Development of novel ASO-based therapeutics for CMT1A

Abstract: The objective of this project is to develop a safe, effective antisense oligonucleotide with Phosphorodiamidate Morpholino Oligomer (PMO) backbone chemistry capable of significantly reducing PMP22 protein production in Schwann cells, which is titratable in its dosing characteristics. For patients with CMT1A, the most common form of CMT, PMP22 over production of this protein drives disease progression. We have previously performed rigorous analysis of the PMP22 gene sequence, which has led to the design of numerous ASOs that have been shown to effectively alter PMP22 mRNA production. These PMOs have been designed to alter exon splicing, resulting in an “exon-skipped” product that is severely truncated early in the translation process, effectively reducing PMP22 protein production. Importantly, however, PMP22 production is not completely eliminated since this would also be detrimental. CMT1A is a remarkably common rare disease that is caused by the overexpression of a protein involved in the function of nerves in the periphery. The protein, PMP22, acts much like an insulator, allowing nerves to fire their signal properly. While too much of PMP22 is bad for the cell, too little of PMP22 is also a problem and therefore any therapeutic strategy cannot simply knock-out the expression of the important gene. The molecular genetics of CMT1A makes this disease particularly amenable for nucleic acid-based therapeutics designed to modulate PMP22 expression since: 1) CMT1A is monogenic; 2) the disease gene has been identified; and 3) inhibition of PMP22 expression can be accomplished through a variety a molecular mechanisms. Currently, no drugs are available for effectively treating the disease progression of CMT1A, thus this highly at risk patient class remains untreated with disease altering therapies. During Phase 1, a number of the PMO ASO candidates will be screened “in vivo”, in a humanized PMP22 mouse model for activity and acute safety. In Aim 1, we will inject selected compounds previously screened in cell based models into mice and monitor the PMP22 mRNA total for full-length and “exon-skipped” mRNA production. in Schwan cells surrounding peripheral nerve tissues (after sacrifice) to confirm efficacy and monitor overall in vivo efficiency. Once active compounds are confirmed, in Aim 2 we will inject molecules into a different cohort of mice and monitor biological activity of nerve function using accepted electrophysiology techniques. Previously, Shift Pharmaceuticals (collaborating with the University of Missouri) has successfully demonstrated the PMO ASO approach for altering exon splicing with another drug candidate (E1v1.11) that has proven to be extremely effective at modifying protein production of SMN protein for Spinal Muscular Atrophy disease, which suggested this approach should be effective in mouse models for CMT. We have also demonstrated in previous studies that E1v1.11 and similar PMOs are very safe when dosed at extremely high levels, indicating that future safety studies of molecules developed for CMT should also demonstrated acceptable safety profiles.