Highly Efficient,Conjugated‐Polymer‐Based Nano‐Photosensitizers for Selectively Targeted Two‐Photon Photodynamic Therapy and Imaging of Cancer Cells

Two‐photon photodynamic therapy (2P‐PDT) is a promising noninvasive treatment of cancers and other diseases with three‐dimensional selectivity and deep penetration. However, clinical applications of 2P‐PDT are limited by small two‐photon absorption (TPA) cross sections of traditional photosensitizers. The development of folate receptor targeted nano‐photosensitizers based on conjugated polymers is described. In these nano‐photosensitizers, poly{9,9‐bis[6′′‐(bromohexyl)fluorene‐2,7‐ylenevinylene]‐co‐alt‐1,4‐(2,5‐dicyanophenylene)}, which is a conjugated polymer with a large TPA cross section, acts as a two‐photon light‐harvesting material to significantly enhance the two‐photon properties of the doped photosensitizer tetraphenylporphyrin (TPP) through energy transfer. These nanoparticles displayed up to 1020‐fold enhancement in two‐photon excitation emission and about 870‐fold enhancement in the two‐photon‐induced singlet oxygen generation capability of TPP. Surface‐functionalized folic acid groups make these nanoparticles highly selective in targeting and killing KB cancer cells over NIH/3T3 normal cells. The 2P‐PDT activity of these nanoparticles was significantly improved, potentially up to about 1000 times, as implied by the enhancement factors of two‐photon excitation emission and singlet oxygen generation. These nanoparticles could act as novel two‐photon nano‐photosensitizers with combined advantages of low dark cytotoxicity, targeted 2P‐PDT with high selectivity, and simultaneous two‐photon fluorescence imaging capability; these are all required for ideal two‐photon photosensitizers.     

Synthesis and In Vitro Photodynamic Activities of an Integrin‐Targeting cRGD‐Conjugated Zinc(II) Phthalocyanine

A 1,4‐disubstituted zinc(II) phthalocyanine conjugated with a cyclic Arg‐Gly‐Asp‐D ‐Phe‐Lys (cRGDfK) moiety through a triazole linker was prepared and characterized by UV/Vis spectroscopy and high‐resolution ESI‐MS. The conjugate showed a relatively weak fluorescence emission in N,N‐dimethylformamide (Φ_F=0.08), but it was a very efficient singlet oxygen generator (Φ_Δ=0.80) as a result of the di‐α‐substituted structure. Owing to the presence of the cyclic peptide sequence cRGDfK, which is a well‐known α_vβ₃‐integrin antagonist, this conjugate exhibited significantly higher cellular uptake toward the α_vβ₃⁺ U87‐MG cells compared with the α_vβ₃^? MCF‐7 cells, as determined by flow cytometry and fluorescence microscopy. The photocytotoxicity of this compound against these two cell lines, however, was comparable owing to the similar efficiency of intracellular reactive oxygen species generation. Confocal microscopic studies also revealed that this conjugate localized preferentially in the lysosomes, but not in the nucleus, endoplasmic reticulum, and mitochondria of the U87‐MG cells.     

酞菁在光动力治疗中的应用

光动力治疗因具有低毒、副作用小、抗癌广谱、高选择性等优势,正吸引着人们越来越多的关注。提高光敏剂的选择性和光毒性已经成为研究的热点。本文简单介绍了光敏剂的发展历程,并对酞菁类第三代光动力治疗光敏剂的最新研究进展进行了论述。     

酞菁在光动力治疗中的应用

光动力治疗因具有低毒、副作用小、抗癌广谱、高选择性等优势, 正吸引着人们越来越多的关注。提高光敏剂的选择性和光毒性已经成为研究的热点。本文简单介绍了光敏剂的发展历程, 并对酞菁类第三代光动力治疗光敏剂的最新研究进展进行了论述。     

可激活抗癌光敏剂

光动力治疗（Photodynamic therapy,PDT）是利用光敏剂在光照下促使分子氧转为具有细胞毒性的活性氧,从而达到破坏靶细胞和靶组织效应的一种治疗手段。可激活光敏剂（Activatable photosensitizers,aPSs）是指事先屏蔽了光敏效应的光敏剂,只在特定因素下,如与肿瘤相关的特异性酶、酸性pH、核酸等的激活下,光敏剂转为激活状态,从而发挥诊断或者治疗的作用。可激活光敏剂由于具有更高的选择性而备受瞩目,成为医用光敏剂领域的研究前沿热点。本文将总结和分析近年来可激活抗癌光敏剂的研究现状和构效关系,以期为后续的相关研究提供参考。     

基于长波长光激发的光敏剂和载体在肿瘤光动力治疗中的应用

光动力疗法是近年来兴起的一种新型的微创性治疗肿瘤的方法,目前已经成功地应用于临床上多种恶性肿瘤治疗中,并取得了良好的效果。然而,由于生物组织对可见光的吸收和散射,使得光线无法穿透组织到达身体内的目标区域,所以该疗法更适用于浅表肿瘤的治疗。长波长光尤其是近红外光具有良好的组织穿透深度,其在治疗组织深处的肿瘤方面具有显著的优势。基于长波长光激发的光敏剂及载体在实体肿瘤的治疗领域已经取得了丰硕的研究成果。本文将从光敏剂的研发、双光子激光的使用、上转换纳米粒子的引入等方面简要概述近十年来用于光动力治疗中的组装体系,以及长波长激发光在光动力治疗方面的发展趋势。     

Near‐IR Absorbing BODIPY Derivatives as Glutathione‐Activated Photosensitizers for Selective Photodynamic Action

Enhanced spatiotemporal selectivity in photonic sensitization of dissolved molecular oxygen is an important target for improving the potential and the practical applications of photodynamic therapy. Considering the high intracellular glutathione concentrations within cancer cells, a series of BODIPY‐based sensitizers that can generate cytotoxic singlet oxygen only after glutathione‐mediated cleavage of the electron‐sink module were designed and synthesized. Cell culture studies not only validate our design, but also suggest an additional role for the relatively hydrophobic quencher module in the internalization of the photosensitizer.     

Highly Charged Ruthenium(II) Polypyridyl Complexes as Lysosome‐Localized Photosensitizers for Two‐Photon Photodynamic Therapy

Photodynamic therapy (PDT) is a noninvasive medical technique that has received increasing attention over the last years and been applied for the treatment of certain types of cancer. However, the currently clinically used PDT agents have several limitations, such as low water solubility, poor photostability, and limited selectivity towards cancer cells, aside from having very low two‐photon cross‐sections around 800 nm, which limits their potential use in TP‐PDT. To tackle these drawbacks, three highly positively charged ruthenium(II) polypyridyl complexes were synthesized. These complexes selectively localize in the lysosomes, an ideal localization for PDT purposes. One of these complexes showed an impressive phototoxicity index upon irradiation at 800 nm in 3D HeLa multicellular tumor spheroids and thus holds great promise for applications in two‐photon photodynamic therapy.     

Pheophytin Derived Near‐Infrared‐Light Responsive Carbon Dot Assembly as a New Phototheranotic Agent for Bioimaging and Photodynamic Therapy

Carbon dots (CDs), a kind of phototheranostic agent with the capability of simultaneous bioimaging and phototherapy [i.e., photodynamic therapy (PDT) or photothermal therapy (PTT)], have received considerable attention because of their remarkable properties, including flexibility for surface modification, high biocompatibility, low toxicity and photo‐induced activity for malignant tumor cells. Among numerous carbon sources, it has been found that natural biomass are good candidates for the preparation of CD phototheranostic agents. In this study, pheophytin, a type of Mg‐free chlorophyll derivative and also a natural product with low toxicity, was used as a raw carbon source for the synthesis of CDs by using a microwave method. The obtained hydrophobic CDs exhibited a maximum near‐infrared (NIR) emission peak at approximately 680 nm, and high singlet oxygen (¹O₂) generation with a quantum yield of 0.62. The self‐assembled CDs from the as‐prepared CDs with DSPE‐mPEG2000 retained efficient ¹O₂ generation. The obtained carbon dot assembly was not only an efficient fluorescence (FL) imaging agent but also a smart PDT agent. Our studies indicated that the obtained hydrophilic CD assembly holds great potential as a new phototheranostic agent for cancer therapy. This work provides a new route for synthesis of CDs and proposes a readily available candidate for tumor treatment.     

Specific Light‐Up Bioprobe with Aggregation‐Induced Emission and Activatable Photoactivity for the Targeted and Image‐Guided Photodynamic Ablation of Cancer Cells

Activatable photosensitizers (PSs) have been widely used for the simultaneous fluorescence imaging and photodynamic ablation of cancer cells. However, the ready aggregation of traditional PSs in aqueous media can lead to fluorescence quenching as well as reduced phototoxicity even in the activated form. We have developed a series of PSs that show aggregation‐enhanced emission and phototoxicity and thus the exact opposite behavior to that of previously reported PSs. We further developed a dual‐targeted enzyme‐activatable bioprobe based on the optimized photosensitizer and describe simultaneous light‐up fluorescence imaging and activated photodynamic therapy for specific cancer cells. The design of smart probes should thus open new opportunities for targeted and image‐guided photodynamic therapy.     

Nanobody-Ferritin Conjugate for Targeted Photodynamic Therapy

Ferritin is an iron-storage protein nanocage that is assembled from 24 subunits. The hollow cavity of ferritin enables its encapsulation of various therapeutic agents; therefore, ferritin has been intensively investigated for drug delivery. The use of antibody-ferritin conjugates provides an effective approach for targeted drug delivery. However, the complicated preparation and limited protein stability hamper wide applications of this system. Herein, we designed a novel nanobody-ferritin platform (Nb-Ftn) for targeted drug delivery. The site-specific conjugation between nanobody and ferritin is achieved by transglutaminase-catalyzed protein ligation. This ligation strategy allows the Nb conjugation after drug loading in ferritin, which avoids deactivation of the nanobody under the harsh pH environment required for drug encapsulation. To verify the tumor targeting of this Nb-Ftn platform, a photodynamic reagent, manganese phthalocyanine (MnPc), was loaded into the ferritin cavity, and an anti-EGFR nanobody was conjugated to the surface of the ferritin. The ferritin nanocage can encapsulate about 82 MnPc molecules. This MnPc@Nb-Ftn conjugate can be efficiently internalized by EGFR positive A431 cancer cells, but not by EGFR negative MCF-7 cells. Upon 730 nm laser irradiation, MnPc@Nb-Ftn selectively killed EGFR positive A431 cells by generating reactive oxygen species (ROS), whereas no obvious damage was observed on MCF-7 cells. Given that ferritin can be used for encapsulation of various therapeutic agents, this work provides a strategy for facile construction of nanobody-ferritin for targeted drug delivery.     

Simple Peptide‐Tuned Self‐Assembly of Photosensitizers towards Anticancer Photodynamic Therapy

Peptide‐tuned self‐assembly of functional components offers a strategy towards improved properties and unique functions of materials, but the requirement of many different functions and a lack of understanding of complex structures present a high barrier for applications. Herein, we report a photosensitive drug delivery system for photodynamic therapy (PDT) by a simple dipeptide‐ or amphiphilic amino‐acid‐tuned self‐assembly of photosensitizers (PSs). The assembled nanodrugs exhibit multiple favorable therapeutic features, including tunable size, high loading efficiency, and on‐demand drug release responding to pH, surfactant, and enzyme stimuli, as well as preferable cellular uptake and biodistribution. These features result in greatly enhanced PDT efficacy in vitro and in vivo, leading to almost complete tumor eradication in mice receiving a single drug dose and a single exposure to light.     

Ultra‐pH‐Responsive and Tumor‐Penetrating Nanoplatform for Targeted siRNA Delivery with Robust Anti‐Cancer Efficacy

RNA interference (RNAi) gene silencing technologies have shown significant potential for treating various diseases, including cancer. However, clinical success in cancer therapy remains elusive, mainly owing to suboptimal in vivo delivery of RNAi therapeutics such as small interference RNA (siRNA) to tumors. Herein, we developed a library of polymers that respond to a narrow pH change (ultra‐pH‐responsive), and demonstrated the utility of these materials in targeted and deep tumor‐penetrating nanoparticle (NP) for in vivo RNAi. The new NP platform is mainly composed of the following key components: i) internalizing RGD (iRGD) to enhance tumor targeting and tissue penetration; ii) polyethylene glycol (PEG) chains to prolong blood circulation; and iii) sharp pH‐responsive hydrophobic polymer to improve endosome escape. Through systematic studies of structure–function relationship, the optimized RNAi NPs (<70 nm) showed efficient gene silencing and significant inhibition of tumor growth with negligible toxicities in vivo.     

Near‐Infrared Light and pH‐Responsive Polypyrrole@Polyacrylic acid/Fluorescent Mesoporous Silica Nanoparticles for Imaging and Chemo‐Photothermal Cancer Therapy

We have rationally designed a new theranostic agent by coating near‐infrared (NIR) light‐absorbing polypyrrole (PPY) with poly(acrylic acid) (PAA), in which PAA acts as a nanoreactor and template, followed by growing small fluorescent silica nanoparticles (fSiO₂ NPs) inside the PAA networks, resulting in the formation of polypyrrole@polyacrylic acid/fluorescent mesoporous silica (PPY@PAA/fmSiO₂) core–shell NPs. Meanwhile, DOX‐loaded PPY@PAA/fmSiO₂ NPs as pH and NIR dual‐sensitive drug delivery vehicles were employed for fluorescence imaging and chemo‐photothermal synergetic therapy in vitro and in vivo. The results demonstrate that the PPY@PAA/fmSiO₂ NPs show high in vivo tumor uptake by the enhanced permeability and retention (EPR) effect after intravenous injection as revealed by in vivo fluorescence imaging, which is very helpful for visualizing the location of the tumor. Moreover, the obtained NPs inhibit tumor growth (95.6 % of tumors were eliminated) because of the combination of chemo‐photothermal therapy, which offers a synergistically improved therapeutic outcome compared with the use of either therapy alone. Therefore, the present study provides new insights into developing NIR and pH‐stimuli responsive PPY‐based multifunctional platform for cancer theranostics.     

A Multifunctional Nanomicelle for Real‐Time Targeted Imaging and Precise Near‐Infrared Cancer Therapy

Simultaneous targeted cancer imaging, therapy and real‐time therapeutic monitoring can prevent over‐ or undertreatment. This work describes the design of a multifunctional nanomicelle for recognition and precise near‐infrared (NIR) cancer therapy. The nanomicelle encapsulates a new pH‐activatable fluorescent probe and a robust NIR photosensitizer, R16FP, and is functionalized with a newly screened cancer‐specific aptamer for targeting viable cancer cells. The fluorescent probe can light up the lysosomes for real‐time imaging. Upon NIR irradiation, R16FP‐mediated generation of reactive oxygen species causes lysosomal destruction and subsequently trigger lysosomal cell death. Meanwhile the fluorescent probe can reflect the cellular status and in situ visualize the treatment process. This protocol can provide molecular information for precise therapy and therapeutic monitoring.     

Mitochondrial‐DNA‐Targeted IrIII‐Containing Metallohelices with Tunable Photodynamic Therapy Efficacy in Cancer Cells

The development of DNA‐targeted photodynamic therapy (PDT) agents for cancer treatment has drawn substantial attention. Herein, the design and synthesis of dinuclear Ir^III‐containing luminescent metallohelices with tunable PDT efficacy that target mitochondrial DNA in cancer cells are reported. The metallohelices are fabricated using dynamic imine‐coupling chemistry between aldehyde end‐capped fac‐Ir(ppy)₃ handles and linear alkanediamine spacers, followed by reduction of the imine linkages. The length and odd–even character of the diamine alkyl linker determined the stereochemistry (helicates vs. mesocates). Compared to the helicates, the mesocates exhibit improved apoptosis‐induction upon white‐light irradiation. Molecular docking studies indicate that the mesocate with a proper length of diamine spacers shows stronger affinity for the minor groove of DNA. This study highlights the potential of DNA‐targeting Ir^III‐containing metallohelices as PDT agents.     

Development of Biotechnological Photosensitizers for Photodynamic Therapy: Cancer Research and Treatment—From Benchtop to Clinical Practice

Photodynamic therapy (PDT) is a noninvasive therapeutic approach that has been applied in studies for the treatment of various diseases. In this context, PDT has been suggested as a new therapy or adjuvant therapy to traditional cancer therapy. The mode of action of PDT consists of the generation of singlet oxygen (¹O₂) and reactive oxygen species (ROS) through the administration of a compound called photosensitizer (PS), a light source, and molecular oxygen (³O₂). This combination generates controlled photochemical reactions (photodynamic mechanisms) that produce ROS, such as singlet oxygen (¹O₂), which can induce apoptosis and/or cell death induced by necrosis, degeneration of the tumor vasculature, stimulation of the antitumor immune response, and induction of inflammatory reactions in the illuminated region. However, the traditional compounds used in PDT limit its application. In this context, compounds of biotechnological origin with photosensitizing activity in association with nanotechnology are being used in PDT, aiming at its application in several types of cancer but with less toxicity toward neighboring tissues and better absorption of light for more aggressive types of cancer. In this review, we present studies involving innovatively developed PS that aimed to improve the efficiency of PDT in cancer treatment. Specifically, we focused on the clinical translation and application of PS of natural origin on cancer.     

靶标性酞菁类光敏剂的光动力疗法研究进展

光动力治疗（Photodynamic therapy,PDT）作为一种有别于传统癌症治疗方式的新型疗法,近些年来受到了科学家们越来越多的关注.它凭借着自身创伤性小,毒性低微,适用性好,可协同手术治疗以及可重复治疗等独特优势,在许多肿瘤的治疗方面有着广泛的应用.本文简要概述了光动力疗法的原理以及光敏剂的发展历程,并对理想光敏剂的特点作了总结.目前,以酞菁类化合物为主的第三代光敏剂已经成为光动力疗法的研究热点,然而如何提高光敏剂分子的靶向性达到精准的光动力治疗仍然是亟待解决的问题.因此,主要综述了近年来靶向性酞菁类光敏剂的研究进展,并对未来光敏剂的重点研究方向做出了展望.从目前来看,如何克服癌症低氧微环境的限制,发展Type I型不依赖氧的体系以及光穿透力强的靶向光敏剂在光动力治疗方面存在着巨大的潜质,有望成为新一代十分优良的光动力疗法用光敏剂.     

Bioorthogonal Turn-On BODIPY-Peptide Photosensitizers for Tailored Photodynamic Therapy

Photodynamic therapy (PDT) leads to cancer remission via the production of cytotoxic species under photosensitizer (PS) irradiation. However, concomitant damage and dark toxicity can both hinder its use. With this in mind, we have implemented a versatile peptide-based platform of bioorthogonally activatable BODIPY-tetrazine PSs. Confocal microscopy and phototoxicity studies demonstrated that the incorporation of the PS, as a bifunctional module, into a peptide enabled spatial and conditional control of singlet oxygen (¹O₂) generation. Comparing subcellular distribution, PS confined in the cytoplasmic membrane achieved the highest toxicities (IC₅₀=0.096±0.003 μm ) after activation and without apparent dark toxicity. Our tunable approach will inspire novel probes towards smart PDT.