ESPRIT Technology (Exon Skipping Pre–mRNA Interference Technology) or Directed RNA Alternative Gene Splicing
The Human Genome Project revealed that humans have far fewer genes than expected, and that most human proteins arise from alternative RNA splicing, a process that produces multiple messenger RNAs (mRNAs) and, consequently, multiple proteins from a single gene. For the majority of genes, these proteins have different functions.
Alternative splicing pathways can be affected in a number of diseases such that the production of beneficial proteins is reduced or they are no longer made or even that harmful proteins are made instead. AVI’s technology enables manipulation of splicing to restore production of desired proteins, thus making it a therapeutic platform in many disease situations.
In human DNA, the genetic information that codes for protein is not contiguous and is stored into packets called exons, which are separated by non–coding information called introns During processing of precursor mRNA, which is copied from the DNA template, introns are removed and exons spliced together to create the mature mRNA. In alternative splicing this process goes in more than one way, creating multiple messenger RNAs and, hence, multiple proteins. AVI’s NeuGene chemistry can be used to manipulate splicing in a way that is distinct from conventional antisense approaches. This process is called ESPRIT (Exon Skipping Pre–mRNA Interference Technology.)
By targeting elements in precursor RNA that are essential for splicing, NeuGene antisense compounds force the cellular machinery to skip over targeted exons, creating an altered mRNA template. In a disease, ESPRIT is 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, or partially restored, by forcing skipping of the exon. This approach may be used to overcome the devastating consequences of certain disease–causing mutations.
AVI’s first application of this alternative splicing ESPRIT technology is for the genetic disorder, Duchenne muscular dystrophy (DMD). AVI and its collaborators have conducted a series of preclinical studies that suggest there is potential clinical value in using NeuGene compounds to reduce the seriously degenerative DMD to a less severe form, like Becker muscular dystrophy, BMD.
Muscular dystrophy is the common name for several progressive hereditary diseases that cause muscles to weaken and degenerate. Each type has its own hereditary pattern, age of onset and rate of muscle loss. Different genetic alterations cause different types of MD. It is estimated that, worldwide, between 50,000 and 250,000 individuals are affected annually.
The gene that codes for an important muscle protein, called dystrophin, is one of the longest human genes identified to date. Dystrophin acts as the shock absorber that provides strength and stability to muscle cells when they contract. Dystrophin is also believed to carry signals between the inside and outside of muscle fibers. Without dystrophin, muscles are unable to operate properly and eventually suffer progressive damage.
The dystrophin gene is carried on the X chromosome. Young men therefore are more susceptible to dystrophin abnormalities because they have only one X chromosome. (Females have two X chromosomes — one inherited from the mother and one from the father.) When a boy is diagnosed with DMD, there is a deficiency of dystrophin, leading to progressive deterioration of muscle fibres. This is because a mutation in the gene changes the DNA and the copied precursor mRNA and completely prevents production of dystrophin protein
In BMD, a mutation is milder, allowing production of partially functional dystrophin protein. Those with this naturally–occurring form of BMD live a more normal and productive lives than those with DMD.
Preclincial studies have shown that AVI’s NeuGene compounds can target the exon in precursor mRNA and force the cell machinery to perform a kind of fine genetic surgery, snipping the faulty exon out and resulting in a form of mRNA that produces a partially functional dystrophin protein. With protein in a muscle cell, DMD is converted to a form of the disease similar to the naturally–occurring, and less severe, BMD.
ESPRIT is not limited to genetic disorders. AVI and its collaborators are exploring the use of ESPRIT for treating Rheumatoid arthritis, Type 1 Diabetes, Multiple Sclerosis and other diseases, especially those inflammatory in nature.