The field of RNAi therapeutics has quickly adapted to the treatment of ocular diseases. Although the eye provides a unique system for the delivery of siRNAs, its complex structure and composition fostered the development of novel strategies for efficient gene silencing in the target compartment. Moreover, anterior and posterior segments differ in their multiple drug barriers and clearance mechanisms. This chapter summarizes the recent achievements in terms of routes of administration, chemical modifications, and delivery systems for siRNAs that specifically apply to eye disorders. Methods employed for siRNA detection/quantitation in ocular tissues are also described, together with safety concerns that need to be addressed to fulfill regulatory requirements of new drug approval. Even though RNAi therapies for ocular diseases have not yet translated into patient care, we document herein the rising number of candidate drugs currently under preclinical or clinical development.

Citation: Benitez-Del-Castillo JM, Moreno-Montañés J, Jiménez-Alfaro I, et al. Safety and efficacy clinical trials for SYL1001, a novel short interfering RNA for the treatment of dry eye disease. Invest Ophthalmol Vis Sci. 2016;57:6447–6454. DOI:10.1167/ iovs.16-20303 PURPOSE. To evaluate the efficacy and safety of SYL1001, a short interfering (si) RNA targeting the transient receptor potential cation channel subfamily V member 1 (TRPV1), for the treatment of dry eye disease (DED).

Purpose To evaluate the efficacy and safety of SYL1001, a short interfering (si) RNA targeting the transient receptor potential cation channel subfamily V member 1 (TRPV1), for the treatment of dry eye disease (DED). Methods This study combines a phase I and two phase II clinical trials to test different doses of SYL1001 in a total of 156 healthy subjects and patients with DED. After 10 days of treatment, the primary efficacy endpoints were the effect on (1) the scoring in the Visual Analogue Scale (VAS) and Ocular Surface Disease Index (OSDI) questionnaires, and (2) ocular tolerance evaluated by corneal fluorescein staining and conjunctival hyperemia. Secondary endpoints included the assessment of systemic and local tolerance. Results Topical administration of SYL1001 1.125% once daily produced a significant decrease in VAS scores compared with placebo from day 4 until the end of treatment (change from baseline at day 10: -1.73 ± 0.32 vs. -0.91 ± 0.34; P = 0.013). For all treatments, OSDI scores were significantly reduced compared to their respective baseline values (P < 0.01), although no significant changes were detected between groups. Conjunctival hyperemia (quantified as normal or abnormal) significantly improved after instillation of SYL1001 1.125% compared with placebo (50% vs. 20%; P < 0.05). Excellent tolerability was reported, with no differences in the rates of occurrence of adverse events between groups. Conclusion These trials achieved their primary endpoints of identifying the most effective dose of SYL1001 (1.125%). SYL1001 showed a large safety margin and may provide novel therapeutic opportunity for the relief of dry eye. (ClinicalTrials.gov numbers, NCT01438281, NCT01776658, and NCT02455999.).

RNA interference (RNAi) is a posttranscriptional mechanism of gene regulation present in eukaryotic cells. Inducers of RNAi are small molecules of RNA that act in the cyto‐ plasm where they are able to impair translation of a specific mRNA to protein, hence modifying gene expression. The discovery of this mechanism in mammals led to the de‐ velopment of a new class of therapeutics with the aim of exploiting this endogenous mechanism of action. In the last decade, great efforts have been put into understanding RNAi and translating this accumulated knowledge into the design of modern therapeu‐ tics. With several compounds in phase III clinical development, the field is getting closer to its first market authorization. Here we make a thorough overview of the field of RNAi therapeutics in ophthalmology, one of the fields in which RNAi has been most successful.

RNA interference is a cellular mechanism by which small molecules of double stranded RNA modulate gene expression acting on the concentration and/or availability of a given messenger RNA. Almost 10 years after Fire and Mello received the Nobel Prize for the discovery of this mechanism in flat worms, RNA interference is on the edge of becoming a new class of therapeutics. With various phase III studies underway, the following years will determine whether RNAi-therapeutics can rise up to the challenge and become mainstream medicines. The present review gives a thorough overview of the current status of this technology focusing on the path to the clinic of this new class of compounds.

Glaucoma is a progressive ocular syndrome characterized by degeneration of the optic nerve and irreversible visual field loss. Elevated intraocular pressure (IOP) is the main risk factor for glaucoma. Increased IOP is the result of an imbalance between synthesis and outflow of aqueous humor (AH). Blocking β2 adrenergic receptor (ADRB2) has shown to reduce IOP by decreasing production of AH at the ciliary body (CB). SYL040012 is a siRNA designed to specifically silence ADRB2 currently under development for glaucoma treatment. Here, we show that SYL040012 specifically reduces ADRB2 expression in cell cultures and eye tissues. The compound enters the eye shortly after administration in eye drops and is rapidly distributed among structures of the anterior segment of the eye. In addition, SYL040012 is actively taken up by cells of the CB but not by cells of systemic organs such as the lungs, where inhibition of ADRB2 could cause undesirable side effects. Moreover, SYL040012 reduces IOP in normotensive and hypertensive animal models and the effect appears to be long lasting and extremely well tolerated both locally and systemically.

RNA interference is an endogenous mechanism present in most eukaryotic cells that enables degradation of specific mRNAs. Pharmacological exploitation of this mechanism for therapeutic purposes attracted a whole amount of attention in its initial years, but was later hampered due to difficulties in delivery of the pharmacological agents to the appropriate organ or tissue. Advances in recent years have to a certain level started to address this specific issue. Genetic diseases are caused by aberrations in gene sequences or structure; these particular abnormalities are in theory easily addressable by RNAi therapeutics. Sequencing of the human genome has largely contributed to the identification of alterations responsible for genetic conditions, thus facilitating the design of compounds that can address these diseases. This review addresses the currently on-going programs with the aim of developing RNAi and other antisense compounds for the treatment of genetic conditions and the pros and cons that these products may encounter along the way. The authors have focused on those programs that have reached clinical trials or are very close to do so.

INTRODUCTION The superfamily of transient receptor potential (TRP) cation channels is involved in nociception. Members of this family, such as the vanilloid receptor type 1 (TRPV1) channel, are activated by a wide range of stimuli including heat (⟩43°C), low pH (⟨6.5), hypoxia, and hypertonicity. Here we report TRPV1 expression in rabbit and human eyes. MATERIAL AND METHODS We analyzed the expression of TRPV1 mRNA by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and protein by immunohistochemistry in eyes of New Zealand White rabbits and humans. RESULTS In rabbit and human eyes, TRPV1 protein was present in all layers of the corneal epithelium, but only in the basal layer of the conjunctiva. It was also in the ciliary and lens epithelia of both species as well as in the secretory cells of the rabbit lacrimal gland. The retinal pigment epithelium was positive for this protein in both species. TRPV1 was also present in rabbit Müller cells, where it had a similar pattern of expression to vimentin intermediate filaments. Analysis by qRT-PCR showed that TRPV1 mRNA was found in all of the structures where the protein was present. The highest level was in the lens and the lowest in the retina. CONCLUSION TRPV1 is expressed in cells that are particularly active in Ca²⁺ exchange as well as in cells with significant water transport activity. Because TRPV1 is a Ca²⁺ channel, it probably functions in the regulation of both water and Ca²⁺ movements in ocular tissues.

The central dogma of biology describes the transfer of biological information from DNA through to protein (Crick, 1970). In the first phase, known as transcription, DNA is converted into a complementary sequence of messenger RNA (mRNA). This mRNA allows the genetic message to be communicated outside of the nucleus, to other areas of the cell, where it is then translated into protein by ribosomes. Most human diseases arise from increased function or dysfunction of proteins within the body. Since these proteins are generated from DNA via mRNA, modulation of this flow of genetic information can convey a therapeutic effect on the disease state. Mammalian cells possess the genetic instruction to make 50,000 to 100,000 different proteins but only 10-20% of these are found in any single cell. Therefore, a gene must contain instructions for the regulation of the production of protein in correct amounts and at the correct time for each cell type. Gene regulation is one of the most complex molecular processes known, involving up to 10% of the proteins that cells produce. In 1998, Andrew Fire and Craig Mello described RNAi as an endogenous gene expression pathway activated by double-stranded RNA (dsRNA) in the worm Caenorhabditis elegans. For this pioneering work, Fire and Mello were awarded the 2006 Nobel Prize in Physiology or Medicine. The discovery of the natural RNAi mechanism for sequence-specific gene silencing launched a new era in antisense technology. During the 1990s, a number of genesilencing phenomena that occurred at the posttranscriptional level were discovered in plants, fungi, animals and ciliates, introducing the concept of post-transcriptional gene silencing (PTGS) or RNA silencing (Baulcombe, 2000; Matzke et al., 2001). The most important technologies for gene suppression are: antisense oligonucleotides, aptamers, ribozymes and RNA interference (RNAi). The first report that gene expression could be modulated by the use of reverse complementary (antisense) oligonucleotides was made in 1978. Antisense molecules are synthetic segments of DNA or RNA, designed to mirror specific mRNA sequences and block protein production, these molecules are designed to inhibit translation of a target gene to protein via interaction with mRNA. Aptamers are single-strand DNA or RNA oligomers, which can bind to a given ligand with high affinity and specificity due to their particular 3-D structures and thereby antagonize the biologic function of the ligand. Recent developments demonstrate that aptamers are valuable tools for diagnostics, purification processes, target validation, drug discovery and therapeutics. Ribozymes are