光动力活性氧的研究进展

Reactive oxygen species in photodynamic therapy

在光动力疗法(photodynamic therapy,PDT)治疗癌症的过程中,由光敏剂介导产生的活性氧起到了关键作用.本文主要从PDT三要素(光、氧气、光敏剂)所涉及的光敏剂靶向性、光照频率转换、氧气递送等方面介绍了增加靶部位活性氧(reactive oxygen species,ROS)的方法;总结了用于单线态氧直接检测的光电倍增管、单光子雪崩二极管、负反馈雪崩二极管检测器,以及间接检测单线态氧、羟基或超氧阴离子的新型荧光或化学探针;描述了ROS引发的从基因、蛋白质到细胞层面的凋亡信号通路以及免疫反应诱导肿瘤细胞凋亡的作用机制.

Photosensitizer-mediated production of reactive oxygen species（ROS） plays a key role in photodynamic therapy（PDT）. Reactive oxygen species mainly includes singlet oxygen, hydrogen peroxide, hydroxyl radical, superoxide anion radical and so on, among which singlet oxygen is the most important reactive oxygen species. In this paper, we firstly introduce the basic property of reactive oxygen species, generation and elimination of endogenous reactive oxygen species and generation mechanism of exogenous reactive oxygen species based on light, oxygen and photosensitizer. Next, we focus on the photosensitizers used to generate reactive oxygen species, factors that affect the yield of reactive oxygen species, and methods to increase the reactive oxygen species concentration at the tumor site. There are many factors that can affect the reactive oxygen species concentration at the tumor site, mainly among which are the singlet oxygen yield of the photosensitizer, the targeting of the photosensitizer, the oxygen concentration, and the illumination frequency. To achieve a good PDT effect, many photosensitizers or their nanoparticles with high singlet oxygen generation and good targeting ability are synthesized. Perfluorocarbon is used to deliver oxygen to overcome oxygen deficiency. Upconversion nanoparticles and two-photon absorption are very useful to solve the problem of weak penetration of short-wavelength light. New PDT methods are also introduced in the text, such as PDT combined photothermal therapy or chemotherapy. Then, we summarized various methods and technologies for reactive oxygen species detection, including direct detection of phosphorescence spectrophotometry, fluorescent probes and chemical probes for indirect detection, electron spin resonance, and positron emission tomography. The direct phosphorescence method mainly detects singlet oxygen based on the 1270 nm phosphorescence emission when singlet oxygen returns to the ground state. The first method to enhance the 1270 nm phosphor signal is to use a NIR photomultiplier tube（PMT） or an In Ga As linear array in combination with scanning of the excitation laser beam, and the second one is based on the use of a NIR camera with a filter. Because the lifetime of singlet oxygen is very short, time resolution is especially important. There are basically three main photon counting techniques： gated photon counting（GPC）, multichannel scaling（MCS）, and time-correlated single photon counting（TCSPC）. In addition, singlet oxygen-sensitized delayed fluorescence（SOSDF） can also be used to detect singlet oxygen. Various new types of probes can specifically detect different types of reactive oxygen species, for example, 9, 10-anthracenedipropionic acid and Mito SOX can be used to detect singlet oxygen and superoxide anion in living cells respectively. The fluorescent probe itself does not have fluorescence, but reacts with reactive oxygen species to form an inner oxide, and emits strong fluorescence under the excitation of a certain wavelength of light. The difference of chemical probe is that it does not require light excitation because it can emit light spontaneously after reacted with reactive oxygen species. Electrons spin resonance（ESR） and positron emission tomography（PET） are also available to detect reactive oxygen species by using a probe. Finally, we discussed the mechanism of reactive oxygen species killing tumor cells, mainly in the following three aspects：（1） direct toxicity to tumor cells and induce their necrosis, apoptosis or autophagy;（2） damage on the tumor capillary endothelial cells and destruction of the microvasculature;（3） activation of an acute inflammatory response in host defense mechanisms. The effect of reactive oxygen species on the immune system and the apoptotic pathway of tumor cells from genes, proteins to the cell level were described in detail.