Defining and targeting mitochondrial dysfunction in cellular models of succinate dehydrogenase (SDH)-mutated tumours

背景与研究目的我正在研究一组通常被称为PPGL的肿瘤（拉丁名称Phaeochromocytoma和ParaGangLioma的缩写）。这些肿瘤大多是不扩散的“良性”肿瘤，但当它们扩散到身体的其他部位时，它们就被定义为癌症。对于癌变的PPGL没有好的治疗方法。为了设计更好的治疗方法，我们需要了解是什么导致PPGL癌变。癌变PPGL的最常见原因是琥珀酸脱氢酶（SDH）基因密码中的遗传突变（“拼写错误”）。这种酶有4个部分，分别是A、B、C和d。这些部分中的任何一部分发生突变都会导致这种酶功能不良或根本不起作用。令人担忧的是，与由不同SDH基因（a、C或d）突变引起的肿瘤患者相比，携带B突变的患者更容易发生癌变的PPGL。我的目的是调查SDH- b肿瘤比其他SDH突变的肿瘤更容易癌变的原因。研究设计背景每个细胞都有许多称为线粒体的“发电厂”，它们承载代谢过程并为细胞产生燃料/能量。SDH是在线粒体中发现的。SDH是细胞代谢的重要酶，但当SDH出现故障时，会积累一种叫做琥珀酸盐的化学物质。高水平的琥珀酸引起细胞进一步的变化，从而导致肿瘤的发展。但是，虽然所有SDH肿瘤都含有高水平的琥珀酸盐，但发生了其他事情，主要是在B肿瘤中，使它们癌变。我认为这另一个因素与导致线粒体问题的B突变有关。线粒体出现的问题会影响其结构、产生燃料的功能和“生命周期”。线粒体代谢的一个副作用是产生分子（特别是活性氧），可以破坏DNA。通常情况下，我们的细胞很擅长修复这种损伤，但如果修复机制有缺陷，那么DNA损伤就无法得到纠正，可能导致癌症变化。我们知道，特定的修复机制可能会因高水平的琥珀酸盐（SDH酶功能障碍的影响）而出现缺陷，但我们不知道修复机制是否会因SDH部分（a、B、C或D）发生突变而受到不同的影响。为了模拟患者的情况，我正在研究除了一个SDH部分（A、B、C或D）被删除之外的相同细胞，这是一个重大突变的影响。对于细胞来说，这是一个细微的差别，但却会产生严重的后果。如果我们能发现缺乏B的细胞发生了什么，使它们从良性肿瘤细胞转变为癌细胞，那么我们就能设计出阻止这种变化发生的治疗方法。我将寻找线粒体不同方面的变化（结构、代谢功能、对细胞“压力”的反应、其“生命周期”的变化），看看缺乏SDH-B的细胞有什么独特之处，就像患有SDH-B肿瘤的患者一样。我将测试现有的癌症治疗和代谢治疗对这些细胞的影响。我希望我的研究结果能够为癌症性PPGL的进一步研究提供信息，或者为设计新的治疗方法奠定基础。我的研究可能会确定一个目标，用于开发早期检测癌变PPGL的技术，或者可以准确预测哪些PPGL会癌变。SDH PPGL研究的进展将有助于管理由SDH突变引起的罕见肿瘤，如特定类型的肾癌和胃癌。与有缺陷的DNA修复机制相关的发现可以应用于发生这种情况的其他癌症（例如乳腺癌、肠癌），并且可能对线粒体的非癌性疾病有影响。

Context & research aimI am researching a group of tumours commonly referred to as PPGL (an abbreviation for Latin names Phaeochromocytoma and ParaGangLioma.) These tumours are mostly non-spreading "benign" tumours, but when they do spread to other parts of the body, they are defined as cancer. There are no good treatments for cancerous PPGL. In order to design better treatments, we need to understand what makes PPGL turn cancerous.The most common cause of cancerous PPGL is an inherited mutation (a "spelling mistake") in the genetic code for an enzyme called succinate dehydrogenase (SDH). This enzyme has 4 parts, named A, B, C, and D. A mutation in any one of these parts causes the enzyme to function poorly or not at all. Worryingly, patients with a B mutation are even more likely to get cancerous PPGL compared to patients whose tumour was caused by a mutation in a different SDH gene (A, C, or D.) My aim is to investigate the reason why SDH-B tumours are more likely than tumours with other SDH mutations to become cancerous. Background to research designEach cell has many "power houses" called mitochondria that host metabolic processes and generate fuel/energy for the cell. It is in mitochondria where SDH is found. SDH is an important enzyme for metabolism of the cell but when SDH malfunctions, there is accumulation of a chemical called succinate. High levels of succinate cause further changes in the cell that lead to tumour development. But while all SDH tumours have high levels of succinate, something else happens, mostly in the B tumours, to make them become cancerous. I propose that this other factor is related to the B mutation causing problems for mitochondria. Problems that arise in mitochondria can impact on its structure, its function in producing fuel, and its "life cycle". A side effect of metabolism in mitochondria is the generation of molecules (specifically, reactive oxygen species) that can damage DNA. Usually, our cells are very good at fixing this damage but if the repair mechanisms are faulty, then the DNA damage goes uncorrected, potentially leading to cancerous changes. We know that a particular repair mechanism can become faulty from high levels of succinate (the effect of SDH enzyme dysfunction), but we do not know if the repair mechanism is affected differently depending on which SDH part (A, B, C, or D) is mutated. To mimic what happens in patients, I am researching with cells that are the same except for one SDH part (A, B, C, or D) being deleted, which is the effect of a significant mutation. This is a subtle difference for a cell but one that can have serious consequences. If we can discover what happens in the cells lacking B to make them change from benign tumour cells to cancerous cells, then we can design treatments that block this change from happening. I will look for changes in different aspects of the mitochondria (structure, metabolic function, responses to cellular "stress", changes to its "life cycle") to see what is unique to cells that lack SDH-B, as occurs in patients with SDH-B tumours. I will test the effects of existing cancer treatments and metabolism treatments on these cells.ApplicationsI hope that findings from my research will be able to inform which treatments ought to be investigated further for cancerous PPGL, or form the basis for designing new treatments. My research may identify a target for developing techniques that detect cancerous PPGL earlier or that can predict precisely which PPGL will become cancerous.Progress in SDH PPGL research will help in the management of rarer tumours due to SDH mutations, such as particular types of kidney and stomach cancer. Findings related to the faulty DNA repair mechanism can be applied to other cancers where this occurs (e.g. breast, bowel) and there may be implications for non-cancerous diseases of mitochondria.