Transport of phosphorothioate oligonucleotides in kidney: implications for molecular therapy

Cytosolic malate dehydrogenase confers selectivity of the nucleic acid-conducting channel

We have described previously a cell surface channel that is highly selective for nucleic acids. Nucleic acid conductance is 10 pS and the channel is at least 10,000-fold more selective for oligodeoxynucleotides than any anion tested (1). Herein we provide evidence that the nucleic acid-conducting channel (NACh) is a heteromultimeric complex of at least two proteins; a 45-kDa pore-forming subunit (p45) and a 36-kDa regulatory subunit (p36). Reconstitution of p45 in planar lipid bilayers resulted in formation of a channel which gated in the absence of nucleic acid and which was more selective for anions (including oligonucleotide) than cations. This channel exhibited transitions from one level of current to another (or to the closed state); however the incidence of transitions was rare. Channel activity was not observed when p36 was reconstituted alone. Reconstitution of p36 with p45 restored nucleic acid dependence and selectivity to the channel. Protein sequence analysis identified p36 as cytosolic malate dehydrogenase (cMDH). Experiments were performed to prove that cMDH is a regulatory subunit of NACh. Selective activity was observed when p45 was reconstituted with pig heart cMDH but not with mitochondrial MDH. Both the enzyme substrate l-malate and antiserum raised against cMDH block NACh activity. These data demonstrate that a nucleic acid conducting channel is a complex of at least two proteins, p45 and cMDH. Furthermore, these data establish that cMDH confers nucleic acid selectivity of the channel.

Impaired endocytosis may represent an obstacle to gene therapy in polycystic kidney disease

BACKGROUND

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease and a frequent cause of chronic renal failure. The cloning of the PKD1 and PKD2 genes, which are mutated in the great majority of patients with this disease, opens up the opportunity for somatic gene therapy by introduction of the wild-type gene or cDNA. Several publications have provided evidence, that many portions of the nephron and the collecting duct can form cysts, including the proximal tubule. Alterations in the proximal tubule may prevent the efficient endocytosis of filtered proteins and thus contribute to proteinuria, a frequent symptom in patients with polycystic kidney disease. At the same time this may also negatively affect various gene therapy strategies, since endocytosis is important for the uptake of foreign DNA at least under some circumstances. In the (cy/+) rat, a widely used animal model for ADPKD, cysts almost exclusively develop from proximal tubules, and we have therefore investigated whether proteinuria and defective endocytosis also occur in this model.

METHODS

Proteinuria was demonstrated by direct measurement and by protein gel electrophoresis of urines from 16 week-old (cy/+) rats. Endocytosis was investigated by injection of FITC-dextran and immunohistochemical staining with anti-ClC-5 and anti-megalin antibodies.

RESULTS

Similar to the observations made in ADPKD patients, proteinuria also develops in the (cy/+) rat. Using FITC-labeled dextran as an in vivo tracer for renal tubular endosomal function, we could show that portions of cyst-lining epithelia from proximal tubules have lost the ability to endocytose, which is necessary for the reabsorption of albumin and lower-molecular-weight proteins. By immunohistochemistry the expression of other proteins implicated in endocytosis, such as the chloride channel ClC-5 and the albumin receptor megalin, correlated well with the presence and absence of FITC-dextran in cyst wall epithelia.

CONCLUSION

These data indicate that proteinuria and albuminuria in the (cy/+) rat model for ADPKD are due to a loss of the endocytic machinery in epithelia of proximal tubular cysts. Such a defect may also reduce the efficacy of certain gene therapy protocols.

Electroporation-mediated gene transfer that targets glomeruli

Electroporation has been applied to introducing DNA into several organs; however, gene expression was localized around the injected area. Examined was the efficiency of intrarenal injection of DNA followed by in vivo electroporation, using FITC-labeled oligodeoxynucleotides (FITC-ODN) and plasmid DNA expressing beta-galactosidase or luciferase. FITC-ODN or expression vectors were injected into the left renal artery; thereafter, the left kidney was electroporated between a pair of tweezer-type electrodes. FITC-ODN were transferred into all glomeruli, and transfected cells were identified as mesangial cells. Four d after transfection of the pCAGGS-LacZ gene, beta-galactosidase expression was observed in 75% of glomeruli. To compare the transfection efficacy by electroporation with that by the hemagglutinating virus of Japan (HVJ) liposome method, a luciferase reporter gene, pActLuc, was transferred into glomeruli by either electroporation or the HVJ liposome method. On day 4, electroporation resulted in higher glomerular luciferase activity than did the HVJ liposome method. We also observed that co-transfection of pcEBNA, an expression vector for Epstein-Barr virus nuclear antigen, and poriP-cLuc, oriP-harboring vector, resulted in an eightfold higher luciferase gene expression than simple poriP-cLUC: No histologic damages were seen in glomeruli or tubular epithelial cells. In conclusion, gene transfer into renal artery followed by electroporation was an effective and simple strategy for gene transfer that targets glomerular mesangial cells.

Potential roles of antisense technology in cancer chemotherapy

Antisense technology may play a major role in cancer chemotherapy. It is clearly a tool of exceptional value in the functionalization of genes and their validation as potential targets for cancer chemotherapy. Additionally, there is now substantial evidence that antisense drugs are safe, and a growing body of data showing activity in animal models of human disease including cancer, and suggesting efficacy in patients with cancer. In this article, I review the progress in the technology, the anticancer antisense drugs in development and potential roles that antisense technology might play.

Synthetic oligonucleotides as therapeutics: the coming of age

Synthetic oligonucleotides (ODNs) are short nucleic acid chains that can act in a sequence specific manner to control gene expression. Significant progress has been made in the development of synthetic ODN therapeutics since the first demonstration of gene inhibition by antisense ODNs in a cell culture system two decades ago. This new class of therapeutic agents can potentially target any abnormally expressed genes in a broad range of diseases from viral infections to psychoneurological disorders. A number of "first" generation synthetic ODNs have entered into human clinical trials in the last few years. The eminent approval of the first ODN for the treatment of cytomaglovirus retinitis by the FDA in USA will provide much excitement that this new class of compounds holds great promise as a therapeutic "magic bullet". However, many obstacles still exist in the development of this technology. In this review, the current status of synthetic ODN chemistry, drug delivery methods, mechanisms of ODN action, potential clinical applications and its limitations in a wide range of human disorders will be described.

Delivery systems for antisense oligonucleotides

In vitro, the efficacy of the antisense approach is strongly increased by systems delivering oligodeoxyribonucleotides (ODNs) to cells. Up to now, most of the developed vectors favor ODN entrance by a mechanism based on endocytosis. Such is the case for particulate systems, including liposomes (cationic or non-cationic), cationic polyelectrolytes, and delivery systems targeted to specific receptors. Under these conditions, endosomal compartments may represent a dead end for ODNs. Current research attempts to develop conditions for escaping from these compartments. A new class of vectors acts by passive permeabilization of the plasma membrane. It includes peptides, streptolysin O, and cationic derivatives of polyene antibiotics. In vivo, the interest of a delivery system, up to now, has appeared limited. Development of vectors insensitive to the presence of serum seems to be a prerequisite for future improvements.

Quantification of DNA binding to cell-surfaces by flow cytometry

DNA binding to cell-surfaces has been documented in several studies. The interaction of DNA with cells has been shown to have therapeutic potential as a non-viral form of gene delivery and DNA vaccination. Recently, bacterial DNA binding and internalization has been demonstrated in some cells to trigger secretion of cytokines and cell activation. Previous studies to quantify DNA binding to cells have used radiolabeled DNA. Here we report a non-radioactive assay for quantification of cell-surface DNA binding based on the isoparametric analysis of flow cytometric data as described by Chatelier et al., Embo J., 5 (1986) 1181. This assay has the advantage over previously used procedures in not employing radioactive material and being able to discriminate viable from non-viable cells that bind DNA. With the importance of understanding the interaction of DNA with cells, this assay may have application for the identification and characterization of reagents designed to either enhance or inhibit DNA binding to cells.

Gene therapy for kidney disease

Gene therapy has distinct potential to treat disease at the most fundamental level. However, the ability to pursue gene therapy for renal disease has been limited by the availability of an adequate system for gene delivery to the kidney and for regulation of transgene expression. Presently, there are several limitations to overcome before clinical use of viral vector systems for targeting kidney can be considered. Non-viral vectors such as haemagglutinating virus of Japan (HVJ)-liposome mediated gene transfer and cationic liposome are promising but need to be improved. Given that the systemic delivery of the functional protein can serve as therapy for the renal diseases, skeletal muscle targeting gene therapy might be an alternative strategy for the treatment of renal disease. Gene therapy to the transplant kidney may potentially improve the graft outcome by reducing acute and chronic rejection. We review emerging strategies of gene transfer with reference to the kidney and discuss the potential application of gene therapy to renal diseases.

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.

Inhibition of monocyte chemoattractant protein-1 expression in tubular epithelium attenuates tubulointerstitial alteration in rat Goodpasture syndrome

BACKGROUND

To examine the role of monocyte chemoattractant protein-1 (MCP-1) expressed by tubular epithelium in tubulointerstitial alterations in situ, the level of MCP-1 mRNA in tubular epithelium was lowered selectively in the rat model of Goodpasture syndrome (GPS).

METHODS

Intravenously administered antisense oligodeoxynucleotide (ODN) is taken up by renal tubular epithelium and has been found to block expression of target genes in rats. MCP-1 antisense ODN was injected into GPS rats every second day from days 27 to 35 after immunization (this represents the time when renal MCP-1 mRNA level was increased and interstitial mononuclear cell infiltration was aggravated).

RESULTS

In addition to a reduction in the level of tubular MCP-1 mRNA, antisense ODN treatment attenuated monocyte infiltration significantly and preserved renal function in GPS rats. However, ODN injection did not affect glomerular MCP-1 expression and glomerular histopathology, and there were no significant changes in the urinary protein excretion rate.

CONCLUSION

Our findings provide direct evidence that MCP-1, expressed by tubular epithelium, plays a pivotal role in mediating secondary tubulointerstitial alterations in the GPS model.

Osteopontin expressed by renal tubular epithelium mediates interstitial monocyte infiltration in rats

In this study, we have shown that intravenously administered antisense oligodeoxynucleotide (ODN) was demonstrated to be taken up by tubular epithelium, after which it blocked mRNA expression of target genes in normal and nephritic rats. Therefore, we injected osteopontin (OPN) antisense ODN to Goodpasture syndrome (GPS) rats every second day between days 27 and 35, the time when renal OPN expression increased and interstitial monocyte infiltration was aggravated. In parallel to blockade of tubular OPN expression, this treatment significantly attenuated monocyte infiltration and preserved renal plasma flow in GPS rats at day 37, compared with sense ODN-treated and untreated GPS rats. No significant changes were observed in OPN mRNA level by RT-PCR and histopathology of the glomeruli after ODN treatment, which was compatible with an absence of differences in the urinary protein excretion rate. In conclusion, OPN expressed by tubular epithelium played a pivotal role in mediating peritubular monocyte infiltration consequent to glomerular disease.

Effects of ICAM-1 antisense oligonucleotide on the tubulointerstitium in mice with unilateral ureteral obstruction

Effects of ICAM-1 antisense oligonucleotide on the renal tubulointerstitium in mice with unilateral ureteral obstruction.

BACKGROUND

To extend our previous study of the therapy of the renal lesions of unilateral ureteral obstruction (UUO) in mice by an inhibitor of intercellular adhesion molecule-1 (ICAM-1), we investigated the blocking effects of ICAM-1 antisense oligonucleotides (ASONs) on the ICAM-1 expression in mouse kidney.

METHODS

First, ICAM-1 ASON was transducted into mouse renal tubular epithelial cells to investigate the effects of ICAM-1 ASON in vitro. Second, fluorescein isothiocyanate (FITC)-labeled ICAM-1 ASON was injected intravenously to determine the distribution of the ASON in vivo. Third, the expression of ICAM-1 in kidney and the changes of renal morphology were observed to investigate the therapeutic effects of ICAM-1 ASON on the UUO mice in vivo.

RESULTS

The expressions of ICAM-1 in the epithelial cells induced by interleukin-1beta were inhibited by ICAM-1 ASON at the dosages of 100 and 200 nmol/L. Twenty-four hours after an introvenous injection with FITC-labeled ICAM-1 ASON, the highest level of fluorescein was detected within the proximal tubules in mouse kidney. Results of immunohistology and Northern blot showed that the ICAM-1 expression was markedly reduced in the obstructed kidney after treatment with ICAM-1 ASON. The ASON also alleviated the infiltration of inflammatory cells and accumulation of the extracellular matrix in the tubulointerstitium of UUO mice without apparent side effects.

CONCLUSION

Our data demonstrate that ICAM-1 ASON is taken up primarily by the proximal tubular cells of mouse kidney. ICAM-1 ASON can selectively inhibit the ICAM-1 expression of the renal tubular cells both in vitro and in vivo.

Crry, a complement regulatory protein, modulates renal interstitial disease induced by proteinuria

Crry, a complement regulatory protein, modulates renal interstitial disease induced by proteinuria.

BACKGROUND

Recent studies have suggested a role for urinary complement components in mediating tubulointerstitial damage, which is known to have a good correlation with progression of chronic renal diseases. Although accumulating evidence suggests that complement regulatory proteins play an important protective role in glomeruli, their role in renal tubules remains unclear. In order to establish the role of a complement regulatory protein, Crry, in renal tubular injury, we employed a molecular biological approach to block the expression of Crry in tubules of animals with proteinuria induced with puromycin aminonucleoside nephritis (PAN). Methods and Results. Two different antisense oligodeoxynucleotides (ODNs) against Crry were designed and applied to cultured rat mesangial cells in vitro in order to establish their efficacy. Antisense ODN treatment resulted in decreased expression of Crry protein associated with increased sensitivity to complement attack in cell lysis assays compared with control ODN treatment or no treatment (44.7, 1.50, and 1.34%, respectively). Antisense ODNs did not affect the expression of Thy1 as a control, confirming the specificity of our ODNs. In vivo, we performed selective right renal artery perfusion to administer antisense ODNs to the kidney and showed prominent uptake of ODNs by proximal tubular cells. Reduced expression of Crry protein was demonstrated in proximal tubular cells in antisense ODNs-treated kidneys. Normal rats treated with the antisense ODNs did not show any pathological changes. However, in PAN, rats with massive proteinuria showed increased deposition of C3 and C5b-9 in tubules in antisense-treated kidneys, and histological assessment revealed more severe tubulointerstitial injury in antisense-treated animals compared with controls.

CONCLUSION

These results establish a pathogenic role for complement in leading to tubulointerstitial injury during proteinuria and, to our knowledge for the first time, show a protective role of a complement regulatory protein, Crry, in renal interstitial disease.

Oligonucleotides tethered to a short polyguanylic acid stretch are targeted to macrophages: enhanced antiviral activity of a vesicular stomatitis virus-specific antisense oligonucleotide

The poor membrane permeability of oligonucleotides is one of the major problems of antisense technology. Here we report the construction of designer oligonucleotides for targeted delivery to macrophages. The oligonucleotides tethered to a 10-mer poly(G) sequence at their 3' ends were recognized by scavenger receptors on macrophages and were taken up about 8- to 10-fold as efficiently as those oligonucleotides that either lacked a poly(G) tail or that contained a 10-mer poly(C) tail instead of the poly(G) tail. The enhanced uptake of poly(G) constructs was inhibited in the presence of poly(G) and other known ligands of the scavenger receptor. The bioefficacy of poly(G)-mediated targeting of antisense oligonucleotides (ANS) was demonstrated by using vesicular stomatitis virus (VSV) as a model system. The ability of ANS directed against the translation initiation site of N protein mRNA of VSV to inhibit virus replication was assessed. The ANS with the 10-mer poly(G) sequences (ANS-G) brought about significant inhibition of VSV replication in J774E cells (a murine monocyte/macrophage cell line) and Chinese hamster ovary (CHO) cell transfectants expressing scavenger receptors. The ANS lacking a 10-mer poly(G) stretch were ineffective. The inhibition of VSV replication due to ANS-G was completely abrogated in the presence of 10-mer poly(G), indicating that the antisense effect of the ANS-G molecule was a consequence of scavenger receptor-mediated enhanced uptake. Importantly, antisense molecules linked exclusively by natural phosphodiester bonds were as bioeffective as those synthesized with a mixed backbone of phosphodiester and phosphorothioate. Taken together, these results suggest that macrophage-directed designer ANS against infective agents may simply be obtained by adding a short stretch of guanylic acid sequence to the desired specific ANS during solid-phase synthesis. This nucleic acid-based strategy, which utilizes homogeneous preparation of ANS, may find applications in directed manipulation of macrophage metabolism for a variety of purposes as well as in therapy of a broad spectrum of macrophage-related disorders amenable to the antisense approach.

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.

Pharmacokinetics and tissue disposition in monkeys of an antisense oligonucleotide inhibitor of Ha-ras encapsulated in stealth liposomes

PURPOSE

This study examined the pharmacokinetics and tissue distribution of an antisense oligonucleotide ISIS 2503, formulated in stealth (pegylated) liposomes (encapsulated) or in phosphate-buffered saline (unencapsulated).

METHODS

Encapsulated or unencapsulated ISIS 2503 was administered to rhesus monkeys by intravenous infusion. The concentrations of ISIS 2503 and metabolites in blood, plasma, and tissue samples were determined by capillary gel electrophoresis.

RESULTS

Plasma concentrations of encapsulated ISIS 2503 decreased mono-exponentially after infusion with a mean half-life of 57.8 hours. In contrast, the concentration of unencapsulated ISIS 2503 in plasma decreased rapidly with a mean half-life of 1.07 hours. Both encapsulated and unencapsulated ISIS 2503 distributed widely into tissues. Encapsulated ISIS 2503 distributed primarily to the reticulo-endothelial system and there were few metabolites observed. In contrast, unencapsulated ISIS 2503 distributed rapidly to tissue with highest concentration seen in kidney and liver. Nuclease-mediated metabolism was extensive for unencapsulated oligonucleotide in plasma and tissues.

CONCLUSIONS

The data suggest that stealth liposomes protect ISIS 2503 from nucleases in blood and tissues, slow tissue uptake, and slow the rate of clearance from the systemic circulation. These attributes may make these formulations attractive for delivering oligonucleotides to sites with increased vasculature permeability such as tumors or sites of inflammation.

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.

Comparison of binding of N3'-->P5' phosphoramidate and phosphorothioate oligonucleotides to cell surface proteins of cultured cells

The binding of uniformly modified N3'-->P5' phosphoramidate and stereorandom and stereopure phosphorothioate oligonucleotides (ODN) to cell surface proteins was studied, using both a fibroblast and an epithelial cell line, to assess the effect of different analog backbone types and base composition on cell surface protein binding. Marked differences were observed, both quantitative and qualitative, in the proteins to which individual ODN bound. One phosphoramidate, antisense to the insulin-like growth factor-1 (IGF-1) receptor (IGF-1R), bound to different proteins than did either a 6-base mismatch phosphoramidate IGF-1R sequence or a sense N-ras sequence. The latter bound poorly to the fibroblast line and predominantly to a 46 kDa protein in the epithelial line, as did many of the other ODN. This binding was not so marked as that of the isosequential end-capped phosphodiester N-ras sequence, which bound to this protein in both cell lines. Stereopure and stereorandom phosphorothioates containing a G-quartet (shown in other studies to form high-order tetrad structures), antisense to c-myc, exhibited considerable nonspecific binding to many proteins, as did the isosequential phosphoramidate. In particular, this ODN sequence gave notable binding to high molecular weight proteins. In general, binding of the c-myc ODN to proteins of 28-30, 46, 67, and 70-90 kDa was found in this study.

Selective inhibition of the renal dopamine subtype D1A receptor induces antinatriuresis in conscious rats

Both dopamine D1-like (D1A and D1B) and D2-like (D2, D3, and D4) receptor subfamilies are present in the kidney. Blockade of the intrarenal D1-like receptor family is associated with natriuresis and diuresis. Because the D1A and D1B receptor subtypes are not distinguishable by currently available dopaminergic agents, their functional role remains undefined. In the present study, the effect of selective inhibition of the renal D1A receptor with phosphorothioated antisense oligodeoxynucleotide (AS-ODN) was investigated in conscious uninephrectomized rats. After renal interstitial administration of Texas red-labeled D1A receptor AS-ODN, intense fluorescent signal was localized in the renal tubular epithelium and vasculature. In rats on normal salt intake, AS-ODN injected interstitially into the kidney reduced daily urinary sodium excretion (1.4+/-0.04 versus 0.8+/-0.2 mEq/d, n=5, P<0.05) and urine output (16.9+/-3.8 versus 12.5+/-3.6 mL/d, n=5, P<0.05). In rats on high sodium intake, continuous renal interstitial administration of D1A receptor AS-ODN transiently decreased daily urinary sodium excretion (5.4+/-0.5 versus 4.2+/-0.3 mEq/d, n=7, P<0.01) and urine output (27.6+/-4.5 versus 18.1+/-1.8 mL/d, n=7, P<0.01). Neither vehicle nor sense oligodeoxynucleotide had significant effects. Systolic blood pressure remained unchanged. The renal D1A receptor protein was significantly decreased by 35% and 46% at the end of the study in AS-ODN-treated rats on normal and high salt intake, respectively, whereas the D1B receptor and beta-actin were not affected. These results provide the first direct evidence that the renal D1A receptor subtype plays an important role in the control of sodium excretion.

Co-administration of polyanions with a phosphorothioate oligodeoxynucleotide (CGP 69846A): a role for the scavenger receptor in its in vivo disposition

The effects of co-administering polyanions on the pharmacokinetics of a 20-mer phosphorothioate oligodeoxynucleotide (CGP 69846A), and the role of scavenger receptors in its in vivo disposition, have been investigated. Following i.v. administration, CGP 69846A was rapidly cleared from the plasma and distributed amongst high (e.g. kidney, liver, spleen), low (e.g. skeletal muscle) and negligible (e.g. brain) accumulating tissues. In addition it was shown that: 1) dextran sulphate co-administration has a dose-dependent effect on the disposition of CGP 69846A; 2) CGP 69846A undergoes renal filtration and renal accumulation largely results from tubular reabsorption; 3) cross-inhibition studies are consistent with CGP 69846A being recognized by scavenger receptors in vitro and in vivo; and 4) the scavenger receptor may be an important determinant for the in vivo disposition of CGP 69846A in mice. These studies contribute toward an increased understanding of the mechanism underlying the pharmacokinetic behaviour of phosphorothioate oligodeoxynucleotides.

The influence of DNA sequence on the immunostimulatory properties of plasmid DNA vectors

To determine the influence of DNA sequence on immunostimulatory properties of vaccine vectors, we tested the induction of in vitro and in vivo immune responses by plasmids modified to contain extended runs of dG sequences. Studies with oligonucleotides indicate that dG sequences can directly stimulate B cells as well as enhance the activity of immunostimulatory CpG motifs because of interaction with the macrophage scavenger receptor (MSR); this receptor can bind a variety of polyanions including dG sequences. To modify vectors, we introduced stretches of 20-60 dG residues into the pCMV-beta and pSG5rab.gp vectors and measured the ability of these plasmids to induce IL-12 and IFN-gamma production by murine splenocytes. The induction of in vivo antibody responses to rabies glycoprotein was also assessed with the pSG5rab.gp vectors. In in vitro cultures, cytokine production induced by plasmids with and without dG sequences was similar. Furthermore, the addition of dG sequences to pSG5rab.gp vectors failed to enhance the anti-rabies glycoprotein response to immunization. To assess further mechanisms by which plasmids stimulate macrophages, we measured the effects of MSR ligands on in vitro cytokine induction. In in vitro cultures, poly(G), dG30, and fucoidan inhibited IL-12 induction by plasmids. IL-12 induction was also inhibited by mammalian DNA but was unaffected by polyanions that are not MSR ligands. Together, these results suggest that the addition of 20 to 60-base dG sequences to plasmids does not significantly affect their properties as immunostimulators or vaccines. Furthermore, these results suggest that MSR ligands can block cytokine induction by plasmid DNA whether or not the plasmid contains extended runs of dG.

Pharmacokinetics and biodistribution of a nucleotide-based thrombin inhibitor in rats

PURPOSE

To characterize the pharmacokinetic and tissue distribution profiles of a nucleotide-based thrombin inhibitor (GS522, phosphodiester oligonucleotide, GGTTGGTGTGGTTGG) following intravenous administration to rats.

METHODS

Pharmacokinetic study: 10 mg/kg, 20 mg/kg, 30 mg/kg (6 animals/dose) were administered to rats by rapid injection into the femoral vein. Blood samples were collected over a 45 minute period. Plasma concentrations of GS522 were determined using capillary gel electrophoresis with laser-induced fluorescence detection. Biodistribution Study: 10 mg/kg (400 microl, 31.46 microCi/ml) of 3H-GS522 was administered to rats by rapid injection into the femoral vein. The animals were sacrificed by decapitation at 1, 5, 10, 30, 60, 360 minutes post-dose (3 rats/point). Brain, blood, duodenum, eyes, heart, kidney, liver, lungs, muscle, pancreas, skin, spleen and vein samples were collected, processed and quantitated using liquid scintillation counting.

RESULTS

The pharmacokinetic profile declines in multiexponential manner, exhibiting extremely fast distribution and elimination (t1/2 = 7.6-9.0 min, Cl = 22.0-28.0 ml/min, V = 83.9-132.4 ml/kg). GS522 follows linear pharmacokinetics, with the area under the curve being proportional to the dose (Rsq = 0.9744). Highest radioactivity levels were detected in kidney, liver and blood (39.7, 15.7 and 15.3% dose/ respective organ). Less than 1% of the dose was detected in the heart, spleen and lungs, and >0.3% of the dose was found in the brain and eyes. The oligonucleotide associated radioactivity was uniformly distributed between the brain regions (left and right lobe and cerebellum). Six hours following the dose administration a statistically significant increase (p < 0.05) in radioactivity levels was observed in the brain, eyes, skin, liver, pancreas and vein.

CONCLUSIONS

The pharmacokinetic and biodistribution profiles of GS522 following intravenous administration to rats at three doses were characterized. The oligonucleotide associated radioactivity was widely distributed in tissues. The amount of radioactivity sharply decreased with time in most tissues. Kidney, liver and muscle were the main sites of accumulation. The oligonucleotide associated radioactivity did not cross the blood brain barrier to an appreciable extent. In addition, a statistically significant increase (p < 0.05) in the radioactivity levels observed in select tissues suggested a re-uptake mechanism for intact oligonucleotide or its degradation products.

Interaction of human plasma membrane proteins and oligodeoxynucleotides

Two oligodeoxynucleotide (oligodN) binding proteins of 100-110 kDa on plasma membranes of human cell lines were recently identified by us. These two proteins seemed to play a role in oligodN uptake. In this study, the impact of the chain length and the sequence of the oligodN on the interaction with those two proteins was investigated. Chain length of oligodN was an important determinant, but not the sole determinant for the interaction. Binding affinity of oligodNs was determined predominantly by base composition, where pyrimidine bases but not purine bases were required in the sequence to retain high affinity. The binding kinetics of the homopolymers of deoxycytidine (dC21) and deoxythymidine (dT21) suggests that the proteins may have different binding sites, with one site preferring thymine bases and the other cytosine bases. Moreover, some additional plasma membrane proteins were identified, with an apparent molecular mass ranging from 40 to 58 kDa, which could bind thymine bases but not cytosine bases.

Identification and characterization of a cell membrane nucleic acid channel

We have identified a 45-kDa protein purified from rat renal brush border membrane that binds short single-stranded nucleic acid sequences. This activity was purified, reconstituted in proteoliposomes, and then fused with model planar lipid bilayers. In voltage-clamp experiments, the reconstituted 45-kDa protein functioned as a gated channel that allows the passage of nucleic acids. Channel activity was observed immediately after addition of oligonucleotide. Channel activity was not observed in the absence of purified protein or of oligonucleotide or when protein was heat-inactivated prior to forming proteoliposomes. In the presence of symmetrical buffered solution and oligonucleotide, current passed linearly over the range of holding potentials tested. Conductance was 10.4 +/- 0.4 picosiemens (pS) and reversal potential was 0.2 +/- 1.7 mV. There was no difference in channel conductance or reversal potential between phosphodiester and phosphorothioate oligonucleotides. Ion-substitution experiments documented a shift in reversal potential only when a concentration gradient for oligonucleotide was established, indicating that movement of oligonucleotide alone was responsible for current. Movement of oligonucleotide across the bilayer was confirmed by using 32P-labeled oligonucleotides. Channel open probability decreased significantly in the presence of heparan sulfate. These studies provide evidence for a cell surface channel that conducts nucleic acids.

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.

Strategies of gene transfer to the kidney

Kidney targeted gene transfer has been a realistic goal for many researchers since 1991, but unfortunately, to date there is no reliable gene transfer technique for gene therapy of renal diseases. However, at the experimental level, several in vivo gene transfer methods have attempted to target certain renal structures, for example, the HVJ-liposome method and renal perfusion of adenovirus for glomerular cells, intravenous injection of oligonucleotides (ODNs) for proximal tubule, intra-arterial injection of adenovirus followed by cold incubation with a vasodilator for interstitial vasculature of the outer medulla, and adenoviral injection into the renal pelvis for the inner medullary collecting duct. As an ex vivo gene transfer method targeting the glomerulus, the transfusion of genetically-modified mesangial cells has been attempted. Implantation of genetically-modified tubular epithelial cells into the subcapsular region has been employed for ex vivo transfection to the interstitium. Gene therapy has focused particularly on the transplanted kidney, where an exogenous gene can transferred in advance. In the future, an inducible system and individual cell targeting strategy should be developed. The improvement of gene transfer techniques, especially vectors for delivering genes, is crucial. The potential application of gene transfer technologies is enormous while the therapeutic approaches have just begun to be explored. Therapeutic interventions of the process of progression of glomerulonephritis in the rat have been directed towards inhibiting the actions of growth factors. Obviously, molecular biological intervention is coming of age and there is a tremendous excitement over its potential. We believe that gene transfer techniques will become common tools for the dissection of molecular aspects of diseases and possibly for gene therapy in the field of nephrology.

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.

Nephritogenic T cells use granzyme C as a cytotoxic mediator

Cytoplasmic granules of cytotoxic T lymphocytes contain several proteins that may be involved in cell-mediated cytotoxicity. We have previously described nephritogenic T cell clones that are cytotoxic to cultured renal proximal tubular epithelial cells (MCT). One of these clones, M52.34.1, expresses perforin, a cytotoxic mediator. We investigated the expression of other granule-associated proteases of M52.34.1. Granzymes A and B have been extensively studied in T cell-mediated cytotoxicity, and associated with tissue destruction in models of transplantation. However, the activity of other granzymes has not been as extensively investigated. We focused our studies on granzyme C. Northern blots showed very high levels of granzymes B and C mRNA expression in M52.34.1 cells 3 days following T cell activation. There was no expression of granzyme A mRNA. An antisense oligonucleotide made from the 5'-upstream region of the murine granzyme C exon 1 inhibited granzyme C mRNA expression in M52.34.1 when added at a concentration of 50 microM to the culture medium for 2 days. There was no inhibition of granzyme C mRNA expression with the sense oligonucleotide. The granzyme C antisense oligonucleotide inhibited M52.34.1 cytotoxicity to MCT at effector:target ratios of 20:1 and 40:1. M52.34.1 cells mediate inflammatory interstitial nephritis following adoptive transfer. If T cells were resuspended in 200 microM of the antisense oligonucleotide prior to subcapsular transfer, the recipient kidneys showed markedly diminished tubular cell destruction, suggesting that granzyme C can also be an important mediator of cytotoxicity in vivo.

Lack of toxicity associated with the systemic administration of antisense oligonucleotides for treatment of rats bearing LNCaP prostate tumors

Antisense oligonucleotides (oligos) are now in clinical trials for the treatment of a variety of diseases. However, concern is sometimes expressed as to the toxicity of such compounds, particularly those with phosphorothioated backbones. We have previously reported (J. Surg. Oncol. 62, 194, 1996) our experience in treating nude mice bearing human PC-3 prostate tumors with phosphorothioated antisense oligos directed against mRNA encoding transforming growth factor-alpha (TGF-alpha) and the epidermal growth factor receptor (EGFR). This therapy resulted in a 75% (9/12) response rate for the intralesional treatment and a 100% (3/3) response rate for the systemic administration utilizing Alzet diffusion pumps. In the current study, athymic nude rats bearing orthotopically implanted LNCaP tumors, whose establishment was confirmed by the expression of human PSA, were implanted subcutaneously with Alzet diffusion pumps and treated systemically for 14 days with a total of 1 mg of each oligo (2 mg total). Controls consisted of five untreated rats similarly inoculated with LNCaP cells, but which did not receive antisense oligos. After 2 weeks the rats were sacrificed and serum samples were evaluated for BUN, creatinine, LDH and SGOT. Lungs, kidneys, livers, spleens and prostates were also removed for pathologic evaluation. There were no serum marker differences between groups nor was there histologic evidence of oligo toxicity seen in any evaluated tissue. Of interest was the observation that the livers and spleens, as well as prostates, of treated animals revealed mild lymphocytic infiltration compared to controls. We conclude that at this level of administration, there is no toxicity associated with 14-day oligo treatment.

Fluorescence microscopic comparison of the binding of phosphodiester and phosphorothioate (antisense) oligodeoxyribonucleotides to subcellular structures, including intermediate filaments, the endoplasmic reticulum, and the nuclear interior

To detect potential intracellular binding sites for antisense oligodeoxyribonucleotides (ODN), 3'-fluorescence-tagged phosphodiester (P) and phosphorothioate (S) analogs of a series of model and vimentin and actin antisense ODN were applied to digitonin-permeabilized fibroblast and epithelial PtK2 cells. Fluorescence microscopy revealed binding of the ODN to intermediate filaments (IFs) with a preference for cytokeratin IFs, cytoplasmic membranes (endoplasmic reticulum), and, above all, the nuclear interior. The affinity of the ODN for these cellular substructures was dependent on their base composition, and the S-ODN were by far superior to the corresponding P-ODN in binding activity. Fluorescence polarization measurements of the interaction of ODN with purified IF proteins in vitro confirmed the differential, high-affinity binding of S-ODN to IFs. In permeabilized cells, the ODN readily migrated into the nucleus where, at ambient temperature, preferentially the S-ODN gave rise to a multitude of large, irregular aggregates. Nuclear uptake of the ODN was considerably and differentially inhibited by wheat germ agglutinin. High-affinity S-ODN, but not P-ODN, additionally reacted with a structure presumably identical with the nuclear lamina. Simultaneously, they cause decompaction of chromatin, whereby the S-ODN aggregates appeared as compact inclusions in homogeneously dispersed chromatin. After microinjection of S-ODN into intact cells, these effects were not observed, although the nucleic acids rapidly moved into the nucleus and condensed into a large number of well-defined, spherical speckles or longitudinal rodlets. The methylphosphonate analogs of some of the ODN used exhibited only extremely low affinities for intracellular constituents. These results show that excess amounts of S-ODN saturate a host of both low-affinity and high-affinity binding sites on cellular substructures, whereas limited quantities as used for microinjection recognize only the high-affinity binding sites. The results support the notion that the nonsequence-specific, often toxic effects of antisense S-ODN result from their strong binding to cellular components and substructures involved in replicational, transcriptional, and translational processes. On the other hand, the association of the ODN with membranes and cytoskeletal and karyoskeletal elements may serve to optimize their sequence-specific interaction with their intended target sites and also increase their cellular retention potential. These cellular structures would thus fulfill a depot function.

Mac-1 (CD11b/CD18) is an oligodeoxynucleotide-binding protein

We have studied the interactions of phosphodiester and phosphorothioate oligodeoxynucleotides with Mac-1 (CD11b/CD18; alpha M beta 2), a heparin-binding integrin found predominantly on the surface of polymorphonuclear leukocytes (PMNs), macrophages and natural killer cells. Binding of a homopolymer of thymidine occurred on both the alpha M and beta 2 subunits. Soluble fibrinogen, a natural ligand for Mac-1, was an excellent competitor of the binding of a phosphorothioate oligodeoxynucleotide to both TNF-alpha-activated and nonactivated PMNs. Upregulation of cell-surface Mac-1 expression increased cell-surface binding of oligodeoxynucleotides. Binding was inhibited by anti-Mac-1 monoclonal antibodies, and the increase in cell-surface binding was correlated with a three- to fourfold increase in internalization by PMNs. An oligodeoxynucleotide inhibited beta 2-dependent migration through Matrigel, but the production of reactive oxygen species in PMNs adherent to fibrinogen dramatically increased. Thus, our data demonstrate that Mac-1 is a cell-surface receptor for oligodeoxynucleotides that can mediate their internalization and that this binding may have important functional consequences.

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.

Molecular therapy for renal diseases

The introduction of molecular therapy through the delivery of nucleic acids either as oligonucleotides or genetic constructs holds enormous promise for the treatment of renal disease. Significant barriers remain, however, before successful organ-specific molecular therapy can be applied to the kidney. These include the development of methods to target the kidney selectively, the definition of vectors that transduce renal tissue, the identification of appropriate molecular targets, the development of constructs that are regulated and expressed for long periods of time, the demonstration of efficacy in vivo, and the demonstration of safety in humans. As the genetic and pathophysiologic basis of renal disease is clarified, obvious targets for therapy will be defined, for example, polycystin in polycystic kidney disease, human immunodeficiency virus (HIV) type 1 in HIV-associated nephropathy, alpha-galactosidase A in Fabry's disease, insulin in diabetic nephropathy, and the "minor" collagen IV chains in Alport's syndrome. In addition, several potential mediators of progressive renal disease may be amenable to molecular therapeutic strategies, such as interleukin-6, basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), and transforming growth factor-beta(TGF-beta). To test the in vivo efficacy of molecular therapy, appropriate animal models for these disease states must be developed, an area that has received too little attention. For the successful delivery of genetic constructs to the kidney, both viral and nonviral vector systems will be required. The kidney has a major advantage over other solid organs since it is accessible by many routes, including intrarenal artery infusion, retrograde delivery through the uroexcretory pathways, and ex vivo during transplantation. To further restrict expression to the kidney, tropic vectors and tissue-specific promoters also must be developed. For the purpose of inhibition of endogenous or exogenous genes, current therapeutic modalities include the delivery of antisense oligodeoxynucleotides or ribozymes. For these approaches to succeed, we must gain a much better understanding of the nature of their transport into the kidney, requirements for specificity, and in vivo mechanisms of action. The danger of a rush to clinical application is that superficial approaches to these issues will likely fail and enthusiasm will be lost for an area that should be one of the most exciting developments in therapeutics in the next decade.

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.

In vivo targeting of inducible NO synthase with oligodeoxynucleotides protects rat kidney against ischemia

Gene products of all three distinct nitric oxide synthases are present in the mammalian kidney. This mosaic topography of nitric oxide synthase (NOS) isoforms probably reflects distinct functional role played by each enzyme. While nitric oxide (NO) is cytotoxic to isolated renal tubules, inhibition of NO production in vivo invariably results in the aggravation of renal dysfunction in various models of acute renal failure. We reasoned that the existing ambiguity on the role of nitric oxide in acute renal failure is in part due to the lack of selective NOS inhibitors. Phosphorothioated derivatives of antisense oligodeoxynucleotides targeting a conserved sequence within the open reading frame of the cDNA encoding the inducible NOS (iNOS) were designed to produce a selective knock-down of this enzyme. In vivo use of these antisense constructs attenuated acute renal failure in rats subjected to renal ischemia. This effect was due, at least in part, to the rescue of tubular epithelium from lethal injury. Application of antisense constructs did not affect endothelial NOS, as evidenced by a spared NO release after the infusion of bradykinin during in vivo monitoring with an NO-selective microelectrode. In conclusion, the data provide direct evidence for the cytotoxic effects of NO produced via iNOS in the course of ischemic acute renal failure, and offer a novel method to selectively prevent the induction of this enzyme.

In vivo suppression of the renal Na+/Pi cotransporter by antisense oligonucleotides

A 20-mer phosphorothioate oligonucleotide (AS1) was designed to hybridize to the message for the rat kidney sodium phosphate cotransporter NaPi-2 close to the translation initiation site. Single intravenous doses of this oligonucleotide were given to rats maintained on a low phosphorus diet to increase NaPi-2 expression. At 3 days after oligonucleotide infusion, rats receiving 2.5 micromol of AS1 exhibited a reduction in renal NaPi-2 to cyclophilin mRNA ratio by 40% +/- 17%, and rats receiving 7.5 micromol of AS1 exhibited a reduction in NaPi-2 to cyclophilin mRNA ratio by 46% +/- 21%. Reversed-sequence AS1 was without effect. The higher dose of 7.5 micromol of AS1 also reduced the rate of phosphate uptake into renal brush border membrane vesicles and the expression of NaPi-2 protein detected by Western blotting in these vesicles. Reversed sequence AS1 was again without effect on these parameters. These results suggest that systemically infused oligonucleotides can exert antisense effects in the renal proximal tubule.

Exploiting the potential of antisense: beyond phosphorothioate oligodeoxynucleotides

Phosphorothioate oligodeoxynucleotides, designed as nuclease-resistant antisense agents, appear to have a number of surprising biological effects that are unrelated to their intended antisense activity. These effects may be useful in themselves, but must be understood for the full potential of antisense technology to be realized.

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.