Recent Advances in Activatable Organic Photosensitizers for Specific Photodynamic Therapy

Selective antibacterial and antibiofilm activity of chlorinated hemicyanine against gram-positive bacteria

Antibiotic-free therapies are highly needed due to the limited success of conventional approaches especially against biofilm related infections. In this direction, antimicrobial phototherapy, either in the form of antimicrobial photothermal therapy (aPTT) or antimicrobial photodynamic therapy (aPDT), have appeared to be highly promising candidates in recent years. These are local and promising approaches for antibiotic resistant bacterial infections and biofilms. Organic small photosensitizers (PSs) are extensively preferred in antimicrobial phototherapy applications as they offer a great opportunity to combine therapeutic action (aPTT, aPDT or both) with fluorescence imaging on a single molecule. In this study, the bactericidal effect of cationic chlorinated hemicyanine (Cl-Hem)-based type I PS, which can function as a dual aPDT/aPTT agent, was investigated on both planktonic cells and biofilms of different gram-positive (E. faecalis and S. epidermidis) and gram-negative bacteria (P. aeruginosa and K. pneumoniae) with and without 640 nm laser irradiation. Cl-Hem was shown to induce a selective phototheranostic activity against gram-positive bacteria (E. faecalis and S. epidermidis). Cl-Hem exhibited both dose and laser irradiation time dependent bactericidal effect on planktonic and biofilms of S. epidermidis. These results clearly showed that highly potent Cl-Hem can treat resistant microbial infections, while allowing fluorescence detection at the same time. High biofilm reduction observed with combined aPDT/aPTT action of Cl-Hem together with its non-cytotoxic nature points out that Cl-Hem is a promising PS for antibacterial and antibiofilm treatments.

Enzyme-Activatable Near-Infrared Hemicyanines as Modular Scaffolds for in vivo Photodynamic Therapy

Photodynamic therapy is an anti-cancer treatment that requires illumination of photosensitizers to induce local cell death. Current near-infrared organic photosensitizers are built from large and non-modular structures that cannot be tuned to improve safety and minimize off-target toxicity. This work describes a novel chemical platform to generate enzyme-activatable near-infrared photosensitizers. We optimized the Se-bridged hemicyanine scaffold to include caging groups and biocompatible moieties, and generated cathepsin-triggered photosensitizers for effective ablation of human glioblastoma cells. Furthermore, we demonstrated that enzyme-activatable Se-bridged hemicyanines are effective photosensitizers for the safe ablation of microtumors in vivo, creating new avenues in the chemical design of targeted anti-cancer photodynamic therapy agents.

A Novel Boron Dipyrromethene-Erlotinib Conjugate for Precise Photodynamic Therapy against Liver Cancer

Photodynamic Therapy (PDT) is recognized for its exceptional effectiveness as a promising cancer treatment method. However, it is noted that overexposure to the dosage and sunlight in traditional PDT can result in damage to healthy tissues, due to the low tumor selectivity of currently available photosensitizers (PSs). To address this challenge, we introduce herein a new strategy where the small molecule-targeted agent, erlotinib, is integrated into a boron dipyrromethene (BODIPY)-based PS to form conjugate 6 to enhance the precision of PDT. This conjugate demonstrates optical absorption, fluorescence emission, and singlet oxygen generation efficiency comparable to the reference compound 7, which lacks erlotinib. In vitro studies reveal that, after internalization, conjugate 6 predominantly accumulates in the lysosomes of HepG2 cells, exhibiting significant photocytotoxicity with an IC50 value of 3.01 µM. A distinct preference for HepG2 cells over HELF cells is observed with conjugate 6 but not with compound 7. In vivo experiments further confirm that conjugate 6 has a specific affinity for tumor tissues, and the combination treatment of conjugate 6 with laser illumination can effectively eradicate H22 tumors in mice with outstanding biosafety. This study presents a novel and potential PS for achieving precise PDT against cancer.

Chlorin e6-Conjugated Mesoporous Titania Nanorods as Potential Nanoplatform for Photo-Chemotherapy

Photodynamic therapy (PDT) has developed as an efficient strategy for cancer treatment. PDT involves the production of reactive oxygen species (ROS) by light irradiation after activating a photosensitizer (PS) in the presence of O2. PS-coupled nanomaterials offer additional advantages, as they can merge the effects of PDT with conventional enabling-combined photo-chemotherapeutics effects. In this work, mesoporous titania nanorods were surface-immobilized with Chlorin e6 (Ce6) conjugated through 3-(aminopropyl)-trimethoxysilane as a coupling agent. The mesoporous nanorods act as nano vehicles for doxorubicin delivery, and the Ce6 provides a visible light-responsive production of ROS to induce PDT. The nanomaterials were characterized by XRD, DRS, FTIR, TGA, N2 adsorption-desorption isotherms at 77 K, and TEM. The obtained materials were tested for their singlet oxygen and hydroxyl radical generation capacity using fluorescence assays. In vitro cell viability experiments with HeLa cells showed that the prepared materials are not cytotoxic in the dark, and that they exhibit photodynamic activity when irradiated with LED light (150 W m-2). Drug-loading experiments with doxorubicin (DOX) as a model chemotherapeutic drug showed that the nanostructures efficiently encapsulated DOX. The DOX-nanomaterial formulations show chemo-cytotoxic effects on Hela cells. Combined photo-chemotoxicity experiments show enhanced effects on HeLa cell viability, indicating that the conjugated nanorods are promising for use in combined therapy driven by LED light irradiation.

Enhancing Precision in Photodynamic Therapy: Innovations in Light-Driven and Bioorthogonal Activation

Over the past few decades, photodynamic therapy (PDT) has evolved as a minimally invasive treatment modality offering precise control over cancer and various other diseases. To address inherent challenges associated with PDT, researchers have been exploring two promising avenues: the development of intelligent photosensitizers activated through light-induced energy transfers, charges, or electron transfers, and the disruption of photosensitive bonds. Moreover, there is a growing emphasis on the bioorthogonal delivery or activation of photosensitizers within tumors, enabling targeted deployment and activation of these intelligent photosensitive systems in specific tissues, thus achieving highly precise PDT. This concise review highlights advancements made over the last decade in the realm of light-activated or bioorthogonal photosensitizers, comparing their efficacy and shaping future directions in the advancement of photodynamic therapy.

A Bioorthogonal Antidote Against the Photosensitivity after Photodynamic Therapy

As an effective and non-invasive treatment modality for cancer, photodynamic therapy (PDT) has attracted considerable interest. With the recent advances in the photosensitizing agents, the fiber-optic systems, and other aspects, its application is extended to a wide range of superficial and localized cancers. However, for the few clinically used photosensitizers, most of them suffer from the drawback of causing prolonged photosensitivity after the treatment. As a result, post-PDT management is also a crucial issue. Herein, a facile bioorthogonal approach is reported that can effectively suppress this common side effect of PDT in nude mice. It involves the use of an antidote that contains a black-hole quencher BHQ-3 conjugated with a bicyclo[6.1.0]non-4-yne (BCN) moiety and a tetrazine-substituted boron dipyrromethene-based photosensitizer. By using tumor-bearing nude mice as an animal model, it is demonstrated that after PDT with this photosensitizer, the administration of the antidote can effectively quench the photodynamic activity of the residual photosensitizer by bringing the BHQ-3 quencher close to the photosensitizing unit through a rapid click reaction. It results in substantial reduction in skin damage upon light irradiation. The overall results demonstrate that this simple and facile strategy can provide an effective means for minimizing the photosensitivity after PDT.

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.

Emergence of Lipid Droplets in the Mechanisms of Carcinogenesis and Therapeutic Responses

Cancer shares common risk factors with cardiovascular diseases such as dyslipidemia, obesity and inflammation. In both cases, dysregulations of lipid metabolism occur, and lipid vesicles emerge as important factors that can influence carcinogenesis. In this review, the role of different lipids known to be involved in cancer and its response to treatments is detailed. In particular, lipid droplets (LDs), initially described for their role in lipid storage, exert multiple functions, from the physiological prevention of LD coalescence and regulation of endoplasmic reticulum homeostasis to pathological involvement in tumor progression and aggressiveness. Analysis of LDs highlights the importance of phosphatidylcholine metabolism and the diversity of lipid synthesis enzymes. In many cancers, the phosphatidylcholine pathways are disrupted, modifying the expression of genes coding for metabolic enzymes. Tumor microenvironment conditions, such as hypoxia, different types of stress or inflammatory conditions, are also important determinants of LD behavior in cancer cells. Therefore, LDs represent therapeutic targets in cancer, and many lipid mediators have emerged as potential biomarkers for cancer onset, progression, and/or resistance.

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

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

A hypoxia-activatable theranostic agent with intrinsic endoplasmic reticulum affinity and type-I photosensitivity

A unique photosensitizer (PS), ERPS, with intrinsic endoplasmic reticulum (ER)-targeting ability and low oxygen-depletion type-I photosensitivity, is developed and used as a scaffold to construct an activatable theranostic agent for precise photodynamic therapy (PDT). The ER-targeted feature coupled with type-I photosensitivity endows ERPS with high phototoxicity toward tumor cells under both normoxic and hypoxic conditions. In addition, caging the phenol group of ERPS with a nitroreductase-sensitive triggering group provided a hypoxia-activatable PS (ERPSIm) that is encapsulated within a polymeric micelle to obtain a water-stable Im@NP nanoparticle for in vivo applications. After intravenous administration to 4T1 tumor-bearing BALB/c mice, Im@NP demonstrated highly efficient imaging-guided PDT ablation of implanted tumors. This is because the delivered ERPSIm cargos of Im@NP are specifically activated in the hypoxic microenvironment of solid tumor, and the activated ERPS molecules have efficient ER-targeted type-I photosensitivity.

Nanoparticles-based phototherapy systems for cancer treatment: Current status and clinical potential

Remarkable progress in phototherapy has been made in recent decades, due to its non-invasiveness and instant therapeutic efficacy. In addition, with the rapid development of nanoscience and nanotechnology, phototherapy systems based on nanoparticles or nanocomposites also evolved as an emerging hotspot in nanomedicine research, especially in cancer. In this review, first we briefly introduce the history of phototherapy, and the mechanisms of phototherapy in cancer treatment. Then, we summarize the representative development over the past three to five years in nanoparticle-based phototherapy and highlight the design of the innovative nanoparticles thereof. Finally, we discuss the feasibility and the potential of the nanoparticle-based phototherapy systems in clinical anticancer therapeutic applications, aiming to predict future research directions in this field. Our review is a tutorial work, aiming at providing useful insights to researchers in the field of nanotechnology, nanoscience and cancer.

Lysosome-targeting phenalenones as efficient type I/II photosensitizers for anticancer photodynamic therapy

Development of safe and effective photosensitizers is important for enhancing the efficacy of photodynamic cancer therapy. Phenalenone is a type II photosensitizer with a high singlet oxygen quantum yield; however, its short UV absorption wavelength hinders its application in cancer imaging and in vivo photodynamic therapy. In this study, we report a new redshift phenalenone derivative, 6-amino-5-iodo-1H-phenalen-1-one (SDU Red [SR]), as a lysosome-targeting photosensitizer for triple-negative breast cancer therapy. SDU Red produced singlet oxygen (Type II reactive oxygen species [ROS]) and superoxide anion radicals (Type I ROS) upon light irradiation. It also exhibited good photostability and a remarkable phototherapeutic index (PI > 76) against triple-negative breast cancer MDA-MB-231 cancer cells. Additionally, we designed two amide derivatives, SRE-I and SRE-II, with decreased fluorescence and photosensitizing capabilities based on SDU Red as activatable photosensitizers for photodynamic cancer therapy. SRE-I and SRE-II could be further converted into the active photosensitizer SDU Red via carboxylesterase-catalyzed amide bond cleavage. Moreover, SDU Red and SRE-II induced DNA damage and cell apoptosis in the presence of light. Therefore, SRE-II can act as a promising theranostic agent for triple-negative breast cancer.

Recent Advances in Hydrogel-Based Phototherapy for Tumor Treatment

Phototherapeutic agent-based phototherapies activated by light have proven to be safe modalities for the treatment of various malignant tumor indications. The two main modalities of phototherapies include photothermal therapy, which causes localized thermal damage to target lesions, and photodynamic therapy, which causes localized chemical damage by generated reactive oxygen species (ROS). Conventional phototherapies suffer a major shortcoming in their clinical application due to their phototoxicity, which primarily arises from the uncontrolled distribution of phototherapeutic agents in vivo. For successful antitumor phototherapy, it is essential to ensure the generation of heat or ROS specifically occurs at the tumor site. To minimize the reverse side effects of phototherapy while improving its therapeutic performance, extensive research has focused on developing hydrogel-based phototherapy for tumor treatment. The utilization of hydrogels as drug carriers allows for the sustained delivery of phototherapeutic agents to tumor sites, thereby limiting their adverse effects. Herein, we summarize the recent advancements in the design of hydrogels for antitumor phototherapy, offer a comprehensive overview of the latest advances in hydrogel-based phototherapy and its combination with other therapeutic modalities for tumor treatment, and discuss the current clinical status of hydrogel-based antitumor phototherapy.

Enzyme-Responsive Double-Locked Photodynamic Molecular Beacon for Targeted Photodynamic Anticancer Therapy

An advanced photodynamic molecular beacon (PMB) was designed and synthesized, in which a distyryl boron dipyrromethene (DSBDP)-based photosensitizer and a Black Hole Quencher 3 moiety were connected via two peptide segments containing the sequences PLGVR and GFLG, respectively, of a cyclic peptide. These two short peptide sequences are well-known substrates of matrix metalloproteinase-2 (MMP-2) and cathepsin B, respectively, both of which are overexpressed in a wide range of cancer cells either extracellularly (for MMP-2) or intracellularly (for cathepsin B). Owing to the efficient Förster resonance energy transfer between the two components, this PMB was fully quenched in the native form. Only upon interaction with both MMP-2 and cathepsin B, either in a buffer solution or in cancer cells, both of the segments were cleaved specifically, and the two components could be completely separated, thereby restoring the photodynamic activities of the DSBDP moiety. This PMB could also be activated in tumors, and it effectively suppressed the tumor growth in A549 tumor-bearing nude mice upon laser irradiation without causing notable side effects. In particular, it did not cause skin photosensitivity, which is a very common side effect of photodynamic therapy (PDT) using conventional "always-on" photosensitizers. The overall results showed that this "double-locked" PMB functioned as a biological AND logic gate that could only be unlocked by the coexistence of two tumor-associated enzymes, which could greatly enhance the tumor specificity in PDT.

Multifunctional AIE Nanosphere-Based "Nanobomb" for Trimodal Imaging-Guided Photothermal/Photodynamic/Pharmacological Therapy of Drug-Resistant Bacterial Infections

Injudicious or inappropriate use of antibiotics has led to the prevalence of drug-resistant bacteria, posing a huge menace to global health. Here, a self-assembled aggregation-induced emission (AIE) nanosphere (AIE-PEG₁₀₀₀ NPs) that simultaneously possesses near-infrared region II (NIR-II) fluorescence emissive, photothermal, and photodynamic properties is prepared using a multifunctional AIE luminogen (AIE-4COOH). The AIE-PEG₁₀₀₀ NPs were encapsulated with teicoplanin (Tei) and ammonium bicarbonate (AB) into lipid nanovesicles to form a laser-activated "nanobomb" (AIE-Tei@AB NVs) for the multimodal theranostics of drug-resistant bacterial infections. In vivo experiments validate that the "nanobomb" enables high-performance NIR-II fluorescence, infrared thermal, and ultrasound (AB decomposition during the photothermal process to produce numerous CO₂/NH₃ bubbles, which is an efficient ultrasound contrast agent) imaging of multidrug-resistant bacteria-infected foci after intravenous administration of AIE-Tei@AB NVs followed by 660 nm laser stimulation. The highly efficient photothermal and photodynamic features of AIE-Tei@AB NVs, combined with the excellent pharmacological property of rapidly released Tei during bubble generation and NV disintegration, collectively promote broad-spectrum eradication of three clinically isolated multidrug-resistant bacteria strains and rapid healing of infected wounds. This multimodal imaging-guided synergistic therapeutic strategy can be extended for the theranostics of superbugs.

Chlorin e6: A Promising Photosensitizer in Photo-Based Cancer Nanomedicine

Conventional cancer treatment modalities are often associated with major therapeutic limitations and severe side effects. Photodynamic therapy is a localized noninvasive mode of treatment that has given a different direction to cancer research due to its effectivity against a wide range of cancers and minimal side effects. A photosensitizer is the key component of photodynamic therapy (PDT) that generates cytotoxic reactive oxygen species to eradicate cancer cells. As the therapeutic effectivity of PDT greatly depends upon the photosensitizer, great efforts have been made to search for an ideal photosensitizer. Chlorin e6 is a FDA approved second generation photosensitizer that meets the desired clinical properties for PDT. It is known for its high reactive oxygen species (ROS) generation ability and anticancer potency against many types of cancer. Hydrophobicity is a major drawback of Ce6 that leads to its poor biodistribution and rapid clearance from the circulatory system. To overcome this drawback, researchers have designed and fabricated several types of nanosystems, which can enhance Ce6 solubility and thereby enhance its bioavailability. These nanosystems also improve tumor accumulation of Ce6 by selectively targeting the cancer cells through passive and active targeting. In addition, Ce6 has been employed in many combination therapies like chemo-photodynamic therapy, photoimmunotherapy, and combined photodynamic-photothermal therapy. A combination therapy is more curative than a single therapy due to the synergistic effects of individual therapies. Ce6-based nanosystems for combination therapies have shown excellent results in various studies and provide a promising platform for cancer treatment.

Quantum Yield of DNA Strand Breaks under Photoexcitation of a Molecular Ruby

Photodynamic therapy (PDT) used for treating cancer relies on the generation of highly reactive oxygen species, for example, singlet oxygen ¹ O₂ , by light-induced excitation of a photosensitizer (PS) in the presence of molecular oxygen, inducing DNA damage in close proximity of the PS. Although many precious metal complexes have been explored as PS for PDT and received clinical approval, only recently, the potential of photoactive complexes of non-noble metals as PS has been discovered. Using the DNA origami technology that can absolutely quantify DNA strand break cross sections, we assessed the potential of the luminescent transition metal complex [Cr(ddpd)₂ ]³⁺ (ddpd=N,N'-dimethyl-N,N'-dipyridine-2-ylpyridine-2,6-diamine) to damage DNA in an air-saturated aqueous environment upon UV/Vis illumination. The quantum yield for strand breakage, that is, the ratio of DNA strand breaks to the number of absorbed photons, was determined to 1-4 %, indicating efficient transformation of photons into DNA strand breaks by [Cr(ddpd)₂ ]³⁺ .

Mitochondria-Driven Dye Rearrangement That Enables Spatiotemporally Controlled Photomedicine

Reversibly controlling the dye arrangements in living systems has great potential to realize spatiotemporally controlled photomedicine. However, tuning or even maintaining a certain arrangement of dyes in a complex living environments is extremely challenging due to the interference of the various biological species. Herein, a conceptual supramolecular strategy to engineer a switchable photosensitizer (PS) via mitochondria-mediated dynamic interconversion between monomer and J-aggregation, enabling specific activation of the mitochondria-targeting photodynamic therapy (PDT) and hibernation after mitochondria damage is presented. The presented mitochondria-mediated "activate-then-hibernate" PS design enables a fascinating spatiotemporally controlled PDT in which spatially controlled mitochondrial-targeting enhances therapeutic efficacy and temporally controlled activation-then-hibernation averts off-target damage during PDT and tissue damage after clinical treatment, thus offering significant potential for biological research and clinical needs.

Accurate Vertical Excitation Energies of BODIPY/Aza-BODIPY Derivatives from Excited-State Mean-Field Calculations

We report a benchmark study of vertical excitation energies and oscillator strengths for the HOMO → LUMO transitions of 17 boron–dipyrromethene (BODIPY) structures, showing a large variety of ring sizes and substituents. Results obtained at the time-dependent density functional theory (TDDFT) and at the delta-self-consistent-field (ΔSCF) by using 13 different exchange correlation kernels (within LDA, GGA, hybrid, and range-separated approximations) are benchmarked against the experimental excitation energies when available. It is found that the time-independent ΔSCF DFT method, when used in combination with hybrid PBE0 and B3LYP functionals, largely outperforms TDDFT and can be quite competitive, in terms of accuracy, with computationally more costly wave function based methods such as CC2 and CASPT2.

Immunosonodynamic Therapy Designed with Activatable Sonosensitizer and Immune Stimulant Imiquimod

Sonodynamic therapy (SDT) has garnered extensive attention as a noninvasive treatment for deep tumors. Furthermore, imiquimod (R837), an FDA-approved toll-like receptor 7 agonist, is commonly used in clinical settings as an immune adjuvant. We prepared an activatable sonodynamic sensitizer platform (MR) based on glutathione-sensitive disulfide bonds linking Leu-MB, the reduced form of methylene blue (MB), and R837 to achieve efficient combinatory SDT and immunotherapy for tumors without harming normal tissues. We also used the amphiphilic polymer C₁₈PMH-PEG to create self-assembled MB-R837-PEG (MRP) nanoparticles for immunosonodynamic therapy (iSDT). iSDT is a cancer treatment that combines activatable SDT and immunotherapy. Our iSDT demonstrated an excellent sonodynamic effect only at the tumor site, demonstrating high specificity in killing tumor cells when compared to SDT reported in the literature. The iSDT improves its tumor-killing effect by inducing an immune response, which is accomplished by secreted immune adjuvants in the tumor site. MRP was selectively activated by glutathione in the tumor microenvironment to release MB and R837, exhibiting excellent antitumor sonodynamic and immune responses. In addition, when combined with an α-PD-L1 antibody for immune checkpoint blockade, this therapy effectively inhibited tumor metastasis. Furthermore, mice treated with iSDT and α-PD-L1 antibody did not develop tumors even after tumor reinoculation, indicating that long-term immune memory was achieved. The concept of sonodynamic sensitizer preparation as a next-generation iSDT based on a noninvasive synergistic therapeutic modality applicable in the near future is presented in this study.

An oxygen-economical nano-photosensitizer with a high photodynamic therapeutic outcome via simultaneous reduction of the cellular respiration and oxygen depletion of PDT

The development of photodynamic nanomedicines that can alleviate intratumoral oxygen deficiency during photodynamic therapy (PDT) is of great significance for improving the therapeutic outcome of solid tumors characterized by severe hypoxia. Massive oxygen consumption due to vigorous cellular respiration, i.e., mitochondrial-associated oxidative phosphorylation (OXPHOS), is another major cause of severe tumor hypoxia in addition to insufficient oxygen supply. Moreover, oxygen depletion during PDT further exacerbates the shortage of intratumoral oxygen. In this work, we engineered a novel oxygen-economical nano-photosensitizer via co-encapsulation of an OXPHOS inhibitor (ATO) and a newly developed type-I photosensitizer (IPS) into a polymeric micelle of PEG-b-PCL. By controlling the length of hydrophobic PCL segments, we successfully optimized the micelle size to around 30 nm for enhanced tumor penetration. The orchestration of the two functional components, ATO and IPS, can simultaneously hinder the two major tumor oxygen-consuming pathways, where ATO targets mitochondrial complex III to inhibit cellular respiration, while IPS generates ROS through a low oxygen-consuming type-I photochemical pathway, enabling remarkable PDT efficacies in both hypoxic cells and a 4T1 tumor-bearing BALB/c mouse model. This work sheds new light on the construction of nano-photosensitizers to rejuvenate PDT against hypoxic solid tumors.

Lipid Droplets in Cancer: From Composition and Role to Imaging and Therapeutics

Cancer is the second most common cause of death worldwide, having its origin in the abnormal growth of cells. Available chemotherapeutics still present major drawbacks, usually associated with high toxicity and poor distribution, with only a small fraction of drugs reaching the tumour sites. Thus, it is urgent to develop novel therapeutic strategies. Cancer cells can reprogram their lipid metabolism to sustain uncontrolled proliferation, and, therefore, accumulate a higher amount of lipid droplets (LDs). LDs are cytoplasmic organelles that store neutral lipids and are hypothesized to sequester anti-cancer drugs, leading to reduced efficacy. Thus, the increased biogenesis of LDs in neoplastic conditions makes them suitable targets for anticancer therapy and for the development of new dyes for cancer cells imaging. In recent years, cancer nanotherapeutics offered some exciting possibilities, including improvement tumour detection and eradication. In this review we summarize LDs biogenesis, structure and composition, and highlight their role in cancer theranostics.

Enzyme activatable photodynamic therapy agents targeting melanoma

A tyrosinase activatable photosensitizer is developed with selective phototoxicity to melanoma cells.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy

This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

Visible-Light-Mediated Modification and Manipulation of Biomacromolecules

Chemically modified biomacromolecules-i.e., proteins, nucleic acids, glycans, and lipids-have become crucial tools in chemical biology. They are extensively used not only to elucidate cellular processes but also in industrial applications, particularly in the context of biopharmaceuticals. In order to enable maximum scope for optimization, it is pivotal to have a diverse array of biomacromolecule modification methods at one's disposal. Chemistry has driven many significant advances in this area, and especially recently, numerous novel visible-light-induced photochemical approaches have emerged. In these reactions, light serves as an external source of energy, enabling access to highly reactive intermediates under exceedingly mild conditions and with exquisite spatiotemporal control. While UV-induced transformations on biomacromolecules date back decades, visible light has the unmistakable advantage of being considerably more biocompatible, and a spectrum of visible-light-driven methods is now available, chiefly for proteins and nucleic acids. This review will discuss modifications of native functional groups (FGs), including functionalization, labeling, and cross-linking techniques as well as the utility of oxidative degradation mediated by photochemically generated reactive oxygen species. Furthermore, transformations at non-native, bioorthogonal FGs on biomacromolecules will be addressed, including photoclick chemistry and DNA-encoded library synthesis as well as methods that allow manipulation of the activity of a biomacromolecule.

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.

A Novel Photosensitizer for Lipid Droplet-Location Photodynamic Therapy

Lipid droplets (LDs), an extremely important cellular organelle, are responsible for the storage of neutral lipids in multiple biological processes, which could be a potential target site for photodynamic therapy (PDT) of cancer. Herein, a lipid droplet–targeted photosensitizer (BODSeI) is developed, allowing for fluorescence imaging–guided PDT. Owing to the location of lipid droplets, BODSeI demonstrates enhanced PDT efficiency with an extremely low IC50 value (around 125 nM). Besides, BODSeI shows good biocompatibility and high photostability. Therefore, BODSeI is promising for droplet-location PDT, which may trigger wide interest for exploring the pathway of lipid droplet–location PDT.

Photodynamic Therapy-Current Limitations and Novel Approaches

Photodynamic therapy (PDT) mostly relies on the generation of singlet oxygen, via the excitation of a photosensitizer, so that target tumor cells can be destroyed. PDT can be applied in the settings of several malignant diseases. In fact, the earliest preclinical applications date back to 1900’s. Dougherty reported the treatment of skin tumors by PDT in 1978. Several further studies around 1980 demonstrated the effectiveness of PDT. Thus, the technique has attracted the attention of numerous researchers since then. Hematoporphyrin derivative received the FDA approval as a clinical application of PDT in 1995. We have indeed witnessed a considerable progress in the field over the last century. Given the fact that PDT has a favorable adverse event profile and can enhance anti-tumor immune responses as well as demonstrating minimally invasive characteristics, it is disappointing that PDT is not broadly utilized in the clinical setting for the treatment of malignant and/or non-malignant diseases. Several issues still hinder the development of PDT, such as those related with light, tissue oxygenation and inherent properties of the photosensitizers. Various photosensitizers have been designed/synthesized in order to overcome the limitations. In this Review, we provide a general overview of the mechanisms of action in terms of PDT in cancer, including the effects on immune system and vasculature as well as mechanisms related with tumor cell destruction. We will also briefly mention the application of PDT for non-malignant diseases. The current limitations of PDT utilization in cancer will be reviewed, since identifying problems associated with design/synthesis of photosensitizers as well as application of light and tissue oxygenation might pave the way for more effective PDT approaches. Furthermore, novel promising approaches to improve outcome in PDT such as selectivity, bioengineering, subcellular/organelle targeting, etc. will also be discussed in detail, since the potential of pioneering and exceptional approaches that aim to overcome the limitations and reveal the full potential of PDT in terms of clinical translation are undoubtedly exciting. A better understanding of novel concepts in the field (e.g. enhanced, two-stage, fractional PDT) will most likely prove to be very useful for pursuing and improving effective PDT strategies.

The TDDFT Excitation Energies of the BODIPYs; The DFT and TDDFT Challenge Continues

The derivatives of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) are pivotal ingredients for a large number of functional, stimuli-responsive materials and therapeutic molecules based on their photophysical properties, and there is a urgent need to understand and predict their optical traits prior to investing a large amount of resources in preparing them. Density functional theory (DFT) and time-dependent DFT (TDDFT) computations were performed to calculate the excitation energies of the lowest-energy singlet excited state of a large series of common BODIPY derivatives employing various functional aiming at the best possible combination providing the least deviations from the experimental values. Using the common "fudge" correction, a series of combinations was investigated, and a methodology is proposed offering equal or better performances than what is reported in the literature.