Chemical and material communication between the optic nerves in rats

Update on Clinical Trial Endpoints in Gene Therapy Trials for Inherited Retinal Diseases

Inherited retinal diseases (IRDs) encompass a wide spectrum of rare conditions characterized by diverse phenotypes associated with hundreds of genetic variations, often leading to progressive visual impairment and profound vision loss. Multiple natural history studies and clinical trials exploring gene therapy for various IRDs are ongoing. Outcomes for ophthalmic trials measure visual changes in three main categories-structural, functional, and patient-focused outcomes. Since IRDs may range from congenital with poor central vision from birth to affecting the peripheral retina initially and progressing insidiously with visual acuity affected late in the disease course, typical outcome measures such as central visual acuity and ocular coherence tomography (OCT) imaging of the macula may not provide adequate representation of therapeutic outcomes including alterations in disease course. Thus, alternative unique outcome measures are necessary to assess loss of peripheral vision, color vision, night vision, and contrast sensitivity in IRDs. These differences have complicated the assessment of clinical outcomes for IRD therapies, and the clinical trials for IRDs have had to design novel specialized endpoints to demonstrate treatment efficacy. As genetic engineering and gene therapy techniques continue to advance with growing investment from industry and accelerated approval tracks for orphan conditions, the clinical trials must continue to improve their assessments to demonstrate safety and efficacy of new gene therapies that aim to come to market. Here, we will provide an overview of the current gene therapy approaches, review various endpoints for measuring visual function, highlight those that are utilized in recent gene therapy trials, and provide an overview of stage 2 and 3 IRD trials through the second quarter of 2024.

The AMPK-dependent inhibition of autophagy plays a crucial role in protecting photoreceptor from photooxidative injury

Excessive light exposure can potentially cause irreversible damage to the various photoreceptor cells, and this aspect has been considered as an important factor leading to the progression of the different retinal diseases. AMP-activated protein kinase (AMPK) and the mammalian target of rapamycin (mTOR) are crucial intracellular signaling hubs involved in the regulation of cellular metabolism, energy homeostasis, cellular growth and autophagy. A number of previous studies have indicated that either AMPK activation or mTOR inhibition can promote autophagy in most cases. In the current study, we have established an in vitro as well as in vivo photooxidation-damaged photoreceptor model and investigated the possible influence of visible light exposure in the AMPK/mTOR/autophagy signaling pathway. We have also explored the potential regulatory effects of AMPK/mTOR on light-induced autophagy and protection achieved by suppressing autophagy in photooxidation-damaged photoreceptors. We observed that light exposure led to a significant activation of mTOR and autophagy in the photoreceptor cells. However, intriguingly, AMPK activation or mTOR inhibition significantly inhibited rather than promoting autophagy, which was termed as AMPK-dependent inhibition of autophagy. In addition, either indirectly suppressing autophagy by AMPK activation/ mTOR inhibition or directly blocking autophagy with an inhibitor exerted a significant protective effect on the photoreceptor cells against the photooxidative damage. Neuroprotective effects caused by the AMPK-dependent inhibition of autophagy were also verified with a retinal light injured mouse model in vivo. Overall, our findings demonstrated that AMPK / mTOR pathway could inhibit autophagy through AMPK-dependent inhibition of autophagy to significantly protect the photoreceptors from photooxidative injury, which may aid to further develop novel targeted retinal neuroprotective drugs.

Binocular benefit following monocular subretinal AAV injection in a mouse model of autosomal dominant retinitis pigmentosa (adRP)

Autosomal dominant retinitis pigmentosa (adRP) is frequently caused by mutations in RHO, the gene for rhodopsin. In previous experiments in dogs with the T4R mutation in RHO, an AAV2/5 vector expressing an shRNA directed to human and dog RHO mRNA and an shRNA-resistant human RHO cDNA (AAV-RHO820-shRNA820) prevented retinal degeneration for more than eight months following injection. It is crucial, however, to determine if this RNA replacement vector acts in a mutation-independent and species-independent manner. We, therefore, injected mice transgenic for human P23H RHO with this vector unilaterally at postnatal day 30. We monitored their retinal structure by using spectral-domain optical coherence tomography (SD-OCT) and retinal function using electroretinography (ERG) for nine months. We compared these to P23H RHO transgenic mice injected unilaterally with a control vector. Though retinas continued to thin over time, compared to control injected eyes, treatment with AAV-RHO820-shRNA820 slowed the loss of photoreceptor cells and the decrease in ERG amplitudes during the nine-month study period. Unexpectedly, we also observed the preservation of retinal structure and function in the untreated contralateral eyes of AAV-RHO820-shRNA820 treated mice. PCR analysis and western blots showed that a low amount of vector from injected eyes was present in uninjected eyes. In addition, protective neurotrophic factors bFGF and GDNF were elevated in both eyes of treated mice. Our finding suggests that using this or similar RNA replacement vectors in human gene therapy may provide clinical benefit to both eyes of patients with adRP.

Leber Hereditary Optic Neuropathy: Molecular Pathophysiology and Updates on Gene Therapy

Molecular pathophysiology of LHON was reviewed and the current status of gene therapy for LHON is updated.

Variation in retinal nerve fiber layer thickness at different stages of Leber's hereditary optic neuropathy in patients with the ND4 G11778A mutation

PURPOSE

To investigate retinal nerve fiber layer (RNFL) thickness changes at different stages of Leber's hereditary optic neuropathy (LHON) in patients bearing the ND4 G11778A mutation.

METHODS

Ninety-eight clinically diagnosed, G11778A-positive LHON patients underwent 538 optical coherence tomography (OCT) examinations from September 2015 to September 2017. Patients were grouped based on disease duration at examination. Fifty healthy volunteers underwent 100 examinations as controls. Differences in RNFL thickness were compared across groups.

RESULTS

During the onset of LHON patients with G11778A mutation, the thickness of nerve fiber layer in temporal quadrant decreased slowly within 1-3 months (p > .05), then entered in the rapid thinning period, which generally lasted until about 12 months of the course of disease (p < .05), and no obvious change occurred in the stable stage (p > .05); The optic nerve fiber layer in other quadrants was usually stayed in a significant thickening period within 1-3 months (p < .05), then entered in the rapid thinning period, which generally lasted until about 24 months of the course of disease (p < .05), and no obvious change occurred in the stable stage (p > .05) .

CONCLUSION

In LHON patients with G11778A mutation, the thickness of optic nerve fiber layer in the temporal side will experience slow thinning stage, rapid thinning stage and stable stage; The thickness of optic nerve fiber layer in other directions varies with the course of disease. Generally, it will experience five periods: significant thickening period, swelling period, recovery period, rapid thinning period and stable period.

Bilateral visual improvement with unilateral gene therapy injection for Leber hereditary optic neuropathy

REVERSE is a randomized, double-masked, sham-controlled, multicenter, phase 3 clinical trial that evaluated the efficacy of a single intravitreal injection of rAAV2/2-ND4 in subjects with visual loss from Leber hereditary optic neuropathy (LHON). A total of 37 subjects carrying the m.11778G>A (MT-ND4) mutation and with duration of vision loss between 6 to 12 months were treated. Each subject's right eye was randomly assigned in a 1:1 ratio to treatment with rAAV2/2-ND4 (GS010) or sham injection. The left eye received the treatment not allocated to the right eye. Unexpectedly, sustained visual improvement was observed in both eyes over the 96-week follow-up period. At week 96, rAAV2/2-ND4-treated eyes showed a mean improvement in best-corrected visual acuity (BCVA) of -0.308 LogMAR (+15 ETDRS letters). A mean improvement of -0.259 LogMAR (+13 ETDRS letters) was observed in the sham-treated eyes. Consequently, the primary end point, defined as the difference in the change in BCVA from baseline to week 48 between the two treatment groups, was not met (P = 0.894). At week 96, 25 subjects (68%) had a clinically relevant recovery in BCVA from baseline in at least one eye, and 29 subjects (78%) had an improvement in vision in both eyes. A nonhuman primate study was conducted to investigate this bilateral improvement. Evidence of transfer of viral vector DNA from the injected eye to the anterior segment, retina, and optic nerve of the contralateral noninjected eye supports a plausible mechanistic explanation for the unexpected bilateral improvement in visual function after unilateral injection.

Three Cases of Leber's Hereditary Optic Neuropathy with Rapid Increase in Visual Acuity After Gene Therapy

BACKGROUND

During the first few trials of gene therapy for Leber's hereditary optic neuropathy performed by our group, the visual acuity of the patients increased gradually over several months, or even years. However, in the current round of gene therapy for Leber's hereditary optic neuropathy, we noted that the visual acuity of three patients increased rapidly, within a few days after treatment.

CASE PRESENTATION

Three patients who were diagnosed with mitochondrial gene 11778 mutation (associated with a G-to-A transition at Mt-11778 in the ND4 subunit gene of complex I of mitochondrial DNA that changes an arginine to histidine at amino acid 340) by genetic diagnosis were followed up three times before gene therapy, which lasted for 1 year, without spontaneous improvement of vision. Visual acuity in one or both eyes of each of the three patients increased rapidly after the initial gene therapy treatment.

CONCLUSION

We suspect that in some patients with Leber's hereditary optic neuropathy, a portion of the retinal ganglion cells might remain in a "dormant" state for a certain period of time; these may be activated, within an optimal timeframe, during gene therapy for Leber's hereditary optic neuropathy.

Multilocus Mitochondrial Mutations Do Not Directly Affect the Efficacy of Gene Therapy for Leber Hereditary Optic Neuropathy

PURPOSE

Clinical trials of gene therapy for Leber hereditary optic neuropathy (LHON) were conducted in 9 volunteers with the mitochondrial mutation, G11778A in ND4. The purpose of this study was to investigate whether multilocus mitochondrial mutations directly influence the efficacy of gene therapy for LHON.

METHODS

Nine volunteers with LHON participated in a clinical trial with intravitreal injection of an adenoviral vector expressing wild-type ND4. Patients were subsequently divided into 2 groups: according to the differences in therapy efficacy and based on improvements in visual acuity. Full mitochondrial DNA sequences of the 2 groups of patients were generated and compared using PubMed, PolyPhen, and PROVEAN. Furthermore, the association between the detected mutations and clinical effects of gene therapy was analyzed.

RESULTS

Best-corrected visual acuity (BCVA) significantly improved (≥0.3 log of minimum angle of resolution [logMAR]) in 7 patients 6 months after gene therapy, whereas there was no significant change in BCVA (<0.3 logMAR) of the remaining 2 patients. All 9 patients carried the G1178A mutation in addition to other nonsynonymous mutations. Among these mutations, some were predicted to be neutral and deleterious. Meanwhile, different mitochondrial mutations in the group in which treatment was ineffective, compared with those in responders, were at nucleotide positions 6569 (CO1; Patient 3), 9641 (CO3; Patient 3), and 4491 (ND2; Patient 5).

CONCLUSIONS

Detection of the 3 primary mitochondrial mutations causing LHON is sufficient for screening before gene therapy; sequencing of the entire mitochondrial genome is unnecessary before treatment. Patients with LHON can respond to targeted gene therapy irrespective of additional multilocus mitochondrial mutations.

The Progress of Gene Therapy for Leber's Optic Hereditary Neuropathy

Introduction:

Leber’s Optic Hereditary Neuropathy (LHON) is a common cause of teenaged blindness in both eyes for which there is currently no effective treatment. In 1871, the German ophthal-mologist Theodor Leber was the first to describe the clinical characteristics of his namesake disease, and through unremitting efforts over the past 100 years, researchers have continued to increase their under-standing of LHON. In recent years, using gene therapy, several groups have obtained breakthroughs in the treatment of the disease.

Conclusion:

In this article, we will review the challenging journey that researchers faced towards our current understanding of LHON, and describe the transition of gene therapy research for LHON from the bench to bedside.

Preconditioning with carbon monoxide inhalation promotes retinal ganglion cell survival against optic nerve crush via inhibition of the apoptotic pathway

Optic neurodegeneration, in addition to central nervous trauma, initiates impairments to neurons resulting in retinal ganglion cell (RGC) damage. Carbon monoxide (CO) has been observed to elicit neuroprotection in various experimental models. The present study investigated the potential retinal neuroprotection of preconditioning with CO inhalation in a rat model of optic nerve crush (ONC). Adult male Sprague‑Dawley rats were preconditioned with inhaled CO (250 ppm) or air for 1 h prior to ONC. Animals were euthanized at 1 or 2 weeks following surgery. RGC densities were quantified by hematoxylin and eosin (H&E) staining and FluoroGold labeling. Visual function was measured via flash visual evoked potentials (FVEP). Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, and caspase‑9 and caspase‑3 activity in the retinas, were assessed at 2 weeks post‑ONC. The RGC density of CO + crush rats was significantly increased compared with that of the corresponding crush‑only rats at 2 weeks (survival rate, 66.2 vs. 48.2% as demonstrated by H&E staining, P<0.01; and 67.6 vs. 37.6% as demonstrated by FluoroGold labeling, P<0.05). FVEP measures indicated a significantly better‑preserved latency and amplitude of the P1 wave in the CO + crush rats compared with the crush‑only rats. The TUNEL assays demonstrated fewer apoptotic cells in the CO + crush group compared with the crush‑only group, accompanied by the suppression of caspase‑9 and caspase‑3 activity. The results of the present study suggested that inhaled CO preconditioning may be neuroprotective against ONC insult via inhibition of neuronal apoptosis.

Evaluation of Leber's hereditary optic neuropathy patients prior to a gene therapy clinical trial

Gene therapy may be a promising approach for the treatment of Leber hereditary optic neuropathy. The aim of this study was to evaluate patients with this condition who were recruited into an upcoming gene therapy clinical trial and to assess any changes in the detection parameters to provide support for the clinical trial. Sixteen patients with Leber hereditary optic neuropathy were evaluated using visual function tests 12 months before the initiation of gene therapy. Then, the results of visual acuity (VA), visual field (VF), RNFL (retinal nerve fiber layer) thickness, and Pattern-reversal Visual evoked potential (PR-VEP) were compared and analyzed. A total of 32 eyes of 16 patients were evaluated. Based on the best-corrected visual acuity (BCVA), 24 eyes were relatively stable compared with the baseline evaluation, and 8 eyes had significant changes, including 5 eyes that showed improvement and 3 eyes that showed impairment. In all eyes, the changes in the best-corrected visual acuity were significantly correlated with the changes in the visual field index (VFI), mean defect (MD), and P100 of the visual evoked potential. In the eyes with relatively stable BCVA and those with an obvious improvement in the BCVA, only the visual mean defect showed a significant change; the other indicators were not significantly different. Aside from the patients showing a tendency of spontaneous improvement, the others were in accordance with the requirement. The effects of Leber hereditary optical neuropathy (LHON) gene therapy should be evaluated primarily based on visual acuity. Additionally, visual field, neural fiber thickness, and electrophysiology should be considered in the evaluation.

Long-term outcomes of gene therapy for the treatment of Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a disease that leads to blindness. Gene therapy has been investigated with some success, and could lead to important advancements in treating LHON. This was a prospective, open-label trial involving 9 LHON patients at Tongji Hospital, Wuhan, China, from August 2011 to December 2015. The purpose of this study was to evaluate the long-term outcomes of gene therapy for LHON. Nine LHON patients voluntarily received an intravitreal injection of rAAV2-ND4. Systemic examinations and visual function tests were performed during the 36-month follow-up period to determine the safety and efficacy of this gene therapy. Based on successful experiments in an animal model of LHON, 1 subject also received an rAAV2-ND4 injection in the second eye 12 months after gene therapy was administered in the first eye. Recovery of visual acuity was defined as the primary outcome of this study. Changes in the visual field, visual evoked potential (VEP), optical coherence tomography findings, liver and kidney function, and antibodies against AAV2 were defined as secondary endpoints. Eight patients (Patients 2–9) received unilateral gene therapy and visual function improvement was observed in both treated eyes (Patients 4, 6, 7, and 8) and untreated eyes (Patients 2, 3, 4, 6 and 8). Visual regression fluctuations, defined as changes in visual acuity greater than or equal to 0.3 logMAR, were observed in Patients 2 and 9. Age at disease onset, disease duration, and the amount of remaining optic nerve fibers did not have a significant effect on the visual function improvement. The visual field and pattern reversal VEP also improved. The patient (Patient 1) who received gene therapy in both eyes had improved visual acuity in the injected eye after the first treatment. Unfortunately, visual acuity in this eye decreased 3 months after he received gene therapy in the second eye. Animal experiments suggested that ND4 expression remains stable in the contralateral eye after intravitreal injections. No serious safety problem was observed in the 3-year follow-up of the 9 participants enrolled in this virus-based gene therapy. Meanwhile, our results support the use of intravitreal rAAV2-ND4 as an aggressive maneuver in our clinical trial. Further study in additional patients and in these 9 subjects is needed to better understand the effects of rAAV2-ND4 gene therapy on LHON and to increase the applications of this technique.

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A long-term study of efficacy of gene therapy for Leber's hereditary optic neuropathy.

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No serious adverse effects were noted in the 9 participants over a 3-year period.

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Five patients experienced an improvement in visual function.

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Gene therapy is a promising treatment for Leber's hereditary optic neuropathy.

There are currently no effective treatments for Leber's hereditary optic neuropathy (LHON). Short-term studies using virus-based gene therapy have yielded promising results. We performed systemic examinations and visual function tests to evaluate the long-term safety and efficacy of gene therapy for LHON. Over a 3-year follow-up period, five out of nine patients had visual function improvement, and no serious adverse effects were noted.

A retrospective analysis of characteristics of visual field damage in patients with Leber's hereditary optic neuropathy

The objective of this study is to investigate the characteristics and the evolution of visual field damage caused by Leber’s hereditary optic neuropathy (LHON) and to provide clinical data for the diagnosis of LHON. Parameters of visual field in 32 consecutive patients (49 eyes) with LHON who were confirmed by genetic diagnostic tests were retrospectively measured within 1 week, between three to six months, and at six months after onset. Visual field defects revealed central scotoma in 26 eyes (53.1 %), paracentral scotoma in 12 eyes (24.5 %), ceco-central defects in 6 eyes (12.2 %), blind spot enlargenment in 3 eyes (6.1 %), quadrantanopia in 2 eyes (4.1 %) within 1 week after onset. After 3 to 6 months, ceco-central defects were detected in 22 eyes (44.9 %), central isopter constriction in 10 eyes (20.4 %), hemianopia or quadrantanopia in 5 eyes (10.2 %), central scotoma in 4 eyes (8.2 %), and paracentral scotoma in 1 eye (2.0 %). After 6 months, central isopter constriction was observed in 18 eyes (36.7 %), diffuse defects in 21 eyes (42.9 %), ceco-central defects in 3 eyes (6.1 %), hemianopia or quadrantanopia in 5 eyes (10.2 %), and central scotoma in 2 eyes (4.1 %). LHON at different stages was characterized by different focal visual field defects: visual field defects in LHON patients within 1 week after onset were mostly central or paracentral scotoma, which was enlarged around the ceco-central defect, or connected to form a blind spot after 3–6 months. Diffuse and central isopter constriction defects were usually developed after 6 months. Damages firstly appeared in papillomacular bundle and gradually expanded outward. These characteristics of visual field defects reported in this study might provide a clinical basis for better diagnosis of LHON.