Photodynamic antimicrobial chemotherapy with the novel amino acid-porphyrin conjugate 4I: In vitro and in vivo studies

Photodynamic antimicrobial chemotherapy (PACT), as a novel and effective therapeutic modality to eradicate drug resistant bacteria without provoking multidrug resistance, has attracted increasing attention. This study examined the antimicrobial efficacy of the novel cationic amino acid-porphyrin conjugate 4I with four lysine groups against two different clinical isolated strains (drug sensitive and multidrug resistant) of the Acinetobacter baumannii species and its toxicity on murine dermal fibroblasts in vitro, as well as the therapeutic effect of PACT on acute, potentially lethal multidrug resistant strain excisional wound infections in vivo. The PACT protocol exposed 4I to illumination, exhibiting high antimicrobial efficacy on two different strains due to a high yield of reactive oxygen species (ROS) and non-selectivity to microorganisms. The photoinactivation effects of 4I against two different strains were dose-dependent. At 3.9 μM and 7.8 μM, PACT induced 6 log units of inactivation of sensitive and multidrug resistant strains. In contrast, 4I alone and illumination alone treatments had no visibly antimicrobial effect. Moreover, cytotoxicity tests revealed the great safety of the photosensitizer 4I in mice. In the in vivo study, we found 4I-mediated PACT was not only able to kill bacteria but also accelerated wound recovery. Compared with non-treated mice, over 2.89 log reduction of multidrug resistant Acinetobacter baumannii strain was reached in PACT treat mice at 24 h post-treatment. These results imply that 4I-mediated PACT therapy is an effective and safe alternative to conventional antibiotic therapy and has clinical potential for superficial drug-resistant bacterial infections.光动力抗菌化学疗法（Photodynamic antimicrobial chemotherapy, PACT）作为一种可在不诱导多重耐药的前提下根除耐药菌的新型高效治疗手段，受到了越来越广泛的关注。本研究针对含四个赖氨酸基团的新型阳离子氨基酸-卟啉偶联物4I，考察其对鲍曼不动杆菌两株临床分离菌株（药物敏感株与多重耐药株）的抗菌活性，以及体外对小鼠皮肤成纤维细胞的毒性；同时评估了PACT对体内急性、可致命的多重耐药株切除伤口感染的治疗效果。PACT方案将4I予以光照处理后，因活性氧（ROS）产量高且对微生物无选择性，对两株菌株展现出优异的抗菌效果。4I对两株菌株的光灭活作用呈剂量依赖性：在3.9 μM与7.8 μM浓度下，PACT可使敏感株与多重耐药株的活菌数降低6 log单位。与之相比，单独使用4I组与单纯光照组均未表现出可观测的抗菌效果。此外，细胞毒性实验证实光敏剂4I对小鼠具有良好的安全性。体内实验结果显示，4I介导的PACT不仅可杀灭细菌，还能加速伤口愈合。与未给药小鼠相比，PACT治疗组小鼠在给药后24小时，其体内多重耐药鲍曼不动杆菌的活菌数可降低2.89 log以上。以上结果表明，4I介导的PACT疗法是传统抗生素治疗的安全有效替代方案，对浅表耐药菌感染具有临床应用潜力。