Making sense with antisense

Professorial lecture by Professor Linda Popplewell

Rare diseases are defined as those which affect less than one in 2,000 people. Since there are more than 7,000 different rare diseases, statistically this means one in seventeen people will develop a rare disease. Virtually all rare diseases are caused by gene mutations that are either inherited or arise spontaneously, are generally progressive in nature and become life-limiting and life-threatening. Treatments, if available, focus on targeting the symptoms of the disease rather than the cause and are often associated with toxic side effects with prolonged repeat dosing. The development of specific therapies directed to addressing the disease mutation itself would potentially improve clinical outcomes.

My research has focused on the application of three technologies, namely gene replacement, genome editing and RNA interference, to the development of gene therapies for various rare diseases. In particular, we have exploited the process of antisense oligonucleotide (AO)-induced exon skipping for the muscle wasting condition Duchenne muscular dystrophy (DMD) and neurofibromatosis type 1 (NF1), a disease that results in nerve tumours. These two diseases are caused by a wide range of mutations that result in loss of dystrophin, a muscle stabiliser, in DMD, and the tumour suppressor neurofibromin in NF1. Certain mutation subsets in both diseases cause disruption of the RNA reading frame so that, rather than being translated into protein, the mutated RNA undergoes degradation and disease ensues. AOs can be designed to mask exons, the coding part of a gene, so that they are spliced out during the maturation of the RNA restoring the reading frame so that shortened but functional protein is expressed.

The preclinical work up of the AOs involves using in silico design tools to interrogate the sequences to be targeted, with experimental comparative analyses of exon skipping efficacy to restore protein expression and function in patient cells followed by confirmation of activity in other relevant models. The development of AOs for NF1 are now at the model testing stage, while some of the AOs for DMD we have developed are now being clinically trialled. One of these AOs, with applicability to 15% of DMD patients, is now a conditionally FDA approved medicine. After three years of treatment, this AO gives a highly significant increase in dystrophin protein expression which protects muscle against turnover. Treated patients, when compared to untreated age-matched patients, have improved walking ability, have a decreased loss in ambulation and a lower decline in respiratory function. This highlights the power of AOs to make sense of unreadable RNA and provide hope to patients with particular rare disease mutations.