Recent advances in drug discovery of phototherapeutic non-porphyrinic anticancer agents

Phototherapy in cancer treatment: strategies and challenges

Phototherapy has emerged as a promising modality in cancer treatment, garnering considerable attention for its minimal side effects, exceptional spatial selectivity, and optimal preservation of normal tissue function. This innovative approach primarily encompasses three distinct paradigms: Photodynamic Therapy (PDT), Photothermal Therapy (PTT), and Photoimmunotherapy (PIT). Each of these modalities exerts its antitumor effects through unique mechanisms-specifically, the generation of reactive oxygen species (ROS), heat, and immune responses, respectively. However, significant challenges impede the advancement and clinical application of phototherapy. These include inadequate ROS production rates, subpar photothermal conversion efficiency, difficulties in tumor targeting, and unfavorable physicochemical properties inherent to traditional phototherapeutic agents (PTs). Additionally, the hypoxic microenvironment typical of tumors complicates therapeutic efficacy due to limited agent penetration in deep-seated lesions. To address these limitations, ongoing research is fervently exploring innovative solutions. The unique advantages offered by nano-PTs and nanocarrier systems aim to enhance traditional approaches' effectiveness. Strategies such as generating oxygen in situ within tumors or inhibiting mitochondrial respiration while targeting the HIF-1α pathway may alleviate tumor hypoxia. Moreover, utilizing self-luminescent materials, near-infrared excitation sources, non-photoactivated sensitizers, and wireless light delivery systems can improve light penetration. Furthermore, integrating immunoadjuvants and modulating immunosuppressive cell populations while deploying immune checkpoint inhibitors holds promise for enhancing immunogenic cell death through PIT. This review seeks to elucidate the fundamental principles and biological implications of phototherapy while discussing dominant mechanisms and advanced strategies designed to overcome existing challenges-ultimately illuminating pathways for future research aimed at amplifying this intervention's therapeutic efficacy.

Self-assembled HO-1i-Pt(IV) nanomedicine targeting p38/MAPK and MDR pathways for cancer chemo-immunotherapy

Platinum(II)-based antitumor drugs are widely used in clinics but limited by severe side effects and resistance. Multi-target Platinum(IV) complexes are emerging as ideal alternatives. Heme oxygenase-1 (HO-1) works as a rate-limiting step in heme degradation and is overexpressed in malignant tumors. Herein, HO-1i-based Platinum(IV) prodrugs are prepared and candidate complex 15 is further developed into self-assembled nanoparticles (15-NPs). 15 and 15-NPs significantly increase cytotoxicity, particularly in HepG2 (74.77- and 96.14-fold increases) and A549cisR (38.6- and 47.24-fold increases), while reducing toxicity towards normal cells compared to cisplatin. In vitro experiments show 15 and 15-NPs activated multiple pathways, including p38/MAPK- and MDR-related proteins, achieving multi-target synergistic chemosensitization and anti-resistance, further verified by RNA-sequencing analysis. In vivo tests demonstrate that 15 and 15-NPs efficiently inhibit tumor growth and systemic toxicity, especially 15-NPs with optimal tumor-inhibition rate and survival (80% and 100%), superior to cisplatin (40% and 50%), attributing to its extra endocytosis, EPR effect, and precisely tumor-targeted release besides the advantage of a free HO-1i-Pt(IV) prodrug. Additionally, 15 and 15-NPs distinctly regulate T-cell and macrophage functions, thereby exhibiting a chemoimmuno-combined action. This study highlights that multi-functional Platinum(IV) prodrug target-delivered to tumors via carrier-free nanoparticles may represent an effective modality for improving cancer therapy.

Laser-Free Photosensitive Systems in Cancer Therapy: A Comprehensive Review

Photodynamic therapy (PDT) involves the use of photosensitizers (PSs) that, upon activation by specific wavelengths of light, generate reactive oxygen species (ROS), including singlet oxygen (1O2) and hydroxyl radicals (·OH), within the targeted tissue, typically tumor cells. The generated ROS induces cellular damage, disrupts cellular processes, and ultimately leads to apoptosis or necrosis of the tumor cells. However, the clinical application of PDT is significantly hindered by the limited tissue penetration ability of light. To address this limitation, laser-free self-luminescent photosensitive systems have emerged as potential solutions for achieving deep-tissue PDT and imaging. This review provides a comprehensive analysis of various laser-independent photosensitive systems, with a particular emphasis on those based on resonance energy transfer (RET), chemically induced electron exchange luminescence (CIEEL), and Cherenkov radiation energy transfer (CRET). The aim is to offer a theoretical framework for the development of novel photodynamic systems and to reassess the application potential of certain previously overlooked photosensitizers (PSs).

A novel cyanine photosensitizer for sequential dual-site GSH depletion and ROS-potentiated cancer photodynamic therapy

The efficacy of photodynamic therapy (PDT) is often limited by the reductive microenvironment in tumor cells due to the high level of glutathione (GSH) and glutathione peroxidase 4 (GPX4), which maintain redox homeostasis. Therefore, designing a GSH-responsive photosensitizer that depletes intracellular GSH is a promising strategy to enhance PDT selectivity and efficacy. Herein, we present a GSH-selective sequentially responsive theranostic photosensitizer, Cy-Res. This cyanine agent targeting mitochondria effectively depletes two GSH molecules, leading to the generation of abundant ROS and exacerbating oxidative stress. Additionally, it achieves an 80-fold fluorescence enhancement upon response to GSH, enabling selective imaging of tumor cells. By mitigating GSH's impact on PDT, Cy-ResNPs achieves synergistic and efficient PDT treatment of invasive melanoma under low-power irradiation (808 nm, 80 mW/cm2). The inhibitory processes downregulate GPX4, increase apoptotic proteins like Bax, and promote mixed cell death involving both ferroptosis and apoptosis. Overall, this study offers new insights and strategies for the development of GSH-responsive theranostic agents, highlighting their potential for application in tumor diagnosis and therapy.

Spectroscopic Investigation of Coumarin Based Novel Fluorescent TURN OFF Sensor for the Selective Detection of Fe3+: In-vitro Live Cell Imaging Application

The novel TURN-OFF fluorescent sensors 4-(Benzo[1,3]dioxol-5-yloxymethyl)-7-hydroxy-chromen-2-one (4BHC) and 4-(6-Bromo-benzo[1,3]dioxol-5-yloxymethyl)-7-hydroxy-chromen-2-one (4BBHC) are designed and synthesized for the spectrofluorometric detection of the biologically important Fe3+ ions, which has sensitive and selective fluorescence quenching over other competitive metal ions. The effectiveness of the sensors and rapid response are validated through UV-Visible, and fluorescence spectral changes. These spectral changes could be due to the formation of coordination bond between ligand and metal ion. The binding stoichiometry of both sensors with Fe3+ ions is studied with the help of Job's plot, which gives a 1:2 coordination ratio; this is further confirmed through DFT, IR and NMR studies. The association constants of 4BHC and 4BBHC are calculated through Benesie-Hildebrand plots, and they are found to be 6 × 104 M-1 and 11.2 × 104 M-1 respectively. Following, LOD is calculated to define the range of sensitivity of the proposed sensors and is found to be 3.43 μM and 2.14 μM respectively. The chemical hardness parameter suggested that both sensors are soft molecules. In addition, low cytotoxicity levels of 4BHC and 4BBHC led to the demonstration of their efficacy in In-Vitro imaging of Fe3+ ions inside living cells, which ensures that these sensors are promising candidates for bioimaging.

Toluidine blue O demethylated photoproducts as type II photosensitizers

Toluidine blue O (TBO) is a type I-type II photosensitizer that has shown good efficacy and selectivity in antimicrobial and anticancer photodynamic therapy applications. However, its complex photochemistry with multiple photoproducts hinders its application as a photosensitizer. We have previously described the mechanism for photooxidative demethylation of TBO which in acetonitrile yields two main products: demethylated-TBO (d-TBO) and double-demethylated-TBO (dd-TBO). In the current work, we describe the photophysical properties of these two photoproducts. In acetonitrile and phosphate buffer, demethylation induces an hypsochromic shift in the absorption and fluorescence emission maxima. Fluorescence quantum yields increase slightly for the demethylated photoproducts, in agreement with the lengthening of the fluorescence lifetimes. Triplet excited states lifetimes in the presence of oxygen decreased slightly upon demethylation. However, the singlet oxygen quantum yield increased significantly reaching unity for the dd-TBO photoproduct. These results are interpreted in terms of the competing pathways of TBO photochemistry. For TBO, demethylation is the main pathway for deactivation of the excited state, while for d-TBO, demethylation and singlet oxygen generation are significant. For dd-TBO, singlet oxygen generation is the main deactivation pathway. Overall, TBO demethylated photoproducts demonstrate good potential as candidates for photodynamic therapy applications.

Photodynamic bactericidal nanomaterials in food packaging: From principle to application

Compared to traditional preservatives, photodynamic inactivation (PDI) offers a promising bactericidal approach due to its nontoxic nature and low propensity for microbial resistance. In this paper, we initially investigate the principles and antibacterial mechanisms underlying PDI. We then review factors influencing PDI's germicidal efficacy in food preservation. Furthermore, we delve into the application potential of PDI nanomaterials, such as quantum dots, titanium dioxide, and graphene, in packaging and films. Special attention is given to the impact of PDI treatment on food quality and the potential for microbial tolerance development. Last, we discuss the migration and safety of PDI nanomaterials. The chemical basis of PDI involves the generation of reactive oxygen species through the activation of endogenous or exogenous photosensitizers. Its primary antibacterial mechanisms encompass the disruption of cell membranes, impairment of cellular functions, and inhibition of quorum sensing. The multi-target action of PDI significantly reduces the likelihood of resistance development. PDI has great potential for application in the field of antibacterial packaging. The information contained in this paper will provide effective reference for the design of new antibacterial packaging.

A New Demand for Improved Selectivity and Potency of Cyanine Dyes as Antiproliferative Agents Against Colorectal Cancer Cells

Cancer treatment remains a significant challenge, with chemotherapy still being one of the most common therapeutic approaches. Based on our initial studies of symmetric monomethine cyanine dyes, which showed potential against colorectal cancer, this study explored several asymmetric cyanines, aiming to develop more potent and selective antitumor agents, particularly against colorectal cancer. In pursuit of this goal, we have designed, synthesized, and structurally characterized twelve new cyanine dyes. Their antiproliferative effects were then investigated in vitro against both tumor and non-tumor cell lines. Notably, the two most promising dyes in terms of potency and selectivity against Caco-2 colorectal cancer cells were derived from the combination of N-methylbenzoxazole and N-methylquinoline (dye 5), as well as N-ethylbenzothiazole and N-ethyl-6-nitrobenzothiazole (dye 10). The potential mechanisms behind their antiproliferative action were also explored, revealing that both dyes penetrate cells and localize within the cytoplasm and nucleus. Furthermore, dye 5 was found to slightly induce apoptosis without causing significant cell cycle arrest, in contrast to dye 10, which increased the number of cells in the G0/G1 phase. Interestingly, both dyes exhibited marked topoisomerase II inhibitory effects, particularly cyanine 5, which may further explain their antiproliferative activity. Additionally, drug-likeness properties were predicted for both dyes. Overall, cyanine 5 emerged as the most promising candidate for further investigation as a potential treatment for colorectal cancer.

Preparation of Composite Hydrogels Based on Cysteine-Silver Sol and Methylene Blue as Promising Systems for Anticancer Photodynamic Therapy

In this study, a novel supramolecular composite, "photogels", was synthesized by mixing of cysteine-silver sol (CSS) and methylene blue (MB). A complex of modern physico-chemical methods of analysis such as viscosimetry, UV spectroscopy, dynamic and electrophoretic light scattering, scanning electron microscopy and energy-dispersive X-ray spectroscopy showed that MB molecules are uniformly localized mainly in the space between fibers of the gel-network formed by CSS particles. Molecules of the dye also bind with the surface of CSS particles by non-covalent interactions. This fact is reflected in the appearance of a synergistic anticancer effect of gels against human squamous cell carcinoma even in the absence of light irradiation. A mild toxic influence of hydrogels was observed in normal keratinocyte cells. Photodynamic exposure significantly increased gel activity, and there remained a synergistic effect. The study of free-radical oxidation in cells has shown that gels are not only capable of generating reactive oxygen species, but also have other targets of action. Flow cytometric analysis allowed us to find out that obtained hydrogels caused cell cycle arrest both without irradiation and with light exposure. The obtained gels are of considerable interest both from the point of view of academics and applied science, for example, in the photodynamic therapy of superficial neoplasms.

Recent advances for enhanced photodynamic therapy: from new mechanisms to innovative strategies

Photodynamic therapy (PDT) has been developed as a potential cancer treatment approach owing to its non-invasiveness, spatiotemporal control and limited side effects. Currently, great efforts have been made to improve the PDT effect in terms of safety and efficiency. In this review, we highlight recent advances in innovative strategies for enhanced PDT, including (1) the development of novel radicals, (2) design of activatable photosensitizers based on the TME and light, and (3) photocatalytic NADH oxidation to damage the mitochondrial electron transport chain. Additionally, the new mechanisms for PDT are also presented as an inspiration for the design of novel PSs. Finally, we discuss the current challenges and future prospects in the clinical practice of these innovative strategies. It is hoped that this review will provide a new angle for understanding the relationship between the intratumoural redox environment and PDT mechanisms, and new ideas for the future development of smart PDT systems.

Structure-Activity Relationship of Benzophenazine Derivatives for Homogeneous and Heterogenized Photooxygenation Catalysis

Singlet oxygen is a powerful oxidant used in various applications, such as organic synthesis, medicine, and environmental remediation. Organic and inorganic photosensitizers are commonly used to generate this reactive species through energy transfer with the triplet ground state of oxygen. We describe here a series of novel benzophenazine derivatives as a promising class of photosensitizers for singlet oxygen photosensitization. In this study, we investigated the structure-activity relationship of these benzophenazine derivatives. Akin to a molecular compass, the southern fragment was first functionalized with either aromatic tertiary amines, alkyl tertiary amines, aromatic sulfur groups, alkyl sulfur groups, or cyclic ethers. Enhanced photophysical properties (in terms of triplet excited-state lifetime, absorption wavelength, triplet state energy, and O2 quenching capabilities) were obtained with cyclic ether and sulfur groups. Conversely, the presence of an amine moiety was detrimental to the photocatalysts. The western and northern fragments were also investigated and slightly undesirable to negligible changes in photophysical properties were observed. The most promising candidate was then immobilized on silica nanoparticles and its photoactivity was evaluated in the citronellol photooxidation reaction. A high NMR yield of 97 % in desired product was obtained, with only a slight decrease over several recycling runs (85 % in the fourth run). These results provide insights into the design of efficient photosensitizers for singlet oxygen generation and the development of heterogeneous systems.

Ligand Regulation Strategy to Modulate ROS Nature in a Rhodamine-Iridium(III) Hybrid System for Phototherapy

The efficacy of photodynamic therapy (PDT) is highly dependent on the photosensitizer features. The reactive oxygen species (ROS) generated by photosensitizers is proven to be associated with immunotherapy by triggering immunogenic cell death (ICD) as well. In this work, we establish a rhodamine-iridium(III) hybrid model functioning as a photosensitizer to comprehensively understand its performance and potential applications in photodynamic immunotherapy. Especially, the correlation between the ROS generation efficiency and the energy level of the Ir(III)-based excited state (T1'), modulated by the cyclometalating (C∧N) ligand, is systematically investigated and correlated. We prove that in addition to the direct population of the rhodamine triplet state (T1) formed through the intersystem crossing process with the assistance of a heavy Ir(III) metal center, the fine-tuned T1' state could act as a relay to provide an additional pathway for promoting the cascade energy transfer process that leads to enhanced ROS generation ability. Moreover, type I ROS can be effectively produced by introducing sulfur-containing thiophene units in C∧N ligands, providing a stronger M1 macrophage-activation efficiency under hypoxia to evoke in vivo antitumor immunity. Overall, our work provides a fundamental guideline for the molecular design and exploration of advanced transition-metal-based photosensitizers for biomedical applications.

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.

Nanoscale Metal-Organic Frameworks Combined with Metal Nanoparticles and Metal Oxide/Peroxide to Relieve Tumor Hypoxia for Enhanced Photodynamic Therapy

Photodynamic therapy (PDT) is a clinically approved noninvasive tumor therapy that can selectively kill malignant tumor cells, with promising use in the treatment of various cancers. PDT is typically composed of three important parts: the specific wavelength of light, photosensitizer (PS), and oxygen. With the progressing investigation on PDT treatment, the most recent attention has focused on improving photodynamic efficiency. Tumor hypoxia has always been a critical factor hindering the efficacy of PDT. Nanoscale metal-organic frameworks (nMOF), the fourth generation of PS, present great potential in photodynamic therapy. In particular, nMOF combined with metal nanoparticles and metal oxide/peroxide has demonstrated unique properties for enhanced PDT. The metal and metal oxide nanoparticles can catalyze H2O2 to generate oxygen or automatically produces oxygen, alleviating the hypoxia and improving the photodynamic efficiency. Metal peroxide nanoparticles can spontaneously produce oxygen in water or under acidic conditions. Therefore, this Review summarizes the recent development of nMOF combined with metal nanoparticles (platinum nanoparticles and gold nanoparticles) and metal oxide/peroxide (manganese dioxide, ferric oxide, cerium oxide, calcium peroxide, and magnesium peroxide) for enhanced photodynamic therapy by alleviating tumor hypoxia. Finally, future perspectives of nMOF combined nanomaterials in PDT are put forward.

Recent Progress in Type I Aggregation-Induced Emission Photosensitizers for Photodynamic Therapy

In modern medicine, precision diagnosis and treatment using optical materials, such as fluorescence/photoacoustic imaging-guided photodynamic therapy (PDT), are becoming increasingly popular. Photosensitizers (PSs) are the most important component of PDT. Different from conventional PSs with planar molecular structures, which are susceptible to quenching effects caused by aggregation, the distinct advantages of AIE fluorogens open up new avenues for the development of image-guided PDT with improved treatment accuracy and efficacy in practical applications. It is critical that as much of the energy absorbed by optical materials is dissipated into the pathways required to maximize biomedical applications as possible. Intersystem crossing (ISC) represents a key step during the energy conversion process that determines many fundamental optical properties, such as increasing the efficiency of reactive oxygen species (ROS) production from PSs, thus enhancing PDT efficacy. Although some review articles have summarized the accomplishments of various optical materials in imaging and therapeutics, few of them have focused on how to improve the phototherapeutic applications, especially PDT, by adjusting the ISC process of organic optics materials. In this review, we emphasize the latest advances in the reasonable design of AIE-active PSs with type I photochemical mechanism for anticancer or antibacterial applications based on ISC modulation, as well as discuss the future prospects and challenges of them. In order to maximize the anticancer or antibacterial effects of type I AIE PSs, it is the aim of this review to offer advice for their design with the best energy conversion.

Free and Poly-Methyl-Methacrylate-Bounded BODIPYs: Photodynamic and Antimigratory Effects in 2D and 3D Cancer Models

Several limitations, including dark toxicity, reduced tumor tissue selectivity, low photostability and poor biocompatibility hamper the clinical use of Photodynamic therapy (PDT) in cancer treatment. To overcome these limitations, new PSs have been synthetized, and often combined with drug delivery systems, to improve selectivity and reduce toxicity. In this context, BODIPYs (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) have recently emerged as promising and easy-to-handle scaffolds for the preparation of effective PDT antitumor agents. In this study, the anticancer photodynamic effect of newly prepared negatively charged polymethyl methacrylate (nPMMA)-bounded BODIPYs (3@nPMMA and 6@nPMMA) was evaluated on a panel of 2D- and 3D-cultured cancer cell lines and compared with free BODIPYs. In particular, the effect on cell viability was evaluated, along with their ability to accumulate into the cells, induce apoptotic and/or necrotic cell death, and inhibit cellular migration. Our results indicated that 3@nPMMA and 6@nPMMA reduce cancer cell viability in 3D models of HC116 and MCF7 cells more effectively than the corresponding free compounds. Importantly, we demonstrated that MDA-MB231 and SKOV3 cell migration ability was significantly impaired by the PDT treatment mediated by 3@nPMMA and 6@nPMMA nanoparticles, likely indicating the capability of this approach to reduce metastatic tumor potential.

Aggregation-Induced Emission Luminogens for Enhanced Photodynamic Therapy: From Organelle Targeting to Tumor Targeting

Photodynamic therapy (PDT) has attracted much attention in the field of anticancer treatment. However, PDT has to face challenges, such as aggregation caused by quenching of reactive oxygen species (ROS), and short 1O2 lifetime, which lead to unsatisfactory therapeutic effect. Aggregation-induced emission luminogen (AIEgens)-based photosensitizers (PSs) showed enhanced ROS generation upon aggregation, which showed great potential for hypoxic tumor treatment with enhanced PDT effect. In this review, we summarized the design strategies and applications of AIEgen-based PSs with improved PDT efficacy since 2019. Firstly, we introduce the research background and some basic knowledge in the related field. Secondly, the recent approaches of AIEgen-based PSs for enhanced PDT are summarized in two categories: (1) organelle-targeting PSs that could cause direct damage to organelles to enhance PDT effects, and (2) PSs with tumor-targeting abilities to selectively suppress tumor growth and reduce side effects. Finally, current challenges and future opportunities are discussed. We hope this review can offer new insights and inspirations for the development of AIEgen-based PSs for better PDT effect.

Cellular Hypoxia Mitigation by Dandelion-like Nanoparticles for Synergistic Photodynamic Therapy of Oral Squamous Cell Carcinoma

Hypoxia at the tumor site limits the therapeutic effects of photodynamic therapy (PDT) in oral squamous cell carcinoma (OSCC), which is an oxygen-consumption process. Inhibiting cellular oxygen consumption and reducing cellular ATP production are expected to enhance PDT. In this study, we designed and constructed dandelion-like size-shrinkable nanoparticles for tumor-targeted delivery of hypoxia regulator resveratrol (RES) and photodynamic agent chlorine e6 (CE6). Both drugs were co-encapsulated in small-sized micelles modified with EGFR targeting ligand GE11, which was further conjugated on hyaluronic nanogel (NG) to afford RC-GMN. After targeted accumulation in tumors mediated by GE11 and enhanced penetration and retention (EPR) effects, RC-GMN was degraded by hyaluronidase (HAase) and resulted in small-sized micelles, allowing for deep penetration and dual-receptor-mediated cellular internalization. Resveratrol inhibited cellular oxygen consumption and provided sufficient oxygen for PDT, which consequently activated PDT to produce reactive oxygen species (ROS). Notably, we found that autophagy was overactivated in PDT, which was further strengthened by the hypoxia regulator resveratrol, elevating autophagic cell death. The synergistic effects of resveratrol and CE6 promoted autophagic cell death and apoptosis in the enhanced PDT, resulting in stronger antitumor effects in the orthotopic OSCC model. Therefore, the facilitated delivery of hypoxia regulator enhanced PDT efficacy by elevating oxygen content in tumor cells and inducing autophagic cell death and apoptosis, which offers an alternative strategy for enhancing the PDT effects against OSCC.

Potential Biochemical Pesticide-Synthesis of Neofuranocoumarin and Inhibition the Proliferation of Spodoptera frugiperda Cells through Activating the Mitochondrial Pathway

Furanocoumarins, the secondary metabolites of plants, are considered to be natural insecticides and fungicides because they prevent the invasion of plant pathogenic microorganisms and the predation of herbivorous insects. In this study, novel 2-arylfuranocoumarin derivatives were designed to synthesize by condensation, esterification, bromination, and Wittig reaction. The results showed an excellent photosensitive activity of 2-thiophenylfuranocoumarin (I34). Cell Counting Kit-8 detected that I34 could inhibit the proliferation of Spodoptera frugiperda (Sf9) cells in a time- and concentration-dependent manner under ultraviolet A (UV-A) light for 3 min. The inverted microscope revealed that cells treated with I34 swelled, the membrane was ruptured, and apoptotic bodies appeared. The flow cytometry detected that I34 could induce apoptosis of Sf9 cells, increase the level of intracellular reactive oxygen species (ROS), decrease the mitochondrial membrane potential, and block cell cycle arrest in the G2/M phase. Transmission electron microscopy detected cell mitochondrial cristae damage, matrix degradation, and mitochondrial vacuolation. Further enzyme activity detection revealed that the enzyme activities of apoptosis-related proteins caspase-3 and caspase-9 increased significantly (p < 0.05). Finally, Western blotting analysis detected that the phosphorylation level of Akt and Bad and the expression of the apoptosis inhibitor protein Bcl-XL were inhibited, cleaved-PARP and P53 were increased, and cytochrome C was released from the mitochondria into the cytoplasm. Moreover, under UV-A irradiation, I34 promoted the increase in ROS in Sf9 cells, activated the mitochondrial apoptotic signal transduction pathway, and finally, inhibited cell proliferation. Thus, novel furanocoumarins exhibit a potential application prospect as a biochemical pesticide.

'Lights, squaraines, action!' - the role of squaraine dyes in photodynamic therapy

Since they were first synthesized in 1965 by Treibs and Jacob, squaraine dyes have revolutionized the polymethine dyes' 'universe' and their potential applications due to their indisputable physical, chemical and biological properties. After 30 years and up to the present, various research teams have dedicated themselves to studying the squaraines' photodynamic therapy application using in vitro and in vivo models. The various structural modifications made to these compounds, as well as the influence they have shown to have in their phototherapeutic activity, are the main focus of the present review. Finally, the most evident limitations of this class of dyes, as well as future perspectives in the sense of hypothetically successfully overcoming them, are suggested by the authors.

An Insight into Symmetrical Cyanine Dyes as Promising Selective Antiproliferative Agents in Caco-2 Colorectal Cancer Cells

Cancer remains one of the diseases with the highest worldwide incidence. Several cytotoxic approaches have been used over the years to overcome this public health threat, such as chemotherapy, radiotherapy, and photodynamic therapy (PDT). Cyanine dyes are a class of compounds that have been extensively studied as PDT sensitisers; nevertheless, their antiproliferative potential in the absence of a light source has been scarcely explored. Herein, the synthesis of eighteen symmetric mono-, tri-, and heptamethine cyanine dyes and their evaluation as potential anticancer agents is described. The influences of the heterocyclic nature, counterion, and methine chain length on the antiproliferative effects and selectivities were analysed, and relevant structure-activity relationship data were gathered. The impact of light on the cytotoxic activity of the most promising dye was also assessed and discussed. Most of the monomethine and trimethine cyanine dyes under study demonstrated a high antiproliferative effect on human tumour cell lines of colorectal (Caco-2), breast (MCF-7), and prostate (PC-3) cancer at the initial screening (10 µM). However, concentration-viability curves showed higher potency and selectivity for the Caco-2 cell line. A monomethine cyanine dye derived from benzoxazole was the most promising compound (IC₅₀ for Caco-2 = 0.67 µM and a selectivity index of 20.9 for Caco-2 versus normal human dermal fibroblasts (NHDF)) and led to Caco-2 cell cycle arrest at the G0/G1 phase. Complementary in silico studies predicted good intestinal absorption and oral bioavailability for this cyanine dye.

Nuclease-like metalloscissors: Biomimetic candidates for cancer and bacterial and viral infections therapy

Despite the extensive and rapid discovery of modern drugs for treatment of cancer, microbial infections, and viral illnesses; these diseases are still among major global health concerns. To take inspiration from natural nucleases and also the therapeutic potential of metallopeptide antibiotics such as the bleomycin family, artificial metallonucleases with the ability of promoting DNA/RNA cleavage and eventually affecting cellular biological processes can be introduced as a new class of therapeutic candidates. Metal complexes can be considered as one of the main categories of artificial metalloscissors, which can prompt nucleic acid strand scission. Accordingly, biologists, inorganic chemists, and medicinal inorganic chemists worldwide have been designing, synthesizing and evaluating the biological properties of metal complexes as artificial metalloscissors. In this review, we try to highlight the recent studies conducted on the nuclease-like metalloscissors and their potential therapeutic applications. Under the light of the concurrent Covid-19 pandemic, the human need for new therapeutics was highlighted much more than ever before. The nuclease-like metalloscissors with the potential of RNA cleavage of invading viral pathogens hence deserve prime attention.

Mechanistic Insights into the Ameliorating Effect of Melanogenesis of Psoralen Derivatives in B16F10 Melanoma Cells

The objectives of this study were to investigate the melanogenetic potential of the psoralen derivatives 5-hydroxypsoralen, 5-methoxypsoralen, 8-hydroxypsoralen, 8-methoxypsoralen, and 5,8-dimethoxypsoralen in B16F10 melanoma cells. The results indicated that melanin production is significantly stimulated in B16F10 melanoma cells with 5-methoxypsoralen, 8-methoxypsoralen, and 5,8-dimethoxypsoralen, especially for 5-methoxypsoralen (bergapten), as reported previously. In addition, Western blot results showed that the protein levels of microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2) increase after bergapten treatment for the first time. The results also showed that bergapten promotes the phosphorylation of Akt at Ser 473 and glycogen synthase kinase-3β at Ser 9. Moreover, bergapten increased the content of β-catenin in the cell cytoplasm and nucleus by reducing the phosphorylated β-catenin (p-β-catenin) content. The results also indicated that bergapten regulates melanogenesis by upregulating the phosphorylation of p38 and JNK-mitogen-activated protein kinase. Taken together, these findings suggest that the regulation of melanogenesis by bergapten may be mediated by the β-catenin and MAPK signaling pathways and that bergapten might provide new insights into the pathogenesis of pigmented diseases.

Polymethine dyes for PDT: recent advances and perspectives to drive future applications

It has been proved that the effectiveness of photodynamic therapy (PDT) is closely related to the intrinsic features of the photosensitizer (PS). Over the recent years, several efforts have been devoted to the discovery of novel and more efficient photosensitizers showing higher efficacy and lower side effects. In this context, squaraine and cyanine dyes have been reported to potentially overcome the drawbacks related to the traditional PSs. In fact, squaraines and cyanines are characterized by sharp and intense absorption bands and narrow emission bands with high extinction coefficients typically in the red and near-infrared region, good photo and thermal stability and a strong fluorescent emission in organic solvents. In addition, biocompatibility and low toxicity make them suitable for biological applications. Despite these interesting intrinsic features, their chemical instability and self-aggregation properties in biological media still limit their use in PDT. To overcome these drawbacks, the self-assembly and incorporation into smart nanoparticle systems are forwarded promising approaches that can control their physicochemical properties, providing rational solutions for the limitation of free dye administration in the PDT application. The present review summarizes the latest advances in squaraine and cyanine dyes for PDT application, analyzing the different strategies, i.e.the self-assembly and the incorporation into nanoparticles, to further enhance their photochemical properties and therapeutic potential. The in vivo assessments are still limited, thus further delaying their effective application in PDT.

Synthesis of N-aryl-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-amines and their photodynamic properties in the human skin melanoma cell line G361

A small series of N-aryl-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-amines was synthesized from easily accessible 1-phenyl-1H-pyrazol-3-ol via 7-iodo-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridine and 7-iodo-4-methyl-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridine intermediates and their subsequent use in palladium catalyzed Buchwald-Hartwig cross-coupling reaction with various anilines. Majority of the compounds were not significantly cytotoxic to melanoma G361 cells in the dark up to 10 µM concentration, but their activity could be increased by irradiation with visible blue light (414 nm). The most active compound 10 possessed EC₅₀ values of 3.5, 1.6 and 0.9 µM in cells irradiated with 1, 5 and 10 J/cm², respectively. The treatment caused generation of reactive oxygen species in cells and extensive DNA damage, documented by the comet assay and by detection of phosphorylated histone H2A.X, followed by apoptotic cell death. Our results suggest that N-aryl-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-amines could serve as a potential source of photosensitizing compounds with anticancer activities.

Feature-Based Molecular Networking-An Exciting Tool to Spot Species of the Genus Cortinarius with Hidden Photosensitizers

Fungi have developed a wide array of defense strategies to overcome mechanical injuries and pathogen infections. Recently, photoactivity has been discovered by showing that pigments isolated from Cortinarius uliginosus produce singlet oxygen under irradiation. To test if this phenomenon is limited to dermocyboid Cortinarii, six colourful Cortinarius species belonging to different classical subgenera (i.e., Dermocybe, Leprocybe, Myxacium, Phlegmacium, and Telamonia) were investigated. Fungal extracts were explored by the combination of in vitro photobiological methods, UHPLC coupled to high-resolution tandem mass spectrometry (UHPLC-HRMS2), feature-based molecular networking (FBMN), and metabolite dereplication techniques. The fungi C. rubrophyllus (Dermocybe) and C. xanthophyllus (Phlegmacium) exhibited promising photobiological activity in a low concentration range (1-7 µg/mL). Using UHPLC-HRMS2-based metabolomic tools, the underlying photoactive principle was investigated. Several monomeric and dimeric anthraquinones were annotated as compounds responsible for the photoactivity. Furthermore, the results showed that light-induced activity is not restricted to a single subgenus, but rather is a trait of Cortinarius species of different phylogenetic lineages and is linked to the presence of fungal anthraquinones. This study highlights the genus Cortinarius as a promising source for novel photopharmaceuticals. Additionally, we showed that putative dereplication of natural photosensitizers can be done by FBMN.

Innovative strategies for enhanced tumor photodynamic therapy

Photodynamic therapy (PDT) is an approved and promising treatment approach that utilizes a photosensitizer (PS) to produce cytotoxic reactive oxygen species (ROS) through irradiation to achieve tumor noninvasive therapy. However, the limited singlet oxygen generation, the nonspecific uptake of PS in normal cells, and tumor hypoxia have become major challenges in conventional PDT, impeding its development and further clinical application. This review summarizes an overview of recent advances for the enhanced PDT. The development of PDT with innovative strategies, including molecular engineering and heavy atom-free photosensitizers is presented and future directions in this promising field are also provided. This review aims to highlight the recent advances in PDT and discuss the potential strategies that show promise in overcoming the challenges of PDT.

Iridium oxide nanoparticles mediated enhanced photodynamic therapy combined with photothermal therapy in the treatment of breast cancer

Photodynamic therapy (PDT) of tumor has achieved good results, but the treatment efficiency is not high due to the lack of effective photosensitizers and tumor hypoxia. In this study, iridium dioxide nanoparticles (IrO₂ NPs) with excellent photothermal/photodynamic effects and catalase like activity were synthesized by a simple method. The combination of glucose oxidase (GOx) and IrO₂ NPs is formed by hyaluronic acid (HA), which have the activities of glucose oxidase and catalase, can target tumor sites and form in situ amplifiers in tumor microenvironment (IrO₂-GOx@HA NPs). Firstly, GOx convert the high levels of glucose in the tumor to hydrogen peroxide (H₂O₂), and then IrO₂ NPs convert H₂O₂ to oxygen (O₂), which can enhance the type II of PDT. IrO₂ NPs also can be used as a thermosensitive agent for photothermal therapy (PTT). In cancer cells, IrO₂-GOx@HA NPs-mediated amplifier enhances the effect of type II of PDT, aggravating the apoptosis of breast cancer (4T1) cells and cooperating with its own PTT to further improve the overall treatment effect. Under simulated hypoxic conditions of tumor tissue, it was found that IrO₂-GOx@HA NPs treatment can effectively relieve hypoxia inside tumor tissue. In addition, the results in vivo further proved that, IrO₂-GOx@HA NPs can enhance the role of II PDT and cooperate with PTT to treat breast cancer effectively. The results highlight the prospect of IrO₂-GOx@HA NPs in controlling and regulating tumor hypoxia to overcome the limitations of current cancer therapy.

Design and synthesis of zinc protoporphyrin IX-adamantane/cyclodextrin/cellulose nanocrystals complexes for anticancer photodynamic therapy

Two protoporphyrin IX (PpIX) adamantane derivatives were synthesized and then metallated with zinc. The Zn-PpIX derivatives, exhibiting a high singlet oxygen quantum yield, were tested for their photodynamic activity against the HT-29 cell line. In order to enhance their water-solubility and their cellular bioavailability, these photosensitizers were encapsulated into the hydrophobic cavity of cyclodextrins (CD) previously attached to cellulose nanocrystals (CNCs) via electrostatic interactions. Under illumination, the encapsulated adamantanyl-porphyrins exerted an enhanced in vitro cytotoxicity, as compared with the corresponding free photosensitizers.

Nanoscale photosensitizer with tumor-selective turn-on fluorescence and activatable photodynamic therapy treatment for COX-2 overexpressed cancer cells

Effective targeting and in situ imaging-guided treatment are particularly important for accurate clinical photodynamic therapy (PDT) of malignant tumors. Herein, we propose a single molecule, named IMC-DAH-SQ, which possesses dual-targeting components, including structure-inherent targeting (SIT) and cyclooxygenase-2 (COX-2) targeting units, and controllable turn-on near infrared (NIR) fluorescence. Due to its amphiphilicity, IMC-DAH-SQ assembles into a nanoprobe with low background fluorescence. After incubation with tumor cells, the SIT and COX-2 recognition characteristics of IMC-DAH-SQ endow it with preferential tumor-targeting activity. The strong binding with overexpressed COX-2 can collapse the nanoprobe to monomers after accumulation in tumor cells, leading to turn-on NIR fluorescence that is completely different from normal cells. Additionally, benefiting from the single molecular model tactic, the nanoprobe has the advantages of simple synthesis without ever considering the loading rate and separation between the photosensitizer and targeting unit. Other favorite features, including superior biocompatibility, weak dark toxicity, and mitochondria enrichment capability, are implemented. All these traits not only afford nanoprobe precision tumor cell targeting capability but also provide promising imaging-guided antitumor therapy. We believe that the single molecular protocol will establish a novel strategy for simultaneous diagnosis and anticancer medicine treatment utilizing versatile but small compounds.

Exploiting a Neutral BODIPY Copolymer as an Effective Agent for Photodynamic Antimicrobial Inactivation

We report the synthesis and photophysical properties of a neutral BODIPY photosensitizing copolymer (poly-8-(4-hydroxymethylphenyl)-4,4-difluoro-2,6-diethynyl-4-bora-3a,4a-diaza-s-indacene) containing ethynylbenzene links between the BODIPY units. The copolymer absorbs further towards the red in the UV-vis spectrum compared to the BODIPY precursor. Photolysis of the polymer produces a singlet excited state which crosses to the triplet surface in less than 300 ps. This triplet state was used to form singlet oxygen with a quantum yield of 0.34. The steps leading to population of the triplet state were studied using time-resolved spectroscopic techniques spanning the pico- to nanosecond timescales. The ability of the BODIPY polymer to generate a biocidal species for bactericidal activity in both solution- and coating-based studies was assessed. When the BODIPY copolymer was dropcast onto a surface, 4 log and 6 log reductions in colony forming units/ml representative of Gram-positive and Gram-negative bacteria, respectively, under illumination at 525 nm were observed. The potent broad-spectrum antimicrobial activity of a neutral metal-free copolymer when exposed to visible light conditions may have potential clinical applications in infection management.

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

Photodynamic therapy (PDT), a therapeutic mode involving light triggering, has been recognized as an attractive oncotherapy treatment. However, nonnegligible challenges remain for its further clinical use, including finite tumor suppression, poor tumor targeting, and limited therapeutic depth. The photosensitizer (PS), being the most important element of PDT, plays a decisive role in PDT treatment. This review summarizes recent progress made in the development of PSs for overcoming the above challenges. This progress has included PSs developed to display enhanced tolerance of the tumor microenvironment, improved tumor-specific selectivity, and feasibility of use in deep tissue. Based on their molecular photophysical properties and design directions, the PSs are classified by parent structures, which are discussed in detail from the molecular design to application. Finally, a brief summary of current strategies for designing PSs and future perspectives are also presented. We expect the information provided in this review to spur the further design of PSs and the clinical development of PDT-mediated cancer treatments.

Synthesis and Photoactivated Toxicity of 2-Thiophenylfuranocoumarin Induce Midgut Damage and Apoptosis in Aedes aegypti Larvae

Furanocoumarins are photoactive compounds derived from secondary plant metabolites. They possess many bioactivities, including antioxidative, anticancer, insecticidal, and bactericidal activities. Here, we designed a new scheme for synthesizing 2-arylfuranocoumarin derivatives by condensation, esterification, bromination, and Wittig reaction. We found that 2-thiophenylfuranocoumarin (Iy) had excellent photosensitive activity. Three Iy concentrations (LC₂₅, LC₅₀, and LC₇₅) were used to treat the fourth instar larvae of Aedes aegypti (A. aegypti). The photoactivated toxicity, sublethal dose, mitochondrial dysfunction, oxidative stress level, intestinal barrier dysfunction, and apoptosis were studied. The results showed that Iy induced reactive oxygen species (ROS) production in midgut cells under ultraviolet light. Ultrastructural analysis demonstrated that mitochondria were damaged, and the activities of related enzymes were inhibited. Ultimately, Iy exposure led to excessive ROS production followed by the inhibition of antioxidant enzymes, including SOD, CAT, GPx, and GR, which diminished ROS elimination and escalated oxidative stress in midgut cells, aggravating the degree of oxidative damage in these cells. Histopathological changes were observed in the midgut, which led to intestinal barrier dysfunction. When the elimination of ROS was blocked and it accumulated in cells, apoptosis-related genes, including AeDronc, AeCaspase7, and AeCaspase8, were induced and activated. In addition, Iy affected the growth and development of A. aegypti at sublethal concentrations, and there was an obvious post-lethal effect. Thus, we found that Iy caused midgut damage and apoptosis in A. aegypti larvae under ultraviolet light, which preliminarily revealed the mode of action of Iy in A. aegypti.

Development of red-light cleavable PEG-PLA nanoparticles as delivery systems for cancer therapy

The development of targeted delivery systems can improve the selectivity of cancer drugs. Additionally, a system that promotes the controlled delivery of the drug triggered by an external stimulus in the exact target tissue is highly desirable. Regarding the light stimulus, the NIR window (650-950 nm) is the most suitable due to its higher capacity of penetration in human tissues and less harmful effects on normal cells. In this work, new red-light-responsive nanoparticles for doxorubicin delivery were developed. The nanoparticles were based on cleavable di-block copolymers of poly(ethylene glycol) (PEG) and poly(lactic acid) (PLA) linked by a red-light sensitive segment (1,2-bis(2-hydroxyethylthio)ethylene, BHETE). The PEG-BHETE-PLA copolymers were synthesized under mild conditions and exhibited a narrow polydispersity. The nanoparticles presented a size between 53 and 133 nm, with a doxorubicin loading capacity between 1.2 and 4.4 wt%. Release study of the encapsulated doxorubicin confirms the light-triggered nanoparticle disassembly process. In vitro cytotoxicity tests in MCF7 cell line, for the light-triggered nanoparticles, showed a decrease in cancer cells' viability higher than 25% compared to non-irradiated cells. Due to the promising results obtained with the light-sensitive PEG-BHETE-PLA nanoparticles, these materials have great potential to be used in drug delivery systems for cancer therapy.

Conjugation of Phthalocyanine Photosensitizer with Poly(amidoamine) Dendrimer: Improved Solubility, Disaggregation and Photoactivity Against HepG2 Cells

OBJECTIVE

To improve solubility and to reduce aggregation, ZnPcC4 was conjugated to a third-generation poly-amidoamine dendrimer with amino end group (G3-PAMAM-NH2), which acts as a novel photodynamic therapy (PDT) drug carrier system.

METHODS

The phthalocyanines were synthesized by construction reaction. The nano drug was obtained from the conjugation of ZnPcC4 to G3-PAMAM-NH2, using EDC and NHS as coupling agents. The ZnPcC4@G3-PAMAM-NH2 conjugation was characterized by UV-Vis and MS. The 1O2 quantum yield of ZnPcC4@G3-PAMAM-NH2 in water was measured by the chemiluminescence method. The in vitro PDT responses of the studied photosensitizers were studied in hepatocellular carcinoma cell line HepG2 by MTT assay.

RESULTS

At ZnPcC4/G3-PAMAM-NH2 raw ratio of 100/1, the ZnPcC4 conjugate had improved solubility and reduced aggregation tendency in aqueous solution. At this optimum molar ratio, ZnPcC4- G3-PAMAM-NH2 inhibited HepG2 cells, with a half-maximal inhibitory concentration of 1.67 µg/mL upon infrared light exposure. The controls, including dark conditions, or media as well as G3-PAMAM-NH2 exposure, exhibited no inhibitory response.

CONCLUSION

The conjugation of phthalocyanine photosensitizer ZnPcC4 to poly-amidoamine dendrimer G3-PAMAM-NH2 improved the PDT outcomes, in which the optimized binding ratio of ZnPcC4 to G3-PAMAM-NH2 was 6:1.

Fatty Acid Conjugates of Toluidine Blue O as Amphiphilic Photosensitizers: Synthesis, Solubility, Photophysics and Photochemical Properties†

Toluidine blue O (TBO) is a water-soluble photosensitizer that has been used in photodynamic antimicrobial and anticancer treatments, but suffers from limited solubility in hydrophobic media. In an effort to incrementally increase TBO's hydrophobicity, we describe the synthesis of hexanoic (TBOC6) and myristic (TBOC14) fatty acid derivatives of TBO formed in low to moderate percent yields by condensation with the free amine site. Covalently linking 6 and 14 carbon chains led to modifications of not only TBO's solubility, but also its photophysical and photochemical properties. TBOC6 and TBOC14 derivatives were more soluble in organic solvents and showed hypsochromic shifts in their absorption and emission bands. The solubility in phosphate buffer solution was low for both TBOC6 and TBOC14, but unexpectedly slightly greater in the latter. Both TBOC6 and TBOC14 showed decreased triplet excited-state lifetimes and singlet oxygen quantum yields in acetonitrile, which was attributed to heightened aggregation of these conjugates particularly at high concentrations due to the hydrophobic "tails." While in diluted aqueous buffer solution, indirect measurements showed similar efficiency in singlet oxygen generation for TBOC14 compared to TBO. This work demonstrates a facile synthesis of fatty acid TBO derivatives leading to amphiphilic compounds with a delocalized cationic "head" group and hydrophobic "tails" for potential to accumulate into biological membranes or membrane/aqueous interfaces in PDT applications.

Application of rare earth-doped nanoparticles in biological imaging and tumor treatment

Rare earth-doped nanoparticles have been widely used in disease diagnosis, drug delivery, tumor therapy, and bioimaging. Among various bioimaging methods, the fluorescence imaging technology based on the rare earth-doped nanoparticles can visually display the cell activity and lesion evolution in living animals, which is a powerful tool in biological technology and has being widely applied in medical and biological fields. Especially in the band of near infrared (700–1700 nm), the emissions show the characteristics of deep penetration due to low absorption, low photon scattering, and low autofluorescence interference. Furthermore, the rare earth-doped nanoparticles can be endowed with the water solubility, biocompatibility, drug-loading ability, and the targeting ability for different tumors by surface functionalization. This confirms its potential in the cancer diagnosis and treatment. In this review, we summarized the recent progress in the application of rare earth-doped nanoparticles in the field of bioimaging and tumor treatment. The luminescent mechanism, properties, and structure design were also discussed.

Exploring BODIPY Derivatives as Singlet Oxygen Photosensitizers for PDT

This minireview is devoted to honoring the memory of Dr. Thomas Dougherty, a pioneer of modern photodynamic therapy (PDT). It compiles the most important inputs made by our research group since 2012 in the development of new photosensitizers based on BODIPY chromophore which, thanks to the rich BODIPY chemistry, allows a finely tuned design of the photophysical properties of this family of dyes to serve as efficient photosensitizers for the generation of singlet oxygen. These two factors, photophysical tuning and workable chemistry, have turned BODIPY chromophore as one of the most promising dyes for the development of improved photosensitizers for PDT. In this line, this minireview is mainly related to the establishment of chemical methods and structural designs for enabling efficient singlet oxygen generation in BODIPYs. The approaches include the incorporation of heavy atoms, such as halogens (iodine or bromine) in different number and positions on the BODIPY scaffold, and also transition metal atoms, by their complexation with Ir(III) center, for instance. On the other hand, low-toxicity approaches, without involving heavy metals, have been developed by preparing several orthogonal BODIPY dimers with different substitution patterns. The advantages and drawbacks of all these diverse molecular designs based on BODIPY structural framework are described.

Structurally Characterized BODIPY-Appended Oxidovanadium(IV) β-Diketonates for Mitochondria-Targeted Photocytotoxicity

Mixed-ligand oxidovanadium(IV) β-diketonates having NNN-donor dipicolylamine-conjugated to boron-dipyrromethene (BODIPY in L₁) and diiodo-BODIPY (in L₂) moieties, namely, [VO(L₁)(acac)]Cl (1), [VO(L₂)(acac)]Cl (2), and [VO(L₁)(dbm)]Cl (3), where acac and dbm are monoanionic O,O-donor acetylacetone and 1,3-diphenyl-1,3-propanedione, were prepared, characterized, and tested for their photoinduced anticancer activity in visible light. Complexes 1 and 2 were structurally characterized as their PF₆ ^- salts (1a and 2a) by X-ray crystallography. They showed V^IVN₃O₃ six-coordinate geometry with dipicolylamine base as the facial ligand. The non-iodinated BODIPY complexes displayed absorption maxima at ∼501 nm, while it is ∼535 nm for the di-iodinated 2 in 10% DMSO-PBS buffer medium (pH = 7.2). Complexes 1 and 3 being green emissive (λ_em, ∼512 nm; λ_ex, 470 nm; Φ_F, ∼0.10) in 10% aqueous DMSO were used for cellular imaging studies. Complex 3 localized primarily in the mitochondria of the cervical HeLa cells with a co-localization coefficient value of 0.7. The non-emissive diiodo-BODIPY complex 2 showed generation of singlet oxygen (Φ_Δ ≈ 0.47) on light activation. Annexin-V assay showed singlet oxygen-mediated cellular apoptosis, making this complex a targeted PDT agent.

Furocoumarins as multi-target agents in the treatment of cystic fibrosis

Multi-target molecular entities, offer a path to progress both in understanding causes of disease and in defining effective small molecule treatments. Coumarin and its derivatives belong to an important group of natural compounds with diverse biological properties. They are found in vegetables and plants for which literature reports thousands of publications for the great variety of biological applications among which the photoprotective effects, thus being considered multi-targeting agents. Their furan condensed analogues constitute the family of furocoumarins, less represented in the literature, endowed with photosensitizing properties and often used for the treatment of skin diseases such as vitiligo and psoriasis. Despite the study of biological properties of linear and angular furocumarins dates back to ancient times, mainly as photosensitizers, these small molecules still represent an attractive scaffold for further development and applications in several therapeutic fields. The aim of the present review is to summarize the most promising chemical entities belonging to the class of furocumarins and coumarins, emerged in the last decades, and the methods used for their synthesis with a particular focus on main targets involved in the cystic fibrosis treatment.

Synthesis, Photochemical and In Vitro Cytotoxic Evaluation of New Iodinated Aminosquaraines as Potential Sensitizers for Photodynamic Therapy

In this work, several benzothiazole-based aminosquaraine dyes, displaying strong absorption within the so-called phototherapeutic window (650⁻800 nm), were synthesized. The ability, of all the new dyes, to generate singlet oxygen was assessed by determining the correspondent phosphorescence emission and through the comparison with a standard. The quantum yields of singlet oxygen generation were determined and exhibited to be strongly dependent on the nature of the amino substituents introduced in the squaric ring. The photodynamic activity of the synthesized dyes was tested against four human tumor cell lines: breast (MCF-7), lung (NCI-H460), cervical (HeLa) and hepatocellular (HepG2) carcinomas; and a non-tumor porcine liver primary cell culture (PLP2). All the compounds synthesized were found to be able to inhibit tumor cells growth upon irradiation more than in the dark, in most of the cases, very significantly. Considering the photodynamic activity exhibited and the low toxicity displayed for the non-tumor cells, some of the synthetized dyes can be regarded as potential candidates as photosensitizers for PDT.

Fourfold Filtered Statistical/Computational Approach for the Identification of Imidazole Compounds as HO-1 Inhibitors from Natural Products

Over-regulation of Heme oxygenase 1 (HO-1) has been recently identified in many types of human cancer, and in these cases, poor clinical outcomes are normally reported. Indeed, the inhibition of HO-1 is being considered as an anticancer approach. Imidazole scaffold is normally present in most of the classical HO-1 inhibitors and seems indispensable to the inhibitory activity due to its strong interaction with the Fe(II) of the heme group. In this paper, we searched for new potentially HO-1 inhibitors among three different databases: Marine Natural Products (MNP), ZINC Natural Products (ZNP) and Super Natural II (SN2). 484,527 compounds were retrieved from the databases and filtered through four statistical/computational filters (2D descriptors, 2D-QSAR pharmacophoric model, 3D-QSAR pharmacophoric model, and docking). Different imidazole-based compounds were suggested by our methodology to be potentially active in inhibiting the HO-1, and the results have been rationalized by the bioactivity of the filtered molecules reported in the literature.

Intracellular Catalysis with Selected Metal Complexes and Metallic Nanoparticles: Advances toward the Development of Catalytic Metallodrugs

Platinum-containing drugs (e.g., cisplatin) are among the most frequently used chemotherapeutic agents. Their tremendous success has spurred research and development of other metal-based drugs, with notable achievements. Generally, the vast majority of metal-based drug candidates in clinical and developmental stages are stoichiometric agents, i.e., each metal complex reacts only once with their biological target. Additionally, many of these metal complexes are involved in side reactions, which not only reduce the effective amount of the drug but may also cause toxicity. On a separate note, transition metal complexes and nanoparticles have a well-established history of being potent catalysts for selective molecular transformations, with examples such as the Mo- and Ru-based catalysts for metathesis reactions (Nobel Prize in 2005) or palladium catalysts for C-C bond forming reactions such as Heck, Negishi, or Suzuki reactions (Nobel Prize in 2010). Also, notably, no direct biological equivalent of these transformations exists in a biological environment such as bacteria or mammalian cells. It is, therefore, only logical that recent interest has focused on developing transition-metal based catalytic systems that are capable of performing transformations inside cells, with the aim of inducing medicinally relevant cellular changes. Because unlike in stoichiometric reactions, a catalytically active compound may turn over many substrate molecules, only very small amounts of such a catalytic metallodrug are required to achieve a desired pharmacologic effect, and therefore, toxicity and side reactions are reduced. Furthermore, performing catalytic reactions in biological systems also opens the door for new methodologies to study the behavior of biomolecules in their natural state, e.g., via in situ labeling or by increasing/depleting their concentration at will. There is, of course, an art to the choice of catalysts and reactions which have to be compatible with biological conditions, namely an aqueous, oxygen-containing environment. In this review, we aim to describe new developments that bring together the far-distant worlds of transition-metal based catalysis and metal-based drugs, in what is termed "catalytic metallodrugs". Here we will focus on transformations that have been performed on small biomolecules (such as shifting equilibria like in the NAD⁺/NADH or GSH/GSSG couples), on non-natural molecules such as dyes for imaging purposes, or on biomacromolecules such as proteins. Neither reactions involving release (e.g., CO) or transformation of small molecules (e.g., ¹O₂ production), degradation of biomolecules such as proteins, RNA or DNA nor light-induced medicinal chemistry (e.g., photodynamic therapy) are covered, even if metal complexes are centrally involved in those. In each section, we describe the (inorganic) chemistry involved, as well as selected examples of biological applications in the hope that this snapshot of a new but quickly developing field will indeed inspire novel research and unprecedented interactions across disciplinary boundaries.

Multinuclear Ru(ii) and Ir(iii) decorated tetraphenylporphyrins as efficient PDT agents

Two novel multi-metallic porphyrin complexes were synthesised and evaluated as effective PDT agents against human breast epithelial cells (SKBR-3).