Applications (TSOs & SSOs)

Translation Suppressing Oligomers ™ (TSO)

As a therapeutic approach, TSOs provide a platform to address the 80% of identified genetic targets not druggable by current approaches such as small molecules or monoclonal antibodies.

Translation Suppressing Oligomers (TSO) are PMO based antisense compounds that interfere with gene expression or other mRNA–dependent cellular processes by binding to their specific target sequence in mRNA. The primary application of TSOs is to stop or suppress the translation of a specific protein through this binding process, thus inducing a desired therapeutic effect.

TSOs have high mRNA binding and act by a simple steric–blocking mechanism instead of by RNAse H–mediated or RISC–mediated mRNA degradation. AVI uses several PMO analogues as TSOs to achieve gene downregulation or silencing of targeted mRNA sequences.

Splice Switching Oligomers ™ (SSO)

Splice Switching Oligomers (SSOs) are PMO based compounds that can direct alternative splicing by forcing the cellular splicing machinery towards desired pathways. Sometimes these pathways are entirely novel, they are not seen in the human body and could produce important therapeutic outcomes. SSOs exploit pre–mRNA splicing to control gene function and produce a therapeutic benefit.

SSOs are designed to block disease related splicing pathways and simultaneously promote the production of desired mRNAs and their proteins. The SSO mechanism of action thus prevents the production of disease related proteins, in favor of increased levels of therapeutic proteins.

The field of directed alternative splicing represents an especially exciting opportunity for AVI BioPharma. This new area of RNA–based drug discovery and development is positioned at the crucial interface of genomes, regulatory networks and evolution, a rapidly emerging, ubiquitous and dynamic mechanism of gene regulation.

The genetic information stored in human DNA is dispersed in short DNA stretches, called exons, that code for fragments of the protein and which are separated by long non–coding pieces of DNA called introns. During processing of precursor or pre–mRNA, which is copied from the DNA template, introns are removed and exons spliced together to create the mature mRNA. In mRNA the exons are brought together, the genetic information is now contiguous and full protein is translated During alternative splicing , this process can go via more than one pathway, creating multiple messenger RNAs and, hence, multiple proteins. AVI’s SSOs can be used to manipulate splicing in a way that is distinct from conventional antisense or siRNA based approaches.

By targeting elements in precursor RNA that are essential for splicing, SSO compounds force the cellular machinery to skip over targeted exons, creating an altered mRNA template. In a disease situation, SSOs are intended to prevent formation of harmful proteins and help to restore beneficial proteins. When the exon contains a disease–causing mutation, for example, the resulting altered protein may have its function restored, partially restored or neutralized, by forcing skipping of the exon. This approach may be used to overcome the devastating consequences of certain disease–causing mutations.

The Human Genome Project revealed that humans have far fewer genes than expected from comparison to so–called lower organisms. Very many human proteins arise through alternative RNA splicing, a process that produces multiple mRNA and protein isoforms from a single gene. For the majority of genes, alternative splicing produces multiple proteins which can have slightly or profoundly different functions. Some pairs of splice variants have exactly opposite effects. Alternative splicing pathways are affected in many different diseases such that disease- related protein isoforms are over–produced and the desirable forms are decreased. AVI’s PMO based SSO technology enables manipulation of splicing to restore production of desired proteins and is therefore a novel therapeutic platform.

Therapeutic applications of SSOs include:

  • Inhibition of mRNA production via a kinetically favored process
  • Repair of RNA mutations
  • Expression of novel proteins
  • Alteration of protein compartmentalization
  • The ability to flip the control switch on specific gene targets
  • Alteration of the profile of protein isoforms

The field of directed alternative splicing represents an exciting opportunity for AVI BioPharma. This new area of RNA-based drug discovery and development is positioned at the crucial interface of genomes, regulatory networks and evolution, and has rapidly emerged as a ubiquitous and dynamic mechanism of gene regulation. Supported by a growing stream of new insights and discoveries derived from the fields of genomics, bioinformatics and molecular biology, this area promises to be a rich source of therapeutic applications in the future.