A smart and visible way to switch the aromaticity of silicon(IV) phthalocyanines.

Unlike traditional methods of modifying phthalocyanines (Pcs), we herein report a smart and visible way to switch the aromaticity of silicon(IV) phthalocyanines via a reversible nucleophilic addition reaction of the Pc skeleton induced by alkalis and acids, leading to an interesting allochroism phenomenon and the switching of photosensitive activities.

A Sulfur-Bridging Sulfonate-Modified Zinc(II) Phthalocyanine Nanoliposome Possessing Hybrid Type I and Type II Photoreactions with Efficient Photodynamic Anticancer Effects.

Phthalocyanines are potentially promising photosensitizers (PSs) for photodynamic therapy (PDT), but the inherent defects such as aggregation-caused quenching effects and non-specific toxicity severely hinder their further application in PDT. Herein, we synthesized two zinc(II) phthalocyanines (PcSA and PcOA) monosubstituted with a sulphonate group in the alpha position with "O bridge" and "S bridge" as bonds and prepared a liposomal nanophotosensitizer (PcSA@Lip) by thin-film hydration method to regulate the aggregation of PcSA in the aqueous solution and enhance its tumor targeting ability. PcSA@Lip exhibited highly efficient production of superoxide radical (O2∙-) and singlet oxygen (1O2) in water under light irradiation, which were 2.6-fold and 15.4-fold higher than those of free PcSA, respectively. Furthermore, PcSA@Lip was able to accumulate selectively in tumors after intravenous injection with the fluorescence intensity ratio of tumors to livers was 4.1:1. The significant tumor inhibition effects resulted in a 98% tumor inhibition rate after PcSA@Lip was injected intravenously at an ultra-low PcSA@Lip dose (0.8 nmol g-1 PcSA) and light dose (30 J cm-2). Therefore, the liposomal PcSA@Lip is a prospective nanophotosensitizer possessing hybrid type I and type II photoreactions with efficient photodynamic anticancer effects.

Thermosensitive Liposomal Nanoplatform Based on Metal-Free Phthalocyanine with Copper(II)-Regulated Photoactivities.

This work reports the development of a multifunctional thermosensitive liposomal nanoplatform (PcS4 @Lip-FA) based on a metal-free phthalocyanine modified with tetra-sulfonates (PcPS4 ), which exhibited photodynamic and photothermal activities simultaneously. Upon irradiation with a near infrared laser, thermosensitive PcS4 @Lip-FA could release PcS4 as a result of the local hyperthermia of PcS4 . Interestingly, PcS4 could easily chelate with Cu2+ , leading to the enhancement of photothermal activity and decrease of photodynamic activity. In addition, in vivo fluorescence imaging revealed that PcS4 @Lip-FA could selectively accumulate in tumor tissue of H22 tumor-bearing mice after tail vein injection, and exhibited a significant anticancer phototherapeutic effect, with a tumor inhibition rate of 83.5 %. Therefore, PcPS4 @Lip-FA has realized fluorescence imaging-guided combined cancer treatment, providing a promising multifunctional nanoplatform for cancer diagnostics and therapy.

Molecular and Supramolecular Approach to Highly Photocytotoxic Phthalocyanines with Dual Cell Uptake Pathways and Albumin-Enhanced Tumor Targeting.

Phototherapy for non-invasive cancer treatment has been extensively studied. An urgent challenge in phototherapy application is to fabricate appropriate targeted agents to achieve efficient therapeutic effect. Herein, a molecular and supramolecular approach for targeting phototherapy was reasonably designed and realized through the axial sulfonate modification of silicon(IV) phthalocyanines (Pcs), followed by supramolecular interaction with albumin. This approach can not only improve the photoactivities (e.g., fluorescence emission and reactive oxygen species production) of the Pcs but also enhance their tumor targeting. Most importantly, one of the deigned Pcs (4) can target HepG2 cells through dual cell pathways, leading to an extremely high phototoxicity with an EC50 (i.e., concentration of Pcs to kill 50% of cells under light irradiation) value of 2.0 nM. This finding presents a feasible strategy to realize efficient targeting phototherapy.

Aggregation-Enhanced Sonodynamic Activity of Phthalocyanine-Artesunate Conjugates.

The clinical prospect of sonodynamic therapy (SDT) has not been fully realized due to the scarcity of efficient sonosensitizers. Herein, we designed phthalocyanine-artesunate conjugates (e.g. ZnPcT4 A), which could generate up to ca. 10-fold more reactive oxygen species (ROS) than the known sonosensitizer protoporphyrin IX. Meanwhile, an interesting and significant finding of aggregation-enhanced sonodynamic activity (AESA) was observed for the first time. ZnPcT4 A showed about 60-fold higher sonodynamic ROS generation in the aggregated form than in the disaggregated form in aqueous solutions. That could be attributed to the boosted ultrasonic cavitation of nanostructures. The level of the AESA effect depended on the aggregation ability of sonosensitizer molecules and the particle size of their aggregates. Moreover, biological studies demonstrated that ZnPcT4 A had high anticancer activities and biosafety. This study thus opens up a new avenue the development of efficient organic sonosensitizers.

Nanostructured Phthalocyanine Assemblies with Efficient Synergistic Effect of Type I Photoreaction and Photothermal Action to Overcome Tumor Hypoxia in Photodynamic Therapy.

Most photodynamic therapy (PDT) paradigms work through the highly O2-dependent type II photoreaction to generate singlet oxygen (1O2). The hypoxic microenvironment of solid tumors severely hampers therapeutic outcomes. Here, we present a novel design that could transfer the photophysical and photochemical properties of traditional phthalocyanine-based photosensitizers from type II photoreaction to efficient type I photoreaction and vibrational relaxation-induced photothermal conversion. These features enable the obtained nanostructured phthalocyanine assemblies (e.g., NanoPcAF) to display excellent phototherapies under both normoxic and hypoxic conditions. Moreover, NanoPcAF has a high level of accumulation in tumor tissues after intravenous injection, and 94% of tumor growth is inhibited in a preclinical model at a NanoPcAF dose of 0.8 nmol g-1 and light dose of 300 J cm-2.

A pH-sensitive nanoagent self-assembled from a highly negatively-charged phthalocyanine with excellent biosafety for photothermal therapy.

Photothermal therapy (PTT) is a promising strategy for cancer treatment. However, the development of highly efficient photothermal agents with excellent biosafety, particularly with low liver retention, is very meaningful for clinical applications, but it is also challenging. We herein prepared a pH-sensitive nanoagent (NanoPc3) by the self-assembly of a zinc(ii) phthalocyanine substituted with hexadeca-sulphonates linked by hydrazone bonds for photoacoustic imaging and PTT. Due to the highly negative surface potential (-30.80 mV in water), NanoPc3 could effectively escape the phagocytosis of the reticuloendothelial system and be rapidly cleared from normal tissues, leading to little accumulation in the liver and excellent biosafety. The highly negatively-charged NanoPc3 changed into nearly neutral nanoparticles (NanoPc3H) under slightly acidic conditions, resulting in enhanced cellular uptake and retention time in tumor tissues. Moreover, the tumor of H22 tumor-bearing mice treated with NanoPc3 almost disappeared, suggesting an outstanding photothermal antitumor effect. NanoPc3 also hardly showed skin phototoxicity under irradiation. Its excellent antitumor effect and biosafety make NanoPc3 highly promising in clinical applications. This work will provide a new strategy for the design of tumor-targeted photothermal nanoagents with high biosafety.

A phthalocyanine-based self-assembled nanophotosensitizer for efficient in vivo photodynamic anticancer therapy.

To develop highly efficient photosensitizers for photodynamic therapy, herein a zinc(II) phthalocyanine-folate conjugate (PcN-FA) used to construct an activatable nanophotosensitizer (NanoPcN-FA) through a facile self-assembly. The self-assembled nanophotosensitizer (NanoPcN) without folate-modification was used as a negative control. After self-assembly, the photoactivities of NanoPcN-FA was quenched. The in vitro studies showed that NanoPcN-FA could be taken in by folate-receptor (FR)-positive SKOV3 cells and activated in the cells. It also exhibited slightly higher photocytotoxicity against SKOV3 cells than NanoPcN. Moreover, the competitive assay confirmed that the cellular uptake of NanoPcN-FA was through a FR-mediated process. Finally, the in vivo results indicated that NanoPcN-FA could target tumor tissue of S180 rat ascitic tumor-bearing mice due to the folic acid (FA) ligand, leading to a highly efficient antitumor photodynamic efficacy with the tumor inhibition rate of 95%.

A non-aggregated zinc(II) phthalocyanine with hexadeca cations for antitumor and antibacterial photodynamic therapies.

With a view to developing highly efficient photosensitizers for both antitumor and antimicrobial photodynamic therapies, herein, we reported a super cationic zinc(II) phthalocyanine (Pc4), which was prepared through the quaternization of the N, N-dimethyl-3-aminophenoxyl-hexadeca-substituted precursor Pc3. Meanwhile, two disubstituted analogues (Pc1 and Pc2) were also prepared as controls. The cationic Pc2 and Pc4 had higher photoactivities including fluorescence and singlet oxygen than the neutral counterparts Pc1 and Pc3, probably because of the inhibition of intramolecular charge transfer (ICT) effect of the amino groups. With the bulky steric effect and high hydrophilicity, Pc4 presented non-aggregated behavior in aqueous solutions. Therefore, it exhibited the highest in vitro photodynamic activity toward HepG2 cancer cells with an IC50 value as low as 0.04 µM. Furthermore, Pc4 showed a highly efficient in vivo PDT effect on H22 tumor-bearing mice with 98.7% tumor growth inhibition. In addition, Pc4 also exhibited an excellent in vitro and in vivo photodynamic inactivation against S. aureus. The results indicate that the non-aggregated hexadeca-cationic Pc4 could serve as a promising photosensitizer for both antitumor and antimicrobial photodynamic therapies.

A non-aggregated silicon(IV) phthalocyanine-lactose conjugate for photodynamic therapy.

To develop a highly efficient photosensitizer for photodynamic therapy (PDT), we have designed and synthesized a phthalocyanine-lactose conjugate (Pc-Lac) through axial modification of silicon(IV) phthalocyanine with lactose moieties. With the lactose substituents, Pc-Lac is highly hydrophilic and non-aggregated with efficient reactive oxygen species (ROS) generation in aqueous media. With these desirable properties, Pc-Lac shows high photocytotoxicity and cellular uptake toward HepG2 cells. In addition, in vivo fluorescence imaging shows that Pc-Lac could selectively remain at tumor site, leading to its enhanced photodynamic efficacy against H22 tumor-bearing mice. Therefore, Pc-Lac shows a great potential as a highly efficient molecular photosensitizer for PDT.

Noncovalent Indocyanine Green Conjugate of C-Phycocyanin: Preparation and Tumor-Associated Macrophages-Targeted Photothermal Therapeutics.

Fabrication of a multifunctional near-infrared (NIR) theranostic nanoplatform has attracted increasing attention. Indocyanine green (ICG), a clinic-approved NIR fluorescence-imaging agent, is an excellent photothermal agent candidate. However, the stability and tumor targeting are still great obstacles for its wide application. In this work, C-phycocyanin (CPC) as a tumor-associated macrophages (TAMs) targeted vehicle was used to fabricate noncovalent ICG conjugate of CPC (ICG@CPC) via self-assembly in aqueous media. Compared to free ICG, ICG@CPC displays improved stabilities in aqueous solutions and under light irradiation and threefold increase in photothermal conversion efficiency. The in vitro results indicated that ICG@CPC could be selectively internalized into J774A.1 cells via SR-A-mediated endocytosis and lead to enhanced photocytotoxicity against J774A.1 cells. In vivo results showed that ICG@CPC had significantly improved drug accumulation in the tumor and photothermal therapeutic efficacy relative to ICG alone. This study for the first time utilizes CPC as a TAMs-targeted nanocarrier for ICG and may promote further rational design of ICG-based photothermal nanodrugs for precise and efficient cancer theranosis.

Artesunate-Based Multifunctional Nanoplatform for Photothermal/Photoinduced Thermodynamic Synergistic Anticancer Therapy.

Thermodynamic therapy (TDT), one that uses heat to activate thermosensitizers and produce reactive oxygen species (ROS), has recently emerged as an attractive approach for cancer therapy. However, the development of safe and efficient thermosensitizers for TDT remains a big challenge. Here, we have found that artesunate (ARS) could produce ROS upon heating. Based on this interesting result, we have designed and prepared a pH-sensitive liposomal nanoplatform (ICG-ARS@NPs) composed of indocyanine green (ICG) and ARS for photoinduced TDT as well as photothermal therapy (PTT). Under the slightly acidic conditions in tumor tissues, the pH-sensitive liposomal ICG-ARS@NPs were able to release their drug cargos. Upon near-infrared irradiation, the photothermal agent ICG generated in situ hyperthermia and triggered the thermal sensitizing activity of ARS to produce ROS, resulting in damage to cancer cells and tumor tissues. The heat-induced ROS generation of ARS was also confirmed both in vitro and in vivo. In addition, because of their specific tumor targeting and synergistic photothermal and thermodynamic effects, ICG-ARS@NPs exhibited highly efficient anticancer therapeutic efficacy in H22 tumor-bearing mice. We believe that this work will promote the exploration of TDT for cancer therapy as well as the application of the old drug, artemisinin.

Size-Tunable Targeting-Triggered Nanophotosensitizers Based on Self-Assembly of a Phthalocyanine-Biotin Conjugate for Photodynamic Therapy.

Self-assembled phototheranostic nanomaterials used for photodynamic therapy (PDT) have attracted increasing attention owing to their several advantages. Herein, we developed a novel strategy for size-tunable self-assembled nanophotosensitizers for PDT through a simple method. A series of switchable self-assembled nanophotosensitizers (NanoPc90, NanoPc40, NanoPc20, and NanoPc10) of different particle sizes were readily prepared based on an amphiphilic silicon(IV) phthalocyanine (SiPc)-biotin conjugate by regulating the amount of the Cremophor EL surfactant used. The photoactivities, including fluorescence and reactive oxygen species (ROS), of the self-assemblies could be regulated by the particle size. The self-assemblies could be specifically disassembled by tumor-overexpressing biotin receptors, leading to the recovery of quenched photoactivities. Demonstrated by the competitive assay, the self-assemblies were able to enter HepG2 cells through a biotin-receptor-mediated pathway, followed by biotin-receptor-triggered fluorescence recovery at the cellular level. Moreover, the particle size could also affect the in vitro and in vivo PDT effects and tumor targeting. The photocytotoxicity of NanoPc20 against HepG2 cells was more potent compared to that of NanoPc90 because of its strong intracellular fluorescence, higher intracellular ROS generation, and different subcellular localization. In addition, NanoPc20 showed higher in vivo tumor targeting and photodynamic therapeutic efficacy than NanoPc90. This work would provide a valuable reference for the development of self-assembled nanophotosensitizers for cancer diagnosis and therapy.

A pH-responsive stellate mesoporous silica based nanophotosensitizer for in vivo cancer diagnosis and targeted photodynamic therapy.

Development of a photosensitizer that can achieve tumor specificity, improve therapeutic efficacy, and reduce side effects remains a challenge for photodynamic therapy (PDT). In this work, a pH-sensitive activatable nanophotosensitizer (SMSN-ZnPc1) has been elaborately designed, which could be readily prepared by using a functionalized zinc(ii) phthalocyanine (ZnPc) to conjugate with stellate mesoporous silica nanoparticles (SMSNs) through an acid-sensitive hydrazone bond. Meanwhile, a non-activatable analogue SMSN-ZnPc2 has also been prepared as a negative control. The fluorescence emission and singlet oxygen generation of the photosensitizer are essentially quenched in the intact nanophotosensitizer. However, these properties of SMSN-ZnPc1 can be restored greatly both in acidic solutions and at the cellular level. More importantly, after intravenous administration, SMSN-ZnPc1 can also be selectively activated at the tumor site and exhibit efficient tumor growth inhibition in S180 rat ascitic tumor-bearing KM mice with negligible systemic toxicity. It thus may serve as a promising nanoplatform for cancer diagnosis and targeted PDT.

Synthesis and photodynamic activities of integrin-targeting silicon(IV) phthalocyanine-cRGD conjugates.

A series of novel symmetric or unsymmetric silicon (IV) phthalocyanines axially substituted with cyclic Arg-Gly-Asp (cRGD) ligands through different ethylene glycol chains have been synthesized by a facile and mild "click" reaction. All the compounds show efficient photosensitizing activities in N,N-dimethylformamide, and are essentially non-aggregated in RPMI 1640 medium with 0.05% Cremophor EL. Owing to the presence of two cRGD ligands, the conjugate 6b exhibits highest selectivity toward αvß3+ HT-29 cells in photocytotoxicities. It shows higher cellular uptake and ROS generation efficiency toward the αvß3+ HT-29 cells compared with that of αvß3- MCF-7 cells. The competitive cellular uptake and subcellular localization indicate that 6b is internalized mainly through integrin-mediated endocytosis. In addition, the in vivo studies showed that 6b can mainly accumulate in tumor sites and show a significant PDT effect resulting in 75% tumor growth inhibition. The results indicate that 6b is a highly promising photosensitizer for targeted photodynamic therapy.

Progress in the development of nanosensitizers for X-ray-induced photodynamic therapy.

In recent years, photodynamic therapy has been applied in cancer treatment because of its high selectivity and marginal invasion properties. However, the excitation light used has limited ability to penetrate tissue, which creates a stumbling block for its future development. To overcome this, X-rays have been introduced to transmit energy to deeper tissues. Given that a large number of X-ray-induced sensitizers have been designed to facilitate X-ray excitation and generate reactive oxygen species (ROS), this has led to the concept of X-ray-induced photodynamic therapy (X-PDT). After 10 years of development, this treatment now shows good therapeutic effects as well as shortcomings. Going forward, it will be important to improve tumor targeting and a standard deep-seated tumor model should be established.

New application of phthalocyanine molecules: from photodynamic therapy to photothermal therapy by means of structural regulation rather than formation of aggregates.

Phthalocyanine (Pc) molecules exhibit high extinction coefficients in near-infrared region, rendering them well-suited for phototherapies, but most of their applications are limited to the field of photodynamic therapy (PDT). Herein, for the first time, we illustrate that Pc molecules can be endowed with excellent photothermal properties by means of structural regulation rather than formation of aggregates. Three representative Pc derivatives show efficient activities of photothermal therapy (PTT) against human hepatocellular carcinoma cells. Among them, copper phthalocyanine (PcC1) exhibits a high in vivo PTT efficacy against mice bearing S180 tumors. The unique investigation in this article should light up a perspective of Pc's new applications for PTT, which enable to make up the inherent defects of PDT.

Synthesis and biological characterization of novel rose bengal derivatives with improved amphiphilicity for sono-photodynamic therapy.

Sono-Photodynamic therapy (SPDT) utilizing ultrasound and light has been demonstrated that this novel approach can lower dosage resulting in reduction of the potential side effects caused by sensitizers. Recently, a new formulation of rose bengal (RB) as an intralesional injection has completed clinical trials phase II for PDT treatment of melanoma cancer. However, the inherent unfavorable pharmacological properties of RB hindered its extensive clinical development. With the aim to identify new RB derivatives (RBDs) with enhanced photodynamic and sonodynamic anticancer efficiency, a series of amphiphilic RBDs have been designed, synthesized and biological characterized. Among them, RBD4 significantly improved cellular uptake and enhanced intracellular ROS generation efficiency upon light and ultrasound irradiation, resulting in dramatically improved anticancer potency. Notably, RBD4 has a relative potency similar to sinoporphyrin sodium (DVDMS), indicating its further potential application for SPDT.

Facile Supramolecular Approach to Nucleic-Acid-Driven Activatable Nanotheranostics That Overcome Drawbacks of Photodynamic Therapy.

Supramolecular chemistry provides a "bottom-up" method to fabricate nanostructures for biomedical applications. Herein, we report a facile strategy to directly assemble a phthalocyanine photosensitizer (PcS) with an anticancer drug mitoxantrone (MA) to form uniform nanostructures (PcS-MA), which not only display nanoscale optical properties but also have the capability of undergoing nucleic-acid-responsive disassembly. These supramolecular assemblies possess activatable fluorescence emission and singlet oxygen generation associated with the formation of free PcS, mild photothermal heating, and a concomitant chemotherapeutic effect associated with the formation of free MA. In vivo evaluations indicate that PcS-MA nanostructures have a high level of accumulation in tumor tissues, are capable of being used for cancer imaging, and have significantly improved anticancer effect compared to that of PcS. This study demonstrates an attractive strategy for overcoming the limitations of photodynamic cancer therapy.

A Tumor-pH-Responsive Supramolecular Photosensitizer for Activatable Photodynamic Therapy with Minimal In Vivo Skin Phototoxicity.

A major challenge in photodynamic therapy (PDT) is the development of new tumor-targeting photosensitizers. The tumor-specific activation is considered to be an effective strategy for designing these photosensitizers. Herein, we describe a novel tumor-pH-responsive supramolecular photosensitizer, LDH-ZnPcS8, which is not photoactive under neutral conditions but is precisely and efficiently activated in a slightly acidic environment (pH 6.5). LDH-ZnPcS8 is prepared by using a simple coprecipitation method based on the electrostatic interaction between negatively charged octasulfonate-modified zinc(II) phthalocyanine (ZnPcS8) and cationic hydroxide layers of layered double hydroxide (LDH). The in vitro photodynamic activities of LDH-ZnPcS8 in cancer cells are dramatically enhanced relative to those of ZnPcS8 alone. The results of in vivo fluorescence imaging demonstrate that the nanohybrid is activated in tumor tissues, where it displays an excellent PDT effect resulting in 95.3% tumor growth inhibition. Furthermore, the minimal skin phototoxicity of LDH-ZnPcS8 highlights its high potential as a novel photosensitizer for activatable PDT.