光动力疗法基础研究与临床应用的新进展 
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Photodynamic therapy (PDT) is an effective treatment modality for different types of cancer, vascular-related diseases, and microbiological infections. PDT uses photosensitizer (PS), the light of a specific wavelength, and molecular oxygen to produce highly toxic reactive oxygen species (ROS), which causes cell death via different mechanisms such as vessel constriction, immunological response, and cell damage by apoptosis, autophagy, and necrosis pathways. Fundamental studies of PDT suggest that ROS yield can be affected by various factors such as transportation efficiency and tumor-targeting ability of PSs, illumination strategy of excitation sources, oxygen supply or dependence of the ROS-generation process, and combination with other therapeutic methods, hence directly determining the therapeutic efficacy. Additionally, the relationship between treatment dose and PDT efficacy is still under investigation. The evaluation for PDT indirectly but considerably affects the PDT efficacy by accurately monitoring dosimetric parameters of PDT, which is followed by efficiently regulating and upgrading the therapeutic scheme. In this study, the recent advances in PSs, light sources, tissue oxygenation, synergistic treatment, and dosimetry for improving the clinical PDT efficacy are summarized.
Several novel PSs such as C60, black phosphorus, graphene quantum dots, and PSs with aggregation-induced emission, have been developed to improve the quantum yield of 1O2. The delivery efficiency of PSs has been improved by different PS delivery strategies and the tumor-microenvironment-responsive release scheme. PS absorption has been enhanced by organelle targeting and photochemical internalization, and PS hypoxia resistance has been resolved through loading with oxygen carriers or oxygen-generating reactants. Further, PS development with the synergistic therapeutic function will be used to enhance PDT efficacy.
As for PDT excitation sources, solar light, broad-spectrum lamps, lasers, light-emitting diodes (LEDs), X-ray sources, ultrasonic sources, and in vivo self-excited light sources capable of bioluminescence, chemiluminescence and Cherenkov light, have been widely studied. LEDs and lasers are the most popular light sources in clinical practice. Particularly, wearable, implantable, and disposable PDT light sources have progressed significantly because of the development of inorganic LED arrays, flexible LEDs, and wireless-driven LEDs. Further, in vivo self-excited light source has been studied to eliminate the absorption and scattering of light by biological tissues. Additionally, new illumination schemes of light fractionation and metronomic PDTs have been proposed to ensure oxygen supply during PDT treatment.
Oxygen carriers with high oxygen storage capacity or the chemical reaction substance can be delivered to the target lesion for in situ oxygen generation, which is the most popular method of enhancing oxygen supply for PDT. Additionally, hypoxia-activated linkers or prodrugs have been used to compensate for the low efficacy caused by hypoxia. However, reducing oxygen consumption during PDT can be achieved by limiting certain oxygen-consuming intracellular chemical reactions or reducing oxygen dependence using types Ⅰ or Ⅲ PDT.
To improve the therapeutic efficacy, PDT has been combined with clinical surgery, radiotherapy, chemotherapy, photothermal therapy, sonodynamic therapy, magnetic hyperthermia, and immunotherapy. Three or more modes for synergistic treatment with PDT have been presented. Further, simultaneously employing two PSs targeting different subcellular organelle is also employed to improve PDT efficacy.
Advanced optical imaging techniques such as hyperspectral imaging, Doppler optical coherence tomography, photoacoustic imaging measurement, and 1O2 luminescence imaging have been used successfully to monitor the dosimetric parameters from the original single-point/point-by-point signal acquisition to 2D imaging. The development of the detector has significantly improved the sensitivity, resolution, field of view, and speed of the optical imaging system. For example, the spatiotemporal detection of 1O2 luminescence can be accomplished by combining time-resolved scanning imaging and steady-state wide-field imaging.
Clinical applications of PDT are primarily used for tumor-, vascular-, and microbial-targeting treatments. Vascular-targeting PDT has been successfully demonstrated for treating vascular-related diseases such as age-related macular degeneration and port-wine stain. Additionally, PDT is effective against bacteria, viruses, and fungi in clinical applications.
Despite its clinical effectiveness, PDT is currently underutilized because of the non-fully satisfied and expensive PS, unclear dose-efficiency relationship, and difficulties in translating proof-of-principle research. To further improve PDT efficacy, ongoing research is being pursued to develop the multifunctional nano-PS, wearable LED and self-excited light sources, and the spatiotemporal multimodal optical imaging platform for monitoring and optimizing dosimetric parameters for pre-, during-, and post-PDT.
1 引言
光动力疗法(PDT)是一种联合利用光敏剂(PS)、光和氧分子，通过光动力反应选择性地治疗恶性肿瘤、血管性病变和微生物感染等疾病的新型疗法[1]。PDT作为光治疗的一种重要方法，已逐渐成为继手术、放疗和化疗之后治疗肿瘤的第四种微创疗法，同时还是治疗鲜红斑痣等特殊疾病的首选疗法。PDT治疗前预先给患者注射或局部涂抹光敏剂，经过一定时间代谢之后，光敏剂被选择性地潴留在肿瘤或病变组织中，此时用特定波长的光源直接辐照病灶进行治疗。光敏剂、光和氧分子是PDT的三个基本要素。在特定波长光源的辐照下，潴留在靶组织中的基态光敏剂吸收光子的能量，激发跃迁到第一激发态，这些激发态光敏剂分子通过系间穿越(ISC)跃迁到激发三重态，处在激发三重态的光敏剂分子可以和基态氧分子(3O2)发生能量交换，从而产生具有生物毒性的活性氧(ROS)或自由基等活性物质，其中单线态氧(1O2)已被认为是Ⅱ型光动力反应的主要毒性物质。1O2可以氧化周围的生物分子，对它们造成不可逆的损伤，从而达到治疗的目的。
国际光动力协会(IPA)学术会议是另外一个反映PDT研究进展的重要专题大会，该会议每隔两年举办一次。特别值得一提的是，第19届IPA会议将于2023年再次在上海召开，这是一次充分展示我国PDT研究进展的盛会。在国内，亚洲光子学(Photonics Asia)会议、中国光学学会学术大会、全国激光技术与光电子学学术会议等会议均设有PDT专题。此外，福建师范大学联合柏林洪堡大学已成功主办了3届中德“单线态氧及其光动力效应”双边学术研讨会，重点关注1O2介导PDT的作用机制和疗效关系的研究。在学术期刊方面，Elsevier于2004年创办新刊Photodiagnosis and Photodynamic Therapy，以集中报道PDT领域的研究新进展；Photochemistry and Photobiology和《中国激光医学杂志》每期刊发的论文中至少有1/3属于PDT研究。
本文首先简要回顾PDT的研究现状。然后，以提高PDT疗效为目标，重点分析光敏剂、光源、组织氧含量、协同治疗、量效评估等基础研究以及临床应用的研究进展。最后，探讨了临床个性化精准PDT及其推广应用所面临挑战和发展方向。
2 光敏剂
光敏剂作为PDT的关键要素之一，其性能直接决定PDT的疗效及其临床应用与推广。自1993年光卟啉(Photofrin®)被批准用于临床PDT治疗以来，提升和优化光敏剂的性能和功能始终是国际前沿研究热点[2-3]。如
表 1. 获临床应用批准或正在临床试验的光敏剂
Table 1. Photosensitizers with clinical approval or under clinical trials
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由于光卟啉存在化学组分复杂、水溶性低、癌细胞选择性弱、最大吸收峰波长短，以及要求避光时间长等不足，研究人员针对以上问题，致力于研发第二代新型光敏剂。第二代光敏剂大多为卟啉衍生物、金属酞菁和稠环醌类化合物等。与第一代光敏剂相比，第二代光敏剂不仅提高了肿瘤靶向能力，还通过调控吸收波长以增强治疗深度。此外，在缩短在体代谢时间和提高疗效等方面均有不同程度改进。由5-氨基酮戊酸(5-ALA)生成的原卟啉IX(PpIX)、氨基酮戊酸甲酯(MAL，Metvix®)、替莫泊芬注射剂(Foscan®)、他拉泊芬注射剂(NPe6，Laserphyrin®)和维替泊芬(Visudyne®)等，显著降低了病灶区域以外正常皮肤的光毒性，且能被生物组织中穿透力更强的光激发。其他获得临床许可应用的第二代光敏剂包括氨基乙酰丙酸盐酸盐(Levulan®)、焦脱镁叶绿素(HPPH)、盐酸氨基乙酰丙(Ameluz®)等，钯菌绿素(Tookad®)、瑞达泊芬(Redaporfin)、锡红紫素(tin ethyl etiopurpurin，SnET2，Purlytin, Photrex)、Lutrin®、德克萨斯卟啉(Lu-Tex)、Antrin®、二氢卟吩e6(Fotolon®)、Radachlorin®、金丝桃蒽醌(Hypericin)、Chalcogenopyrylium dyes、Phenothiazinium dye-methylene blue、Phenothiazinium dye-Nile blue and derivatives、Phenothiazinium dye-toluidine blue、Cyanines、ADPM06、福大赛因(Photocynine)和华卟啉钠(DVDMS)等光敏剂已进入临床试验阶段。在我国，北京制药工业研究所于1982年首次研制出BHpD(商品名：血卟啉注射液)，并于2001年获得国家药品实验批准文号。目前，国产血卟啉注射液喜泊芬(HiPorfin)已实现产业化，并被批准用于口腔、膀胱、支气管、肺、消化系统等多系统和多部位的浅表肿瘤和癌前病变，以及鲜红斑痣(PWS)等良性血管疾病的PDT。与此同时，盐酸氨酮戊酸外用散(艾拉，2007年5月上市)和注射用海姆泊芬(复美达，2016年10月上市)经国家药品监督管理局(NMPA)批准分别用于治疗尖锐湿疣和PWS，其中海姆泊芬是获批用于治疗PWS的新型光敏剂。此外，还有两种正在临床试验的新型光敏剂：第一种是2014年获得NMPA的Ⅱ期药物临床试验批准的福大赛因，Ⅰ期和Ⅱ期临床试验研究结果表明该光敏剂对治疗食道癌安全有效；第二种是2015年4月获准用于食管癌Ⅰ期临床治疗的DVDMS。
然而，第二代光敏剂仍然存在水溶性偏低和靶向特异性弱等不足。近年来，研发集高1O2量子产率、主动靶向传输、肿瘤的诊断(如MRI和分子荧光成像等)、治疗(高热治疗和PDT)、剂量监测(单态氧探针和氧分子探针等)，以及疗效评估(细胞凋亡探针、MRI和生物化学发光等)等功能于一体的第三代“功能型光敏剂”备受关注[4-6]。如
在临床应用中，理想PDT新型光敏剂应具备的基本特征包括：1)材料来源广泛，易于化学合成，具有良好的生物相容性；2)化学组分和构效明确；3)最大吸收峰位于近红外波段，有利于提高治疗深度；4)光敏化1O2量子产率高；5)光稳定性好，光漂白效应不显著；6)具有明确细胞或组织靶向性，即特异性强；7)药物毒副作用小，在体代谢排除速度快；8)同时具有本文所探讨的其他诊断和疗效监测等功能。
3 PDT光源
3.1 PDT光源
光源作为PDT的三大要素之一，其发光波长、辐照方式以及剂量直接决定PDT的选择性和疗效[19-20]。如
与此同时，由于受限于光在人体组织中的穿透深度，以及X射线和声波激发光敏剂极低的1O2量子产率，开发PDT体内自发光光源是另外一个重要发展方向[24-25]。尽管激发效率较低，体内自激发光源的最大优势在于可以避免体外辐照中组织对光的吸收和散射，进而提高光在组织中的穿透和治疗深度；同时，由于自激发光主要集中在治疗靶组织内部，对周围正常组织损伤小，极大地提高了治疗的精准性和安全性[26-27]。
如
表 2. PDT辐射源及相应的发光波长
Table 2. Irradiation sources for PDT and their wavelengths
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3.2 辐射源照光方式
临床治疗时，一般采用较高的光通量密度进行连续辐照，这种方式容易造成组织中氧的消耗速率远远大于氧从周围血管通过扩散补给的速率，从而降低了PDT疗效。为了保证治疗过程中氧的供给，人们提出了“间断性 PDT”和“节律性PDT(mPDT)”两种新的治疗模式。当治疗光剂量相同时，间断性 PDT 采用间断性光照方式，避免组织中氧的快速耗竭；节律性 PDT 则是通过降低光通量密度和延长治疗时间来维持组织氧分压，进而获得稳定的1O2产量。与此同时，如果PDT光源采用脉冲照光方式，尤其是超脉冲照光方式，可有效提高PDT疗效。实验结果表明：采用脉冲和超脉冲照光方式时，可以有效避免组织热损伤和缺氧(氧在脉冲间隔时间内获得补给)。由于组织体的光学特性随温度变化而改变，基于脉冲的照光方式可最小化由温度变化导致的组织光学特性改变，从而实现更加精确和稳定的治疗[28]。
4 组织氧含量
在Ⅱ型PDT中，氧分子参与光敏化的动力学反应过程，直接决定光敏化1O2产量和PDT疗效。表征含氧量的主要参量包括氧分压(pO2)、氧浓度和血红蛋白氧饱和度(HbSat)等，组织含氧量受到以下因素的影响：1)治疗靶组织的微环境，以实体肿瘤为例，组织乏氧是PDT疗效受限的关键影响因素；2)Ⅱ型PDT属于耗氧反应，组织氧含量将随着治疗时间的延长而减小；3)PDT过程中引起供氧微血管的封闭，限制氧后续供给，导致组织缺氧。如
4.3 增强氧供给
氧载体具有强储氧能力，是增强PDT氧供给最为常用的方法[30]。氧载体由血红蛋白分子等天然物质、无机物或有机聚合物制成，通过物理吸附氧分子并将其运输到病灶位置，以确保光敏化过程中氧的供给和补给。哺乳动物主要利用体内血红蛋白运输氧气，单个红细胞(RBC)含有20～200亿个血红蛋白分子，每个血红蛋白分子可与氧自由结合或分离。RBC和血红蛋白分子具有良好的生物相容性，已被广泛应用于肿瘤的增强供氧[31]。基于血红蛋白的氧载体，通过键合连接或封装于光敏剂，与光敏剂一起潴留于病灶并释放氧，有效改善乏氧环境。此外，全氟碳纳米颗粒、含氟多肽以及含氟聚合物均具有很好的载氧功能[32]。有机高分子材料中的金属-有机骨架、共价有机高分子和共价有机骨架因具有多孔结构和较大表面积而被应用于氧气储存和药物传递[33]。
除了氧载体，将化学反应物送至病灶，通过化学反应在靶点生成氧气，也可提高组织的含氧量。在肿瘤微环境中具有高浓度的H2O2，而H2O2与MnO2是PDT最常采用的生成氧气的反应物[34]，通过将含MnO2的光敏剂递送到治疗病灶，MnO2被H2O2还原为Mn2＋并同时生成氧气。随后，Mn2＋进一步与H2O2反应生成MnO2，MnO2与H2O2反应生成O2，并重新被还原为Mn2＋，重复以上反应。H2O2与MnO2优良的溶解性，以及Mn2＋的快速代谢，使得该方法的生物安全性高。同时，CaO2在潮湿环境下逐渐释放氧气，有利于解决PDT组织含氧量不足的难题[35]。此外，分解氧化物/过氧化物也可释放氧气，这种反应因无金属参与而具有良好的生物相容性[36]。将光敏剂与光合细菌结合的自供氧方法因具有生物安全性高、调控性能好、产氧量高、成本低等优点，已在PDT治疗心血管疾病中得到初步应用[37]。
4.4 降低氧损耗
利用氧载体或利用化学反应可以增强组织的含氧量，但这些方法的氧气释放速度较快，只能暂时缓解或改善乏氧环境。为此，延缓或降低氧耗是另一种改善组织乏氧的有效方法。通过优化辐照方案减缓氧气消耗是实现持续供氧的方法之一。对病灶的连续辐照导致氧气迅速消耗，为避免过快缺氧，采用的辐照方案包括：低光通量密度并延长辐照时间；间歇式辐照，即分段模式或脉冲模式。这两种方法均延缓氧耗过程，在PDT过程中实现均匀持续供氧。
PDT采用具有乏氧环境响应性的可分裂连接物或前药参与治疗，以改善由乏氧导致的较低疗效问题。利用乏氧环境响应性的可分裂连接物将光敏剂与化疗药物结合，在辐照条件下，光敏剂消耗氧气生成1O2，导致组织内出现乏氧环境，乏氧条件使连接物断裂，释放诱导癌细胞损伤的化疗药物参与肿瘤治疗。与乏氧环境响应性的可分裂连接物的间接作用不同，AQ4N、替拉扎明等乏氧环境响应性前药在PDT后出现氧耗竭时，直接产生细胞毒性物质用于治疗[38-39]。
同时，减少PDT耗氧量或降低氧依赖也是有效的解决方法。部分细胞内化学反应如线粒体相关氧化磷酸化(OXPHOS)十分耗氧，但采用抑制药物，如阿托伐醌，可高效抑制OXPHOS的活性，降低氧消耗量[40]。此外，在PDT过程中组织体含氧量的差异将引发作用机制Ⅰ型和Ⅱ型光化学反应的变化。当体系中含氧量充足时，Ⅱ型光化学反应占主导地位；当组织体含氧量降低到pO2<2 mmHg (1 mmHg＝133.322 Pa)时，Ⅰ型光化学反应变为主导作用。使用Ⅰ型PDT替代氧需求较高的Ⅱ型PDT可降低治疗过程中的氧需求量[41]。目前适用于临床Ⅰ型PDT的光敏剂数量远少于Ⅱ型，其中无机光敏剂如ZnO 纳米棒、TiO2 纳米颗粒等在光辐照下生成电子-空穴对，随后与H2O分子反应生成羟基自由基。另外，Ⅲ型PDT(即光激活化疗，PACT)允许电子从激发的光敏剂传递至DNA等生物分子，通过无氧PDT过程在乏氧环境中开展有效治疗[42]。
5 协同治疗
临床手术是最简单直观的方法；化疗和放疗可获得较高的肿瘤抑制率；光热疗法(PTT)、PDT和磁热疗(MHT)的毒副作用小且肿瘤选择性良好；与其他疗法相比，免疫疗法在抑制肿瘤转移和复发方面独具优越性；声动力疗法(SDT)的超声激发源实现了深部病灶的治疗。如
临床肿瘤切除手术，即便完全切除病灶，也仅适用于治愈非恶性肿瘤，而对于恶性肿瘤，切除手术治疗要复杂得多。大量临床实践证明，手术切除不能切除体内所有肿瘤细胞，不仅存在术后复发转移的可能，而且存在术后出现严重并发症的风险。因此，肿瘤切除手术联合PDT可进一步杀死残留癌细胞，降低肿瘤复发概率。此外，肿瘤体积过大导致手术难度与风险提高，且大创口面积增加了患者术后感染风险，延长了恢复周期。为此，对大体积肿瘤病患采用PDT进行术前预处理，可缩减肿瘤体积，利于后续切除手术与术后康复。PDT与临床肿瘤切除手术的结合可降低手术难度，减少病患感染风险，缩短治疗周期。PDT-化疗协同治疗须采用纳米平台共同负载光敏剂和化疗药物，或将化疗药物直接负载于纳米光敏剂上。当到达靶点后，光敏剂在光辐照下产生ROS，而化疗药物通过肿瘤微环境刺激响应得到释放。PDT-化疗协同治疗的优点之一是增加肿瘤细胞对PDT所产生ROS的细胞毒性敏感度，从而在较低剂量下得到有效治疗，以抑制高剂量药物产生的不良副作用。此外，化疗药物的外排效应对治疗效果产生负面影响，该效应涉及蛋白在PDT-化疗协同治疗中由ROS导致的失活，可达到可观的化疗药物利用率。因此，PDT-化疗协同治疗保留了病灶选择性好以及治疗效率高的优势。PDT-放射疗法协同治疗虽然降低了PDT的精准度，但三维适形放疗等技术的出现为提高协同治疗精度提供了可能。在PDT-放疗协同治疗中，由于两种模式激发设备的不同，治疗无法同时进行，这就提高了治疗过程的复杂性。然而，在X射线-PDT中，由于光敏剂中含有X射线换能器，将X射线光子转换为光敏剂可吸收的光子，实现PDT和放疗同时进行。此外，研究表明，PDT-放疗协同疗法中光敏剂与重金属元素结合有利于增强放疗效果，但其对患者的伤害程度有待评估。PTT是与PDT进行协同治疗的最常用疗法，二者的激发源均为光源，且皆落在NIR区域(PDT光源的波长约为650 nm, PTT光源的波长约为810 nm)，但传统PDT-PTT协同治疗仍需两个不同发光波长的激光器分别激发，这就增加了治疗装置设计和操作的复杂性。解决该问题的最直接方法是同时利用PDT和PTT的重叠吸收光谱区域，采用单个落于该区域的激发光。在PTT-PDT协同治疗中，所使用的敏化剂吸收入射NIR光子产生ROS，同时将NIR由光能转化为热能，产生过高的热量来杀伤病灶细胞。该过程中，由PTT诱导的热效应除了具有增强抑癌作用，还加速瘤内血液循环，改善PDT中的氧供应。在PDT-免疫疗法协同治疗中，主要由PDT造成肿瘤组织损伤，诱导炎症反应，进而协同免疫疗法发挥抗肿瘤效应。具有细胞毒性的T细胞在炎症反应中被激活并转运到靶点位置，杀伤肿瘤细胞。在PDT-免疫疗法协同治疗中，必需共同使用免疫佐剂与光敏剂。与单一的免疫治疗相比，PDT-免疫协同疗法克服了传统疗法对肿瘤有限治疗的局限，发挥了更好的防复发、抗转移作用。PDT-MHT协同治疗采用Fe3O4和γ-Fe2O3等磁性纳米粒子与MHT装置所产生的交变磁场相互作用。磁性纳米粒子由于兼具药物载体与外磁场可导等特性，已被应用于PDT的精准给药。因此，PDT-MHT协同治疗同时实现了精准给药与协同效应，达到了高效抗肿瘤效果。PDT-SDT协同疗法，即声光动力疗法，由PDT的光源和SDT的声源引发。SDT是PDT的衍生疗法，通过超声波激发声敏剂产生ROS。声动力学的ROS产生机制尚未明确，但高温热解和基于空化效应的声致发光被广泛认为是最重要的作用机制。包括玫瑰红在内的部分传统有机光敏剂，兼具光子和超声波双重响应性。SDT-PDT协同治疗不仅发挥了PDT高效性，还充分利用了超声波的强穿透能力，从而有效提高治疗深度。
为了进一步探索PDT协同治疗的效率，三模态甚至是更多模态，其中包括PDT/放疗/化疗[45]、PDT/光热/光免疫治疗[46]、PDT/光热/化疗[47]、PDT/化疗/免疫治疗[48]、PDT/光热/放疗[49]、PDT/磁热疗/光热/化疗[50]等的协同治疗已有报道。在PDT协同治疗中，放疗、化疗和PTT是应用最为普遍的协同疗法，这是因为这3种疗法在技术上相对成熟，疗效评估中量效关系明确。免疫疗法具有独特、无可替代的抗肿瘤复发和转移功能，其在PDT协同治疗中的作用备受关注，也是近年来发展的一个重要方向。
6 量效评估
临床研究结果表明：在相同光敏剂剂量(按患者的体重给药)、给药-照光时间间隔、光通量密度(mW/cm2)和治疗时间的情况下，PDT疗效往往因为患者的个体差异而呈现显著差异[51-52]。除了上述剂量参数，PDT疗效还受治疗前、中、后的靶组织光学特性、组织微环境、血流速度、光敏剂在体分布及其光漂白、治疗光在体分布、1O2产量，以及组织生物响应等剂量参数的影响。随着基础研究的不断深入和临床应用的广泛开展，如何精确量化PDT剂量，并根据患者的个体差异进行PDT剂量的实时监测、调整和优化已成为亟待解决的挑战性难题[53-54]。如
如
如
表 3. 监测PDT剂量参数的光学技术
Table 3. Optical techniques for monitoring dosimetric parameters in PDT
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基于对剂量参数的时空分辨定量测量，如何实现对PDT 靶向作用精度、强度和深度的精准调控是实现个性化精准PDT的前提。例如，1O2发光成像因无法甄别1O2发光的动力学信息而缺乏对信号来源的直接验证，本课题组正在开发时间分辨扫描成像和稳态宽场成像联合的时空分辨1O2发光成像系统。该系统有望在快速获取高分辨1O2发光图像的同时，同步获得感兴趣区域(ROI)的1O2发光信号的动力学信息(包括光敏剂的三重态寿命和1O2寿命)，为建立1O2-PDT剂量学提供理论参考。
7 临床应用
如
7.3 肿瘤靶向
如
7.4 血管靶向
不同于肿瘤靶向，V-PDT通过血管内的光敏剂在光敏化过程中所产生的1O2等ROS造成血管损伤，血管损伤过程中会产生、释放、聚集或激活凝血酶(prothrombin -thrombin)，导致血凝、血栓和血管封闭等，引起病灶供氧和运氧不足，从而导致细胞死亡和组织坏死[71-72]。血管靶向已成为 PDT的三大临床应用领域之一，目前已开展治疗的血管性疾病包括：1)皮肤微血管疾病，如PWS，它是一种先天性、良性血管畸形，好发于面颈部。20世纪90年代初顾瑛提出利用V-PDT治疗PWS，经过近30年的临床实践，证明了该疗法的安全性和有效性，目前已成为治疗PWS的首选疗法。2)眼底微血管疾病，如年龄相关性黄斑变性(AMD)，脉络膜新生血管是AMD的典型临床表现和致盲原因，临床治疗难度大。与传统激光光凝疗法相比，V-PDT对AMD不仅疗效好，而且对病灶周围的正常黄斑组织损伤小。3)消化道黏膜微血管疾病，包括食道静脉曲张、胃窦血管扩张、放射性胃肠炎等。这类疾病往往容易导致患者出现严重的贫血，且由于病变范围弥散，治疗非常棘手。V-PDT因选择性好、创伤小、康复周期短且疗效安全持久，在治疗黏膜微血管疾病方面已显示其独特优势。4)血管特别丰富的肿瘤，如老年男性常见的前列腺癌。由以色列魏茨曼科学研究院和以色列Steba生物技术公司联合研发的TOOKAD®已被欧洲药品管理局批准用于治疗前列腺癌，且疗效显著。
7.5 微生物靶向
病原微生物的多样性和快速变异使其治疗面临着巨大挑战，其中滥用抗生素及其引发的耐药问题尤为突出。微生物靶向PDT(aPDT)作用于微生物的靶点主要在细胞壁和细胞膜，具有多靶点的杀伤作用，不易产生耐药，已成为临床治疗中抗细菌、抗病毒和抗真菌的有效方法[73-74]。aPDT对微生物的杀伤作用主要有两种机制：1)ROS(含1O2)破坏细胞壁，导致细胞内物质泄漏或使膜转运系统及相关蛋白酶失活；2)ROS不可逆地损伤微生物遗传物质DNA的碱基和糖组分，从而破坏DNA的双链结构，干扰正常的增殖和生理代谢。
相对于PDT在肿瘤靶向和血管靶向中的临床应用，微生物靶向治疗还处于起步阶段。临床研究表明，微生物靶向治疗的抗菌谱非常广，并在多种细菌、病毒及真菌感染方面展示出良好的应用前景。目前，PDT抗细菌的临床适应症包括伤口感染、慢性溃疡感染、痤疮以及牙周疾病等。值得关注的是，细菌结构差异导致不同细菌对PDT敏感性存在显著差异。为了最大化PDT抗菌效率，建立PDT抗不同菌种的剂量学是未来的研究重点。病毒作为最小致病因子，具有强感染性，是人类传染病的重要来源。已知高危型人乳头状瘤病毒(HPV)是引起女性下生殖道(宫颈、阴道、外阴)肿瘤及其癌前病变的重要病因，随着高危型HPV感染的低龄化，对高效、保护器官功能的治疗技术提出了新的需求，而PDT具有的治疗优势正符合这个需求，因此，PDT在抗高危型HPV中得到了越来越广泛的应用。在引起人类皮肤和黏膜感染的低危型HPV所致的尖锐湿疣感染中，由于PDT不仅能清除临床感染病灶，对肉眼不可见的亚临床感染也具有清除作用，与传统手术治疗相比，PDT能有效降低其复发概率。在体表、体腔真菌感染性疾病治疗方面，PDT的优势初步显现，Qiu等[75]采用PDT治疗2例食管早癌合并食管广泛白色念珠菌感染的患者，经过1～2次PDT治疗后患者已经痊愈，其食管的结构和功能也得到了很好的保护。口咽/食管念珠菌病是人类免疫缺陷病毒(HIV)患者最常见的机会性感染。采用亚甲基蓝aPDT治疗HIV患者合并的口咽/食管念珠菌病已取得了令人较为满意的临床疗效[76]。此外，PDT在角膜、皮肤、口腔、指甲等真菌感染疾病治疗中也得到初步应用。由于各种真菌含有丰富的色素，可能会减弱光敏剂对辐照光的有效吸收，因此选用的光敏剂最大吸收峰应避开真菌色素的吸收峰。
自开展临床应用以来，PDT在国内越来越多的医院得到了应用及推广。中国人民解放军总医院开创了V-PDT治疗PWS的先河，并长期开展PDT治疗体表、体腔肿瘤，如皮肤肿瘤和食管癌等；近年来，还成功开展V-PDT治疗消化道微血管出血性病变，aPDT治疗高危型HPV感染和食管真菌感染等。哈尔滨医科大学附属第二医院开展PDT治疗脑胶质瘤。首都医科大学附属北京同仁医院眼科中心开展PDT治疗老年眼底黄斑变性。应急总医院开展PDT治疗呼吸道肿瘤等。上海市皮肤病医院开展PDT治疗皮肤肿瘤、尖锐湿疣和中重度痤疮等。南方医科大学中西医结合医院利用PDT治疗头颈部和消化道肿瘤、鼻咽癌以及乳腺外佩吉特病等。中国人民解放军南部战区总医院基于LED开展PDT治疗皮肤肿瘤和PWS。
8 挑战与展望
尽管PDT进入正式临床许可应用已近30年，但仍然面临诸多挑战：1)现有临床许可光敏剂价格居高不下，且药效特性不尽理想；2)PDT在离体细胞和活体动物试验中所得到的结论，难以直接、快速地实现临床转化应用；3)由于患者之间存在个体差异，以及治疗病灶组织内部具有各向异性，难以揭示光敏化生物作用机制和建立定量评估PDT疗效的量效关系；4)缺乏明确的量效关系，极大地限制了PDT的临床应用推广。
如
图 9. 监测PDT治疗前、中和后的剂量参数
Fig. 9. Monitoring dosimetric parameters for pre-，during-，and post-PDT
为了监测Ⅱ型PDT治疗前、中、后的靶组织光学特性、组织微环境、血流速度、光敏剂在体分布及其光漂白、治疗光的在体分布、1O2产量，以及组织生物学响应等剂量参数，亟待研发多模态时空分辨光学成像平台。在此基础上，阐明光敏剂剂量、光剂量和组织微环境对光敏化1O2产量的定量影响，进而优化和调控治疗方案以提高PDT疗效。在临床应用中，建立1O2-PDT剂量学是实现临床PDT个性化和精准治疗的理论基础。
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Article Outline
李步洪, 陈天龙, 林立, 陈兵, 邱海霞, 顾瑛. 光动力疗法基础研究与临床应用的新进展[J]. 中国激光, 2022, 49(5): 0507101. Buhong Li, Tianlong Chen, Li Lin, Bing Chen, Haixia Qiu, Ying Gu. Recent Progress in Photodynamic Therapy: From Fundamental Research to Clinical Applications[J]. Chinese Journal of Lasers, 2022, 49(5): 0507101.
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