光免疫治疗(photoimmunotherapy, PIT)是一项无创或微创肿瘤治疗的新方法，通过光照抗体与光敏剂的偶联物，特异破坏肿瘤细胞。传统的光敏剂要进入特定细胞器并依赖活性氧发挥光毒性，限制了PIT的应用。最新发现，基于近红外光敏剂IRDye 700DX的PIT，通过特异性破坏胞膜引起细胞坏死，对活性氧的依赖性弱，更能高效杀伤肿瘤细胞。完整抗体的肿瘤穿透力弱，申请人前期制备了特异结合结直肠癌抗原GPA33的小分子抗体A33scFv-Fc。因此，本项目拟选IRDye 700DX为光敏剂，用A33scFv-Fc为结直肠癌导向载体，制备新型的光敏剂。通过体外观察A33scFv-Fc-IR700杀伤结直肠癌细胞的活性，确定其治疗的特异性与敏感性；建立皮下、原位移植瘤模型，评估光敏剂治疗结直肠癌的可行性与安全性；同时探讨其杀伤肿瘤的机制，为靶向诊疗结直肠癌提供理论依据。

Photoimmunotherapy (PIT) is a minimally invasive cancer treatment modality based on an antibody-photosensitizer conjugate. PIT involves the administration of a photosensitizer, followed by its excitation with low-energy light of a specific wavelength, which triggers oxidative photodamage and subsequent death of the targeted cells. The new hydrophilic photosensitizer, IRDye 700DX, conjugate to an antibody that binds to the target cell and is exposed to NIR light. Cell necrosis is rapid and irreversible due to structural damage to the cell membrane. And IRDye 700DX-PIT seems independent on internalization and ROS formation. The drawbacks of intact IgG molecules for diagnosis are larger molecular weight, incomplete tumor penetration and low blood clearance. Consequently, we developed smaller antibodies against GPA33. The A33scFv-Fc antibody can rapidly, specifically localized to colonic tumor grafts, suggesting that the A33scFv-Fc might be a promising agent for targeting colorectal cancer. Based on past research evidences, we will develop a target specific PIT based on A33scFv-Fc-IR700. To investigate the efficacy and safety of the IR700-PIT for treating colorectal cancer cells and tumor grafts in mice models. And its potential for PIT application in colorectal cancer treatment would be evaluated in this project.