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Mariya Moosajee, Dhani Tracey-White, Matthew Smart, Carmen Bertoni, Timor Baasov, Andrew Webster; Comparative analysis of small molecule drugs for nonsense suppression therapy in Choroideremia. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1105.
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© 2017 Association for Research in Vision and Ophthalmology.
Small molecule drugs such as ataluren (PTC124), designer aminoglycosides (NB74, NB84 and NB124), and readthrough compounds (RTC13 and RTC14) have been shown to suppress disease-causing nonsense mutations, thus partially restoring full-length functional protein. This is a pharmacological form of gene therapy acting in a disease and gene independent manner. Choroideremia (CHM) is an X-linked recessive chorioretinal dystrophy with an incidence of 1:50,000-100,000. Over one-third of CHM patients harbour nonsense mutations in the CHM gene. The choroideremia zebrafish (chm-/-, p.Q32X UAA in exon 2) was used to compare the safety and efficacy of a range of nonsense suppression drugs to identify potential candidates for further preclinical development.
Dose response studies were conducted in wildtype embryos from 10 hours post fertilization (hpf) till day 5 with ataluren, NB74, NB84, NB124 and RTC13. Using the optimum dose: survival, morphology, renal function (through pericardial microinjections of rhodamine) and oto-toxicity (using 4-Di-2-ASP staining), retinal histology, levels of oxidative stress and cell death were measured. In addition, the presence of functional rep1 protein was assayed by western blot analysis and in vitro prenylation tests.
Ataluren (10μM), NB84 (3μM) and RTC13 (10μM) were the most efficacious compounds. Treated chm-/- embryos lived 2.0-fold longer, p<0.001 compared to untreated with significant rescue of retinal degeneration at day 6 and 10, and reduced levels of apoptotic cell death and oxidative stress. NB124 (10μM) had minimal effect on mutant embryos and was most toxic. NB74 (40μM) had more nonsense suppression activity than NB124, but did not exceed that of NB84. Western blot detected rep1 protein in ataluren, NB74, NB84 and RTC13 treated chm-/- samples with associated active prenylation suggesting restoration of function following these drug treatments.
This study provides ‘proof-of-concept’ for using nonsense suppression drugs, and highlights three candidates, ataluren, NB84 and RTC13, which have the most potential for treating nonsense-mediated choroideremia. Affected males develop night blindness in early childhood with progression to complete loss of vision in late adulthood. Thus, early administration could arrest disease progression and even prevent this form of genetic blindness.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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