Recent Progress in Upconversion Photodynamic Therapy

Photodynamic therapy for cancer: mechanisms, photosensitizers, nanocarriers, and clinical studies

Photodynamic therapy (PDT) is a temporally and spatially precisely controllable, noninvasive, and potentially highly efficient method of phototherapy. The three components of PDT primarily include photosensitizers, oxygen, and light. PDT employs specific wavelengths of light to active photosensitizers at the tumor site, generating reactive oxygen species that are fatal to tumor cells. Nevertheless, traditional photosensitizers have disadvantages such as poor water solubility, severe oxygen-dependency, and low targetability, and the light is difficult to penetrate the deep tumor tissue, which remains the toughest task in the application of PDT in the clinic. Here, we systematically summarize the development and the molecular mechanisms of photosensitizers, and the challenges of PDT in tumor management, highlighting the advantages of nanocarriers-based PDT against cancer. The development of third generation photosensitizers has opened up new horizons in PDT, and the cooperation between nanocarriers and PDT has attained satisfactory achievements. Finally, the clinical studies of PDT are discussed. Overall, we present an overview and our perspective of PDT in the field of tumor management, and we believe this work will provide a new insight into tumor-based PDT.

Comparison of the Differences between Two-Photon Excitation, Upconversion, and Conventional Photodynamic Therapy on Cancers in In Vitro and In Vivo Studies

Photodynamic therapy (PDT) is a minimally invasive treatment for several diseases. It combines light energy with a photosensitizer (PS) to destroy the targeted cells or tissues. A PS itself is a non-toxic substance, but it becomes toxic to the target cells through the activation of light at a specific wavelength. There are some limitations of PDT, although it has been used in clinical studies for a long time. Two-photon excitation (TPE) and upconversion (UC) for PDT have been recently developed. A TPE nanoparticle-based PS combines the advantages of TPE and nanotechnology that has emerged as an attractive therapeutic agent for near-infrared red (NIR) light-excited PDT, whilst UC is also used for the NIR light-triggered drug release, activation of 'caged' imaging, or therapeutic molecules during PDT process for the diagnosis, imaging, and treatment of cancers.

METHODS

Nine electronic databases were searched, including WanFang Data, PubMed, Science Direct, Scopus, Web of Science, Springer Link, SciFinder, and China National Knowledge Infrastructure (CNKI), without any language constraints. TPE and UCNP were evaluated to determine if they had different effects from PDT on cancers. All eligible studies were analyzed and summarized in this review.

RESULTS

TPE-PDT and UCNP-PDT have a high cell or tissue penetration ability through the excitation of NIR light to activate PS molecules. This is much better than the conventional PDT induced by visible or ultraviolet (UV) light. These studies showed a greater PDT efficacy, which was determined by enhanced generation of reactive oxygen species (ROS) and reduced cell viability, as well as inhibited abnormal cell growth for the treatment of cancers.

CONCLUSIONS

Conventional PDT involves Type I and Type II reactions for the generation of ROS in the treatment of cancer cells, but there are some limitations. Recently, TPE-PDT and UCNP-PDT have been developed to overcome these problems with the help of nanotechnology in in vitro and in vivo studies.

Designing Composite Stimuli-Responsive Hydrogels for Wound Healing Applications: The State-of-the-Art and Recent Discoveries

Effective wound treatment has become one of the most important challenges for healthcare as it continues to be one of the leading causes of death worldwide. Therefore, wound care technologies significantly evolved in order to provide a holistic approach based on various designs of functional wound dressings. Among them, hydrogels have been widely used for wound treatment due to their biocompatibility and similarity to the extracellular matrix. The hydrogel formula offers the control of an optimal wound moisture level due to its ability to absorb excess fluid from the wound or release moisture as needed. Additionally, hydrogels can be successfully integrated with a plethora of biologically active components (e.g., nanoparticles, pharmaceuticals, natural extracts, peptides), thus enhancing the performance of resulting composite hydrogels in wound healing applications. In this review, the-state-of-the-art discoveries related to stimuli-responsive hydrogel-based dressings have been summarized, taking into account their antimicrobial, anti-inflammatory, antioxidant, and hemostatic properties, as well as other effects (e.g., re-epithelialization, vascularization, and restoration of the tissue) resulting from their use.

Recent Advances in Chemistry, Mechanism, and Applications of Quantum Dots in Photodynamic and Photothermal Therapy

Semiconductor quantum dots (QD) are a kind of nanoparticle with unique optical properties that have attracted a lot of attention in recent years. In this paper, the characteristics of these nanoparticles and their applications in nanophototherapy have been reviewed. Phototherapy, including photodynamic therapy (PDT) and photothermal therapy (PTT), has gained special importance because of its high accuracy and local treatment due to the activation of the drug at the tumor site. PDT is a new way of cancer treatment that is performed by activating light-sensitive compounds named photosensitizers (PS) by light. PSs cause the destruction of diseased tissue through the production of singlet oxygen. PTT is another non-invasive method that induces cell death through the conversion of near-infrared light (NIR) into heat in the tumor situation by the photothermal agent (PA). Through using energy transfer via the FRET (Förster resonance energy transfer) process, QDs provide light absorption wavelength for both methods and cover the optical weaknesses of phototherapy agents.

Temoporfin-Conjugated Upconversion Nanoparticles for NIR-Induced Photodynamic Therapy: Studies with Pancreatic Adenocarcinoma Cells In Vitro and In Vivo

Upconverting nanoparticles are interesting materials that have the potential for use in many applications ranging from solar energy harvesting to biosensing, light-triggered drug delivery, and photodynamic therapy (PDT). One of the main requirements for the particles is their surface modification, in our case using poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) and temoporfin (THPC) photosensitizer to ensure the colloidal and chemical stability of the particles in aqueous media and the formation of singlet oxygen after NIR irradiation, respectively. Codoping of Fe2+, Yb3+, and Er3+ ions in the NaYF4 host induced upconversion emission of particles in the red region, which is dominant for achieving direct excitation of THPC. Novel monodisperse PMVEMA-coated upconversion NaYF4:Yb3+,Er3+,Fe2+ nanoparticles (UCNPs) with chemically bonded THPC were found to efficiently transfer energy and generate singlet oxygen. The cytotoxicity of the UCNPs was determined in the human pancreatic adenocarcinoma cell lines Capan-2, PANC-01, and PA-TU-8902. In vitro data demonstrated enhanced uptake of UCNP@PMVEMA-THPC particles by rat INS-1E insulinoma cells, followed by significant cell destruction after excitation with a 980 nm laser. Intratumoral administration of these nanoconjugates into a mouse model of human pancreatic adenocarcinoma caused extensive necrosis at the tumor site, followed by tumor suppression after NIR-induced PDT. In vitro and in vivo results thus suggest that this nanoconjugate is a promising candidate for NIR-induced PDT of cancer.

Bright photon upconversion in LiYbF4:Tm3+@LiYF4 nanoparticles and their application for singlet oxygen generation and in immunoassay for SARS-CoV-2 nucleoprotein

Photon upconversion is an intensively investigated phenomenon in the materials sciences due to its unique applications, mainly in biomedicine for disease prevention and treatment. This study reports the synthesis and properties of tetragonal LiYbF4:Tm3+@LiYF4 core@shell nanoparticles (NPs) and their applications. The NPs had sizes ranging from 18.5 to 23.7 nm. As a result of the energy transfer between Yb3+ and Tm3+ ions, the synthesized NPs show intense emission in the ultraviolet (UV) range up to 347 nm under 975 nm excitation. The bright emission in the UV range allows for singlet oxygen generation in the presence of hematoporphyrin on the surface of NPs. Our studies show that irradiation with a 975 nm laser of the functionalized NPs allows for the production of amounts of singlet oxygen easily detectable by Singlet Oxygen Sensor Green. The high emission intensity of NPs at 800 nm allowed the application of the synthesized NPs in an upconversion-linked immunosorbent assay (ULISA) for highly sensitive detection of the nucleoprotein from SARS-CoV-2, the causative agent of Covid-19. This article proves that LiYbF4:Tm3+@LiYF4 core@shell nanoparticles can be perfect alternatives for the most commonly studied upconverting NPs based on the NaYF4 host compound and are good candidates for biomedical applications.

Bacterial outer membrane vesicles as drug delivery carrier for photodynamic anticancer therapy

Photodynamic Therapy (PDT) is an effective tumor treatment strategy that not only induces photocytotoxicity to kill tumor cells directly but also activates the immune system in the body to generate tumor-specific immunity, preventing cancer metastasis and recurrence. However, some limitations of PDT limit the therapeutic efficacy in deep tumors. Previous studies have used different types of nanoparticles (NPs) as drug carriers of photosensitizers (PSs) to overcome the shortcomings of PDT and improve therapeutic efficacy. Among them, bacterial outer membrane vesicles (OMVs) have natural advantages as carriers for PS delivery. In addition to the targeted delivery of PSs into tumor cells, their unique immunogenicity helps them to serve as immune adjuvants to enhance the PDT-induced immune effect, providing new ideas for photodynamic anticancer therapy. Therefore, in this review, we will introduce the biogenesis and anticancer functions of OMVs and the research on them as drug delivery carriers in PDT. Finally, we also discuss the challenges and prospects of OMVs as a versatile drug delivery carrier for photodynamic anticancer therapy.

The use of nanomaterials in advancing photodynamic therapy (PDT) for deep-seated tumors and synergy with radiotherapy

Photodynamic therapy (PDT) has been under development for at least 40 years. Multiple studies have demonstrated significant anti-tumor efficacy with limited toxicity concerns. PDT was expected to become a major new therapeutic option in treating localized cancer. However, despite a shifting focus in oncology to aggressive local therapies, PDT has not to date gained widespread acceptance as a standard-of-care option. A major factor is the technical challenge of treating deep-seated and large tumors, due to the limited penetration and variability of the activating light in tissue. Poor tumor selectivity of PDT sensitizers has been problematic for many applications. Attempts to mitigate these limitations with the use of multiple interstitial fiberoptic catheters to deliver the light, new generations of photosensitizer with longer-wavelength activation, oxygen independence and better tumor specificity, as well as improved dosimetry and treatment planning are starting to show encouraging results. Nanomaterials used either as photosensitizers per se or to improve delivery of molecular photosensitizers is an emerging area of research. PDT can also benefit radiotherapy patients due to its complementary and potentially synergistic mechanisms-of-action, ability to treat radioresistant tumors and upregulation of anti-tumoral immune effects. Furthermore, recent advances may allow ionizing radiation energy, including high-energy X-rays, to replace external light sources, opening a novel therapeutic strategy (radioPDT), which is facilitated by novel nanomaterials. This may provide the best of both worlds by combining the precise targeting and treatment depth/volume capabilities of radiation therapy with the high therapeutic index and biological advantages of PDT, without increasing toxicities. Achieving this, however, will require novel agents, primarily developed with nanomaterials. This is under active investigation by many research groups using different approaches.

Nanocarriers for photodynamic-gene therapy

The use of nanotechnology in medicine has important potential applications, including in anticancer strategies. Nanomedicine has made it possible to overcome the limitations of conventional monotherapies, in addition to improving therapeutic results by means of synergistic or cumulative effects. A highlight is the combination of gene therapy (GT) and photodynamic therapy (PDT), which are alternative anticancer approaches that have attracted attention in the last decade. In this review, strategies involving the combination of PDT and GT will be discussed, together with the role of nanocarriers (nonviral vectors) in this synergistic therapeutic approach, including aspects related to the design of nanomaterials, responsiveness, the interaction of the nanomaterial with the biological environment, and anticancer performance in studies in vitro and in vivo.

Photodynamic Therapy for Colorectal Cancer: An Update and a Look to the Future

This review provides an update on the current state of photodynamic therapy (PDT) for colorectal cancer (CRC) and explores potential future directions in this field. PDT has emerged as a promising minimally invasive treatment modality that utilizes photosensitizers and specific light wavelengths to induce cell death in targeted tumor tissues. In recent years, significant progress has been made in understanding the underlying mechanisms, optimizing treatment protocols, and improving the efficacy of PDT for CRC. This article highlights key advancements in PDT techniques, including novel photosensitizers, light sources, and delivery methods. Furthermore, it discusses ongoing research efforts and potential future directions, such as combination therapies and nanotechnology-based approaches. By elucidating the current landscape and providing insights into future directions, this review aims to guide researchers and clinicians in harnessing the full potential of PDT for the effective management of CRC.

Combination of Two Photosensitisers in Anticancer, Antimicrobial and Upconversion Photodynamic Therapy

Photodynamic therapy (PDT) is a special form of phototherapy in which oxygen is needed, in addition to light and a drug called a photosensitiser (PS), to create cytotoxic species that can destroy cancer cells and various pathogens. PDT is often used in combination with other antitumor and antimicrobial therapies to sensitise cells to other agents, minimise the risk of resistance and improve overall outcomes. Furthermore, the aim of combining two photosensitising agents in PDT is to overcome the shortcomings of the monotherapeutic approach and the limitations of individual agents, as well as to achieve synergistic or additive effects, which allows the administration of PSs in lower concentrations, consequently reducing dark toxicity and preventing skin photosensitivity. The most common strategies in anticancer PDT use two PSs to combine the targeting of different organelles and cell-death mechanisms and, in addition to cancer cells, simultaneously target tumour vasculature and induce immune responses. The use of PDT with upconversion nanoparticles is a promising approach to the treatment of deep tissues and the goal of using two PSs is to improve drug loading and singlet oxygen production. In antimicrobial PDT, two PSs are often combined to generate various reactive oxygen species through both Type I and Type II processes.

Cancer nanomedicine toward clinical translation: Obstacles, opportunities, and future prospects

With the integration of nanotechnology into the medical field at large, great strides have been made in the development of nanomedicines for tackling different diseases, including cancers. To date, various cancer nanomedicines have demonstrated success in preclinical studies, improving therapeutic outcomes, prolonging survival, and/or decreasing side effects. However, the translation from bench to bedside remains challenging. While a number of nanomedicines have entered clinical trials, only a few have been approved for clinical applications. In this review, we highlight the most recent progress in cancer nanomedicine, discuss current clinical advances and challenges for the translation of cancer nanomedicines, and provide our viewpoints on accelerating clinical translation. We expect this review to benefit the future development of cancer nanotherapeutics specifically from the clinical perspective.

Light-Enhanced Cytotoxicity of Doxorubicin by Photoactivation

The combination of photodynamic therapy with chemotherapy (photochemotherapy, PCT) can lead to additive or synergistic antitumor effects. Usually, two different molecules, a photosensitizer (PS) and a chemotherapeutic drug are used in PCT. Doxorubicin is one of the most successful chemotherapy drugs. Despite its high efficacy, two factors limit its clinical use: severe side effects and the development of chemoresistance. Doxorubicin is a chromophore, able to absorb light in the visible range, making it a potential PS. Here, we exploited the intrinsic photosensitizing properties of doxorubicin to enhance its anticancer activity in leukemia, breast, and epidermoid carcinoma cells, upon irradiation. Light can selectively trigger the local generation of reactive oxygen species (ROS), following photophysical pathways. Doxorubicin showed a concentration-dependent ability to generate peroxides and singlet oxygen upon irradiation. The underlying mechanisms leading to the increase in its cytotoxic activity were intracellular ROS generation and the induction of necrotic cell death. The nuclear localization of doxorubicin represents an added value for its use as a PS. The use of doxorubicin in PCT, simultaneously acting as a chemotherapeutic agent and a PS, may allow (i) an increase in the anticancer effects of the drug, and (ii) a decrease in its dose, and thus, its dose-related adverse effects.

Multifunctional Superparticles for Magnetically Targeted NIR-II Imaging and Photodynamic Therapy

Theranostics, the combination of diagnostics and therapies, has been considered as a promising strategy for clinical cancer treatment. Nonetheless, building a smart theranostic system with multifunction for different on-demand applications still remains elusive. Herein, an easy and user-friendly microemulsion based method is developed to modularly assemble upconversion nanoparticles (UCNPs) and Fe₃ O₄ nanoparticles together, forming multifunctional UCNPs/Fe₃ O₄ superparticles with highly integrated functionalities including the 808 nm excitation for real-time NIR-II imaging, magnetic targeting, and the upconversion luminescence upon 980 nm excitation for on-demand photodynamic therapy (PDT). With a magnet placed nearby the tumor, in vivo NIR-II imaging uncovers that superparticles tend to migrate toward the tumor and exhibit intense tumor accumulation, ≈6 folds higher than that without magnetic targeting 2 h after intravenous injection. NIR laser irradiation is then used to trigger PDT, obtaining an outstanding tumor elimination under magnetic tumor targeting, which shows a high potential to be applied in targeted cancer theranostics.

Eosin Y-Functionalized Upconverting Nanoparticles: Nanophotosensitizers and Deep Tissue Bioimaging Agents for Simultaneous Therapeutic and Diagnostic Applications

Functionalized upconverting nanoparticles (UCNPs) are promising theragnostic nanomaterials for simultaneous therapeutic and diagnostic purposes. We present two types of non-toxic eosin Y (EY) nanoconjugates derived from UCNPs as novel nanophotosensitizers (nano-PS) and deep-tissue bioimaging agents employing light at 800 nm. This excitation wavelength ensures minimum cell damage, since the absorption of water is negligible, and increases tissue penetration, enhancing the specificity of the photodynamic treatment (PDT). These UCNPs are uniquely qualified to fulfil three important roles: as nanocarriers, as energy-transfer materials, and as contrast agents. First, the UCNPs enable the transport of EY across the cell membrane of living HeLa cells that would not be possible otherwise. This cellular internalization facilitates the use of such EY-functionalized UCNPs as nano-PS and allows the generation of reactive oxygen species (ROS) under 800 nm light inside the cell. This becomes possible due to the upconversion and energy transfer processes within the UCNPs, circumventing the excitation of EY by green light, which is incompatible with deep tissue applications. Moreover, the functionalized UCNPs present deep tissue NIR-II fluorescence under 808 nm excitation, thus demonstrating their potential as bioimaging agents in the NIR-II biological window.

Enhanced Photodynamic Therapy: A Review of Combined Energy Sources

Photodynamic therapy (PDT) has been used in recent years as a non-invasive treatment for cancer, due to the side effects of traditional treatments such as surgery, radiotherapy, and chemotherapy. This therapeutic technique requires a photosensitizer, light energy, and oxygen to produce reactive oxygen species (ROS) which mediate cellular toxicity. PDT is a useful non-invasive therapy for cancer treatment, but it has some limitations that need to be overcome, such as low-light-penetration depths, non-targeting photosensitizers, and tumor hypoxia. This review focuses on the latest innovative strategies based on the synergistic use of other energy sources, such as non-visible radiation of the electromagnetic spectrum (microwaves, infrared, and X-rays), ultrasound, and electric/magnetic fields, to overcome PDT limitations and enhance the therapeutic effect of PDT. The main principles, mechanisms, and crucial elements of PDT are also addressed.

Advanced techniques for performing photodynamic therapy in deep-seated tissues

Photodynamic therapy (PDT) is a promising localized cancer treatment modality. It has been used successfully to treat a range of dermatological conditions with comparable efficacy to conventional treatments. However, some drawbacks limit the clinical utility of PDT in treating deep-seated tumors. Notably, the penetration limitation of UV and visible light, commonly applied to activate photosensitizers, makes PDT incompetent in treating deep-seated tumors. Development in light delivery technologies, especially fiber optics, led to improved clinical strategies for accessing deep tissues for irradiation. However, PDT efficacy issues remained partly due to light penetration limitations. In this review, we first summarized the current PDT applications for deep-seated tumor treatment. Then, the most recent progress in advanced techniques to overcome the light penetration limitation in PDT, including using functional nanomaterials that can either self-illuminate or be activated by near-infrared (NIR) light and X-rays as transducers, and implantable light delivery devices were discussed. Finally, current challenges and future opportunities of these technologies were discussed, which we hope may inspire the development of more effective techniques to enhance PDT efficacy against deep-seated tumors.

Construction and evaluation of curcumin upconversion nanocarriers decorated with MnO2 for tumor photodynamic therapy

The limited tissue penetration depth and tumor hypoxic microenvironment have become the two pivotal obstacles that alleviate the antineoplastic efficacy in tumor photodynamic therapy (PDT). In the research, MnO₂-decorated upconversion nanoparticles (UCSMn) have been designed to generate certain oxygen within the solid tumor, and also increase the light penetrating depth due to the optical conversion ability derived from upconversion nanoparticles. Furthermore, upconversion nanoparticles as the inner core are coated by mesoporous silica for the loading of curcumin as photosensitizer and chemotherapeutics, and then a MnO₂ shell is proceeding to grow via redox method. When reaching the tumor tissue, the MnO₂ nanoshells of UCSMn could be rapidly degraded into manganese ions (Mn²⁺) owing to the reaction with H₂O₂ in acidic tumor microenvironment, meanwhile producing oxygen and facilitating curcumin release. Once the tumor is illuminated by 980 nm light, the upconversion nanoparticles can transform the infrared light to visible light of 450 nm and 475.5 nm, which can be efficiently absorbed by curcumin, and then produce singlet oxygen to induce tumor cell apoptosis. Curcumin played a dual role which can not only be acted as a photosensitizer, but also a chemotherapeutic agent to further reinforce the antitumor activity. In short, the intelligent nanostructure has the potential to overcome the above-mentioned shortcomings existed in PDT and eventually do work well in the hypoxia tumors. MnO₂-decorated upconversion nanoparticle to solve the tissue penetration and tumor hypoxic microenvironment for tumor photodynamic therapy.

Light-activated nanomaterials for tumor immunotherapy

Tumor immunotherapy mainly relies on activating the immune system to achieve antitumor treatment. However, the present tumor immunotherapy used in the clinic showed low treatment efficacy with high systematic toxicity. To overcome the shortcomings of traditional drugs for immunotherapy, a series of antitumor immunotherapies based on nanomaterials have been developed to enhance the body’s antitumor immune response and reduce systematic toxicity. Due to the noninvasiveness, remote controllability, and high temporal and spatial resolution of light, photocontrolled nanomaterials irradiated by excitation light have been widely used in drug delivery and photocontrolled switching. This review aims to highlight recent advances in antitumor immunotherapy based on photocontrolled nanomaterials. We emphasized the advantages of nanocomposites for antitumor immunotherapy and highlighted the latest progress of antitumor immunotherapy based on photoactivated nanomaterials. Finally, the challenges and future prospects of light-activated nanomaterials in antitumor immunity are discussed.

Aggregation-Induced Emission Luminogens for Cell Death Research

Cell death is closely related to various diseases, and monitoring and controlling cell death is a promising strategy to develop efficient therapy. Aggregation-induced emission luminogens (AIEgens) are ideal candidates for developing novel theranostic agents because of their intriguing properties in the aggregate state. The rational application of AIE materials in cell death-related research is still in its infancy but has shown great clinical potential. This review discussed the research frontier and our understanding of AIE materials in various subroutines of cell death, including apoptosis, necrosis, immunogenic cell death, pyroptosis, autophagy, lysosome-dependent cell death, and ferroptosis. We hope that the new insights can be offered to this growing field and attract more researchers to provide valuable contributions.

Phytoglycogen Encapsulation of Lanthanide-Based Nanoparticles as an Optical Imaging Platform with Therapeutic Potential

Lanthanide-based upconverting nanoparticles (UCNPs) are largely sought-after for biomedical applications ranging from bioimaging to therapy. A straightforward strategy is proposed here using the naturally sourced polymer phytoglycogen to coencapsulate UCNPs with hydrophobic photosensitizers as an optical imaging platform and light-induced therapeutic agents. The resulting multifunctional sub-micrometer-sized luminescent beads are shown to be cytocompatible as carrier materials, which encourages the assessment of their potential in biomedical applications. The loading of UCNPs of various elemental compositions enables multicolor hyperspectral imaging of the UCNP-loaded beads, endowing these materials with the potential to serve as luminescent tags for multiplexed imaging or simultaneous detection of different moieties under near-infrared (NIR) excitation. Coencapsulation of UCNPs and Rose Bengal opens the door for potential application of these microcarriers for collagen crosslinking. Alternatively, coloading UCNPs with Chlorin e6 enables NIR-light triggered generation of reactive oxygen species. Overall, the developed encapsulation methodology offers a straightforward and noncytotoxic strategy yielding water-dispersible UCNPs while preserving their bright and color-tunable upconversion emission that would allow them to fulfill their potential as multifunctional platforms for biomedical applications.

Multi-variable compensated quantum yield measurements of upconverting nanoparticles with high dynamic range: a systematic approach

Non-linear materials such as upconverting nanoparticles (UCNPs) are emerging technology with fast-growing applications in various fields. The power density dependence of the emission quantum yield (QY) of these non-linear materials makes them challenging to characterize using currently available commercial QY systems. We propose a multimodal system to measure QY over a wide dynamic range (1:104), which takes into account and compensates for various distorting parameters (scattering, beam profile, inner filter effect and bandwidth of emission lines). For this, a beam shaping approach enabling speckle free beam profiles of two different sizes (530 µm or 106 µm) was employed. This provides low noise high-resolution QY curves. In particular, at low power densities, a signal-to-noise ratio of >50 was found. A Tm-based core-shell UCNP with excitation at 976 nm and emission at 804 nm was investigated with the system.

Recent Advances in Near Infrared Upconverting Nanomaterials for Targeted Photodynamic Therapy of Cancer

Photodynamic therapy (PDT) is a well-established treatment of cancer that uses the toxic reactive oxygen species, including singlet oxygen (1O2), generated by photosensitiser drugs following irradiation of a specific wavelength to destroy the cancerous cells and tumours. Visible light is commonly used as the excitation source in PDT, which is not ideal for cancer treatment due to its reduced tissue penetration, and thus inefficiency to treat deep-lying tumours. Additionally, these wavelengths exhibit elevated autofluorescence background from the biological tissues which hinders optical biomedical imaging. An alternative to UV-Vis irradiation is the use of near infrared (NIR) excitation for PDT. This can be achieved using upconverting nanoparticles (UCNPs) functionalised with photosensitiser (PS) drugs where UCNPs can be used as an indirect excitation source for the activation of PS drugs yielding to the production of singlet 1O2 following NIR excitation. The use of nanoparticles for PDT is also beneficial due to their tumour targeting capability, either passively via the enhanced permeability and retention (EPR) effect or actively via stimuli-responsive targeting and ligand-mediated targeting (ie. using recognition units that can bind specific receptors only present or overexpressed on tumour cells). Here, we review recent advances in NIR upconverting nanomaterials for PDT of cancer with a clear distinction between those reported nanoparticles that could potentially target the tumour due to accumulation via the EPR effect (passive targeting) and nanoparticle-based systems that contain targeting agents with the aim of actively target the tumour via a molecular recognition process.

Deep-Tissue Activation of Photonanomedicines: An Update and Clinical Perspectives

Simple Summary

Photodynamic therapy (PDT) is a light-activated treatment modality, which is being clinically used and further developed for a number of premalignancies, solid tumors, and disseminated cancers. Nanomedicines that facilitate PDT (photonanomedicines, PNMs) have transformed its safety, efficacy, and capacity for multifunctionality. This review focuses on the state of the art in deep-tissue activation technologies for PNMs and explores how their preclinical use can evolve towards clinical translation by harnessing current clinically available instrumentation.

Abstract

With the continued development of nanomaterials over the past two decades, specialized photonanomedicines (light-activable nanomedicines, PNMs) have evolved to become excitable by alternative energy sources that typically penetrate tissue deeper than visible light. These sources include electromagnetic radiation lying outside the visible near-infrared spectrum, high energy particles, and acoustic waves, amongst others. Various direct activation mechanisms have leveraged unique facets of specialized nanomaterials, such as upconversion, scintillation, and radiosensitization, as well as several others, in order to activate PNMs. Other indirect activation mechanisms have leveraged the effect of the interaction of deeply penetrating energy sources with tissue in order to activate proximal PNMs. These indirect mechanisms include sonoluminescence and Cerenkov radiation. Such direct and indirect deep-tissue activation has been explored extensively in the preclinical setting to facilitate deep-tissue anticancer photodynamic therapy (PDT); however, clinical translation of these approaches is yet to be explored. This review provides a summary of the state of the art in deep-tissue excitation of PNMs and explores the translatability of such excitation mechanisms towards their clinical adoption. A special emphasis is placed on how current clinical instrumentation can be repurposed to achieve deep-tissue PDT with the mechanisms discussed in this review, thereby further expediting the translation of these highly promising strategies.

Enhancement of Upconversion Luminescence by the Construction of a 3Yb-Er-Hf Sublattice Energy Cluster and Surface Defect Elimination

Nanotetragonal LiYF₄:RE (Tm,Er,Ho) is a kind of excellent upconversion luminescence (UCL) material potentially used in many fields, while the enhancement of UC emission and regulation of luminescence lifetime are still a challenge. Herein, a strategy was reported to enhance UCL performance with the aid of the construction of a 3Yb-Er-Hf sublattice energy cluster with the introduction of Hf⁴⁺ and the interception of surface defect fluorescence quenching. UCL was obviously decreased by Hf⁴⁺ doping without surface defect elimination, but after the interception of surface defect quenching, UCL was dramatically enhanced more than 300-fold with an Er³⁺/Hf⁴⁺ mole ratio of 1:1. The contribution of UCL enhancement by the construction of a 3Yb-Er-Hf sublattice energy cluster is about 1.5 times of the sample without energy cluster construction. Interestingly, the lifetime of UCL can also be regulated by this strategy. According to the results of systematical microstructure analyses and UCL performance behaviors examined by X-ray powder diffraction (XRD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), and fluorescence spectrophotometry (FS) methods, the possible mechanism of UCL enhancement was proposed. This work may be an inspiration for researchers to design and develop high-performance UCL nanomaterials.

Dimensional Reduction Enhances Photodynamic Therapy of Metal-Organic Nanophotosensitizers

Herein we report that dimensional reduction from three-dimensional nanoscale metal-organic frameworks (nMOFs) to two-dimensional nanoscale metal-organic layers (nMOLs) increases the frequency of encounters between photosensitizers and oxygen and facilitates the diffusion of singlet oxygen from the nMOL to significantly enhance photodynamic therapy. The nMOFs and nMOLs share the same M₁₂-oxo (M = Zr, Hf) secondary building units and 5,15-di-p-benzoatoporphyrin (DBP) ligands but exhibit three-dimensional and two-dimensional topologies, respectively. Molecular dynamics simulations and experimental studies revealed that the nMOLs with a monolayer morphology enhanced the generation of reactive oxygen species and exhibited over an order of magnitude higher cytotoxicity over the nMOFs. In a mouse model of triple-negative breast cancer, Hf-DBP nMOL showed 49.1% more tumor inhibition, an 80% higher cure rate, and 16.3-fold lower metastasis potential than Hf-DBP nMOF.

Self-Assembly of Upconversion Nanoparticles Based Materials and Their Emerging Applications

In the past few decades, significant progress of the conventional upconversion nanoparticles (UCNPs) based nanoplatform has been achieved in many fields, and with the development of nanoscience and nanotechnology, more and more complex situations need a UCNPs based nanoplatform having multifunctions for specific multimodal or multiplexed applications. Through self-assembly, different UCNPs or UCNPs with other materials could be combined together within an entity. It is more like an ideal UCNPs nanoplatform, a unique system with the properties defined by its individual components as well as by the morphology of the composite. Various designs can show their different desired properties depending on the application situation. This review provides a complete summary on the optimization of the synthesis method for the recently designed UCNPs assemblies and summarizes various applications, including dual-modality cell imaging, molecular delivery, detection, and programmed control therapy. The challenges and limitations the UCNPs assembly faces and the potential solutions in this field are also presented.

NIR light‐triggered peroxynitrite anion production via direct lanthanide‐triplet photosensitization for enhanced photodynamic therapy

Peroxynitrite anion (ONOO−), a product derived from reaction between reactive oxygen species (ROS) and nitric oxide (NO), is considered to be a more toxic reactive specie than most ROS for...

Metal-Based Aggregation-Induced Emission Theranostic Systems

Efficient theranostic systems can realize better outcomes in disease treatment because of precise diagnosis and the concomitant effective therapy. Aggregation-induced emission luminogens (AIEgens) are a unique type of organic emitters with intriguing photophysical properties in the aggregate state. Among the AIEgens studied for biomedical applications, so far, metal-based AIE systems have shown great potential in theranostics due to the enhanced multimodal bioimaging ability and therapeutic effect. This research field has been growing rapidly, and many rationally designed systems with promising activities to cancer and other diseases have been reported recently. In this review, we summarized the recent progress of metal-based AIE materials in bioimaging and biological theranostics, and deciphered the pertinent design strategies. We hope that this review can offer new insights into the development of this growing field.

Current Strategies for Tumor Photodynamic Therapy Combined With Immunotherapy

Photodynamic therapy (PDT) is a low invasive antitumor therapy with fewer side effects. On the other hand, immunotherapy also has significant clinical applications in the treatment of cancer. Both therapies, on their own, have some limitations and are incapable of meeting the demands of the current cancer treatment. The efficacy of PDT and immunotherapy against tumor metastasis and tumor recurrence may be improved by combination strategies. In this review, we discussed the possibility that PDT could be used to activate immune responses by inducing immunogenic cell death or generating cancer vaccines. Furthermore, we explored the latest advances in PDT antitumor therapy in combination with some immunotherapy such as immune adjuvants, inhibitors of immune suppression, and immune checkpoint blockade.

Emerging strategies in developing multifunctional nanomaterials for cancer nanotheranostics

Cancer involves a collection of diseases with a common trait - dysregulation in cell proliferation. At present, traditional therapeutic strategies against cancer have limitations in tackling various tumors in clinical settings. These include chemotherapeutic resistance and the inability to overcome intrinsic physiological barriers to drug delivery. Nanomaterials have presented promising strategies for tumor treatment in recent years. Nanotheranostics combine therapeutic and bioimaging functionalities at the single nanoparticle level and have experienced tremendous growth over the past few years. This review highlights recent developments of advanced nanomaterials and nanotheranostics in three main directions: stimulus-responsive nanomaterials, nanocarriers targeting the tumor microenvironment, and emerging nanomaterials that integrate with phototherapies and immunotherapies. We also discuss the cytotoxicity and outlook of next-generation nanomaterials towards clinical implementation.

Prospects for More Efficient Multi-Photon Absorption Photosensitizers Exhibiting Both Reactive Oxygen Species Generation and Luminescence

The use of two-photon absorption (TPA) for such applications as microscopy, imaging, and photodynamic therapy (PDT) offers several advantages over the usual one-photon excitation. This creates a need for photosensitizers that exhibit both strong two-photon absorption and the highly efficient generation of reactive oxygen species (ROS), as well as, ideally, bright luminescence. This review focuses on different strategies utilized to improve the TPA properties of various multi-photon absorbing species that have the required photophysical properties. Along with well-known families of photosensitizers, including porphyrins, we also describe other promising organic and organometallic structures and more complex systems involving organic and inorganic nanoparticles. We concentrate on the published studies that provide two-photon absorption cross-section values and the singlet oxygen (or other ROS) and luminescence quantum yields, which are crucial for potential use within PDT and diagnostics. We hope that this review will aid in the design and modification of novel TPA photosensitizers, which can help in exploiting the features of nonlinear absorption processes.

The ROS-generating photosensitizer-free NaYF4:Yb,Tm@SiO2upconverting nanoparticles for photodynamic therapy application

In this work we adapt rare-earth-ion-doped NaYF₄nanoparticles coated with a silicon oxide shell (NaYF₄:20%Yb,0.2%Tm@SiO₂) for biological and medical applications (for example, imaging of cancer cells and therapy at the nano level). The wide upconversion emission range under 980 nm excitation allows one to use the nanoparticles for cancer cell (4T1) photodynamic therapy (PDT) without a photosensitizer. The reactive oxygen species (ROS) are generated by Tm/Yb ion upconversion emission (blue and UV light). Thein vitroPDT was tested on 4T1 cells incubated with NaYF₄:20%Yb,0.2%Tm@SiO₂nanoparticles and irradiated with NIR light. After 24 h, cell viability decreased to below 10%, demonstrating very good treatment efficiency. High modification susceptibility of the SiO₂shell allows for attachment of biological molecules (specific antibodies). In this work we attached the anti-human IgG antibody to silane-PEG-NHS-modified NaYF₄:20%Yb,0.2%Tm@SiO₂nanoparticles and a specifically marked membrane model by bio-conjugation. Thus, it was possible to perform a selective search (a high-quality optical method with a very low-level organic background) and eventually damage the targeted cancer cells. The study focuses on therapeutic properties of NaYF₄:20%Yb,0.2%Tm@SiO₂nanoparticles and demonstrates, upon biological functionalization, their potential for targeted therapy.

Recent Advances in Photosensitizers as Multifunctional Theranostic Agents for Imaging-Guided Photodynamic Therapy of Cancer

In recent years tremendous effort has been invested in the field of cancer diagnosis and treatment with an overall goal of improving cancer management, therapeutic outcome, patient survival, and quality of life. Photodynamic Therapy (PDT), which works on the principle of light-induced activation of photosensitizers (PS) leading to Reactive Oxygen Species (ROS) mediated cancer cell killing has received increased attention as a promising alternative to overcome several limitations of conventional cancer therapies. Compared to conventional therapies, PDT offers the advantages of selectivity, minimal invasiveness, localized treatment, and spatio-temporal control which minimizes the overall therapeutic side effects and can be repeated as needed without interfering with other treatments and inducing treatment resistance. Overall PDT efficacy requires proper planning of various parameters like localization and concentration of PS at the tumor site, light dose, oxygen concentration and heterogeneity of the tumor microenvironment, which can be achieved with advanced imaging techniques. Consequently, there has been tremendous interest in the rationale design of PS formulations to exploit their theranostic potential to unleash the imperative contribution of medical imaging in the context of successful PDT outcomes. Further, recent advances in PS formulations as activatable phototheranostic agents have shown promising potential for finely controlled imaging-guided PDT due to their propensity to specifically turning on diagnostic signals simultaneously with photodynamic effects in response to the tumor-specific stimuli. In this review, we have summarized the recent progress in the development of PS-based multifunctional theranostic agents for biomedical applications in multimodal imaging combined with PDT. We also present the role of different imaging modalities; magnetic resonance, optical, nuclear, acoustic, and photoacoustic in improving the pre-and post-PDT effects. We anticipate that the information presented in this review will encourage future development and design of PSs for improved image-guided PDT for cancer treatment.

Theranostic Applications of Nanoparticle-Mediated Photoactivated Therapies

Nanoparticle-mediated light-activated therapies, such as photodynamic therapy and photothermal therapy, are earnestly being viewed as efficient interventional strategies against several cancer types. Theranostics is a key hallmark of cancer nanomedicine since it allows diagnosis and therapy of both primary and metastatic cancer using a single nanoprobe. Advanced in vivo diagnostic imaging using theranostic nanoparticles not only provides precise information about the location of tumor/s but also outlines the narrow time window corresponding to the maximum tumor-specific drug accumulation. Such information plays a critical role in guiding light-activated therapies with high spatio-temporal accuracy. Furthermore, theranostics facilitates monitoring the progression of therapy in real time. Herein, we provide a general review of the application of theranostic nanoparticles for in vivo image-guided light-activated therapy in cancer. The imaging modalities considered here include fluorescence imaging, photoacoustic imaging, thermal imaging, magnetic resonance imaging, X-ray computed tomography, positron emission tomography, and single-photon emission computed tomography. The review concludes with a brief discussion about the broad scope of theranostic light-activated nanomedicine.

Enhanced anti-tumor efficacy by inhibiting HIF-1α to reprogram TAMs via core-satellite upconverting nanoparticles with curcumin mediated photodynamic therapy

Tumor hypoxic stress after photodynamic therapy (PDT) will be inevitably exacerbated by the vascular blocking effects and oxygen consumption in the tumor microenvironment (TME) which usually leads to compromised efficacy and clinical performance. Increasing evidence links the hypoxia induced up-regulation of hypoxia inducible factor 1α (HIF-1α) with immunosuppressive TME, including the polarization of M2 phenotype tumor associated macrophages (TAMs), which promote the recurrence and metastasis. Here, we reported NIR-triggered core-satellite upconverting nanoparticles (CSNPs) with curcumin (Cur) embedded as a difunctional photosensitizer, which could realize PDT in deep tumors with long excitation wavelength (980 nm) and reverse the immunosuppressive TME induced by up-regulated HIF-1α at the same time. This Cur-loaded CSNPs (Cur-CSNPs)-mediated PDT could successfully induce the immunogenic cell death (ICD) of triple negative breast cancer (TNBC) cell lines (4T1 and MDA-MB-231) in vitro and repolarize the 4T1 cells co-cultured TAMs from pro-tumor M2 to the anti-tumor M1 phenotype. Furthermore, Cur-CSNPs-mediated PDT could suppress the 4T1 tumor growth in primary and distant sites through the synergistic immunotherapeutic effects in vivo by priming M1 type TAMs and CD4+/CD8+ T cells' infiltration. Our data highlight the novel application of CSNPs-embedded Cur as a difunctional photosensitizer to enhance the anti-tumor efficacy of PDT.

Light Technology for Efficient and Effective Photodynamic Therapy: A Critical Review

Photodynamic therapy (PDT) is a cancer treatment with strong potential over well-established standard therapies in certain cases. Non-ionising radiation, localisation, possible repeated treatments, and stimulation of immunological response are some of the main beneficial features of PDT. Despite the great potential, its application remains challenging. Limited light penetration depth, non-ideal photosensitisers, complex dosimetry, and complicated implementations in the clinic are some limiting factors hindering the extended use of PDT. To surpass actual technological paradigms, radically new sources, light-based devices, advanced photosensitisers, measurement devices, and innovative application strategies are under extensive investigation. The main aim of this review is to highlight the advantages/pitfalls, technical challenges and opportunities of PDT, with a focus on technologies for light activation of photosensitisers, such as light sources, delivery devices, and systems. In this vein, a broad overview of the current status of superficial, interstitial, and deep PDT modalities-and a critical review of light sources and their effects on the PDT process-are presented. Insight into the technical advancements and remaining challenges of optical sources and light devices is provided from a physical and bioengineering perspective.

Low-Temperature-Induced Controllable Transversal Shell Growth of NaLnF4 Nanocrystals

Highly controllable anisotropic shell growth is essential for further engineering the function and properties of lanthanide-doped luminescence nanocrystals, especially in some of the advanced applications such as multi-mode bioimaging, security coding and three-dimensional (3D) display. However, the understanding of the transversal shell growth mechanism is still limited today, because the shell growth direction is impacted by multiple complex factors, such as the anisotropy of surface ligand-binding energy, anisotropic core–shell lattice mismatch, the size of cores and varied shell crystalline stability. Herein, we report a highly controlled transversal shell growth method for hexagonal sodium rare-earth tetrafluoride (β-NaLnF₄) nanocrystals. Exploiting the relationship between reaction temperature and shell growth direction, we found that the shell growth direction could be tuned from longitudinal to transversal by decreasing the reaction temperature from 310 °C to 280 °C. In addition to the reaction temperature, we also discussed the roles of other factors in the transversal shell growth of nanocrystals. A suitable core size and a relative lower shell precursor concentration could promote transversal shell growth, although different shell hosts played a minor role in changing the shell growth direction.

Orthogonal Emissive Upconversion Nanoparticles: Material Design and Applications

Upconversion nanoparticles (UCNPs) have gone beyond traditional fluorophores in a lot of fields due to the outstanding features such as sharp excitation and emission bands, chemical and photo stability of high quality, low auto fluorescence, and high tissue permeation depth of the near-infrared irradiation light used for excitation. Conventional UCNPs carrying single/multiple emissions under a single excitation wavelength can be only employed in concurrent activation, orthogonal emissive upconversion nanoparticles (OUCNPs) with the emissions, a kind of luminescence reliant on excitation, in which by switching the external excitation different lanthanide activators can adopt independent way to control the emission, is more like an ideal UCNPs nanoplatform which can switch their activated emissions depending upon the different application for which it is used at the right time when necessary. This review summaries what has been achieved on the synthesis optimization of designed OUCNPs in recent years and sums up various applications including bioimaging, photo-switching, and programmable control process. And also, the limitations OUCNPs face, and the efforts that have been made to overcome these limitations are discussed.

Mathematical modeling and experimental analysis of the efficacy of photodynamic therapy in conjunction with photo thermal therapy and PEG-coated Au-doped TiO2 nanostructures to target MCF-7 cancerous cells

Some nanoscale morphologies of titanium oxide nanostructures blend with gold nanoparticles and act as satellites and targeted weapon methodologies in biomedical applications. Simultaneously, titanium oxide can play an important role when combined with gold after blending with polyethylene glycol (PEG). Our experimental approach is novel with respect to the plasmonic role of metal nanoparticles as an efficient PDT drug. The current experimental strategy floats the comprehensive and facile way of experimental strategy on the critical influence that titanium with gold nanoparticles used as novel photosensitizing agents after significant biodistribution of proposed nanostructures toward targeted site. In addition, different morphologies of PEG-coated Au-doped titanium nanostructures were shown to provide various therapeutic effects due to a wide range of electromagnetic field development. This confirms a significantly amplified population of hot electron generation adjacent to the interface between Au and TiO₂ nanostructures, leading to maximum cancerous cell injury in the MCF-7 cell line. The experimental results were confirmed by applying a least squares fit math model which verified our results with 99% goodness of fit. These results can pave the way for comprehensive rational designs for satisfactory response of performance phototherapeutic model mechanisms along with new horizons of photothermal therapy (HET) and photodynamic therapy (HET) operating under visible and near-infrared (NIR) light.

UVA-Triggered Drug Release and Photo-Protection of Skin

Light has attracted special attention as a stimulus for triggered drug delivery systems (DDS) due to its intrinsic features of being spatially and temporally tunable. Ultraviolet A (UVA) radiation has recently been used as a source of external light stimuli to control the release of drugs using a "switch on- switch off" procedure. This review discusses the promising potential of UVA radiation as the light source of choice for photo-controlled drug release from a range of photo-responsive and photolabile nanostructures via photo-isomerization, photo-cleavage, photo-crosslinking, and photo-induced rearrangement. In addition to its clinical use, we will also provide here an overview of the recent UVA-responsive drug release approaches that are developed for phototherapy and skin photoprotection.

What NIR photodynamic activation offers molecular targeted nanomedicines: Perspectives into the conundrum of tumor specificity and selectivity

Near infrared (NIR) photodynamic activation is playing increasingly critical roles in cutting-edge anti-cancer nanomedicines, which include spatiotemporal control over induction of therapy, photodynamic priming, and phototriggered immunotherapy. Molecular targeted photonanomedicines (mt-PNMs) are tumor-specific nanoscale drug delivery systems, which capitalize on the unparalleled spatio-temporal precision of NIR photodynamic activation to augment the accuracy of tumor tissue treatment. mt-PNMs are emerging as a paradigm approach for the targeted treatment of solid tumors, yet remain highly complex and multifaceted. While ligand targeted nanomedicines in general suffer from interdependent challenges in biophysics, surface chemistry and nanotechnology, mt-PNMs provide distinct opportunities to synergistically potentiate the effects of ligand targeting. This review provides what we believe to be a much-need demarcation between the processes involved in tumor specificity (biomolecular recognition events) and tumor selectivity (preferential tumor accumulation) of ligand targeted nanomedicines, such as mt-PNMs, and elaborate on what NIR photodynamic activation has to offer. We discuss the interplay between both tumor specificity and tumor selectivity and the degree to which both may play central roles in cutting-edge NIR photoactivable nanotechnologies. A special emphasis is made on NIR photoactivable biomimetic nanotechnologies that capitalize on both specificity and selectivity phenomena to augment the safety and efficacy of photodynamic anti-tumor regimens.

NIR Photoregulated Theranostic System Based on Hexagonal-Phase Upconverting Nanoparticles for Tumor-Targeted Photodynamic Therapy and Fluorescence Imaging

Although photodynamic therapy (PDT) is an effective, minimally invasive therapeutic modality with advantages in highly localized and specific tumor treatments, large and deep-seated cancers within the body cannot be successfully treated due to low transparency to visible light. To improve the therapeutic efficiency of tumor treatment in deep tissue and reduce the side effects in normal tissue, this study developed a near-infrared (NIR)-triggered upconversion nanoparticle (UCNP)-based photosensitizer (PS) carrier as a new theranostics system. The NaYF4:Yb/Er UCNPs were synthesized by a hydrothermal method, producing nanoparticles of a uniformly small size (≈20 nm) and crystalline morphology of the hexagonal phase. These UCNPs were modified with folic acid-conjugated biocompatible block copolymers through a bidentate dihydrolipoic acid linker. The polymer modified hexagonal phase UCNPs (FA-PEAH-UCNPs) showed an improved dispersibility in the aqueous solution and strong NIR-to-vis upconversion fluorescence. The hydrophobic PS, pheophorbide a (Pha), was then conjugated to the stable vectors. Moreover, these UCNP-based Pha carriers containing tumor targeting folic acid ligands exhibited the significantly enhanced cellular uptake efficiency as well as PDT treatment efficiency. These results suggested that this system could extend the excitation wavelength of PDT to the NIR region and effectively improve therapeutic efficiency of PSs.