Tricyclo-DNA: promising antisense oligonucleotides for the treatment of neuromuscular diseases

Antisense oligonucleotides (ASO) hold promise for therapeutic splice-switching correction in many genetic diseases; however, despite advances in chemistry and design, systemic use of ASOs is still limited due to poor tissue/cellular uptake. This talk will describe the therapeutic potential of ASOs made of tricyclo-DNA (tcDNA), which displays unique pharmacological properties and unprecedented uptake in many tissues after systemic administration. These outstanding properties have been demonstrated in different mouse models of genetic diseases such as Duchenne muscular dystrophy (DMD) and Spinal muscular atrophy (SMA). DMD is a neurogenetic disease typically caused by frame-shifting deletions or nonsense mutations in the gene encoding dystrophin and characterized by progressive muscle weakness, cardiomyopathy, respiratory failure and neurocognitive impairment. While current naked ASOs do not significantly enter the heart or cross the blood brain barrier, systemic delivery of tcDNA-ASOs allow high levels of dystrophin rescue in skeletal muscles as well as in heart and to a lower extent in the brain. Our results have demonstrated physiological improvement of the cardio-respiratory functions and correction of behavioural features linked to the emotional/cognitive deficiency associated with the lack of dystrophin. Although initial results indicated an encouraging safety profile for tcDNA-ASOs in mice, we showed a clear impact of phosphorothioate bonds (PS) on their biodistribution, efficacy but also toxicity. Moreover our work on the human DMD exon 51 revealed a sequence-dependent toxicity of some PS-tcDNA-ASO candidates, which we characterized and eliminated using a new detoxification method. Altogether, these findings led us to develop a new generation of PS-free tcDNA-ASO, conjugated to a lipid, displaying a much higher therapeutic index and safer toxicological profile. A clinical trial evaluating this new generation of conjugated tcDNA-ASO is currently being prepared.