Fluolab【Angew.Chem.】大连理工彭孝军、樊江莉、杜健军|突破200倍光动力治疗指数：Angew基于能量间隔律揭示SOCT-ISC光敏化“火山型”规律
通讯作者： Jianjun Du, Jiangli Fan, Xiaojun Peng
文章概要
引言
光动力治疗（PDT）的效能核心在于光敏剂产生活性氧的能力。近年来，无重原子光敏剂因其低毒性和长三线态寿命备受关注，其中自旋轨道电荷转移系间窜越（SOCT-ISC） 机制因其模块化设计和可调动力学成为研究热点。然而，研究人员发现了一个动力学悖论：极高的光诱导电子转移（PeT）效率并不总能转化为高产率的系间窜越。这种现象暗示了系统中存在未知的动力学瓶颈。大连理工大学彭孝军院士团队及其合作者通过构建一系列C2位功能化的氰基染料库，旨在揭示电荷分离态（CS态）能量与单线态氧产率之间的深层逻辑，为理性设计下一代高效光敏剂提供理论支撑。
Design principle, mechanistic insight, and therapeutic strategy of C2-modified cyanine photosensitizers. (A) Chemical structures of the C2-modified cyanine dye library, superimposed with a graphical representation of their fluorescence quantum yield () and singlet oxygen quantum yields () on the electromagnetic spectrum. (B) Schematic illustration of the competing excited-state kinetic pathways in C2-modified cyanine dyes. (C) Correlation plot revealing the decisive relationship between the energy level of the charge-separated (CS) state and the resulting . (D) Proposed mechanism of action for the optimized photosensitizer TCy-Pyr in PDT.
主要实验及结论
研究团队首先通过模块化的合成策略，制备了10种具有不同电子供体强度的C2修饰五甲川氰胺染料（Cy5）。光物理性质表征发现，这些染料在近红外区域表现出强烈的吸收，且随着取代基供电子能力的增强，荧光量子产率显著下降，并伴随着明显的电荷转移（CT）发射信号。实验观察到一个显著的 “火山型”曲线关系：单线态氧量子产率起初随PeT效率的提升而增加，但在超过临界点（如染料8）后，产率反而急剧下降。这表明盲目追求PeT效率会引发严重的动力学惩罚。
Photophysical characterization and structure–property relationships of C2-modified cyanine dyes. Normalized absorption (A) and emission (B) spectra of representative cyanine dyes in dichloromethane (DCM). (C) Normalized emission spectra of dye 8 (TCy-Pyr) in solvents of varying polarity (dioxane, DCM, and acetonitrile). (D) of the C2-modified dye series in solvents of different polarities. (E) Fluorescence decay profiles of TCy-Pyr and TCy-H in DCM. (F) Comparative 1O2 generation capability assessed by the normalized degradation of the DPBF probe under 660 nm irradiation (2 mW cm−2). (G) Electron spin resonance spectra of TCy-Pyr and TCy-H under light irradiation using TEMP as trap. (H) Volcano plot illustrating the non-linear correlation between fluorescence quenching efficiency (a proxy for PeT efficiency) and .
Theoretical insights into the excited-state dynamics and kinetic competition in C2-modified cyanine dyes. (A) Schematic illustration of the acceptor-photoinduced electron transfer (a-PeT) mechanism, accompanied by the computed FMOs of TCy-Pyr. (B) Energy level diagram comparing the frontier orbitals of TCy-H and the C2-modified series. Calculated excited-state relaxation dynamics (C) and the corresponding electron–hole analysis (D) for TCy-Pyr. Key parameters including the donor–acceptor dihedral angle (θ), electron–hole distance (D), and charge-transfer character (CT index) are monitored along the relaxation coordinate. (E) Estimated for the CS to T2 transition across the dye series, calculated using the Marcus empirical formula. (F) Computed for the CS to S0 pathway based on non-adiabatic coupling matrix elements. (G) Comparison of key parameters governing non-radiative decay—total Huang–Rhys factor (ΣSi), reorganization energy (λ), and RMSD—between the charge-separated and ground states for TCy-Pyr and dye 9.
为了深入理解这一机制，团队利用飞秒瞬态吸收光谱（fs-TA） 和量子化学计算对激发态动力学进行了剖析。研究发现，PeT过程产生的CS态是一个关键的分叉点，它面临着系间窜越（ISC） 与内转换（IC） 通路的激烈竞争。根据能量间隔律，当CS态能量被过度稳定（即能量降低）时，非辐射复合（内转换）的速率会呈指数级增长。计算结果证实，在强供体体系中，内转换速率甚至超过了系间窜越速率，从而关闭了三线态通道。基于此，团队识别出性能最优的分子TCy-Pyr，它在维持高效PeT的同时，保证了CS态能量处于临界阈值之上，从而实现了高达16.9%的单线态氧产率。
Unraveling excited-state dynamics via time-resolved transient absorption spectroscopy. Femtosecond transient absorption (fs-TA) spectra of the TCy-H (A), TCy-Pyr (B), and dye 9 (C) in DCM. (D) Representative kinetic traces monitored at selected probe wavelengths for TCy-H (500 and 675 nm), TCy-Pyr (510, 675, and 750 nm), and dye 9 (510, 675, and 750 nm). (E) Species-associated difference spectra (SADS) obtained from global target analysis of the fs-TA data for TCy-H, TCy-Pyr, and dye 9. (F) Corresponding population dynamics of the excited-state species resolved from the global analysis. (G) Nanosecond transient absorption (ns-TA) spectra of TCy-H and TCy-Pyr in deaerated DCM. Decay kinetics of the triplet state for TCy-H (H) and TCy-Pyr (I) on the nanosecond timescale.
Environment-responsive self-assembly and intracellular activation of TCy-Pyr. (A) Normalized absorption spectra of TCy-Pyr in DCM (monomeric state) and aqueous solution (aggregated state). (B) DLS analysis showing size distribution and (C) TEM image visualizing the morphology of the nanostructures. (D) ESP surface maps and (E) corresponding quantitative statistical analysis of ESP regions for TCy-H and TCy-Pyr. (F) Analysis of weak intermolecular interactions in TCy-Pyr aggregates. (G) Time-dependent fluorescence intensity of 4T1 cells co-incubated with TCy-H or TCy-Pyr (n = 5). (H) Normalized fluorescence spectra and _Φ_f of TCy-Pyr in aqueous solution, DCM, and cellular environments. (I) Fluorescence lifetime of TCy-Pyr in aqueous solution and cellular milieu.
在生物应用方面，TCy-Pyr表现出独特的环境响应型自组装行为。在水溶液中，该分子自发形成纳米颗粒，通过增强渗透与滞留（EPR）效应实现了优异的肿瘤靶向性。进入细胞后，在内质网的疏水环境中，纳米颗粒解聚恢复为单体活性状态。体外细胞实验显示，TCy-Pyr的光动力治疗指数（PI）达到约200，远超传统光敏剂。机制研究表明，该光敏剂特异性富集于内质网，诱发强烈的内质网应激和钙离子泄漏，最终通过细胞凋亡和细胞副凋亡（Paraptosis） 的双重路径高效杀伤肿瘤细胞。在4T1荷瘤小鼠模型中，单次注射及低剂量光照即可实现超过91%的肿瘤抑制率，且具有极高的生物安全性。
In vitro biological evaluation of TCy-Pyr in cancer cells. (A) Subcellular colocalization images of TCy-Pyr with ER-Tracker Blue in 4T1 cells; Pearson's correlation coefficient (P) is indicated. (B) Flow cytometric analysis of ROS generation under different conditions. (C) In vitro PDT efficacy: IC50 (µM) and photodynamic therapeutic index (PI) of TCy-Pyr, TCy-H, TCy-Br, and MB in 4T1 and HepG2 cells. (D) Live/Dead (green/red) cell staining of 4T1 cells treated with different treatments. (E) ER morphology changes in 4T1 cells with different treatments. (F) Changes in cytosolic Ca2+ concentration, monitored using Fluo-4 AM probe with different treatments. (G) Confocal fluorescence images of 4T1 cells stained with Annexin V-FITC/PI. (H) Morphological changes of 4T1 cells observed by optical micros-copy and (I) TEM after different treatments.
Molecular insights into the therapeutic mechanism and immunogenicity of TCy-Pyr. (A) Pearson correlation analysis. (B) Volcano map of differential genes. (C) KEGG plot analysis of differential genes obtained from the 4T1 cells incubated with or without PDT. (D) Western blot analysis of key protein markers associated with ER stress, autophagy, apoptosis, and paraptosis across different treatment groups. . (E) Live/Dead (green/red) cell staining of 4T1 cells treated with different treatments. (F) Diagram of apoptosis and paraptosis induced by TCy-Pyr in 4T1 cells.
In vivo biodistribution, tumor-targeting capability, and biosafety profile of TCy-Pyr. (A) In vivo real-time fluorescence im-aging and (B) tumor site fluorescence intensity analysis of 4T1 tumor-bearing mice after intravenous injection of TCy-H and TCy-Pyr (n = 3). (C, D) Fluorescence images and (E, F) corresponding fluorescence intensity quantification of major organs and tumors harvested at 24 and 120 h post-injection (n = 3). (G) Representative H&E-stained images of major organs from mice treated with TCy-Pyr at 0 h (Control), 24 h, and 120 h. *p < 0.05, **p < 0.01, and ***p < 0.001, by Student's t test.
In vivo photodynamic therapeutic efficacy and histological evaluation of TCy-Pyr in 4T1 tumor-bearing mice. (A) Schematic of the 4T1 tumor model establishment (initial volume ∼50 mm3) and the PDT therapeutic regimen. (B) Experimental group design (n = 5). (C) Individual tumor-growth curve of tumor-bearing mice in different treatment groups. (D) Tumor volumes and (E) weight of 4T1-bearing mice after different treatments. (F) Photographs of the tumor collected at the end of the therapeutic period. (G) Changes in body weight of the 4T1-bearing mice after different treatments. (H) H&E-stained images and (I) Ki67 immunohistochemistry analysis of tumors collected from 4T1-bearing mice after different treatments. *p < 0.05, **p < 0.01, and ***p < 0.001, by Student's t test.
总结及展望
该研究不仅揭示了SOCT-ISC机制中PeT热力学与激发态弛豫路径之间的复杂相互作用，更提出了一套通用的理性设计原则。通过精确调节CS态能量水平，可以有效规避能量间隔律导致的动力学瓶颈。TCy-Pyr作为这一理论指导下的典范分子，展示了从基础机理研究到高性能临床前应用的转化潜力。这项工作为开发下一代无重原子、高靶向性的光敏剂开辟了新路径，也为未来精准光动力医疗提供了强有力的分子工具库。