iPSC and age-related diseases: Case study AMD
Age-related macular degeneration (AMD) is a leading cause of vision loss in people over the age of 50, accounting for 90% of blindness in this population. There are dry and wet forms of the disease and to date, there are limited treatment options for the wet form and none for dry AMD. The exact cause of the disease is unknown, but it is suspected that it results from a combination of hereditary and environmental factors, with smoking and diet being implicated. Globally, more than 190 million people are affected by AMD and this figure is expected to increase to more than 285 million by the year 2040. The estimated global cost of the disease currently stands at $343bn, with $255bn in direct healthcare costs.
Significant research effort has been targeted towards identification of the genes involved in permanent vision loss through photoreceptor and/or retinal pigment epithelium (RPE) cell dysfunction or cell death. So far, mutations in over 250 genes are known to be involved. Despite a good understanding of the genotype-phenotype relationship in AMD, this has not translated into predictive in vitro and in vivo models to understand disease mechanisms.
Partnership on iPSC-derived RPE cells
To drive the search for treatments for this devastating disease, it is vital to identify and develop new models which enable elucidation of retinal disease mechanisms and reliably predict the efficacy of therapeutic compounds. To address these challenges, Evotec has teamed up with the Centre for Regenerative Therapies (CRTD) in Dresden, Germany. The CRTD has a longstanding interest in degenerative processes and has contributed significantly to our understanding of retinal diseases in recent years. The joint TargetRD project is based on Evotec’s know-how in induced pluripotent stem cell (iPSC) technology, generating iPSC-derived RPE cells from AMD patients.
RPE cells are essential for visual function and a key component for light detection by photoreceptor neurons. They also are crucial for maintaining the blood-retina-barrier, for the transport of diverse biomolecules, ions, and fluids in and out of the retinal tissue, and recycling of the visual chromophore retinal molecule.
Even more important is their ability for phagocytosis: A single RPE cell is in contact with about 30 photoreceptor cells and responsible for the phagocytosis and removal of the distal portions of the photoreceptor outer segments that are phagocytozed in the course of a day. This is an important process with up to 10% eliminated daily, meaning the entire population of photoreceptor outer segments is turned over every 2 weeks. Maintaining, repairing, or replacing RPE cells therefore is crucial for the management of AMD, but also for other retinal degenerative diseases.
So far, research has been hampered by limited access to RPE cells. There are immortalized retinal cell lines available, but they lack the typical cell morphology or function of their in vivo counterparts, e.g. pigmentation, polarization, and expression of certain proteins. Likewise, artificial organoids, so-called 3D-cups, are not ideal since they are difficult to grow and differentiate and not suited for high-throughput profiling of compounds.
This situation is now improving as Evotec and CRTD succeeded in developing a protocol to efficiently and robustly produce high quality human iPSC-derived RPE cells at industrial scale from patient cells. This means that partners can not only investigate disease pathology directly in this highly relevant retinal cell type but for the first time also study disease phenotypes and mechanisms within the context of a patient’s genome. Moreover, the TargetRD platform enables the study of individual, overlapping functional and morphological changes from iPSC-RPE cells derived from patients with different genetic backgrounds, providing an opportunity to unravel complex AMD disease phenotypes.
Promising first results
Already, the partners were able to show the utility of the TargetRD platform by analyzing iPSC-RPE cells carrying a patient mutation resulting a lysosomal storage disorder. Amongst other symptoms, patients with this type of mutation develop severe retinal degeneration, leading to complete blindness early in life. Using the various phenotypic and functional assays established, it was possible to demonstrate impaired trans-epithelial resistance in patient cells. This indicates that in this case, patient RPE cells are unable to form the tight monolayer required for normal RPE cell function. Furthermore, patient RPE cells have, as expected, impaired lysosomal activity and are unable to phagocytose photo- receptor outer segments (POS) at the same rate as control RPE cells. Since all assays are able to support high-throughput screening, the partners can use the TargetRD platform to identify phenotypic and functional disease phenotypes from patient cells, enabling novel drug discovery approaches.
Furthermore, the project combines Evotec’s drug discovery expertise and the academic excellence of the CRTD to achieve significant progress towards developing therapies much needed by the patients.
Both partners believe this is a very promising approach that enables successful drug discovery programs for retinal degenerations coupled to a high likelihood of successful translation into the clinic.