Antiangiogenic Eye Gene Therapy

Associations between the Complement System and Choroidal Neovascularization in Wet Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness affecting the elderly in the Western world. The most severe form of AMD, wet AMD (wAMD), is characterized by choroidal neovascularization (CNV) and acute vision loss. The current treatment for these patients comprises monthly intravitreal injections of anti-vascular endothelial growth factor (VEGF) antibodies, but this treatment is expensive, uncomfortable for the patient, and only effective in some individuals. AMD is a complex disease that has strong associations with the complement system. All three initiating complement pathways may be relevant in CNV formation, but most evidence indicates a major role for the alternative pathway (AP) and for the terminal complement complex, as well as certain complement peptides generated upon complement activation. Since the complement system is associated with AMD and CNV, a complement inhibitor may be a therapeutic option for patients with wAMD. The aim of this review is to (i) reflect on the possible complement targets in the context of wAMD pathology, (ii) investigate the results of prior clinical trials with complement inhibitors for wAMD patients, and (iii) outline important considerations when developing a future strategy for the treatment of wAMD.

IGFBP‑rP1‑silencing promotes hypoxia‑induced angiogenic potential of choroidal endothelial cells via the RAF/MEK/ERK signaling pathway

Insulin-like growth factor binding protein-related protein 1 (IGFBP-rP1) has been reported to have various functions in different cellular contexts. Our previous investigation discovered that IGFBP-rP1 inhibited retinal angiogenesis in vitro and in vivo by inhibiting the pro-angiogenic effect of VEGF and downregulating VEGF expression. Recently, IGFBP-rP1 was confirmed to be downregulated in the aqueous humor of patients with neovascular age-related macular degeneration compared with controls; however, its specific role remains unknown. The present study applied the technique of gene silencing, reverse transcription-quantitative PCR, western blotting, cell viability assays, cell motility assays and tube formation assays. Chemical hypoxic conditions and choroidal endothelial (RF/6A) cells were used to explore the effect of IGFBP-rP1-silencing on the phenotype activation of RF/6A cells under hypoxic conditions and to elucidate the underlying mechanisms. siRNA achieved IGFBP-rP1-silencing in RF/6A cells without cytotoxicity. IGFBP-rP1-silencing significantly restored the viability of RF/6A cells in hypoxia and enhanced hypoxia-induced migration and capillary-like tube formation of RF/6A cells. Furthermore, IGFBP-rP1-silencing significantly upregulated the expression of B-RAF, phosphorylated (p)-MEK, p-ERK and VEGF in RF/6A cells under hypoxic conditions; however, these upregulations were inhibited by exogenous IGFBP-rP1. These data indicated that silencing IGFBP-rP1 expression in RF/6A cells effectively promoted the hypoxia-induced angiogenic potential of choroidal endothelial cells by upregulating RAF/MEK/ERK signaling pathway activation and VEGF expression.

Gene Therapy Intervention in Neovascular Eye Disease: A Recent Update

Aberrant growth of blood vessels (neovascularization) is a key feature of severe eye diseases that can cause legal blindness, including neovascular age-related macular degeneration (nAMD) and diabetic retinopathy (DR). The development of anti-vascular endothelial growth factor (VEGF) agents has revolutionized the treatment of ocular neovascularization. Novel proangiogenic targets, such as angiopoietin and platelet-derived growth factor (PDGF), are under development for patients who respond poorly to anti-VEGF therapy and to reduce adverse effects from long-term VEGF inhibition. A rapidly advancing area is gene therapy, which may provide significant therapeutic benefits. Viral vector-mediated transgene delivery provides the potential for continuous production of antiangiogenic proteins, which would avoid the need for repeated anti-VEGF injections. Gene silencing with RNA interference to target ocular angiogenesis has been investigated in clinical trials. Proof-of-concept gene therapy studies using gene-editing tools such as CRISPR-Cas have already been shown to be effective in suppressing neovascularization in animal models, highlighting the therapeutic potential of the system for treatment of aberrant ocular angiogenesis. This review provides updates on the development of anti-VEGF agents and novel antiangiogenic targets. We also summarize current gene therapy strategies already in clinical trials and those with the latest approaches utilizing CRISPR-Cas gene editing against aberrant ocular neovascularization.

The role of hypoxia-inducible factors in neovascular age-related macular degeneration: a gene therapy perspective

Understanding the mechanisms that underlie age-related macular degeneration (AMD) has led to the identification of key molecules. Hypoxia-inducible transcription factors (HIFs) have been associated with choroidal neovascularization and the progression of AMD into the neovascular clinical phenotype (nAMD). HIFs regulate the expression of multiple growth factors and cytokines involved in angiogenesis and inflammation, hallmarks of nAMD. This knowledge has propelled the development of a new group of therapeutic strategies focused on gene therapy. The present review provides an update on current gene therapies in ocular angiogenesis, particularly nAMD, from both basic and clinical perspectives.

Suppression of Choroidal Neovascularization by AAV-Based Dual-Acting Antiangiogenic Gene Therapy

Vascular endothelial growth factor A (VEGFA) is involved in the pathogenesis of vasoproliferative retinal diseases, such as exudative age-related macular degeneration (AMD). The objective of this study was to investigate whether dual-acting therapy based on the simultaneous expression of anti-VEGFA microRNAs (miRNAs) and the secreted, antiangiogenic protein pigment endothelial-derived factor (PEDF) delivered by adeno-associated virus (AAV) vectors provides improved protection against choroidal neovascularization (CNV). To investigate this, a multigenic AAV vector allowing retina pigment epithelium (RPE)-specific expression of anti-VEGFA miRNAs and PEDF was engineered. Robust expression of PEDF, driven by the RPE-specific vitelliform macular dystrophy 2 promoter, was observed in human cells and in mouse retina. A significant reduction in CNV was observed in a laser-induced CNV mouse model 57 days post-injection of the AAV5 particles conveying either anti-VEGFA miRNA and PEDF dual therapy or anti-VEGFA miRNA monotherapy. Overall, CNV reduction was most prominent in animals receiving dual-acting therapy. In both cases, the reduction in CNV was accompanied by a significant attenuation of VEGFA. In conclusion, the presented data reveal that gene therapy targeting VEGFA via multigenic AAV vectors displays combined efficacy, suggesting that dual-acting therapy is an important tool in future eye gene therapy for the treatment of neovascular ocular diseases, including AMD.

CRISPR Gene Therapy of the Eye: Targeted Knockout of Vegfa in Mouse Retina by Lentiviral Delivery

Genome editing and knockout by virus-based delivery of CRISPR/Cas9 may provide a new option to cure inherited and acquired ocular diseases. Here we describe development and application of lentivirus-based delivery vectors enabling knockout of the Vegfa gene. We show that Streptococcus pyogenes (Sp) Cas9 and single-guide RNAs (sgRNAs) delivered by such vectors selectively can ablate the vascular endothelial growth factor A (Vegfa) gene in mouse retina following a single administration. These findings may contribute to the development of a new therapeutic path in the treatment of ocular diseases including exudative age-related macular degeneration (AMD).

Serotonin in the gut: Blessing or a curse

Serotonin (5-hydroxytryptamine or 5-HT) once most extensively studied as a neurotransmitter of the central nervous system, is seen to be predominantly secreted in the gut. About 95% of 5-HT is estimated to be found in gut mainly within the enterochromaffin cells whereas about 5% is found in the brain. 5-HT is an important enteric signaling molecule and is well known for playing a key role in sensory-motor and secretory functions in the gut. In recent times, studies uncovering various new functions of gut-derived 5-HT indicate that many more are yet to be discovered in coming days. Recent studies revealed that 5-HT plays a pivotal role in immune cell activation and generation/perpetuation of inflammation in the gut. In addition to its various roles in the gut, there are now emerging evidences that suggest an important role of gut-derived 5-HT in other biological processes beyond the gut, such as bone remodeling and metabolic homeostasis. This review focuses to briefly summarize the accumulated and newly updated role of 5-HT in the maintenance of normal gut physiology and in the pathogenesis of inflammation in the gut. The collected information about this multifaceted signaling molecule may aid in distinguishing its good and bad effects which may lead to the development of novel strategies to overcome the unwanted effect, such as in inflammatory bowel disease.

c-Jun-mediated microRNA-302d-3p induces RPE dedifferentiation by targeting p21Waf1/Cip1

Dedifferentiation of retinal pigment epithelium (RPE) cells and choroidal neovascularization (CNV) contributes to the pathogenesis of age-related macular degeneration (AMD). MicroRNAs (miRNAs) have crucial roles in AMD onset and progression. We thus aim to investigate the effects of miRNAs on RPE dedifferentiation and endothelium cell (EC) behavior, and analyze its downstream pathways. We have previously identified miR-302d-3p as the most downregulated miRNA signature along with RPE differentiation. Herein, in vitro study supported that miR-302d-3p induces RPE dedifferentiation typified by reduction of RPE characteristic markers, interrupts its phagocytosis, and promotes its migration, proliferation, and cell-cycle progression. c-Jun was identified as a potential upstream transcript factor for MIR302D, which might modulate RPE function by regulating miR-302d-3p expression. P21^Waf1/Cip1, a cyclin-dependent kinase inhibitor encoded by the CDKN1A gene, was identified as a downstream target of miR-302d-3p. Our data suggested that p21^Waf1/Cip1 could promote RPE differentiation, and inhibit its proliferation, migration, and cell-cycle progression. We also demonstrated that miR-302d-3p suppresses RPE differentiation through directly targeting p21^Waf1/Cip1. In addition, the miR-302d-3p/CDKN1A axis was also involved in regulating tube formation of ECs, indicating its potential involvement in CNV formation. Taken together, our study implies that miR-302d-3p, regulated by c-Jun, contributes to the pathogenesis of both atrophic and exudative AMD. MiR-302d-3p promotes RPE dedifferentiation, migration, proliferation and cell-cycle progression, inhibits RPE phagocytosis, and induces abnormal EC behavior by targeting p21^Waf1/Cip1. Pharmacological miR-302d-3p inhibitors are prospective therapeutic options for prevention and treatment of AMD.

Delivery of Adeno-Associated Virus Vectors in Adult Mammalian Inner-Ear Cell Subtypes Without Auditory Dysfunction

Hearing loss, including genetic hearing loss, is one of the most common forms of sensory deficits in humans with limited options of treatment. Adeno-associated virus (AAV)-mediated gene transfer has been shown to recover auditory functions effectively in mouse models of genetic deafness when delivered at neonatal stages. However, the mouse cochlea is still developing at those time points, whereas in humans, the newborn inner ears are already fully mature. For effective gene therapy to treat genetic deafness, it is necessary to determine whether AAV-mediated therapy can be equally effective in the fully mature mouse inner ear without causing damage to the inner ear. This study tested several AAV serotypes by canalostomy in adult mice. It is shown that most AAVs transduce the sensory inner hair cells efficiently, but are less efficient at transducing outer hair cells. A subset of AAVs also transduces non-sensory cochlear cell types. Neither the surgical procedure of canalostomy nor the AAV serotypes damage hair cells or impair normal hearing. The studies indicate that canalostomy can be a viable route for safe and efficient gene delivery, and they expand the repertoire of AAVs to target diverse cell types in the adult inner ear.

Dissecting microRNA dysregulation in age-related macular degeneration: new targets for eye gene therapy

MicroRNAs (miRNAs) are key regulators of gene expression in humans. Overexpression or depletion of individual miRNAs is associated with human disease. Current knowledge suggests that the retina is influenced by miRNAs and that dysregulation of miRNAs as well as alterations in components of the miRNA biogenesis machinery are involved in retinal diseases, including age-related macular degeneration (AMD). Furthermore, recent studies have indicated that the vitreous has a specific panel of circulating miRNAs and that this panel varies according to the specific pathological stress experienced by the retinal cells. MicroRNA (miRNA) profiling indicates subtype-specific miRNA profiles for late-stage AMD highlighting the importance of proper miRNA regulation in AMD. This review will describe the function of important miRNAs involved in inflammation, oxidative stress and pathological neovascularization, the key molecular mechanisms leading to AMD, and focus on dysregulated miRNAs as potential therapeutic targets in AMD.

Suppression of Choroidal Neovascularization in Mice by Subretinal Delivery of Multigenic Lentiviral Vectors Encoding Anti-Angiogenic MicroRNAs

Lentivirus-based vectors have been used for the development of potent gene therapies. Here, application of a multigenic lentiviral vector (LV) producing multiple anti-angiogenic microRNAs following subretinal delivery in a laser-induced choroidal neovascularization (CNV) mouse model is presented. This versatile LV, carrying back-to-back RNApolII-driven expression cassettes, enables combined expression of microRNAs targeting vascular endothelial growth factor A (Vegfa) mRNA and fluorescent reporters. In addition, by including a vitelliform macular dystrophy 2 (VMD2) promoter, expression of microRNAs is restricted to the retinal pigment epithelial (RPE) cells. Six days post injection (PI), robust and widespread fluorescent signals of eGFP are already observed in the retina by funduscopy. The eGFP expression peaks at day 21 PI and persists with stable expression for at least 9 months. In parallel, prominent AsRED co-expression, encoded from the VMD2-driven microRNA expression cassette, is evident in retinal sections and flat-mounts, revealing RPE-specific expression of microRNAs. Furthermore, LV-delivered microRNAs targeting the Vegfa gene in RPE cells reduced the size of laser-induced CNV in mice 28 days PI, as a consequence of diminished VEGF levels, suggesting that LVs delivered locally are powerful tools in the development of gene therapy-based strategies for treatment of age-related macular degeneration.

Development of Multigenic Lentiviral Vectors for Cell-Specific Expression of Antiangiogenic miRNAs and Protein Factors

Generation of lentivirus (LV)-based vectors holding multiple gene cassettes for coexpression of several therapeutic factors provides potent tools in both gene delivery studies as well as in gene therapy. Here we describe the development of such multigenic LV gene delivery vectors enabling cell-specific coexpression of antiangiogenic microRNA (miRNA) and protein factors and, if preferred, a fluorescent reporter, from RNApol(II)-driven expression cassettes orientated in a back-to-back fashion. This configuration may contribute to the development of new combination therapies for amelioration of diseases involving intraocular neovascularization including exudative age-related macular degeneration (AMD).

In Vivo Knockout of the Vegfa Gene by Lentiviral Delivery of CRISPR/Cas9 in Mouse Retinal Pigment Epithelium Cells

Virus-based gene therapy by CRISPR/Cas9-mediated genome editing and knockout may provide a new option for treatment of inherited and acquired ocular diseases of the retina. In support of this notion, we show that Streptococcus pyogenes (Sp) Cas9, delivered by lentiviral vectors (LVs), can be used in vivo to selectively ablate the vascular endothelial growth factor A (Vegfa) gene in mice. By generating LVs encoding SpCas9 targeted to Vegfa, and in parallel the fluorescent eGFP marker protein, we demonstrate robust knockout of Vegfa that leads to a significant reduction of VEGFA protein in transduced cells. Three of the designed single-guide RNAs (sgRNAs) induce in vitro indel formation at high frequencies (44%-93%). A single unilateral subretinal injection facilitates RPE-specific localization of the vector and disruption of Vegfa in isolated eGFP⁺ RPE cells obtained from mice five weeks after LV administration. Notably, sgRNA delivery results in the disruption of Vegfa with an in vivo indel formation efficacy of up to 84%. Sequencing of Vegfa-specific amplicons reveals formation of indels, including 4-bp deletions and 2-bp insertions. Taken together, our data demonstrate the capacity of lentivirus-delivered SpCas9 and sgRNAs as a developing therapeutic path in the treatment of ocular diseases, including age-related macular degeneration.

BJ-1108, a 6-Amino-2,4,5-Trimethylpyridin-3-ol Analog, Inhibits Serotonin-Induced Angiogenesis and Tumor Growth through PI3K/NOX Pathway

5-Hydroxytryptamine (5-HT) induces proliferation of cancer cells and vascular cells. In addition to 5-HT production by several cancer cells including gastrointestinal and breast cancer, a significant level of 5-HT is released from activated platelets in the thrombotic environment of tumors, suggesting that inhibition of 5-HT signaling may constitute a new target for antiangiogenic anticancer drug discovery. In the current study we clearly demonstrate that 5-HT-induced angiogenesis was mediated through the 5-HT₁ receptor-linked Gβγ/Src/PI3K pathway, but not through the MAPK/ERK/p38 pathway. In addition, 5-HT induced production of NADPH oxidase (NOX)-derived reactive oxygen species (ROS). In an effort to develop new molecularly targeted anticancer agents against 5-HT action in tumor growth, we demonstrate that BJ-1108, a derivative of 6-amino-2,4,5-trimethylpyridin-3-ol, significantly inhibited 5-HT-induced angiogenesis. In addition, BJ-1108 induced a significant reduction in the size and weight of excised tumors in breast cancer cell-inoculated CAM assay, showing proportionate suppression of tumor growth along with inhibition of angiogenesis. In human umbilical vein endothelial cells (HUVECs), BJ-1108 significantly suppressed 5-HT-induced ROS generation and phosphorylation of PI3K/Akt but not of Src. Unlike NOX inhibitors, BJ-1108, which showed better antioxidant activity than vitamin C, barely suppressed superoxide anion induced by mevalonate or geranylgeranyl pyrophosphate which directly activates NOX without help from other signaling molecules in HUVECs, implying that the anti-angiogenic action of BJ-1108 was not mediated through direct action on NOX activation, or free radical scavenging activity. In conclusion, BJ-1108 inhibited 5-HT-induced angiogenesis through PI3K/NOX signaling but not through Src, ERK, or p38.