**1. Introduction: antisense technology**

The advancement in the next-generation sequencing enables us to identify the genetic heritages of several diseases, such as cancer, Parkinson's, rheumatoid arthritis, and Alzheimer's, which brings to attention the development of personalized medicine [1]. This knowledge has been well adapted and accepted for diagnosis, but the field still lags toward pharmaceutical interventions to address the genetic defects underlying diseases. At present, small molecules and proteins are the two major classes of US Food and Drug Administration (FDA)-approved drugs [2]. Small-molecule drugs inhibit target proteins through competitive binding, whereas protein-based drugs (such as antibodies) can bind with high specificity to several targets. The size and stability of proteins are the major limitations of their utility for majority of disease targets [2], and both protein and small-molecule drugs cannot target every disease-relevant protein or gene. Thus, there is a current need to develop the drugs for personalized genomics. The mRNA- and DNA-based drugs are therapeutically more promising and have the great potential to cure the genetic defect [1]. The RNA-based drugs have emerged as a promising candidate to treat

diseases at the genetic (gene and RNA) levels. The delivery of therapeutic RNA has been limited due to several numbers of factors such as nucleic acid design, delivery methods, and materials for transport of RNA drugs to the site of interest [1]. The current advancement in RNA and RNA-protein therapy has shown the great potential for the development of RNA delivery, and the clinical applications of RNA-based drugs have been proven by modulating gene/protein expression and gene editing [1].

An approach to fight disease by utilizing short DNA-like molecules is known as antisense oligonucleotides. This is the most effective and commonly used technology to regulate the gene expression and drugs for targeted gene therapy. These antisense oligonucleotides bind to messenger RNA (mRNA) and impair the protein production and inhibit the gene expression. The antisense molecules are synthetic replica of specific mRNA sequence to block the function of the specific target gene of interest in the human genome. Recently, antisense therapy has emerged as a promising tool to treat various diseases, and for treatment, several antisense drugs have been approved by the FDA. For antisense gene therapy, chemically engineered oligonucleotides complementary to specific mRNA are inserted into the cells which stop the translation of the specific protein. Similarly, the antisense drug contains the vital molecule—"the noncoding mRNA"—which blocks the translation of a specific protein. The antisense oligonucleotides could be very useful to treat the viral diseases, genetic/hereditary diseases, as well as cancers. The naturally occurring oligonucleotides bear poor stability and very low specificity and have a lot of side effects in vivo. The therapeutic use of oligonucleotides can be achieved by enhancing the stability and specificity of the molecules and reducing the side effects by chemical modification. The most common therapeutic oligonucleotides are small interfering RNA, ribozyme, DNAzyme, anti-gene, CpG, decoy, and aptamer. The chemical modification of antisense oligonucleotides can improve their ability to enter the cells to bind the specific target gene sequences which further disrupt the targeted gene function. Several antisense RNA and antisense oligonucleotide delivery systems such as virus vectors (retrovirus, adenovirus, and adenoassociated virus) and liposomes have been developed to carry the antisense RNA or oligonucleotides through the cell membrane into the cytoplasm and nucleus. The oligonucleotides mainly target the ribonucleic acid (RNA), whereas small molecules and antibodies primarily target proteins due to their chemical properties and distinct molecular mechanism of action. The mRNA codes for protein to noncoding RNAs (such as microRNA, transfer RNA, small interfering RNAs, ribosomal RNA, and long noncoding RNAs). The main function of noncoding RNAs is the transfer of genetic information from DNA to protein [3]. The major therapeutic approach to target RNA-based therapy is antisense oligonucleotides because of their high affinity, selectivity, ease of chemical modifications, and less toxicity. This chapter will provide a comprehensive overview of antisense therapy and their major therapeutic approaches.

The remarkable progress in the field of gene therapy and antisense therapy is apparent from numerous gene therapy- and antisense therapy-based clinical trials that are currently underway worldwide.

Gendicine (Ad-p53), the first gene therapy-based product, was approved in China for the treatment of head and neck squamous cell carcinoma in conjunction with radiotherapy. One AON drug, Vitravene, had been also approved for the local treatment of cytomegalovirus-induced retinitis, and several others are in clinical trials, including those siRNAs, miRNAs, and ribozymes that are targeting the mRNA of different oncogenes and other cancer-promoting genes.

Although the application of gene therapy and antisense therapy to mediate tumor regression is well demonstrated in experimental and clinical settings, impediment

**3**

*Antisense Therapy: An Overview*

therapy.

*DOI: http://dx.doi.org/10.5772/intechopen.86867*

**2. Pharmacology of antisense drugs**

remains when translating this into large clinical application. The main obstacles that remained in cancer gene therapy and antisense therapy are the lack of delivery systems that successfully deliver an efficacious dose of a therapeutic gene (s) or antisense drug(s) to the targeted tumor site. Targeted gene or antisense drug delivery to distant tumors for therapeutic approaches is a demanding task that urges the development of delivery vectors capable of overcoming many barriers. Many scientists have used viral and non-viral vectors to deliver the therapeutic gene or antisense compound in to the targeted tumor cells or tissues. Although the results of early gene therapy- and antisense therapy-based clinical trials using either viral or non-viral vectors have been encouraging, still it is difficult to find a single method that meets

Limitations of the present vector technologies have slowed the progress of gene therapy and antisense therapy for cancer to the clinic. Thus, the development of appropriate delivery systems for targeting therapeutic genes and antisense agents into targeted tumor cells and tissues is one of the potential approaches that have to be further explored in the future in order to augment gene therapy and antisense therapy against a wide range of cancers. It is hoped that the next generation of carriers could be a promising technology for systemic cancer gene therapy and antisense

The antisense oligonucleotides have the potential to manipulate the gene expression which prompted the field toward the therapeutic application and value of oligonucleotides as potential drugs and their targets [4]. The direct route to target RNA in a selective way is a well-established platform for drug discovery. The well-defined mechanisms, uncomplicated and easy to design, bring antisense oligonucleotides as a promising candidate for therapeutic development. The therapeutic potential of antisense drugs for the treatment of several diseases is already translated from bench to bedside, and many antisense drugs have entered into clinical trials for the treatment. The first patent on antisense therapy was granted to Molecular Biosystems company in 1991 for developing the antisense compounds. The first FDA-approved antisense product drug was afovirsen developed by Ionis Pharmaceuticals in 1992 which was a phosphorothioate oligonucleotide that targeted mRNA sequence of the E2 gene, which is associated with human papillomavirus transcription and replication. Later oblimersen, a phosphorothioate oligonucleotide, was designed to target the Bcl-2 protein for the treatment of melanoma and certain leukemias. Unfortunately, both the drugs failed in the clinical trial programs due to lack of efficacy and failure to demonstrate overall survival benefits and dose-limiting toxicity. Currently, several gene therapy- and antisense therapy-based clinical trials are ongoing. The major challenge of antisense drugs is effective and safe delivery to the target. The advancement toward antisense-based drug delivery is in progress. Several chemical modifications, novel chemistries, better formulation, and design of oligonucleotide not only have improved the potency and tolerability of antisense drug but also have enhanced the drug distribution to the targeted RNA inside the cells [5, 6]. The clinical application of antisense drugs requires safe and efficient carrier system, and currently, the viral and non-viral vectors are the most common methods used to deliver the antisense drugs specifically to the target tissues and cells. The viral vector-based delivery is most advantageous due to their high transfection efficiency [7]. Also, the new chemistries and better antisense oligonucleotide designs further improve the unwanted side effects, safety, and tolerability. From the last three decades, several antisense drugs have entered

all the conditions for an ideal gene transfer and vector expression.

#### *Antisense Therapy: An Overview DOI: http://dx.doi.org/10.5772/intechopen.86867*

*Antisense Therapy*

gene editing [1].

diseases at the genetic (gene and RNA) levels. The delivery of therapeutic RNA has been limited due to several numbers of factors such as nucleic acid design, delivery methods, and materials for transport of RNA drugs to the site of interest [1]. The current advancement in RNA and RNA-protein therapy has shown the great potential for the development of RNA delivery, and the clinical applications of RNA-based drugs have been proven by modulating gene/protein expression and

An approach to fight disease by utilizing short DNA-like molecules is known as antisense oligonucleotides. This is the most effective and commonly used technology to regulate the gene expression and drugs for targeted gene therapy. These antisense oligonucleotides bind to messenger RNA (mRNA) and impair the protein production and inhibit the gene expression. The antisense molecules are synthetic replica of specific mRNA sequence to block the function of the specific target gene of interest in the human genome. Recently, antisense therapy has emerged as a promising tool to treat various diseases, and for treatment, several antisense drugs have been approved by the FDA. For antisense gene therapy, chemically engineered oligonucleotides complementary to specific mRNA are inserted into the cells which stop the translation of the specific protein. Similarly, the antisense drug contains the vital molecule—"the noncoding mRNA"—which blocks the translation of a specific protein. The antisense oligonucleotides could be very useful to treat the viral diseases, genetic/hereditary diseases, as well as cancers. The naturally occurring oligonucleotides bear poor stability and very low specificity and have a lot of side effects in vivo. The therapeutic use of oligonucleotides can be achieved by enhancing the stability and specificity of the molecules and reducing the side effects by chemical modification. The most common therapeutic oligonucleotides are small interfering RNA, ribozyme, DNAzyme, anti-gene, CpG, decoy, and aptamer. The chemical modification of antisense oligonucleotides can improve their ability to enter the cells to bind the specific target gene sequences which further disrupt the targeted gene function. Several antisense RNA and antisense oligonucleotide delivery systems such as virus vectors (retrovirus, adenovirus, and adenoassociated virus) and liposomes have been developed to carry the antisense RNA or oligonucleotides through the cell membrane into the cytoplasm and nucleus. The oligonucleotides mainly target the ribonucleic acid (RNA), whereas small molecules and antibodies primarily target proteins due to their chemical properties and distinct molecular mechanism of action. The mRNA codes for protein to noncoding RNAs (such as microRNA, transfer RNA, small interfering RNAs, ribosomal RNA, and long noncoding RNAs). The main function of noncoding RNAs is the transfer of genetic information from DNA to protein [3]. The major therapeutic approach to target RNA-based therapy is antisense oligonucleotides because of their high affinity, selectivity, ease of chemical modifications, and less toxicity. This chapter will provide a comprehensive overview of antisense therapy and their major therapeutic

The remarkable progress in the field of gene therapy and antisense therapy is apparent from numerous gene therapy- and antisense therapy-based clinical trials

Gendicine (Ad-p53), the first gene therapy-based product, was approved in China for the treatment of head and neck squamous cell carcinoma in conjunction with radiotherapy. One AON drug, Vitravene, had been also approved for the local treatment of cytomegalovirus-induced retinitis, and several others are in clinical trials, including those siRNAs, miRNAs, and ribozymes that are targeting the

Although the application of gene therapy and antisense therapy to mediate tumor regression is well demonstrated in experimental and clinical settings, impediment

mRNA of different oncogenes and other cancer-promoting genes.

**2**

approaches.

that are currently underway worldwide.

remains when translating this into large clinical application. The main obstacles that remained in cancer gene therapy and antisense therapy are the lack of delivery systems that successfully deliver an efficacious dose of a therapeutic gene (s) or antisense drug(s) to the targeted tumor site. Targeted gene or antisense drug delivery to distant tumors for therapeutic approaches is a demanding task that urges the development of delivery vectors capable of overcoming many barriers. Many scientists have used viral and non-viral vectors to deliver the therapeutic gene or antisense compound in to the targeted tumor cells or tissues. Although the results of early gene therapy- and antisense therapy-based clinical trials using either viral or non-viral vectors have been encouraging, still it is difficult to find a single method that meets all the conditions for an ideal gene transfer and vector expression.

Limitations of the present vector technologies have slowed the progress of gene therapy and antisense therapy for cancer to the clinic. Thus, the development of appropriate delivery systems for targeting therapeutic genes and antisense agents into targeted tumor cells and tissues is one of the potential approaches that have to be further explored in the future in order to augment gene therapy and antisense therapy against a wide range of cancers. It is hoped that the next generation of carriers could be a promising technology for systemic cancer gene therapy and antisense therapy.
