Recent progress in photosensitizers for overcoming the challenges of photodynamic therapy: from molecular design to application

Deepened Photodynamic Therapy through Skin Optical Clearing Technology in the Visible Light Window

The trade-off that shorter wavelength light facilitates the efficient generation of reactive oxygen species (ROS) from photosensitizer (PS) while facing the drawback of limited penetration depth through skin tissue restricts the further development of photodynamic therapy (PDT). Here, we address this contradiction and achieve visible-light-tailored deep PDT combined with the skin optical clearing technology. With the help of the prepared skin optical clearing gel, the refractive index inhomogeneity between skin tissue components is greatly attenuated, and the light scattering effect within the skin tissue is remarkably reduced. As a consequence, the transmittance of visible light at 600 nm through in vitro porcine skin and in vivo mouse skin after treatment increases from approximately 10 and 40 to 70 and 70%, respectively. Furthermore, in the tumor cell eradication experiment, the local ROS generation efficiency in the experimental group is several times higher than that in the control group owing to improved visible transmittance, which is thus responsible for the complete eradication of tumor cells, even when shaded by skin tissue. The results suggest that this strategy may serve as a valuable supplement to the current deep PDT strategies.

Metal-based nanoparticles in cancer therapy: Exploring photodynamic therapy and its interplay with regulated cell death pathways

Photodynamic therapy (PDT) represents a non-invasive treatment strategy currently utilized in the clinical management of selected cancers and infections. This technique is predicated on the administration of a photosensitizer (PS) and subsequent irradiation with light of specific wavelengths, thereby generating reactive oxygen species (ROS) within targeted cells. The cellular effects of PDT are dependent on both the localization of the PS and the severity of ROS challenge, potentially leading to the stimulation of various cell death modalities. For many years, the concept of regulated cell death (RCD) triggered by photodynamic reactions predominantly encompassed apoptosis, necrosis, and autophagy. However, in recent decades, further explorations have unveiled additional cell death modalities, such as necroptosis, ferroptosis, cuproptosis, pyroptosis, parthanatos, and immunogenic cell death (ICD), which helps to achieve tumor cell elimination. Recently, nanoparticles (NPs) have demonstrated substantial advantages over traditional PSs and become important components of PDT, due to their improved physicochemical properties, such as enhanced solubility and superior specificity for targeted cells. This review aims to summarize recent advancements in the applications of different metal-based NPs as PSs or delivery systems for optimized PDT in cancer treatment. Furthermore, it mechanistically highlights the contribution of RCD pathways during PDT with metal NPs and how these forms of cell death can improve specific PDT regimens in cancer therapy.

NIR ditriphenylamine Indole-BODIPY photosensitizer: synthesis, photodynamic therapy in A549 cells and two-photon fluorescence imaging in zebrafish

In this study, the ditriphenylamine Indole-BODIPY photosensitizer T2BDP-lyso was synthesized for near-infrared photodynamic therapy and two-photon fluorescence imaging. The photosensitizer T2BDP-lyso exhibits absorption above 700 nm and emission above 800 nm, respectively. Theoretical calculations show the energy gap from the excited state S1 to the excited state T2 is 0.14 eV, which indicated that the photosensitizer T2BDP-lyso could reach the triplet state by intersystem crossing from the singlet state. Under NIR light, the singlet oxygen yield of photosensitizer T2BDP-lyso was calculated to be 0.64 in CH2Cl2. The photosensitizer T2BDP-lyso can effectively produce reactive oxygen species in A549 cells and zebrafish under 660 nm light for 5 min. The photosensitizer T2BDP-lyso exhibited lower dark toxicity and higher phototoxicity (IC50 = 1.49 μM), as well as lysosomal targeting ability (Pearson coefficient = 0.89). In the AO/EB double staining assay simulating photodynamic therapy at the cellular level, 3 μM of T2BDP-lyso light for 10 min was effective in killing cancer cells. Moreover, the photosensitizer T2BDP-lyso has a large two-photon absorption cross section at 1050 nm, which was calculated to be 138.7 GM in THF by Z-scan method, and two-photon fluorescence imaging was performed in zebrafish. The above results indicate the potential application of the photosensitizer T2BDP-lyso in near-infrared photodynamic therapy and two-photon fluorescence imaging.

Highly photoactive Ir(III)-Pt(IV) heterometallic conjugates for anticancer therapy

For the first time, this study reported the photoactivatable activity of Ir(III)-Pt(IV) heterometallic conjugates, which were stable in the dark and activated to release oxaliplatin and Ir within 3 min of irradiation. The conjugates induced apoptosis and immunologic cell death through Pt-DNA binding and reactive oxygen species generation upon irradiation. This work developed photoactivatable heterometallic agents for anticancer therapy.

Low-symmetry A3 B-type 6H-1,4-diazepinoporphyrazines with anti-Kasha effect as promising photosensitizers

A series of tribenzo[g,l,q]-6H-1,4-diazepino[2,3-b]porphyrazines has been synthesized. A temperature-dependent steric effect was applied in the mixed Linstead macrocyclization of phthalonitrile and 5,7-bis(2'-arylethenyl)-6-propyl-6H-1,4-diazepine-2,3-dicarbonitrile to achieve high yield of low-symmetry A3 B-type Mg(II) tribenzo[g,l,q]-6H-1,4-diazepino[2,3-b]porphyrazinate. The analysis of photophysical and photochemical properties of the obtained complexes showed the anti-Kasha effect: the ultrafast spin changes successfully compete with the IC. TD-DFT calculations showed that the presence of 1,4-diazepine heterocycle in the porphyrazine structure leads to the formation of additional charge-transfer triplet state T2 . We propose, it could participate in the pumping of T1x state alongside with T1y state (these states are degenerate in D4h symmetry) and, therefore, increase singlet oxygen (1 Δg ) generation. Stable micellar nanoparticles have been obtained based on the tribenzo[g,l,q]-6H-1,4-diazepino[2,3-b]porphyrazine Mg(II) and Zn(II) complexes using polyvinylpyrrolidone. The nanoparticles effectively interact with model biological structures (FBS and brain homogenate), leading to disaggregation of the macrocycles. They also exhibit pronounced phototoxic effects in MCF-7 cells upon red light irradiation. We propose that enhancement in PDT activity could be explained by their increased resistance to aggregation due to the presence of n-propyl substituent directly attached to the C6 position of the 1,4-diazepine moiety. The demonstrated results show the promising potential of tribenzo-6H-1,4-diazepinoporphyrazines as heavy atom-free photosensitizers.

Reactive Reductive Species Participating Photodynamic Therapy for Cancer Treatment

Although the development of oxidative photodynamic therapy (O-PDT) based on reactive oxygen species (ROS) has led to great progress in cancer treatment, tumor hypoxia, cellular adaptation and intrinsic antioxidant defenses are still obstacles at this stage. Fortunately, with the discovery and development of reactive reductive species (RRS) in the PDT process, reductive PDT (R-PDT) is receiving increasing research interest. R-PDT with oxygen-independence is an effective reduction therapy that promises excellent therapeutic efficacy in extremely hypoxic or even anaerobic environments. In the concept, we introduce representative strategies to boost the type-I photosensitizing pathway, and then focus on the most recent R-PDT involving hydrogen radical (H⋅) and the single electron transfer (SET) process.

Metallopolymer strategy to explore hypoxic active narrow-bandgap photosensitizers for effective cancer photodynamic therapy

Practical photodynamic therapy calls for high-performance, less O2-dependent, long-wavelength-light-activated photosensitizers to suit the hypoxic tumor microenvironment. Iridium-based photosensitizers exhibit excellent photocatalytic performance, but the in vivo applications are hindered by conventional O2-dependent Type-II photochemistry and poor absorption. Here we show a general metallopolymerization strategy for engineering iridium complexes exhibiting Type-I photochemistry and enhancing absorption intensity in the blue to near-infrared region. Reactive oxygen species generation of metallopolymer Ir-P1, where the iridium atom is covalently coupled to the polymer backbone, is over 80 times higher than that of its mother polymer without iridium under 680 nm irradiation. This strategy also works effectively when the iridium atom is directly included (Ir-P2) in the polymer backbones, exhibiting wide generality. The metallopolymer nanoparticles exhibiting efficient O2•- generation are conjugated with integrin αvβ3 binding cRGD to achieve targeted photodynamic therapy.

Lipid Droplet Targeting Type I Photosensitizer for Ferroptosis via Lipid Peroxidation Accumulation

As an iron-dependent lipid peroxidation (LPO) mediated cell death pathway, ferroptosis offers promises for anti-tumor treatment. Photodynamic therapy (PDT) is an ideal way to generate reactive oxygen species (ROS) for LPO. However, the conventional PDT normally functions on subcellular organelles, such as endoplasmic reticulum, mitochondria, and lysosome, causing rapid cell death before triggering ferroptosis. Herein, the first lipid droplet (Ld)-targeting type I photosensitizer (PS) with enhanced superoxide anion (O2 -· ) production, termed MNBS, is reported. The newly designed PS selectively localizes at Ld in cells, and causes cellular LPO accumulation by generating sufficient O2 -· upon irradiation, and subsequently induces ferroptosis mediated chronical PDT, achieving high-efficient anti-tumor PDT in hypoxia and normoxia. Theoretical calculations and comprehensive characterizations indicate that the Ld targeting property and enhanced O2 -· generation of MNBS originate from the elevated H-aggregation tendency owing to dispersed molecular electrostatic distribution. Further in vivo studies using MNBS-encapsulated liposomes demonstrate the excellent anti-cancer efficacy as well as anti-metastatic activity. This study offers a paradigm of H-aggregation reinforced type I PS to achieve ferroptosis-mediated PDT.

NaYF4 :Yb/Er@Mn3 O4 @GOX Nanocomposite for Upconversion Fluorescence Imaging and Synergistic Cascade Cancer Therapy by Apoptosis and Ferroptosis

The cell elimination strategy based on reactive oxygen species (ROS) is a promising method for tumor therapy. However, its efficacy is significantly limited by ROS deficiency caused by H2 O2 substrate deficiency and up-regulation of cellular antioxidant defense induced by high glutathione (GSH) content in tumor cells. To overcome these obstacles, a multifunctional self-cascaded nanocomposite: glucose oxidase (GOX) loaded NaYF4 :Yb/Er@Mn3 O4 (UC@Mn3 O4 , labeled as UCMn) is constructed. Only in tumor microenvironment, it can be specifically activated through a series of cascades to boost ROS production via a strategy of open source (H2 O2 self-supplying ability). The increased ROS can enhance lipid peroxidation and induce tumor cell apoptosis by activating the protein caspase. More importantly, the nanozyme can consume GSH to inhibit glutathione peroxidase 4 (GPX4) activity, which limits tumor cell resistance to oxidative damage and triggers the tumor cell ferroptosis. Therefore, this strategy is expected to overcome the resistance of tumor to oxidative damage and achieve efficient oxidative damage of tumor. Further, degradation of the Mn3 O4 layer induced by GSH and acidic environment can promote the fluorescence recovery of UC fluorescent nuclear for tumor imaging to complete efficient integration of diagnosis and treatment for tumor.

Internal Light Sources-Mediated Photodynamic Therapy Nanoplatforms: Hope for the Resolution of the Traditional Penetration Problem

Photodynamic therapy (PDT) is an alternative cancer treatment technique with a noninvasive nature, high selectivity, and minimal adverse effects. The indispensable light source used in PDT is a critical factor in determining the energy conversion of photosensitizers (PSs). Traditional light sources are primarily concentrated in the visible light region, severely limiting their penetration depth and making them prone to scattering and absorption when applied to biological tissues. For that reason, its efficacy in treating deep-seated lesions is often inadequate. Self-exciting PDT, also known as auto-PDT (APDT), is an attractive option for circumventing the limited penetration depth of traditional PDT and has acquired significant attention. APDT employs depth-independent internal light sources to excite PSs through resonance or radiative energy transfer. APDT has considerable potential for treating deep-tissue malignancies. To facilitate many researchers' comprehension of the latest research progress in this field and inspire the emergence of more novel research results. This review introduces internal light generation mechanisms and characteristics and provides an overview of current research progress based on the recently reported APDT nanoplatforms. The current challenges and possible solutions of APDT nanoplatforms are also presented and provide insights for future research in the final section of this article.

Recent advances in aggregation-induced emission-active type I photosensitizers with near-infrared fluorescence: From materials design to therapeutic platform fabrication

Near-infrared (NIR) fluorescence imaging-guided photodynamic therapy (PDT) technology plays an important role in treating various diseases and still attracts increasing research interests for developing novel photosensitizers (PSs) with outstanding performances. Conventional PSs such as porphyrin and rhodamine derivatives have easy self-aggregation properties in the physiological environment due to their inherent hydrophobic nature caused by their rigid molecular structure that induces strong intermolecular stacking π-π interaction, leading to serious fluorescence quenching and cytotoxic reactive oxygen species (ROS) reduction. Meanwhile, hypoxia is an inherent barrier in the microenvironment of solid tumors, seriously restricting the therapeutic outcome of conventional PDT. Aforementioned disadvantages should be overcome urgently to enhance the therapeutic effect of PSs. Novel NIR fluorescence-guided type I PSs with aggregation-induced emission (AIE), which features the advantages of improving fluorescent intensity and ROS generation efficiency at aggregation as well as outstanding oxygen tolerance, bring hope for resolving aforementioned problems simultaneously. At present, plenty of research works fully demonstrates the advancement of AIE-active PDT based on type I PSs. In this review, cutting-edge advances focusing on AIE-active NIR type I PSs that include the aspects of the photochemical mechanism of type I ROS generation, various molecular structures of reported type I PSs with NIR fluorescence and their design strategies, and typical anticancer applications are summarized. Finally, a brief conclusion is obtained, and the underlying challenges and prospects of AIE-active type I PSs are proposed.

Assessment of Some Unsymmetrical Porphyrins as Promising Molecules for Photodynamic Therapy of Cutaneous Disorders

In order to select for further development novel photosensitizers for photodynamic therapy in cutaneous disorders, three unsymmetrical porphyrins, namely 5-(4-hydroxy-3-methoxyphenyl)-10,15,20-tris-(4-acetoxy-3-methoxyphenyl) porphyrin (P2.2), 5-(2-hydroxy-5-methoxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl) porphyrin (P3.2), and 5-(2,4-dihydroxyphenyl)-10,15,20-tris-(4-acetoxy-3-methoxyphenyl) porphyrin (P4.2), along with their fully symmetrical counterparts 5,10,15,20-tetrakis-(4-acetoxy-3-methoxyphenyl) porphyrin (P2.1) and 5,10,15,20-tetrakis-(4-carboxymethylphenyl) porphyrin (P3.1) were comparatively evaluated. The absorption and fluorescence properties, as well as atomic force microscopy measurements were performed to evaluate the photophysical characteristics as well as morphological and textural properties of the mentioned porphyrins. The cellular uptake of compounds and the effect of photodynamic therapy on the viability, proliferation, and necrosis of human HaCaT keratinocytes, human Hs27 skin fibroblasts, human skin SCL II squamous cell carcinoma, and B16F10 melanoma cells were assessed in vitro, in correlation with the structural and photophysical properties of the investigated porphyrins, and with the predictions regarding diffusion through cell membranes and ADMET properties. All samples were found to be isotropic and self-similar, with slightly different degrees of aggregability, had a relatively low predicted toxicity (class V), and a predicted long half-life after systemic administration. The in vitro study performed on non-malignant and malignant skin-relevant cells highlighted that the asymmetric P2.2 porphyrin qualified among the five investigated porphyrins to be a promising photosensitizer candidate for PDT in skin disorders. P2.2 was shown to accumulate well within cells, and induced by PDT a massive decrease in the number of metabolically active skin cells, partly due to cell death by necrosis. P2.2 had in this respect a better behavior than the symmetric P.2.1 compound and the related asymmetric compound P4.2. The strong action of P2.2-mediated PDT on normal skin cells might be an important drawback for further development of this compound. Meanwhile, the P3.1 and P3.2 compounds were not able to accumulate well in skin cells, and did not elicit significant PDT in vitro. Taken together, our experiments suggest that P2.2 can be a promising candidate for the development of novel photosensitizers for PDT in skin disorders.

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

Development of Ruthenium Nanophotocages with Red or Near-Infrared Light-Responsiveness

The development of light-triggered ruthenium (Ru) nanophotocages has revolutionized conventional methods of drug administration, thereby facilitating cancer therapy in a noninvasive and temperate manner. Ru nanophotocages employ a distinct approach known as photoactivated chemotherapy (PACT), wherein light-induced ligand dissociation yields a toxic metal complex or a ligand capable of performing other functions such as optically controlled protein degradation and drug delivery. Simultaneously, this process is accompanied by the generation of reactive oxygen species (ROS), which serve as an effective anticancer agent in combination with PACT and photodynamic therapy (PDT). Due to its exceptional attributes of extended tissue penetration, and minimized tissue damage, red light or near-infrared light is widely acknowledged as the "phototherapeutic window" (650-900 nm). In this Concept, we present an overview of the most recent advancements in Ru nanophotocages within the phototherapeutic range. Diverse aspects, including design principles, photocaging efficacy, photoactivation mechanisms, and potential applications in the field of biomedical chemistry, are discussed. Questions and challenges regarding their synthesis, characterization, and applications are also discussed. This Concept would foster further exploration into the realm of Ru nanophotocages.

Exploration of Thermally Activated Delayed Fluorescence (TADF)-Based Photoredox Catalyst To Establish the Mechanisms of Action for Photodynamic Therapy

The mechanisms of action (MoA) have been proposed to further reduce the O2 dependence of photodynamic therapy (PDT) significantly. However, the triplet states of traditional photosensitizers are relatively short and also are easily deactivated by the quenching of H2O or O2. This is not conducive for the electron transfer in the photocatalytic process and poses a great obstacle to establish the MoA. Therefore, we selected and synthesized a zirconium(IV) complex (Zr(MesPDPPh)2) reported by Milsmann to address this issue. The specific symmetric and intact geometry endowed Zr(MesPDPPh)2 NPs with long-lived triplet excited state (τ = 350 μs), desired sensitized ability, and improved anti-interfering performance on O2, which was matched with the requirements of photoredox catalyst significantly. The results showed that while PDT (I) and PDT (II) could be achieved simultaneously by leveraging Zr(MesPDPPh)2 NPs, it also could be served as a rare example of thermally activated delayed fluorescence (TADF)-based photoredox catalyst to implement the MoA of PDT. It involved the oxidation of NADH and the establishment of catalytic cycle collaborating by O2 and cytochrome c (cyt c) in normoxia and hypoxia, respectively. As a result, the oxygen-free PDT and tumor-growth inhibition was realized.

Protein-Porphyrin Complex Photosensitizers for Anticancer and Antimicrobial Photodynamic Therapies

Photodynamic therapy (PDT) efficiently induces apoptosis through visible-light irradiation of photosensitizers (PSs) within tumors and microbial cells. Porphyrin analogues serve as widely utilized photosensitizing agents with their therapeutic abilities being governed by molecular structures and central metal ions. However, these macrocyclic compounds tend to agglutinate and form stacks in aqueous environments, resulting in a loss of photochemical activity. To overcome this limitation, encapsulation within liposomes and polymer micelles enables the dispersion of porphyrins as monomolecular entities in aqueous solutions, preventing undesirable deactivation. Recently, the use of reconstituted hemoproteins containing various metal-porphyrins and protein cages incorporating porphyrins has garnered significant interest as a new generation of biocompatible PSs. In this concept paper, we provide a comprehensive review of recent developments and trends of protein-porphyrin complex PSs for applications in anticancer and antimicrobial PDTs.

Targeted and Oxygen-Enriched Nanoplatform for Enhanced Photodynamic Therapy: In Vitro 2D Cell and 3D Spheroid Model Evaluation

Hypoxic microenvironment and limited penetration of photosensitizers within solid tumors are two crucial factors that restrict photodynamic therapy (PDT) efficacy. Herein, a new fluorinated mixed micelle (M60@PFC-Ce6) is developed as a tumor-penetrating and oxygen-enriching nanoplatform, which consists of chlorin e6 (Ce6) and perfluorocarbons (PFCs) co-loaded into fluorinated micelles to relieve hypoxia conditions as well as folate as targeting ligand that facilitates the selective biodistribution within tumor solids. The incorporation of fluorinated copolymers into mixed micelles exhibits not only a great increase in the oxygen-loading capacity, but also improves the stability of liquid PFCs emulsion within micelles without leakage. M60@PFC-Ce6 shows excellent oxygen delivery capability, good intracellular reactive oxygen species (ROS) generation, and superior phototoxicity in vitro for both 2D monolayer of cells and 3D multicellular spheroid model. These results indicate the enriched oxygen delivery and increased cellular uptake resulting from folate-targeted ability to enhance ROS production and PDT efficacy. The penetration study of M60@PFC-Ce6 into a 3D spheroid confirms that small micellar size and folate-conjugation are beneficial for micelles to penetrate and accumulate within spheroids. Thus, a new nanoplatform with enriched oxygen-carrying amounts, better drug penetration, and stable micellar properties that relieve tumor hypoxia and improve PDT efficacy is provided.

Nuclear PARP1-Targeted Photosensitizer as a Dual-Mode DNA-Damaging Agent and Immune Activator for Tumor Ablation

Photodynamic therapy is a promising cancer therapeutic method that can damage DNA via photoinduced reactive oxygen species production. However, tumor cells can initiate DNA repair pathways to resist oxidative damage. In this study, a nuclear-targeted photosensitizer PARP-PS with a poly (ADP-ribose) polymerase 1 (PARP1) inhibitory effect is developed based on the reported PARP1 inhibitor, rucaparib. As a dual-mode DNA-damaging agent, PARP-PS damages DNA upon photoirradiation and enhances oxidative DNA damage by blocking the DNA repair pathway via PARP1 inhibition and degradation. Both in vitro and in vivo investigations demonstrate that PARP-PS exhibits high antitumor activity with few side effects in breast cancer. In addition, PARP-PS can act as an immunogenic cell death inducer to activate immune responses characterized by the promotion of cytotoxic T lymphocyte activation and tumor infiltration. Therefore, PARP-PS is a potential multimodal antitumor agent with synergistic phototherapeutic, chemotherapeutic, and immunotherapeutic effects.

Multifunctional Nanoplatform for NIR-II Imaging-Guided Synergistic Oncotherapy

Tumors are a major public health issue of concern to humans, seriously threatening the safety of people's lives and property. With the increasing demand for early and accurate diagnosis and efficient treatment of tumors, noninvasive optical imaging (including fluorescence imaging and photoacoustic imaging) and tumor synergistic therapies (phototherapy synergistic with chemotherapy, phototherapy synergistic with immunotherapy, etc.) have received increasing attention. In particular, light in the near-infrared second region (NIR-II) has triggered great research interest due to its penetration depth, minimal tissue autofluorescence, and reduced tissue absorption and scattering. Nanomaterials with many advantages, such as high brightness, great photostability, tunable photophysical properties, and excellent biosafety offer unlimited possibilities and are being investigated for NIR-II tumor imaging-guided synergistic oncotherapy. In recent years, many researchers have tried various approaches to investigate nanomaterials, including gold nanomaterials, two-dimensional materials, metal sulfide oxides, polymers, carbon nanomaterials, NIR-II dyes, and other nanomaterials for tumor diagnostic and therapeutic integrated nanoplatform construction. In this paper, the application of multifunctional nanomaterials in tumor NIR-II imaging and collaborative therapy in the past three years is briefly reviewed, and the current research status is summarized and prospected, with a view to contributing to future tumor therapy.

Valkyrie Probes: A Novel Class of Enzyme-Activatable Photosensitizers based on Sulfur- and Seleno-Rosamines with Pyridinium Unit

The rational design of activatable photosensitizers (aPSs) uncaged by specific disease biomarkers is currently booming due to their positive attributes to achieve targeted photodynamic therapy (PDT). In this context, we present here the synthesis and detailed photophysical characterization of a novel class of hetero-rosamine dyes bearing sulfur or selenium as bridging heavy atom and 4-pyridyl meso-substituent as optically tunable group. The main feature of such photoactive platforms is the spectacular change of their spectral properties depending on the caging/decaging status of their 4-pyridyl moiety (cationic pyridinium vs. neutral pyridine). The preparation of two alkaline phosphatase (ALP)-responsive probes (named Valkyrie probes) was achieved through formal N-quaternarization with 4-phosphoryloxybenzyl, the traditional recognition moiety for this important diagnostic enzyme. Bio-analytical validations including fluorescence/singlet oxygen phosphorescence enzyme assays and RP-HPLC-fluorescence/-MS analyses have enabled us to demonstrate the viability and effectiveness of this novel photosensitizer activation strategy. Since sulfur-containing Valkyrie probe also retains high fluorogenicity in the orange-red spectral range, this study highlights meso-pyridyl-substituted S-pyronin scaffolds as valuable candidates for the rapid construction of molecular phototheranostic platforms suitable for combined fluorescence diagnosis and PDT.

Advancing glioblastoma imaging: Exploring the potential of organic fluorophore-based red emissive carbon dots

Over time, the interest in developing stable photosensitizers (PS) which both absorb and emit light in the red region (650 and 950 nm) has gained noticeable interest. Recently, carbon dots (CDs) have become the material of focus to act as a PS due to their high extinction coefficient, low cytotoxicity, and both high photo and thermal stability. In this work, a Federal and Drug Association (FDA) approved Near Infra-Red (NIR) organic fluorophore used for photo-imaging, indocyanine green (ICG), has been explored as a precursor to develop water-soluble red emissive CDs which possess red emission at 697 nm. Furthermore, our material was found to yield favorable red-imaging capabilities of glioblastoma stem-like cells (GSCs) meanwhile boasting low toxicity. Additionally with post modifications, our CDs have been found to have selectivity towards tumors over healthy tissue as well as crossing the blood-brain barrier (BBB) in zebrafish models.

Glycolysis inhibition for synergistic phototherapy of triple-negative breast cancer

Phototherapy is a local and precise therapeutic technique for tumor treatment. However, the therapeutic effects of photothermal and photodynamic therapies are inevitably encountered by hypoxia of the tumor microenvironment and heat shock protein induced by hyperthermia, respectively. Herein, we found that mannose, a glucose analog, could reverse tumor hypoxia by inhibiting glycolysis of cancer cells and suppressing the expression of heat shock protein through inhibiting cellular adenosine triphosphate (ATP) generation. Next, we used lipid nanoparticles simultaneously loaded with indocyanine green (ICG) and mannose molecules, named imLipo, for tumor therapy. Both in vitro and in vivo experiments evidenced that the imLipo nanoplatform has significant therapeutic efficacy through synergistic phototherapy under single near-infrared laser irradiation. This work shows that glycolysis inhibition can overcome the challenges of phototherapy. In addition, all three parts (mannose, ICG, and lipid) of imLipo are clinically approved and our designed nanoplatforms have great potential for future tumor treatment.

Bioorthogonal chemistry for prodrug activation in vivo

Prodrugs have emerged as a major strategy for addressing clinical challenges by improving drug pharmacokinetics, reducing toxicity, and enhancing treatment efficacy. The emergence of new bioorthogonal chemistry has greatly facilitated the development of prodrug strategies, enabling their activation through chemical and physical stimuli. This "on-demand" activation using bioorthogonal chemistry has revolutionized the research and development of prodrugs. Consequently, prodrug activation has garnered significant attention and emerged as an exciting field of translational research. This review summarizes the latest advancements in prodrug activation by utilizing bioorthogonal chemistry and mainly focuses on the activation of small-molecule prodrugs and antibody-drug conjugates. In addition, this review also discusses the opportunities and challenges of translating these advancements into clinical practice.

Carbon network-hosted porphyrin as a highly biocompatible nanophotosensitizer for enhanced photodynamic therapy

Photodynamic therapy (PDT) has the characteristics of being simple and non-invasive, and with on-demand light control. However, most photosensitizers exhibit strong hydrophobicity, low quantum yields in water and low tumor selectivity. In this study, carbon network-hosted porphyrins (CPs) with high biocompatibility and efficient singlet oxygen (1O2) generation were developed to reduce the biotoxicity of photosensitizers and avoid quenching caused by hydrophobic aggregation for enhanced PDT. The CPs were prepared by a simple solid-phase synthesis method using porphyrin, green non-toxic citric acid and urea as the raw materials. The CPs exhibited excellent water solubility and high biocompatibility. Even when the concentration reached 1.5 mg mL-1, cells still had good biological activity. By separately fixing the porphyrins in the carbon network, the CPs avoided aggregation-induced inactivation and had high generation efficiency of 1O2. Furthermore, in order to improve the PDT effect, the CPs were modified with the upper nuclear targeting peptide TAT (T-CPs), which was used to target the nucleus and generate 1O2in situ to directly destroy genetic material. The proposed strategy provides a simple and green path to prepare nanophotosensitizers with high biocompatibility and efficient 1O2 generation for PDT.

Ru(II)-Cyanine Complexes as Promising Photodynamic Photosensitizers for the Treatment of Hypoxic Tumours with Highly Penetrating 770 nm Near-Infrared Light

Light-activated treatments, such as photodynamic therapy (PDT), provide temporal and spatial control over a specific cytotoxic response by exploiting toxicity differences between irradiated and dark conditions. In this work, a novel strategy for developing near infrared (NIR)-activatable Ru(II) polypyridyl-based photosensitizers (PSs) was successfully developed through the incorporation of symmetric heptamethine cyanine dyes in the metal complex via a phenanthrimidazole ligand. Owing to their strong absorption in the NIR region, the PSs could be efficiently photoactivated with highly penetrating NIR light (770 nm), leading to high photocytotoxicities towards several cancer cell lines under both normoxic and hypoxic conditions. Notably, our lead PS (Ru-Cyn-1), which accumulated in the mitochondria, exhibited a good photocytotoxic activity under challenging low-oxygen concentration (2 % O2 ) upon NIR light irradiation conditions (770 nm), owing to a combination of type I and II PDT mechanisms. The fact that the PS Protoporphyrin IX (PpIX), the metabolite of the clinically approved 5-ALA PS, was found inactive under the same challenging conditions positions Ru-Cyn-1 complex as a promising PDT agent for the treatment of deep-seated hypoxic tumours.

A Photochemical Study of Photo-Induced Electron Transfer from DNAs to a Cationic Phthalocyanine Derivative

Water-soluble cationic gallium(III)-Pc complex (GaPc) is capable of photogenerating ROSs but does not exhibit photocytotoxicity in vivo. GaPc binds selectively, through a π-π stacking interaction, to the 5'-terminal G-quartet of a G-quadruplex DNA. The photo-excited state of GaPc of the complex is effectively quenched through electron transfer (ET) from the ground state of DNA guanine (G) bases to the photo-excited state of GaPc (ET(G-GaPc)). Hence the loss of the photocytotoxicity of GaPc in vivo is most likely to be due to the effective quenching of its photo-excited state through ET(G-GaPc). In this study, we investigated the photochemical properties of GaPc in the presence of duplex DNAs formed from a series of sequences to elucidate the nature of ET(G-GaPc). We found that ET(G-GaPc) is allowed in electrostatic complexes between GaPc and G-containing duplex DNAs and that the rate of ET(G-GaPc) (kET(G-GaPc)) can be reasonably interpreted in terms of the distance between Pc moiety of GaPc and DNA G base in the complex. We also found that the quantum yields of singlet oxygen (1O2) generation (ΦΔs) determined for the GaPc-duplex DNA complexes were similar to the value reported for free GaPc (Fujishiro R, Sonoyama H, Ide Y, et al (2019) J Inorg Biochem 192:7-16), indicating that ET(G-GaPc) in the complex is rather limited. These results clearly demonstrated that photocytotoxicity of GaPc is crucially affected by ET(G-GaPc). Thus elucidation of interaction of a photosensitizer with biomolecules, i.e., an initial process in PDT, would be helpful to understand its subsequent photochemical processes.

Prolonging Treatment Window of Photodynamic Therapy with Self-Amplified H2 O2 -Activated Photodynamic/Chemo Combination Therapeutic Nanomedicines

Photodynamic therapy (PDT) is a promising approach to cancer therapy. However, the relatively short tumor retention time of photosensitizers (PSs) makes it difficult to catch the optimal treatment time and restricts multiple PDT within a single injection. In this study, a tumor-specific phototheranostic nanomedicine (DPPa NP) is developed for photodynamic/chemo combination therapy with a prolonged PDT treatment window. DPPa NP is prepared via encapsulating a hydrophobic oxidized bovine serum albumin (BSA-SOH)-conjugatable PS DPPa with amphiphilic H2 O2 -activatable chlorambucil (CL) prodrug mPEG-TK-CL. The released CL under H2 O2 treatment can not only kill tumor cells but also upregulate reactive oxygen species levels within tumor cells, leading to the almost full release of cargoes. The released DPPa may conjugate with overexpressed BSA-SOH, which results in the recovery of the fluorescence signal and photodynamic effect. More importantly, such conjugation transfers DPPa from a small molecule PS into a macromolecular PS with a long tumor retention time and treatment window of PDT, which enables multiple PDT. This study thus provides an effective strategy to prolong the treatment window of PDT and enables tumor-specific fluorescence imaging-guided combination therapy.

Dextran-based micelles for combinational chemo-photodynamic therapy of tumors via in vivo chemiluminescence

Natural polysaccharides, represented by dextran, chitosan, and hyaluronic acid, are widely approved for use as pharmaceutical excipients and are important carrier materials for the design of advanced drug delivery systems, particularly in the field of anticancer drug delivery. The combination of stimuli-activable prodrug based chemotherapy and photodynamic therapy (PDT) has attracted increasing attention. Recent studies have verified the effectiveness of this strategy in the treatment of multiple aggressive cancers. However, in such combination, the stimuli-responsive chemotherapy and PDT have their own problems that need to be overcome. The uneven distribution of endogenous stimuli within tumor tissues makes it difficult for prodrug to be completely activated. And the inadequate tissue penetration depth of external light results in low efficiency of PDT. Aiming at these two bottlenecks, we designed a biocompatible dextran based - multi-component nanomedicine (PCL-NPs) that integrate a chemiluminescence agent luminol, a photosensitizer chlorine e6 (Ce6), and a reactive oxygen species (ROS)-activable thioketal-based paclitaxel (PTX) prodrug. The presence of overexpressed hydrogen peroxide (H2O2) inside tumor oxidizes the luminol moiety to generate in-situ light for PDT through chemiluminescence resonance energy transfer (CRET). The singlet oxygen (1O2) produced in this process not only directly kills tumor cells but also amplifies oxidative stress to accelerate the activation of PTX prodrug. We propose that the PCL-NPs have great therapeutic potential by simultaneously enhancing chemotherapy and PDT in a combination therapy.

Copper-Bacteriochlorin Nanosheet as a Specific Pyroptosis Inducer for Robust Tumor Immunotherapy

Pyroptosis is increasingly considered a new weathervane in cancer immune therapy. However, triggering specific pyroptotic tumor cell death while preserving normal cells still remains a major challenge. Herein, a brand-new pyroptosis inducer, copper-bacteriochlorin nanosheet (Cu-TBB), is designed. The synthesized Cu-TBB can be activated to an "on" state in the tumor microenvironment with glutathione (GSH) overexpression, leading to the release of Cu+ and TBB, respectively. Intriguingly, the released Cu+ can drive cascade reactions to produce O2 -• and highly toxic ·OH in cells. Additionally, the released TBB can also generate O2 -• and 1 O2 upon 750 nm laser irradiation. Encouragingly, both Cu+ -driven cascade reactions and photodynamic therapy pathways result in potent pyroptosis along with dendritic cell maturation and T cell priming, thus simultaneously eliminating the primary tumors and inhibiting the distant tumor growth and metastases. Conclusively, the well-designed Cu-TBB nanosheet is shown to trigger specific pyroptosis in vitro and in vivo, leading to enhanced tumor immunogenicity and antitumor efficacy while minimizing systemic side effects.

Synchronized activating therapeutic nano-agent: Enhancement and tracing for hypoxia-induced chemotherapy

Prodrug is a potential regime to overcome serious adverse events and off-target effects of chemotherapy agents. Among various prodrug activators, hypoxia stands out owing to the generalizability and prominence in tumor micro-environment. However, existing hypoxia activating prodrugs generally face the limitations of stringent structural requirements, the lack of feedback and the singularity of therapeutic modality, which is imputed to the traditional paradigm that recognition groups must be located at the terminus of prodrugs. Herein, a multifunctional nano-prodrug Mal@Cy-NTR-CB has been designed. In this nano-prodrug, a self-destructive tether is introduced to break the mindset, and achieves the activation by hypoxia of chemotherapy based on Chlorambucil (CB), whose efficacy can be augmented and traced by photodynamic therapy (PDT) and fluorescence from Cyanine dyes (Cy). In addition, Maleimide (Mal) carried by the nano-shells can regulate glutathione (GSH) content, preventing 1O2 scavenging, so as to realize PDT sensitization. Experiments demonstrate that Mal@Cy-NTR-CB specifically responds to hypoxic tumors, and achieve synchronous activation, enhancement and feedback of chemotherapy and PDT, inhibiting the tumor growth effectively. This study broadens the design ideas of activatable prodrugs and provides the possibility of multifunctional nano-prodrugs to improve the generalization and prognosis in precision oncology.

A biocompatible pure organic porous nanocage for enhanced photodynamic therapy

Porphyrin-based photosensitizers have been widely utilized in photodynamic therapy (PDT), but they suffer from deteriorating fluorescence and reactive oxygen species (ROS) due to their close π-π stacking. Herein, a biocompatible pure organic porphyrin nanocage (Py-Cage) with enhanced both type I and type II ROS generation is reported for PDT. The porphyrin skeleton within the Py-Cage is spatially separated by four biphenyls to avoid the close π-π stacking within the nanocage. The Py-Cage showed a large cavity and high porosity with a Brunauer-Emmett-Teller surface area of over 300 m2 g-1, facilitating a close contact between the Py-Cage and oxygen, as well as the fast release of ROS to the surrounding microenvironment. The Py-Cage shows superb ROS generation performance over its precursors and commercial ones such as Chlorin E6 and Rose Bengal. Intriguingly, the cationic π-conjugated Py-Cage also shows promising type I ROS (superoxide and hydroxyl radicals) generation that is more promising for hypoxic tumor treatment. Both in vitro cell and in vivo animal experiments further confirm the excellent antitumor activity of the Py-Cage. As compared to conventional metal coordination approaches to improve PDT efficacy of porphyrin derivatives, the pure organic porous Py-Cage demonstrates excellent biocompatibility, which is further verified in both mice and rats. This work of an organic porous nanocage shall provide a new paradigm for the design of novel, biocompatible and effective photosensitizers for PDT.

Local monitoring of photosensitizer transient states provides feedback for enhanced efficiency and targeting selectivity in photodynamic therapy

Photodynamic therapy (PDT) fundamentally relies on local generation of PDT precursor states in added photosensitizers (PS), particularly triplet and photo-radical states. Monitoring these states in situ can provide important feedback but is difficult in practice. The states are strongly influenced by local oxygenation, pH and redox conditions, often varying significantly at PDT treatment sites. To overcome this problem, we followed local PDT precursor state populations of PS compounds, via their fluorescence intensity response to systematically varied excitation light modulation. Thereby, we could demonstrate local monitoring of PDT precursor states of methylene blue (MB) and IRdye700DX (IR700), and determined their transitions rates under different oxygenation, pH and redox conditions. By fiber-optics, using one fiber for both excitation and fluorescence detection, the triplet and photo-radical state kinetics of locally applied MB and IR700 could then be monitored in a tissue sample. Finally, potassium iodide and ascorbate were added as possible PDT adjuvants, enhancing intersystem crossing and photoreduction, respectively, and their effects on the PDT precursor states of MB and IR700 could be locally monitored. Taken together, the presented procedure overcomes current methodological limitations and can offer feedback, guiding both excitation and PDT adjuvant application, and thereby more efficient and targeted PDT treatments.

Integrating Pillar[5]arene and BODIPY for a Supramolecular Nanoplatform To Achieve Synergistic Photodynamic Therapy and Chemotherapy

BODIPY photosensitizers have been integrated with a hypoxia-activated prodrug to achieve synergistic photodynamic therapy (PDT) and chemotherapy. A novel BODIPY derivative BDP-CN was designed and synthesized. It had two cyano groups to make it complex well with a water-soluble pillar[5]arene. Their association constant was calculated to be (6.8±0.9)×106  M-1 . After self-assembly in water, regular spherical nanocarriers can be formed; these were used to encapsulate the hypoxia-activated prodrug tirapazamine (TPZ). BDP-CN displayed excellent photodynamic activity to complete PDT. In this process, O2 can be continuously consumed to activate TPZ to allow it to be converted to a benzotriazinyl (BTZ) radical with high cytotoxicity to complete chemotherapy. As a result, the formed nanoparticles showed excellent synergistic photodynamic therapy and chemotherapy efficacy. The synergistic therapy mechanism is discussed in detail.

A "Chase and Block" Strategy for Enhanced Cancer Therapy with Hypoxia-Promoted Photodynamic Therapy and Autophagy Inhibition Based on Upconversion Nanocomposites

The combination of hypoxia-promoted photodynamic therapy (PDT) and autophagy modulation has shown strong potential in the treatment of hypoxic tumors. Here, a novel design is put forward for synergistic PDT and autophagy inhibition to amplify the effect of cancer therapy by a "chase and block" strategy. Specifically, the organic photosensitive molecule (denoted FL) is encapsulated in a hydrophobic layer between multi-band emitted upconversion nanoparticles (UCNPs) and the amphiphilic polymer DSPE-PEG-COOH, allowing FL to fully exploit the luminescence spectrum of UCNPs under near-infrared (NIR) light irradiation. The FL is specifically activated by nitroreductase in the tumor microenvironment (TME), enabling hypoxia-promoted PDT and thus performing a "chase" strategy for cancer therapy. Additionally, the nanosystem is combined with an autophagy-inhibiting melittin pro-peptide (denoted as MEL), which could be triggered by the highly expressed legumain in tumor cells to inhibit the autophagy procedure by disrupting the lysosomal membrane, thus "blocking" the cancer cells from rescuing themselves and amplifying the killing effect of PDT. Both FL and MEL can be specifically activated by TME and the upconversion luminescence imaging of UCNPs offers a tracer function for the treatment. Therefore, UCNPs@FL-MEL might be an important reference for the design and development of future nanotherapeutic agents.

Exosome camouflaged coordination-assembled Iridium(III) photosensitizers for apoptosis-autophagy-ferroptosis induced combination therapy against melanoma

Melanoma represents the most fatal form of skin cancer due to its resistance mechanisms and high capacity for the development of metastases. Among other medicinal techniques, photodynamic therapy is receiving increasing attention. Despite promising results, the application of photodynamic therapy is inherently limited due to interference from melanin, poor tissue penetration of photosensitizers, low loading into drug delivery systems, and a lack of tumor selectivity. To overcome these limitations, herein, the coordination-driven assembly of Ir(III) complex photosensitizers with Fe(III) ions into nanopolymers for combined photodynamic therapy and chemodynamic therapy is reported. While remaining stable under physiological conditions, the nanopolymers dissociated in the tumor microenvironment. Upon exposure to light, the Ir(III) complexes produced singlet oxygen and superoxide anion radicals, inducing cell death by apoptosis and autophagy. The Fe(III) ions were reduced to Fe(II) upon depletion of glutathione and reduction of the GPX4 levels, triggering cell death by ferroptosis. To provide tumor selectivity, the nanopolymers were further camouflaged with exosomes. The generated nanoparticles were found to eradicate a melanoma tumor as well as inhibit the formation of metastases inside a mouse model.

Multifunctional nanoadjuvant-driven microenvironment modulation for enhanced photothermal immunotherapy in breast cancer

Intracellular redox imbalance, achieved by exploiting the tumor microenvironment (TME), has emerged as a promising strategy for cancer therapy. In this study, we developed a multifunctional nanoadjuvant, termed GITFe/Z-HA, by modified a metal-organic backbone Fe/ZIF-8 with hyaluronic acid (HA) targeting. The nanocarriers were loaded with glucose oxidase (Gox), neoindocyanine green (IR820) and tilazamine (TPZ). This design aimed to achieve a cascade reaction within tumor cells, mediated by Gox, Fe3+, and IR820, which consumes intrinsic glucose and oxygen, leading to an elevated production of reactive oxygen species (ROS). This cascade reaction creates a hypoxic environment conducive for TPZ to exert its therapeutic action. Consequently, the combination of photothermal therapy (PTT), photodynamic therapy (PDT), and chemotherapy demonstrates a good synergistic effect. Moreover, the imbalanced ROS/glutathione (GSH) induced by this treatment approach, along with PTT, promote immunogenic cell death (ICD). This ICD triggers the release of damage-related molecular patterns and CD8+ lymphocyte infiltration sensitizes the immune checkpoint blockade (αPD-L1) response, thereby eliciting a systemic anti-tumor immune response. Collectively, this comprehensive treatment regimen, driven by environmentally stimulated multiple pathways, overcomes the limitations of single therapeutic modalities, thereby improving tumor outcomes. Additionally, these findings provide valuable insights for strategies aimed at modulating the tumor immune microenvironment.

Dual-Pronged Attack: pH-Driven Membrane-Anchored NIR Dual-Type Nano-Photosensitizer Excites Immunogenic Pyroptosis and Sequester Immune Checkpoint for Enhanced Prostate Cancer Photo-Immunotherapy

Prostate cancer (PCa) is a frustrating immunogenic "cold" tumor and generally receives unsatisfied immunotherapy outcomes in the clinic. Pyroptosis is an excellent immunogenic cell death form that can effectively activate the antitumor immune response, promote cytotoxic T-lymphocyte infiltration, and convert tumors from "cold" to "hot." However, the in vivo application of pyroptosis drugs is seriously limited, and the upregulation of tumor PD-L1 caused by photo-immunotherapy further promotes immune escape. Herein, a new nano-photosensitizer (YBS-BMS NPs-RKC) with pH-response integrating immunogenic pyroptosis induction and immune checkpoint blockade is developed. The pH-responsive polymer equipped with the cell membrane anchoring peptide RKC is used as the carrier and further encapsulated with the near-infrared-activated semiconductor polymer photosensitizer YBS and a PD-1/PD-L1 complex small molecule inhibitor BMS-202. The pH-driven membrane-anchoring and pyroptosis activation of YBS-BMS NPs-RKC is clearly demonstrated. In vitro and in vivo studies have shown that this dual-pronged therapy stimulates a powerful antitumor immune response to suppress primary tumor progression and evokes long-term immune memory to inhibit tumor relapse and metastasis. This work provides an effective self-synergistic platform for PCa immunotherapy and a new idea for developing more biocompatible photo-controlled pyroptosis inducers.

Discovery of a photosensitizing PI3K inhibitor for tumor therapy: Design, synthesis and in vitro biological evaluation

In drug development, optical triggering of cancer therapy is increasingly used. Herein, we report a novel photosensitive PI3K inhibitor FD2157, which bears a photoprotecting moiety and can be efficiently cleaved with enhanced anticancer activity upon short-term light irradiation. In biological assessment, FD2157 exhibited remarkably enhanced anticancer activity in inhibition of PI3K pathway against melanoma cell lines upon light irradiation (4 min). Hence, this photosensitive PI3K inhibitor FD2157 may represent a valuable tool compound for studying the PI3K pathway and further optimization toward light-triggered cancer treatment.

Silica-Based Platform Decorated with Conjugated Polymer Dots and Prussian Blue for Improved Photodynamic Cancer Therapy

To advance cancer treatment, we have developed a novel composite material consisting of conjugated polymer dots (CPDs) and Prussian blue (PB) particles, which were immobilized on, and encapsulated within, silica particles, respectively. The CPDs functioned as both a photosensitizer and a photodynamic agent, and the PB acted as a photothermal agent. The silica platform provided a biocompatible matrix that brought the two components into close proximity. Under laser irradiation, the fluorescence from the CPDs in the composite material enabled cell imaging and was subsequently converted to thermal energy by PB. This efficient energy transfer was accomplished because of the spectral overlap between the emission of donor CPDs and the absorbance of acceptor PB. The increase in local temperature in the cells resulted in a significant increase in the amount of reactive oxygen species (ROS) generated by CPDs, in which their independent use did not produce sufficient ROS for cancer cell treatment. To assess the impact of the enhanced ROS generation by the composite material, we conducted experiments using cancer cells under 532 nm laser irradiation. The results showed that with the increase in local temperature, the generated ROS increased by 30% compared with the control, which did not contain PB. When the silica-based composite material was positioned at the periphery of the tumor for 120 h, it led to a much slower tumor growth than other materials tested. By using a CPD-based photodynamic therapy platform, a new simplified approach to designing and preparing cancer treatments could be achieved, which included photothermal PB-assisted enhanced ROS generation using a single laser. This advancement opens up an exciting new opportunity for effective cancer treatment.

Radio- and Photosensitizing Os(II)-Based Nanocage for Combined Radio-/Chemo-/X-ray-Induced Photodynamic Therapies, NIR Imaging, and Drug Delivery

Integration of clinical imaging and collaborative multimodal therapies into a single nanomaterial for multipurpose diagnosis and treatment is of great interest to theranostic nanomedicine. Here, we report a rational design of a discrete Os-based metal-organic nanocage Pd6(OsL3)828+ (MOC-43) as a versatile theranostic nanoplatform to meet the following demands simultaneously: (1) synergistic treatments of radio-, chemo-, and X-ray-induced photodynamic therapies (X-PDT) for breast cancer, (2) NIR imaging for cancer cell tracking and tumor-targeting, and (3) anticancer drug transport through a host-guest strategy. The nanoscale MOC-43 incorporates high-Z Os-element to interact with X-ray irradiation for dual radiosensitization and photosensitization, showing efficient energy transfer to endogenous oxygen in cancer cells to enhance X-PDT efficacy. It also features intrinsic NIR emission originating from metal-to-ligand charge transfer (MLCT) as an excellent imaging probe. Meanwhile, its 12 pockets can capture and concentrate low-water-soluble molecules for anticancer drug delivery. These multifunctions are implemented and demonstrated by micellization of coumarin-loaded cages with DSPE-PEG2000 into coumarin ⊂ MOC-43 nanoparticles (CMNPs) for efficient subcellular endocytosis and uptake. The cancer treatments in vitro/in vivo show promising antitumor performance, providing a conceptual protocol to combine cage-cargo drug transport with diagnosis and treatment for collaborative cancer theranostics by virtue of multifunction synergism on a single-nanomaterial platform.

Increasing the Selectivity of Light-Active Antimicrobial Agents - Or How To Get a Photosensitizer to the Desired Target

Photosensitizers combine the inherent reactivity of reactive oxygen species with the sophisticated reaction control of light. Through selective targeting, these light-active molecules have the potential to overcome certain limitations in drug discovery. Ongoing advances in the synthesis and evaluation of photosensitizer conjugates with biomolecules such as antibodies, peptides, or small-molecule drugs are leading to increasingly powerful agents for the eradication of a growing number of microbial species. This review article, therefore, summarizes challenges and opportunities in the development of selective photosensitizers and their conjugates described in recent literature. This provides adequate insight for newcomers and those interested in this field.

Beyond traditional light: NIR-II light-activated photosensitizers for cancer therapy

With increasing demand for the accurate and safe treatment of cancer, non-invasive photodynamic therapy (PDT) has received widespread attention. However, most conventional photosensitizers are typically excited by short-wavelength visible light (400-700 nm), thus substantially hindering the penetration of light and the therapeutic effectiveness of the PDT procedure. Fortunately, near-infrared (NIR) light (>700 nm), in particular, light in the second near-infrared region (NIR-II, 1000-1700 nm) has a higher upper radiation limit, greater tissue tolerance, and deeper tissue penetration compared with traditional short-wavelength light excitation, and shows considerable potential in the clinical treatment of cancer. Therefore, it is of paramount importance and clinical value to develop photosensitizers that are excited by NIR-II light. In this review, for the first time we focus completely on recent progress made with various NIR-II photosensitizers for cancer treatment via PDT, and we briefly present the ongoing challenges and prospects of currently developed NIR-II photosensitizers for clinical practice in the near future. We believe that the above topics will inspire broad interest in researchers from interdisciplinary fields that include chemistry, materials science, pharmaceuticals, and clinical medicine, and provide insightful perspectives for exploiting new NIR-II photosensitizers for biomedical applications.

Bifunctional Cascading Nanozymes Based on Carbon Dots Promotes Photodynamic Therapy by Regulating Hypoxia and Glycolysis

Photodynamic therapy (PDT) still faces great challenges with suitable photosensitizers, oxygen supply, and reactive oxygen species (ROS) accumulation, especially in the tumor microenvironment, feathering hypoxia, and high glucose metabolism. Herein, a carbon dots (CDs)-based bifunctional nanosystem (MnZ@Au), acting as photosensitizer and nanozyme with cascading glucose oxidase (GOx)- and catalase (CAT)-like reactivity, was developed for improving hypoxia and regulating glucose metabolism to enhance PDT. The MnZ@Au was constructed using Mn-doped CDs (Mn-CDs) as a core and zeolitic imidazolate framework-8 (ZIF-8) as a shell to form a hybrid (MnZ), followed by anchoring ultrasmall Au nanoparticles (AuNPs) onto the surface of MnZ through the ion exchange and in situ reduction methods. MnZ@Au catalyzed glucose consumption and oxygen generation by cascading GOx- and CAT-like nanozyme reactions, which was further enhanced by its own photothermal properties. In vitro and in vivo studies also confirmed that MnZ@Au greatly improved CDs penetration, promoted ROS accumulation, and enhanced PDT efficacy, leading to efficient tumor growth inhibition in the breast tumor model. Besides, MnZ@Au enabled photoacoustic (PA) imaging to provide a mapping of Mn-CDs distribution and oxygen saturation, showing the real-time catalytic process of MnZ@Au in vivo. 18F-Fluorodeoxyglucose positron emission tomography (18F-FDG PET) imaging also validated the decreased glucose uptake in tumors treated by MnZ@Au. Therefore, the integrated design provided a promising strategy to utilize and regulate the tumor microenvironment, promote penetration, enhance PDT, and finally prevent tumor deterioration.

A Cascade Strategy Boosting Hydroxyl Radical Generation with Aggregation-Induced Emission Photosensitizers-Albumin Complex for Photodynamic Therapy

Effective photodynamic therapy (PDT) requires photosensitizers (PSs) to massively generate type I reactive oxygen species (ROS) in a less oxygen-dependent manner in the hypoxia tumor microenvironment. Herein, we present a cascade strategy to boost type I ROS, especially hydroxyl radical (OH·-), generation with an aggregation-induced emission (AIE) photosensitizer-albumin complex for hypoxia-tolerant PDT. The cationic AIE PS TPAQ-Py-PF6 (TPA = triphenylamine, Q = anthraquinone, Py = pyridine) contains three important moieties to cooperatively enhance free radical generation: the AIE-active TPA unit ensures the effective triplet exciton generation in aggregate, the anthraquinone moiety possesses the redox cycling ability to promote electron transfer, while the cationic methylpyridinium cation further increases intramolecular charge transfer and electron separation processes. Inserting the cationic TPAQ-Py-PF6 into the hydrophobic domain of bovine serum albumin nanoparticles (BSA NPs) could greatly immobilize its molecular geometry to further increase triplet exciton generation, while the electron-rich microenvironment of BSA ultimately leads to OH·- generation. Both experimental and theoretical results confirm the effectiveness of our molecular cationization and BSA immobilization cascade strategy for enhancing OH·- generation. In vitro and in vivo experiments validate the excellent antitumor PDT performance of BSA NPs, superior to the conventional polymeric encapsulation approach. Such a multidimensional cascade strategy for specially boosting OH·- generation shall hold great potential in hypoxia-tolerant PDT and related antitumor applications.

A Targeting Singlet Oxygen Battery for Multidrug-Resistant Bacterial Deep-Tissue Infections

Traditional photodynamic therapy (PDT) is dependent on externally applied light and oxygen, and the depth of penetration of these factors can be insufficient for the treatment of deep infections. The short half-life and short diffusion distance of reactive oxygen species (ROS) also limit the antibacterial efficiency of PDT. Herein, we designed a targeting singlet oxygen delivery system, CARG-Py, for irradiation-free and oxygen-free PDT. This system was converted to the "singlet oxygen battery" CARG-1 O2 and released singlet oxygen without external irradiation or oxygen. CARG-1 O2 is composed of pyridones coupled to a targeting peptide that improves the utilization of singlet oxygen in deep multidrug-resistant bacterial infections. CARG-1 O2 was shown to damage DNA, protein, and membranes by increasing the level of reactive oxygen inside bacteria; the attacking of multiple biomolecular sites caused the death of methicillin-resistant Staphylococcus aureus (MRSA). An in vivo study in a MRSA-infected mouse model of pneumonia demonstrated the potential of CARG-1 O2 for the efficient treatment of deep infections. This work provides a new strategy to improve traditional PDT for irradiation- and oxygen-free treatment of deep infections while improving convenience of PDT.

Aggregation-induced type I&II photosensitivity and photodegradability-based molecular backbones for synergistic antibacterial and cancer phototherapy via photodynamic and photothermal therapies

The clinical applications of phototherapy nanomaterials are still limited due to concerns regarding their phototoxicity and efficacy. Herein, we report a novel type of D-π-A molecular backbone that induces type I/II photosensitivity and photodegradability by forming J-aggregates. The photodegradation rate can be regulated by changing the donor groups to regulate the photosensitivity of their aggregates because the photodegradability performance results from their oxidation by 1O2 generated by their type II photosensitivity. AID4 NPs possess faster photodegradation because of their better type I&II photosensitivity, which can also self-regulate by inhibiting type II and improving type I under hypoxic conditions. Moreover, they exhibited good photothermal and photoacoustic performance for improving their therapeutic effect by a synergistic effect and achieving photoacoustic imaging in vivo. The experimental result also showed that they can be effective for antibacterial and anti-tumor treatment and the photodegradation products of AID4 NPs possess low biological toxicity in the dark or under light. This study could provide a novel strategy for improving the safety and treatment effects of phototherapy.

Hyperbranched Polymers: Recent Advances in Photodynamic Therapy against Cancer

Hyperbranched polymers are a class of three-dimensional dendritic polymers with highly branched architectures. Their unique structural features endow them with promising physical and chemical properties, such as abundant surface functional groups, intramolecular cavities, and low viscosity. Therefore, hyperbranched-polymer-constructed cargo delivery carriers have drawn increasing interest and are being utilized in many biomedical applications. When applied for photodynamic therapy, photosensitizers are encapsulated in or covalently incorporated into hyperbranched polymers to improve their solubility, stability, and targeting efficiency and promote the therapeutic efficacy. This review will focus on the state-of-the-art studies concerning recent progress in hyperbranched-polymer-fabricated phototherapeutic nanomaterials with emphases on the building-block structures, synthetic strategies, and their combination with the codelivered diagnostics and synergistic therapeutics. We expect to bring our demonstration to the field to increase the understanding of the structure-property relationships and promote the further development of advanced photodynamic-therapy nanosystems.

High quantum efficiency ruthenium coordination complex photosensitizer for improved radiation-activated Photodynamic Therapy

Traditional external light-based Photodynamic Therapy (PDT)'s application is limited to the surface and minimal thickness tumors because of the inefficiency of light in penetrating deep-seated tumors. To address this, the emerging field of radiation-activated PDT (radioPDT) uses X-rays to trigger photosensitizer-containing nanoparticles (NPs). A key consideration in radioPDT is the energy transfer efficiency from X-rays to the photosensitizer for ultimately generating the phototoxic reactive oxygen species (ROS). In this study, we developed a new variant of pegylated poly-lactic-co-glycolic (PEG-PLGA) encapsulated nanoscintillators (NSCs) along with a new, highly efficient ruthenium-based photosensitizer (Ru/radioPDT). Characterization of this NP via transmission electron microscopy, dynamic light scattering, UV-Vis spectroscopy, and inductively coupled plasma mass-spectroscopy showed an NP size of 120 nm, polydispersity index (PDI) of less than 0.25, high NSCs loading efficiency over 90% and in vitro accumulation within the cytosolic structure of endoplasmic reticulum and lysosome. The therapeutic efficacy of Ru/radioPDT was determined using PC3 cell viability and clonogenic assays. Ru/radioPDT exhibited minimal cell toxicity until activated by radiation to induce significant cancer cell kill over radiation alone. Compared to protoporphyrin IX-mediated radioPDT (PPIX/radioPDT), Ru/radioPDT showed higher capacity for singlet oxygen generation, maintaining a comparable cytotoxic effect on PC3 cells.

Red emitting carbon dots: surface modifications and bioapplications

Quantum dots (QDs), and carbon quantum dots (CDs) in particular, have received significant attention for their special characteristics. These particles, on the scale of several nanometers, are often produced using simple and green methods, with naturally occurring organic precursors. In addition to facile production methods, CDs present advantageous applications in the field of medicine, primarily for bioimaging, antibacterial and therapeutics. Also, CDs present great potential for surface modification through methods like doping or material mixing during synthesis. However, the bulk of current literature focuses on CDs emitting in the blue wavelengths which are not very suitable for biological applications. Red emitting CDs are therefore of additional interest due to their brightness, photostability, novelty and deeper tissue penetration. In this review article, red CDs, their methods of production, and their biological applications for translational research are explored in depth, with emphasis on the effects of surface modifications and doping.

Highly Efficient Photosensitizers with Molecular Vibrational Torsion for Cancer Photodynamic Therapy

The development of highly effective photosensitizers (PSs) for photodynamic therapy remains a great challenge at present. Most PSs rely on the heavy-atom effect or the spin-orbit charge-transfer intersystem crossing (SOCT-ISC) effect to promote ISC, which brings about additional cytotoxicity, and the latter is susceptible to the interference of solvent environment. Herein, an immanent universal property named photoinduced molecular vibrational torsion (PVT)-enhanced spin-orbit coupling (PVT-SOC) in PSs has been first revealed. PVT is verified to be a widespread intrinsic property of quinoid cyanine (QCy) dyes that occurs on an extremely short time scale (10-10 s) and can be captured by transient spectra. The PVT property can provide reinforced SOC as the occurrence of ISC predicted by the El Sayed rules (1ππ*-3nπ*), which ensures efficient photosensitization ability for QCy dyes. Hence, QTCy7-Ac exhibited the highest singlet oxygen yield (13-fold higher than that of TCy7) and lossless fluorescence quantum yield (ΦF) under near-infrared (NIR) irradiation. The preeminent photochemical properties accompanied by high biosecurity enable it to effectively perform photoablation in solid tumors. The revelation of this property supplies a new route for constructing high-performance PSs for achieving enhanced cancer phototherapy.