Hydrogels for combined delivery of novel growth factor mimetics and small molecule ligands for treatment of CNS damage

中枢神经系统（CNS）损伤和疾病是导致残疾的主要原因，可导致认知障碍、感觉功能丧失、瘫痪、慢性疼痛和生活质量严重受损等症状。中枢神经系统损伤有多种可能的原因，包括脑或脊髓的创伤性损伤，由血管疾病或中风引起的缺血或缺氧，以及各种先天性或退行性疾病。尽管深入研究了解急性和慢性中枢神经系统损伤，有限的治疗方案可用于大多数情况。在中枢神经系统应用的药物的配方和递送方面存在重大挑战，这些挑战可以通过开发新的制药技术来解决。众所周知，多种小分子配体和生长因子可正向调节中枢神经系统损伤和神经退行性变。例如，神经胶质细胞系源性神经营养因子（GDNF）、神经生长因子（NGF）和脑源性神经营养因子（BDNF）等生长因子已被证明可以促进帕金森病和阿尔茨海默病模型中的神经元再生，在早期临床试验中具有一定的前景目前，将生长因子输送到中枢神经系统依赖于直接输注蛋白质，或通过基因或细胞治疗产生蛋白质。细胞疗法是长期向大脑输送生长因子的首选方法，但是需要免疫抑制来防止免疫反应的激活，而且这种方法的成本和复杂性令人望而却步。目前仍迫切需要安全有效、适合规模化生产、且不会引起不良宿主免疫和炎症反应的治疗中枢神经系统损伤的新方法。生长因子本身的直接递送消除了治疗中对细胞和基因治疗以及免疫抑制的需要，但将这些蛋白质递送到中枢神经系统存在固有的困难。此外，如果已知负责受体激活的生长因子的结构域，这些可以被合成并用于治疗本身。这种方法的可行性已经在BDNF和ngf的肽模拟物中得到了证明。减少活性剂的大小也有一个优势，即递送配方可以装载更高的剂量，这意味着不需要细胞或基因治疗或频繁重复给药，就可以进行长期治疗。这种方法的一个缺点是，给药后中枢神经系统中可用的生长因子剂量受到低血脑屏障通透性和蛋白质体内半衰期差的限制。本项目旨在通过开发一种促进神经再生和中枢神经系统功能恢复的小分子配体和生长因子模拟物的水凝胶局部递送配方来解决这一问题。水凝胶是一种3D聚合物网络，具有亲水性和生物相容性，并且可以装载随着聚合物生物降解而缓慢释放的货物。随着时间的推移，货物的稳定释放对该项目至关重要，因为生长因子受体在暴露于持续高水平的生长因子时可能变得脱敏。此外，水凝胶模拟神经系统的结构和机械特性，从而最大限度地减少宿主组织的不良反应，使其成为中枢神经系统治疗的理想输送系统。将合成具有神经再生意义的配体和生长因子模拟物并将其纳入水凝胶配方中，以确保活性物质的长期局部释放并防止过早降解。开发的配方将被表征和测试使用体外细胞模型的中枢神经系统损伤。

Central nervous system (CNS) damage and disease is a leading cause of disability, resulting in symptoms such as cognitive impairment, loss of sensory function, paralysis, chronic pain and severely impaired quality of life. CNS damage has a variety of possible causes, including traumatic injury to the brain or spinal cord, ischaemia or hypoxia resulting from vascular disorders or stroke, and a wide range of congenital or degenerative diseases. Despite intensive research into understanding both acute and chronic CNS damage, limited treatment options are available for most conditions. There are major challenges around the formulation and delivery of medicines for application in the CNS which can be addressed through the development of new pharmaceutical technology.It is known that CNS damage and neurodegeneration can be positively modulated by a variety of small molecule ligands and growth factors. For example, growth factors such as glial cell line-derived neurotrophic factor (GDNF), nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) have been shown to promote neuronal regeneration in models of Parkinson's and Alzheimer's disease with some promise in early clinical tests.1 At present, the delivery of growth factors to the CNS relies on either direct infusion of the protein, or production of the protein via gene or cell therapies. Cell therapies are the method of choice for delivery of growth factors to the brain over long periods, however immunosuppression is required to prevent activation of the immune response and the cost and complexity of this approach is prohibitive. There remains a critical need for new treatments for CNS damage which are safe and effective, suitable for scalable manufacture, and do not cause adverse host immune and inflammatory responses.Direct delivery of growth factors themselves eliminates the need for cell and gene therapies and immunosuppression in treatment, but there are inherent difficulties in delivering these proteins to the CNS. Further, if the domain of the growth factor responsible for receptor activation is known, these could be synthesised and used as therapies themselves. The viability of this approach has previously been demonstrated with peptide mimetics of BDNF and NGF.2,3 Decreasing the size of the active agent also has the advantage that delivery formulations can be loaded with higher doses, meaning that longer-term treatments become possible without cell or gene therapies or frequently repeated dosing. One drawback of this approach is that the dose of growth factor available in the CNS after administration is limited by low blood-brain-barrier permeability and poor in vivo half-life of the proteins.This project aims to address this issue by developing a hydrogel local delivery formulation for small molecule ligands and growth factor mimetics which will promote neural regeneration and restoration of CNS function. Hydrogels are 3D polymeric networks which are hydrophilic and biocompatible, and can be loaded with cargoes which are released slowly over time as the polymer biodegrades. Steady release of cargo over time is essential for this project, because growth factor receptors can become desensitised when exposed to continually high levels of growth factor. Additionally, hydrogels mimic the architecture and mechanical properties of the nervous system which minimises adverse host tissue responses, making them ideal delivery systems for CNS therapies. Ligands and growth factor mimetics with implications in neuroregeneration will be synthesised and incorporated into hydrogel formulations to ensure long-term local release of the active agents and prevent premature degradation. The developed formulations will be characterised and tested using in vitro cellular models of CNS damage.