Innovative therapeutic approaches for neurodegenerative disorders: drug repurposing and cell therapy

Neurodegenerative diseases (NDs) are a group of heterogeneous disorders characterized by progressive dysfunction and loss of neurons that encompass many different entities. Due to a neuron’s impossibility of renewing itself, this loss is irreversible and is usually followed by the collapse of the structure and function of neural networks, triggering the breakdown of the core communicative circuitry. Involvement of functional systems differs between disorders and is associated with a broad spectrum of clinical presentations. At present, the management of neurodegenerative disorders is often disease-specific, and research into therapy mainly focuses on classical pharmacological approaches and advanced therapies (cell and gene therapy). Several pharmacological therapies are currently accepted, which either target the disease pathogenesis or try to improve the symptoms experienced. Current treatments cannot prevent or completely arrest the progression of NDs; thus, with time, the efficacy of these treatments may be reduced. Hence, the detection of new targets for drug action is a priority. Drug repurposing, the application of an existing therapeutic to a new disease indication, is a recent and valuable strategy that overcomes several shortcomings of the de novo development of new drugs; indeed, it holds the promise of rapid clinical impact at a lower cost, by accelerating the discovery of new candidate molecules while reducing its economic impact and increasing the chances of clinical development and testing phases. This strategy has various advantages and has opened new scenarios, particularly in the context of rare diseases, such as mitochondrial or neurodegenerative diseases. Finding new indications can rapidly benefit patients for either approved or failed drugs for which safety has already been established. An engaging alternative therapeutical option is cell therapy, which involves the transplantation of stem cells for the regeneration of neural tissue, the stabilization of the neuronal networks, and the provision of neurotrophic support. Cell therapy aims to improve the repair response of dysfunctional and damaged tissue; however, restoring neuronal connectivity, both local and long-range, remains a substantial problem. Recently, 3D organoid technology has emerged as the latest frontier in regenerative medicine for treating CNS disorders. Most of the research on cell-based therapy for neurodegenerative diseases has been conducted preclinically in animal models, in which there are positive signs that, despite disrupted organization, connections with host cells can improve functionality. However, significant challenges remain regarding whether and how promising preclinical findings can be translated into clinical trials. Developing innovative approaches to treat neurodegenerative disorders. My PhD is focused on testing two different strategies to treat neurodegenerative disorders: (1) a drug-repurposing strategy for neurodegenerative disorders caused by OXPHOS-related defects and (2) the regeneration of brain damage by tissue graft. For the first aim, we demonstrated that neuronal progenitor cells derived from patients who carry different homoplasmic mutations in the ATP6 gene all present constant biochemical and phenotypic traits that are independent of the pathogenic variant, confirming their suitability as tools for phenotypic drug screening. Sildenafil was able to ameliorate the abnormalities in all patient-derived cell lines. Our data strongly suggest that the therapeutic effect is being carried out through the activation of the cGMP cascade. We were also able to demonstrate that dopaminergic neurons derived from patient-NPCs exhibited a branching defect and that this phenotype was positively affected by treatment with Sildenafil. Overall, these data point to Sildenafil being a good candidate for managing Leigh Syndrome. For the second aim, we focused on the self-repair process of dysfunctional brain circuits with the use of transplantable brain tissue, in the context of Temporal Lobe Epilepsy, which presents several symptoms mainly affecting the hippocampus, and is often resistant to anti-epileptic drugs. As a starting point we derived rat-brain organoids and evaluated their growth, morphology, cellular composition, differentiation, maturation, and functionality. As a second step, we started to set up a protocol for brain organoid transplantation in a rat model. Preliminary results showed that after transplantation, organoids can differentiate within the host brain, highlighting the potential for integration with the host networks and further boosting the potential use of organoids for brain regeneration.