Karotki Aliaksandr, Khurana Mamta, Lepock James R, Wilson Brian C
Division of Biophysics and Bioimaging, Ontario Cancer Institute, University of Toronto, Toronto, Ontario, Canada.
Photochem Photobiol. 2006 Mar-Apr;82(2):443-52. doi: 10.1562/2005-08-24-RA-657.
Photodynamic therapy (PDT), the use of light-activated drugs (photosensitizers), is an emerging treatment modality for tumors as well as various nononcologic conditions. Single-photon (1-gamma) PDT is limited by low specificity of the photosensitizer, leading to damage to healthy tissue adjacent to the diseased target tissue. One solution is to use simultaneous two-photon (2-gamma) excitation with ultrafast pulses of near-IR light. Due to the nonlinear interaction mechanism, 2-gamma excitation with a focused beam is localized in three dimensions, allowing treatment volumes on the order of femtoliters. We propose that this will be valuable in PDT of age-related macular degeneration (AMD), which causes blindness due to abnormal choroidal neovasculature and which is currently treated by 1-gamma PDT. Here, Photofrin has been used as the photosensitizer to demonstrate proof-of-principle of 2-gamma killing of vascular endothelial cells in vitro. The 2-gamma absorption properties of Photofrin were investigated in the 750-900 nm excitation wavelength range. It was shown that 2-gamma excitation dominates over 1-gamma excitation above 800 nm. The 2-gamma absorption spectrum of Photofrin in the 800-900 nm excitation wavelength range was measured. The 2-gamma cross section decreased from about 10 GM (1 GM = 10(-50) cm4 s/photon) at 800 nm to 5 GM at 900 nm. Adherent YPEN-1 endothelial cells were then incubated with Photofrin for 24 h and then treated by PDT at 850 nm where the 1-gamma contribution was negligible. Cell death was monitored with the use of 2-gamma scanning laser microscopy. The light doses required for killing were high (6300 J cm(-2) for approximately 50% killing), but 2-gamma cytotoxicity was unequivocally demonstrated. Although Photofrin is, per se, not a good choice for 2-gamma PDT due to its low 2-gamma cross section, this work provides baseline data to guide the development of novel photosensitizers with much higher 2-gamma cross sections (>100 GM), which will be required for 2-gamma PDT of AMD (and other conditions) to be clinically practical.
光动力疗法（PDT），即使用光激活药物（光敏剂），是一种新兴的肿瘤及多种非肿瘤疾病治疗方式。单光子（1-γ）光动力疗法受限于光敏剂的低特异性，会导致病变靶组织附近的健康组织受损。一种解决方案是使用近红外光的超快脉冲进行同步双光子（2-γ）激发。由于非线性相互作用机制，聚焦光束的2-γ激发在三维空间中是局部化的，可实现飞升至皮升量级的治疗体积。我们认为这对于年龄相关性黄斑变性（AMD）的光动力疗法将具有重要价值，AMD因脉络膜新生血管异常而导致失明，目前采用1-γ光动力疗法进行治疗。在此，使用卟吩姆钠作为光敏剂来证明体外2-γ杀伤血管内皮细胞的原理。在750 - 900 nm激发波长范围内研究了卟吩姆钠的2-γ吸收特性。结果表明，在800 nm以上，2-γ激发优于1-γ激发。测量了卟吩姆钠在800 - 900 nm激发波长范围内的2-γ吸收光谱。2-γ截面从800 nm处的约10 GM（1 GM = 10⁻⁵⁰ cm⁴ s/光子）降至900 nm处的5 GM。然后将贴壁的YPEN-1内皮细胞与卟吩姆钠孵育24小时，随后在850 nm处进行光动力疗法治疗，此时1-γ贡献可忽略不计。使用2-γ扫描激光显微镜监测细胞死亡情况。杀伤所需的光剂量很高（约50%杀伤需要6300 J cm⁻²），但明确证明了2-γ细胞毒性。尽管由于卟吩姆钠的2-γ截面较低，其本身并非2-γ光动力疗法的理想选择，但这项工作提供了基线数据，以指导开发具有更高2-γ截面（>100 GM）的新型光敏剂，这是AMD（及其他病症）的2-γ光动力疗法在临床上切实可行所必需的。
