Biodistribution and metabolism of a mixed backbone oligonucleotide (GEM 231) following single and multiple dose administration in mice

Biodistribution and metabolism of a mixed backbone oligonucleotide (MBO), GEM 231, targeted to the RIalpha subunit of protein kinase A has been studied in normal and tumor xenografted mice. The study has been carried out using [35S]-labeled MBO following single and multiple administrations of doses varying from 2 to 50 mg/kg. MBO showed wide tissue distribution following intravenous and subcutaneous administration. The highest concentration of MBO was in the kidney and liver. The general disposition of MBO was followed by digitized autoradiographic pictures of tumored mice and further confirmed wide tissue disposition and also showed defined intratumor uptake of MBO. Multiple dose administration showed increased disposition in the majority of the tissues/organs, with the exception of the kidneys. Analysis of the extracted MBO by polyacrylamide gel electrophoresis (PAGE) showed the presence of primarily intact MBO along with its degraded forms. Based on our radioactivity levels, the primary route of excretion was in urine, analysis of which showed mainly degraded forms of MBO.

Stereo-enriched phosphorothioate oligodeoxynucleotides: synthesis, biophysical and biological properties

Stereo-enriched [Rp] and [Sp]-phosphorothioate oligodeoxynucleotides are synthesized using oxazaphospholidine derivatized monomers. Three different designs of phosphorothioate oligodeoxynucleotides (PS-oligos), (i) stereo-enriched all-[Rp] or all-[Sp] PS-linkages, (ii) stereo-random mixture of PS-linkages, and (iii) segments containing certain number of stereo-enriched [Rp] and [Sp] PS-linkages ([Sp-Rp-Sp] or [Rp-Sp-Rp]), have been studied. Thermal melting studies of these PS-oligos with RNA complementary strands showed that the binding affinities are in the order [Rp] > [Sp-Rp-Sp]-[Rp-Sp-Rp] > stereo-random > [Sp]. Circular dichroism (CD) studies suggest that the stereochemistry of the PS-oligo does not affect the global conformation of the duplex. The in vitro nuclease stability of these PS-oligos is in the order [Sp] > [Sp-Rp-Sp] > stereo-random > [Rp]. The RNase H activation is in the order [Rp] > stereo-random > [Rp-Sp-Rp] > [Sp] > [Sp-Rp-Sp]. Studies in a cancer cell line of PS-oligos targeted to MDM2 mRNA showed that all oligos had similar biological activity under the experimental conditions employed. Protein- and enzyme-binding studies showed insignificant stereo-dependent binding to proteins. The [Sp] and [Sp-Rp-Sp] chimeric and stereo-random PS-oligos that contained a CpG motif showed higher cell proliferation than [Rp] PS-oligo of the same sequence.

Cellular distribution of phosphorothioate oligonucleotide following intravenous administration in mice

Oligonucleotides are promising therapeutic agents for the prevention or treatment of a variety of diseases. The therapeutic potential of oligonucleotide therapy depends greatly on the bioavailability of oligonucleotides to their target cells and organs. We previously reported the pharmacokinetics and distribution of phosphorothioate oligonucleotide in mice using [35S]-labeled oligonucleotide ([35S]-oligo). To extend this study, we administered 30 mg/kg of fluorescent-labeled oligonucleotide (FITC-oligo) to mice and examined oligonucleotide distribution by measuring the fluorescence intensity in various cells and tissues using flow cytometry. Following FITC-oligo administration, fluorescence was detected in all the tissues examined. In terms of the fluorescent intensity, accumulation was greatest in liver and kidney, intermediate in spleen and bone marrow, and very low in peripheral blood mononuclear cells (PBMC). At 4 hours after administration, the level of oligonucleotide uptake in PBMC, spleen lymphocytes, and bone marrow cells revealed the following pattern: monocytes/macrophages > B cells > T cells. Confocal microscopy detected intracellular fluorescence in PBMC prepared under the same conditions as those for flow cytometry. These studies provide a rationale for designing cell targets for antisense therapeutics.

Pharmacokinetics and metabolism of an oligodeoxynucleotide phosphorothioate (GEM91) in cynomolgus monkeys following intravenous infusion

The pharmacokinetics and metabolism of an antisense oligonucleotide phosphorothioate (GEM91) were studied in cynomolgus monkeys following intravenous infusion. [35S]-Labeled GEM91 was administered to 12 monkeys by means of a 2-hour intravenous infusion at a dose of 4 mg/kg. Plasma pharmacokinetic analysis revealed that the maximum plasma concentration was 41.7 microg equivalents/ml, which was achieved in 2.13 hours. The plasma elimination half-life was 55.8 hours based on radioactivity levels. Urinary excretion represented the major pathway of elimination, with 70% of the administered dose excreted in urine over 240 hours. The oligonucleotide was widely distributed to tissues. The highest concentrations were observed in the liver and kidney. Analysis of the extracted oligonucleotide following post-labeling with [32p] on polyacrylamide gel electrophoresis showed the presence of both intact and degraded oligonucleotide in plasma, kidney, liver, spleen, and lymph nodes. Based on the methods used for post-labeling (either 3'-end or 5'-end), different patterns of bands were observed on polyacrylamide gel electrophoresis, suggesting metabolic modification of the administered oligonucleotide.

In vivo metabolic profile of a phosphorothioate oligodeoxyribonucleotide

Antisense phosphorothioate oligodeoxyribonucleotides (PS oligonucleotides) have the ability to inhibit individual gene expression in the potential treatment of cancer and viral diseases. Following administration in vivo, PS oligonucleotides are rapidly cleared from the plasma and distributed to various organs. However, the manner in which administered oligonucleotides are metabolized in plasma and tissues is poorly understood. In this study, a 25-mer PS oligonucleotide (GEM91) complementary to the gag gene mRNA of the human immunodeficiency virus (HIV-1) was administered to mice through intravenous injections to investigate its metabolism. The PS oligonucleotide was extracted from plasma at 1 hour postadministration and from kidney and liver at 24 hours postadministration. After extraction, the PS oligonucleotide and its metabolites were tailed with dA and annealed to a dT-tailed plasmid. The recombinant plasmid was ligated and used to transform competent bacteria. The region of interest containing the PS oligonucleotide was then sequenced. Our results show that degradation of the PS oligonucleotide in plasma was primarily from the 3'-end. However, in kidney and liver, degradation was primarily from the 3'-end, but a large proportion of the PS oligonucleotide was degraded from the 5'-end as well. We also studied the metabolism of PS oligonucleotide in plasma after 2-hour intravenous infusion in HIV-infected patients. The degradation of the PS oligonucleotide in plasma was primarily from the 3'-end. This study is important in understanding the metabolism of antisense PS oligonucleotide in vivo in general but also provides guidance for designing second-generation antisense oligonucleotides with improved stability and safety profile.

Mixed-backbone oligonucleotides as second generation antisense oligonucleotides: in vitro and in vivo studies

Antisense oligonucleotides are being evaluated in clinical trials as novel therapeutic agents. To further improve the properties of antisense oligonucleotides, we have designed mixed-backbone oligonucleotides (MBOs) that contain phosphorothioate segments at the 3' and 5' ends and have a modified oligodeoxynucleotide or oligoribonucleotide segment located in the central portion of the oligonucleotide. Some of these MBOs indicate improved properties compared with phosphorothioate oligodeoxynucleotides with respect to affinity to RNA, RNase H activation, and anti-HIV activity. In addition, more acceptable pharmacological, in vivo degradation and pharmacokinetic profiles were obtained with these MBOs.

Hybrid oligonucleotides: synthesis, biophysical properties, stability studies, and biological activity

We have designed and synthesized hybrid oligonucleotides 2-5, as analogues of oligodeoxynucleoside phosphorothioates, in an effort to have agents with improved 'antisense activity' with reduced phosphorothioate content. The hybrid oligonucleotides contain segments of 2'-O-methyl ribonucleoside phosphoric diesters and oligodeoxynucleoside phosphorothioates. Thus, compared with the 'all' phosphorothioate analogues 1 and 6, the analogues 2-5 showed significantly reduced effect on complement activation. In addition, thermal denaturation studies with complementary RNA revealed that the analogues 2-5 had higher Tm compared with that with oligodeoxynucleoside phosphorothioates. Additionally, the RNA component of the oligo/ RNA duplex is efficiently cleaved by RNase H, the site of endonucleolytic cleavage being dictated by the length of the oligodeoxynucleoside phosphorothioate segment.

Antibody-dependent cell-mediated cytotoxicity directed by a human monoclonal antibody reactive with gp120 of HIV-1

We used a human monoclonal antibody (MAb; 15e) to identify an antibody-dependent cell-mediated cytotoxicity (ADCC) epitope on HIV-1 gp120. 15e has been shown to recognize a conformation-dependent epitope on gp120 which is important in both CD4 binding and neutralizing of HIV-1 infection. 15e binds to gp120 of HIV-1IIIB but not HIV-1RF. Using a standard ADCC assay, 15e was found to mediate ADCC against cells infected with HIV-1IIIB but not HIV-1RF. 15e did not mediate ADCC against cells with recombinant gp120 bound to surface CD4, indicating that 15e does not mediate innocent bystander ADCC against uninfected CD4 cells. To better define the 15e epitope, we performed ADCC against target cells infected with a vaccinia vector which expresses processed HIV-1IIIB gp160 from which the third variable region was deleted (amino acids, 312-328). MAb 15e efficiently mediated ADCC against cells expressing this altered form of gp120, indicating that this region is not contributing to the conformational epitope defined by 15e. 15e defines an important epitope in the human immune response to HIV-1 infection. Antibodies with 15e-like activity may be useful in immunoprophylaxis or immunotherapy of HIV-1 infection.