Antiviral activity of an oligo(nucleoside methylphosphonate) that targets HSV-1 immediate-early pre-mRNA 4,5 is augmented by cotreatment with replication-defective adenovirus

Ocular delivery of nucleic acids: antisense oligonucleotides, aptamers and siRNA

Nucleic acids have gained a lot of interest for the treatment of ocular diseases. The first to enter in clinic has been Vitravene an antisense oligonucleotide for the treatment of cytomegalovirus (CMV) infection and more recently, research on aptamers have led to the marketing of anti-vascular endothelial growth factor (VEGF) inhibitor (Macugen) for the treatment of age-related macular degeneration (AMD). The siRNAs appear very promising as they are very potent inhibitors of protein expression. Despite their potential, nucleic acids therapeutic targets of nucleic acid-based drugs are mainly located in the posterior segment of the eye requiring invasive administration which can be harmful if repeated. Their intracellular penetration in some cases needs to be enhanced. This is the reason why adequate delivery systems were designed either to insure cellular penetration, protection against degradation or to allow long-term delivery. A combination of both effects was also developed for an implantable system. In conclusion, the intraocular administration of nucleic acids offers interesting perspectives for the treatment of ocular diseases.

Intravitreal administration of antisense oligonucleotides: potential of liposomal delivery

Antisense oligonucleotides are short synthetic fragments of genes that are able to inhibit gene expression after being internalized by cells. They can therefore be used as antiviral compounds particularly, for the treatment of ocular viral infections (i.e. Herpes simplex virus or Cytomegalovirus, CMV). Antisense oligonucleotides are however poorly stable in biological fluids and their intracellular penetration is limited. Although oligonucleotides are now currently used in therapeutics for the treatment of CMV by intravitreal injection (Vitravene) their main drawbacks impose to repeat the number of administrations which can be very harmful and damaging. A system that is able to permit a protection of oligonucleotides against degradation and their slow delivery into the vitreous would be more favorable for improving patient compliance. The use of liposomes for intravitreal administration can be very promising since these lipid vesicles are able to protect oligonucleotides against degradation by nucleases and they allow to increase the retention time of many drugs in the vitreous. In this review, the potentialities of liposomes for the intravitreal delivery of oligonucleotides will be discussed.

Antisense inhibition of virus infections

This chapter summarizes the new approaches to identify novel antiviral drug targets and to develop novel antiviral strategies. The chapter also reviews genetic pharmacology as it relates to antiviral antisense research and drug development. Antisense oligonucleotides are selective compounds by virtue of their interaction with specific segments of RNA. For potential antivirals, identification of appropriate target RNA sequences for antisense oligonucleotides is performed at two levels: the optimal gene within the virus, and the optimal sequence within the RNA. The importance of these oligonucleotide modifications in designing effective drugs is just now being evaluated, both in animal model systems and in the clinic. The first generation of widely used antisense oligonucleotides has been the phosphorothioate (PS) compounds and a body of data on biodistribution, pharmacokinetics, and metabolism in animals and in humans is now available. Since the identification and sequencing of human immunodeficiency virus (HIV), there has been a strong interest in identifying a potent oligonucleotide inhibitor that would have the potential for development as a therapy for acquired immunodeficiency syndrome (AIDS). Numerous phosphorothioate oligonucleotides, with no apparent antisense sequence specificity, can have an anti-herpes simplex virus (HSV) effect. Oligonucleotides can be effective anti-influenza agents in cell culture assays. Hepatitis B virus (HBV) X protein that is a transactivator has been also reported to be targeted successfully by antisense oligonucleotides in vivo. Several of picornaviruses have been targets for antisense oligonucleotide inhibition, and the studies demonstrate the versatility of the antisense approach. However, the fact that oligonucleotides may contribute numerous mechanisms toward the antiviral activity, in addition to the antisense mechanism, may in some cases be an asset in the pursuit of clinically useful antiviral drugs.