Essay Prep Flashcards
Write a description of the medical problem your therapy will address
- Wet Age-Related Macular Degeneration (AMD) is a leading cause of vision loss among people aged 50 and older.
- It primarily affects the central vision, which is critical for essential day to day function
- Wet AMD is a complex multifactorial disease with the exact cause of the disease being unknown.
- However, genetic factors have been identified and smoking has been shown to increase risk.
- Furthermore, high levels of vascular endothelial growth factor (VEGF) have been associated with wet-AMD
This disease is characterised by
- This disease is characterized by the abnormal growth of new blood vessels under the retina (choroidal neovascularization).
- These vessels are fragile, leaking blood or fluid into the macula, which damages the photoreceptors and leads to vision loss.
Stat
Around 1 in 3 people over the age of 75 are affected by AMD, with the “wet” form being more aggressive compared to “dry” and is responsible for 90% of severe vision loss cases.
Describe the interventions currently in use to address that medical problem
- The conventional treatment for wet AMD involves the use of anti-VEGF drugs (e.g., ranibizumab, Aflibercept) that are injected directly into the eye.
- These drugs bind VEGF or compete for its receptor, blocking its activity, thus blocking angiogenesis
Limitations of these interventions
Several significant limitations:
- Expense: Anti-VEGF drugs are costly, with Aflibercept being the costliest drug to the Australian government 2019-2020, costing almost $400 million
- Frequent Administration: Due to the degradation of the drug, patients require intravitreal injections every 4-8 weeks, leading to a high treatment burden and discomfort.
- Infection Risk: Repeated injections carry an increased risk of infection or other complications.
- Limited Efficacy: Not all patients respond adequately to treatment, and vision may still deteriorate.
How your proposed therapy might overcome those
limitations
- A cutting-edge development in the treatment of wet AMD is gene therapy using the rAAV-sFLT-1 vector.
- This therapy involves the transfection of retinal cells to produce sFLT-1, a soluble form of the VEGFR1 receptor, and a highly potent inhibitor of VEGF.
- Unlike conventional therapies, this gene therapy could provide a continuous, long-term inhibition of VEGF, reducing the need for frequent injections and potentially offering a more cost-effective and sustained treatment approach
Hypothesis
Transfection of retinal cells with sFLT-1, using the rAAV vector will significantly reduce retinal VEGF activity, inhibiting choroidal neovascularization and preserving photoreceptor integrity in the Kimba mouse model. This approach will provide a significant, longer lasting improvement in vision compared to current anti-VEGF injections, in those without either treatment
Experimental design
- Subjects: Kimba mouse model, which naturally exhibits features similar to human wet AMD, including neovascularization, without the need for artificial induction of AMD.
- Mice will be divided into three groups, each containing 15 mice (statistically significant results, accounting for potential variability): rAAV-sFLT-1 treated, standard anti-VEGF drug treated, and a control group with no treatment
- Gene Therapy Administration: Deliver the rAAV-sFLT-1 vector via a single intravitreal injection. This vector will enable retinal cells to produce sFLT-1 continuously, inhibiting VEGF activity.
- Standard Treatment Group: Administer standard anti-VEGF injections (Aflibercept) every 4 weeks to mirror the conventional treatment regime
Outcome measures
- Fluorescein Angiography: Perform at baseline and at several time points (1, 4, and 8 weeks) to monitor changes in blood vessel leakage and neovascularization.
- Electroretinography (ERG): Conduct ERG to assess retinal function by measuring the electrical responses of various cell types in the retina
- Biodistribution Studies: Perform biodistribution analysis to assess the dissemination of the rAAV-sFLT-1 vector in various tissues. This will involve sampling tissues beyond the retina to confirm that the vector remains localized or to evaluate any off-target spread.
- Quality Control (QC): Include repeated measurements and independent verification of sFLT-1 expression using Western blot analysis to ensure consistent gene expression.
Ethics
- Experiments will be conducted following Australian ethical guidelines for the humane treatment of animal models.
- Efforts will be made to minimize discomfort, and use of animals will be justified by the potential to develop a more effective treatment for wet AMD.
- Three Rs (Replacement, Reduction and Refinement) will be adhered to)
Stats
Use ANOVA to analyze differences across groups, with significance determined at p<0.05. Results will be further validated by performing redundant tests, including RNA analysis for sFLT-1 expression.
Potential difficulties / limitations of your experimental approach
- Variable Gene Expression: There might be variability in how much sFLT-1 each cell produces, which could lead to inconsistent treatment outcomes.
- Long-Term Effects Unknown: The long-term safety and efficacy of continuous sFLT-1 expression remain uncertain.
- Animal Model Limitations: Results from Kimba mice might not translate directly to humans due to species differences. Further studies would be needed before clinical trials.
Future studies
- Explore Controlled Expression: methods to regulate sFLT-1 expression levels, potentially using inducible gene expression systems to manage treatment effects and minimize risks.
- Larger Animal Models: Before clinical trials, testing in larger, more human-like animal models (such as non-human primates) would help to better assess the translatability of the gene therapy’s effects and safety.
- Long-Term Safety Trials: Conduct extended studies to monitor for delayed adverse effects, to establish the long-term safety profile of continuous VEGF inhibition.
General ethical limitations of these kinds of treatments
- Informed Consent
- Justice and Accessibility
- Animal Welfare in Preclinical Testing
- Managing Patient Expectations (Avoiding Overpromising)
