Combined Magneto-Optical and Fluorescence Lifetime Imaging Microscopy: Towards Cellular Level Magnetic Hyperthermia

近年来，化疗和放疗等传统癌症治疗方法的进步大大提高了癌症存活率。然而，这些技术不可避免地会导致一些健康组织和细胞的损伤，从而产生有害的副作用。因此，世界各地的许多研究人员都在致力于开发针对肿瘤的靶向癌症疗法，从而在不影响周围健康组织的情况下摧毁癌细胞。其中一种被称为热疗的技术是利用热源将肿瘤局部温度瞬间升高到42摄氏度以上，从而诱导癌细胞死亡。然而，传统技术很难以一种可控的、无创的方式产生局部加热。另一种替代方法是使用磁热疗（或“热疗法”），这是一种实验性的癌症治疗方法，它使用的是只有人类头发宽度的1/5000的微小磁性颗粒（纳米颗粒）。这些纳米粒子可以引导来自外部高频交变磁场的能量，从而产生局部热点。由于加热只能发生在纳米颗粒存在的地方，因此该技术是真正的局部技术，并且可以通过在肿瘤内积累纳米颗粒来获得效果。磁热疗法已经产生了令人鼓舞的结果，表明它可以缩小肿瘤的大小，并且在最近的临床试验中，它与放射治疗相结合，对癌症生存时间有显着影响。然而，这些结果是通过在肿瘤周围分散非常浓缩的磁性纳米颗粒液体来实现的。虽然这代表了肿瘤的局部加热，但为了防止癌症扩散，必须杀死每一个癌细胞，因此需要细胞水平的加热效应。因此，很多工作都集中在用磁性纳米粒子给单个癌细胞贴上标签上，要么将它们与细胞膜结合，要么让它们被细胞吞噬。原则上，这些颗粒应该能够直接加热细胞，从而引发细胞死亡。然而，到目前为止，这类实验的结果有些令人失望，因为纳米颗粒的磁性和发热性能似乎一旦与细胞联系在一起就会发生变化。为了理解这种行为，首先有必要能够探测真实细胞环境中纳米颗粒的特性，并了解这些特性如何根据颗粒的微观位置而变化，即它们位于细胞内部或外部的位置。进行这种测量的能力将使人们能够系统地评估纳米颗粒的设计和位置，以及所使用的磁场条件，如何有利于增强磁性，从而提高细胞水平的加热。这样的研究将极大地推动对磁热疗的研究，使其更接近于成为一种可行的临床治疗方法。然而，目前还没有这样的工具来执行这项工作。因此，这个项目的目的是创造一种新型的显微镜，可以在细胞环境中探测纳米颗粒的磁性和加热特性。这将通过利用某些光学现象的磁依赖性来实现，比如众所周知的法拉第效应，并将它们与基于荧光的专业技术相结合来测量局部温度。随着仪器的各个组成部分逐渐成型，它们将被用于评估一系列定制纳米颗粒的性能，以了解如何实现足够强的细胞级磁热疗效果。我们有信心，在这个项目中生产的新仪器将提供纳米颗粒评估所需的阶级性进步，使磁热疗成为对抗癌症的可行和必要技术。

Advances in conventional cancer treatments such as chemotherapy and radiotherapy have provided vast improvements in cancer survival rates over recent years. However these techniques inevitably lead to the damage of some healthy tissue and cells, resulting in harmful side effects. Many researchers around the world are therefore working to develop targeted cancer therapies that are tumor-specific, and so destroy cancer cells without affecting surrounding healthy tissue. One such technique, known as hyperthermia, uses heat sources to induce cancer cell death by transiently raising the local temperature in the tumor to above 42 deg C. However, generating local heating in a controlled and non-invasive fashion is difficult with conventional techniques. An alternative method is to use magnetic hyperthermia (or 'thermotherapy') which is an experimental cancer treatment that uses microscopic magnetic particles (nanoparticles) that are only 1/5000th of the width of a human hair. These nanoparticles can channel the energy from an external high-frequency alternating magnetic field in order to create local hot spots. As heating can only occur where nanoparticles are present, the technique is truly local and effects can be obtained by accumulating nanoparticles within tumors. Magnetic hyperthermia has produced encouraging results that show it can reduce the size of tumors, and in recent clinical trials where it was combined with radiotherapy, a significant effect on cancer survival times was reported. However these results were achieved by dispersing very concentrated magnetic nanoparticle fluids around the tumor. Although this represents local heating of the tumor, in order to prevent the cancer from spreading it is essential to kill each and every cancer cell, and so a cellular level heating effect is required. Much work has therefore focused on labelling individual cancer cells with magnetic nanoparticles, either by binding them to cell membranes or by allowing them to be engulfed by the cells. In principle these particles should then be able to heat the cells directly to trigger cell death. However the results of such experiments to date have been somewhat disappointing because it seems the magnetic and heating properties of the nanoparticles can change once they are associated with cells. In order to understand this behaviour it is first necessary to be able to probe the properties of the nanoparticles in real cellular environments, and to see how these vary depending on the microscopic location of the particles, i.e. where they reside inside or externally to cells. The ability to make such measurements would enable a systematic evaluation of how the design and location of the nanoparticles, as well as the magnetic field conditions used, could favourably enhance the magnetic properties and consequently the cellular level heating. Such a study would dramatically boost research on magnetic hyperthermia, taking it much closer to realisation as a viable clinical therapy. However at present no such instrument exists in order to perform this work. Therefore the aim of this project is to create a new type of microscope that can probe both the magnetic and heating properties of nanoparticles in cellular environments. This will be done by exploiting the magnetic dependence of certain optical phenomena, such as the well-known Faraday effect, and combining them with specialist fluorescence based techniques to measure local temperature. As the various components of the instrument take shape they will be used to evaluate the performance of a range of bespoke nanoparticles in order to understand how sufficiently strong cellular-level magnetic hyperthermia effects can be achieved. We are confident that the new instrument produced in this project will provide the step-change advancement required in nanoparticle evaluation to enable magnetic hyperthermia to be a viable and essential technology in the fight against cancer.