Oncologic photodynamic therapy: clinical strategies that modulate mechanisms of action

Cobaltabis(dicarbollide) Interaction with DNA Resolved at the Atomic Scale

Boron neutron capture therapy represents a promising avenue for cancer treatment that requires nontoxic drugs with a high boron content efficiently distributed into cancerous cells. The metallacarborane o-cobaltabis(dicarbollide) ([COSAN]-) fulfills these requirements and constitutes an attractive candidate. Nevertheless, the interaction of this promising drug with nucleic acids, the assumed target of the biological damage, is poorly understood since contradictory results are reported in the literature. This work establishes the DNA/[COSAN]- interaction strength, mechanism, and time scale at the atomistic level by using a combination of microsecond-molecular dynamics and hybrid quantum mechanics/molecular mechanics simulations and by quantifying the absolute binding free energy. Results show that the DNA/[COSAN]- interaction is highly dependent on the ionic strength of the medium. A relatively weak DNA major groove binding (ΔGbind= -2.49 kcal/mol) driven mostly by dihydrogen B-H···H-N bonding is observed in the simulations only at a high NaCl concentration, whereas DNA intercalation mode is deemed highly unlikely.

Photodynamic Therapy in the Treatment of Cancer-The Selection of Synthetic Photosensitizers

Photodynamic therapy (PDT) is a promising cancer treatment method that uses photosensitizing (PS) compounds to selectively destroy tumor cells using laser light. This review discusses the main advantages of PDT, such as its low invasiveness, minimal systemic toxicity and low risk of complications. Special attention is paid to photosensitizers obtained by chemical synthesis. Three generations of photosensitizers are presented, starting with the first, based on porphyrins, through the second generation, including modified porphyrins, chlorins, 5-aminolevulinic acid (ALA) and its derivative hexyl aminolevulinate (HAL), to the third generation, which is based on the use of nanotechnology to increase the selectivity of therapy. In addition, current research trends are highlighted, including the search for new photosensitizers that can overcome the limitations of existing therapies, such as heavy-atom-free nonporphyrinoid photosensitizers, antibody-drug conjugates (ADCs) or photosensitizers with a near-infrared (NIR) absorption peak. Finally, the prospects for the development of PDTs are presented, taking into account advances in nanotechnology and biomedical engineering. The references include both older and newer works. In many cases, when writing about a given group of first- or second-generation photosensitizers, older publications are used because the properties of the compounds described therein have not changed over the years. Moreover, older articles provide information that serves as an introduction to a given group of drugs.

Porphyrin-based covalent organic frameworks from design, synthesis to biological applications

Covalent organic frameworks (COFs) constitute a class of highly functional porous materials composed of lightweight elements interconnected by covalent bonds, characterized by structural order, high crystallinity, and large specific surface area. The integration of naturally occurring porphyrin molecules, renowned for their inherent rigidity and conjugate planarity, as building blocks in COFs has garnered significant attention. This strategic incorporation addresses the limitations associated with free-standing porphyrins, resulting in the creation of well-organized porous crystal structures with molecular-level directional arrangements. The unique optical, electrical, and biochemical properties inherent to porphyrin molecules endow these COFs with diversified applications, particularly in the realm of biology. This review comprehensively explores the synthesis and modulation strategies employed in the development of porphyrin-based COFs and delves into their multifaceted applications in biological contexts. A chronological depiction of the evolution from design to application is presented, accompanied by an analysis of the existing challenges. Furthermore, this review offers directional guidance for the structural design of porphyrin-based COFs and underscores their promising prospects in the field of biology.

Cytotoxic and Immunomodulatory Effects of Hypericin as a Photosensitizer in Photodynamic Therapy Used on Skin Cell Cultures

Determination of the hypericin-photodynamic (HY-PDT) effect on the secretion of cytokines secreted by the skin cells, may be the basis for using the immunomodulatory effect of photodynamic action in the treatment of inflammatory skin diseases. The study aimed to evaluate the cytotoxic and immunomodulatory effects of hypericin (HY) in photodynamic therapy (PDT) performed in vitro on cultures of selected skin cell lines. The study used two human cell lines, primary dermal fibroblast (HDFa) and primary epidermal keratinocytes (HEKa). The MTT test was used to define the metabolic activity of treated cells. Cell supernatants subjected to sublethal PDT were assessed to determine the interleukins: IL-2, IL-8, IL-10, IL-11, IL-19, IL-22, and metalloproteinase 1 (MMP-1). The results confirm the destructive effect of HY-PDT and the immunomodulatory effects of sublethal doses on the selected skin cells, depending on the concentration of HY and the light doses. No statistically significant differences were noted in IL-2 and IL-10 concentration after HY-PDT for HEKa and HDFa lines. After using HY-PDT, the concentration of IL-8, MMP-1, IL-22, and IL-11 significantly decreased in the HEKa line. Moreover, the concentration of IL-19 and MMP-1 significantly decreased in the HDFa line. The concentration of IL-11 in the HDFa line after using only the HY, without the light, increased but decreased after HY-PDT. Our experiment confirmed that HY-PDT has not only a cytotoxic effect but, used in sublethal doses, also presents immunomodulatory properties. These may be an advantage of HY-PDT when used in the treatment of persistent skin inflammation, connected with the release of pro-inflammatory cytokines resistant to conventional treatment methods.

Tools of clinical Photodynamic Therapy (PDT): A Mini Compendium

Unlike surgical instruments and endoscopic equipment, Photodynamic Therapy (PDT) devices are not readily available or accessible to the clinicians who may like to add this form of treatment modality for selected patients and on an ad hock basis. There is in fact a vacuum in finding the "tools" of PDT for those clinicians who are not part of a "Centre" with a built-in knowledge base and contacts for manufacturers. In this compendium the Yorkshire Laser Centre /YLC in the UK, (the Project of the Moghissi Laser Trust - (Charity number 326689) requested three experienced clinicians (RA, ZH, KM) to produce essential information on the use of and equipment for PDT in the clinic. The YLC also sponsored a researcher (ID) to search and compile a detailed but non-exhaustive list of approved photosensitizing agents, pharmaceutical companies, light sources and laser manufacturers with appropriate delivery devices for PDT. Thus, this Mini -Compendium is the end result of what is hoped to be a useful adjunct for practitioners, scientists and students of PDT.

The role of redox-mediated lysosomal dysfunction and therapeutic strategies

Redox homeostasis refers to the dynamic equilibrium between oxidant and reducing agent in the body which plays a crucial role in maintaining normal physiological activities of the body. The imbalance of redox homeostasis can lead to the development of various human diseases. Lysosomes regulate the degradation of cellular proteins and play an important role in influencing cell function and fate, and lysosomal dysfunction is closely associated with the development of various diseases. In addition, several studies have shown that redox homeostasis plays a direct or indirect role in regulating lysosomes. Therefore, this paper systematically reviews the role and mechanisms of redox homeostasis in the regulation of lysosomal function. Therapeutic strategies based on the regulation of redox exerted to disrupt or restore lysosomal function are further discussed. Uncovering the role of redox in the regulation of lysosomes helps to point new directions for the treatment of many human diseases.

Nanoencapsulation of Methylene-Blue for Enhanced Skin Cancer Cell Phototoxicity and Cutaneous Penetration in Association with Sonophoresis

Photodynamic therapy (PDT) using methylene blue (MB) as a photosensitizer has emerged as an alternative treatment for skin cancers, such as squamous cell carcinoma (SCC). To increase the cutaneous penetration of the drug, some strategies are used, such as the association of nanocarriers and physical methods. Thus, herein we address the development of nanoparticles based on poly-Ɛ-caprolactone (PCL), optimized with the Box-Behnken factorial design, for topical application of MB associated with sonophoresis. The MB-nanoparticles were developed using the double emulsification-solvent evaporation technique and the optimized formulation resulted in an average size of 156.93 ± 8.27 nm, a polydispersion index of 0.11 ± 0.05, encapsulation efficiency of 94.22 ± 2.19% and zeta potential of -10.08 ± 1.12 mV. Morphological evaluation by scanning electron microscopy showed spherical nanoparticles. In vitro release studies show an initial burst compatible with the first-order mathematical model. The nanoparticle showed satisfactory generation of reactive oxygen species. The MTT assay was used to assess cytotoxicity and IC₅₀; values of 79.84; 40.46; 22.37; 9.90 µM were obtained, respectively, for the MB-solution and the MB-nanoparticle without and with light irradiation after 2 h of incubation. Analysis using confocal microscopy showed high cellular uptake for the MB-nanoparticle. With regard to skin penetration, a higher concentration of MB was observed in the epidermis + dermis, corresponding to 9.81, 5.27 μg/cm² in passive penetration and 24.31 and 23.81 μg/cm² after sonophoresis, for solution-MB and nanoparticle-MB, respectively. To the best of our knowledge, this is the first report of MB encapsulation in PCL nanoparticles for application in skin cancer using PDT.

Revisiting the evidence of photodynamic therapy for oral potentially malignant disorders and oral squamous cell carcinoma: an overview of systematic reviews

BACKGROUND

This study summarized the available evidence about the use of photodynamic therapy (PDT) for the management of oral potentially malignant disorders (OPMD) and oral squamous cell carcinoma (OSCC).

METHODS

An overview of systematic reviews was undertaken based on the 2020 PRISMA statement. Electronic searches were performed in five databases. Studies published up to November 2022 were included. Risk of bias was assessed with the AMSTAR 2 tool.

RESULTS

A total of 30 studies enrolling 9,245 individuals with OPMD (n=7,487) or OSCC (n=1,758) met the selection criteria. All studies examined the efficacy and/or safety of PDT. OPMD were investigated individually in 82.8% of the studies, the most common being oral lichen planus and actinic cheilitis. OSCC was addressed separately in 10.3% of the studies, while only 6.9% evaluated both OPMD and OSCC. Fourteen different types of photosensitizers were described. PDT was used according to the following setting parameters: 417-670 nm, 10-500 mW/cm², 1.5-200 J/cm², and 0.5-143 minutes. Regarding OPMD, leukoerythroplakia showed the best response rates, while oral lichen planus presented a partial or no response in nearly 75% of documented cases. A complete response was observed in 85.9% of OSCC cases, while 14.1% had no resolution.

CONCLUSION

Overall, the response to PDT depended on the type of OPMD/OSCC and the parameters used. Although PDT is an emerging candidate for the treatment of OPMD and OSCC, there is heterogeneity of the methodologies used and the clinical data obtained, particularly regarding the follow-up period.

Combining Radiotherapy (RT) and Photodynamic Therapy (PDT): Clinical Studies on Conventional RT-PDT Approaches and Novel Nanoparticle-Based RT-PDT Approaches under Preclinical Evaluation

Radiotherapy (RT) is the primary standard of care for many locally advanced cancers. Often times, however, the efficacy of RT is limited due to radio-resistance that cancer cells develop. Photodynamic therapy (PDT) has gained importance as an alternative local therapy. Because its mechanism involves minimal acquired resistance, PDT is a useful adjunct to RT. This review discusses recent advances in combining RT with PDT for cancer treatment. In the first part of this review, we will discuss clinical trials on RT + PDT combination therapies. All these approaches suffer from the same inherent limitations as any current PDT methods; (i) visible light has a short penetration depth in human tissue (<∼10 mm), and (ii) it is difficult to illuminate the entire tumor homogeneously by external/interstitial laser irradiation. To address these limitations, scintillating nanoparticle-mediated RT-PDT approaches have been explored in which nanoparticles convert X-rays (RT) into visible light (PDT); high-energy X-rays can reach deep into the body to irradiate cancers uniformly and precisely. The second part of this review will discuss recent efforts in developing and applying nanoparticles for RT-PDT applications.

Hydrogen sulfide decreases photodynamic therapy outcome through the modulation of the cellular redox state

Photodynamic therapy (PDT) is a non-surgical treatment that has been approved for its human medical use in many cancers. PDT involves the interaction of a photosensitizer (PS) with light. The amino acid 5- aminolevulinic acid (ALA) can be used as a pro-PS, leading to the synthesis of Protoporphyrin IX. Hydrogen sulfide (H₂S) is an endogenously produced gas that belongs to the gasotransmitter family, which can diffuse through biological membranes and have relevant physiological effects such as cardiovascular functions, vasodilatation, inflammation, cell cycle and neuro-modulation. It was also proposed to have cytoprotective effects. We aimed to study the modulatory effects of H₂S on ALAPDT in the mammary adenocarcinoma cell line LM2. Exposure of the cells to NaHS (donor of H₂S) in concentrations up to 10 mM impaired the response to ALA-PDT in a dose-dependent manner. The addition of 3 doses of NaHS showed the highest effect. This decreased response to the photodynamic treatment was correlated to an increase in the GSH levels, catalase activity, a dose dependent reduction of PpIX and increased intracellular ALA, decreased levels of oxidized proteins and a decrease of PDT-induced ROS. NaHS also reduced the levels of singlet oxygen in an in vitro assay. H₂S also protected other cells of different origins against PDT mediated by ALA and other PSs. These results suggest that H₂S has a role in the modulation of the redox state of the cells, and thus impairs the response to ALA-PDT through multifactor pathways. These findings could contribute to developing new strategies to improve the effectiveness of PDT particularly mediated by ALA or other ROS-related treatments.

Biomimetic smart mesoporous carbon nanozyme as a dual-GSH depletion agent and O2 generator for enhanced photodynamic therapy

Photodynamic therapy (PDT) has been thriving in the theranostics of cancer in recent years. However, due to a series of problems such as high concentration of GSH and insufficient O₂ partial pressure in the tumor micro-environment, it is difficult to achieve the desired therapeutic effects with single PDT. Mesoporous carbon (MC-COOH) has been widely used in photothermal therapy (PTT) due to its high photothermal conversion efficiency and drug loading. In addition, we have discovered that MC-COOH owned high-efficiency glutathione oxidase-like activity for intracellular lasting GSH consumption. Hence, a smart mesoporous carbon nanozyme (CCM) was designed as a dual-GSH depletion agent and O₂ generator combined with PTT to overcome the dilemma of PDT. MnO₂-doped carbon nanozyme (MC-Mn) was developed as the photothermal vehicles for the efficient loading of photosensitizer (Ce6). Subsequently, 4T1 membrane-coated nanozyme (Ce6/CCM) was constructed to achieve homologous targeting capability. The carbon nanozyme owned the sustained dual-GSH depletion function through MC-COOH and MnO₂, which greatly destroyed the antioxidant system of the tumor. Meanwhile, MnO₂ could produce affluent O₂ in the presence of H₂O₂, thereby alleviating the hypoxic state of tumor tissues and further promoting the generation of ROS. In addition, the novel carbon nanozyme was designed as photoacoustic imaging (PAI) agent and magnetic resonance imaging (MRI) contrast for real-time imaging during tumor therapy. In summary, this work showed that the biomimetic carbon nanozyme could be used as dual-GSH depletion agent and O₂ generator for dual-mode imaging-guided PTT-PDT. STATEMENT OF SIGNIFICANCE: - MC-COOH with highly efficient GSH-OXD activity was first discovered and applied in PDT. - MnO₂ acted as an O₂ generator and GSH depletion agent to enhance PDT. - The tumor-targeting ability of the nanozyme was improved by cell membrane camouflage. - CCM nanozyme possesses both PAI and MRI dual-mode imaging modalities to guide PDT/PTT.

Picolylamine-functionalized benz[e]indole squaraine dyes: Synthetic approach, characterization and in vitro efficacy as potential anticancer phototherapeutic agents

Squaraine dyes are a family of compounds known for their relevant photophysical and photochemical properties potentially useful as photosensitizing agents. Since pyridines have been introduced into the skeleton of several families of compounds to enhance their pharmacological activity, and this approach had not yet been performed on squaraines, novel dyes derived from benz[e]indole functionalized with picolyl- and dipicolylamine and N-ethyl and -hexyl chains were designed and synthesized. After being fully characterized, their interaction with human albumin was in vitro and in silico evaluated. Dyes were further assessed for their phototoxicity activity, and the most interesting ones were studied regarding cell localization and induction of morphological cell changes, genotoxicity, apoptosis and cell cycle arrest. The molecules with N-ethyl chains showed the greatest in vitro light-dependent cytotoxic effects, particularly the zwitterionic squaraine dye and the one bearing a single pyridine unit, which also exhibited a more significant interaction with human albumin. Phenotypically, the cells incubated with these squaraines became smaller and rounded after irradiation, the effects varying with the tested concentration. Genotoxic effects were observed even without irradiation, being more evident for the N-ethyl picolylamine-derived dye. The fluorescence emitted by Rhodamine 123 largely coincided with that emitted by the dyes, suggesting that they are found preferentially in mitochondria. After irradiation, an increase in the subG1 population was verified by propidium iodide-staining analysis by flow cytometry, indicative of cell death by apoptosis.

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.

A rapid antimicrobial photodynamic water treatment strategy utilizing a xanthene dye with subsequent removal by Goethite Nanoparticles

Although widely accepted as a water sterilisation technique, chlorination results in the production of potentially harmful by-products, mainly Trihalomethanes. Furthermore, the chlorination process requires specialised infrastructure, management and high costs. In this research paper a potential alternative sterilisation technique was investigated. This rapid three-step process utilized Goethite Nanoparticles and the photosensitising capabilities of a xanthene dye. Rose Bengal (RB) a compound primarily used as a stain to diagnose damaged tissue in the eye was utilized under visible light excitation to sterilise water containing gram-positive Staphylococcus aureus and Bacillus cereus. Bacterial reductions (cfu/ml) of up to 6log10 are reported at RB concentrations of 0.5 mg/L and 10 mg/L for S. aureus and B. cereus, respectively. Goethite Nanoparticles (GNP's), an iron oxyhydroxide, were synthesised by co-precipitation of iron salts and used to adsorb RB post-sterilisation. Poly-vinyl Alcohol (PVA) functionalised GNP's were synthesised to highlight the adsorbent capabilities of the GNP surface. The adsorption capacity for uncoated GNPs was 476.19 mg/g, this reduced to 170.4 mg/g for PVA-GNP's, highlighting the highly porous nature of the synthesised GNP surface. Adsorption was optimal in slightly acidic conditions (pH5-6). The adsorption parameters best followed Lagergens Pseudo-second order kinetics with correlation coefficients close to unity. At the highest envisaged RB concentration (10 mg/L) approximately 20 mg/L GNP's was required to remove the dye from solution post-treatment. Flame Atomic Absorption analysis of the water post-removal revealed Iron concentrations of 0.058 mg/L. This correlates to removal efficacy of 99.71% with residual iron levels below the EU recommended limit of 0.2 mg/L.

A new natural detector for irradiations with blue LED light source in photodynamic therapy measurements via UV-Vis spectroscopy

Photodynamic therapy has been recently studied, bringing innovations regarding the reduction of exposure time to light by the patient. This work aimed to investigate the feasibility of using Coutarea hexandra (Jacq.) K. Schum (CHS) as a detector in photodynamic therapy measurements. For this, an irradiator containing a blue LED bulb lamp was utilized. The CHS samples were irradiated with ten doses from 0.60 up to 6.0 kJ/cm², and six concentrations were prepared (1, 2, 3, 4, 5, and 6 mg/ml) for the CHS detector samples. After irradiation, the detector samples were evaluated using UV-Vis spectrophotometry. The results showed the behavior of the CHS detector with doses and concentrations, its sensitivity, and its linearity was also evaluated both by Wavelength Method (WM) and the Kernel Principal Component Regression (KPCR) Statistical Method. The values obtained indicate that this method can be applied to the CHS sample detector. In conclusion, the CHS is a promising detector in the field of photodynamic therapy.

Photodynamic Therapy for the Treatment and Diagnosis of Cancer-A Review of the Current Clinical Status

Photodynamic therapy (PDT) has been used as an anti-tumor treatment method for a long time and photosensitizers (PS) can be used in various types of tumors. Originally, light is an effective tool that has been used in the treatment of diseases for ages. The effects of combination of specific dyes with light illumination was demonstrated at the beginning of 20th century and novel PDT approaches have been developed ever since. Main strategies of current studies are to reduce off-target effects and improve pharmacokinetic properties. Given the high interest and vast literature about the topic, approval of PDT as the first drug/device combination by the FDA should come as no surprise. PDT consists of two stages of treatment, combining light energy with a PS in order to destruct tumor cells after activation by light. In general, PDT has fewer side effects and toxicity than chemotherapy and/or radiotherapy. In addition to the purpose of treatment, several types of PSs can be used for diagnostic purposes for tumors. Such approaches are called photodynamic diagnosis (PDD). In this Review, we provide a general overview of the clinical applications of PDT in cancer, including the diagnostic and therapeutic approaches. Assessment of PDT therapeutic efficacy in the clinic will be discussed, since identifying predictors to determine the response to treatment is crucial. In addition, examples of PDT in various types of tumors will be discussed. Furthermore, combination of PDT with other therapy modalities such as chemotherapy, radiotherapy, surgery and immunotherapy will be emphasized, since such approaches seem to be promising in terms of enhancing effectiveness against tumor. The combination of PDT with other treatments may yield better results than by single treatments. Moreover, the utilization of lower doses in a combination therapy setting may cause less side effects and better results than single therapy. A better understanding of the effectiveness of PDT in a combination setting in the clinic as well as the optimization of such complex multimodal treatments may expand the clinical applications of PDT.

Photodynamic therapy of cutaneous T-cell lymphoma cell lines mediated by 5-aminolevulinic acid and derivatives

The delta-amino acid 5-aminolevulinic acid (ALA), is the precursor of the endogenous photosensitiser Protoporphyrin IX (PpIX), and is currently approved for Photodynamic Therapy (PDT) of certain superficial cancers. However, ALA-PDT is not very effective in diseases in which T-cells play a significant role. Cutaneous T-cell lymphomas (CTCL) is a group of non-Hodgkin malignant diseases, which includes mycosis fungoides (MF) and Sézary syndrome (SS). In previous work, we have designed new ALA esters synthesised by three-component Passerini reactions, and some of them showed higher performance as compared to ALA. This work aimed to determine the efficacy as pro-photosensitisers of five new ALA esters of 2-hydroxy-N-arylacetamides (1f, 1 g, 1 h, 1i and 1 k) of higher lipophilicity than ALA in Myla cells of MF and HuT-78 cells of SS. We have also tested its effectiveness against ALA and the already marketed ALA methyl ester (Me-ALA) and ALA hexyl ester (He-ALA). Both cell Myla and SS cells were effectively and equally photoinactivated by ALA-PDT. Besides, the concentration of ALA required to induce half the maximal porphyrin synthesis was 209 μM for Myla and 169 μM for HuT-78 cells. As a criterion of efficacy, we calculated the concentration of the ALA derivatives necessary to induce half the plateau porphyrin values obtained from ALA. These values were achieved at concentrations 4 and 12 times lower compared to ALA, according to the derivative used. For He-ALA, concentrations were 24 to 25 times lower than required for ALA for inducing comparable porphyrin synthesis in both CTCL cells. The light doses for inducing 50% of cell death (LD50) for He-ALA, 1f, 1 g, 1 h and 1i were around 18 and 25 J/cm² for Myla and HuT-78 cells respectively, after exposure to 0.05 mM concentrations of the compounds. On the other hand, the LD50s for the compound 1 k were 40 and 57 J/cm² for Myla and HuT-78, respectively. In contrast, 0.05 mM of ALA and Me-ALA did not provoke photokilling since the concentration employed was far below the porphyrin saturation point for these compounds. Our results suggest the potential use of ALA derivatives for topical application in PDT treatment of MF and extracorporeal PDT for the depletion of activated T-cells in SS.

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.

Application of photodynamic therapy in immune-related diseases

Photodynamic therapy (PDT) is a therapeutic modality that utilizes photodamage caused by photosensitizers and oxygen after exposure to a specific wavelength of light. Owing to its low toxicity, high selectivity, and minimally invasive properties, PDT has been widely applied to treat various malignant tumors, premalignant lesions, and infectious diseases. Moreover, there is growing evidence of its immunomodulatory effects and potential for the treatment of immune-related diseases. This review mainly focuses on the effect of PDT on immunity and its application in immune-related diseases.

An Alternating Irradiation Strategy-Driven Combination Therapy of PDT and RNAi for Highly Efficient Inhibition of Tumor Growth and Metastasis

Hypoxia and hypoxia induced overexpression of vascular endothelial growth factor (VEGF) not only seriously affects the treatment effects of photodynamic therapy (PDT) but also promotes tumor metastasis. Herein, an alternating irradiation strategy (referred to as alternate use of low/high dose of light [ALHDL] irradiation)-driven combination therapy of PDT and RNA interference (RNAi) is developed to synergistically inhibit tumor growth and metastasis. A cationic amphipathic peptide (ALS) served as a carrier in the co-delivery system of photochlor (HPPH) and siVEGF (ALSH/siVEGF). At the beginning of ALHDL-driven ALSH/siVEGF treatment, short-term LDL irradiation can facilitate the tumor penetration, cellular uptake, and endosome escape of ALSH/siVEGF. Moreover, accompanied by HDL-mediated rapid cell apoptosis and LDL-mediated efficient VEGF silencing, the joint use of PDT and RNAi achieved remarkable antitumor effects both in vitro and in vivo. Importantly, benefited from the excellent performance of ALHDL in slowing the rapid deterioration of the anoxic environment of tumors, and ALSH/siVEGF treatment-mediated highly improved VEGF silencing efficacy and inhibitory effect on angiogenesis, the liver and lung metastases of HeLa cells have been successfully suppressed. Together, this study clearly indicates that ALHDL-driven combination therapy of PDT and RNAi is a highly effective modality for inhibition of tumor growth and metastasis.

Light-assisted gadofullerene nanoparticles disrupt tumor vasculatures for potent melanoma treatment

The traditional photodynamic therapy (PDT) using a photosensitizer and oxygen under light generates reactive oxygen species (ROS) to kill tumor cells. However, its treatment efficiency is limited by insufficient oxygen in tumor cells. Herein, β-alanine modified gadofullerene nanoparticles (GFNPs) were explored to disrupt tumor vasculatures assisted by light for potent melanoma treatment. As tumor vasculatures are oxygen-rich, the yields of photo-induced singlet oxygen (1O2) by GFNPs are not subjected to the hypoxemia of tumor tissues. Different from the small molecule photosensitizer Chlorin e6 (Ce6), GFNPs realize high-efficiency tumor vascular disruption under light observed by using the mice tumor vascular dorsal skin fold chamber (DSFC) model. The tumor vascular disruption efficiency of GFNPs is size-dependent, and the smallest one (hydration diameter of ca. 126 nm) is more efficient. Mechanistically, the high yields of photo-induced 1O2 by GFNPs can lead to the destruction of the tumor vascular endothelial adherent junction protein-VE cadherin and the decrease of tumor vascular endothelial cells-CD31 proteins, inducing rapid tumor necrosis. In conclusion, our work provides an insight into the design of well-sized nanoparticles to powerfully treat melanoma assisted by light, as well as greatly extending the applications of PDT for robust tumor therapy.

Novel porphyrazine-based photodynamic anti-cancer therapy induces immunogenic cell death

The immunogenicity of dying cancer cells determines the efficacy of anti-cancer therapy. Photodynamic therapy (PDT) can induce immunogenic cell death (ICD), which is characterized by the emission of damage-associated molecular patterns (DAMPs) from dying cells. This emission can trigger effective anti-tumor immunity. Only a few photosensitizers are known to induce ICD and, therefore, there is a need for development of new photosensitizers that can induce ICD. The purpose of this work was to analyze whether photosensitizers developed in-house from porphyrazines (pz I and pz III) can induce ICD in vitro and in vivo when used in PDT. We indetified the optimal concentrations of the photosensitizers and found that, at a light dose of 20 J/cm² (λ_ex 615-635 nm), both pz I and pz III efficiently induced cell death in cancer cells. We demonstrate that pz I localized predominantly in the Golgi apparatus and lysosomes while pz III in the endoplasmic reticulum and lysosomes. The cell death induced by pz I-PDT was inhibited by zVAD-fmk (apoptosis inhibitor) but not by ferrostatin-1 and DFO (ferroptosis inhibitors) or by necrostatin-1 s (necroptosis inhibitor). By contrast, the cell death induced by pz III-PDT was inhibited by z-VAD-fmk and by the necroptosis inhibitor, necrostatin-1 s. Cancer cells induced by pz I-PDT or pz III-PDT released HMGB1 and ATP and were engulfed by bone marrow-derived dendritic cells, which then matured and became activated in vitro. We demonstrate that cancer cells, after induction of cell death by pz I-PDT or pz III-PDT, are protective when used in the mouse model of prophylactic tumor vaccination. By vaccinating immunodeficient mice, we prove the role of the adaptive immune system in protecting against tumours. All together, we have shown that two novel porphyrazines developed in-house are potent ICD inducers that could be effectively applied in PDT of cancer.

Stacking Effects on Anthraquinone/DNA Charge-Transfer Electronically Excited States

The design of more efficient photosensitizers is a matter of great importance in the field of cancer treatment by means of photodynamic therapy. One of the main processes involved in the activation of apoptosis in cancer cells is the oxidative stress on DNA once a photosensitizer is excited by light. As a consequence, it is very relevant to investigate in detail the binding modes of the chromophore with DNA, and the nature of the electronically excited states that participate in the induction of DNA damage, for example, charge-transfer states. In this work, we investigate the electronic structure of the anthraquinone photosensitizer intercalated into a double-stranded poly(dG-dC) decamer model of DNA. First, the different geometric configurations are analyzed by means of classical molecular dynamics simulations. Then, the excited states for the most relevant poses of anthraquinone inside the binding pocket are computed by an electrostatic-embedding quantum mechanics/molecular mechanics approach, where anthraquinone and one of the nearby guanine residues are described quantum mechanically to take into account intermolecular charge-transfer states. The excited states are characterized as monomer, exciton, excimer, and charge-transfer states based on the analysis of the transition density matrix, and each of these contributions to the total density of states and absorption spectrum is discussed in terms of the stacking interactions. These results are relevant as they represent the footing for future studies on the reactivity of anthraquinone derivatives with DNA and give insights on possible geometrical configurations that potentially favor the oxidative stress of DNA.

Efficacy of Photodynamic Anti-Microbial Chemotherapy for Acanthamoeba Keratitis In Vivo

BACKGROUND AND OBJECTIVES

Acanthamoeba keratitis is a sight-threatening infectious disease that is difficult to treat. The aim of this study was to evaluate TONS504 (cationic chlorin derivative photosensitizer)-mediated photodynamic antimicrobial chemotherapy (PACT) in vivo as a potential treatment for Acanthamoeba keratitis.

STUDY DESIGN/MATERIALS AND METHODS

Acanthamoeba keratitis was induced by soft contact lenses incubated with 1 × 10⁵ /ml Acanthamoeba castellanii, which were placed over debrided corneas with temporary tarsorrhaphy. Thirty-eight male Japanese white rabbits were randomly divided into three groups (normal eye, no treatment, and treatment groups). TONS504 was administered as eye drops at 1 mg/ml, followed by light-emitting diode irradiation after the establishment of keratitis at 7 days after infectious contact lens exposure. All animals were evaluated under a slit-lamp microscope every 3 days for 6 days after the treatment. Clinical scores based on corneal epithelial defects detected by fluorescein staining, stromal opacity edema, and vascular infiltration into the cornea were determined. After 6 days, the eyes were enucleated for histopathological analysis.

RESULTS

Clinical signs of infection in the treatment group were markedly reduced for up to 6 days after treatment. Histopathology showed a regular arrangement of stromal fibers and a small number of inflammatory cells in 58% of the corneas. However, 42% of corneas in the treatment group showed infiltrating neutrophils and irregular alignment of stromal collagen fibers.

CONCLUSIONS

Our TONS504-PACT achieved complete recovery from keratitis in 58% of the rabbit models. Further studies are required to determine the conditions for the maximal effectiveness of our TONS504-PACT for Acanthamoeba keratitis. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Boto R, Ferreira D, R. Fernandes J, Almeida P, F. V. Ferreira L, Souto EB, Silva AM, V. Reis L. Quinoline‑ and Benzoselenazole-Derived Unsymmetrical Squaraine Cyanine Dyes: Design, Synthesis, Photophysicochemical Features and Light-Triggerable Antiproliferative Effects against Breast Cancer Cell Lines

Photodynamic therapy is an innovative treatment approach broadly directed towards oncological diseases. Its applicability and efficiency are closely related to the interaction of three main components, namely a photosensitizer, light and molecular triplet oxygen, which should drive cell death. Recently, several studies have demonstrated that squaraine cyanine dyes have a set of photophysical and photochemical properties that have made of these compounds’ potential photosensitizers for this therapeutic modality. In the present research work, we describe the synthesis and characterization of four quinoline- and benzoselenazole-derived unsymmetrical squaraine cyanine dyes. Except for the precursor of aminosquaraine dyes, i.e., O-methylated derivative, all dyes were evaluated for their behavior and absorption capacity in different organic and aqueous solvents, their ability to form singlet oxygen, their light-stability, and in vitro phototherapeutic effects against two human breast cancer cell cultures (BT-474 and MCF-7). Regardless of the nature of the used solvents, the synthesized dyes showed intense absorption in the red and near-infrared spectral regions, despite the formation of aggregates in aqueous media. Dyes showed high light-stability against light exposure. Despite the low ability to produce singlet oxygen, aminosquaraine dyes demonstrated worthy in vitro phototherapeutic activity.

In vitro phototherapeutic effects of indolenine-based mono- and dithiosquaraine cyanine dyes against Caco-2 and HepG2 human cancer cell lines

Photodynamic therapy is a noninvasive approach for the treatment of oncological and nononcological diseases which has attempted to address the shortcomings and disadvantages of conventional cancer therapies. Given the scarcity of photosensitizers that exhibit desirable characteristics for its potential application in this therapeutic strategy, the main aims of this work were the study of the photophysical and photochemical properties, and the in vitro photobiological activity of several squaraine cyanine dyes. Thus, herein, the synthesis of indolenine-based N-methyl and N-ethyl mono- and dithiosquaraine dyes, the study of their spectroscopical properties, aggregation behavior, photodegradation and singlet oxygen production ability, and the further application of the previously synthesized dyes in colorectal adenocarninoma and hepatocellular carcinoma cell lines to evaluate their phototherapeutic effects, are described. Thionation significantly favored the ability to singlet oxygen production, and moderate photostability was observed for squaraine and monothionated dyes. Squaraine and monothiosquaraine cyanine dyes showed high promise within the tested concentration range regarding their potential application as cancer photodynamic therapy photosensitizers. Squaraine dyes' monothionation resulted in the preparation of compounds with poor photocytotoxicity, which was an undesirable effect on their phototherapeutic application.

Oxidative Stress and Photodynamic Therapy of Skin Cancers: Mechanisms, Challenges and Promising Developments

Ultraviolet radiation is one of the most pervasive environmental interactions with humans. Chronic ultraviolet irradiation increases the danger of skin carcinogenesis. Probably, oxidative stress is the most important mechanism by which ultraviolet radiation implements its damaging effects on normal cells. However, notwithstanding the data referring to the negative effects exerted by light radiation and oxidative stress on carcinogenesis, both factors are used in the treatment of skin cancer. Photodynamic therapy (PDT) consists of the administration of a photosensitiser, which undergoes excitation after suitable irradiation emitted from a light source and generates reactive oxygen species. Oxidative stress causes a condition in which cellular components, including DNA, proteins, and lipids, are oxidised and injured. Antitumor effects result from the combination of direct tumour cell photodamage, the destruction of tumour vasculature and the activation of an immune response. In this review, we report the data present in literature dealing with the main signalling molecular pathways modified by oxidative stress after photodynamic therapy to target skin cancer cells. Moreover, we describe the progress made in the design of anti-skin cancer photosensitisers, and the new possibilities of increasing the efficacy of PDT via the use of molecules capable of developing a synergistic antineoplastic action.

Curcumin and silver nanoparticles carried out from polysaccharide-based hydrogels improved the photodynamic properties of curcumin through metal-enhanced singlet oxygen effect

Colorectal cancer (CRC) has a high incidence and resistance to conventional treatments. Curcumin (CUR) is a promising natural product in the treatment of CRC with excellent in vitro results. However, its low bioavailability is a limiting factor in clinical applications. To overcome, CUR was incorporated into hydrogels constituted by chitosan (CHT) and chondroitin sulfate (CS), natural biopolymers, capable of controlled release. Hydrogels were synthesized in ionic liquids (ILs, [Hmim][HSO₄]) improving the solubility of CHT and the hydrogel properties. Furthermore, CUR was combined with silver nanoparticles (AgNPs) and visible light by Photodynamic Therapy (PDT), which, through the MEO effect (Metal-Enhanced Singlet Oxygen), leads to cell death. It is highlighted the green synthesis of AgNPs using an ultrasound bath. The CHT/CS hydrogels loaded with CUR/AgNPs were properly characterized. Cellular assays showed that the hydrogels (CHT/CS) were not cytotoxic to healthy tissues. However, PDT selective illumination led to inhibition of Caco-2 human colon cancer cells by the CHT/CS/CUR-AgNPs (CC₅₀ = 91.5 μg mL^-1 of hydrogel). The cellular uptake assays showed, in addition to the therapeutic action, that the CUR can works as a diagnostic fluorescence probe (theranostic system). Finally, we highlight our commitment to work with reagents, solvents, and methodologies aiming at the principles of green chemistry.

In situ self-assembly of conjugated polyelectrolytes for cancer targeted imaging and photodynamic therapy

The construction of intelligent self-assembly systems with cancer targeting photodynamic therapy abilities is highly required for increasing the precise therapeutic efficiency in clinical treatment. Herein, a cationic water soluble conjugated polymer (PFT-SH) functionalized with thiol groups was designed and synthesized via a palladium-catalyzed Suzuki coupling reaction. Firstly, PFT-SH can enter cells and form loose aggregations by hydrophobic and π-π stacking interactions. Secondly, a high level of H₂O₂ in cancer cells oxidizes sulfhydryl groups to disulfide bonds and then forms more and larger aggregations. Finally, PFT-SH showed remarkable ROS producing ability under white light irradiation with 78% quantum yields (Φ_Δ). Due to this unique self-aggregation property, PFT-SH was successfully used to achieve in situ self-assembly specifically inside cancer cells for targeted imaging. Both the specific aggregation of PFT-SH in cancer cells and its ROS producing ability led to its use in the targeted killing of cancer cells through efficient photodynamic therapy.

Imaging of singlet oxygen feedback delayed fluorescence and lysosome permeabilization in tumor in vivo during photodynamic therapy with aluminum phthalocyanine

Significance: Singlet oxygen is a key cytotoxic agent in photodynamic therapy (PDT). As such, its imaging is highly desirable, but existing direct imaging methods are still limited by the exceptionally low yield of the luminescence signal. Singlet oxygen feedback delayed fluorescence (SOFDF) of the photosensitizer is a higher yield alternative for indirect measurement of this signal. <p> Aim: The aim was to explore feasibility of SOFDF imaging in vivo in tumor-bearing mice during PDT and investigate how SOFDF images can be transformed into images of singlet oxygen. In addition, we study whether lysosome permeabilization can be visualized through fluorescence lifetime.</p> <p> Approach: Mice were intravenously injected with 2.5 mg/kg of photosensitizer aluminum(III) phthalocyanine tetrasulfonate (AlPcS₄) 20 h prior to experiments, having subcutaneous BxPC3 pancreas tumors. Time-resolved delayed fluorescence and prompt fluorescence (PF) were imaged using an intensified time-gated camera with 10-Hz pulsed laser excitation at 690 nm. </p> <p> Results: Delayed emission from AlPcS₄ was detected with lifetimes 7 to 11  μs, which was attributed to SOFDF and shown to be oxygen-dependent. Singlet oxygen images were approximated by the ratio of SOFDF/PF at each pixel. SOFDF images of a good quality could be captured within several seconds with a radiant exposure of ∼20  mJ  /  cm². In addition, lifetime images of AlPcS₄ PF in ns-time domain enabled us to visualize the event of lysosome permeabilization, as the lifetime increased from ∼4.7 to 5.2 ns. </p> <p> Conclusions: Imaging of SOFDF in vivo in mouse tumor during PDT with AlPcS₄ is feasible, and it is a promising method for singlet molecular oxygen monitoring. Moreover, the time-gated approach also enables visualization of the lysosome permeabilization that alters the PF lifetime. </p>

Comparative analysis of single- and dual-wavelength photodynamic therapy regimes with chlorin-based photosensitizers: animal study

Two pronounced absorption peaks in blue and red ranges of the chlorin-based photosensitizer (PS) absorption spectrum provide additional benefits in photodynamic therapy (PDT) performance. Differing optical properties of biological tissues in these ranges allow for both dual-wavelength diagnostics and PDT performance. We provide a comparative analysis of different PDT regimes performed with blue and red lights and their combination, with doses varying from 50 to 150  J  /  cm². The study was performed on the intact skin of a rabbit ear inner surface, with the use of chlorin e6 as a PS. PDT procedure protocol included monitoring of the treated site with fluorescence imaging technique to evaluate PS accumulation and photobleaching, as well as with optical coherence tomography (OCT) to register morphological and functional responses of the tissue. Optical diagnostic observations were compared with the results of histopathology examination. We demonstrated that PDT procedures with the considered regimes induce weaker organism reaction manifested by edema in normal tissue as compared to irradiation-only exposures with the same light doses. The light doses delivered with red light induce weaker tissue reaction as compared to the same doses delivered with blue light only or with a combination of red and blue lights in equal parts. Results of in-vivo OCT monitoring of tissue reaction are in agreement with the results of histopathology study.

In Situ-Induced Multivalent Anticancer Drug Clusters in Cancer Cells for Enhancing Drug Efficacy

Increasing intracellular drug concentration is an effective way for cancer chemotherapeutics to enhance efficacy and combat drug resistance. In this work, a series of anticancer drug conjugates were prepared by linking thiol-modified oligo( p-phenylene vinylene) with paclitaxel, vincristine, teniposide, tamoxifen, doxorubicin, or podophyllotoxin (OPV-S-Drugs) through a Michael addition reaction. These OPV-S-Drugs could undergo intracellular assembly and aggregation upon oxidation to yield multivalent anticancer drug clusters, which inhibited their diffusion from cancer cells. The intracellular aggregation of OPV-S-Drugs originates from π–π stacking and hydrophobic interactions between OPV backbones, followed by cross-linking via disulfide bond formation in the presence of reactive oxygen species (ROS). The drug clusters occur only in the cytoplasm of cancer cells expressing high ROS levels, but not in healthy mammalian cells, thus reducing the cytotoxicity to normal cells. Specifically, the super-toxicity of podophyllotoxin to normal cells was obviously suppressed while the drug efficacy was maintained through our new strategy. The diverse action mechanisms of OPV-S-Drugs toward cancer cells is proposed.

Photophysicochemical and photodynamic therapy properties of metallophthalocyanines linked to gold speckled silica nanoparticles

This work reports on the linkage of 2(3),9(10),16(17),23(24) tetrakis [(benzo[d]thiazol-2-yl phenoxy) phthalocyaninato] zinc(II) (1) and indium(III) chloride (2) to gold speckled silica (GSS) nanoparticles via gold to sulphur (Au-S) and gold to nitrogen (Au-N) self-assembly to form the conjugates: 1-GSS and 2-GSS. The formed conjugates were characterized using microscopic and spectroscopic techniques, and the photophysicochemical properties and photodynamic therapy (PDT) activity against human breast adenocarcinoma cell line (MCF-7 cells) were studied. The conjugates afforded decrease in fluorescence quantum yields with corresponding increase in triplet and singlet oxygen quantum yields when compared to phthalocyanines alone. Singlet oxygen is cytotoxic to cancer cells hence it is important for PDT. The in vitro dark toxicity of complex 2 and 2-GSS against MCF-7 cells showed ≥93% viable cells within concentration ranges of 10-160 μg/mL. 2-GSS showed enhanced PDT activity with less than 50% viable cells at 80 μg/mL as compared to 2 and GSS alone which showed >60% viable cells within 10-160 μg/mL. The observed improvements in the PDT activity of 2-GSS could be attributed to the high singlet oxygen generation of 2-GSS compared to 2 alone in addition to the phototoxicity of GSS.

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

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

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

Photodynamic Therapy Mediated by Aloe-Emodin Inhibited Angiogenesis and Cell Metastasis Through Activating MAPK Signaling Pathway on HUVECs

Photodynamic therapy is a clinically used, minimally invasive therapeutic procedure that involves the application of photosensitizers which can locate in target cells and so be irradiated at a corresponding wavelength. Laser light irradiation activation of photosensitizers generates free reactive oxygen species, which induces selective cytotoxic activity in target cells. Within recent years, aloe-emodin as a photosensitizer has been successfully applied in photodynamic therapy applications. Angiogenesis plays an important role in tumor growth and metastasis; thus, the development of a novel target treatment for angiogenesis is essential in order to improve treatment therapeutics for cancer treatment. An essential step in angiogenesis involves the formation of tube-like structures during matrix degradation, rearrangement, and apoptosis of endothelial cells. In the present study, we investigated the mechanisms of photocytotoxicity induced by aloe-emodin in human umbilical vein endothelial cells. Analysis of cell proliferation results noted a significant decrease in cultured cells which received various concentrations of aloe-emodin and photodynamic therapy–induced light doses. Additionally, mitochondrial mechanisms of apoptotic cell death were observed in aloe-emodin photodynamic therapy–treated cells, as tube formation assays noted angiogenesis suppression after treatment. The capacity of migration and invasion of human umbilical vein endothelial cells was measured using the transwell assay and demonstrated that aloe-emodin photodynamic therapy significantly inhibited the migration and invasion of human umbilical vein endothelial cells. The expression of p38, extracellular signal-regulated kinase, the c-Jun N-terminal kinases, and vascular endothelial growth factor suggested that the cellular metastasis was related to mitogen-activated protein kinase signal pathway. Furthermore, disorganization of F action cytoskeleton components was observed after aloe-emodin photodynamic therapy. Overall, the findings from this study suggest that aloe-emodin photodynamic therapy inhibited angiogenesis and cellular metastasis in human umbilical vein endothelial cells by activating the mitogen-activated protein kinase apoptotic signaling cell death pathway.

The good, the bad, and the ugly - controlling singlet oxygen through design of photosensitizers and delivery systems for photodynamic therapy

Singlet oxygen, although integral to photodynamic therapy, is notoriously uncontrollable, suffers from poor selectivity and has fast decomposition rates in biological media. Across the scientific community, there is a conscious effort to refine singlet oxygen interactions and initiate selective and controlled release to produce a consistent and reproducible therapeutic effect in target tissue. This perspective aims to provide an insight into the contemporary design principles behind photosensitizers and drug delivery systems that depend on a singlet oxygen response or controlled release. The discussion will be accompanied by in vitro and in vivo examples, in an attempt to highlight advancements in the field and future prospects for the more widespread application of photodynamic therapy.

New Ru(ii) photocages operative with near-IR light: new platform for drug delivery in the PDT window

A series of Ru(ii) complexes bearing the tridentate 2,6-di(quinolin-2-yl)pyridine (dqpy) ligand were designed to undergo photoinduced ligand dissociation with red/near-IR light. The complexes [Ru(dqpy)(L)(CH3CN)]2+, where L = 2,2'-bipyridine (bpy, 1), 4,4'dimethyl-2,2'-bipyridine (Me2bpy, 2), and 1,10-phenanthroline (phen, 3). Complexes 1-3 exhibit red-shifted lowest energy metal-to-ligand charge transfer (MLCT) absorption maxima at ∼600 nm, as compared to the corresponding tpy (2,2';6',2''-terpyridine) complexes with MLCT bands at ∼565 nm which appear as shoulders to the MLCT bands at ∼455 nm. This shift is attributed to the lower energy LUMO afforded by the dqpy ligand when compared to tpy, as evidenced by the shift of the first reduction wave to ∼0.3 V more positive potentials in the former. In addition, the lowest MLCT maximum of [Ru(dqpy)(acac)(CH3CN)]+ (4; acac- = acetylacetonate) is observed at 770 nm, attributed to the additional increase in energy of the HOMO afforded by the presence of the π-donating acac- ligand and supported by calculations. Complexes 1-3 undergo ligand substitution upon irradiation with red light, λ irr ≥ 610 nm, and the ligand substitution photochemistry of 4 is accessible with near-IR light, λ irr ≥ 715 nm and λ irr = 735 nm. Complexes 1-4 exhibit similar quantum yields of ligand exchange, Φ L, with 450 and 600 nm irradiation, however, that of 4 is 2-3 times greater than those measured for 1-3. This enhancement is explained by the difference in ligand contributions to the HOMO. Density functional theory calculations predict partial dqpy ππ* character in the MLCT states of 1-3 and a mixed Ru/acac- → dqpy metal/ligand-to-ligand charge transfer (ML-LCT) state in 4. The photoreactivity of 1-4 with tissue-penetrating red and near-IR light, together with their exceptional dark stability (>48 h), makes the new Ru(ii)-dqpy platform ideal for the development of new complexes for photoinduced drug release and for other applications that require broad absorption from the ultraviolet and visible ranges into the near-IR, such as solar energy conversion.

An In Vitro Approach to Photodynamic Therapy

Photodynamic therapy (PDT) is a medical procedure that involves incubation of an exogenously applied photosensitizer (PS) followed by visible light photoactivation to induce cell apoptosis. The Federal Drug Administration has approved PDT for the treatment of actinic keratosis, and clinical guidelines recommend PDT as a treatment for certain non-melanoma skin cancers and acne vulgaris. PDT is an advantageous therapeutic modality as it is low cost, non-invasive, and associated with minimal adverse events and scaring. In the first step of PDT, a PS is applied and allowed to accumulate intracellularly. Subsequent light irradiation induces reactive oxygen species formation, which may ultimately lead to cell apoptosis, membrane disruption, mitochondrial damage, immune modulation, keratinocyte proliferation, and collagen turnover. Herein, we present an in vitro method to study PDT in an adherent cell line. This treatment protocol is designed to simulate PDT and may be adjusted to studying the use of PDT with various cell lines, photosensitizers, incubation temperatures, or photoactivation wavelengths. Squamous cell carcinoma cells were incubated with 0, 0.5, 1.0, and 2 mM 5-aminolevulinic acid (5-ALA) for 30 min and photoactivated with 417 nm blue light for 1,000 s. The primary outcome measure was apoptosis and necrosis, as measured by annexin-V and 7-aminoactinomycin D flow cytometry. There was a dose-dependent increase in cell apoptosis following thirty-minute incubation of 5-ALA. To achieve high inter-test validity, it is important to maintain consistent incubation and light parameters when performing in vitro PDT experiments. PDT is a useful clinical procedure and in vitro research may allow for the development of novel PSs, optimization of protocols, and new indications for PDT.

Photodynamic therapy with chlorin-based photosensitizer at 405 nm: numerical, morphological, and clinical study

Employment of chlorin-based photosensitizers (PSs) provides additional advantages to photodynamic therapy (PDT) due to absorption peak around 405 nm allowing for superficial impact and efficient antimicrobial therapy. We report on the morphological and clinical study of the efficiency of PDT at 405 nm employing chlorin-based PS. Numerical studies demonstrated difference in the distribution of absorbed dose at 405 nm in comparison with traditionally employed wavelength of 660 nm and difference in the in-depth absorbed dose distribution for skin and mucous tissues. Morphological study was performed at the inner surface of rabbit ear with histological examinations at different periods after PDT procedure. Animal study revealed tissue reaction to PDT consisting in edema manifested most in 3 days after the procedure and neoangiogenesis. OCT diagnostics was confirmed by histological examination. Clinical study included antimicrobial PDT of pharynx chronic inflammatory diseases. It revealed no side effects or complications of the PDT procedure. Pharyngoscopy indicated reduction of inflammatory manifestations, and, in particular cases, hypervascularization was observed. Morphological changes were also detected in the course of monitoring, which are in agreement with pharyngoscopy results. Microbiologic study after PDT revealed no pathogenic bacteria; however, in particular cases, saprophytic flora was detected.

Epidermal growth factor receptor (EGFR) density may not be the only determinant for the efficacy of EGFR-targeted photoimmunotherapy in human head and neck cancer cell lines

OBJECTIVE

The aim of this study was to investigate the effects of targeted photoimmunotherapy (PIT) in vitro on cell lines with various expression levels of epidermal growth factor receptor (EGFR) using an anti-EGFR targeted conjugate composed of Cetuximab and IR700DX, phthalocyanine dye.

MATERIALS AND METHODS

Relative EGFR density and cell binding assay was conducted in three human head & neck cancer cell lines (scc-U2, scc-U8, and OSC19) and one reference cell line A431. After incubation with the conjugate for 1 or 24 hours, cellular uptake and localization were investigated by confocal laser scanning microscopy and quantified by image analysis. Cell survival was determined using the MTS assay and alamarBlue assay after PIT with a 690 nm laser to a dose of 7 J.cm^-2 (at 5 mW.cm^-2 ). The mode of cell death was examined with flow cytometry using apoptosis/necrosis staining by Annexin V/propidium iodide, together with immunoblots of anti-apoptotic Bcl-2 family proteins Bcl-2 and Bcl-xL.

RESULTS

A431 cells had the highest EGFR density followed by OSC19, and then scc-U2 and scc-U8. The conjugates were localized both on the surface and in the cytosol of the cells after 1- and 24-hour incubation. After 24-hour incubation the granular pattern was more pronounced and in a similar pattern of a lysosomal probe, suggesting that the uptake of conjugates by cells was via receptor-mediated endocytosis. The results obtained from the quantitative imaging analysis correlate with the level of EGFR expression. Targeted PIT killed scc-U8 and A431 cells efficiently; while scc-U2 and OSC19 were less sensitive to this treatment, despite having similar EGFR density, uptake and localization pattern. Scc-U2 cells showed less apoptotic cell dealth than in A431 after 24-hour targeted PIT. Immunoblots showed significantly higher expression of anti-apoptotic Bcl-2 and Bcl-xL proteins in scc-U2 cell lines compared to scc-U8.

CONCLUSION

Our study suggests that the effectiveness of EGFR targeted PIT is not only dependent upon EGFR density. Intrinsic biological properties of tumor cell lines also play a role in determining the efficacy of targeted PIT. We have shown that in scc-U2 cells this difference may be caused by differences in the apoptopic pathway. Lasers Surg. Med. 50:513-522, 2018. © 2018 Wiley Periodicals, Inc.

A threshold dose distribution approach for the study of PDT resistance development: A threshold distribution approach for the study of PDT resistance

Photodynamic therapy (PDT) is a technique with well-established principles that often demands repeated applications for sequential elimination of tumor cells. An important question concerns the way surviving cells from a treatment behave in the subsequent one. Threshold dose is a core concept in PDT dosimetry, as the minimum amount of energy to be delivered for cell destruction via PDT. Concepts of threshold distribution have shown to be an important tool for PDT results analysis in vitro. In this study, we used some of these concepts for demonstrating subsequent treatments with partial elimination of cells modify the distribution, which represents an increased resistance of the cells to the photodynamic action. HepG2 and HepaRG were used as models of tumor and normal liver cells and a protocol to induce resistance, consisted of repeated PDT sessions using Photogem® as a photosensitizer, was applied to the tumor ones. The response of these cells to PDT was assessed using a standard viability assay and the dose response curves were used for deriving the threshold distributions. The changes in the distribution revealed that the resistance protocol effectively eliminated the most sensitive cells. Nevertheless, HepaRG cell line was the most resistant one among the cells analyzed, which indicates a specificity in clinical applications that enables the use of high doses and drug concentrations with minimal damage to the surrounding normal tissue.