INNOVATIONS IN RETINA

Gene Therapy for Retinal

BY ARON SHAPIRO

he eye is an ideal target for therapy. It is relatively small and highly compartmentalized, and it is an immune-privileged organ with well- ”The culmination of decades of defined targetable diseases known to benefit fromT prolonged therapy. It is also fairly easy to distin- scientific efforts resulted in the first guish both potential side effects and treatment benefits. approved clinical trial Gene therapy utilizes a viral vector to carry the in 1990.” desired genetic information—nucleic acids that encode a protein(s) of interest—to target cells; vectors that are successfully transduced into target cells utilize the cell’s machinery to express the protein(s) of interest. The goal carrying the p53 gene, and it was approved by the State of gene therapy is to provide a sustained therapeutic Food and Drug Administration of China for head and benefit via continual expression of the protein(s) that neck squamous cell carcinoma. Another significant step modulate the pathogenesis of the relevant . came in November 2012, when the European Medicines Although a full review of gene therapy is beyond the Agency first approved a gene therapy.6 Glybera, a des- scope of this article, this brief review provides an over- ignated orphan medication, is intended to treat lipo- view of current avenues of gene therapy research, focus- protein lipase (LPL) deficiency, a rare inherited disorder. ing on those that have progressed to clinical settings. Patients with the disorder cannot produce enough LPL, an enzyme responsible for breaking down fats, and fre- THE GENE THERAPY MOVEMENT quently experience life-threatening pancreatitis attacks. It has been more than a half century since the funda- Glybera uses an adeno-associated (AAV) vector to mental principles behind gene therapy were established.1 add working copies of the LPL gene into muscle cells to In the 1940s, nucleic acids were identified as the carriers enable production of the enzyme in muscle cells. of genetic information.2 The development of virus-based methods for delivering therapeutic to patients in A PRIMER ON VIRAL VECTORS the 1960s, coupled with the advent of recombinant DNA Viral vectors are a conduit for transferring genes to technology in the 1970s, kept the prospect of genetic human cells. There are two main categories: integrating medicine moving forward.3 The culmination of decades vectors and nonintegrating vectors. Integrating vectors of scientific efforts resulted in the first approved gene insert themselves into the recipient’s genome; nonin- therapy clinical trial in 1990. The study, run by Blaese and tegrating vectors usually form an extrachromosomal colleagues at the National Institutes of Health, involved genetic element.3 retroviral-mediated transfer of the gene encoding the Transduction with lentiviral vectors is a commonly enzyme adenosine deaminase into T cells of two children used method. Lentiviral vectors are integrating vectors with severe combined immunodeficiency.4 capable of rapidly infecting dividing and nondividing Despite the historically slow transition of genomic cells.7 They have a relatively large transgene carrying discoveries from the laboratory to the clinic, gene capacity.7 AAV vectors, which are nonintegrating vec- therapy is now emerging as a viable means of treating a tors, are among the most commonly used delivery sys- multitude of inherited diseases. In 2003, China became tems for ocular gene therapy. AAV is a member of the the first country to approve the commercial produc- Dependovirus group of the parvovirus family. Wild-type tion of a genetic therapy.5 The treatment, sold under AAVs are not implicated in disease (only associated the brand name Gendicine, is an adenovirus vector with mild immune responses) when unaccompanied by

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a “helper” adenovirus to coinfect cells.1 AAV serotypes are determined by the sequence of their capsid pro- teins. Several AAV serotypes have been identified, but ”Gene therapy is quickly becoming the most widely characterized and well-studied is AAV serotype 2 (AAV2). a reality for patients with inherited retinal diseases, as a number of PROGRAMS ON THE RISE therapies are now in clinical trials.” Gene therapy is quickly becoming a reality for patients with inherited retinal diseases, as a number of therapies are now in clinical trials. Avalanche Biotechnologies, which announced a and currently has five ongoing ophthalmic development collaborative agreement with Regeneron last year,8 programs in multiple indications.14 AGTC is developing is a biotechnology company with several novel gene gene therapy for X-linked juvenile retinoschisis (XLRS), an therapies in the pipeline. It has developed a technology inherited, early-onset retinal degenerative disease caused platform called Ocular BioFactory, wherein libraries of by mutations in the RS1 gene; it has received orphan non-naturally occurring are created through designations for this indication in both the United States mutagenesis. These libraries are screened for favorable and the European Union.14 Initial clinical data are expect- properties, and, through a process of directed evolu- ed to be released in the second half of 2015. tion, viral vectors with advantageous properties are Achromatopsia is an inherited condition associated produced. Its lead product, AVA-101, uses the AAV2 with visual acuity loss, light sensitivity, and reduced vector. Avalanche is developing its lead product to (sometimes complete) loss of color discrimination. be delivered as a single subretinal injection for the Although several genes can cause the disease, the most treatment of wet age-related common are CNGB3 and CNGA3. AGTC is working on (AMD). The AAV2 vector used by AVA-101 contains a program based on these genes: the therapy for CNGB3 a gene encoding sFLT-1, which is a naturally occurring has received orphan designation in the United States and anti-VEGF protein. When sFLT-1 is expressed by host the European Union, with initial clinical data anticipated retinal cells, it inhibits the formation of new blood ves- late in 2015, and the therapy for CNGA3 is slotted to sels, thereby reducing pathologic neovascularization.9 begin investigational new drug application–enabling AVA-101 is currently being studied in a phase 1/2a studies in the second half of 2015.14 trial10; top-line results are expected in mid-2015. Genzyme, a division of Sanofi, in-licensed AGTC’s AAV Spark Therapeutics’s most advanced product candi- program for wet AMD in 2004.15 The two companies are date for inherited retinal therapies, SPK-RPE65, which now working independently on their own AAV initia- utilizes an AAV vector, is currently in phase 3 devel- tives. Genzyme’s intravitreal injection of AAV2-sFLT01 is opment. Researchers are investigating the product as currently being studied in a phase 1 trial.16 a treatment for inherited retinal dystrophies caused Oxford Biomedica is widely known for its LentiVector by mutations in the RPE65 gene; earlier trials demon- platform, which is based on the recombinant equine strated the therapy’s safety and efficacy.11 Mutations in infectious anemia virus (EIAV). EIAV can be used in RPE65 are linked to ocular disease including subtypes many therapeutic areas but has specific advantages in of Leber congenital amaurosis (LCA) and retinitis pig- neurologic and ocular disorders. The company has five mentosa.12 Spark has received orphan product designa- ocular therapies, three of which are in active clinical tri- tion in both the United States and the European Union als: RetinoStat in a phase 1 study for treatment of wet for the treatment of patients with LCA due to RPE65 AMD17,18; StarGen in a phase 1/2a trial for treatment mutations. Late last year, SPK-RPE65 also received of Stargardt disease19,20; and UshStat in a phase 1/2a breakthrough therapy designation from the US Food study for treatment of Usher syndrome 1B.21,22 Oxford and Drug Administration (FDA) for the treatment of Biomedica announced a collaboration with Sanofi last nyctalopia (night blindness) in patients with LCA.13 A year.23 phase 3 trial of the safety and efficacy of gene therapy NightstaRx recently received orphan drug designation to address RPE65 mutations in subjects with LCA is from the FDA and the European Medicines Agency for ongoing, with data expected to be released in the sec- its lead program, AAV2-REP1, an AAV vector–based ond half of 2015.12 gene therapy to treat choroideremia,24 a rare X-linked The Applied Genetics Testing Corporation (AGTC) hereditary retinal dystrophy. Initial findings of the phase has developed an AAV-vector–manufacturing platform 1/2 trial reported that, 6 months after treatment with

APRIL 2015 RETINA TODAY 25 INNOVATIONS IN RETINA

the therapy, the first six subjects showed subjective improvement in their vision in dim light.25 The trial is ongoing, with the next six subjects receiving a higher dose of the viral therapy.26

CONCLUSION Vision loss from retinal disease is increasing. However, with a number of gene therapies moving forward in the clinic, there may soon be novel therapeutic options for these complex diseases. The approval of the first gene therapy in the European Union is a positive indicator for an approval in the United States. These new tech- nologies have the potential to become life-changing options for thousands of patients with inherited ocular diseases. n

Aron Shapiro is vice president of retina at Ora in Andover, Massachusetts.

1. Friedmann T. A brief history of gene therapy. Nat Genet. 1992;2(2):93-98. 2. Liu MM, Tuo J, Chan CC. Republished review: Gene therapy for ocular diseases. Postgrad Med J. 2011;87(1029):487-495. 3. Sheridan C. Gene therapy finds its niche. Nat Biotechnol. 2011;29(2):121-128. 4. Blaese RM, Culver KW, Miller AD, et al. T lymphocyte-directed gene therapy for ADA-SCID: initial trial results after 4 years. Science. 1995;270(5235):475-480. 5. Pearson S, Jia H, Kandachi K. China approves first gene therapy. Nat Biotechnol. 2004;22(1):3-4. 6. European Medicines Agency recommends first gene therapy for approval. http://www.ema.europa.eu/docs/ en_GB/document_library/Press_release/2012/07/WC500130146.pdf. Accessed February 27, 2015. 7. Greenberg K, Lee E, Schaffer D, Flannery J. Gene delivery to the retina using lentiviral vectors. In: Hollyfield J, Anderson R, LaVail M, eds. Retinal Degenerative Diseases. New York: Springer US; 2006:255-266. 8. Regeneron and Avalanche Biotechnologies announce collaboration to develop next-generation gene therapy products in ophthalmology [press release]. Tarrytown, NY: Avalanche Biotech; May 5, 2014. 9. Avalance Biotech: Pipeline: AVA-101. http://www.avalanchebiotech.com/pipeline-AVA-101.php. Accessed March 11, 2015. 10. Safety and efficacy study of rAAV.sFlt-1 in patients with exudative age-related macular degeneration (AMD). https://clinicaltrials.gov/ct2/show/NCT01494805. Accessed March 11, 2015. 11. Safety and efficacy study in subjects with Leber congenital amaurosis. https://clinicaltrials.gov/ct2/show/NC T00999609?term=Spark+Therapeutics&cond=inherited+retinal+dystrophies&rank=1. Accessed February 20, 2015. 12. Spark Therapeutics: inherited retinal dystrophies: overview: SPK-RPE65. http://www.sparktx.com/pipeline/ inherited-retinal-dystrophies#SPK-RPE65v. Accessed February 20, 2015. 13. Spark Therapeutics receives FDA breakthrough therapy designation for its lead product candidate, SPK-RPE65 [press release]. Philadelphia, PA: Spark Therapeutics; November 6, 2014. 14. AGTC: Products. http://www.agtc.com/products. Accessed February 26, 2015. 15. Genzyme, AGTC announce gene therapy collaboration [press release]. AGTC; December 6, 2004. 16. Safety and tolerability study of AAV2-sFLT01 in patients with neovascular age-related macular degeneration (AMD). https://clinicaltrials.gov/ct2/show/NCT01024998. Accessed February 26, 2015. 17. Phase I dose escalation safety study of RetinoStat in advanced age-related macular degeneration (AMD) (GEM). https://clinicaltrials.gov/ct2/show/NCT01301443?term=retinostat&rank=2. Accessed February 26, 2015. 18. A follow-up study to evaluate the safety of RetinoStat in patients with age-related macular degeneration. https://clinicaltrials.gov/ct2/show/NCT01678872?term=retinostat&rank=1. Accessed February 26, 2015. 19. Phase I/IIa study of StarGen in patients with Stargardt macular degeneration. https://clinicaltrials.gov/ct2/ show/NCT01367444?term=StarGen&rank=1. Accessed February 26, 2015. 20. A study to determine the long term safety, tolerability and biological activity of StarGen in patients with Stargardt’s macular degeneration. https://clinicaltrials.gov/ct2/show/NCT01736592?term=StarGen&rank=2. Accessed February 26, 2015. 21. Study of UshStat in patients with associated with Usher syndrome type 1B. https:// clinicaltrials.gov/ct2/show/NCT01505062?term=UshStat&rank=2. Accessed February 26, 2015. 22. A study to determine the long-term safety, tolerability and biological activity of UshStat in patients with Usher syndrome type 1B. https://clinicaltrials.gov/ct2/show/NCT02065011?term=UshStat&rank=1. Accessed February 26, 2015. 23. Oxford BioMedica and Sanofi Amend Terms for Ocular Licence [press release]. Oxford, UK: Oxford Biomedica; February 17, 2014. 24. NightStaRx: Project AAV2-REP1. http://www.nightstarx.com/technology/project-aav2-rep1/. Accessed March 12, 2015. 25. MacLaren RE, Groppe M, Barnard AR, et al. Retinal gene therapy in patients with choroideremia: initial findings from a phase 1/2 clinical trial. Lancet. 2014;383(9923):1129-1137. 26. Gene Therapy for Blindness Caused by Choroideremia. https://clinicaltrials.gov/ct2/show/ NCT01461213?term=AAV2-REP1.&rank=1. Accessed March 12, 2015.

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