Pharmacokinetics and tolerability of intravenous trecovirsen (GEM 91), an antisense phosphorothioate oligonucleotide, in HIV-positive subjects

So Pathogenic or So What?-A Brief Overview of SIV Pathogenesis with an Emphasis on Cure Research

HIV infection requires lifelong antiretroviral therapy (ART) to control disease progression. Although ART has greatly extended the life expectancy of persons living with HIV (PWH), PWH nonetheless suffer from an increase in AIDS-related and non-AIDS related comorbidities resulting from HIV pathogenesis. Thus, an HIV cure is imperative to improve the quality of life of PWH. In this review, we discuss the origins of various SIV strains utilized in cure and comorbidity research as well as their respective animal species used. We briefly detail the life cycle of HIV and describe the pathogenesis of HIV/SIV and the integral role of chronic immune activation and inflammation on disease progression and comorbidities, with comparisons between pathogenic infections and nonpathogenic infections that occur in natural hosts of SIVs. We further discuss the various HIV cure strategies being explored with an emphasis on immunological therapies and "shock and kill".

Introduction and History of the Chemistry of Nucleic Acids Therapeutics

This introduction charts the history of the development of the major chemical modifications that have influenced the development of nucleic acids therapeutics focusing in particular on antisense oligonucleotide analogues carrying modifications in the backbone and sugar. Brief mention is made of siRNA development and other applications that have by and large utilized the same modifications. We also point out the pitfalls of the use of nucleic acids as drugs, such as their unwanted interactions with pattern recognition receptors, which can be mitigated by chemical modification or used as immunotherapeutic agents.

Assessing the impact of nonspecific binding on oligonucleotide bioanalysis

Aim: Accurate and reliable quantification of oligonucleotides can be difficult, which has led to an increased focus on bioanalytical methods for more robust analyses. Recent advances toward mitigating sample losses on liquid chromatography (LC) systems have produced recovery advantages for oligonucleotide separations. Results & methodology: LC instruments and columns constructed from MP35N metal alloy and stainless steel columns were compared against LC hardware modified with hybrid inorganic-organic silica surfaces. Designed to minimize metal-analyte adsorption, these surfaces demonstrated a 73% increase in 25-mer phosphorothioate oligonucleotide recovery using ion-pairing reversed-phase LC versus standard LC surfaces, most particularly upon initial use. Conclusion: Hybrid silica chromatographic surfaces improve the performance, detection limits and reproducibility of oligonucleotide bioanalytical assays.

The Use of Toll-Like Receptor Agonists in HIV-1 Cure Strategies

Toll-like receptors (TLRs) are a family of pattern recognition receptors and part of the first line of defense against invading microbes. In humans, we know of 10 different TLRs, which are expressed to varying degrees in immune cell subsets. Engaging TLRs through their specific ligands leads to activation of the innate immune system and secondarily priming of the adaptive immune system. Because of these unique properties, TLR agonists have been investigated as immunotherapy in cancer treatment for many years, but in recent years there has also been growing interest in the use of TLR agonists in the context of human immunodeficiency virus type 1 (HIV-1) cure research. The primary obstacle to curing HIV-1 is the presence of a latent viral reservoir in transcriptionally silent immune cells. Due to the very limited transcription of the integrated HIV-1 proviruses, latently infected cells cannot be targeted and cleared by immune effector mechanisms. TLR agonists are very interesting in this context because of their potential dual effects as latency reverting agents (LRAs) and immune modulatory compounds. Here, we review preclinical and clinical data on the impact of TLR stimulation on HIV-1 latency as well as antiviral and HIV-1-specific immunity. We also focus on the promising role of TLR agonists in combination strategies in HIV-1 cure research. Different combinations of TLR agonists and broadly neutralizing antibodies or TLRs agonists as adjuvants in HIV-1 vaccines have shown very encouraging results in non-human primate experiments and these concepts are now moving into clinical testing.

Antisense molecules: A new class of drugs

An improved understanding of disease pathogenesis leads to identification of novel therapeutic targets. From a pharmacologic point of view, these can be addressed by small chemical compounds, so-called biologicals (eg, mAbs and recombinant proteins), or by a rather new class of molecule based on the antisense concept. Recently, a new wave of clinical studies exploring antisense strategies is evolving. In addition to cancer, they include predominantly trials on infectious and noninfectious diseases, such as chronic inflammatory and metabolic conditions. This article, based on a systematic PubMed literature search, highlights recent developments in this emerging field.

Sequence confirmation of chemically modified RNAs using exonuclease digestion and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A broadly applicable, robust, and rapid method for complete sequence confirmation of highly modified oligonucleotides containing a mixture of 2'-deoxy, 2'-fluoro, 2'-o-methyl, abasic and ribonucleotides is presented. The passenger (sense) and guide (antisense) strands from synthetic short interfering RNA duplexes (siRNA) were digested individually using both 5'- and 3'-exonucleases and the resulting ladders were analyzed using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Conditions for enzymatic digestion and MALDI-TOF mass analysis were investigated and optimized, and the digestion pattern and sequence coverage of each strand was discussed. Complete sequence confirmation for the antisense strands of four synthetic RNA duplexes was obtained, whereas a three-base sequence gap in the 5'-end was observed for all four sense strands. A general strategy is proposed for routine sequence confirmation of highly modified oligonucleotides, and the potential for complete automation of the method is also discussed.

Advances in antisense oligonucleotide development for target identification, validation, and as novel therapeutics

Antisense oligonucleotides (As-ODNs) are single stranded, synthetically prepared strands of deoxynucleotide sequences, usually 18–21 nucleotides in length, complementary to the mRNA sequence of the target gene. As-ODNs are able to selectively bind cognate mRNA sequences by sequence-specific hybridization. This results in cleavage or disablement of the mRNA and, thus, inhibits the expression of the target gene. The specificity of the As approach is based on the probability that, in the human genome, any sequence longer than a minimal number of nucleotides (nt), 13 for RNA and 17 for DNA, normally occurs only once. The potential applications of As-ODNs are numerous because mRNA is ubiquitous and is more accessible to manipulation than DNA. With the publication of the human genome sequence, it has become theoretically possible to inhibit mRNA of almost any gene by As-ODNs, in order to get a better understanding of gene function, investigate its role in disease pathology and to study novel therapeutic targets for the diseases caused by dysregulated gene expression. The conceptual simplicity, the availability of gene sequence information from the human genome, the inexpensive availability of synthetic oligonucleotides and the possibility of rational drug design makes As-ODNs powerful tools for target identification, validation and therapeutic intervention. In this review we discuss the latest developments in antisense oligonucleotide design, delivery, pharmacokinetics and potential side effects, as well as its uses in target identification and validation, and finally focus on the current developments of antisense oligonucleotides in therapeutic intervention in various diseases.

Efficient inhibition of HIV-1 expression by LNA modified antisense oligonucleotides and DNAzymes targeted to functionally selected binding sites

BACKGROUND

A primary concern when targeting HIV-1 RNA by means of antisense related technologies is the accessibility of the targets. Using a library selection approach to define the most accessible sites for 20-mer oligonucleotides annealing within the highly structured 5'-UTR of the HIV-1 genome we have shown that there are at least four optimal targets available.

RESULTS

The biological effect of antisense DNA and LNA oligonucleotides, DNA- and LNAzymes targeted to the four most accessible sites was tested for their abilities to block reverse transcription and dimerization of the HIV-1 RNA template in vitro, and to suppress HIV-1 production in cell culture. The neutralization of HIV-1 expression declined in the following order: antisense LNA > LNAzymes > DNAzymes and antisense DNA. The LNA modifications strongly enhanced the in vivo inhibitory activity of all the antisense constructs and some of the DNAzymes. Notably, two of the LNA modified antisense oligonucleotides inhibited HIV-1 production in cell culture very efficiently at concentration as low as 4 nM.

CONCLUSION

LNAs targeted to experimentally selected binding sites can function as very potent inhibitors of HIV-1 expression in cell culture and may potentially be developed as antiviral drug in patients.

The future of antisense oligonucleotides in the treatment of respiratory diseases

Antisense oligonucleotides (ASO) are short synthetic DNA molecules designed to inhibit translation of a targeted gene to protein via interaction with messenger RNA. More recently, small interfering (si)RNA have been developed as potent tools to specifically inhibit gene expression. ASO directed against signaling molecules, cytokine receptors, and transcription factors involved in allergic immune and inflammatory responses, have been applied in experimental models of asthma and demonstrate potential as therapeutics. Several ASO-based drugs directed against oncogenes have been developed for therapy of lung cancer, and some have recently reached clinical trials. ASO and siRNA to respiratory syncytial virus infection have demonstrated good potential to treat this condition, particularly in combination with an antiviral drug. Although ASO-based therapeutics are promising for lung diseases, issues of specificity, identification of correct molecular targets, delivery and carrier systems, as well as potential adverse effects must be carefully evaluated before clinical application.

Toxicology of antisense therapeutics

Targeting unique mRNA molecules using antisense approaches, based on sequence specificity of double-stranded nucleic acid interactions should, in theory, allow for design of drugs with high specificity for intended targets. Antisense-induced degradation or inhibition of translation of a target mRNA is potentially capable of inhibiting the expression of any target protein. In fact, a large number of proteins of widely varied character have been successfully downregulated using an assortment of antisense-based approaches. The most prevalent approach has been to use antisense oligonucleotides (ASOs), which have progressed through the preclinical development stages including pharmacokinetics and toxicological studies. A small number of ASOs are currently in human clinical trials. These trials have highlighted several toxicities that are attributable to the chemical structure of the ASOs, and not to the particular ASO or target mRNA sequence. These include mild thrombocytopenia and hyperglycemia, activation of the complement and coagulation cascades, and hypotension. Dose-limiting toxicities have been related to hepatocellular degeneration leading to decreased levels of albumin and cholesterol. Despite these toxicities, which are generally mild and readily treatable with available standard medications, the clinical trials have clearly shown that ASOs can be safely administered to patients. Alternative chemistries of ASOs are also being pursued by many investigators to improve specificity and antisense efficacy and to reduce toxicity. In the design of ASOs for anticancer therapeutics in particular, the goal is often to enhance the cytotoxicity of traditional drugs toward cancer cells or to reduce the toxicity to normal cells to improve the therapeutic index of existing clinically relevant cancer chemotherapy drugs. We predict that use of antisense ASOs in combination with small molecule therapeutics against the target protein encoded by the antisense-targeted mRNA, or an alternate target in the same or a connected biological pathway, will likely be the most beneficial application of this emerging class of therapeutic agent.

Antisense and siRNA as agonists of Toll-like receptors

About 25 years ago, researchers first demonstrated that a short synthetic oligodeoxynucleotide, referred to as antisense, can inhibit replication of Rous sarcoma virus through hybridization to viral RNA. Since then, several hybridization-based oligonucleotide approaches have been developed to elucidate the functions of genes and their potential as therapeutic agents. Short-interfering (si) RNA is the most recent example. To effectively inhibit gene expression, an antisense or siRNA must be resistant to nucleases, be taken up efficiently by cells, hybridize efficiently with the target mRNA and activate selective degradation of the target mRNA or block its translation without causing undesirable side effects. However, both antisense and siRNA agents have been shown to exert non-target-related biological effects including immune stimulation. Do antisense and siRNA agents work as ligands for Toll-like receptors (TLRs), a family of pathogen-associated, molecular pattern recognition receptors?

Inhibition of human immunodeficiency virus type 1 replication by P-stereodefined oligo(nucleoside phosphorothioate)s in a long-term infection model

Oligo(nucleoside phosphorothioate)s (S-ODNs), if prepared by conventional methods, consist of a mixture of diastereomers by virtue of the asymmetry of the phosphorus atom involved in the internucleotide linkages. This may affect the stability of the complexes formed between S-ODNs and complementary oligoribonucleotides, which is commonly accepted as the most important factor in determining the efficacy of an antisense approach. Using HIV-1-infected MOLT-4 cells via a long-term culture approach, we studied the influence of the P-chirality sense of stereodefined 28mer oligo(nucleoside phosphorothioate)s, [All-Rp]-S-ODN-gag-28-AUG and [All-Sp]-S-ODN-gag-28-AUG, complementary to the sequence starting at the AUG initiation codon of the gag mRNA of HIV-1, upon the anti-HIV-1 activity. The [All-Sp]-S-ODN-gag-28-AUG at a low concentration of 0.5 microM can completely suppress HIV-1(gag) p24 antigen expression in HIV-1-infected MOLT-4 clone 8 cells for 32 days. Cells treated with [All-Rp]-S-ODN-gag-28-AUG (0.5 microM) showed a high level of the antigen expression at day 16. Furthermore, satisfactory suppression could not be achieved from a random [Mix]-S-ODN-gag-28-AUG, consisting of a diastereomeric mixture of the oligonucleotides. Our results suggest that chemotherapy based upon the use of stereodefined antisense [All-Sp] S-ODN may be a more effective method for reducing the viral burden in HIV-1-infected individuals.

Nucleic-acid therapeutics: basic principles and recent applications

The sequencing of the human genome and the elucidation of many molecular pathways that are important in disease have provided unprecedented opportunities for the development of new therapeutics. The types of molecule in development are increasingly varied, and include antisense oligonucleotides and ribozymes. Antisense technology and catalytic nucleic-acid enzymes are important tools for blocking the expression of abnormal genes. One FDA-approved antisense drug is already in the clinic for the treatment of cytomegalovirus retinitis, and other nucleic-acid therapies are undergoing clinical trials. This article reviews different strategies for modulating gene expression, and discusses the successes and problems that are associated with this type of therapy.

Inhibition of human immunodeficiency virus type 1 activity in vitro by a new self-stabilized oligonucleotide with guanosine-thymidine quadruplex motifs

An oligonucleotide with a dimeric hairpin guanosine quadruplex (basket type structure) (dG3T4G3-s), containing phosphorothioate groups, was able to inhibit human immunodeficiency virus type 1 (HIV-1)-induced syncytium formation and virus production (as measured by p24 core antigen expression) in peripheral blood mononuclear cells. This oligonucleotide lacks primary sequence homology with the complementary (antisense) sequences to the HIV-1 genome. Furthermore, this oligonucleotide may have increased nuclease resistance. The activity of this oligonucleotide was increased when the phosphodiester backbone was replaced with a phosphorothioate backbone. In vivo results showed that dG3T4G3-s was capable of blocking the interaction between gp120 and CD4. We also found that dG3T4G3-s specifically inhibits the entry of T-cell line-tropic HIV-1 into cells. This compound is a viable candidate for evaluation as a therapeutic agent against HIV-1 in humans.

Oligodeoxynucleotide-mediated inhibition of c-myb gene expression in autografted bone marrow: a pilot study

Antisense oligodeoxynucleotide (ODN) drugs might be more effective if their delivery was optimized and they were targeted to short-lived proteins encoded by messenger RNA (mRNA) species with equally short half-lives. To test this hypothesis, an ODN targeted to the c-myb proto-oncogene was developed and used to purge marrow autografts administered to allograft-ineligible chronic myelogenous leukemia patients. CD34(+) marrow cells were purged with ODN for either 24 (n = 19) or 72 (n = 5) hours. After purging, Myb mRNA levels declined substantially in approximately 50% of patients. Analysis of bcr/abl expression in long-term culture-initiating cells suggested that purging had been accomplished at a primitive cell level in more than 50% of patients and was ODN dependent. Day-100 cytogenetics were evaluated in surviving patients who engrafted without infusion of unmanipulated "backup" marrow (n = 14). Whereas all patients were approximately 100% Philadelphia chromosome-positive (Ph(+)) before transplantation, 2 patients had complete cytogenetic remissions; 3 patients had fewer than 33% Ph(+) metaphases; and 8 remained 100% Ph(+). One patient's marrow yielded no metaphases, but fluorescent in situ hybridization evaluation approximately 18 months after transplantation revealed approximately 45% bcr/abl(+) cells, suggesting that 6 of 14 patients had originally obtained a major cytogenetic response. Conclusions regarding clinical efficacy of ODN marrow purging cannot be drawn from this small pilot study. Nevertheless, these results lead to the speculation that enhanced delivery of ODN, targeted to critical proteins of short half-life, might lead to the development of more effective nucleic acid drugs and the enhanced clinical utility of these compounds in the future.

In vivo pro-apoptotic and antitumor efficacy of a c-Raf antisense phosphorothioate oligonucleotide: relationship to tumor size

Previously, we have shown that a phosphorothioate antisense oligonucleotide (ODN) targeted against c-raf RNA (ISIS5132; cRaf-AS) induces apoptosis in human tumor cells. We now show that the same ODN also efficiently triggers apoptosis in human tumor xenografts in nu/nu mice. Although cRaf-AS showed a clearly inhibitory effect on the growth of established tumors (approximately 150 mm3) compared to a mismatched control ODN (MM), tumor progression was not prevented. This correlated with a partial refractoriness of the tumor to cRaf-AS-induced cell killing, which seemed to be due to an inhomogeneous and inefficient penetration of the ODN into the tumor tissue rather than cellular resistance. In agreement with this conclusion, we found that growth of small tumors (<50 mm3) was completely inhibited concomitantly with an accumulation of the ODN throughout the tumor. These data show that the cRaf-AS is a highly efficacious antitumor agent, provided accessibility into the tumor tissue is warranted, and suggest that PS-AS-ODN treatment may be particularly useful in an adjuvant setting.

Inhibition of human colon cancer cell growth by antisense oligodeoxynucleotides targeted at basic fibroblast growth factor

BACKGROUND

Basic fibroblast growth factor has been shown to be mitogenic in colon cancer cell lines. In human malignant melanoma cells, antisense oligodeoxynucleotides targeted against basic fibroblast growth factor messenger RNA significantly inhibit cell growth. However, the efficacy of such an antisense oligodeoxynucleotide strategy has not been evaluated for colon cancer cells.

AIM

To investigate whether basic fibroblast growth factor can stimulate the growth of HT-29 human colon cancer cells and whether antisense oligodeoxynucleotides can inhibit growth of these cells at baseline.

METHODS

Western blotting analyses were used to confirm the presence of basic fibroblast growth factor protein in this cell line. Cell growth was assessed after 2, 4 and 6 days of treatment by cell counting using the trypan blue exclusion method. Phosphorothioate-modified oligodeoxynucleotides (10 microM) were used, complementary to codon 60 of the basic fibroblast growth factor messenger RNA. Cationic liposomes (DOTAP) were used to enhance the cellular uptake of the oligodeoxynucleotides.

RESULTS

Western blotting demonstrated the presence of basic fibroblast growth factor protein in this cell line. Basic fibroblast growth factor (1-40 ng/mL) dose-dependently stimulated cell growth and peak values were obtained at a dose of 20 ng/mL. By contrast, antisense oligodeoxynucleotide treatment significantly inhibited cell growth compared with the sense oligodeoxynucleotide-treated cells (P=0.007). This inhibition was reversed by the addition of basic fibroblast growth factor, 20 ng/mL.

CONCLUSION

Treatment targeted against basic fibroblast growth factor messenger RNA inhibits growth of HT-29 human colon cancer cells. This finding may provide a rationale for the therapeutic use of antisense oligodeoxynucleotides targeted at basic fibroblast growth factor for the treatment of colon cancer.

Tyrosine hydroxylase antisense gene therapy causes hypotensive effects in the spontaneously hypertensive rats

We investigated the effect of antisense oligodeoxynucleotides (AS ODN) against tyrosine hydroxylase (TH) on hypertension and sympathetic nervous system activity in spontaneously hypertensive rats (SHR). Systolic blood pressure (SBP) in SHR treated with TH AS ODN (50, 200 microg/rat, i.v.) was significantly lower than that of control SHR. Epinephrine and norepinephrine levels, TH activity, and TH protein levels in the adrenal medulla of SHR were reduced concomitant with TH AS ODN treatment-induced changes in SBP. In contrast, TH AS ODN (200 microg/rat) had no effect on SBP in Wistar-Kyoto rats (WKY), despite significantly decreased catecholamine levels, TH activity, and TH protein levels. These findings suggest that peripheral systemic injection of TH AS ODN may be effective as hypotensive therapy in SHR.

Specific inhibition of estrogen receptor alpha function by antisense oligodeoxyribonucleotides

We have tested the effect of a range of antisense oligodeoxyribonucleotides (ODN) directed against the human estrogen receptor alpha (ERalpha) on ERalpha protein expression and function. Antisense ERalpha ODN transfected into the ERalpha-positive human breast carcinoma cell line MCF7-K2 showed variable responses dependent on the oligo used. The most active antisense ODN (oligo 7) decreased the levels of ERa protein by 61% as measured by Western blot analysis. Exogenous 17beta-estradiol (17beta-E2), but not 17alpha-E2, augmented this effect, with a threshold effect at 10(-8) M 17beta-E2. The inhibitory effect of antisense ERa oligo 7 was confirmed by measurement of functional ERalpha protein. 3H-17beta-E2 binding to MCF7 cell extracts was inhibited to approximately 40% of control values in the presence of oligo 7. Antisense-transfected MCF7-K2 cell cultures produced a further 30% binding reduction in the presence of exogenous 17beta-E2. An inhibitory effect on 17beta-E2-dependent cell function was confirmed by the demonstration that ERalpha oligo 7-transfected MCF7-K2 cells failed to exhibit 17beta-E2-stimulated cell proliferation. Exogenous 17beta-E2 enhanced the inhibitory effect of the antisense ODN by increasing ODN transfection efficiency but without ERalpha catabolism via the proteosomal pathway, suggesting an effect of 17beta-E2 on the plasma membrane and the existence of different ERalpha degradation pathways in the MCF7-K2 cell subclone. As 17beta-E2 had no effect on ERalpha protein degradation, we conclude that the observed reduction of ERalpha protein levels is due solely to the presence of the antisense ERalpha ODN. Antisense ERalpha ODN molecules, therefore, may form the basis of effective therapies against ERalpha-dependent malignancies.

Antisense oligonucleotides complementary to immunoglobulin sequences of BCL-2/immunoglobulin fusion transcript induce apoptosis of t(14;18) lymphoma cells

Antisense oligodeoxyribonucleotides directed at the bcl-2 translational start site downregulate bcl-2 and inhibit growth of the t(14;18)-positive lymphoma line WSU-FSCCL. Non-specific downregulation of bcl-2 expression is expected to be toxic to normal cells as well. The t(14;18) translocation results in a fusion transcript containing the entire bcl-2 coding sequence with a 3' breakpoint fused to the immunoglobulin J(H) region and the c mu heavy chain. We postulated that these immunoglobulin sequences would be a specific target for downregulation of the fusion gene. Here, we have demonstrated that antisense oligodeoxyribonucleotides targeted to immunoglobulin c(mu) sequences downregulate bcl-2 protein expression and induce apoptosis of WSU-FSCCL cells. Inhibiting growth of malignant cells by targeting non-oncogenic sequences other than breakpoints of fusion transcripts expands the potential for tumour-specific genetic manipulation.

Suppression of gene expression by targeted disruption of messenger RNA: available options and current strategies

At least three different approaches may be used for gene targeting including: A) gene knockout by homologous recombination; B) employment of synthetic oligonucleotides capable of hybridizing with DNA or RNA, and C) use of polyamides and other natural DNA-bonding molecules called lexitropsins. Targeting mRNA is attractive because mRNA is more accessible than the corresponding gene. Three basic strategies have emerged for this purpose, the most familiar being to introduce antisense nucleic acids into a cell in the hopes that they will form Watson-Crick base pairs with the targeted gene's mRNA. Duplexed mRNA cannot be translated, and almost certainly initiates processes which lead to its destruction. The antisense nucleic acid can take the form of RNA expressed from a vector which has been transfected into the cell, or take the form of a DNA or RNA oligonucleotide which can be introduced into cells through a variety of means. DNA and RNA oligonucleotides can be modified for stability as well as engineered to contain inherent cleaving activity. It has also been proven that because RNA and DNA are very similar chemical compounds, DNA molecules with enzymatic activity could also be developed. This assumption proved correct and led to the development of a "general-purpose" RNA-cleaving DNA enzyme. The attraction of DNAzymes over ribozymes is that they are very inexpensive to make and that because they are composed of DNA and not RNA, they are inherently more stable than ribozymes. Although mRNA targeting is impeccable in theory, many additional considerations must be taken into account in applying these strategies in living cells including mRNA site selection, drug delivery and intracellular localization of the antisense agent. Nevertheless, the ongoing revolution in cell and molecular biology, combined with advances in the emerging disciplines of genomics and informatics, has made the concept of nontoxic, cancer-specific therapies more viable then ever and continues to drive interest in this field.

Antisense oligonucleotides as therapeutic agents

Antisense oligonucleotides can block the expression of specific target genes involved in the development of human diseases. Therapeutic applications of antisense techniques are currently under investigation in many different fields. The use of antisense molecules to modify gene expression is variable in its efficacy and reliability, raising objections about their use as therapeutic agents. However, preliminary results of several clinical studies demonstrated the safety and to some extent the efficacy of antisense oligodeoxynucleotides (ODNs) in patients with malignant diseases. Clinical response was observed in some patients suffering from ovarian cancer who were treated with antisense targeted against the gene encoding for the protein kinase C-alpha. Some hematological diseases treated with antisense oligos targeted against the bcr/abl and the bcl2 mRNAs have shown promising clinical response. Antisense therapy has been useful in the treatment of cardiovascular disorders such as restenosis after angioplasty, vascular bypass graft occlusion, and transplant coronary vasculopathy. Antisense oligonucleotides also have shown promise as antiviral agents. Several investigators are performing trials with oligonucleotides targeted against the human immunodeficiency virus-1 (HIV-1) and hepatitis viruses. Phosphorothioate ODNs now have reached phase I and II in clinical trials for the treatment of cancer and viral infections, so far demonstrating an acceptable safety and pharmacokinetic profile for continuing their development. The new drug Vitravene, based on a phosphorothioate oligonucleotide designed to inhibit the human cytomegalovirus (CMV), promises that some substantial successes can be reached with the antisense technique.

Antisense oligonucleotides as therapeutic agents

Antisense oligonucleotides can block the expression of specific target genes involved in the development of human diseases. Therapeutic applications of antisense techniques are currently under investigation in many different fields. The use of antisense molecules to modify gene expression is variable in its efficacy and reliability, raising objections about their use as therapeutic agents. However, preliminary results of several clinical studies demonstrated the safety and to some extent the efficacy of antisense oligodeoxynucleotides (ODNs) in patients with malignant diseases. Clinical response was observed in some patients suffering from ovarian cancer who were treated with antisense targeted against the gene encoding for the protein kinase C-alpha. Some hematological diseases treated with antisense oligos targeted against the bcr/abl and the bcl2 mRNAs have shown promising clinical response. Antisense therapy has been useful in the treatment of cardiovascular disorders such as restenosis after angioplasty, vascular bypass graft occlusion, and transplant coronary vasculopathy. Antisense oligonucleotides also have shown promise as antiviral agents. Several investigators are performing trials with oligonucleotides targeted against the human immunodeficiency virus-1 (HIV-1) and hepatitis viruses. Phosphorothioate ODNs now have reached phase I and II in clinical trials for the treatment of cancer and viral infections, so far demonstrating an acceptable safety and pharmacokinetic profile for continuing their development. The new drug Vitravene, based on a phosphorothioate oligonucleotide designed to inhibit the human cytomegalovirus (CMV), promises that some substantial successes can be reached with the antisense technique.