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

近年来，常规癌症治疗（如化疗和放疗）的进展大大提高了癌症生存率。然而，这些技术不可避免地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正在努力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。一种这样的技术，称为热疗，使用热源通过将肿瘤中的局部温度瞬时升高到42摄氏度以上来诱导癌细胞死亡。然而，用常规技术难以以受控且非侵入性的方式产生局部加热。另一种方法是使用磁热疗（或“热疗”），这是一种实验性的癌症治疗方法，使用的微观磁性颗粒（纳米颗粒）只有人类头发宽度的1/5000。这些纳米颗粒可以从外部高频交变磁场中引导能量，以产生局部热点。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，并且可以通过在肿瘤内积累纳米颗粒来获得效果。 磁热疗已经产生了令人鼓舞的结果，表明它可以减小肿瘤的大小，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，这些结果是通过将非常浓缩的磁性纳米颗粒流体分散在肿瘤周围来实现的。虽然这代表肿瘤的局部加热，但为了防止癌症扩散，必须杀死每个癌细胞，因此需要细胞水平的加热效应。因此，许多工作都集中在用磁性纳米粒子标记单个癌细胞，要么将它们结合到细胞膜上，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以触发细胞死亡。然而，到目前为止，这些实验的结果有些令人失望，因为似乎纳米颗粒的磁性和加热特性一旦与细胞结合就会发生变化。 为了理解这种行为，首先需要能够探测纳米颗粒在真实的细胞环境中的性质，并观察这些性质如何根据颗粒的微观位置而变化，即它们在细胞内部或外部的位置。进行这种测量的能力将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能够有利地增强磁特性并因此增强细胞水平加热。这样的研究将极大地促进磁热疗的研究，使其更接近于实现作为一种可行的临床治疗。然而，目前还没有这样的文书来进行这项工作。因此，该项目的目的是创建一种新型的显微镜，可以探测细胞环境中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完成，例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。随着仪器的各种组件成形，它们将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应。我们相信，该项目中生产的新仪器将提供纳米颗粒评估所需的阶跃式进步，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.