Histidylated oligolysines increase the transmembrane passage and the biological activity of antisense oligonucleotides

Advanced Delivery Systems Based on Lysine or Lysine Polymers

Polylysine and materials that integrate lysine form promising drug delivery platforms. As a cationic macromolecule, a polylysine polymer electrostatically interacts with cells and is efficiently internalized, thereby enabling intracellular delivery. Although polylysine is intrinsically pH-responsive, the conjugation with different functional groups imparts smart, stimuli-responsive traits by adding pH-, temperature-, hypoxia-, redox-, and enzyme-responsive features for enhanced delivery of therapeutic agents. Because of such characteristics, polylysine has been used to deliver various cargos such as small-molecule drugs, genes, proteins, and imaging agents. Furthermore, modifying contrast agents with polylysine has been shown to improve performance, including increasing cellular uptake and stability. In this review, the use of lysine residues, peptides, and polymers in various drug delivery systems has been discussed comprehensively to provide insight into the design and robust manufacturing of lysine-based delivery platforms.

The Multifaceted Histidine-Based Carriers for Nucleic Acid Delivery: Advances and Challenges

Histidines incorporated into carriers of nucleic acids may enhance the extracellular stability of the nanoparticle, yet aid in the intracellular disruption of the nanoparticle, enabling the release of the nucleic acid. Moreover, protonation of histidines in the endosomes may result in endosomal swelling with subsequent lysis. These properties of histidine are based on its five-member imidazole ring in which the two nitrogen atoms may form hydrogen bonds or act as a base in acidic environments. A wide variety of carriers have integrated histidines or histidine-rich domains, which include peptides, polyethylenimine, polysaccharides, platform delivery systems, viral phages, mesoporous silica particles, and liposomes. Histidine-rich carriers have played key roles in our understanding of the stability of nanocarriers and the escape of the nucleic acids from endosomes. These carriers show great promise and offer marked potential in delivering plasmids, siRNA, and mRNA to their intracellular targets.

Self-Crosslinking Lipopeptide/DNA/PEGylated Particles: A New Platform for DNA Vaccination Designed for Assembly in Aqueous Solution

Delivery of plasmids for gene expression in vivo is an inefficient process that requires improvement and optimization to unlock the clinical potential of DNA vaccines. With ease of manufacture and biocompatibility in mind, we explored condensation of DNA in aqueous solution with a self-crosslinking, endosome-escaping lipopeptide (LP), stearoyl-Cys-His-His-Lys-Lys-Lys-amide (stearoyl-CH₂K₃), to produce cationic LP/DNA complexes. To test whether poly(ethylene glycol) (PEG)-ylation of these cationic complexes to neutralize the surface charge would improve the distribution, gene expression, and immune responses poly(ethylene glycol), these LP/DNA complexes were combined with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG₂₀₀₀). Fluorescence imaging illustrated that the cationic complexes exhibited the highest degree of localization and lowest degree of dispersion throughout the injected muscle, suggesting impaired mobility of cationic particles upon administration. Nanoluciferase reporter assays over a 90-day period demonstrated that gene expression levels in muscle were highest for PEGylated particles, with over a 200-fold higher level of expression than the cationic particles observed at 30 days. Humoral and cell-mediated immune responses were evaluated in vivo after injection of an ovalbumin expression plasmid. PEGylation improved both immune responses to the DNA complexes in mice. Overall, this suggests that PEGylation of cationic lipopeptide complexes can significantly improve both the transgene expression and immunogenicity of intramuscular DNA vaccines.

Stimulus-Responsive Peptide for Effective Delivery and Release of DNA in Plants

For efficient gene delivery in plant systems, nonviral vector and DNA complexes require extracellular stability, cell wall/membrane translocation capability, and the ability to mediate both endosomal escape and intracellular DNA release. Peptides make appealing gene delivery vectors due to their DNA-binding, cell-penetrating, and endosome escape properties. However, DNA release within cells has so far been inefficient, which results in poor and delayed gene expression, while the lack of understanding of both internalization and trafficking mechanisms is a further obstacle to the design of efficient peptide gene delivery vectors. Here, we report successful gene delivery into plants using a cellular environment-responsive vector, BPCH7, which is an efficient cell-penetrating peptide with a cyclic DNA-binding domain that is formed by a disulfide bond between two cysteines. The cyclic structure of BPCH7 confers high avidity attachment to DNA in vitro. Following endocytosis into cells, disulfide bond cleavage facilitated by intracellular glutathione induces structural changes within BPCH7 that enable the release of the associated DNA cargo. Comparative studies with BPKH, a cell-penetrating peptide with a linear DNA-binding domain, show that BPCH7 maximized and expedited gene transfer in cells and unveil for the first time the crucial role of plant stomata in the internalization of peptide-DNA complexes.

Determining the effects of PEI adsorption on the permeability of 1,2-dipalmitoylphosphatidylcholine/bis(monoacylglycero)phosphate membranes under osmotic stress

Polycations are used for a number of biological applications, including antibiotics and gene therapy. One aspect of the use of polycation gene carriers such as polyethylenemine (PEI) in gene therapy that is not well understood is their ability to escape from the vesicles they are internalized in. Here, in an attempt to gain a better understanding of PEI interaction with endosomal lipids under osmotic stress, we performed investigations using monolayers and vesicles derived from a mixture of neutral and negative lipids (1,2-dipalmitoylphosphatidylcholine (DPPC) and bis(monoacylglycero)phosphate (BMP), respectively). X-ray reflectivity (XR) and Langmuir trough measurements confirmed PEI adsorption to the negatively charged membrane. Confocal microscopy imaging indicated that PEI adsorption actually increases the overall integrity of the DPPC/BMP vesicle against osmotic stresses while also causing overall deformation and permeabilization of the lipid membrane, thus leading to leakage of contents from the interior of the vesicle. These confocal microscopy observations were also supported by data gathered by dynamic light scattering (DLS).

STATEMENT OF SIGNIFICANCE

In recent decades, researchers have investigated polyamine-based gene delivery systems as useful alternatives to viral gene carriers. One step that is crucial to the performance of polyamine gene carriers such as polyethylenemine (PEI) is escape from late endosomal vesicles during intracellular delivery. However, the ability of polyamine/DNA polyplexes to effectively escape from endosomes is a little-understood part of the gene therapy techniques that use these polyplexes. Here, we performed investigations using monolayers and vesicles derived from a mixture of neutral and negative lipids (1,2-dipalmitoylphosphatidylcholine (DPPC) and bis(monoacylglycero)phosphate (BMP), respectively) as model systems for late endosomes in order to examine the interactions of PEI with the DPPC/BMP membranes and study the subsequent effects on the stability and permeability of these membranes.

Solid-phase supported design of carriers for therapeutic nucleic acid delivery

Nucleic acid molecules are important therapeutic agents in the field of antisense oligonucleotide, RNA interference, and gene therapies. Since nucleic acids are not able to cross cell membranes and enter efficiently into cells on their own, the development of efficient, safe, and precise delivery systems is the crucial challenge for development of nucleic acid therapeutics. For the delivery of nucleic acids to their intracellular site of action, either the cytosol or the nucleus, several extracellular and intracellular barriers have to be overcome. Multifunctional carriers may handle the different special requirements of each barrier. The complexity of such macromolecules however poses a new hurdle in medical translation, which is the chemical production in reproducible and well-defined form. Solid-phase assisted synthesis (SPS) presents a solution for this challenge. The current review provides an overview on the design and SPS of precise sequence-defined synthetic carriers for nucleic acid cargos.

Synthesis and evaluation of pH-sensitive, self-assembled chitosan-based nanoparticles as efficient doxorubicin carriers

A novel pH-responsive polymer based on amphiphilic N-acetyl histidine and arginine-grafted chitosan was synthesized using N-acetyl histidine as hydrophobic segment and arginine as hydrophilic segment by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-mediated coupling reactions as anticancer drug delivery system for doxorubicin. The structure of the synthesized polymer was confirmed by Fourier transform infrared and ¹H nuclear magnetic resonance analysis. Due to self-association behavior, N-acetyl histidine and arginine-grafted chitosan structured nanoparticles with in size range of 204 nm. N-acetyl histidine and arginine-grafted chitosan with different substitution degree of N-acetyl histidine were initially prepared and characterized. The critical micelle concentration decreased with increasing substitution degree of N-acetyl histidine. Furthermore, N-acetyl histidine and arginine-grafted chitosan nanoparticles exhibited an acidic pH-triggered aggregation and disassembling nature. The doxorubicin-encapsulated nanoparticles based on synthesized conjugate ( N-acetyl histidine and arginine-grafted chitosan/doxorubicin nanoparticles) showed a sustained drug release pattern, which could be hastened under acidic pH conditions but delayed with increasing substitution degree of N-acetyl histidine. Anticancer effects demonstrated that N-acetyl histidine and arginine-grafted chitosan/doxorubicin nanoparticles could suppress both sensitive and resistant human breast tumor cell line (MCF-7) efficiently in a dose- and time-dependent pattern. Confocal microscopy results evidenced increased cellular uptake and enhanced retention of the synthesized nanoparticles in drug-resistant cells demonstrating better efficacy of nanoparticles over native doxorubicin. These results suggest that N-acetyl histidine and arginine-grafted chitosan/doxorubicin nanoparticles might be promising carriers for delivery of hydrophobic drug doxorubicin against drug-resistant tumors.

Tissue-specific Calibration of Real-time PCR Facilitates Absolute Quantification of Plasmid DNA in Biodistribution Studies

Analysis of the tissue distribution of plasmid DNA after administration of nonviral gene delivery systems is best accomplished using quantitative real-time polymerase chain reaction (qPCR), although published strategies do not allow determination of the absolute mass of plasmid delivered to different tissues. Generally, data is expressed as the mass of plasmid relative to the mass of genomic DNA (gDNA) in the sample. This strategy is adequate for comparisons of efficiency of delivery to a single site but it does not allow direct comparison of delivery to multiple tissues, as the mass of gDNA extracted per unit mass of each tissue is different. We show here that by constructing qPCR standard curves for each tissue it is possible to determine the dose of intact plasmid remaining in each tissue, which is a more useful parameter when comparing the fates of different formulations of DNA. We exemplify the use of this tissue-specific qPCR method by comparing the delivery of naked DNA, cationic DNA complexes, and neutral PEGylated DNA complexes after intramuscular injection. Generally, larger masses of intact plasmid were present 24 hours after injection of DNA complexes, and neutral complexes resulted in delivery of a larger mass of intact plasmid to the spleen.

A cell-penetrating foldamer with a bioreducible linkage for intracellular delivery of DNA

Despite significant advances in foldamer chemistry, tailored delivery systems based on foldamer architectures, which provide a high level of control over secondary structure, are curiously rare among non-viral technologies for transporting nucleic acids into cells. A potent pH-responsive, bioreducible cell-penetrating foldamer (CPF) was developed through covalent dimerization of a short (8-mer) amphipathic oligourea sequence bearing histidine-type units. This CPF exhibits a high capacity to assemble with pDNA and mediates efficient delivery of nucleic acids into the cell. Furthermore, it does not adversely affect cellular viability and was shown to compare favorably with a cognate peptide transfection agent based on His-rich sequences.

Bioreducible polycations as shuttles for therapeutic nucleic acid and protein transfection

SIGNIFICANCE

Nucleic acids such as gene-encoding DNAs, gene-silencing small interfering RNAs, or recombinant proteins addressing intracellular molecular targets present a major new therapeutic modality, provided efficient solutions for intracellular delivery can be found. The different physiological redox environments inside and outside the cell can be utilized for optimizing the involved transport processes.

RECENT ADVANCES

Intracellular delivery of nucleic acids or proteins requires dynamic carriers that discriminate between different cellular locations. Bioreducible cationic polymers can package their therapeutic cargo stably in the extracellular environment, but sense the reducing intracellular cytosolic environment. Based on disulfide cleavage, carriers are degraded into biocompatible fragments and release the cargo in functional form. Disulfide linkages between oligocations, between the carrier and the cargo, or spatial caging of complexed cargo by disulfides have been pursued, with polymers or precise sequence-defined peptides and oligomers.

CRITICAL ISSUES

A quantitative knowledge of the bioreductive capacities within different biological compartments and the involved cellular reduction processes would be greatly helpful for improved carriers with disulfides cleaved within the right compartment at the right time.

FUTURE DIRECTIONS

Novel designs of multifunctional nanocarriers will incorporate macromolecular disulfide entry mechanisms previously optimized by natural evolution of toxins and viruses. In addition to extracellular stabilization and intracellular disassembly, tuned disulfides will contribute to deshielding at the cell surface, or translocation from intracellular compartments to the cytosol.

Mechanisms of nanoparticle-mediated siRNA transfection by melittin-derived peptides

Traditional peptide-mediated siRNA transfection via peptide transduction domains exhibits limited cytoplasmic delivery of siRNA due to endosomal entrapment. This work overcomes these limitations with the use of membrane-destabilizing peptides derived from melittin for the knockdown of NFkB signaling in a model of adult T-cell leukemia/lymphoma. While the mechanism of siRNA delivery into the cytoplasmic compartment by peptide transduction domains has not been well studied, our analysis of melittin derivatives indicates that concurrent nanocomplex disassembly and peptide-mediated endosomolysis are crucial to siRNA transfection. Importantly, in the case of the most active derivative, p5RHH, this process is initiated by acidic pH, indicating that endosomal acidification after macropinocytosis can trigger siRNA release into the cytoplasm. These data provide general principles regarding nanocomplex response to endocytosis, which may guide the development of peptide/siRNA nanocomplex-based transfection.

Influence of histidine incorporation on buffer capacity and gene transfection efficiency of HPMA-co-oligolysine brush polymers

One of the major intracellular barriers to nonviral gene delivery is efficient endosomal escape. The incorporation of histidine residues into polymeric constructs has been found to increase endosomal escape via the proton sponge effect. Statistical and diblock copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA), oligolysine, and oligohistidine were synthesized via reversible-addition fragmentation chain transfer (RAFT) polymerization and tested for in vitro transfection efficiency, buffering ability, and polyplex uptake mechanism via the use of chemical endocytic inhibitors. Interestingly, histidine-containing statistical and diblock polymers exhibited increased buffer capacity in different endosomal pH ranges. Statistical copolymers transfected better than block copolymers that contained similar amounts of histidine. In addition, only the polymer containing the highest incorporation of oligohistidine residues led to increases in transfection efficiency over the HPMA-oligolysine base polymer. Thus, for these polymer architectures, high histidine incorporation may be required for efficient endosomal escape. Furthermore, inhibitor studies indicate that nonacidified caveolae-mediated endocytosis may be the primary route of transfection for these copolymers, suggesting that alternative approaches for increasing endosomal escape may be beneficial for enhancing transfection efficiency with these HPMA-oligolysine copolymers.

Melittin derived peptides for nanoparticle based siRNA transfection

Traditional transfection agents including cationic lipids and polymers have high efficiency but cause cytotoxicity. While cell penetrating peptide based transfection agents exhibit improved cytotoxicity profiles, they do not have the efficiency of existing lipidic agents due to endosomal trapping. As a consequence, we propose an alternative method to efficient peptide based siRNA transfection by starting with melittin, a known pore-forming peptide. By incorporating modifications to decrease cytotoxicity and improve siRNA binding, we have developed p5RHH, which can complex siRNA to form nanoparticles of 190 nm in diameter. p5RHH exhibits high efficiency with GFP knockdown at concentrations as low as 5 nM, with negligible cytotoxicity. To date, p5RHH has shown the ability to transfect B16 cells, Human Umbilical Vein Endothelial Cells, and RAW264.7 cells with high efficiency. These in vitro models demonstrate that p5RHH mediated transfection can block cancer cell proliferation, angiogenesis, and foam cell formation. Moreover, p5RHH/siRNA nanoparticles maintain their size and transfection efficiency in the presence of serum proteins suggesting the potential for use of p5RHH in vivo. These data suggest that our strategy for development of siRNA transfecting peptides can provide an avenue to safe and effective siRNA therapeutics.

An influenza virus-inspired polymer system for the timed release of siRNA

Small interfering RNA silences specific genes by interfering with mRNA translation, and acts to modulate or inhibit specific biological pathways; a therapy that holds great promise in the cure of many diseases. However, the naked small interfering RNA is susceptible to degradation by plasma and tissue nucleases and due to its negative charge unable to cross the cell membrane. Here we report a new polymer carrier designed to mimic the influenza virus escape mechanism from the endosome, followed by a timed release of the small interfering RNA in the cytosol through a self-catalyzed polymer degradation process. Our polymer changes to a negatively charged and non-toxic polymer after the release of small interfering RNA, presenting potential for multiple repeat doses and long-term treatment of diseases.

Buffering capacity and size of siRNA polyplexes influence cytokine levels

Induction of cytokines by small interfering RNA (siRNA) polyplexes has been a significant concern of researchers attempting to minimize the toxicity of this promising therapy. Although cationic carriers of siRNA are known to increase cytokine levels, few systematic studies have been done to determine what properties of the carrier are important to modulate cytokines. Because branched histidine-lysine (HK) peptides are effective carriers of siRNA and their sequence can be readily modified, we selected this class of carrier to determine which sequences of the peptide were important for cytokine induction. With the use of peripheral blood mononuclear cells (PBMCs), the HK peptide with a higher number of histidines (H3K(+H)4b) in complex with siRNA induced lower levels of cytokines compared with other HK (e.g., H2K4b, H3K4b, H3K(+N)4b) siRNA nanoplexes. Notably, these peptides' siRNA polyplexes showed a similar pattern of cytokine induction when injected intravenously in a mouse model, i.e., the HK with higher content of histidines induced cytokines the least. As indicated by the pH-sensitive dye within acidic endosomes, the greater pH-buffering capacity of H3K(+H)4b compared with other HK peptides may explain why cytokine levels were reduced. In addition to buffering capacity, the size of HK polyplexes markedly influenced cytokine production.

Supramolecular assemblies of histidinylated α-cyclodextrin in the presence of DNA scaffold during CDplexes formation

α-Cyclodextrin was transformed in a cationic unit after per substitution with histidine (His-α-CD) and lysine (Lys-α-CD) molecules on the primary face. His-α-CD and Lys-α-CD were used to form electrostatic complexes (CDplexes) with a plasmid DNA encoding luciferase gene, and the ability of CDplexes to transfect mammalian cells was examined using HEK293-T7 cells. The luciferase activity in cells transfected with His-α-CDplexes was 8-fold higher than that obtained Lys-α-CDplexes. When the transfection was carried out in the presence of chloroquine, the luciferase activity with His-α-CDplexes and Lys-α-CDplexes increased 6 and 25 times, respectively. The lower enhancement with His-α-CDplexes confirmed that histidine induced a proton sponge effect inside endosomes upon imidazole protonation, favoring DNA delivery in the cytosol. At the same time, we found that the condensation of DNA with His-α-CD was unexpectedly stronger than that obtained with the lysyl-α-CD counterpart. Moreover, it was as strong as that observed with high molecular weight polylysine. NMR (ROESY and DOSY) investigations in the absence of DNA showed that an inclusion complex is formed between the imidazole ring of histidine and the hydrophobic cavity of CD but no His-α-CD polymers can be formed by intermolecular interactions. These results suggest that intermolecular interactions between imidazole and His-α-CD cavity could be involved to form supramolecular assemblies in the presence of a DNA scaffold leading to DNA condensation into low diameter particles.

Influence of histidine on the release of all-trans retinoic acid from self-assembled glycol chitosan nanoparticles

OBJECTIVE

In this study, the influence of N-acetyl histidine (NAHis) on the all-trans retinoic acid (ATRA) release from the NAHis-conjugated self-assembled glycol chitosan (GC) nanoparticles was investigated.

METHODS

NAHis was conjugated to GC as a hydrophobic moiety to prepare the self-assembled nanoparticles, and ATRA was incorporated into the inner core of the NAHis-GC nanoparticles. The ATRA release from NAHis-GC nanoparticles was performed at 37 degrees C in a phosphate-buffered saline buffer (pH 5.5 or 7.4) for 48 hours.

RESULTS

At a pH of 5.5, less than 20% (w/w) of total loading amount of ATRA was released from the nanoparticles after 48 hours. In contrast, two times greater amount of ATRA was released at a pH of 7.4. The ATRA release rate from the NAHis-GC nanoparticles was significantly slower at a pH of 5.5 than at a pH of 7.4.

CONCLUSION

The release profiles of ATRA that was incorporated into the NAHis-GC nanoparticles were controlled by the NAHis content in the GC nanoparticles.

Chemical vectors for gene delivery: a current review on polymers, peptides and lipids containing histidine or imidazole as nucleic acids carriers

DNA/cationic lipid (lipoplexes), DNA/cationic polymer (polyplexes) and DNA/cationic polymer/cationic lipid (lipopolyplexes) electrostatic complexes are proposed as non-viral nucleic acids delivery systems. These DNA-nanoparticles are taken up by the cells through endocytosis processes, but the low capacity of DNA to escape from endosomes is regarded as the major limitations of their transfection efficiency. Here, we present a current report on a particular class of carriers including the polymers, peptides and lipids, which is based on the exploitation of the imidazole ring as an endosome destabilization device to favour the nucleic acids delivery in the cytosol. The imidazole ring of histidine is a weak base that has the ability to acquire a cationic charge when the pH of the environment drops bellow 6. As it has been demonstrated for poly(histidine), this phenomena can induce membrane fusion and/or membrane permeation in an acidic medium. Moreover, the accumulation of histidine residues inside acidic vesicles can induce a proton sponge effect, which increases their osmolarity and their swelling. The proof of concept has been shown with polylysine partially substituted with histidine residues that has caused a dramatic increase by 3-4.5 orders of magnitude of the transfection efficiency of DNA/polylysine polyplexes. Then, several histidine-rich polymers and peptides as well as lipids with imidazole, imidazolinium or imidazolium polar head have been reported to be efficient carriers to deliver nucleic acids including genes, mRNA or SiRNA in vitro and in vivo. More remarkable, histidylated carriers are often weakly cytotoxic, making them promising chemical vectors for nucleic acids delivery.

Delivery of siRNA mediated by histidine-containing reducible polycations

Histidine containing reducible polycations based on CH(6)K(3)H(6)C monomers (His6 RPCs), are highly effective DNA transfection agents combining pH buffering endosomal escape mechanisms with rapid unpackaging following reduction in the cytoplasm. We examined their ability to mediate siRNA uptake into cells focusing on hepatocyte delivery. Co-delivery of EGFP siRNA with pEGFP plasmid DNA reduced reporter gene expression by 85%. However while DNA transfection efficiency increased with polymer size, with 162 k His6 RPCs proving the most effective, delivery of siRNA alone to EGFP stably expressing cells was only possible using 36-80 k polymers. Analysis of particle sizes showed that 80 k polymers formed more compact siRNA complexes than 162 k polymers. The reducible nature of the polymer was necessary for siRNA activity, since siRNA combined with non-reducible polylysine showed little activity. Incorporation of a targeting peptide from the Plasmodium falciparum circumsporozoite (CS) protein onto His6 RPCs, significantly improved transfection of plasmid DNA and siRNA activity in hepatocytes, but not in most non-liver cells tested. siRNA targeted to the hepatitis B virus surface antigen delivered by CS-His6 RPC, mediated falls in both mRNA and protein expression, suggesting that this delivery system could be developed for potential therapies for viral hepatitis.

Materializing the potential of small interfering RNA via a tumor-targeting nanodelivery system

The field of small interfering RNA (siRNA) as potent sequence-selective inhibitors of transcription is rapidly developing. However, until now, low transfection efficiency, poor tissue penetration, and nonspecific immune stimulation by in vivo administered siRNAs have delayed their therapeutic application. Their potential as anticancer therapeutics hinges on the availability of a vehicle that can be systemically administered, safely and repeatedly, and will deliver the siRNA specifically and efficiently to the tumor, both primary tumors and metastases. We have developed a nanosized immunoliposome-based delivery complex (scL) that, when systemically administered, will preferentially target and deliver molecules useful in gene medicine, including plasmid DNA and antisense oligonucleotides, to tumor cells wherever they occur in the body. This tumor-targeting nanoparticle delivery vehicle can also deliver siRNA to both primary and metastatic disease. We have also enhanced the efficiency of this complex by the inclusion of a pH-sensitive histidine-lysine peptide in the complex (scL-HoKC) and by delivery of a modified hybrid (DNA-RNA) anti-HER-2 siRNA molecule. Scanning probe microscopy confirms that this modified complex maintains its nanoscale size. More importantly, we show that this nanoimmunoliposome anti-HER-2 siRNA complex can sensitize human tumor cells to chemotherapeutics, silence the target gene and affect its downstream pathway components in vivo, and significantly inhibit tumor growth in a pancreatic cancer model. Thus, this complex has the potential to help translate the potent effects of siRNA into a clinically viable anticancer therapeutic.

Novel histidine-conjugated galactosylated cationic liposomes for efficient hepatocyte-selective gene transfer in human hepatoma HepG2 cells

To enhance gene transfection to hepatocytes by cationic liposomes, it is necessary to overcome a number of barriers existing in the process from administration to gene expression. Recently we and other group have demonstrated that the escape of plasmid DNA (pDNA)/cationic liposome complexes (lipoplexes) from the endosome to cytoplasm was rate limiting. In this study, to enhance transfection efficiency by promoting the release of lipoplexes from the endosome to cytoplasm, we proposed utilizing the "proton sponge effect". Here, we synthesized a novel pH-sensitive histidine-modified galactosylated cholesterol derivative (Gal-His-C4-Chol), for a more efficient gene delivery to hepatocytes. Liposomes containing Gal-His-C4-Chol showed much greater transfection activity than conventional Gal-C4-Chol liposomes based on a receptor-mediated mechanism in HepG2 cells. Hence, this finding should contribute to the development of gene therapy using cationic liposomes toward their clinical application.

RETRACTED: Imidazolyl-PEI modified nanoparticles for enhanced gene delivery

The derivatives of polyethylenimine (PEI 25 and 750kDa) were synthesized by partially substituting their amino groups with imidazolyl moieties. The series of imidazolyl-PEIs thus obtained were cross-linked with polyethylene glycol (PEG) to get imidazolyl-PEI-PEG nanoparticles (IPP). The component of hydrophobicity was introduced by grafting the lauryl groups in the maximal substituted IPP nanoparticles (IPPL). The nanoparticles were characterized with respect to DNA interaction, hydrodynamic diameter, zeta potential, in vitro cytotoxicity and transfection efficiency on model cell lines. The IPP and IPPL nanoparticles formed a loose complex with DNA compared to the corresponding native PEI, leading to more efficient unpackaging of DNA. The DNA loading capacity of IPP and IPPL nanoparticles was also lower compared to PEI. The imidazolyl substitution improved the gene delivery efficiency of PEI (750kDa) by nine- to ten-fold and PEI (25kDa) by three- to four-fold. At maximum transfection efficiency, the zeta potential of nanoparticles was positive after forming a complex with DNA. The maximum level of reporter gene expression was mediated by IPPL nanoparticles in both the series. The cytotoxicity, another pertinent problem with cationic polymers, was also negligible in case of IPP and IPPL nanoparticles.

Peptide-guided gene delivery

Although currently less efficient than their viral counterparts, nonviral vectors are under intense investigation as a safer alternative for gene therapy. For successful delivery, the nonviral vector must be able to overcome many barriers to protect DNA and specifically deliver it for efficient gene expression in target cells. The use of peptides as gene delivery vectors is advantageous over other nonviral agents in that they are able to achieve all of these goals. This review will focus on the application of peptides to mediate nonviral gene delivery. By examining the literature over the past 20 years, it becomes clear that no other class of biomolecules are simultaneously capable of DNA condensation, blocking metabolism, endosomal escape, nuclear localization, and receptor targeting. Based on virtually limitless diversity of peptide sequence and function information from nature, it is increasingly clear that peptide-guided gene delivery is still in its infancy.

N-acetyl histidine-conjugated glycol chitosan self-assembled nanoparticles for intracytoplasmic delivery of drugs: Endocytosis, exocytosis and drug release

Nano-sized vesicular systems (nanoparticles), ranging from 10 nm to 1000 nm in size, have potential applications as drug delivery systems. Successful clinical applications require the efficient intracellular delivery of drug-loaded nanoparticles. Here we describe N-acetyl histidine-conjugated glycol chitosan (NAcHis-GC) self-assembled nanoparticles as a promising system for intracytoplasmic delivery of drugs. Because N-acetyl histidine (NAcHis) is hydrophobic at neutral pH, the conjugates formed self-assembled nanoparticles with mean diameters of 150-250 nm. In slightly acidic environments, such as those in endosomes, the nanoparticles were disassembled due to breakdown of the hydrophilic/hydrophobic balance by the protonation of the imidazole group of NAcHis. Cellular internalization and drug release of the pH-sensitive self-assembled nanoparticles were investigated by flow cytometry and confocal microscopy. NAcHis-GC nanoparticles internalized by adsorptive endocytosis were exocytosed or localized in endosomes. The amount of exocytosed nanoparticles was dependent on the pre-incubation time prior to removal of free nanoparticles from the culture media. Flow cytometry and confocal microscopy showed that NAcHis-GC nanoparticles released drugs into the cytosol and cell cycle analysis demonstrated that paclitaxel-incorporated NAcHis-GC nanoparticles were effective in inducing arrest of cell growth.

Nanoparticle formulation enhances the delivery and activity of a vascular endothelial growth factor antisense oligonucleotide in human retinal pigment epithelial cells

The objective of this study was to investigate the delivery and activity of a vascular endothelial growth factor (VEGF) antisense oligonucleotide in a human retinal pigment epithelial cell line (ARPE-19) using a biodegradable nanoparticulate delivery system. A 19-mer antisense phosphorothioate oligonucleotide (PS-ODN) complementary to bases 6-24 relative to the translational start site of the VEGF mRNA, a sense PS-ODN and a mismatch PS-ODN were examined for the inhibition of secretion and mRNA expression of VEGF using an enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction, respectively. Nanoparticles of the antisense oligonucleotides were formulated using a poly(lactide-co-glycolide) (50:50) copolymer using a double emulsion solvent evaporation method. After preparing nanoparticles, drug loading, encapsulation efficiency and particle size were determined. The cells were exposed to either plain solution of oligonucleotide or nanoparticles of oligonucleotide from Day 3 through Day 6. Alternatively, the cells were incubated with PS-ODNs and lipofectin for 4 h on Day 4. In all studies, VEGF secretion and mRNA expression were determined on Day 6. The particle size, drug loading and encapsulation efficiency were 252 nm, 5.5% and 16.5%, respectively. The antisense PS-ODN inhibited VEGF mRNA and protein secretion when delivered using nanoparticles or lipofectin but not in its free form. This was consistent with the ability of nanoparticles and lipofectin to elevate the cellular uptake of the oligonucleotide by 4-fold and 13-fold, respectively. Neither mismatch nor sense oligonucleotides inhibited VEGF secretion. In conclusion, biodegradable nanoparticles enhance cellular delivery of a VEGF antisense oligonucleotide and inhibit VEGF secretion and mRNA expression in a human retinal pigment epithelial cell line.

A branched histidine/lysine peptide, H2K4b, in complex with plasmids encoding antitumor proteins inhibits tumor xenografts

BACKGROUND

In this study we investigated whether a particular branched HK polymer, H2K4b, was an effective in vivo carrier of plasmids expressing the antiangiogenic kringle 1-5 or the tumor suppressor p53.

METHODS

H2K4b was synthesized on a solid-phase peptide synthesizer. Distribution, optimization and time course studies were done in tumor-bearing nude mice by systemically administering H2K4b in complex with a luciferase-expressing plasmid. We examined the amount of tumor angiogenesis in C6 with MDA-MB-435 xenografts utilizing the carmine dye. The ability of H2K4b to carry luciferase plasmids to different tissues was compared with several liposomal carriers. Medium from cells transfected with mKr1-5 was tested for its capacity to inhibit angiogenesis with an in vivo Matrigel assay. We then determined if systemically delivered H2K4b in complex with plasmid encoding mKr1-5 inhibited tumor growth; we also compared the antitumor activity of HK polyplexes containing hKr1-5, mKr1-5, and p53 plasmids.

RESULTS

H2K4b carried the luciferase-expressing plasmid in order of descending efficacy to these tissues: lung, spleen, tumor, and liver. Compared to DOTAP-containing liposomes, H2K4b was a more effective carrier of a luciferase-containing plasmid to extrapulmonary tissues. We then determined that mKr1-5 in complex with H2K4b reduced MDA-MB-435 tumor growth by approximately 50% compared to the control group (P < 0.01). Similarly, H2K4b/mKr1-5 polyplexes reduced the growth of C6 xenografts. In MDA-MB-435 xenografts, p53- and Kr1-5-expressing plasmids in complex with H2K4b had comparable antitumor activity.

CONCLUSION

H2K4b demonstrates potential as a carrier of plasmids encoding antiangiogenic and/or tumor suppressor proteins in a tumor-bearing mouse model.

Design and development of polymers for gene delivery

The lack of safe and efficient gene-delivery methods is a limiting obstacle to human gene therapy. Synthetic gene-delivery agents, although safer than recombinant viruses, generally do not possess the required efficacy. In recent years, a variety of effective polymers have been designed specifically for gene delivery, and much has been learned about their structure-function relationships. With the growing understanding of polymer gene-delivery mechanisms and continued efforts of creative polymer chemists, it is likely that polymer-based gene-delivery systems will become an important tool for human gene therapy.

Drug delivery of oligonucleotides by peptides

Oligonucleotides are promising tools for in vitro studies where specific downregulation of proteins is required. In addition, antisense oligonucleotides have been studied in vivo and have entered clinical trials as new chemical entities with various therapeutic targets such as antiviral drugs or for tumour treatments. The formulation of these substances were widely studied in the past. With this review we will focus on peptides used as drug delivery vehicles for oligonucleotides. Different strategies are summarised. Cationically charged peptides from different origins were used e.g. as cellular penetration enhancers or nuclear localisation tool. Examples are given for Poly-L-lysine alone or in combination with receptor specific targeting ligands such as asialoglycoprotein, galactose, growth factors or transferrin. Another large group of peptides are those with membrane translocating properties. Fusogenic peptides rich in lysine or arginine are reviewed. They have been used for DNA complexation and condensation to form transport vehicles. Some of them, additionally, have so called nuclear localisation properties. Here, DNA sequences, which facilitate intracellular trafficking of macromolecules to the nucleus were explored. Summarizing the present literature, peptides are interesting pharmaceutical excipients and it seems to be feasible to combine the specific properties of peptides to improve drug delivery devices for oligonucleotides in the future.

Modified branched peptides with a histidine-rich tail enhance in vitro gene transfection

Successful gene therapy depends on the development of efficient, non-toxic gene delivery systems. To accomplish this objective, our laboratory has focused on solid-phase synthesized peptide carriers, in which the amino acid sequence can be varied precisely to augment intracellular DNA transport. We previously determined that linear and branched co-polymers of histidine and lysine in combination with liposomes enhanced the efficiency of gene transfection. In this study, we have modified two branched histidine-lysine (HK) peptides by adding a histidine-rich tail. In a variety of cell lines, this histidine-rich tail markedly improved transfection efficiency, presumably by increasing the buffering capacity of the polymer. One polymer with a histidine-rich tail, H2K4bT, compared favorably with the commonly used transfection agents. Together with modification of our transfection protocol, these improved HK peptides alone, without liposomes, are the effective carriers of plasmids into a variety of cells. We anticipate that branched HK peptides will continue to be developed as carriers of nucleic acids for in vitro and in vivo applications.

Protein and peptide parenteral controlled delivery

Protein and peptide delivery has been a challenge due to their limited stability during preparation of formulation, storage and in vitro and in vivo release. These biopolymers have traditionally been administered via intramuscular or subcutaneous routes. Recent efforts have been made to develop formulations for non-invasive routes of administration, including oral, intranasal, transdermal and transmucosal delivery. Despite these efforts, invasive delivery remains the main method of administering peptide and protein drugs. This review focuses on recent developments in injectable, polymeric controlled-release formulations, with an emphasis on hydrogels and particulate systems.

Super pH-sensitive multifunctional polymeric micelle

To endow enhanced tumor specificity and endosome disruption property on the carrier, a multifunctional polymeric micelle was investigated. The micelle exposes the cell interacting ligand (biotin) on the surface under slightly acidic environmental conditions of various solid tumors and is internalized by biotin receptor-mediated endocytosis in a short time period. The micelle also showed pH-dependent dissociation, causing the enhanced release of doxorubicin from the carrier in early endosomal pH. The dissociated micellar components subsequently disrupt endosomal membrane.

Studies on the cellular uptake of substance P and lysine-rich, KLA-derived model peptides

In the last decade many peptides have been shown to be internalized into various cell types by different, poorly characterized mechanisms. This review focuses on uptake studies with substance P (SP) aimed at unravelling the mechanism of peptide-induced mast cell degranulation, and on the characterization of the cellular uptake of designed KLA-derived model peptides. Studies on structure-activity relationships and receptor autoradiography failed to detect specific peptide receptors for the undecapeptide SP on mast cells. In view of these findings, a direct interaction of cationic peptides with heterotrimeric G proteins without the participation of a receptor has been proposed. Such a process would require insertion into and translocation of peptides across the plasma membrane. In order to clarify whether a transport of cationic peptides into rat peritoneal mast cells is possible, transport studies were performed by confocal laser scanning microscopy (CLSM) using fluorescence-labeled Arg(3),Orn(7)-SP and its D-amino acid analog, all-D-Arg(3),Orn(7)-SP, as well as by electron microscopic autoradiography using (3)H-labelled SP and (125)I-labelled all-D-SP. The results obtained by CLSM directly showed translocation of SP peptides into pertussis toxin-treated cells. Kinetic experiments indicated that the translocation process was rapid, occurring within a few seconds. Mast cell degranulation induced by analog of magainin 2 amide, neuropeptide Y and the model peptide acetyl-KLALKLALKALKAALKLA-amide was also found to be very fast, pointing to an extensive translocation of the peptides. In order to learn more about structural requirements for the cellular uptake of peptides, the translocation behavior of a set of systematically modified KLA-based model peptides has been studied in detail. By two different protocols for determining the amount of internalized peptide, evidence was found that the structure of the peptides only marginally affects their uptake, whereas the efflux of cationic, amphipathic peptides is strikingly diminished, thus allowing their enrichment within the cells. Although the mechanism of cellular uptake, consisting of energy-dependent and -independent contributions, is not well understood, KLA-derived peptides have been shown to deliver various cargos (PNAs, peptides) into cells. The results obtained with SP- and KLA-derived peptides are discussed in the context of the current literature.

On the biological activity of anti-ICAM-1 oligonucleotides complexed to non-viral carriers

An important challenge in antisense technology remains the adequate delivery of the oligonucleotides (ON) to individual cells. Understanding the subcellular distribution of ONs and their carrier is essential to explain the (lack of) biological activity. The ability of several cationic carriers to efficiently deliver anti-ICAM-1 oligonucleotides to their site of action was studied using a cell-based assay. In this assay we evaluated the ability of the ONs to downregulate the expression of the ICAM-1-protein in A549 cells. To understand why some carrier/ONs combinations showed biological activity while others failed, flow cytometry and confocal laser scanning microscopy (CLSM) measurements were used to study cellular uptake and intracellular distribution of the (fluorescently labeled) ONs. We showed that free ONs (both PS-ONs and PO-ONs) and ONs complexed to pEGpEI failed to decrease the ICAM-1 protein level. This was due to the inability of the (free or complexed) ONs to enter the cell, as shown by flow cytometry and CLSM. Flow cytometry and CLSM showed cellular uptake when PO-ONs and PS-ONs were complexed to graft-pDMAEMA and Lipofectin. However, while the uptake and intracellular localization seemed similar for ONs complexed to, respectively, graft-pDMAEMA and Lipofectin, the biological activity of the ONs was clearly dependent on their carrier: both PO-ONs and PS-ONs complexed to graft-pDMAEMA reduced the ICAM-1 expression; however, when complexed to Lipofectin only PS-ONs showed biological activity. Also, PS-ONs complexed to graft-pDMAEMA were more active than PO-ONs complexed to graft-pDMAEMA which could not be explained by the results from CLSM and flow cytometry. While the ICAM-1 assay proves whether a certain pharmaceutical carrier successfully delivers ONs or not, it does not answer the important question why one carrier is successful while another one fails. Also, our study shows that flow cytometry and CLSM, although useful techniques, failed to clearly explain the difference in transfection behavior between graft-pDMAEMA and Lipofectin. As ONs become susceptible to degradation by cytosolic DNase as soon as they are released from their carrier, one could argue that a better understanding of the time and (intracellular) place at which the dissociation of the complexes occurs could be crucial to fully explain our observations.

On the Gene Delivery Efficacies of pH-Sensitive Cationic Lipids via Endosomal Protonation

In an effort to probe the importance of endosomal protonation in pH-sensitive, cationic, lipid-mediated, non-viral gene delivery, we have designed and synthesized a novel cholesterol-based, endosomal pH-sensitive, histidylated, cationic amphiphile (lipid 1), its less pH-sensitive counterpart with an electron-deficient, tosylated histidine head group (lipid 2) as well as a third new cholesterol-based, cationic lipid containing no histidine head group (lipid 3). For all the novel liposomes and lipoplexes, we evaluated hysicochemical characteristics, including lipid:DNA interactions, global surface charge, and sizes. As anticipated, lipid 2 showed lower efficacies than lipid 1 for the transfection of 293T7 cells with the cytoplasmic gene expression vector pT7Luc at lipid:DNA mole ratios of 3.6:1 and 1.8:1; both lipids were greatly inhibited in the presence of Bafilomycin A1. This demonstrates the involvement of imidazole ring protonation in the endosomal escape of DNA. Conversely, endosome escape of DNA with lipid 3 seemed to be independent of endosome acidification. However, with nuclear gene expression systems in 293T7, HepG2, and HeLa cells, the transfection efficacies of lipid 2 at a lipid:DNA mole ratio of 3.6:1 were found to be either equal to or somewhat lower than those of lipids 1 and 3. Interestingly, at a lipid:DNA mole ratio of 1.8:1, lipids 2 and 3 were remarkably more transfection efficient than lipid 1 in both HepG2 and HeLa cells. Mechanistic implications of such contrasting relative transfection profiles are delineated.

Enhanced transfection efficiency of a systemically delivered tumor-targeting immunolipoplex by inclusion of a pH-sensitive histidylated oligolysine peptide

Successful cancer gene therapy depends on the development of non-toxic, efficient, tumor cell- specific systemic gene delivery systems. Our laboratory has developed a systemically administered, ligand-liposome complex that can effectively and preferentially deliver its therapeutic payload to both primary and metastatic tumors. To further improve the transfection efficiency of this targeting complex, a synthetic pH-sensitive histidylated oligolysine K[K(H)KKK]5-K(H)KKC (HoKC), designed to aid in endosomal escape and condensation of DNA, was included in the complex. The presence of HoKC increased the in vitro transfection efficiency over that of the original complex. Moreover, no increase in cytotoxicity was observed due to the presence of the HoKC peptide. In a DU145 human prostate cancer xenograft tumor model in athymic nude mice, inclusion of the HoKC peptide did not interfere with the tumor targeting specificity of the i.v. administered ligand/liposome/DNA complex. Most importantly, the level of transgene expression was significantly elevated in the tumors, but not in the normal tissue in those animals receiving the complex incorporating HoKC. The in vivo enhancement of transfection efficiency by this modified gene delivery vehicle could lead to a reduction in the number of administrations required for antitumor efficacy.

Polycation gene delivery systems: escape from endosomes to cytosol

Clinical success of gene therapy based on oligonucleotides (ODNs), ribozymes, RNA and DNA will be greatly dependent on the availability of effective delivery systems. Polycations have gained increasing attention as a non-viral gene delivery vector in the past decades. Significant progress has been made in understanding complex formation between polycations and nucleic acids, entry of the complex into the cells and subsequent entry into the nucleus. Sophisticated molecular architectures of cationic polymers have made the vectors more stable and less susceptible to binding by enzymes or proteins. Incorporation of specific ligands to polycations has resulted in more cell-specific uptake by receptor-mediated mechanisms. However, there are still other barriers limiting the transfection efficiency of polycation gene delivery systems. There is a consensus that polycation-DNA complexes (polyplexes) enter cells via the endocytotic pathway. It is not clearly understood, however, how the polyplexes escape (if they do) from endosomes, how DNA is released from the polyplexes or how the released DNA is expressed. The primary focus of this article is to review various polycation gene delivery systems, which are designed to translocate DNA from endosomes into cytosol. Many polycation gene delivery systems have tried to mimic the mechanisms that viruses use for the endosomal escape. Polycation gene delivery systems are usually coupled with synthetic amphipathic peptides mimicking viral fusogenic peptides, histidine-based gene delivery systems for pH-responsive endosomal escape, polycations with intrinsic endosomolytic activity by the proton sponge mechanism and polyanions to mimic the anionic amphiphilic peptides.

Design strategies to improve soluble macromolecular delivery constructs

Macromolecular therapeutics provide numerous benefits for the delivery of cytotoxic or poorly soluble drugs in vivo. However, these constructs often encounter barriers for drug delivery on both the systemic and subcellular level. Many soluble polymer carriers have been designed to surmount specific physiological barriers individually, but less work has been dedicated to designing an all-encompassing construct that addresses multiple therapeutic barriers at once. Incorporation of multiple agents already individually known to increase effectiveness into one carrier could further improve current drug delivery technology. Recent developments in subcellular delivery of therapeutic agents in soluble macromolecular carriers are discussed in the context of the future possibility for the design of an all-encompassing soluble multi-functional drug delivery vehicle.

Intracellular processing of poly(ethylene imine)/ribozyme complexes can be observed in living cells by using confocal laser scanning microscopy and inhibitor experiments

PURPOSE

Critical steps in the subcellular processing of poly(ethylene imine)/nucleic acid complexes, especially endosomal/lysosomal escape, were visualized by using living cell confocal laser scanning microscopy (CSLM) to obtain an insight into their mechanism.

METHODS

Living cell confocal microscopy was used to examine the intracellular fate of poly(ethylene imine)/ribozyme and poly(L-lysine)/ribozyme complexes over time, in the presence of and without bafilomycin Al, a selective inhibitor of endosomal/lysosomal acidification. The compartment of complex accumulation was identified by confocal microscopy with a fluorescent acidotropic dye. To confirm microscopic data, luciferase reporter gene expression was determined under similar experimental conditions.

RESULTS

Poly(ethylene imine)/ribozyme complexes accumulate in acidic vesicles, most probably lysosomes. Release of complexes occurs in a sudden event, very likely due to bursting of these organelles. After release, poly(ethylene imine) and ribozyme spread throughout the cell, during which slight differences in distribution between cytosol and nucleus are visible. No lysosomal escape was observed with poly(L-lysine)/ribozyme complexes or when poly(ethylene imine)/ ribozyme complexes were applied together with bafilomycin A1. Poly(ethylene imine)/plasmid complexes exhibited a high luciferase expression, which was reduced approximately 200-fold when lysosomal acidification was suppressed with bafilomycin A1.

CONCLUSIONS

Our data provide, for the first time, direct experimental evidence for the escape of poly(ethylene imine)/nucleic acid complexes from the endosomal/lysosomal compartment. CLSM, in conjunction with living cell microscopy, is a promising tool for studying the subcellular fate of polyplexes in nucleic acid/gene delivery.

Histidine-rich peptides and polymers for nucleic acids delivery

Nucleic acids transfer into mammalian cells requires devices to improve their escape from endocytic vesicles where they are mainly confined following cellular uptake. In this review, we describe histidine-rich molecules that enable the transfer of plasmid and oligonucleotides (ODN) in human and non-human cultured cells. An histidine-rich peptide which permeabilizes biological membrane at pH 6.4, favored the transfection mediated by lactosylated polylysine/pDNA complexes. Histidylated polylysine forms cationic particles of 100 nm with a plasmid and yielded a transfection of 3-4.5 orders of magnitude higher than polylysine. The biological activity of antisense ODN was increased more than 20-fold when it was complexed with highly histidylated oligolysine into small cationic spherical particles of 35 nm. Evidence that imidazole protonation mediates the effect of these molecules in endosomes are provided. We also describe a disulfide-containing polylysine conjugate capable of mediating DNA unpackaging in a reductive medium and to increase the transfection efficiency. Overall, these molecules constitute interesting devices for developing non-viral gene delivery systems.

Inhibition of HIV-1 in cell culture by oligonucleotide-loaded nanoparticles

PURPOSE

To investigate the potential use of polymeric nanoparticles for the delivery of antisense oligonucleotides in HIV-1-infected cell cultures.

METHODS

Phosphorothioate oligonucleotides were encapsulated into poly (D,L-lactic acid) nanoparticles. Two models of infected cells were used to test the ability of nanoparticles to deliver them. HeLa P4-2 CD4+ cells, stably transfected with the beta-galactosidase reporter gene, were first used to evaluate the activity of the oligonucleotides on a single-round infection cycle. The acutely infected lymphoid CEM cells were then used to evaluate the inhibition of the viral production of HIV-1 by the oligonucleotides.

RESULTS

The addition to infected CEM cells of nanoparticles containing gag antisense oligonucleotides in the nanomolar range led to strong inhibition of the viral production in a concentration-dependent manner. Similar results were previously observed in HeLa P4-2 CD4+ cells. Nanoparticle-entrapped random-order gag oligonucleotides had similar effects on reverse transcription. However, the reverse transcriptase activity of infected cells treated with nanomolar concentrations of free antisense and random oligonucleotides was not affected.

CONCLUSIONS

These results suggest that poly (D,L-lactic acid) nanoparticles may have great potential as an efficient delivery system for oligonucleotides in HIV natural target cells, i.e., lymphocytic cells.