Nanophotosensitizers toward advanced photodynamic therapy of Cancer

X-ray induced photodynamic therapy with copper-cysteamine nanoparticles in mice tumors

Photodynamic therapy (PDT), a treatment that uses a photosensitizer, molecular oxygen, and light to kill target cells, is a promising cancer treatment method. However, a limitation of PDT is its dependence on light that is not highly penetrating, precluding the treatment of tumors located deep in the body. Copper-cysteamine nanoparticles are a new type of photosensitizer that can generate cytotoxic singlet oxygen molecules upon activation by X-rays. In this paper, we report on the use of copper-cysteamine nanoparticles, designed to be targeted to tumors, for X-ray-induced PDT. In an in vivo study, results show a statistically significant reduction in tumor size under X-ray activation of pH-low insertion peptide-conjugated, copper-cysteamine nanoparticles in mouse tumors. This work confirms the effectiveness of copper-cysteamine nanoparticles as a photosensitizer when activated by radiation and suggests that these Cu-Cy nanoparticles may be good candidates for PDT in deeply seated tumors when combined with X-rays and conjugated to a tumor-targeting molecule.

A Mn(III)-Sealed Metal-Organic Framework Nanosystem for Redox-Unlocked Tumor Theranostics

Here, a Mn(III)-sealed metal-organic framework (MOF) nanosystem based on coordination between Mn(III) and porphyrin (TCPP) via a one-pot method was designed and constructed. Mn(III), as a sealer, not only quenched TCPP-based fluorescence but also inhibited reactive oxygen species (ROS) generation, which made MOFs an "inert" theranostic nanoparticle. Interestingly, upon endocytosis by tumor cells, MOFs were disintegrated into Mn(II) and free TCPP by intracellular glutathione (GSH) in tumor cells, owing to redox reaction between Mn(III) and GSH. This disintegration would lead to consumption of antioxidant GSH and activated Mn(II)-based magnetic resonance imaging (MRI) as well as TCPP-based fluorescent imaging. More importantly, such a GSH-regulated TCPP release could implement controllable ROS generation under irradiation, which avoided side effects (inflammation and damage of normal tissues). As a consequence, after unlocking by GSH, Mn(III)-sealed MOFs could significantly improve the therapeutic efficiency of photodynamic therapy by combining controlled ROS generation and GSH depletion after precise dual tumor homing.

Advanced in silico modeling explains pharmacokinetics and biodistribution of temoporfin nanocrystals in humans

Foscan®, a formulation comprising temoporfin dissolved in a mixture of ethanol and propylene glycol, has been approved in Europe for palliative photodynamic therapy of squamous cell carcinoma of the head and neck. During clinical and preclinical studies it was observed that considering the administration route, the drug presents a rather atypical plasma profile as plasma concentration peaks delayed. Possible explanations, as for example the formation of a drug depot or aggregation after intravenous administration, are discussed in current literature. In the present study an advanced in silico model was developed and evaluated for the detailed description of Foscan® pharmacokinetics. Therefore, in vitro release data obtained from experiments with the dispersion releaser technology investigating dissolution pressures of various release media on the drug as well as in vivo data obtained from a clinical study were included into the in silico models. Furthermore, precipitation experiments were performed in presence of biorelevant media and precipitates were analyzed by nanoparticle tracking analysis. Size analysis and particle fraction were also incorporated in this model and a sensitivity analysis was performed. An optimal description of the in vivo situation based on in vitro release and particle characterization data was achieved, as demonstrated by an absolute average fold error of 1.21. This in vitro-in vivo correlation provides an explanation for the pharmacokinetics of Foscan® in humans.

Photodynamic therapy for cancer: Role of natural products

Photodynamic therapy (PDT) is a promising modality for the treatment of cancer. PDT involves administering a photosensitizing dye, i.e. photosensitizer, that selectively accumulates in tumors, and shining a light source on the lesion with a wavelength matching the absorption spectrum of the photosensitizer, that exerts a cytotoxic effect after excitation. The reactive oxygen species produced during PDT are responsible for the oxidation of biomolecules, which in turn cause cell death and the necrosis of malignant tissue. PDT is a multi-factorial process that generally involves apoptotic death of the tumor cells, degeneration of the tumor vasculature, stimulation of anti-tumor immune response, and induction of inflammatory reactions in the illuminated lesion. Numerous compounds with photosensitizing activity have been introduced commercially. Although many papers have been published with regard to PDT in the last decade, there has been relatively little focus on natural medicinal plant extracts and compounds derived therefrom. Herbal plants and their extracts are natural substances, and in comparison with synthetic chemicals are considered "green". This review focuses on the different mechanisms of PDT and discusses the role of various plant extracts and natural compounds either alone or in combination for carrying out PDT on different types of cancers.

Breaking the Depth Dependence by Nanotechnology-Enhanced X-Ray-Excited Deep Cancer Theranostics

The advancements in nanotechnology have created multifunctional nanomaterials aimed at enhancing diagnostic accuracy and treatment efficacy for cancer. However, the ability to target deep-seated tumors remains one of the most critical challenges for certain nanomedicine applications. To this end, X-ray-excited theranostic techniques provide a means of overcoming the limits of light penetration and tissue attenuation. Herein, a comprehensive overview of the recent advances in nanotechnology-enhanced X-ray-excited imaging and therapeutic methodologies is presented, with an emphasis on the design of multifunctional nanomaterials for contrast-enhanced computed tomography (CT) imaging, X-ray-excited optical luminescence (XEOL) imaging, and X-ray-excited multimodal synchronous/synergistic therapy. The latter is based on the concurrent use of radiotherapy with chemotherapy, gas therapy, photodynamic therapy, or immunotherapy. Moreover, the featured biomedical applications of X-ray-excited deep theranostics are discussed to highlight the advantages of X-ray in high-sensitivity detection and efficient elimination of malignant tumors. Finally, key issues and technical challenges associated with this deep theranostic technology are identified, with the intention of advancing its translation into the clinic.

Postsynthetic Ligand Exchange of Metal-Organic Framework for Photodynamic Therapy

Attributed to the large pore size and excellent stability, the metal-organic framework (MOF), NU-1000, which is formed by the coordination of Zr cluster and 1,3,6,8-tetrakis( p-benzoic acid)pyrene (H₄TBAPy) ligand, has been widely studied in the catalysis research field; however, only a few reports about the biomedical application of NU-1000 could be found in the open literature. In this study, a functional ligand, tetrakis(4-carboxyphenyl)porphyrin (TCPP), was introduced into NU-1000 via a postsynthetic ligand exchange method and the resulting mixed ligand MOF has an excellent photodynamic effect. Finally, in vitro and in vivo assessment about the antitumor efficacy was investigated for the first time. It demonstrates the feasibility of TCPP-substituted NU-1000 to be used for photodynamic therapy and also provides an alternative approach to enrich the function of MOF for various applications via a postsynthetic method.

Ce6-Modified Carbon Dots for Multimodal-Imaging-Guided and Single-NIR-Laser-Triggered Photothermal/Photodynamic Synergistic Cancer Therapy by Reduced Irradiation Power

Photomediated cancer therapy, mainly including photothermal (PT) therapy (PTT) and photodynamic therapy (PDT), has attracted tremendous attention in recent years thanks to its noninvasive and stimuli-responsive features. The single mode of PTT or PDT, however, has obvious drawbacks, either requiring high-power laser irradiation to generate enough heat or only providing limited efficacy due to the hypoxia nature inside tumors. In addition, the reported synergistic PTT/PDT generally utilized two excitation sources to separately activate PTT and PDT, and the problem of high-power laser irradiation for PTT was still not well solved. Herein, a new concept, loading a small amount of photosensitizers onto a PTT agent (both of them can be triggered by a single-near-infrared (NIR) laser), was proposed to evade the shortcomings of PTT and PDT. To validate this idea, minute quantities of photosensitizer chlorin e6 (Ce6) (0.56% of mass) were anchored onto amino-rich red emissive carbon dots (RCDs) that possess superior photothermal (PT) character under 671 nm NIR laser (PT conversion efficiency to be 46%), and meanwhile the PDT of Ce6 can be activated by this laser irradiation as well. The findings demonstrate that Ce6-modified RCDs (named Ce6-RCDs) offer much higher cancer therapy efficacy under a reduced laser power density (i.e., 0.50 W cm^-2 at 671 nm) in vitro and in vivo than the equivalent RCDs or Ce6 under the same irradiation conditions. Besides, the Ce6-RCDs also exhibit multimodal imaging capabilities (i.e., fluorescence (FL), photoacoustic (PA), and PT), which can be employed for guidance of the phototherapy process. This study suggests not only a strategy to enhance cancer phototherapy efficacy but also a promising candidate (i.e., Ce6-RCDs) for multimodal FL/PA/PT imaging-guided and single-NIR-laser-triggered synergistic PTT/PDT for cancers by a reduced irradiation power.

Imaging and therapeutic applications of persistent luminescence nanomaterials

The development of probes for biomolecular imaging and diagnostics is a very active research area. Among the different imaging modalities, optics emerged since it is a noninvasive and cheap imaging technique allowing real time imaging. In vitro, this technique is very useful however in vivo, fluorescence suffers from low signal-to-noise ratio due to tissue autofluorescence under constant excitation. To address this limitation, novel types of optical nanoprobes are actually being developed and among them, persistent luminescence nanoparticles (PLNPs), with long lasting near-infrared (NIR) luminescence capability, allows doing optical imaging without constant excitation and so without autofluorescence. This review will begin by introducing the physical phenomenon associated to the long luminescence decay of such nanoprobes, from minutes to hours after ceasing the excitation. Then we will show how this property can be used to develop in vivo imaging probes and also more recently nanotheranostic agents. Finally, preliminary data on their biocompatibility will be mentioned and we will conclude by envisioning on the future applications and improvements of such nanomaterials.

A series of photosensitizers with incremental positive electric charges for photodynamic antitumor therapy

In recent years, photodynamic therapy (PDT) studies have gained considerable attention as a non-invasive method used to fight cancer. In this study, a series of structurally similar photosensitizers (PSs) with incremental positive electric charges (ZnPc-4, 8 and 12) was investigated via in vitro and in vivo experiments. Photodynamic antitumor studies of these PSs, including phototoxicities, cellular uptake, the production of reactive oxygen species (ROSs) and the process of apoptosis, were conducted in the murine breast carcinoma cell line 4T1. The results indicated that the amount of positive electric charges in PSs is a key factor in influencing the efficacy of PDT. Furthermore, we established a hepatocellular carcinoma (H22) tumor-bearing mouse model to detect the antitumor activities of three PSs. ZnPc-4, 8 and 12 demonstrated significant antitumor effects and no obvious systemic damages in vivo (PDT effects: ZnPc-4 > ZnPc-8 > ZnPc-12), suggesting that the amount of positive electric charges was important to PSs, as well as the PDT effects. Our study not only indicates that ZnPc-4, 8 and 12 were highly potent anticancer PSs, but also suggests that adjusting the amount of positive electric charges is able to promote the PDT effects in cancer therapy.

In recent years, photodynamic therapy (PDT) studies have gained considerable attention as a non-invasive method used to fight cancer.

HSA-Coated Magnetic Nanoparticles for MRI-Guided Photodynamic Cancer Therapy

Background: Photodynamic therapy (PDT) is a promising technique for cancer treatment; however, low tissue permeability for irradiating light and insufficient photosensitizer (PS) accumulation in tumors limit its clinical potential. Nanoparticles are engineered to improve selective drug delivery to tumor sites, but its accumulation is highly variable between tumors and patients. Identifying PS accumulation peak in a personalized manner is crucial for therapeutic outcome. Magnetic nanoparticles (MNPs) provide opportunity for tracking drug accumulation in dynamics using non-invasive magnetic resonance imaging (MRI). The purpose of the study was to evaluate MNP loaded with PS as a theranostic tool for treating cancer in mice xenograft colon cancer models. Methods: MNPs coated with human serum albumin (HSA) were loaded with bacteriochlorine a. MRI, atomic emission spectroscopy (AES) and fluorescent imaging were used to study MNP and drug accumulation rates and dynamics in CT26 tumors. Tumor growth curves were evaluated in animals that received PDT at different time points upon MNP systemic injection. Results: Peak MNP accumulation in tumors was detected by MRI 60 min post injection (pi) and the data were verified by AES and fluorescent imaging. Up to 17% of injected dose/g of tissue was delivered to malignant tissues 24 h after injection. Consistent with MRI predicted drug accumulation peak PDT performed 60 min after intravenous injection was more efficient in inhibiting tumor growth than treatment scheduled 30 min and 240 min pi. Conclusions: PS loading on HAS-coated MNPs is a perspective approach to increase drug delivery to tumor site. Tracking for MNP accumulation by MRI can be used to predict drug concentration peak in tumors and to adjust PDT time scheduling for improved antitumor response.

PLGA-Based Nanoparticles in Cancer Treatment

Nanomedicines can be used for a variety of cancer therapies including tumor-targeted drug delivery, hyperthermia, and photodynamic therapy. Poly (lactic-co-glycolic acid) (PLGA)-based materials are frequently used in such setups. This review article gives an overview of the properties of previously reported PLGA nanoparticles (NPs), their behavior in biological systems, and their use for cancer therapy. Strategies are emphasized to target PLGA NPs to the tumor site passively and actively. Furthermore, combination therapies are introduced that enhance the accumulation of NPs and, thereby, their therapeutic efficacy. In this context, the huge number of reports on PLGA NPs used as drug delivery systems in cancer treatment highlight the potential of PLGA NPs as drug carriers for cancer therapeutics and encourage further translational research.

Recent progress in the engineering of multifunctional colloidal nanoparticles for enhanced photodynamic therapy and bioimaging

This up-to-date review summarizes the design and current fabrication strategies that have been employed in the area of mono- and multifunctional colloidal nanoparticles - nanocarriers well suited for photodynamic therapy (PDT) and diagnostic purposes. Rationally engineered photosensitizer (PS)-loaded nanoparticles may be achieved via either noncovalent (i.e., self-aggregation, interfacial deposition, interfacial polymerization, or core-shell entrapment along with physical adsorption) or covalent (chemical immobilization or conjugation) processes. These PS loading approaches should provide chemical and physical stability to PS payloads. Their hydrophilic surfaces, capable of appreciable surface interactions with biological systems, can be further modified using functional groups (stealth effect) to achieve prolonged circulation in the body after administration and/or grafted by targeting agents (such as ligands, which bind to specific receptors uniquely expressed on the cell surface) or stimuli (e.g., pH, temperature, and light)-responsive moieties to improve their action and targeting efficiency. These attempts may in principle permit efficacious PDT, combination therapies, molecular diagnosis, and - in the case of nanotheranostics - simultaneous monitoring and treatment. Nanophotosensitizers (nano-PSs) should possess appropriate morphologies, sizes, unimodal distributions and surface processes to be successfully delivered to the place of action after systemic administration and should be accumulated in certain tumors by passive and/or active targeting. Additionally, physically facilitating drug delivery systems emerge as a promising approach to enhancing drug delivery, especially for the non-invasive treatment of deep-seated malignant tissues. Recent advances in nano-PSs are scrutinized, with an emphasis on design principles, via the promising use of colloid chemistry and nanotechnology.

Selective Photokilling of Human Pancreatic Cancer Cells Using Cetuximab-Targeted Mesoporous Silica Nanoparticles for Delivery of Zinc Phthalocyanine

Background: Photodynamic therapy (PDT) is a non-invasive and innovative cancer therapy based on the photodynamic effect. In this study, we sought to determine the singlet oxygen production, intracellular uptake, and in vitro photodynamic therapy potential of Cetixumab-targeted, zinc(II) 2,3,9,10,16,17,23,24-octa(tert-butylphenoxy))phthalocyaninato(2-)-N²⁹,N³⁰,N³¹,N³² (ZnPcOBP)-loaded mesoporous silica nanoparticles against pancreatic cancer cells. Results: The quantum yield (Φ_Δ) value of ZnPcOBP was found to be 0.60 in toluene. In vitro cellular studies were performed to determine the dark- and phototoxicity of samples with various concentrations of ZnPcOBP by using pancreatic cells (AsPC-1, PANC-1 and MIA PaCa-2) and 20, 30, and 40 J/cm² light fluences. No dark toxicity was observed for any sample in any cell line. ZnPcOBP alone showed a modest photodynamic activity. However, when incorporated in silica nanoparticles, it showed a relatively high phototoxic effect, which was further enhanced by Cetuximab, a monoclonal antibody that targets the Epidermal Growth Factor Receptor (EGFR). The cell-line dependent photokilling observed correlates well with EGFR expression levels in these cells. Conclusions: Imidazole-capped Cetuximab-targeted mesoporous silica nanoparticles are excellent vehicles for the selective delivery of ZnPcOBP to pancreatic cancer cells expressing the EGFR receptor. The novel nanosystem appears to be a suitable agent for photodynamic therapy of pancreatic tumors.

Utilisation of Targeted Nanoparticle Photosensitiser Drug Delivery Systems for the Enhancement of Photodynamic Therapy

The cancer incidence world-wide has caused an increase in the demand for effective forms of treatment. One unconventional form of treatment for cancer is photodynamic therapy (PDT). PDT has 3 fundamental factors, namely a photosensitiser (PS) drug, light and oxygen. When a PS drug is administered to a patient, it can either passively or actively accumulate within a tumour site and once exposed to a specific wavelength of light, it is excited to produce reactive oxygen species (ROS), resulting in tumour destruction. However, the efficacy of ROS generation for tumour damage is highly dependent on the uptake of the PS in tumour cells. Thus, PS selective/targeted uptake and delivery in tumour cells is a crucial factor in PDT cancer drug absorption studies. Generally, within non-targeted drug delivery mechanisms, only minor amounts of PS are able to passively accumulate in tumour sites (due to the enhanced permeability and retention (EPR) effect) and the remainder distributes into healthy tissues, causing unwanted side effects and poor treatment prognosis. Thus, to improve the efficacy of PDT cancer treatment, research is currently focused on the development of specific receptor-based PS-nanocarrier platform drugs, which promote the active uptake and absorption of PS drugs in tumour sites only, avoiding unwanted side effects, as well as treatment enhancement. Therefore, the aim of this review paper is to focus on current actively targeted or passively delivered PS nanoparticle drug delivery systems, that have been previously investigated for the PDT treatment of cancer and so to deduce their overall efficacy and recent advancements.

Self-Assembly of Monomeric Hydrophobic Photosensitizers with Short Peptides Forming Photodynamic Nanoparticles with Real-Time Tracking Property and without the Need of Release in Vivo

Employing nanoscaled materials as photosensitizer (PS) carriers is an effective strategy to solve the problem of poor solubility and low tumor selectivity of hydrophobic PS in photodynamic therapy (PDT), which compulsorily requires the PS release in PDT implementation. However, the complicated environment in vivo makes it difficult to precisely design and control the release process and the delivery process requires real-time tracking. Developing a delivery strategy of hydrophobic PS in the monomeric form with fluorescent emission and without consideration of the PS release in the PDT process, is in urgent demand. Herein, we report a versatile and potent strategy for fabrication of photodynamic nanoparticles (nanoPSs) with featuring the monomeric PS based on aromatic peptide-modulated self-assembly of porphyrin derivatives. Aromatic peptides within nanoPSs can isolate hydrophobic porphyrins from each other, resulting in monomeric porphyrin delivery with real-time fluorescence tracking property and avoiding self-aggregation and hence porphyrin release. Moreover, partially charged porphyrins tend to expose on the surface of nanoPSs, facilitating production and diffusion of ¹O₂. The highest ¹O₂ yield can be achieved with porphyrin loading as low as 6 wt %, reducing side effects of excessive porphyrin injection. The nanoPSs show enhanced PDT efficacy in vitro and in vivo leading to complete tumor eradication. This study highlights opportunities for development of active photodynamic nanoparticles and provides an alternative strategy for delivery of hydrophobic photosensitive drugs with enhanced therapeutic effects.

Dramatic Enhancement of Quantum Cutting in Lanthanide-Doped Nanocrystals Photosensitized with an Aggregation-Induced Enhanced Emission Dye

Applications of multiphoton processes in lanthanide-doped nanophosphors (NPs) are often limited by relatively weak and narrow absorbance. Here, the concept of an ultimate photosensitization by aggregation-induced enhanced emission (AIEE) dyes to overcome this limitation is introduced. Because AIEE dyes do not suffer from concentration quenching, they can fully cover the NP surface at high density to maximize absorbance while passivating the surface. This concept is applied to multiphoton down-conversion by quantum cutting. Specifically, coating Yb³⁺/Tb³⁺-doped NPs with an AIEE dye designed for efficient energy transfer and attachment to the NPs produces a 2260-fold enhancement of multiphoton down-conversion by quantum cutting with remarkable photostability. In a prototypical application, the quantum cutting of UV photons to near-infrared photons that are matched to the band gap of a silicon solar cell produces an average 4% increase in efficiency under concentrated solar illumination. This provides a general strategy for NP photosensitization that can be applied to both multiphoton up- and down-conversion.

Photo-responsive hollow silica nanoparticles for light-triggered genetic and photodynamic synergistic therapy

The development of multifunctional carriers incorporating genetic and photodynamic therapy (PDT) for synergistic antitumor treatment has attracted intensive interests very recently. However, most of the currently reported systems employ passive gene release strategies depending on tumor microenvironment, which are negatively affected by the heterogeneity of cancer cells, thus resulting in limited controllability in therapeutic progress. Herein, a novel photo-responsive hollow silica nanoparticle (HNP)-based gene and photosensitizer (PS) co-delivery nanovehicle is designed for dual-wavelength light-triggered synergistic gene and PDT therapy. The resultant HNP conjugated with PDMAEMA polycation through a 405-nm light-cleavable Cou-linker, namely, HNP-Cou-PD, exhibits excellent gene condensation capacity, good biocompatibility, outstanding PS loading ability, and light-triggered gene release properties. HNP-Cou-PD with Chlorin e6 (Ce6) loaded inside the silica cavity and a plasmid encoding caspase-8 gene (CSP8) attached to the PDMAEMA outside layer (Ce6-HNP-Cou-PD/CSP8) has been proven to possess better antitumor effects under the irradiation of pre-405-nm and post-670-nm light both in vitro and in vivo because of the light-triggered intracellular gene release and reactive oxygen species (ROS) generation. Therefore, HNP-Cou-PD designed as a gene and PS co-delivery carrier might have promising applications in the future to precisely treat various types of cancers.

STATEMENT OF SIGNIFICANCE

Multifunctional carriers incorporating genetic and photodynamic therapy (PDT) have drawn intense attention very recently, ascribing to their enhanced anticancer effects. However, in the present gene and PDT synergistic system, gene release strategies passively relying on tumor microenvironment often result in no or poor controllability compared with PDT (a spatial and temporal therapeutic modal), which may hinder their synergistic efficacy, especially in an on-demand manner. To resolve this problem, we designed a hollow silica nanoparticle-based dual-wavelength light-responsive gene and photosensitizer (PS) co-delivery platform to achieve photo-triggered gene and PDT synergistic therapy. We believe that our work may have extensive application prospects in precise treatment of various cancers and be of interest to the readership.

Photo-triggered antibacterial and anticancer activities of zinc oxide nanoparticles

ZnO nanoparticles (ZnO NPs) have gained more attention in recent years due to their ability to induce the generation of reactive oxygen species (ROS) under light irradiation. Photo-triggered ROS generation by ZnO NPs and the resulting phototoxicity in cells have found use in antibacterial and anticancer applications. This review highlights recent advances in the development of ZnO NPs and hybrid-type functionalized ZnO NPs for photo-triggered antibacterial and anticancer activities. In addition, various chemical modifications including metal doping, metal hybridization, modification with polymers, and sensitization by organic photosensitizers have been further introduced to enhance the photocatalytic efficiency and ROS generation capability of ZnO NPs. The enhanced ROS generation efficiency of modified ZnO NPs consequently increases their antibacterial and anticancer activities. Additionally, we offer some insights into the design and engineering of next-generation ZnO NPs for more effective antibacterial and anticancer applications.

Multiarm Nanoconjugates for Cancer Cell-Targeted Delivery of Photosensitizers

Photodynamic therapy, a procedure that uses a photosensitizer to enable light therapy selectively at diseased sites, remains underutilized in oncological clinic. To further improve its cancer selectivity, we developed a polymeric nanosystem by conjugating a photosensitizer IRDye 700DX (IR700) and cancer targeting RGD peptide to 8-arm polyethylene glycol (PEG). The resulting nanoconjugates (RGD-8PEG-IR700) exhibited a hydrodynamic size of 6.6 nm with narrow distribution of size. The targeted nanoconjugates showed significantly higher intracellular uptake of IR700 in integrin αvβ3-expressing A375 and SKOV3 cells when compared with nontargeted control 8PEG-IR700, and an excess amount of RGD peptides could abolish this enhancement, indicating a receptor-mediated uptake mechanism for the targeted polymer conjugates. Phototoxicity studies indicated that RGD-8PEG-IR700 produced massive cell killing in A375 cells after photoirradiation with an IC₅₀ value of 57.8 nM for IR700. In contrast, free IR700 and the control 8PEG-IR700 conjugates did not produce any phototoxicity at the concentrations up to 1 μM IR700. Upon photoirradiation, the RGD-8PEG-IR700 could produce sufficient singlet oxygen in the cells and induced cell apoptosis. The studies with three-dimensional tumor spheroids showed that they penetrated tumor spheroids deeply and produced strong phototoxicity. Thus, we conclude that the polymer nanoconjugates may provide a promising delivery system for targeted photodynamic therapy of cancers due to their small size, cancer cell specificity, and minimal side effects.

Phthalocyanine-based photosensitizer with tumor-pH-responsive properties for cancer theranostics

A versatile phthalocyanine-based photosensitizer with tumor-pH-responsive properties for cancer theranostics.

Advanced smart-photosensitizers for more effective cancer treatment

Photodynamic therapy (PDT) based upon the use of light and photosensitizers (PSs) has been used as a novel treatment approach for a variety of tumors. It, however, has several major limitations in the clinic: poor water solubility, long-term phototoxicity, low tumor targeting efficacy, and limited light penetration. With advances in nanotechnology, materials science, and clinical interventional imaging procedures, various smart-PSs have been developed for improving their cancer-therapeutic efficacy while reducing the adverse effects. Here, we briefly review state-of-the-art smart-PSs and discuss the future directions of PDT technology.

LiGa5O8:Cr-based theranostic nanoparticles for imaging-guided X-ray induced photodynamic therapy of deep-seated tumors

Using X-ray as the irradiation source, a photodynamic therapy process can be initiated from under deep tissues. This technology, referred to as X-ray induced PDT, or X-PDT, holds great potential to treat tumors at internal organs. To this end, one question is how to navigate the treatment to tumors with accuracy with external irradiation. Herein we address the issue with a novel, LiGa₅O₈: Cr (LGO:Cr)-based nanoscintillator, which emits persistent, near-infrared X-ray luminescence. This permits deep-tissue optical imaging that can be employed to guide irradiation. Specifically, we encapsulated LGO:Cr nanoparticles and a photosensitizer, 2,3-naphthalocyanine, into mesoporous silica nanoparticles. The nanoparticles were conjugated with cetuximab and systemically injected into H1299 orthotopic non-small cell lung cancer tumor models. The nanoconjugates can efficiently home to tumors in the lung, confirmed by monitoring X-ray luminescence from LGO:Cr. Guided by the imaging, external irradiation was applied, leading to efficient tumor suppression while minimally affecting normal tissues. To the best of our knowledge, the present study is the first to demonstrate, with systematically injected nanoparticles, that X-PDT can suppress growth of deep-seated tumors. The imaging guidance is also new to X-PDT, and is significant to the further transformation of the technology.

Recent Progress in Near Infrared Light Triggered Photodynamic Therapy

Nowadays, photodynamic therapy (PDT) is under the research spotlight as an appealing modality for various malignant tumors. Compared with conventional PDT treatment activated by ultraviolet or visible light, near infrared (NIR) light-triggered PDT possessing deeper penetration to lesion area and lower photodamage to normal tissue holds great potential for in vivo deep-seated tumor. In this review, recent research progress related to the exploration of NIR light responsive PDT nanosystems is summarized. To address current obstacles of PDT treatment and facilitate the effective utilization, several innovative strategies are developed and introduced into PDT nanosystems, including the conjugation with targeted moieties, O₂ self-sufficient PDT, dual photosensitizers (PSs)-loaded PDT nanoplatform, and PDT-involved synergistic therapy. Finally, the potential challenges as well as the prospective for further development are also discussed.

Polyion complex micelle formed from tetraphenylethene containing block copolymer

BACKGROUND

Polymeric micelles attract great attention in drug delivery and therapeutics. Various types of block copolymers have been designed for the application in biomedical fields. If we can introduce additional functional groups to the block copolymers, we can achieve advanced applications. In this regards, we tried to introduce aggregation induced emission enhancement (AIE) unit in the block copolymer.

METHODS

The formation of polyion complex micelle was confirmed by dynamic light scattering and transmission electron microscopy. HeLa cells were incubated with polyion complex micelle and broad-band visible light using a halogen lamp (150 W) was irradiated to evaluate photocytotoxicity of polyion complex (PIC) micelle.

RESULTS

For the design of functional polymeric micelle, aggregation induced emission enhancement unit was introduced in the middle of block copolymer. We newly synthesized a new type block copolymer (PEG-TPE-PEI) possessing tetraphenylethene (TPE) group, as an AIE unit, in the middle of polymeric segments of PEG and PEI, which successfully formed PIC micelle with DP. The formation of PIC micelle was confirmed by dynamic light scattering, ζ potential measurement and transmission electron microscopy.

CONCLUSIONS

PEG-TPE-PEI successfully formed PIC micelle by mixing with negatively charged dendrimer porphyrin. The PIC micelle exhibited photocytotoxicity upon illumination of broadband visible light.

Lab-on-a-chip systems for photodynamic therapy investigations

In recent years photodynamic therapy (PDT) has received widespread attention in cancer treatment due to its smaller surgical trauma, better selectivity towards tumor cells, reduced side effects and possibility of repeatable treatment. Since cancer is the second cause of death worldwide, scientists constantly seek for new potential therapeutic agents including nanotechnology-based photosensitizers used in PDT. The new-designed nanostructures must be carefully studied and well characterized what require analytically useful and powerful tools that enable real progress in nanoscience development. This review describes the current status of PDT investigations using microfluidic Lab-on-a-Chip systems, including recent developments of nanoparticle-based PDT agents, their combinations with different drugs, designs and examples of in vitro applications. This review mainly lays emphasis on biological evaluation of FDA approved photosensitizing agents as well as newly designed nanophotosensitizers. It also highlights the analytical performances of various microfluidic Lab-on-a-chip systems for PDT efficacy analysis on 3D culture and discusses microsystems designs in detail.

Ultrasmall AGuIX theranostic nanoparticles for vascular-targeted interstitial photodynamic therapy of glioblastoma

Despite combined treatments, glioblastoma outcome remains poor with frequent local recurrences, indicating that a more efficient and local therapy is needed. In this way, vascular-targeted photodynamic therapy (VTP) could help tumor eradication by destroying its neovessels. In this study, we designed a polysiloxane-based nanoparticle (NP) combining a magnetic resonance imaging (MRI) contrast agent, a photosensitizer (PS) and a new ligand peptide motif (KDKPPR) targeting neuropilin-1 (NRP-1), a receptor overexpressed by angiogenic endothelial cells of the tumor vasculature. This structure achieves the detection of the tumor tissue and its proliferating part by MRI analysis, followed by its treatment by VTP. The photophysical properties of the PS and the peptide affinity for NRP-1 recombinant protein were preserved after the functionalization of NPs. Cellular uptake of NPs by human umbilical vein endothelial cells (HUVEC) was increased twice compared to NPs without the KDKPPR peptide moiety or conjugated with a scramble peptide. NPs induced no cytotoxicity without light exposure but conferred a photocytotoxic effect to cells after photodynamic therapy (PDT). The in vivo selectivity, evaluated using a skinfold chamber model in mice, confirms that the functionalized NPs with KDKPPR peptide moiety were localized in the tumor vessel wall.

Silicon Phthalocyanines Axially Disubstituted with Erlotinib toward Small-Molecular-Target-Based Photodynamic Therapy

Small-molecular-target-based photodynamic therapy-a promising targeted anticancer strategy-was developed by conjugating zinc(II) phthalocyanine with a small-molecular-target-based anticancer drug. To prevent self-aggregation and avoid problems of phthalocyanine isomerization, two silicon phthalocyanines di-substituted axially with erlotinib have been synthesized and fully characterized. These conjugates are present in monomeric form in various solvents as well as culture media. Cell-based experiments showed that these conjugates localize in lysosomes and mitochondria, while maintaining high photodynamic activities (IC₅₀ values as low as 8 nm under a light dose of 1.5 J cm^-2 ). With erlotinib as the targeting moiety, two conjugates were found to exhibit high specificity for EGFR-overexpressing cancer cells. Various poly(ethylene glycol) (PEG) linker lengths were shown to have an effect on the photophysical/photochemical properties and on in vitro phototoxicity.

Nanomedicine associated with photodynamic therapy for glioblastoma treatment

Glioblastoma, also known as glioblastoma multiforme (GBM), is the most recurrent and malignant astrocytic glioma found in adults. Biologically, GBMs are highly aggressive tumors that often show diffuse infiltration of the brain parenchyma, making complete surgical resection difficult. GBM is not curable with surgery alone because tumor cells typically invade the surrounding brain, rendering complete resection unsafe. Consequently, present-day therapy for malignant glioma remains a great challenge. The location of the invasive tumor cells presents several barriers to therapeutic delivery. The blood-brain barrier regulates the trafficking of molecules to and from the brain. While high-grade brain tumors contain some "leakiness" in their neovasculature, the mechanisms of GBM onset and progression remain largely unknown. Recent advances in the understanding of the signaling pathways that underlie GBM pathogenesis have led to the development of new therapeutic approaches targeting multiple oncogenic signaling aberrations associated with the GBM. Among these, drug delivery nanosystems have been produced to target therapeutic agents and improve their biodistribution and therapeutic index in the tumor. These systems mainly include polymer or lipid-based carriers such as liposomes, metal nanoparticles, polymeric nanospheres and nanocapsules, micelles, dendrimers, nanocrystals, and nanogold. Photodynamic therapy (PDT) is a promising treatment for a variety of oncological diseases. PDT is an efficient, simple, and versatile method that is based on a combination of a photosensitive drug and light (generally laser-diode or laser); these factors are separately relatively harmless but when used together in the presence of oxygen molecules, free radicals are produced that initiate a sequence of biological events, including phototoxicity, vascular damage, and immune responses. Photodynamic pathways activate a cascade of activities, including apoptotic and necrotic cell death in both the tumor and the neovasculature, leading to a permanent lesion and destruction of GBM cells that remain in the healthy tissue. Glioblastoma tumors differ at the molecular level. For example, gene amplification epidermal growth factor receptor and its receptor are more highly expressed in primary GBM than in secondary GBM. Despite these distinguishing features, both types of tumors (primary and secondary) arise as a result dysregulation of numerous intracellular signaling pathways and have standard features, such as increased cell proliferation, survival and resistance to apoptosis, and loss of adhesion and migration, and may show a high degree of invasiveness. PDT may promote significant tumor regression and extend the lifetime of patients who experience glioma progression.

Intracellular "activated" two-photon photodynamic therapy by fluorescent conveyor and photosensitizer co-encapsulating pH-responsive micelles against breast cancer

The application of photodynamic therapy (PDT) for the diagnosis and treatment of cancer is hindered by the intrinsic defects of the currently available photosensitizers (PSs), such as poor water solubility and limited light-penetration depth. In this study, pH-responsive polymeric micelles that co-encapsulate therapeutic PSs and organooxotin two-photon compounds were applied for two-photon PDT (TP-PDT) against breast cancer. The TP-PDT effect of the drug-loaded micelles was “activated” when the micelles turned into aggregates at a triggering pH level. The in vitro therapeutic effect was evaluated on 4T1 murine breast cancer cells by viability assays, real-time morphology collapsing, and reactive oxygen species determination. Time-dependent ex vivo organ distribution and in vivo anticancer efficacy results suggested that the drug carriers could accumulate in tumors and suppress tumor growth by TP-PDT. The delivery system could enhance the solubility and distribution of PSs and, if administered along with a tissue-penetrating prolonged light source, could thus have good potential for cancer therapy.

pH-Responsive Dimeric Zinc(II) Phthalocyanine in Mesoporous Silica Nanoparticles as an Activatable Nanophotosensitizing System for Photodynamic Therapy

An acid-cleavable acetal-linked zinc(II) phthalocyanine dimer with an azido terminal group (cPc) was prepared and conjugated to alkyne-modified mesoporous silica nanoparticles via copper(I)-catalyzed alkyne-azide cycloaddition reaction. For comparison, an amine-linked analogue (nPc) was also prepared as a non-acid-cleavable counterpart. These dimeric phthalocyanines were significantly self-quenched due to the close proximity of the phthalocyanine units inside the mesopores, resulting in much weaker fluorescence emission and singlet oxygen generation, both in N,N-dimethylformamide and in phosphate-buffered saline (PBS), compared with the free molecular counterparts. Under acidic conditions in PBS, the cPc-encapsulated nanosystem was activated in terms of fluorescence emission and singlet oxygen production. After internalization into human colon adenocarcinoma HT29 cells, it exhibited much higher intracellular fluorescence and photocytotoxicity compared to the nanosystem entrapped with nPc. The activation of this nanosystem was also demonstrated in tumor-bearing nude mice. The intratumoral fluorescence intensity increased gradually over 24 h, while for the nPc counterpart the fluorescence remained very weak. The results suggest that this nanosystem serves as a promising activatable nanophotosensitizing agent for photodynamic therapy.

Cyclodextrin-gated mesoporous silica nanoparticles as drug carriers for red light-induced drug release

Long wavelength light-responsive drug delivery systems based on mesoporous silica nanoparticles (MSNs) have attracted much attention in the last few years. In this paper, a red light (660 nm)-responsive drug delivery system based on low-cost cyclodextrin (CD)-gated MSNs containing a photodynamic therapy (PDT) photosensitizer (Chlorin e6, Ce6) was developed for the first time. The drug release experiment in water demonstrated that with the irradiation of red light, Ce6 can be excited to generate singlet oxygen, which can further cleave the singlet oxygen sensitive linker to trigger the departure of CD and the release of cargo. Further in vitro release experiments confirmed that cargo can be released from MSNs with the irradiation of red light and spread into the entire cell. The relative low power density (0.5 W cm^-2) of excitation light together with the short irradiation time (one-three min) result in a low light dose (30-90 J cm^-2) for the drug delivery, contributing to their potential clinical applications.

Design of Tumor Acidity-Responsive Sheddable Nanoparticles for Fluorescence/Magnetic Resonance Imaging-Guided Photodynamic Therapy

Imaging-guided cancer therapy, which integrates diagnostic and therapeutic functionalities into a single system, holds great promise to enhance the accuracy of diagnosis and improve the efficacy of therapy. Specifically, for photodynamic therapy (PDT), it is highly desirable to precisely focus laser light onto the tumor areas to generate reactive oxygen species (ROS) that are cytotoxic tumor cells and avoid light-associated side effects. Herein, a distinct three-layer nanostructured particle with tumor acidity-responsiveness (S-NP) that encapsulates the photosensitizer chlorin e6 (Ce6) and chelates Gd³⁺ is successfully developed for fluorescence/magnetic resonance (MR) dual-model imaging-guided precision PDT. We show clear evidence that the outer PEG layer significantly prolongs circulation time, and the inner poly(ε-caprolactone) (PCL) core can physically encapsulate Ce6. More interestingly, the middle layer of the S-NP, acting as a molecular fence to keep Ce6 in the circulation system, was dismantled by the slightly acidic tumor microenvironment. Afterwards, the PEG shell is deshielded from the S-NP at the tumor tissue, resulting in improved cell uptake, enlarged MR signal intensity, rapid release of Ce6 within tumor cells, and elevated PDT efficacy. Our results suggest that tumor-acidity-responsive nanoparticles with fine design could serve as a theranostic platform with great potential in imaging-guided PDT treatment of cancer.

Complexing Methylene Blue with Phosphorus Dendrimers to Increase Photodynamic Activity

The efficiency of photodynamic therapy is limited mainly due to low selectivity, unfavorable biodistribution of photosensitizers, and long-lasting skin sensitivity to light. However, drug delivery systems based on nanoparticles may overcome the limitations mentioned above. Among others, dendrimers are particularly attractive as carriers, because of their globular architecture and high loading capacity. The goal of the study was to check whether an anionic phosphorus dendrimer is suitable as a carrier of a photosensitizer-methylene blue (MB). As a biological model, basal cell carcinoma cell lines were used. We checked the influence of the MB complexation on its singlet oxygen production ability using a commercial fluorescence probe. Next, cellular uptake, phototoxicity, reactive oxygen species (ROS) generation, and cell death were investigated. The MB-anionic dendrimer complex (MB-1an) was found to generate less singlet oxygen; however, the complex showed higher cellular uptake and phototoxicity against basal cell carcinoma cell lines, which was accompanied with enhanced ROS production. Owing to the obtained results, we conclude that the photodynamic activity of MB complexed with an anionic dendrimer is higher than free MB against basal cell carcinoma cell lines.

Relighting Photosensitizers by Synergistic Integration of Albumin and Perfluorocarbon for Enhanced Photodynamic Therapy

Photodynamic therapy (PDT) is hampered by poor water solubility and skin phototoxicity of photosensitizers (PSs). Incorporation of PSs into nanocarrier (Nano-PDT) has been designed to overcome these problems. However, self-quenching of PSs highly condensed in Nano-PDT significantly reduced singlet oxygen (¹O₂) generation, resulting in unsatisfactory PDT efficacy. Here, we developed a novel tripleffect Nano-PDT, which has a special core-shell nanostructure by synergistic integration of perfluorotributylamine (PFTBA) and human serum albumin (HSA) to improve PDT. It has three mechanisms to relight quenched PSs, thereby generating more ¹O₂. First, PSs uniformly dispersed in the shell, preventing self-quenching caused by π-π stacking. Second, HSA as nanocarrier extends the triplet-state lifetimes of PSs, increasing the amount of ¹O₂. Third, PFTBA as core dissolves and protects¹ O₂ to extend the duration time of action of ¹O₂. Compared with PS-encapsulated Nano-PDT, the self-quenching of PSs in tripleffect Nano-PDT can be effectively overcome. The fluorescence and ¹O₂ generation of PS are increased by approximately 100-fold and 15-fold, respectively. After intravenous injection into tumor-bearing mice, the tumor growth is significantly inhibited, while the PS-encapsulated Nano-PDT has almost no effect. The novel tripleffect Nano-PDT may guide improvement of existing clinical PDT and future PDT design.

V, Nalam MR, Sunkara MV. Chlorin e6 loaded lactoferrin nanoparticles for enhanced photodynamic therapy

The LeN NPs of Lf and Ce6 enhanced the intracellular delivery of the PS improving photo-induced cell death compared to free PS.