Antisense c-myc oligonucleotide cellular uptake and activity

Therapeutic Effects of Ribunucleinate (Ribonucleotides) in Immuno-Inflammatory and Arthritic Diseases

Ribonucleic acids from different organs and from yeast have been used for the treatment of chronic and degenerative diseases in the context of naturopathic medicine in the last 60 years. This chapter provides general information about ribonucleinates as therapeutic agents. Past and present pharmacological and clinical investigations are discussed in the field of the central nervous system, sensory organs, cancer and degenerative diseases of joints and vertebra.

DNA inhibits dsRNA-induced secretion of pro-inflammatory cytokines by gingival fibroblasts

Nucleic acids interacting with pattern-recognizing receptors (PRRs), such as Toll-like-(TLRs), RIG-I-like receptors (RLRs) and dsDNA-receptors activate innate immune response in non-professional immune cells and thus the production of pro-inflammatory cytokines. Along with bacterial and viral nucleic acids, endogenous cell-free and cell-surface-bound extracellular DNA (exDNA and csbDNA) could interact with PRRs and possess immunomodulating activity. To elucidate if exDNA influence innate immunity a comparative study of exDNA, genomic and plasmid DNA on interleukin production in gingival fibroblasts (GF) has been done. All DNA tested have no effect on IL secretion in a broad concentration range (10 ng/ml-1 μg/ml). Simultaneous treatment of cells with DNA and dsRNA analog poly(I:C) leads to inhibition of poly(I:C)-activated secretion of IL-6 and IL-8. Cell-surface-bound DNA possesses two times stronger inhibiting effect as compared to genomic DNA indicating the enrichment of csbDNA in sequences providing such activity. Effects of several recently found specific DNA sequences tightly bound with cell surface have been tested. Joint stimulation of GF with poly(I:C) and deoxyribooligonucleotides (ODN), containing such sequences, demonstrates that both ssODN and dsODN possess sequence-dependent inhibiting effect. Inhibition of IL production after colipofection of ODN and poly(I:C) into cells indicates the involvement of RLRs or other cytoplasmic factors in the effect. The data obtained indicate that endogenous DNA might be involved in regulation of antiviral immune response and sequence-specific ODNs are potential inhibitors of the inflammation induced by viral infection.

Radiolabeled oligonucleotides for antisense imaging

Oligonucleotides radiolabeled with isotopes emitting γ-rays (for SPECT imaging) or positrons (for PET imaging) can be useful for targeting messenger RNA (mRNA) thereby serving as non-invasive imaging tools for detection of gene expression in vivo (antisense imaging). Radiolabeled oligonucleotides may also be used for monitoring their in vivo fate, thereby helping us better understand the barriers to its delivery for antisense targeting. These developments have led to a new area of molecular imaging and targeting, utilizing radiolabeled antisense oligonucleotides. However, the success of antisense imaging relies heavily on overcoming the barriers for its targeted delivery in vivo. Furthermore, the low ability of the radiolabeled antisense oligonucleotide to subsequently internalize into the cell and hybridize with its target mRNA poses additional challenges in realizing its potentials. This review covers the advances in the antisense imaging probe development for PET and SPECT, with an emphasis on radiolabeling strategies, stability, delivery and in vivo targeting.

Cholesterol conjugated oligonucleotide and LNA: a comparison of cellular and nuclear uptake by Hep2 cells enhanced by streptolysin-O

Antisense and antigene oligonucleotides (ONs) are attractive drugs for gene therapy, but major limiting factors for their routine use are inefficient cellular uptake and low accessibility to the target sites. Adding various lipophilic conjugates to the ON improves intracellular delivery as has been previously reported. We studied the cellular delivery of various ON modifications, as well as their cytosolic and nuclear distribution in mammalian Hep2-EGFP-NLS cell line. We compared uptake efficacy of ON and LNA, both conjugated with cholesterol at the 5' end. All ONs were 3' labeled with fluorescent Cy 5 dye. We made a comparison of the ONs uptake efficacy and the kinetics, both adding ONs to the culture medium, and using streptolysin-O (SL-O) permeabilization. The cellular uptake of each ON used in this study was visualized by fluorescent microscopy. We confirmed the results by FACS analysis. We determined the ratio between initial ON-chol concentration (0.4 microM) and the final amount in nucleus.SL-O can highly improve kinetics of ON delivery; not only into the cytoplasm but also to the nucleus, the presumed site of antigene ON action. The most effective nuclear uptake was observed when ON conjugated with cholesterol (ON-chol) and SL-O was used. Nuclear distribution of ON was reached within few minutes. In contrast, ON simply added to the medium reached cytoplasm only and the process of delivery took several hours.

Spinal distribution and metabolism of 2'-O-(2-methoxyethyl)-modified oligonucleotides after intrathecal administration in rats

Intrathecal (IT) delivery of antisense oligodeoxynucleotides (ASO) has been used to study the function of specific gene products in spinal nociception. However, a lack of systematic studies on the spinal distribution and kinetics of IT ASO is a major hurdle to the utilization of this technique. In the present study, we injected rats IT with 2'-O-(2-methoxyethyl) modified phosphorothioate ASO (2'-O-MOE ASO) and examined anatomical and cellular location of the ASO in the spinal cord and dorsal root ganglia (DRG) by immunocytochemistry. At 0.5 h after a single IT injection, immunostaining for ISIS 13920 (a 2'-O-MOE ASO targeting h-ras) localized superficially in the lumbar spinal cord, while at 24 h the immunostaining was distributed throughout the spinal cord and was predominantly intracellular. Double staining with cell type specific antibodies indicated that the ASO was taken up by both glia and neurons. ASO immunoreactivity was also observed in DRG after IT ISIS 13920. Capillary gel electrophoresis analysis showed that ISIS 22703, a 2'-O-MOE ASO targeting the alpha isozyme of protein kinase C (PKC), remained intact in spinal cord tissue and cerebrospinal fluid up to 24 h after the injection and no metabolites were detected. In contrast, after IT ISIS 11300, an unmodified phosphorothioate ASO with the same sequence as ISIS 22703, no full-length compound was detectable at 24 h, and metabolites were seen as early as 0.5 h. IT treatment with ISIS 22703 at doses that effectively down-regulated PKCalpha mRNA in spinal cord did not affect the mRNA expression in DRG. In summary, 2'-O-MOE ASO displayed high stability in spinal tissue after IT delivery, efficiently distributed to spinal cord, and internalized into both neuronal and non-neuronal cells. ASO are able to reach DRG after IT delivery; however, higher doses may be required to reduce target gene in DRG as compared with spinal cord.

Innovations in oligonucleotide drug delivery

Oligonucleotides (ONs) are a new class of therapeutic compounds under investigation for the treatment of a variety of disease states, such as cancer and HIV, and for FDA approval of an anti-CMV retinitis antisense molecule (Vitravene trade mark, Isis Pharmaceuticals). However, these molecules are limited not only by poor cellular uptake, but also by a general lack of understanding regarding the mechanism(s) of ON cellular uptake. As a result, various delivery vehicles have been developed that circumvent the proposed mechanism of uptake, endocytosis, while improving target specific delivery and/or drug stability. This review describes various traditional and novel delivery mechanisms that have been employed to improve ON cellular delivery, cost effectiveness, and therapeutic efficacy.

Beyond Mitomycin: TGF-beta and wound healing

The introduction of the anti-cancer drugs Mitomycin and 5-fluorouracil as anti-scarring agents within the last decade, has greatly improved surgical results of glaucoma filtration surgery. However, a number of problems associated with their use have emerged. At the same time, the transforming growth factor-beta (TGF-beta) has been identified as an important component of wound healing, particularly in the conjunctival scarring response. Recent developments in molecular therapy offer exciting prospects for the modulation of wound healing, specifically those targeting TGF-beta. As TGF-beta is such a potent stimulant of scarring, this review examines its biology and role in ocular wound healing and repair, and discusses promising new approaches to modifying its activity.

Alternative interpretations of the oligonucleotide transport literature: insights from nature

Elucidation of the mechanism of oligonucleotide (ON) cellular internalization has met an impasse at the lipid penetration stage. ON internalization is commonly regarded to involve endocytosis, yet the method by which the ON penetrates the endosome membrane remains a mystery despite more than 10 years of research by multiple laboratories. In addition, the literature regarding this topic is fraught with discrepancies and inconsistencies. Therefore, the goal of this review is to propose and illustrate the feasibility of the notion that the literature discrepancies are perhaps an indication of a complex transport mechanism involving more than one uptake pathway. Accordingly, ON- and cell-differences in uptake may be attributed to differences in the relative importance of these pathways for different cell types and ONs. An example of one such pathway is reviewed and critiqued in this communication with respect to its hypothetical role in ON uptake. Other innovative mechanisms should similarly be considered to stimulate new ideas, discussion and research in this unique and interesting field.

Modulating conjunctival wound healing

Advances in molecular and cell biology have led to an expansion in our knowledge and understanding of the processes involved in wound healing. We review existing and potential therapies modulating the conjunctival scarring response, with particular reference to glaucoma filtration surgery. We discuss how the refinement of present antimetabolite regimens can minimise complications and improve surgical results, and advocate their use in carefully selected patient groups. Perhaps the most promising approach is targeting biological molecules. Hence, use of fully human neutralising monoclonal antibodies to the growth factor TGF beta has potential as a useful strategy for modifying conjunctival scarring. Combination therapies may also afford an improved therapeutic index. It is hoped that future therapies can offer safer, more specific, focal and titratable treatment, with far-reaching clinical applications.

Utilization of antisense oligodeoxynucleotides with embryonic tissues in culture

Experimental embryology has long used manipulation of interacting tissues to examine questions of tissue interaction and differentiation. The potential for specific manipulation of gene expression in such tissues has made the utilization of antisense techniques desirable. However, problems with this methodology have discouraged many investigators from using this approach. Selection of target sequences for antisense oligonucleotides, delivery of oligonucleotides into cells or tissues, and the type of modification of the oligonucleotide to be used all present concerns that must be addressed. This paper describes our approach to selection of target sequence and methods of delivery and describes the synthesis of a methoxyethylamidate-modified antisense oligonucleotide that has proved useful in our studies. This approach has enabled us to explore aspects of tissue interaction in the embryonic heart that would have been difficult to explore in a genetic model.

Characterisation of membrane oligonucleotide-binding proteins and oligonucleotide uptake in keratinocytes

Inadequate cellular compartmentalisation of plasmid DNA and antisense oligodeoxynucleotides (ODNs) is generally considered as a major limitation in their use. In this study, an approach combining in situ visual-isation of rhodamine-labelled ODNs and affinity modification of proteins by radiolabelled-alkylating ODN derivatives has been used to investigate the uptake of ODNs into keratinocytes. We confirm here that unmodified ODNs are efficiently taken up and accumulate in cell nuclei in primary keratinocytes as well as in HaCaT and A431 keratinocyte cell lines. Uptake is fast, irreversible, saturable and not significantly altered by incubation at low temperature. Affinity modification studies in keratinocyte cell lines has revealed two high-affinity, cell-specific interactions between ODNs and proteins of 61-63 kDa and 35 kDa. Trypsin pre-treatment of A431 cells and pre-incubation with polyanions, or with unlabelled nucleic acid competitors, inhibited the accumulation of rhodamine-labelled ODNs in nuclei as well as the affinity labelling of the 61-63 kDa doublet and 35 kDa ODN-binding proteins by reactive ODN derivatives. Finally, cell fractionation studies indicated that these ODN-binding proteins were essentially localised in the plasma membrane. Our results suggest that these ODN-binding proteins might be involved in the recognition and transport of ODNs into keratinocytes.

Sequence dependency of the internalization and distribution of phosphorothioate oligonucleotides in vascular smooth muscle cells

Antisense studies imply the utilization of oligonucleotides (ODN) for sequence-specific down-regulation of genes. This usually consists in assessing antisense sequences versus control sequences (mismatched, inverted, scrambled, randomized or any sequence unrelated to the relevant target). Even though the investigated biological effect (knockdown of an unwanted protein) is observed only with the antisense sequence and weakly, if at all, with any of the control sequences, this is a necessary but not a sufficient condition to demonstrate an antisense effect. Indeed, biochemical parameters such as stability, uptake and subcellular compartmentalization of ODN in a given cellular system are most often sequence-dependent processes. In this work, a series of phosphorothioate ODN of different lengths and sequences were evaluated as to their binding, internalization and subcellular distribution properties in vascular smooth muscle cells. In addition to membrane binding and nuclear accumulation, the partition of ODN in the cytosol of cells was measured by a method based upon controlled permeabilization of the plasma membrane, permitting the recovery of the cytosolic content with minimal damage to the membranes of the endocytic vesicles and lysosomes. We found that the tested ODN showed striking differences in their uptake and distribution in smooth muscle cells. Our results gave rise to the problem of validating the observed biological effects when different sequences of ODN were compared. Cellular studies such as the one presented in this work could help in choosing the proper control sequences among ODN exhibiting similar cell interactions as compared to the antisense sequences. Moreover, this method could be useful for the selection of antisense sequences that can be efficiently internalized and preferentially distributed in the appropriate compartments in cells for in vitro antisense studies.

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.

Pharmacokinetics of oligonucleotides in cell culture

Synthetic oligonucleotides offer interesting perspectives for the regulation of gene expression in normal and pathological situations. Poor uptake in many cell types, inadequate intracellular compartmentalization, often fragmentary knowledge of intracellular behaviour and mechanism of action, and lack of specificity remain major challenges. These limitations strongly urge the design of new oligonucleotide analogues and more efficient antisense strategies. Present achievements and perspectives for further developments will be discussed with emphasis on cell delivery and intracellular fate.

Cellular uptake properties of a 2'-amino/2'-O-methyl-modified chimeric hammerhead ribozyme targeted to the epidermal growth factor receptor mRNA

Catalytic RNA or ribozymes have important potential applications as molecular biological tools in the study of gene expression and as therapeutic inhibitors of disease-causing genes. Very little is known, however, about the cellular uptake mechanisms of exogenously delivered synthetic ribozymes. In this study, we have characterized the uptake properties of a synthetic, 2'-O-methyl-modified ribozyme containing U4/U7 amino groups within the catalytic core of the hammerhead motif. The cellular uptake of the internally [32P]-radiolabeled hammerhead ribozyme in U87-MG glioma cells was temperature, energy, and pH dependent and involved an active process that could be competed with cold ribozyme of the same chemistry and sequence, an all 2'-O-methyl-modified ribozyme of the same sequence, antisense PS-ODNs, and a variety of other polyanions (salmon sperm DNA, spermidine, dextran sulfate, and heparin). Subcellular distribution studies of fluorescently labeled ribozymes confirmed an extranuclear, punctate localization similar to that observed for an endosomal marker, dextran. Our study highlights that hammerhead ribozymes, despite exhibiting a defined secondary structure, enter cells by an endocytic mechanism that appears to be similar to that reported for a variety of antisense ODNs. These observations should facilitate the development of more efficient delivery systems.

[A simple method for the study of cytosolic content of oligonucleotides in cells]

Antisense oligonucleotides are currently used for the specific control of the expression of a selected gene. Their putative targets are located in the cytoplasm (messenger RNA) or the nucleus (pre-messenger RNA or DNA). This approach is conditioned by the presence of the antisense molecule inside the cell at sufficient concentrations and in the appropriate compartments. We propose in this paper a simple method for the study of the cytosolic content of internalized oligonucleotides. This method is based on the selective permeabilization of the plasmic membrane by the detergent digitonin. By complexing to membrane cholesterol, the detergent creates pores through which soluble and diffusible species can escape outside the cells. The selectivity of membrane permeabilization was controlled by using compartment markers: lactate dehydrogenase (LDH) for cytosol, dextrane-rhodamine (DEX) and hexosaminidase (HAM) for endocytic vesicles and lysosomes, respectively. Optimal digitonin concentrations and incubation times have been defined to reach the following pattern of membrane permeabilization: LDH > 80%; DEX and HAM < 15%. The method was applied to monitor the quantity of extractible oligonucleotides from cells after endocytosis. The results showed that phosphodiester and phosphorothioate oligomers are readily available in the cytosol (60-50% of the internalized species), whereas those bearing a hydrophobic moiety (fluorescein, cholesterol) are less diffusible probably owing to membrane binding. Internalization and cytosol partition were found to depend on the chemical nature of the oligonucleotide, and also on the sequence and the cell type. This method could be useful for the selection of antisense molecules that exhibit the best internalization and distribution in cells, and for a more appropriate choice of control sequences in antisense studies.

Interactions of phosphodiester and phosphorothioate oligonucleotides with intestinal epithelial Caco-2 cells

PURPOSE

Oral bioavailability for antisense oligonucleotides has recently been reported but the mechanistic details are not known. The proposed oral delivery of nucleic acids will, therefore, require an understanding of the membrane binding interactions, cell uptake and transport of oligonucleotides across the human gastro-intestinal epithelium. In this initial study, we report on the cell-surface interactions of oligonucleotides with human intestinal cells.

METHODS

We have used the Caco-2 cell line as an in vitro model of the human intestinal epithelium to investigate the membrane binding interactions of 20-mer phosphodiester (PO) and phosphorothioate (PS) oligonucleotides.

RESULTS

The cellular association of both an internally [3H]-labelled and a 5'end [32P]-labelled PS oligonucleotide (3.0% at 0.4 microM extracellular concentration) was similar and was an order of magnitude greater than that of the 5'end [32P]-labelled PO oligonucleotide (0.2%) after 15 minutes incubation in these intestinal cells. The cellular association of PS was highly saturable with association being reduced to 0.9% at 5 microM whereas that of PO was less susceptible to competition (0.2% at 5 microM, 0.1% at 200 microM). Differential temperature-dependence was demonstrated; PS interactions were temperature-independent whereas the cellular association of PO decreased by 75% from 37 degrees C to 17 degrees C. Cell association of oligonucleotides was length and pH-dependent. A decrease in pH from 7.2 to 5.0 resulted in a 2- to 3-fold increase in cell-association for both backbone types. This enhanced association was not due to changes in lipophilicity as the octanol:aqueous buffer distribution coefficients remained constant over this pH range. The ability of NaCl washes to remove surface-bound PS oligonucleotides in a concentration-dependent manner suggests their binding may involve ionic interactions at the cell surface. Cell-surface washing with the proteolytic enzyme, Pronase, removed approximately 50% of the cell-associated oligonucleotide for both backbone types.

CONCLUSIONS

Binding to surface proteins seems a major pathway for binding and internalization for both oligonucleotide chemistries and appear consistent with receptor (binding protein)-mediated endocytosis. Whether this binding protein-mediated entry of oligonucleotides can result in efficient transepithelial transport, however, requires further study.

The influence of polarized epithelial (Caco-2) cell differentiation on the cellular binding of phosphodiester and phosphorothioate oligonucleotides

Cell aging and the degree of cellular differentiation are thought to be important variables governing uptake of oligonucleotides but remain poorly understood. The Caco-2 colon carcinoma cell line has the ability to spontaneously differentiate into enterocytes in vitro and serves as a useful model to further investigate the effect of differentiation on oligonucleotide binding and uptake. In this study, we report that the extent of oligonucleotide association and the expression of cell surface binding proteins are governed by the age and thus the degree of differentiation of Caco-2 epithelial cells in culture. Cellular association (normalized for cell number) of an all phosphodiester (PO), all phosphorothioate (PS), and a phosphodiester oligonucleotide containing two terminal phosphorothioate internucleotide linkages at the 3' end (EC-PO) gradually increased from day 3 to around day 17 of the culture, followed by a plateau, or slight decrease, up to day 21 of the cell aging study. Overall, a threefold to fourfold increase in binding was observed from day 3 to day 17. Oligonucleotide binding was temperature and pH dependent, but the magnitude of the effect was influenced by cell aging and the degree of differentiation. PS oligonucleotides exhibited greater binding (up to threefold) at the basolateral surface compared with the apical surface within the pH range 5-7. These findings could be directly correlated with the expression levels of cell surface oligonucleotide binding proteins during the aging study. A Caco-2 cell surface protein binding complex of around 46 kDa was identified as the major site of binding for both PO and PS oligonucleotides, although the latter also bound to several other proteins, especially at low pH.

Interaction of oligodeoxynucleotides with mammalian cells

Many previous studies have demonstrated that antisense oligodeoxynucleotides (ODNs) bind to surface proteins in a manner compatible with receptor-mediated endocytosis and, unless specifically modified, are internalized into endosomes with little access to the cytoplasmic structures or to the nucleus. Reports vary as to the specific proteins involved in the mechanism, and this study examines the conditions of binding, some proteins that might contribute to the process, and whether changes in binding patterns occur during differentiation. Native gel electrophoresis was used to optimize the surface binding of a phosphorothioate end-capped 16-mer to T15 mouse fibroblast cells, and comparisons are made with some human epithelial tumor cell lines. Binding to individual proteins was visualized using SDS-PAGE and autoradiography. Binding at 4 degrees C was almost exclusively to a 46 kDa protein and decreased in the presence of an excess of unlabeled ODN and heparin but not ATP. Increasing the temperature of ODN binding from 4 degrees C to 37 degrees C for 10 minutes changed the binding pattern observed. ODN binding to the total cytoplasmic and membrane proteins immobilized on a membrane showed a greater number of binding proteins, the most prominent being one of 30 kDa. Examination of the effects of serum on binding were made using the human lung carcinoma cell line COR-L23, which can be grown in serum-free conditions. Serum starvation led to an increased total binding seen on native gels coinciding with increased binding to a 46 kDa protein. Demonstration that changes in binding proteins occur when cells differentiate was made using the premacrophage cell line THP-1. Differentiation of these cells increased the total ODN binding and appeared to initiate the synthesis of some new binding proteins, although binding to a 46 kDa protein was reduced.

Calcium-dependent oligonucleotide cellular uptake

Oligodeoxynucleotides (ONs) are currently being tested in clinical trials as anti-viral and thrombolytic agents. Although ONs are biologically active in almost every cell line examined, these molecules are inefficiently internalized. In addition, the mechanism of ON transport to the active site in either the cytoplasm or nucleus remains ill-defined. Thus, elucidation of the mechanism of ON cellular uptake is necessary for the rational design of optimization of ON cellular uptake, delivery, and targeting. Previous studies in this laboratory have examined the mechanism of ON cellular uptake using a phosphodiester ON which is both biologically active and internalized by the Rauscher Red 5-1.5 mouse erythroleukemia cell line. The uptake is calcium-dependent since uptake is significantly reduced in calcium-free media and enhanced up to 20-fold when incubated in elevated calcium concentrations by a mechanism which may differ from uptake in physiologic calcium. Therefore, the goal of this paper is to further examine the mechanism of calcium-dependent phosphodiester ON uptake in Rauscher cells. First, to determine whether changes in intracellular free calcium [Ca]i may influence ON uptake, [Ca]i was either increased or decreased prior to addition of the ON. Second, to determine whether protein kinase C or calmodulin are involved in uptake, the activity of each of these proteins was either increased or decreased. Neither altering [Ca]i or the activity of protein kinase C or calmodulin altered the extent of ON uptake in these cells. Finally, the effect of other cations were tested for their ability to increase ON uptake. Lanthanum and cadmium increased uptake whereas sodium and magnesium had no effect. These findings suggest that cation-mediated ON cellular uptake may not result from alteration of a calcium-dependent biological process.

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

To clarify the renal disposition characteristics of oligonucleotides at the organ level, the renal handling of model end-capped oligonucleotides, 3'-methoxyethylamine 5'-biotin-decathymidylic acid containing phosphoramidate modifications at 3'- and 5'-terminal internucleoside linkages (T10) and its phosphorothioate (Ts10), were studied in the perfused rat kidney. In a single-pass indicator dilution experiment, venous outflow and urinary excretion patterns and tissue accumulation of radiolabeled oligonucleotides were evaluated under filtering or nonfiltering conditions. No significant binding to bovine serum albumin (BSA) in the perfusate was observed for T10, whereas more than 90% of Ts10 bound to BSA. The steady-state distribution volume of T10 calculated from the venous outflow pattern was larger than that of inulin, which corresponds to the extracellular volume of the kidney, whereas the distribution volume of Ts10 was larger than that of BSA (the intravascular volume). These results suggested their interaction with the vascular wall. Rapid urinary excretion was observed for T10, similar to inulin used as a marker of golmerular filtration rate. On the other hand, urinary excretion of Ts10 was greatly restricted due to its high binding ability (> 90%) to BSA in the perfusate. A significant amount of T10 and Ts10 was accumulated in the kidney (T10, 1.8% of injected dose; Ts10, 1.3%) compared with inulin (0.2%) and BSA (< 0.1%). The accumulation of these oligonucleotides was ascribed to both tubular reabsorption and uptake from the capillary side. In addition, the uptake of T10 from the capillary side was significantly inhibited by simultaneous injection of dextran sulfate, suggesting that the oligonucleotide was taken up as an anionic molecule. These findings will be useful information for the development of delivery systems for antisense oligonucleotides.