Exploiting the alternative splicing of vascular endothelial growth factor (VEGF)

The DNA in humans is made up of around 20,000 genes known as the genome. Genes alone, however, are not enough – the functions of the body are actually performed by proteins, which are created from the instructions in the DNA. The DNA is first copied into a single stranded form, mRNA, which is then used as a template for the construction of proteins by other cellular components. Think of DNA as a recipe book, mRNA as a photocopy of one of the pages and the protein as the final cake you bake using the copy of the instructions.

This complex process allows us to create almost 1,000,000 proteins. The proteome is the entire set of proteins expressed by a genome. But how can 20,000 genes result in fifty times as many protein products? Surely 20,000 recipes lead to 20,000 products? This is where alternative splicing comes in. Initially observed in 1977, alternative splicing allows alterations to the mRNA before it is used to make proteins in order to produce a different product. Pre-mRNA is made of coding regions called exons and non-coding regions called introns. Exons may be included or excluded to create a new protein with a different function to the original. Using our baking analogy, this is the equivalent of adding a flavouring, or changing the flour used to make it gluten free.

With 95% of the human genome known to be alternatively spliced, this is a huge area of research. Given that a change in splicing can result in proteins with different functions, it is unsurprising that abnormal splicing is implicated with disease. We frequently talk about upregulation of a certain gene and how we can target this therapeutically, but sometimes this upregulation is not just a result of how a gene is expressed, but how it is being spliced.

The protein that controls which type of VEGF is produced is an enzyme, SRPK1. Inhibition of SRPK1 with our small molecule inhibitors results in a reduction of VEGF-A_xxxa isoforms such as VEGF-A₁₆₅a, which are commonly high in wAMD, and increases VEGF-A_xxxb isoforms such as VEGF-A₁₆₅b, which leads to a reduction in vessel growth in the back of the eye, and ultimately, the prevention of vision loss. VEGF-A_xxxb isoforms have also been shown to protect cells in the retina from the damage and death commonly seen in wAMD which can lead to geographic atrophy and promotion of angiogenesis, suggesting that our compounds may have an additional mechanism of action over currently available therapies.

Current therapies already involve the inhibition of VEGF-A, but these therapies target all isoforms of VEGF-A regardless of whether they are pro- or anti- angiogenic, and also require injection directly into the eye. Our novel compounds not only increase the ratio of anti- to pro- angiogenic VEGF-A isoforms, they are designed to be delivered as an eye drop rather than as an injection.

Using our innovative technologies, we aim to develop a minimally invasive therapy to prevent vision loss in patients with DMO and wAMD.

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