Sue Fletcher

Purpose : There are no therapeutic options for Retinitis Pigmentosa type 11 (RP11), a blinding inherited retinal disease caused by haploinsufficiency of the PRPF31 (pre-mRNA processing factor 31) gene. VP-001 has been developed to upregulate PRPF31 protein by downregulating CNOT3 protein expression. CNOT3 negatively regulates PRPF31 by interacting with the PRPF31 promoter region. VP-001 successfully downregulated CNOT3 protein by skipping exon 17 of CNOT-3 pre-mRNA, and upregulated PRPF31 gene expression and the protein in patient derived cellular models. No observed adverse effect level (NOAEL) of VP-001 was established in rabbits and monkeys. Subsequently, a single ascending dose first in human study was started to evaluate initial safety and tolerability of VP-001.

Methods : An open-label, single ascending dose study, recruited participants with genetically confirmed PRPF31 mutation in 3 cohorts. Study eyes received an intravitreal injection of VP-001 (3 µg, 10 µg, 30 µg) and are then followed for 24-week and 48-week time period for incidence, severity and relatedness of ocular treatment-emergent adverse events and treatment-emergent serious adverse events. Three subjects are enrolled for each cohort, and the dose escalation is based on review by a safety review committee (SRC) using 4-week and incremental data collected after each cohort dosing. Safety and tolerability are evaluated based on adverse event (ocular and non-ocular) reporting, that includes clinical chemistry parameters, best corrected visual acuity, perimetry, microperimetry, slit lamp and fundus examination, fundus autofluorescence imaging, and spectral-domain optical coherence tomography.

Results : Six participants (3 µg and 10 µg cohorts) were enrolled till date. No drug related adverse events and no intraocular inflammation were observed at 4 weeks for 10 µg cohort, and at 4 weeks and 12 weeks for 3 µg cohort. Third cohort will receive 30 µg dose, and the safety data collected at day 2, day 14 and week 4 will be reviewed by the SRC. Safety of all the participants will be followed for 24 and 48 weeks.

Conclusions : A single intravitreal injection of VP-001 was safe and well tolerated at 3 µg and 10 µg doses. A 30-µg dose is also administered, and if shown safe at week 4, a 75-µg dose cohort may be added to the study based on recommendation by the SRC. Data from all 3 cohorts will be presented.

Duchenne muscular dystrophy (DMD) is an X-linked, relentlessly progressive muscle wasting disorder, caused by mutations in the DMD gene that compromise function of dystrophin, a sub sarcolemmal protein. DMD has a predictable course and limited treatment options, with the majority of cases being caused by frame-shifting deletions of one or more of the 79 exons of DMD. Deletions that do not disrupt the dystrophin open reading frame generally cause the milder allelic disorder, Becker muscular dystrophy (BMD). Antisense oligomer (AO)-mediated splicing manipulation can remove specific exons during transcript processing to reframe the transcript and overcome DMD-causing dystrophin gene lesions to generate shorter, partially functional dystrophin isoforms, and is showing promise as a therapy for DMD. Dystrophin gene structure in patients with mild phenotypes can provide templates for potentially functional dystrophin isoforms. However, such mutations downstream of exon 55 are rare, and the probable consequences of AO-induced exon removal in this region are not known. We report that systemic administration of antisense phosphorodiamidate morpholino oligomer-cell penetrating peptide conjugates to wild-type C57BL/10ScSn mice can remove dystrophin exons to generate in vivo dystrophic models for molecular, physiological and pathology evaluation. Exclusion of selected exons within the b dystroglycan and syntrophin binding domains is elucidating the relative importance of these regions to dystrophin function, and may provide guidelines for the development of therapeutic exon skipping strategies.

Background. Antisense oligonucleotides can redirect the pre-mRNA processing of targeted gene transcripts. Therapeutic alternative splicing can be employed excise a selected exon or enhance recognition of an exon normally excluded from the mature mRNA. Aims. Duchenne muscular dystrophy (DMD), the most common and serious form of childhood muscle wasting, arises from protein truncating mutations in DMD that preclude synthesis of a functional protein. We aim to specifically redirect dystrophin pre-mRNA processing so that one or more exons can be excluded from the mature mRNA. Depending upon the DMD mutation, the reading frame can be restored, or intra-exonic protein truncation mutations can be bypassed, allowing an internally deleted but functional dystrophin isoform to be produced. Methods. Targeting dystrophin exon 51 for excision should restore functional dystrophin expression in the most common subset of DMD deletion patients. An extended placebo-controlled study was initiated under the sponsorship of Sarepta therapeutics in Nationwide Children’s Hospital, Columbus Ohio. Results. The trial has now been extended out to over 2 years and clinically significant differences were observed, with treated boys maintaining similar levels of ambulation over the trial period. No serious adverse events have been reported and the trial remains ongoing. Additional oligomers are being designed to address different dystrophin mutations, and new clinical trials should be underway in 2014. Summary. The promising DMD trial results have renewed enthusiasm to pursue splice intervention therapies for other disorders. Spinal muscular atrophy, cystic fibrosis, facioscapulohumeral muscular dystrophy, asthma, Alzheimer’s, Parkinson’s and stroke are just some of the conditions under investigation. An estimated 15% of human mutations induce aberrant splicing and splice switching oligomers may be used as a personalized genetic therapy, regardless of the mutated gene.