Comparative Evaluation of Wavelength-Dependent Photodynamic Therapy Efficacy Using Representative Red and...

IntroductionThis study aims to investigate and fairly compare the oncological therapeutic efficacy of red photodynamic therapy (Red-PDT) and near-infrared photodynamic therapy (NIR-PDT), to support the selection of suitable photosensitizers (PSs) for optimal PDT.MethodsTwo different representative PSs, trastuzumab-HiLyte Fluor™ 647 conjugate (Tra-HLF647) and trastuzumab-Indocyanine Green conjugate (Tra-ICG), activated by two laser systems at 635 nm and 808 nm, respectively, were used. To ensure a fair comparison, we used the same A4 cell line/tumor model expressing the same target, human epidermal growth factor receptor 2 (HER-2), and employed the same delivery approach. To comprehensively evaluate and compare the potential effects of Tra-HLF647-mediated Red-PDT and Tra-ICG-mediated NIR-PDT, we conducted cell viability imaging assays, intracellular reactive oxygen species (ROS) generation measurements, longitudinal monitoring of tumor volume changes, histological and immunohistochemical (IHC) analyses of tumor sections, and measurements of tumor necrotic depth.ResultsBoth PDTs exerted similar rapid cell death in cell viability imaging assays. There was no significant difference in ROS generation between cells subjected to Red-PDT and NIR-PDT. Both PDTs caused a statistically significant tumor growth delay compared to the control groups; however, no significant difference was detected between the Red-PDT and NIR-PDT groups. The H&E-stained sections of tumors that received Red-PDT and NIR-PDT showed a similar pattern of necrosis-associated features. No conspicuous tissue damage was observed in the control groups. The depth of necrosis, estimated via the coincided accumulation of a fluorescent necrosis marker (AF546-pHLIP) and utilized as an indirect index to approximate laser light penetration, was also nearly identical between tumors treated with Red-PDT and NIR-PDT.ConclusionsTarget-specific Red-PDT and NIR-PDT, using their respective PSs, demonstrated equivalent therapeutic efficacy in tumor models. These findings suggest that wavelength differences between Red-PS and NIR-PS may not critically impact treatment outcomes, offering flexibility in fluorophore selection for future PS conjugate design.