FP0869 : 52 Weeks results of Safety and Efficacy of Optogenetic Therapy for Vision restoration in advanced RPDr. SANTOSH MAHAPATRA
Dr.Gayatri Kanungo, Dr.ANUJA MOHANTY
Abstract
Optogenetics therapy offers the potential for vision restoration by photosensitizing bipolar or ganglion cells. Multi-Characteristic Opsin (MCO) is an engineered opsin that is activated at ambient light avoiding the need for an external amplifyer and associated phototoxicity. AAV2 used to deliver MCO in advanced retinitis pigmentosa (RP) patients. Single intravitreal injection of AAV2-MCO (vMCO) was given and Safety and exploratory efficacy of intravitreal vMCO with dose escalation were evaluated. vMCO was well tolerated with no reported serious adverse events up to 52 weeks of injection. Ocular adverse events were limited to inflammation and IOP rise, which was well controlled with topical medications. Furthermore, exploratory efficacy endpoints demonstrated improvement in visual function and functional vision in the RP subjects in both injected as well as contralateral eyes following a single vMCO and demonstrates tremendous promise in restoring vision for advanced RP.
Full Text
Purpose:
Optogenetics therapy offers the potential for vision restoration in patients with photoreceptor degeneration. Through the delivery of opsin encoding genes, residual retinal neurons take on the photosensitizing function of the photoreceptors. Such an approach focuses on disease phenotype versus a specific genotype deficit, therefore applicable to a wide patient population. Existing optogenetic tools utilize opsins that do not generate adequate electrical current in ambient light requiring an external device for stimulation. Hence, this study aims at targeting bipolar cells modifying them to be ambient light activable photoreceptor cell by intravitreal introduction of multi characteristic opsin carried by Adeno Associated Virus 2 (AAV2) vector.
Methods:
Multi-Characteristic Opsin (MCO) is an engineered opsin that can be used to photosensitize higher order retinal cells with the potential for greater spatial resolution at ambient light levels, thereby avoiding the need for an external amplifying device and associated phototoxicity. AAV2 was used to deliver MCO1 in advanced retinitis pigmentosa subjects. Subjects received prophylactic oral steroids prior to a single intravitreal injection of AAV2-MCO1 (vMCOl). Safety and exploratory efficacy of intravitreal vMCOl dose escalation were evaluated to identify a safe dose.
Results:
vMCOl was well tolerated with no reported serious adverse events at end of the study at 16 weeks. Ocular adverse events were limited to inflammation and rise in intraocular pressure that were controlled with topical medications. Furthermore, exploratory endpoints demonstrated improvement in vision and visual function in retinitis pigmentosa subjects following a single injection.
Conclusions:
vMCOl is well tolerated with no serious adverse events. Higher dose vMCOl appears to improve visual acuity and visual function at 16 weeks compared to baseline measurements and demonstrates tremendous promise in restoring vision for retinitis pigmentosa patients.
Introduction
In retinal degenerative diseases such as Retinitis Pigmentosa (RP), Stargardt disease, Leber congenital amaurosis (LCA) and Cone-rod Dystrophy, the photoreceptors that are responsible for conversion of light into electro-chemical signals, are degenerated. This prevents the generation of photo-induced signals in retina, breaking the vision-sensory related cascade of events within the visual system. Loss of photoreceptor cells and/or loss of photoreceptor cell function are the primary causes of reduced light sensitivity and blindness in advanced stage of retinal dystrophy.
Retinitis Pigmentosa (RP) refers to disorders characterized by degeneration of photoreceptors in the eye, which hinders visual ability by non-functional neuronal activation, and transmission of signals to the visual cortex (1-5). The prevalence of RP is approximately 100,000 patients in the US, out of which ~50,000 patients have advanced retinal dystrophy. Assuming the report of 1 in every 3000 people has RP, India has RP patient population > 460,000. RP is most often inherited as an autosomal recessive trait with large number of cases having this form of inheritance (3, 6, 7). Further, the degree of visual loss increases with ageing (8) and this is a major concern for our demographic changes towards elderly population.
In some people, RP advances so slowly that vision loss does not occur for a long time. In others, the disease progresses faster and may lead to a loss of vision in one or both eyes. Most of the current clinical treatments are primarily focused on slowing down the progression of the disease (9), as there is neither a cure that can stop the degeneration (10) nor a therapy, other than retinal prostheses, that can restore vision lost due to the degeneration (11). Partial restoration of vision involves invasive surgical procedure for retinal implants (12). Two different types of retinal implants are being developed: subretinal and epiretinal implants (13). The subretinal implants are positioned in the area of the retina where the photoreceptor cells reside, between the pigmented epithelium and the bipolar cells (14). These retinal prostheses have been successful in generating visual perception in blind subjects (15-17).
The disadvantages of using such subretinal implants include (i) chronic damage of the implanted electrodes, and (ii) insufficient current produced by microphotodiode from the ambient light to stimulate adjacent neurons (18, 19). The epiretinal implants are placed in the area of the retinal ganglion cells (RGCs) and the device functions by stimulating the RGCs in response to input obtained from a camera that is placed outside of the eye or within an intraocular lens (19, 20). The disadvantages of epiretinal implants include: (i) cellular outgrowth due to surgical implantation, and (ii) disordered stimulation pattern resulting from the electrical stimulation of both the axons and cell bodies of the RGCs (19). Besides being invasive in nature, these methods for restoration of vision in blind patients are based on non-specific cellular activation and have low spatial resolution due to low number of electrodes (higher number or density of electrodes requires more power, leading to damage of neural tissue by heat), and hence able to improve vision with low spatial resolution.
In advanced stages of retinal degenerative diseases such as RP, the photoreceptors that are responsible for conversion of light into electro-chemical signals are degenerated. This prevents the generation of photo-induced signals in retina, breaking the vision-sensory related cascade of events within the visual system. There is no cure for these diseases, especially in the advanced stages. Since higher order neurons are still intact in degenerated retina, several stimulation methods target the higher order neurons, e.g. Bipolar cells and retinal Ganglion
cells, which carry the visual information to the visual cortex. While direct electrical stimulation approaches require mechanical contact of electrodes to the retinal cells, indirect stimulation approaches such as optogenetic stimulation does not necessitate such physical contact.
Thus, the indirect methods provide clear advantage of being non-intrusive. In addition, cellular specificity can be achieved while using optogenetic stimulation. Optogenetic method has been employed for vision restoration in blind mice model either by non-specific stimulation of retina (21) or in a promoter-specific manner including Thyl for RGCs (22-26), mGluR6 targeting ON bipolar cells (27, 28).
The earlier approaches for restoration of vision by optogenetic stimulation of retinal cells use opsins such as ChR2 (21) and others, which requires light intensities order of magnitude higher than ambient lighting conditions. Therefore, clinical success of such opsin molecules in ambient environment for vision restoration is not yet achieved. Further, use of external light source or device (e.g. LED array (29)) to activate such opsins can substantially damage the retinal cells in long-term usage. Therefore, effective optogenetic vision restoration at ambient light level has not been shown yet. By photosensitizing higher order retinal neurons (e.g. bipolar cells) with ambient light-sensitive ion-channel proteins (MCO 010), delivered via safe viral vectors, we aim to restore light sensitivity of retina and thus vision lost due to degenerative diseases.
Methods
The study was conducted in accordance with ICH and GCP guidelines and approval from institutional ethical committee was obtained before commencement of the study. Informed consent was taken from all study subjects in accordance with guidelines of Declaration of Helsinki. The study included all the cases presenting to a tertiary care eye hospital in Eastern India with advanced RP after preliminary screening to fit into to the inclusion and exclusion criteria as noted below
Inclusion Criteria
1. Age > 18 years
2. Ability to comply with testing and all protocol tests.
3. Diagnosis of advanced RP based on
a. Clinical diagnosis and fundus photography
4. Prior documented (if any) retinal electrophysiological evidence of rod cone photoreceptor degeneration
5. Snellen’s visual acuity equivalent LP/NLP in worse (study) eye
6. Visual acuity in the non-study eye of no-better-than finger counting
7. Presence of retinal bipolar cells and retinal nerve fiber layer on OCT testing
8. Women of childbearing potential must have a negative pregnancy test at the screening 9. Males must use effective forms of contraception during the study period
Exclusion Criteria
1. Participation in a clinical study (ocular or non-ocular) with an investigational drug, agent or therapy in the past six months.
2. Concurrent participation in another interventional clinical ocular study.
3. Prior participation in any gene or stem cell therapy (ocular or non-ocular).
4. Pre-existing eye conditions that would preclude the planned treatment (i.e. injection) or interfere with the interpretation of study endpoints or surgical complications (example would include, but not limited to, glaucoma, diseases affecting the optic nerve causing significant visual field loss, active uveitis, corneal or lenticular opacities).
5. Complicating systemic diseases or clinically significant abnormal baseline values.
6. Subjects with any immunological response dysfunction, for example, immuno compromising diseases or use of immunosuppressive medications, among others. Subjects who are positive for hepatitis B, C, and HIV will be excluded.
7. Cataract surgery, intraocular and/or peri-ocular injection in the study eye within the prior three months.
8. Opacity of lens >3+ due to cataract or significant media opacities hindering visualization of fundus or performance of OCT in the study eye.
9. Known sensitivity to any component of the study agent or medications planned for use in the peri-operative period.
10. Current pregnancy or breastfeeding.
11. Subjects will be excluded if immunological studies show presence of neutralizing antibodies to AAV2 above 1:1000.
12.Any other condition that would not allow the potential subject to complete follow-up examinations during the course of the study and, in the opinion of the investigator, makes the potential subject unsuitable for the study.
13.Presence of narrow iridocorneal angles contraindicating pupillary dilation.
14.Presence of any macular pathology causing decrease in vision or retinal detachment involving macula.
15.Active ocular inflammation or recurrent history of idiopathic or autoimmune associated uveitis.
The investigational product (IP) is AAV2 carried Multi-Characteristic Opsin (vMCO1), which has obtained orphan drug designation status by US-FDA. The IP was kept between -70 to -80 0C throughout the transportation & storage. This phase 1/2a clinical study is an open label, dose exploration and expansion in which 3 subjects received low dose (1.75 E11 vg/eye) uniocular intravitreal injection of vMCO1 (in the worst eye). Upon confirming the safety of the low dose, 3 more subjects received the high dose (3.5 E11 vg/eye). Once it was confirmed that the high dose subjects showed safety and tolerability, 5 more subjects received the high dose of 3.5E11 vg/eye through intravitreal administration. The subjects were regularly monitored and followed up according to the schedule (Fig. 1).
The objectives of this Phase 1/2a clinical study are:
a) To evaluate the safety and tolerability of the intravitreal administration of adeno associated virus, serotype 2 (AAV2) carried ambient light activatable Multi Characteristic Opsin (vMCO1) in patients with advanced RP.
b) To define the safety (Phase 1) and confirm highest tolerated dose (Phase 2a) and recommend Phase 2b dose.
Data was collected on a standardised form, which included age, sex, address, presenting vision, ophthalmic examination, investigations, number of follow ups, sequelae, complications and final visual outcome. A detailed history was taken. All subjects underwent comprehensive ophthalmologic examination including Fundus photography for clinical diagnosis of RP. Complete external examination was done by slit lamp biomicroscopy, and intraocular pressure (IOP) was measured by using rebound tonometer (iCare). Fundus was evaluated using 90 D Volk lens and by indirect ophthalmoscopy with 20D lens. Screening for pregnancy (in female patients), HIV, HBSAg, fasting blood sugar (FBS), postprandial blood sugar (PPBS), complete blood count (CBC), lipid profile and renal profile were done for every patient.
Patients underwent intravitreal injection of vMCO1 in the operating room under topical anaesthesia using 30G needle in a micro-titrated syringe. Subjects were on an oral regimen of systemic corticosteroids beginning three days before the administration of vMCO1 (Day -3). The initial dose was 1 mg/kg/day prednisone for seven days, with a maximum prescribed dose of 40 mg/day, regardless of the weight of the subject; this was followed by 0.5 mg/kg/day prednisone for an additional five days, with a maximum prescribed dose of 20 mg/day, regardless of the weight of the subject. Subjects were on systemic corticosteroids for a minimum of 12 days up to a maximum of 30 days, depending on the post-injection inflammation. Subjects with mild inflammation received topical steroids or periocular/sub-Tenon/intravitreal triamcinolone acetonide at the discretion of the investigator. Some subjects were treated for increase in intraocular pressure with IOP lowering medicines.
Subjects underwent recording of Adverse Events as reported by participant or observed by investigator. Further, concurrent medications, vital signs, weight, physical examinations were recorded. OCT imaging, slit lamp biomicroscopy and indirect ophthalmoscopy was used to assess inflammation in the eye. A comprehensive ophthalmic assessment with dilated fundus examination was performed to grade the magnitude of the inflammation by compartment and severity, according to the SUN criteria for anterior chamber (AC) cell and flare (30), and the NEI grading scheme for vitreous haze (30, 31).
Best-corrected visual acuity was measured using Freiburg ACT. In addition, detailed assessment of vision by ElectroRetinogram (ERG), Full-field light Stimulus Threshold, Humphrey Visual Field during baseline and post-injection visits. National Eye institute (NEI) Visual Function Questionnaire was used to record Patient Reported Outcome (PRO). The visual performance status was also evaluated by two novel end points (1) Low Vision Multi parametric test (LVMPT), and (2) Visually guided behavioral assays. Blood was drawn on 4th week for Neutralizing Antibody assay and on 8th week for genotyping.
Results
The vMCO1 safety profile remains satisfactory and was well-tolerated 16 weeks after intravitreal injection. No serious adverse events observed in vMCO-1 injected eyes or contralateral eyes and all dosed subjects continue active participation. Mild to moderate ocular inflammation and increase in IOP in some subjects was treated with topical steroid and/or IOP-lowering drops (Fig. 2). There was no itching, pain or redness of eye reported by the subjects. Furthermore, no significant change in retina thickness was observed at 16 weeks with respect to baseline as measured by OCT. The analysis of AAV2 neutralizing antibody 4 weeks after vMCO1 injection shows no detectable increase, suggesting no systemic immune response.
No subject had an ocular inflammation score greater than 2 at any timepoint during the study (Fig 3). Fig. 3 shows the longitudinal assessment of AE score in the injected and contralateral eyes. To monitor the rate of retinal thinning and to evaluate retinal thinning (if any) due to vMCO1 injection, OCT imaging of retina was carried out in a longitudinal manner. Fig. 4 shows OCT images of injected eye at Baseline and 16 weeks after injection. Longitudinal assessments of retinal thickness in these subjects (Fig. 4) show no dependence on administered dose or change in IOP. Longitudinal monitoring of retinal thickness in injected and contralateral eyes was carried out by OCT imaging and quantified (Fig. 4). Measured average retinal thickness did not change after vMCO1 injection. No significant change in retina thickness was observed at 16 weeks with respect to baseline
Mild to moderate ocular inflammation and increase in IOP in some subjects were observed and were treated with topical steroid and/or IOP-lowering drops (Fig. 2). S-003 (low dose) and S-006 (high dose) had moderate increase in IOP level after injection. Few other subjects had mild increase in IOP, which was controlled via application of topical steroid/IOP-lowering drug without requiring surgery. At 16 weeks, the average IOP level maintained similar to normal values. To evaluate if elevated IOP was related to vMCO-010 injection related intraocular inflammation, ocular adverse events were evaluated by slit lamp and indirect ophthalmoscopy.
Improvements in both visual function and functional vision was reported as early as 4 weeks which further improved through 16 weeks. The Freiburg visual acuity test shows increase in visual acuity as shown in Fig 5. There was no Severe AEs reported upon administration of vMCO1. The safety data demonstrates that vMCO1 has positive safety profile even at the high dose of 3.5E11vg/eye.
Discussion
MCO is an ambient light-activatable ion channel protein, which opens up when exposed to light allowing flow of cations into the cell. To achieve optogenetic stimulation of retinal neurons, the retinal cells especially the ON bipolar cells are generally transfected by a vMCO1(administered intravitreally) to express multi-characteristic opsin (light-sensitive molecular ion-channel), which gets activated, thus depolarizing the opsin-expressing retinal bipolar cells when illuminated by ambient light in broad visible spectrum (characteristics of the multi-characteristic opsin). The photosensitized bipolar cells have shown to drive retinal circuitry functions, activate cortical circuits, and mediate visually guided behaviors.
The vMCO1 safety profile remains satisfactory and was well-tolerated 16 weeks after intravitreal injection. No serious adverse events observed in vMCO1 injected eyes or contralateral eyes and all dosed subjects continue active participation. Mild to moderate ocular inflammation and moderate increase in IOP in some subjects was treated with topical steroid and/or IOP-lowering drops. There was no itching, pain or redness of eye reported by the subjects. Furthermore, no significant change in retina thickness was observed at 16 weeks with respect to baseline as measured by OCT. The analysis of AAV2 neutralizing antibody 4 weeks after injection shows no detectable increase suggesting no systemic immune response.
Conclusions
The overall preliminary safety and efficacy results from the phase 1/2a clinical study demonstrated that the benefit risk balance is strongly in favor vMCO1 for the treatment of patients with vision loss due to RP. Intravitreal optogenetic gene therapy in RP patients with vMCOl is well tolerated with no serious adverse events. Higher dose vMCOl appears to improve visual acuity and visual function at 16 weeks compared to baseline measurements and demonstrates tremendous promise in restoring vision for RP patients.
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