Renal disposition characteristics of oligonucleotides modified at terminal linkages in the perfused rat kidney

Pharmacokinetics and protein binding of cholesterol-conjugated heteroduplex oligonucleotide

Heteroduplex oligonucleotide (HDO) is a novel oligonucleotide therapeutic consisting of an antisense oligonucleotide (ASO) and its complementary RNA. A recent report showed that cholesterol-conjugated HDO (Chol-HDO) exhibited antisense activity in various tissues, including the brain; however, little information is available on the pharmacokinetic and plasma protein-binding properties of HDO and Chol-HDO. In the present study, we investigated the tissue distributions of an ASO, HDO, and Chol-HDO in mice and rats after intravenous injection. Tissue distribution was evaluated by measuring the concentration of ASO in tissue samples using liquid chromatography and tandem mass spectroscopy. ASO and HDO disappeared rapidly from the plasma, whereas Chol-HDO showed prolonged retention in the systemic circulation. The amount of ASO in the brain tissue was highest after injection of Chol-HDO, confirming its efficient delivery to the brain. The tissue distribution of oligonucleotides differed less in rats than in mice. Hepatic uptake of ASO and HDO, but not of Chol-HDO, was significantly inhibited by co-administration with the scavenger receptor inhibitor dextran sulfate sodium. The binding to plasma proteins was evaluated. Compared to ASO, HDO showed lower protein binding, but Chol-HDO showed much higher binding, with remarkable differences in binding to high-density and low-density lipoproteins. The binding of Chol-HDO to these proteins was also confirmed in mouse plasma after injection. These results indicate that the binding of Chol-HDO to plasma proteins, especially lipoproteins, is critical for determining tissue distribution and brain delivery after intravenous injection.

Understanding In Vivo Fate of Nucleic Acid and Gene Medicines for the Rational Design of Drugs

Nucleic acid and genetic medicines are increasingly being developed, owing to their potential to treat a variety of intractable diseases. A comprehensive understanding of the in vivo fate of these agents is vital for the rational design, discovery, and fast and straightforward development of the drugs. In case of intravascular administration of nucleic acids and genetic medicines, interaction with blood components, especially plasma proteins, is unavoidable. However, on the flip side, such interaction can be utilized wisely to manipulate the pharmacokinetics of the agents. In other words, plasma protein binding can help in suppressing the elimination of nucleic acids from the blood stream and deliver naked oligonucleotides and gene carriers into target cells. To control the distribution of these agents in the body, the ligand conjugation method is widely applied. It is also important to understand intracellular localization. In this context, endocytosis pathway, endosomal escape, and nuclear transport should be considered and discussed. Encapsulated nucleic acids and genes must be dissociated from the carriers to exert their activity. In this review, we summarize the in vivo fate of nucleic acid and gene medicines and provide guidelines for the rational design of drugs.

Therapy with 2'-O-Me Phosphorothioate Antisense Oligonucleotides Causes Reversible Proteinuria by Inhibiting Renal Protein Reabsorption

Antisense oligonucleotide therapy has been reported to be associated with renal injury. Here, the mechanism of reversible proteinuria was investigated by combining clinical, pre-clinical, and in vitro data. Urine samples were obtained from Duchenne muscular dystrophy (DMD) patients treated with drisapersen, a modified 2′O-methyl phosphorothioate antisense oligonucleotide (6 mg/kg). Urine and kidney tissue samples were collected from cynomolgus monkeys (Macaca fascicularis) dosed with drisapersen (39 weeks). Cell viability and protein uptake were evaluated in vitro using human conditionally immortalized proximal tubule epithelial cells (ciPTECs). Oligonucleotide treatment in DMD patients was associated with an increase in urinary alpha-1-microglobulin (A1M), which returned to baseline following treatment interruptions. In monkeys, increased urinary A1M correlated with dose-dependent accumulation of oligonucleotide in kidney tissue without evidence of tubular damage. Furthermore, oligonucleotides accumulated in the lysosomes of ciPTECs and reduced the absorption of A1M, albumin, and receptor-associated protein, but did not affect cell viability when incubated for up to 7 days. In conclusion, phosphorothioate oligonucleotides appear to directly compete for receptor-mediated endocytosis in proximal tubules. We postulate that oligonucleotide-induced low molecular weight proteinuria in patients is therefore a transient functional change and not indicative of tubular damage.

Comparative Renal Toxicopathology of Antisense Oligonucleotides

This review summarizes the current understanding of nephrotoxicity related to the administration of therapeutic oligonucleotides, particularly those with 2'-methoxy-ethyl (2'-MOE) modifications. To best understand the effects of antisense oligonucleotides (ASOs) on the kidney, the reader should have a general understanding of renal microanatomy, physiology, and general mechanisms related to toxicity, so a short review is presented. Preclinical-clinical correlates are also discussed. Collectively, the data for PS ODN and 2'-MOE-modified ASOs have shown the laboratory animal species utilized in toxicology studies generally overpredict renal effects of these agents. As such, 2'-MOE ASOs do not appear to pose as much of a risk to patients as the preclinical data would suggest. This observation has been confirmed so far in clinical investigations.

Renal uptake and tolerability of a 2'-O-methoxyethyl modified antisense oligonucleotide (ISIS 113715) in monkey

The primary target organ for uptake of systemically administered phosphorothioate oligonucleotides is the kidney cortex and the proximal tubular epithelium in particular. To determine the effect of oligonucleotide uptake on renal function, a detailed renal physiology study was performed in cynomolgus monkeys treated with 10-40 mg/kg/week ISIS 113715 for 4 weeks. The concentrations of oligonucleotide in the kidney cortex ranged from 1400 to 2600 μg/g. These concentrations were associated with histologic changes in proximal tubular epithelial cells that ranged from the appearance of cytoplasmic basophilic granules to atrophic and degenerative changes at higher concentrations. However, there were no renal functional abnormalities as determined by the typical measurements of blood urea nitrogen, serum creatinine, creatinine clearance, or urine specific gravity. Nor were there changes in glomerular filtration rate, or renal blood flow. Specific urinary markers of tubular epithelial cell damage, such as N-acetyl-glucosaminidase, and α-glutathione-s-transferase were not affected. Tubular function was further evaluated by monitoring the urinary excretion of amino acids, β(2)-microglobulin, or glucose. Renal function was challenged by administering a glucose load and by examining concentrating ability after a 4-h water deprivation. Neither challenge produced any evidence of change in renal function. The only change observed was a low incidence of increased urine protein/creatinine ratio in monkeys treated with ≥40 mg/kg/week which was rapidly reversible. Collectively, these data indicate that ISIS 113715-uptake by the proximal tubular epithelium has little or no effect on renal function at concentrations of 2600 μg/g.

Translational study of microRNAs and its application in kidney disease and hypertension research

MicroRNA research in humans and mammalian model organisms is in a crucial stage of development. Diagnostic and therapeutic values of microRNAs appear promising, but remain to be established. The physiological and pathophysiological significance of microRNAs is generally recognized, but much better understood in some organ systems and disease areas than others. In the present paper, we review several translational studies of microRNAs, including those showing the potential value of therapeutic agents targeting microRNAs and diagnostic or prognostic microRNA markers detectable in body fluids. We discuss the lessons learned and the experience gained from these studies. Several recent studies have begun to explore translational microRNA research in kidney disease and hypertension. Translational research of microRNAs in the kidney faces unique challenges, but provides many opportunities to develop and apply new methods, and to merge complementary basic and clinical approaches.

Strategies for in vivo delivery of siRNAs: recent progress

RNA interference (RNAi) is a post-transcriptional gene-silencing mechanism that involves the degradation of messenger RNA in a highly sequence-specific manner. Double-stranded small interfering RNA (siRNA), consisting of 21-25 nucleotides, can induce RNAi and inhibit the expression of target proteins. Therefore, siRNA is considered a promising therapeutic for treatment of a variety of diseases, including genetic and viral diseases, and cancer. Clinical trials of siRNA are ongoing or have been planned, although some issues need to be addressed. For example, cellular uptake of naked siRNA is extremely low due to its polyanionic nature. Furthermore, siRNA is easily degraded by enzymes in blood, tissues, and cells. Several types of chemically modified siRNA have been produced and investigated to improve stability; these have involved modification of the siRNA backbone, the sugar moiety, and the nucleotide bases of antisense and/or sense strands. Because the accumulation at the target site after administration is extremely low, even if stability is improved, an effective delivery system is required to induce RNAi at the site of action. Delivery strategies can be categorized into physical methods, conjugation methods, and drug delivery system carrier-mediated methods. Physical techniques can enhance siRNA uptake at a specific tissue site using electroporation, pressure, mechanical massage, etc. Terminal modification of siRNAs can enhance their resistance to degradation by exonucleases in serum and tissue. Moreover, modification with a suitable ligand can achieve targeted delivery. Several types of carrier for drug delivery have been developed for siRNA in addition to traditional cationic liposome and cationic polymer systems. Ultrasound and microbubbles or liposomal bubbles have also been used in combination with a carrier for siRNA delivery. New materials with unique characteristics such as carbon nanotubes, gold nanoparticles, and gold nanorods have attracted attention as innovative carriers for siRNA.

Overcoming biological barriers to in vivo efficacy of antisense oligonucleotides

Antisense oligonucleotides as a therapeutic platform have been slow to progress since the approval of the first antisense drug in 1998. Recently, there have been several examples of convincing antisense interventions in animal models and promising clinical trial data. This review considers the factors determining the success of antisense oligonucleotides as therapeutic agents. In order to produce target knockdown after systemic delivery, antisense oligonucleotides must avoid nuclease degradation, reticuloendothelial-system uptake and rapid renal excretion, and extravasate to the target cell type outside the vasculature. They then must enter the target cell, and escape the endosome-lysosome pathway so as to be free to interact with the target mRNA. We consider the significance of these limiting factors based on the literature and our own experience using systemic administration of antisense oligonucleotides.

What happens to the DNA vaccine in fish? A review of current knowledge

The primary function of DNA vaccines, a bacterial plasmid DNA containing a construct for a given protective antigen, is to establish specific and long-lasting protective immunity against diseases where conventional vaccines fail to induce protection. It is acknowledged that less effort has been made to study the fate, in terms of cellular uptake, persistence and degradation, of DNA vaccines after in vivo administration. However, during the last year some papers have given new insights into the fate of DNA vaccines in fish. By comparing the newly acquired information in fish with similar knowledge from studies in mammals, similarities with regard to transport, blood clearance, cellular uptake and degradation of DNA vaccines have been found. But the amount of DNA vaccine redistributed from the administration site after intramuscular administration seems to differ between fish and mammals. This review presents up-to-date and in-depth knowledge concerning the fate of DNA vaccines with emphasis on tissue distribution, cellular uptake and uptake mechanism(s) before finally describing the intracellular hurdles that DNA vaccines need to overcome in order to produce their gene product.

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.

Specific uptake of plasmid DNA without reporter gene expression in Atlantic salmon (Salmo salar L.) kidney after intramuscular administration

In this study we investigated tissue distribution of pDNA after intramuscular and intravenous administration, cellular localisation, receptor-specific uptake, integrity of pDNA and transgene expression in Atlantic salmon (Salmo salar L). Anatomical distribution of plasmid DNA was determined using both radiotracing and fluorescence microscopy. Cellular uptake was studied in cultures of adherent anterior kidney leucocytes. The integrity of the pDNA in vivo was investigated by Southern blot analysis. Transcription of plasmid DNA encoded luciferase gene and protein synthesis were investigated in salmon tissues by means of real-time reverse transcription-polymerase chain reaction and enzyme activity measurements, respectively. Approximately 50% of the total recovered radioactivity was redistributed from the carcass 168h after intramuscular administration and accumulated mainly in the kidneys (37% of total). The majority of radiolabelled plasmid DNA administered intravenously was taken up within the first 15min mainly by the kidney. Intravenous co-administration of trace amounts of radiolabelled plasmid DNA with excess amounts of unlabelled plasmid DNA or formaldehyde treated albumin (a ligand for the scavenger receptors) significantly inhibited accumulation of the radiotracer in the kidney. Fluorescence microscopy demonstrated that fluorescence was localised intracellularly in cells lining the sinusoids of the kidney after intravenous administration of rhodamine-labelled plasmid DNA. Southern blot analysis demonstrated presence of supercoiled plasmid DNA in all organs and tissue samples 168h after intramuscular administration, but degradation products were only revealed at the administration site. Luciferase transcript and activity were only detectable at the administration site 24-168h after intramuscular administration of plasmid DNA. After incubation with trace amounts of radiolabelled plasmid DNA, only minor amounts of radiolabelled plasmid DNA were cell associated in cultures of adherent anterior kidney leucocytes. These results suggested that a substantial portion of radiolabelled plasmid DNA was redistributed from the carcass and was mainly cleared by a receptor-specific uptake in the kidney. Although intact plasmid DNA was detected in the kidney and other tissues, no luciferase transcripts or activity were detected in these samples at any time points investigated (24-168h), except for the administration site following intramuscular administration.

Development of a sensitive and specific in situ hybridization technique for the cellular localization of antisense oligodeoxynucleotide drugs in tissue sections

A sensitive method has been developed for the identification and assessment of phosphorothioate oligonucleotide accumulation in dosed animal tissues using an in situ hybridization approach, which is both sequence specific yet adaptable to every antisense oligonucleotide (ASO), which has been tested to date. Hybridization is accomplished using a digoxigenin-tailed oligonucleotide probe complementary to the ASO target sequence on routinely processed paraffin sections which have been pretreated with a mild target retrieval solution. The DIG-labeled probe is amplified first with an anti-DIG:FITC antibody conjugate followed by an anti:FITC Alexa 488 antibody, then visualized using FITC epifluorescence microscopy. Fluorescent labeling of ASO drug in tissue sections by this method confirms that H&E basophilia previously observed in dosed tissues represents largely intact ASO. However, the fluorescent method enables a wider assessment of tissue distribution in a variety of tissue types due to increased sensitivity and lower signal to noise than can be obtained through an examination of H&E stained tissue sections alone.

Distribution and excretion of a phosphorothioate oligonucleotide in rats with experimentally induced renal injury

The effects of renal injury on the urinary excretion and tissue distribution of a 20-mer phosphorothioate oligonucleotide were investigated in male Sprague-Dawley rats. Renal injury was produced by treating the rats with either 5.0 mg/kg cisplatin or 2.5 mg/kg of a monoclonal antibody (mAb) directed toward Thy1.1. Controls received saline. Three days after cisplatin treatment or 2 days after anti- Thy1.1 treatment, the rats received 10 mg/kg ISIS 3521. Blood was collected at various times to assess the plasma concentrations of ISIS 3521, and rats were killed at various times from 6 to 48 hours after intravenous (i.v.) infusion of oligonucleotide to assess tissue concentrations by capillary gel electrophoresis (CGE). Cisplatin and anti-Thy1.1 antibody produced histologic and biochemical changes consistent with proximal tubular damage and glomerular damage, respectively. Urinary excretion of oligonucleotides was increased 2- to 4-fold of control; however, this amount accounted for only 1% to 2% of dose compared to 0.5% in controls. Proximal tubular damage reduced renal accumulations of ISIS 3521 and other oligonucleotide metabolites, but there were no obvious compensatory increases in concentrations in other organs except for a slight increase in spleen levels of total oligonucleotide. Glomerular damage was not associated with any change in oligonucleotide disposition. Immunohistochemical studies showed no evidence of alterations in the pattern of distribution within the injured kidney. The data suggest that acute renal dysfunction, either renal tubular or glomerular, does not markedly alter the urinary elimination and tissue deposition of a phosphorothioate oligonucleotide.

Nanogels for oligonucleotide delivery to the brain

Systemic delivery of oligonucleotides (ODN) to the central nervous system is needed for development of therapeutic and diagnostic modalities for treatment of neurodegenerative disorders. Macromolecules injected in blood are poorly transported across the blood-brain barrier (BBB) and rapidly cleared from circulation. In this work we propose a novel system for ODN delivery to the brain based on nanoscale network of cross-linked poly(ethylene glycol) and polyethylenimine ("nanogel"). The methods of synthesis of nanogel and its modification with specific targeting molecules are described. Nanogels can bind and encapsulate spontaneously negatively charged ODN, resulting in formation of stable aqueous dispersion of polyelectrolyte complex with particle sizes less than 100 nm. Using polarized monolayers of bovine brain microvessel endothelial cells as an in vitro model this study demonstrates that ODN incorporated in nanogel formulations can be effectively transported across the BBB. The transport efficacy is further increased when the surface of the nanogel is modified with transferrin or insulin. Importantly the ODN is transported across the brain microvessel cells through the transcellular pathway; after transport, ODN remains mostly incorporated in the nanogel and ODN displays little degradation compared to the free ODN. Using mouse model for biodistribution studies in vivo, this work demonstrated that as a result of incorporation into nanogel 1 h after intravenous injection the accumulation of a phosphorothioate ODN in the brain increases by over 15 fold while in liver and spleen decreases by 2-fold compared to the free ODN. Overall, this study suggests that nanogel is a promising system for delivery of ODN to the brain.

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.

Intratumoral pharmacokinetics of oligonucleotides in a tissue-isolated tumor perfusion system

The intratumoral pharmacokinetics of model oligonucleotides were studied in Walker 256 tissue-isolated tumor preparations using an in situ single-pass vascular perfusion technique. A 20-mer phosphodiester (PO) oligonucleotide, its fully phosphorothioated (PS) oligonucleotide counterpart, and an 18-mer phosphorothioated oligonucleotide containing four 2'-O-methylribonucleosides at both the 3'-end and 5'-end (PS-OMe) were used. These oligonucleotides were administered to the tumor in two ways, by constant arterial infusion and by direct intratumoral injection. In the case of constant arterial infusion, the experiments were carried out using perfusate with or without 4.7% bovine serum albumin (BSA). The protein binding of PO, PS, and PS-OMe to BSA was 46%, 87%, and 94%, respectively. No marked difference was observed between the degree of accumulation of the three types of oligonucleotides in the tumor when BSA was present in the perfusate. PS and PS-OMe showed higher degrees of accumulation in tumors compared with PO when no BSA was present. These results indicate that free (i.e., protein unbound) PS-OMe and PS have superior tumor accumulation characteristics. In the intratumoral injection experiments, PS-OMe was retained longer in tumor tissue compared with PS, suggesting that it might be useful for direct local injection into solid tumors. Thus, the present study provides useful information about the basic disposition characteristics of oligonucleotides in solid tumors.

Therapy with antisense TGF-beta1 oligodeoxynucleotides reduces kidney weight and matrix mRNAs in diabetic mice

Inhibition of gene expression by antisense oligodeoxynucleotides (ODNs) relies on their ability to bind complementary mRNA sequences and prevent translation. The proximal tubule is a suitable target for ODN therapy in vivo because circulating ODNs accumulate in the proximal tubule in high concentrations. Because increased proximal tubular transforming growth factor- beta1 (TGF-beta1) expression may mediate diabetic renal hypertrophy, we investigated the effects of antisense TGF-beta1 ODN on the high-glucose-induced proximal tubular epithelial cell hypertrophy in tissue culture and on diabetic renal hypertrophy in vivo. Mouse proximal tubular cells grown in 25 mM D-glucose and exposed to sense ODN as control (1 microM) exhibited increased (3)[H]leucine incorporation by 120% and total TGF-beta1 protein by 50% vs. culture in 5.5 mM D-glucose. Antisense ODN significantly decreased the high-glucose-stimulated TGF-beta1 secretion and leucine incorporation. Continuous infusion for 10 days of ODN (100 microg/day) was achieved via osmotic minipumps in diabetic and nondiabetic mice. Sense ODN-treated streptozotocin-diabetic mice had 15.3% increase in kidney weight, 70% increase in alpha1(IV) collagen and 46% increase in fibronectin mRNA levels compared with nondiabetic mice. Treatment of diabetic mice with antisense ODN partially but significantly decreased kidney TGF-beta1 protein levels and attenuated the increase in kidney weight and the alpha1(IV) collagen and fibronectin mRNAs. In conclusion, therapy with antisense TGF-beta1 ODN decreases TGF-beta1 production and attenuates high-glucose-induced proximal tubular cell hypertrophy in vitro and partially prevents the increase in kidney weight and extracellular matrix expression in diabetic mice.

A nonradioisotope biomedical assay for intact oligonucleotide and its chain-shortened metabolites used for determination of exposure and elimination half-life of antisense drugs in tissue

Rigorous extraction methods coupled with capillary gel electrophoresis (CGE) provide a basis for a nonradiolabel assay for quantitation of intact antisense drug and its numerous chain-shortened metabolites. As part of the validation of the CGE method, we compared the quantitation of unlabeled ISIS 3521 (ISI 641A) and its chain-shortened metabolites with total radioactivity of [(35)S]-ISIS 3521. ISIS 3521 was labeled on the fifth nucleotide linkage from the 5'-end with (35)S by well-established methods. Multiple tissues collected from rats after administration of [(35)S]-ISIS 3521 were assayed by both radiolabel (liquid scintillation spectroscopy) and CGE methods. The CGE method provided accurate quantitation of the drug and its metabolites in kidney cortex and liver tissues. The correlation between methods for multiple tissues over time was excellent with 88.5% of the measurements being statistically equivalent. These data suggest that CGE is an accurate means of quantitating oligonucleotide in tissue and that it compares favorably with traditional radiochemical techniques. Clearance half-lives for total measurable oligonucleotides were equivalent to clearance of total radioactivity in both liver and kidney with the longest clearance half-life associated with the kidney.

Evaluation of the renal effects of an antisense phosphorothioate oligodeoxynucleotide in monkeys

Antisense phosphorothioate oligodeoxynucleotides are therapeutic agents that provide target specificity resulting from Watson-Crick base pairing. However, there are nonspecific effects that in some instances result in toxicity. These compounds accumulate in the kidney and induce renal proximal tubular degeneration at high doses. The relationship between accumulation of phosphorothioate oligodeoxynucleotides in the kidney, indicators of renal toxicity, and histomorphology were investigated in rhesus monkeys. Monkeys received vehicle or an escalating dose regimen of 3, 10, 40, and 80 mg/kg of ISIS 2105 and were then evaluated for changes in clinical pathology indices, urinalysis parameters, and renal histopathology. Urinalysis revealed an increase in protein levels and a slight increase in blood content following the third 40 mg/kg dose and continuing through the 80 mg/kg doses, whereas other urinary markers of renal toxicity were unchanged. Creatinine clearance was slightly decreased in monkeys during the 80 mg/kg dose cycle. Granulation in the cytoplasm of proximal tubular epithelial cells was evident by microscopic examination of kidney and was present at all doses examined and increased with dose. Immunohistochemical staining localized the oligodeoxynucleotide within these granules. Histopathologic changes consisting of minimal to moderate tubular degeneration were present only at the higher doses of 40 and 80 mg/kg and at high tissue concentrations, and these changes occurred concurrent with functional alterations, whereas lower doses (< or = 10 mg/kg) did not affect a pathologic or functional change.

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.

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.

Cellular uptake properties of oligonucleotides in LLC-PK1 renal epithelial cells

The objective of this study was to clarify the renal uptake characteristics of oligonucleotides at a cellular level using LLC-PK1 renal epithelial cells derived from the proximal tubule. The association of [35S]-labeled 20-mer phosphodiester (PO) and phosphorothioate (PS) oligonucleotides with the monolayers of polarized LLC-PK1 cells cultured on polycarbonate filter was characterized after apical or basolateral application. The cellular association of PO and PS at both apical and basolateral membranes was time dependent and temperature dependent, and the apparent association amount of PS was larger than that of PO. The PO and PS association after apical application was saturable, with the apparent Km and Vmax values determined to be 5.4 microM and 0.14 nmol/mg protein for PO and 0.22 microM and 0.11 nmol/mg protein for PS, respectively. In contrast, almost linear kinetics were observed after basolateral application within a tested concentration range. The association was inhibited significantly by sodium azide and chloroquine, suggesting that an energy-dependent endocytotic process was involved. Internalization and subsequent transport to endosome and lysosome compartments of FITC-labeled oligonucleotides were shown by confocal laser scanning microscopy. The present study has demonstrated that both types of oligonucleotides are taken up by LLC-PK1 cells from both apical and basolateral surfaces probably via an endocytosis mechanism.

Perspectives in antisense therapeutics

Modulation of gene expression using oligonucleotides (oligos) is currently an area of intense activity, both from therapeutic, as well as research perspectives. To develop oligos as therapeutic agents, in addition to demonstrable biological activity, in vivo metabolic stability, tissue disposition and pharmacokinetics are important considerations. Oligodeoxynucleoside phosphorothioates are the first-generation antisense analogs that have been studied extensively, and are in clinical trials against a number of disease indications. In an effort to improve the antisense properties of these compounds, mixed-backbone oligos incorporating different chemical modifications have been synthesized and evaluated for antisense activity. The present review will provide an overview of the pharmacokinetics and toxicology following intravenous, intraperitoneal, subcutaneous and oral administration of mixed-backbone oligos as second-generation antisense therapeutics.

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.

Development of targeted delivery systems for nucleic acid drugs

Our increased understanding of disease pathogenesis is the basis for developing novel nucleic acid drugs. The main challenge encountered in this development is how to maintain therapeutically meaningful concentrations of the drugs in the vicinity of their targets for the desired periods. The intrinsic difficulty arises from the fact that nucleic acid drugs are not readily transported across membranes. Hence, their delivery and transport characteristics at the whole body, organ and cellular levels need to be thoroughly examined. Liposomes and receptor-mediated polycation systems are promising carriers for their delivery in vivo. There are many barriers to be overcome for successful antisense and gene therapies. Along with other factors, disposition, stability against nucleases, binding to cell surface receptor and internalization, and intracellular trafficking affect the in vivo delivery and efficacy of nucleic acid drugs. This review article discusses the delivery and transport of these compounds.

Antisense oligonucleotides: towards clinical trials

Antisense oligonucleotides have the ability to selectively block disease-causing genes, thereby inhibiting production of disease-associated proteins. The specificity and application of antisense oligonucleotides have been strongly validated in animal models for various disease targets. Based on the pharmacological, pharmacodynamic and pharmacokinetic profiles, the first generation of antisense oligonucleotides--phosphorothioates--have reached the stage of human clinical trials for various diseases. While ongoing human clinical trials are being carried out to further establishing the safety and efficacy of these oligonucleotides, the experience gained is providing a basis for designing a second generation of antisense oligonucleotides.

Antisense approaches to the gene therapy of cancer--'Recnac'

This review has looked at the wide-ranging research initiatives in the field of antisense technology. It starts with the philosophy behind antisense DNA and the production of antisense RNA from genetic constructs and raises the various problems which are being addressed. These include uptake into cells, targeting the substrate sequence and cells, the stability of the antisense molecules and pharmokinetic considerations within animals. The review talks of the positive results attained in vitro and in vivo in animal and plant experiments but also addresses the problems many workers have faced in the field. It attempts to resolve these differences in terms of the need for further understanding of the mechanisms by which the positive results have been obtained. The novel use of catalytic ribozymes (RNA) in downregulating genes is also discussed in similar terms to antisense DNA and RNA. By taking a case study with a human leukaemia the review delves into the mysteries of how different results can be resolved by improving the design of ribozymes thereby increasing specificity and preventing aberrant reactions. It is concluded that despite a lack of understanding of how the biological effects have come about in vitro and in vivo the clinical and research developments should resolve the issue of antisense potential for rational drug development.

Animal models of antisense oligonucleotides: lessons for use in humans

The ability of oligonucleotides to inhibit genetic expression in a sequence-specific manner has been well documented. Because of their potential for exquisite specificity, oligonucleotides have been proposed as therapeutic agents for a variety of human diseases, including cancers, microbial infections and autoimmune disorders. Approximately 16 clinical trials are currently in progress. However, relatively little is known about the in vivo behaviour of oligonucleotides. Extrapolations from in vitro studies to predict in vivo pharmacokinetics and effects in humans might be difficult and inappropriate. Animal models still remain an essential tool in the development of oligonucleotides as efficient drugs in humans.

Uptake characteristics of oligonucleotides in the isolated rat liver perfusion system

The objective of this study was to examine the hepatic disposition characteristics of 20-mer model phosphodiester oligonucleotide (PO) and its partially phosphorothioated (PS3) and fully phosphorothioated (PS) derivatives in the single-pass isolated rat liver perfusion system. [32P]-labeled oligonucleotides were momentarily introduced into this system through the portal vein as a bolus input mode, and the venous outflow patterns were evaluated using statistical moment analysis. The apparent volumes of distribution of these oligonucleotides were greater than those of reference substances for vascular space (erythrocytes) and extracellular space (human serum albumin), indicating a significant interaction between oligonucleotides and the liver. Significant hepatic uptake of oligonucleotides was also observed. About 20%, 36%, and 52% of the injected dose (3 micrograms/rat) was taken up by the liver during a single passage after bolus injection of PO, PS3, and PS, respectively. In the case of PS injection, slow efflux from the liver was observed in the latter phase of perfusion. This suggests that the hepatic uptake process of these oligonucleotides greatly depended on their types. The results of collagenase perfusion experiments suggest that PS3 oligonucleotides were taken up by both liver parenchymal and nonparenchymal cells. The amount of total recovery in the liver decreased substantially by coadministration of polyinosinic acid, dextran sulfate, polycytidic acid and 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulfonic acid. This suggests that PS3 was taken up by the liver as an anionic molecule in a nonspecific manner.