Layer-specific nanophotonic delivery of therapeutic opsin-encoding genes into retina

Toward successful retinal drug delivery after intravitreal injection: Current strategies to overcome the inner limiting membrane

The global prevalence of retinal disorders leading to vision impairment and blindness is rising to significant numbers and is estimated to continuously increase in the coming years. Although many groundbreaking therapies are available in the expanding field of retinal gene and cell therapy, troublesome delivery after intravitreal (IVT) injection is currently complicating their clinical translation. In this regard, the inner limiting membrane (ILM), the basement membrane located between the vitreous and the retina, is recognized as the main obstacle hindering retinal entry. Overcoming this barrier might hence advance a plethora of potent therapeutics currently available but failing to enter the retina. Aware of the importance to address this drug delivery issue, this review will discuss the current proposed methods to tackle the ILM barrier. First, we will provide an overview of ILM characteristics in health and disease after which we will reflect on the relevance of the ILM barrier role for emerging advanced therapeutic strategies. Seeing the significance of ILM removal for those therapeutics, the current proposed surgical, pharmacological and physical strategies to bypass the ILM will furthermore be highlighted to encourage the entire field of retinal drug delivery after IVT injection forward.

Engineered sensor actuator modulator as aqueous humor outflow actuator for gene therapy of primary open-angle glaucoma

Glaucoma, a blinding eye disease with optic neuropathy, is usually associated with elevated intraocular pressure (IOP). The currently available pharmacological and surgical treatments for glaucoma have significant limitations and side effects, which include systemic reactions to medications, patient non-compliance, eye infections, surgical device failure, and damage to the eye. Here, we present Sensor-Actuator-Modulator (SAM), an engineered double mutant version of the bacterial stretch-activated mechanosensitive channel of large conductance (MscL) that directly senses tension in the membrane lipid bilayer of cells and in response, transiently opens its large nonspecific pore to release cytoplasmic fluid. The heterologously expressed mechanosensitive SAM channel acts as a tension-activated pressure release valve in trabeculocytes. In the trabecular meshwork (TM), SAM is activated by membrane stretch caused by elevated IOP. We have identified several SAM variants that are activated at physiologically relevant pressures. Using this barogenetic technology, we have demonstrated that SAM is functional in cultured TM cells, and successfully transduced in vivo in TM cells by use of AAV2/8. Further, it is effective in enhancing aqueous humor outflow facility leading to lowering the IOP in a mouse model of ocular hypertension.

Recently Approved Drugs for Lowering and Controlling Intraocular Pressure to Reduce Vision Loss in Ocular Hypertensive and Glaucoma Patients

Serious vision loss occurs in patients affected by chronically raised intraocular pressure (IOP), a characteristic of many forms of glaucoma where damage to the optic nerve components causes progressive degeneration of retinal and brain neurons involved in visual perception. While many risk factors abound and have been validated for this glaucomatous optic neuropathy (GON), the major one is ocular hypertension (OHT), which results from the accumulation of excess aqueous humor (AQH) fluid in the anterior chamber of the eye. Millions around the world suffer from this asymptomatic and progressive degenerative eye disease. Since clinical evidence has revealed a strong correlation between the reduction in elevated IOP/OHT and GON progression, many drugs, devices, and surgical techniques have been developed to lower and control IOP. The constant quest for new pharmaceuticals and other modalities with superior therapeutic indices has recently yielded health authority-approved novel drugs with unique pharmacological signatures and mechanism(s) of action and AQH drainage microdevices for effectively and durably treating OHT. A unique nitric oxide-donating conjugate of latanoprost, an FP-receptor prostaglandin (PG; latanoprostene bunod), new rho kinase inhibitors (ripasudil; netarsudil), a novel non-PG EP2-receptor-selective agonist (omidenepag isopropyl), and a form of FP-receptor PG in a slow-release intracameral implant (Durysta) represent the additions to the pharmaceutical toolchest to mitigate the ravages of OHT. Despite these advances, early diagnosis of OHT and glaucoma still lags behind and would benefit from further concerted effort and attention.

Gene-agnostic approaches to treating inherited retinal degenerations

Most patients with inherited retinal degenerations (IRDs) have been waiting for treatments that are "just around the corner" for decades, with only a handful of seminal breakthroughs happening in recent years. Highlighting the difficulties in the quest for curative therapeutics, Luxturna required 16 years of development before finally obtaining United States Food and Drug Administration (FDA) approval and its international equivalents. IRDs are both genetically and phenotypically heterogeneous. While this diversity offers many opportunities for gene-by-gene precision medicine-based approaches, it also poses a significant challenge. For this reason, alternative (or parallel) strategies to identify more comprehensive, across-the-board therapeutics for the genetically and phenotypically diverse IRD patient population are very appealing. Even when gene-specific approaches may be available and become approved for use, many patients may have reached a disease stage whereby these approaches may no longer be viable. Thus, alternate visual preservation or restoration therapeutic approaches are needed at these stages. In this review, we underscore several gene-agnostic approaches that are being developed as therapeutics for IRDs. From retinal supplementation to stem cell transplantation, optogenetic therapy and retinal prosthetics, these strategies would bypass at least in part the need for treating every individual gene or mutation or provide an invaluable complement to them. By considering the diverse patient population and treatment strategies suited for different stages and patterns of retinal degeneration, gene agnostic approaches are very well poised to impact favorably outcomes and prognosis for IRD patients.

Optogenetic Prosthetization of Retinal Bipolar Cells

Abstract

Although the experience of optogenetic retinal prosthetics in animal models dates back to more than 16 years, the first results obtained on humans have only been reported in the last year. Over this period, the main challenges of prosthetics became clear and the approaches to their solution were proposed. In this review, we aim to present the achievements in the field of optogenetic prosthetization of retinal bipolar cells with a focus mainly on relatively recent publications. The review addresses the advantages and disadvantages of bipolar cell prosthetics as compared to the alternative target, retinal ganglion cells, and provides a comparative analysis of the effectiveness of ionotropic light-sensitive proteins (channelrhodopsins) or metabotropic receptors (rhodopsins) as prosthetic tools.

ICG-mediated photodisruption of the inner limiting membrane enhances retinal drug delivery

Many groundbreaking therapies for the treatment of blindness require delivery of biologics or cells to the inner retina by intravitreal injection. Unfortunately, the advancement of these therapies is greatly hampered by delivery difficulties where obstruction of the therapeutics at the inner limiting membrane (ILM) represents the dominant bottleneck. In this proof-of-principle study, we explore an innovative light-based approach to locally ablate the ILM in a minimally invasive and highly controlled manner, thus making the ILM more permeable for therapeutics. More specifically, we demonstrate that pulsed laser irradiation of ILM-bound indocyanine green (ICG), a clinically applied ILM dye, results in the formation of vapor nanobubbles which can disrupt the bovine ILM as well as the extraordinary thick human ILM. We have observed that this photodisruption allows for highly successful retinal delivery of model nanoparticles which are otherwise blocked by the intact ILM. Strikingly, this treatment is furthermore able of enhancing the efficacy of mRNA-loaded lipid nanoparticles within the bovine retina by a factor of 5. In conclusion, this study provides evidence for a light-based approach to overcome the ILM which has the potential to improve the efficacy of all retinal therapies hampered by this delivery barrier.