hepatocytes. We conclude that the Zn2+-coordinated pullulan conjugation is a promising way to enable the plasmid DNA to target to the liver for gene expression as well as to prolong the time duration of gene expression

In vitro transfection of plasmid DNA by amine derivatives of gelatin accompanied with ultrasound irradiation

PURPOSE

The purpose of this study is to examine the ultrasound (US)-enhanced gene expression by the complexes of a plasmid DNA with gelatin derivatives of aminization.

METHODS

Gelatin derivatives with different introduced extents of ethylenediamine (Ed), spermidine (Sd), and spermine (Sm) were prepared with a water-soluble carbodiimide. The molecular size and zeta potential of the gelatin derivatives before and after complexation with the plasmid DNA were examined. After incubation with the complexes with or without US exposure, the DNA expression of rat gastric mucosal cells was measured to evaluate the effect of the type of gelatin derivatives on their gene expression. The cell uptake of the complexes, the cell viability, and the buffering effect of gelatin derivatives were examined.

RESULTS

The apparent molecular size and zeta potential of gelatin derivatives became larger as their aminization extent increased although the Sm gelatin derivative of higher aminization showed a larger value than other corresponding derivatives. Irrespective of the type of gelatin derivatives, the apparent molecular size of plasmid DNA was reduced by increasing the gelatin-DNA mixing ratio to attain a saturated value of about 150 nm. The condensed gelatin-DNA complexes showed the zeta potential of 10-15 mV. The cells incubated with the complex exhibited significantly stronger luciferase activities than free plasmid DNA, and the activity was further enhanced by US irradiation. The enhancement was significant for the Sm derivative compared with the corresponding Ed and Sd derivatives. The amount of plasmid DNA internalized into the cells was significantly increased by the complexation with every gelatin derivative, whereas US irradiation did not significantly increase the DNA internalization. US irradiation had no effect on the viability of cells incubated with every gelatin derivative-plasmid DNA complex, although the viability was decreased by the complex incubation. The buffering capacity of Sm derivative was higher than that of Ed and Sd derivatives and comparable with that of polyethylene amine.

CONCLUSION

Among amine derivatives of gelatin, the Sm derivative enabled the plasmid DNA to induce the US-enhanced gene expression of cells in vitro most effectively because of the superior buffering effect.

The use of synthetic polymers for delivery of therapeutic antisense oligodeoxynucleotides

Developed over the past two decades, the antisense strategy has become a technology of recognised therapeutic potential, and many of the problems raised earlier in its application have been solved to varying extents. However, the adequate delivery of antisense oligodeoxynucleotides to individual cells remains an important and inordinately difficult challenge. Synthetic polymers appeared on this scene in the middle 1980s, and there is a surprisingly large variety used or proposed so far as agents for delivery of oligodeoxynucleotides. After discussing the principles of antisense strategy, certain aspects of the ingestion of macromolecules by cells, and the present situation of delivery procedures, this article analyses in detail the attempts to use synthetic polymers as carrier matrices and or cell membrane permeabilisation agents for delivery of antisense oligodeoxynucleotides. Structural aspects of various polymers, as well as the results, promises and limitations of their use are critically evaluated.

Fluorescence correlation spectroscopy for the characterisation of drug delivery systems

Fluorescence Correlation Spectroscopy (FCS) offers the possibility to measure molecular interactions between active compounds and drug delivery systems such as cationic peptides or polymeric nanoparticles. In order to investigate the potential of FCS for drug carrier design, a complex made of protamine, a cationic peptide, and a 19mer oligonucleotide was characterised. Protamine was used to form proticles, agglomerates consisting of the oligonucleotide and the cationic peptide. The binding kinetics and proticle formation was studied by FCS. Complete binding of the oligonucleotide to protamine was achieved at a 1:2.5 (w/w) ratio. From the diffusion coefficient, D, a mean value for the hydrodynamic diameter was calculated at 53 nm, which was in agreement with data obtained from photon correlation spectroscopy (PCS). Oligonucleotide loading into cationic monomethylaminoethylmethacrylate (MMAEMA) nanoparticles was also determined by this method at 5.6% (5.6 microg per 100 microg of nanoparticles).

Conventional and gemini surfactants embedded within bilayer membranes: contrasting behavior

Laser microelectrophoresis (coupled with conductance, fluorescence, and dynamic light scattering) is shown to be a highly instructive tool in comparing the dynamics of conventional and gemini surfactants embedded within vesicle bilayers. The following can be listed among the more important observations and conclusions: a) Cationic conventional surfactant, added to a "solid" (gel) lipid vesicle containing an anionic phospholipid, charge-neutralizes only half the anionic charge. With a "liquid" (liquid crystalline) vesicle, however, the entire negative charge is neutralized. Thus, the cationic conventional surfactant can "flip-flop" readily only in the liquid membrane. b) A cationic gemini surfactant charge-neutralizes only the anionic lipid in the outer membrane leaflet of either solid or liquid membranes, thus indicating an inability to flip-flop regardless of the phase-state of the bilayer. c) Mixed population experiments show that surfactants can hop from one vesicle to another in liquid but not solid membranes. d) In liquid, but not solid, bilayers, a surface-adsorbed cationic polymer can electrostatically "drag" anionic surfactant from the inner leaflet to the outer leaflet where the polymer resides. e) Peripheral fluorescence quenching experiments show that a cationic polymer, adhered to anionic vesicles, can be forced to dissociate in the presence of high concentrations of salt or an anionic polymer. f) Adsorbed polymer, of opposite charge to that imparted to vesicles by a gemini surfactant, is unable to dislocate surfactant even in a liquid membrane. g) In our systems, ionic polymers will not bind to neutral vesicles made solely of zwitterionic phospholipid. On the other hand, ionic polymers bind to neutral vesicles if charge neutrality is obtained by virtue of the membrane containing equimolar amounts of cationic and anionic surfactant. This is attributable to surfactant segregation within the bilayer. h) Experiments prove that polymer migration can occur among a population of neutral ternary vesicles.

The Use of Scintigraphic Imaging During Liposome Drug Development

Liposomes, spherical lipid bilayers enclosing an aqueous space, have become an important class of drug carriers. This review describes the usefulness of scintigraphic imaging during the development of liposome-based drugs. This imaging modality is particularly helpful for tracking the distribution of liposomes in the body, monitoring the therapeutic responses following administration of liposome-based drugs, and investigating the physiological responses associated with liposome administration. Scintigraphy also can be used to monitor the therapeutic responses of patients given approved liposomal drugs. Several examples describing the potential of this imaging modality during both the preclinical formulation and clinical trial stages of liposomal drug development are included. Techniques for radiolabeling liposomes as well as methods for producing scintigraphic images are also described.

Statistical modelling of the formulation variables in non-viral gene delivery systems

Traditionally, optimisation of a gene delivery formulation utilises a study design that involves altering only one formulation variable at any one time whilst keeping the other variables constant. As gene delivery formulations become more complex, e.g. to include multiple cellular and sub-cellular targeting elements, there will be an increasing requirement to generate and analyse data more efficiently and allow examination of the interaction between variables. This study aims to demonstrate the utility of multifactorial design, specifically a Central Composite Design, in modelling the responses size, zeta potential and in vitro transfection efficiency of some prototypic non-viral gene delivery vectors. i.e. cationic liposome-pDNA complexes, and extending the application of the design strategy to more complex vectors, i.e. tri-component lipid:polycation:DNA (LPD). The modelled predictions of how the above responses change as a function of formulation show consistency with an extensive literature base of data obtained using more traditional approaches, and highlight the robustness and utility of the Central Composite Design in examining key formulation variables in non-viral gene delivery systems. The approach should be further developed to maximise the predictive impact of data across the full range of pharmaceutical sciences.

Synthetic hydrogels as carriers in antisense therapy: preliminary evaluation of an oligodeoxynucleotide covalent conjugate with a copolymer of 1-vinyl-2-pyrrolidinone and 2-hydroxyethyl methacrylate

A major challenge of the antisense therapeutic strategies is the development of improved systems for the delivery of antisense oligodeoxynucleotides (AS ODNs) in order to enhance the cellular uptake, to assure a better efficiency in reaching the target tissue, and to provide sustained delivery over longer periods of time. Because the current methods for delivery (liposomes and cationic polymers) present some disadvantages, the attention was directed toward the use of neutral polymers as carriers for the AS ODNs. Based on our previous work on synthetic hydrogels for vitreous substitution, we developed a poly[1-vinyl-2-pyrrolidinone-co-(2-hydroxyethyl methacrylate)] hydrogel as a potential carrier for AS ODNs. We have previously demonstrated that such hydrogels are not cytotoxic, and they may have growth-promoting effects on cultured fibroblasts. This copolymer also has the advantage of being injectable. In this study, a specific AS ODN was synthesized and then covalently bound to the copolymer via carbodiimide coupling method. The resulting conjugate was subjected to in vitro release experiments over 46 days in the presence of bovine vitreous humor. Compared with the control (no enzyme present), a significant amount of covalently bound ODN was released from the ODN-hydrogel conjugate, suggesting the possibility of using such systems for the sustained delivery of AS ODNs.

Development of gene drug delivery systems based on pharmacokinetic studies

A series of pharmacokinetic studies following systemic or local administration for the development of delivery systems for gene drugs, such as plasmid DNA and oligonucleotides, are reviewed. The pharmacokinetics of gene drugs after intravenous injection into mice was evaluated based on clearance concepts. Pharmacokinetic analysis revealed that the overall disposition characteristics of the gene drug itself were determined by the physicochemical properties of its polyanionic DNA. Based on these findings, liver cell-specific carrier systems via receptor-mediated endocytosis were successfully developed by optimizing physicochemical characteristics. On the other hand, the pharmacokinetics of gene drugs after intratumoral injection were assessed in a tissue-isolated tumor perfusion system. The relationship between the physicochemical properties of gene drug delivery systems and intratumoral pharmacokinetics was determined and the therapeutic effect was also discussed in relation to pharmacokinetics. Collectively, it was demonstrated that a rational design of gene drug delivery systems that can control their in vivo disposition is possible by means of pharmacokinetic studies at whole body, organ and cellular levels.

Bacterial pore-forming hemolysins and their use in the cytosolic delivery of macromolecules

Advances in our understanding of fundamental cell biological processes have facilitated an expansion of therapeutic approaches to altering cellular physiology and phenotype. As many of these methods involve macromolecular agents that act on targets within the nucleus or cytoplasm, achieving their full potential ultimately requires the efficient delivery of these agents across the cell membrane barrier into the cytosol. Various strategies have been employed to enhance cytosolic delivery. These include either directly penetrating the plasma membrane, or avoiding degradation within the hydrolytic environment of the endosomal/lysosomal pathway after endocytic uptake. Some of the more promising methods in this regard have exploited the mechanisms utilized by certain viruses and bacteria for escaping into their host cell's cytosol. In this review, we will discuss some of these methods with an emphasis on the use of pore-forming proteins from bacteria. Particular attention will be drawn to the pH-sensitive endosomolytic bacterial hemolysins, such as listeriolysin O, and the potentiol for their use in cytosolic drug delivery systems.

Physical stability and in-vitro gene expression efficiency of nebulised lipid-peptide-DNA complexes

The lower respiratory tract provides a number of disease targets for gene therapy. Nebulisation is the most practical system for the aerosolisation of non-viral gene delivery systems. The aerosolisation process represents a significant challenge to the maintenance of the physical stability and biological activity of the gene vector. In this study we investigate the role of a condensing polycationic peptide on the stability and efficiency of nebulised lipid-DNA complexes. Complexes prepared from the cationic lipid 1, 2-dioleoyl-3-trimethylammonium propane (DOTAP) and plasmid DNA (pDNA) at mass (w/w) ratios of 12:1, 6:1 and 3:1, and complexes prepared from DOTAP, the polycationic peptide, protamine, and pDNA (LPD) at 3:2:1 w/w ratio were nebulised using a Pari LC Plus jet nebuliser. Samples from the nebuliser reservoir (pre- and post-nebulisation) and from the aerosol mist were collected and investigated for changes, including: particle diameter, retention of in-vitro transfection activity and the relative concentration and nature of the complexed pDNA remaining after the nebulisation procedure. The process of jet nebulisation adversely affected the physical stability of lipid:pDNA complexes with only those formulated at 12:1 w/w DOTAP:pDNA able to maintain their pre-nebulisation particle size distribution (145+/-3 nm pre-nebulisation vs. 142+/-2 nm aerosol mist) and preserve significant pDNA integrity in the reservoir (35% of pre-nebulisation pDNA band intensity). The LPD complexes were smaller (102+/-1 nm pre-nebulisation vs. 113+/-2 nm aerosol mist) with considerably greater retention of pDNA integrity in the reservoir (90% of pre-nebulisation pDNA band intensity). In contrast the concentration of pDNA in the aerosol mist for both the 12:1 w/w DOTAP:pDNA and LPD complexes were significantly reduced (10 and 12% of pre-nebulised values, respectively). Despite reduced pDNA concentration the transfection (% cells transfected) mediated by aerosol mist for the nebulised complexes was comparatively efficient (LPD aerosol mist 26 vs. 40% for pre-nebulised complex; the respective values for 12: 1 w/w DOTAP:pDNA were 12 vs. 28%). The physical stability and biological activity of nebulised lipid:pDNA complexes can be improved by inclusion of a condensing polycationic peptide such as protamine. The incorporation of the peptide precludes the use of potentially toxic excesses of lipid and charge and may act as a platform for the covalent attachment of peptide signals mediating sub-cellular targetting.

Chemically modified nucleic acid aptamers for in vitro selections: evolving evolution

Combinatorial library selections through the systematic evolution of ligands by exponential enrichment (SELEX) technique identify so-called nucleic acid aptamers that bind with high-affinity and specificity to a wide range of selected molecules. However, the modest chemical functionality of nucleic acids poses some limits on their versatility as binders and catalysts, and, furthermore, the sensitivity of pure RNA- and DNA-based aptamers to nucleases restricts their use as therapeutic and diagnostic agents. Here we review synthetic chemistries for modifying nucleotides that have been developed to enhance the affinity of aptamers for targets and to increase their stability in biological fluids. Implementation of in vitro selections with modified nucleotides promises to be an elegant technique for the creation of ligands with novel physical and chemical properties and is anticipated to have a significant impact on biotechnology, diagnostics and drug development. The current molecular designs and applications of modified nucleotides for in vitro selections are reviewed, along with a discussion of future developments expected to further the utility of this approach in both practical and theoretical terms.

Polymer conjugates for tumour targeting and intracytoplasmic delivery. The EPR effect as a common gateway?

Tumour capillaries are frequently hyperpermeable compared with normal vasculature, and thus they offer a much sought-after gateway for targeted delivery of cancer chemotherapy. Phase I clinical trials reported recently describe the first synthetic polymer-drug conjugate to be tested in man. N-(2-Hydroxypropyl)methacrylamide copolymer-doxorubicin (PK1, FCE 28068) displayed antitumour activity in chemotherapy-refractory patients, considerably reduced toxicity compared with doxorubicin, and evidence of tumour-selective targeting. With increasing understanding of the vector- and tumour-related factors that govern vascular permeability, non-viral vectors are being designed for tumour-selective targeting and subsequent intracytoplasmic delivery of macromolecular medicines such as genes, antisense oligonucleotides, proteins and peptides.

Conjugation of plasmid DNAs with lactose via diazocoupling enhances resistance to restriction enzymes and acquires binding affinity to galactose-specific lectin

Oligosaccharide-plasmid DNA conjugates were synthesized simply and effectively via the diazocoupling method. Plasmids (pUC19, pTRI-beta-actin, and pEGFP-C1) were treated with an N-beta-lactoside-substituted diazonium salt to yield diazocoupling products with degree of substitutions of 2.5-3.1 mol% of overall nucleobases. The lactose-pUC19 conjugate was found to resist restriction enzymes more strongly than the nonconjugated plasmid DNA and to acquire a strong binding affinity to galactose-specific lectin RCA(120). The diazocoupling modification of pTRI-beta-actin plasmid DNA little influenced in vitro transcription with T7 RNA polymerase. When lactose-pEGFP-C1 conjugate was transfected to baby hamster kidney (BHK) cells by means of cationic lipids, transduced gene was expressed in BHK cells similarly with the nonconjugated pEGFP-C1. The modification of plasmid DNA with carbohydrate enhanced the resistance to restriction enzymes and developed a strong binding affinity to galactose-specific lectin.

Antisense pharmacodynamics: critical issues in the transport and delivery of antisense oligonucleotides

This review critically examines current understanding of the kinetics and biodistribution of antisense oligonucleotides, both at the cellular level and at the level of the intact organism. The pharmacodynamic relationships between biodistribution and the ultimate biological effects of antisense agents are considered. The problems and advantages inherent in the use of delivery systems are discussed in the light of further enhancing in vivo pharmacological actions of oligonucleotides.

Self-assembly of polyamine-poly(ethylene glycol) copolymers with phosphorothioate oligonucleotides

The cationic copolymers for DNA delivery were synthesized by conjugating poly(ethylene glycol) (PEG) and polyamines: polyspermine (PSP) and polyethyleneimine (PEI). These molecules spontaneously form electrostatic complexes with a model 24-mer phoshorothioate oligonucleotide, T24 (PS-ODN). The copolymer complexes are water soluble. This is a marked contrast with the complexes formed by nonmodified PSP and PEI, which immediately precipitate out of solution. The potentiometric titration study suggests that the amino groups of the copolymers form a cooperative system of salt bonds with the thiophosphate groups of the PS-ODN. The PEG-PEI complexes are stable at physiological pH and ionic strengths. The PEG-PSP complexes are less stable in the presence of the low molecular mass electrolytes compared to the PEG-PEI complexes. The dynamic light scattering and transmission electron microscopy demonstrate that the complex particles are small-ca. 12 nm for PEG-PSP and ca. 32 nm for PEG-PEI. They can be lyophilized and redissolved or stored in solution for up to several months without changing size. The study suggests that as a result of formulation with the PEG-PEI the interactions of PS-ODNs with serum proteins (using the example of bovine serum albumin) are decreased and PS-ODN is protected against nuclease degradation. The simplicity of preparation and long shelf life make these systems attractive as potential pharmaceutical formulations for oligonucleotides.

Extravasation of macromolecules

Macromolecules can extravasate across the normal endothelium by transcapillary pinocytosis as well as by passage through interendothelial cell junctions, gaps or fenestrae. The main biological factors that control extravasation of a solute include regional differences in the capillary structures, the disease state of the organ or tissue, and the rate of blood and lymph supply. Physicochemical properties that are of profound significance in the extravasation of macromolecules are molecular size, shape, charge and hydrophilic/lipophilic balance (HLB) characteristics. Extravasation of small drugs, proteins, oligonucleotides and genes can be controlled by conjugating or forming complexes with macromolecular carriers. This requires a thorough understanding of the relationship between the chemical structures, physicochemical properties and the pharmacokinetics of both carrier and active molecules. This review article discusses the extravasation of macromolecules from the view points of pharmacokinetics and drug delivery systems, with the main emphasis on the extravasation across the liver, kidney and tumor capillaries.

Biodistribution and gene expression of lipid/plasmid complexes after systemic administration

The objectives of this study were to investigate the influence of physicochemical properties of lipid/plasmid complexes on in vivo gene transfer and biodistribution characteristics. Formulations based on 1,2-di-O-octadecenyl-3-trimethylammonium propane (DOTMA) and novel biodegradable cationic lipids, such as ethyl dioleoyl phosphatidylcholine (EDOPC), ethyl palmitoyl myristyl phosphatidylcholine (EPMPC), myristyl myristoyl carnitine ester (MMCE), and oleyl oleoyl L-carnitine ester (DOLCE), were assessed for gene expression after tail vein injection of lipid/plasmid complexes in mice. Gene expression was influenced by cationic lipid structure, cationic lipid-to-colipid molar ratios, plasmid-to-lipid charge ratios, and precondensation liposome size. Detectable levels of human growth hormone (hGH) in serum, human factor IX (hFIX) in plasma, and chloramphenicol acetyltransferase (CAT) in the lung and liver were observed with positively charged lipid/plasmid complexes prepared from 400-nm extruded liposomes with a cationic lipid-to-colipid ratio of 4:1 (mol/mol). Intravenous administration of lipid/CAT plasmid complexes resulted in distribution of plasmid DNA mainly to the lung at 15 min after injection. Plasmid DNA accumulation in the liver increased with time up to 24 hr postinjection. There was a 10-fold decrease in the amount of plasmid DNA in the lung at 15 min after injection, when the lipid/plasmid complex charge ratio was decreased from 3:1 to 0.5:1 (+/-). Bright fluorescent aggregates were evident in in vivo-transfected lung with the positively charged pCMV-CAT/DOLCE:dioleyl phosphatidylethanolamine (DOPE) (1:1, mol/mol) complexes, while more discrete punctate fluorescence was observed with a 4:1 molar ratio of cationic lipid:colipid formulations. Preinjection of polyanions such as plasmid, dextran sulfate, polycytidic acid, and polyinosinic acid decreased hGH expression, whereas the preinjection of both positively charged and neutral liposomes had no effect on hGH serum levels. Of the cationic lipids tested, DOLCE was found to be the most effective potentially biodegradable cationic lipid. A correlation between gene expression and cationic lipid:colipid ratios and lipid-to-plasmid charge ratio was also observed for DOTMA- and DOLCE-based formulations.

Biological effects and cellular uptake of c-myc antisense oligonucleotides and their cationic liposome complexes

The biological effects and cellular uptake of human c-myc antisense oligonucleotides and their liposome complexes were investigated in vitro using human promonocytic leukemia U937 cells. Antisense phosphorothioate oligonucleotides (S-Oligo) significantly inhibited the growth of U937 cells in a dose-dependent manner. However, no significant effect on cell proliferation was observed with unmodified phosphodiester (P-Oligo) and partially phosphorothioated (PS3-Oligo) oligonucleotides with an antisense sequence and S-Oligo with sense and G-quartet control sequences. In cellular uptake experiments, radiolabeled S-Oligo was taken up by U937 cells more than P-Oligo and PS3-Oligo. Similar results were obtained in mouse peritoneal macrophages used for comparison. Confocal microscopic studies demonstrated a significant distribution of FITC-labeled oligonucleotides on the cell surface and in the cytoplasm in a punctate pattern, but not in the nucleus. When complexed with cationic liposomes, cellular uptake of FITC-labeled P-Oligo or S-Oligo was significantly increased and the fluorescence was located mainly in the nucleus, indicating that the uptake and intracellular pharmacokinetics of both oligonucleotides can be modified by complexation. An inhibitory effect of the complexes was observed at a dose which is ineffective in the case of the oligonucleotides alone. However, this effect was also associated with cytotoxicity of the cationic liposomes, suggesting that optimization of this formulation will be necessary to achieve a more efficient delivery of the oligonucleotides to U937 cells.

Physicochemical and disposition characteristics of antisense oligonucleotides complexed with glycosylated poly(L-lysine)

The disposition characteristics of a 20 mer antisense phosphodiester oligonucleotide (PO) and its fully phosphorothioated derivative (PS) alone or complexed with glycosylated poly(L-lysine) (galactosylated polylysine, Gal-PLL; mannosylated polylysine, Man-PLL) were studied in mice in relation to their physicochemical characteristics. Good complex formation was obtained at a ratio of 1:0.6, w/w [oligonucleotides (ODNs)/carrier]. The 1:0.6 weight ratio of ODNs/Gal-PLL and ODNs/Man-PLL complexes had zeta potentials of -27 to -31 mV and mean particle size of 100 to 160 nm. After intravenous injection, 35S-labeled ODNs were eliminated rapidly from the circulation; however, their organ disposition characteristics depended on their type. Complex formation with glycosylated PLL increased the hepatic uptake and decreased the urinary clearance of these ODNs to a great extent. These complexes were taken up by both liver parenchymal cells (PC) and nonparenchymal cells (NPC). However, ODNs/Gal-PLL complexes showed a fairly high PC concentration, whereas ODNs/Man-PLL complexes distributed equally to both PC and NPC. The hepatic uptakes of PS/Gal-PLL and PS/Man-PLL complexes were partially inhibited by prior administration of Gal-BSA and Man-BSA, respectively, suggesting their hepatic uptake via the respective receptor-mediated endocytosis. However, uptake by galactose receptors of Kupffer cells, zeta potential, particle size, and Kupffer cell phagocytosis also seem to influence their uptake process. In conclusion, this study illustrates that ODNs can be delivered to hepatocytes and macrophages via galactose and mannose receptors, respectively.