Treating IRDs: Gene-Specific and Gene-Independent Approaches

A review of the different approaches to treating IRDs.

BY ALESSANDRO IANNACCONE, MD, MS, FARVO

ith more than 300 disease- other approaches are necessary. Thus, this group of retinopathies is primar- causing genes mapped and gene/disease–independent treat- ily of the Leber congenital amaurosis more than 260 cloned,1 the ments (Figure 1B) are a top priority. (LCA) and early-onset retinitis pig- field of inherited retinal dis- This article reviews the state of IRD mentosa type, affecting a relatively eases (IRDs) has experienced treatment approaches. small group of patients with IRDs. Wtremendous advances over the past Thus, much work (and opportunity) is 2 decades. This vast genetic heterogene- GENE/DISEASE–SPECIFIC TREATMENTS ahead in the field for additional gene ity represents both a great opportunity The field of gene augmentation therapies to be tested in human clini- and a remarkable challenge. therapy (gene therapy for short) wit- cal trials and, one hopes, to become The identification of the causes of nessed a major breakthrough with approved treatments for patients with so many forms of IRD and the growing the US FDA approval of voretigene IRDs. A list of such trials is provided in body of knowledge of their functions neparvovec-rzyl (Luxturna, Spark Table 1 in alphabetical order, and the and underlying disease mechanisms Therapeutics) for RPE65-related reti- list is growing rapidly. have allowed the development of nopathies.2,3 Although this approval It should be emphasized that, exciting new gene/disease–specific created major momentum in the field, for gene therapy to be possible, treatment opportunities (Figure 1A). However, the development and deliv- ery to bedside of gene/disease–specific treatments for each of the genes identi- AT A GLANCE

fied to date are daunting tasks that may s require decades for full implementation. The development and delivery to bedside of gene/disease–specific With exciting new treatments treatments for each of the IRD-related genes identified to date is a daunting now aimed at an even more granular task that may take decades. level—targeting not just specific genes but, in fact, specific mutations—the s Most gene therapy trials for IRDs rely on adeno-associated virus task at hand is expanded by several orders of magnitude. Furthermore, vector–based gene therapy and subretinal injection delivery.

gene/disease–specific treatments rely s on persistent target cells and sufficient Efforts are underway to identify improved viral vectors that can achieve ade- visual function to permit efficacy. quate, widespread transfection through the intravitreal route and to develop For the many patients who are out- thin transvitreal cannulas that do not require vitrectomy. side of this window of opportunity,

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Figure 1. Researchers are exploring two pathways for treating IRDs—one that directly addresses underlying genetic dysfunction (A) and one that seeks to address the downstream effects of genetic mutation (B). knowledge of the causal gene for each or areas to be treated must also be implement gene editing strategies.5,6 disease and in each patient is neces- chosen carefully, aiming for areas that For example, a “cut and remove” strat- sary, underscoring the importance display residual target cell integrity egy is being tested in the LCA-CEP290 of genotyping affected patients via and, ideally, measurable function. For Editas trial (Table 1). CLIA-certified diagnostic laboratories. example, there may be little to no Correction of the genetic defect At this stage of the gene therapy benefit in treating eyes with no mea- downstream of the DNA sequence era for IRDs, most trials rely on adeno- surable rod-mediated function if the by targeting messenger RNA (mRNA) associated virus (AAV) vector–based gene to be delivered is a rod-specific instead. In this approach, editing gene therapy and a subretinal injection one. Exceptions to this rule of thumb antisense oligonucleotides (eAONs) approach, as does voretigene. In most exist, however, and the RPE65-related of the ongoing trials, the aim is to retinopathies are a perfect example of deliver a copy of the normal gene into this. In these conditions, there can be a RETINA TODAY photoreceptor or retinal pigment epi- significant mismatch between function thelium cells using the AAV vectors. and structural integrity.4 ON THE ROAD This invasive approach requires a Other emerging strategies for gene full-fledged vitrectomy and retinotomy therapy include the following: This article is adapted from a lecture the to deliver the treatment subretinally. Gene editing using CRISPR/Cas9– author presented at the Duke Fellows A key limitation of this approach is based technology, in which clustered Advanced Vitreous Surgery Course in that it is not possible to deliver gene regularly interspaced short palindrom- April. The 2020 meeting will be held April therapy to the entire retina, but rather ic repeats (CRISPR) complexed with one or more areas must be chosen to a CRISPR-associated (Cas) nuclease 17-18, 2020, in Durham, North Carolina. receive the subretinal bleb that will can be used to create breaks in DNA Visit MedConfs.com for details. define the treated area. Thus, the area sequences that can then be used to

JULY/AUGUST 2019 | RETINA TODAY 17 - - Intravitreal Intravitreal Intravitreal Route of Route of Administration Subretinal Subretinal Subretinal Subretinal Subretinal Subretinal Intravitreal Subretinal Subretinal Subretinal Subretinal Subretinal Subretinal Subretinal Subretinal patients after a singlea after patients

Another trial, for Usherfor trial, Another 7 CEP290 Disease-specific trials, unliketrials, Disease-specific Nonetheless, there is now publishednow is there Nonetheless, ogy is delivering measurable benefitsmeasurable delivering isogy LCA- to injection. andbegun, has 2A, type syndrome relativelythe for planned are more future. near tack at aimed are trials, gene-specific circumventingor mechanisms ling multiple specific treatments for eachfor treatments specific multiple patients.all treat to able be to gene technol eAON-based that evidence rAAV2 vector–based rAAV2 vector–based rAAV2/5 vector–based rAAV8 vector–based rAAV2 vector–based AAV8-RPGR vector–based Lentivirus vector–based Lentivirus vector–based Editing antisense oligonucleotides rAAV2 vector–based rAAV vector–based Treatment Method rAAV2tYF vector–based rAAV2/8 vector–based rAAV2tYF vector–based rAAV2/8 vector–based rAAV2 vector–based CRISPR/Cas9 gene editing Editing antisense oligonucleotides a NCT03602820 NCT02946879 NCT03328130 NCT03374657 NCT03316560 NCT03116113 NCT01367444 NCT01505062 NCT03780257 NCT02416622 NCT02317887 NCT Number NCT02935517 NCT03758404 NCT02599922 NCT03001310 NCT03507686 NCT03496012 NCT03584165 NCT03396042 NCT03140969 Spark Therapeutics MeiraGTx Horama Novartis AGTC NightStar/Biogen Sanofi Sanofi ProQR AGTC National Eye Institute Sponsor AGTC MeiraGTx AGTC MeiraGTx NightStar/Biogen Editas/Allergan ProQR currently mutation- or exon-specific,or mutation- currently developto need a is there meaning in theory, reach any part of the retinathe of part any reach theory, in therapy.to responding of capable hasapproach latter the Although itsadvantages—namely, inherent panretinaland administration of ease treatmentthe of effects reach—the incorrect because time over diminish producedbe to continues mRNA patient.the of DNA mutated the by Therefore, repeated periodic injections istechnology thisAlso, needed. are -

exon 13 REP1 / TABLE 1. ONGOING GENE/DISEASE–SPECIFIC TREATMENT TRIALS TREATMENT GENE/DISEASE–SPECIFIC TABLE 1. ONGOING RPGR RPGR ABCA4 MYO7A USH2A RS1 RS1 CEP290 p.Cys998X mutation CEP290 p.Cys998X mutation RPE65 RPE65 PDE6B RLBP1 Gene/Mutation CNGA3 CNGA3 CNGB3 CNGB3 CHM1

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At present, CRISPR/Cas9–basedpresent, At www.clinicaltrials.gov. X-linked retinoschisis a Stargardt disease Stargardt disease Usher syndrome type 1B Usher syndrome type 2A Retinitis pigmentosa, autosomal Retinitis pigmentosa, autosomal recessive Retinitis pigmentosa, X-linked Choroideremia Choroideremia Leber congenital amaurosis Achromatopsia Achromatopsia Disease technology relies on the same AAVsame the on relies technology currentas approaches vector–based areeAONs whereas therapies, gene injectedbe can that molecules small leastat can, they Thus, intravitreally. after DNA transcription but beforebut transcription DNA after pro resulting the that so translation improvedgreatly or normalized is tein versionmutated the with compared inused being is strategy This thereof. 1). (Table trials ProQR the are used to correct the target defecttarget the correct to used are RETINA TODAY

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TABLE 2. ONGOING DISEASE/MECHANISM–SPECIFIC TREATMENT TRIALS Disease Gene/Mutation Sponsor NCT Numbera Treatment Method Route of Administration Leber congenital amaurosis LRAT, RPE65 QLT/Aegerion NCT01014052 Synthetic 9-cis-retinal Oral NCT01521793 Stargardt disease ABCA4 Acucela NCT03772665 Emixustat Oral ABCA4 Alkeusb NCT02402660 Deuterated vitamin A Oral ABCA4 Moran Eye Center NCT00346853 4-methylpyrazole (4-MP, Antizol) Oral ABCA4 Iveric Bio** NCT03364153 Zimura (complement C5 inhibitor) Intravitreal injection a www.clinicaltrials.gov. b Also ongoing in geographic atrophy.

TABLE 3. GENE/DISEASE–INDEPENDENT TREATMENT TRIALS Disease Sponsor Trial Numbera Treatment Method Route of Administration Nutritional Approaches Retinitis pigmentosa Wilmer Eye Institute, Johns NCT03063021 N-acetyl-cysteine (NAC) Oral Hopkins University Stargardt disease Catholic University of the Sacred NCT01278277 Saffron Oral Heart, Rome Stem Cell–Based Treatments Retinitis pigmentosa JCyte NCT03073733 Dissociated human retinal progenitor Intravitreal injection cells (hRPC) ReNeuron NCT02464436 Human retinal progenitor cells (hRPC) Subretinal transplant Stargardt disease Astellasb NCT01345006 MA09-hRPE, human embryonic stem Subretinal injection cell–derived RPE Artificial Vision/Devices and Hybrid Methods Retinitis pigmentosa Second Sight N/A (FDA approved) Argus II retinal prosthesis Surgical implant + device use Allergan/RetroSense NCT02556736 rAAV2/2 vector–based Intravitreal injection GenSight NCT03326336 rAAV2.7m8 viral vector–based + visual Intravitreal injection + interface stimulating glasses device use

* www.clinicaltrials.gov. ** Also ongoing in geographic atrophy. Abbreviations: FDA, US Food and Drug Administration; N/A, not applicable; RPE, retinal pigment epithelium. defects that are unique to a particular GENE/DISEASE–INDEPENDENT advanced disease for whom gene- condition (Table 2). Examples of these TREATMENTS specific treatments are no longer include the recent trials in patients Nutritional antioxidant and neuro- an option, or are visual restoration with RPE65- and LRAT-associated protective approaches to IRDs have options for conditions in which the LCA using synthetic 9-cis-retinal8,9 been tested with partial success over benefit of gene-specific approaches and trials aimed at impeding the past few decades,10-16 and some is limited to the remaining tissue but vitamin A–mediated lipofuscin accu- evidence-based promising ones are cannot be extended to other more mulation and toxicity in the retinal now being tested as well (Table 3). affected areas (eg, macular atrophy pigment epithelium of patients with Other approaches in this realm are in Stargardt disease). The only such Stargardt disease. mainly aimed at IRD patients with method that is approved by the

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[email protected] Financial disclosure: Consultant (Astellas Institute Professor of Ophthalmology, Duke University Professor of Ophthalmology, Duke University Director, Duke Center for Retinal Degenerations and Ophthalmic Genetic Diseases and Duke Eye and Ophthalmic Genetic Diseases and Duke Eye Center Visual Function Diagnostic Laboratory, Durham, North Carolina for Regenerative Medicine, ClearView Healthcare Partners, Editas Medicine, GLG Group, Guidepoint, Huron Consulting Group, Ionis Pharmaceuticals, IQVIA, Rhythm Pharmaceuticals, Roivant Pharma) School of Medicine, Durham, North Carolina    15. Hughbanks-Wheaton DK, Birch DG, Fish GE, et al. Safety assessment of docosahexaenoic acid in X-linked retinitis pigmentosa: the 4-year DHAX trial. Invest Ophthalmol Vis Sci 2014;132:866-873. 17. da Cruz L, Dorn JD, Humayun MS, et al. Five-year safety and performance results from the Argus II retinal prosthesis system clinical trial. congenital amaurosis caused by RPE65 mutations: safety and efficacy in 15 caused by RPE65 mutations: safety and congenital amaurosis up to 3 years. children and adults followed in TS, Cideciyan AV, et al. Identifying photoreceptors 4. Jacobson SG, Aleman gene therapy RPE65 mutations: prerequisite for human blind eyes caused by success. light: gene and cell O, Marazova K, Sahel JA. Let there be 5. Dalkara D, Goureau therapy for blindness. therapeutic strategies for patients with 6. Zheng A, Li Y, Tsang SH. Personalized retinitis pigmentosa. et al. Effect of an intravitreal antisense 7. Cideciyan AV, Jacobson SG, Drack AV, amaurosis due to a photoreceptor oligonucleotide on vision in Leber congenital cilium defect. medical therapy for retinal degen 8. Iannaccone A, Zarbin MA. A new era in erative disease? 9-cis retinoid for childhood blind 9. Koenekoop RK, Sui R, Sallum J, et al. Oral caused by RPE65 or LRAT mutations: ness due to Leber congenital amaurosis an open-label phase 1b trial. al. A randomized trial of vitamin 10. Berson EL, Rosner B, Sandberg MA, et pigmentosa. A and vitamin E supplementation for retinitis 1993;111:761-772. al. Clinical trial of lutein in 11. Berson EL, Rosner B, Sandberg MA, et vitamin A. patients with retinitis pigmentosa receiving Ophthalmol n n outcomes of the DHAX trial. 16. Hoffman DR, Hughbanks-Wheaton DK, Pearson NS, et al. Four-year placebo-controlled trial of docosahexaenoic acid in X-linked retinitis pigmentosa (DHAX trial): a randomized clinical trial. 2016;123:2248-2254. 18. Ho AC, Humayun MS, Dorn JD, et al. Long-term results from an epiretinal prosthesis to restore sight to the blind. 19. Dalkara D, Duebel J, Sahel JA. Gene therapy for the eye focus on mutation- independent approaches. 20. Baker CK, Flannery JG. Innovative optogenetic strategies for vision restora tion. 21. Sahel JA, Leveillard T. Maintaining cone function in rod-cone dystrophies. Adv 22. Lobanova ES, Finkelstein S, Li J, et al. Increased proteasomal activity sup ports photoreceptor survival in inherited retinal degeneration. 2018;9:1738. 23. Iannaccone A, Radic MZ. Increased protein citrullination as a trigger for resident immune system activation, intraretinal inflammation, and promotion of anti-retinal autoimmunity: intersecting paths in retinal degenerations of potential therapeutic relevance. 24. Wheelock RM, Sieving PA, Aleman TS, et al. Special interest group (SIG) meeting: protection, correction, regeneration: are combination therapies in the future for inherited retinal degenerations? Paper presented at: Association for Research in Vision and Ophthalmology Annual Meeting; April 28, 2019; Vancouver, British Colombia. ALESSANDRO IANNACCONE, MD, MS, FARVO n n 2011;128:403-411. 12. Berson EL, Rosner B, Sandberg MA, et al. Clinical trial of docosahexaenoic acid in patients with retinitis pigmentosa receiving vitamin A treatment. 13. Berson EL, Rosner B, Sandberg MA, et al. Further evaluation of doco sahexaenoic acid in patients with retinitis pigmentosa receiving vitamin A treatment: subgroup analyses. 14. Hoffman DR, Hughbanks-Wheaton DK, Spencer R, et al. Docosahexaenoic acid slows visual field progression in X-linked retinitis pigmentosa: ancillary - . - - - Lancet 24 -

21 n

22,23 Although many challenges remainchallenges many Although Finally, as recently discussed at theat discussed recently as Finally, Other such gene-independentsuch Other Likewise, growth in gene/disease– in growth Likewise, neparvovec (AAV2-hRPE65v2) in patients with RPE65-mediated inherited retinal dystrophy: a randomised, controlled, open-label, phase 3 trial. 2017;390:849-860. 3. Jacobson SG, Cideciyan AV, Ratnakaram R, et al. Gene therapy for Leber for the treatment of IRDs, the field isfield the IRDs, of treatment the for momentum,tremendous experiencing treat of number increasing an and available.becoming are options ment topotential the hold treatments These forprognosis the improve significantly otherwisethese by affected patients atand debilitating, visually progressive, disorders. blinding times 1. RetNet Retinal Information Network. https://sph.uth.edu/Retnet/. Accessed June 19, 2019. 2. Russell S, Bennett J, Wellman JA, et al. Efficacy and safety of voretigene of patients with IRDs. with patients of Vancouver, in meeting 2019 ARVO careof standards the from drawing timethe oncology, in trials clinical and IRDsfor therapies combination for whichin Trials nearing. be to appears mayapproaches gene/disease–specific onesnonspecific with combined be be can agents) neuroprotective (eg, future.near the in envisioned CONCLUSION tive and rescuing effects on cones. on effects rescuing and tive prove could this as such approach An rodprimary with patients for invaluable damagerod much too whom in diseases genewhom in and occurred already has pro normal a restoring at aimed therapy belonger no may rods in expression tein approach.viable a thetargeting include may directions toxicof accumulation intracellular proinflamma certain and compounds retinasthe in occur that changes tory transvitreal cannulas that do not requirenot do that cannulas transvitreal devices. suprachoroidal or vitrectomy a willoptions treatment independent widelymore for opportunity an afford examplesuch One therapies. applicable Sparingby planned being trial the is work is that company French a Vision, rod-derivedwith trials launching on ing thioredoxin-likea factor, viability cone normallyis that molecule antioxidant protec has that and rods by produced ------Thus, 19,20 . In this cate this In .

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Major efforts are also underway tounderway also are efforts Major Options for treatment of geneticof treatment for Options Despite the legitimate excitementlegitimate the Despite Ongoing experimental approachesexperimental Ongoing identify improved viral vectors thatvectors viral improved identify widespread adequate, an achieve can intravitrealthe through rate transfection treat alternative develop to and route thinas such approaches, delivery ment gory are the ELX compounds in devel in compounds ELX the are gory APharmaceuticals. Eloxx by opment usedis approach mechanistic similar anTherapeutics), (PTC Ataluren by intested being drug suspension oral diseases.genetic other conditions caused by nonsense muta nonsense by caused conditions Thesedeveloped. being also are tions ofdelivery subcutaneous include aminoglycosidessynthetic advanced read- translational as optimized or drugs, through further development of CRISPR/Cas9– of development further through higher and treatments, based mRNA-targetingof development put both improve to promise approaches theand therapy gene of efficacy the diseases. treatable of range tremendous momentum it is expe is it momentum tremendous developto need a is there riencing, admin easily more and effective more effortsongoing The treatments. istered viralof limitations the overcome to thetherapies, gene vector–based (ganglion cells) light detection ability byability detection light cells) (ganglion approachessimilar themselves.Other development.under are FUTURE DIRECTIONS theand IRDs of field the surrounding pigments that are normally found onlyfound normally are that pigments microalgae. light-sensitive in pho bypass to aim approaches these theconferring by damage toreceptor nor that cells to light detect to ability minimalor cells) (bipolar no have mally include intravitreally injected or sub or injected intravitreally include andcells stem implanted retinally AAVan use that treatments hybrid todeliver to approach vector–based encodinggenes artificial retina inner the visual light-sensing rhodopsin-like for FDA is the Argus II retinal prosthesisretinal II Argus the is FDA Sight). (Second RETINA TODAY

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