Molecular mechanisms of the effects of photodynamic therapy on the brain: A review of the literature

Malignant gliomas are the most common primary brain tumors in adults. These tumors have a diverse molecular origin and a very poor prognosis. There is a lack of effective treatment at WHO grade IV glioma, and all glioblastomas progress or recur. Current treatments including surgical intervention, radiation therapy, and chemotherapy are insufficient and can cause damage to healthy brain tissue and neurological deficits. The preservation of healthy brain tissue during therapeutic intervention is made extremely difficult by the ability of malignant gliomas to diffusely infiltrate the surrounding brain parenchyma. Photodynamic therapy (PDT) is a treatment modality for glioma that can possibly overcome the inherent shortcommings of traditional therapies. Photodynamic therapy involves the use of a photosensitizer (PS) which, upon absorption of light by photosensitized tissue, triggers photochemical reactions generating reactive oxygen species (ROS) leading to the killing of tumor cells. Research focusing on the effective use of PDT in the treatment of glioma is already underway with promising results. Clinical studies on PDT for the treatment of gliomas have shown it to be a safe therapeutic modality with acceptable levels of side effects. However, some adverse sequelae have been observed during PDT of these tumours, such as increased photosensitivity, increased intracranial pressure or transient aphasia and worsening of pre-existing neurological deficits. Although the clinical sequelae of PDT are well described, the molecular mechanisms of PDT's effects on the healthy brain have not yet been thoroughly characterized. In our work, we attempt to summarize the molecular mechanisms of the effects of photosensitization on neural tissue, brain vasculature and the blood-brain barrier (BBB). We also point to findings presenting molecular approaches to protect the healthy brain from the adverse effects of photodynamic damage.

Enhancing antitumour immunity with photodynamic therapy

In this perspective, we present and discuss pre-clinical and some clinical studies demonstrating that local photodynamic therapy (PDT) per se is a treatment modality that can induce systemic anti-tumour immunity, however, the anti-tumour efficacy is strongly enhanced when PDT is combined with other treatment modalities, e.g., vaccines or ICI therapy. PDT has been recognized for over 30 years as a modality inducing strong immune effects in treated tumours. More recently, PDT has become perceived as a distinct type of immunogenic antitumor modality with an attractive potential for use as unique form of clinical cancer immunotherapy. It can be argued that PDT-inflicted tumour tissue injury provokes in situ vaccination effect. In the end of this perspective paper, we express our opinion of challenges and future directions in the field of PDT and PDT + immunotherapy.

Nexus of NFκB/VEGF/MMP9 signaling in diabetic retinopathy-linked dementia: Management by phenolic acid-enabled nanotherapeutics

AIMS

The purpose of this review is to highlight the therapeutic effectiveness of phenolic acids in slowing the progression of diabetic retinopathy (DR)-linked dementia by addressing the nuclear factor kappa B (NFκB)/matrix metalloproteinase-9 (MMP9)/vascular endothelial growth factor (VEGF) interconnected pathway.

MATERIALS AND METHODS

We searched 80 papers published in the last 20 years using terms like DR, dementia, phenolic acids, NFkB/VEFG/MMP9 signaling, and microRNAs (miRs) in databases including Pub-Med, WOS, and Google Scholar. By encasing phenolic acid in nanoparticles and then controlling its release into the targeted tissues, nanotherapeutics can increase their effectiveness. Results were summarized, and compared, and research gaps were identified throughout the data collection and interpretation.

KEY FINDINGS

Amyloid beta (Aβ) deposition in neuronal cells and drusen sites of the eye leads to the activation of NFkB/VEGF/MMP9 signaling and microRNAs (miR146a and miR155), which in turn energizes the accumulation of pro-inflammatory and pro-angiogenic microenvironments in the brain and retina leading to DR-linked dementia. This study demonstrates the potential of phenolic acid-enabled nanotherapeutics as a functional food or supplement for preventing and treating DR-linked dementia, and oxidative stress-related diseases.

SIGNIFICANCE

The retina has mechanisms to clear metabolic waste including Aβ, but the activation of NFkB/ MMP9/ VEGF signaling leads to fatal pathological consequences. Understanding the role of miR146a and miR155 provides potential therapeutic avenues for managing the complex pathology shared between DR and dementia. In particular, phenolic acid nanotherapeutics offer a dual benefit in retinal regeneration and dementia management.

Recent development of nanomaterials-based PDT to improve immunogenic cell death

Photodynamic therapy (PDT) is a clinically approved therapeutic modality for treating oncological and non-oncological disorders. PDT has proclaimed multiple benefits over further traditional cancer therapies including its minimal systemic toxicity and selective ability to eliminate irradiated tumors. In PDT, a photosensitizing substance localizes in tumor tissues and becomes active when exposed to a particular wavelength of laser light. This produces reactive oxygen species (ROS), which induce neoplastic cells to die and lead to the regression of tumors. The contributions of ROS to PDT-induced tumor destruction are described by three basic processes including direct or indirect cell death, vascular destruction, and immunogenic cell death. However, the efficiency of PDT is significantly limited by the inherent nature and tumor microenvironment. Combining immunotherapy with PDT has recently been shown to improve tumor immunogenicity while decreasing immunoregulatory repression, thereby gently modifying the anticancer immune response with long-term immunological memory effects. This review highlights the fundamental ideas, essential elements, and mechanisms of PDT as well as nanomaterial-based PDT to boost tumor immunogenicity. Moreover, the synergistic use of immunotherapy in combination with PDT to enhance immune responses against tumors is emphasized.

Cyanine dyes in the mitochondria-targeting photodynamic and photothermal therapy

Mitochondrial dysregulation plays a significant role in the carcinogenesis. On the other hand, its destabilization strongly represses the viability and metastatic potential of cancer cells. Photodynamic and photothermal therapies (PDT and PTT) target mitochondria effectively, providing innovative and non-invasive anticancer therapeutic modalities. Cyanine dyes, with strong mitochondrial selectivity, show significant potential in enhancing PDT and PTT. The potential and limitations of cyanine dyes for mitochondrial PDT and PTT are discussed, along with their applications in combination therapies, theranostic techniques, and optimal delivery systems. Additionally, novel approaches for sonodynamic therapy using photoactive cyanine dyes are presented, highlighting advances in cancer treatment.

Molecular Determinants for Photodynamic Therapy Resistance and Improved Photosensitizer Delivery in Glioma

Gliomas account for 24% of all the primary brain and Central Nervous System (CNS) tumors. These tumors are diverse in cellular origin, genetic profile, and morphology but collectively have one of the most dismal prognoses of all cancers. Work is constantly underway to discover a new effective form of glioma therapy. Photodynamic therapy (PDT) may be one of them. It involves the local or systemic application of a photosensitive compound-a photosensitizer (PS)-which accumulates in the affected tissues. Photosensitizer molecules absorb light of the appropriate wavelength, initiating the activation processes leading to the formation of reactive oxygen species and the selective destruction of inappropriate cells. Research focusing on the effective use of PDT in glioma therapy is already underway with promising results. In our work, we provide detailed insights into the molecular changes in glioma after photodynamic therapy. We describe a number of molecules that may contribute to the resistance of glioma cells to PDT, such as the adenosine triphosphate (ATP)-binding cassette efflux transporter G2, glutathione, ferrochelatase, heme oxygenase, and hypoxia-inducible factor 1. We identify molecular targets that can be used to improve the photosensitizer delivery to glioma cells, such as the epithelial growth factor receptor, neuropilin-1, low-density lipoprotein receptor, and neuropeptide Y receptors. We note that PDT can increase the expression of some molecules that reduce the effectiveness of therapy, such as Vascular endothelial growth factor (VEGF), glutamate, and nitric oxide. However, the scientific literature lacks clear data on the effects of PDT on many of the molecules described, and the available reports are often contradictory. In our work, we highlight the gaps in this knowledge and point to directions for further research that may enhance the efficacy of PDT in the treatment of glioma.

Graphene-Based Photodynamic Therapy and Overcoming Cancer Resistance Mechanisms: A Comprehensive Review

Photodynamic therapy (PDT) is a non-invasive therapy that has made significant progress in treating different diseases, including cancer, by utilizing new nanotechnology products such as graphene and its derivatives. Graphene-based materials have large surface area and photothermal effects thereby making them suitable candidates for PDT or photo-active drug carriers. The remarkable photophysical properties of graphene derivates facilitate the efficient generation of reactive oxygen species (ROS) upon light irradiation, which destroys cancer cells. Surface functionalization of graphene and its materials can also enhance their biocompatibility and anticancer activity. The paper delves into the distinct roles played by graphene-based materials in PDT such as photosensitizers (PS) and drug carriers while at the same time considers how these materials could be used to circumvent cancer resistance. This will provide readers with an extensive discussion of various pathways contributing to PDT inefficiency. Consequently, this comprehensive review underscores the vital roles that graphene and its derivatives may play in emerging PDT strategies for cancer treatment and other medical purposes. With a better comprehension of the current state of research and the existing challenges, the integration of graphene-based materials in PDT holds great promise for developing targeted, effective, and personalized cancer treatments.

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

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

Therapeutic potential and limitations of curcumin as antimetastatic agent

Treatment of metastatic cancer is one of the biggest challenges in anticancer therapy. Curcumin is interesting nature polyphenolic compound with unique biological and medicinal effects, including repression of metastases. High impact studies imply that curcumin can modulate the immune system, independently target various metastatic signalling pathways, and repress migration and invasiveness of cancer cells. This review discusses the potential of curcumin as an antimetastatic agent and describes potential mechanisms of its antimetastatic activity. In addition, possible strategies (curcumin formulation, optimization of the method of administration and modification of its structure motif) to overcome its limitation such as low solubility and bioactivity are also presented. These strategies are discussed in the context of clinical trials and relevant biological studies.

Advances in Liposome-Encapsulated Phthalocyanines for Photodynamic Therapy

This updated review aims to describe the current status in the development of liposome-based systems for the targeted delivery of phthalocyanines for photodynamic therapy (PDT). Although a number of other drug delivery systems (DDS) can be found in the literature and have been studied for phthalocyanines or similar photosensitizers (PSs), liposomes are by far the closest to clinical practice. PDT itself finds application not only in the selective destruction of tumour tissues or the treatment of microbial infections, but above all in aesthetic medicine. From the point of view of administration, some PSs can advantageously be delivered through the skin, but for phthalocyanines, systemic administration is more suitable. However, systemic administration places higher demands on advanced DDS, active tissue targeting and reduction of side effects. This review focuses on the already described liposomal DDS for phthalocyanines, but also describes examples of DDS used for structurally related PSs, which can be assumed to be applicable to phthalocyanines as well.

Radiation Type- and Dose-Specific Transcriptional Responses across Healthy and Diseased Mammalian Tissues

Ionizing radiation (IR) is a genuine genotoxic agent and a major modality in cancer treatment. IR disrupts DNA sequences and exerts mutagenic and/or cytotoxic properties that not only alter critical cellular functions but also impact tissues proximal and distal to the irradiated site. Unveiling the molecular events governing the diverse effects of IR at the cellular and organismal levels is relevant for both radiotherapy and radiation protection. Herein, we address changes in the expression of mammalian genes induced after the exposure of a wide range of tissues to various radiation types with distinct biophysical characteristics. First, we constructed a publicly available database, termed RadBioBase, which will be updated at regular intervals. RadBioBase includes comprehensive transcriptomes of mammalian cells across healthy and diseased tissues that respond to a range of radiation types and doses. Pertinent information was derived from a hybrid analysis based on stringent literature mining and transcriptomic studies. An integrative bioinformatics methodology, including functional enrichment analysis and machine learning techniques, was employed to unveil the characteristic biological pathways related to specific radiation types and their association with various diseases. We found that the effects of high linear energy transfer (LET) radiation on cell transcriptomes significantly differ from those caused by low LET and are consistent with immunomodulation, inflammation, oxidative stress responses and cell death. The transcriptome changes also depend on the dose since low doses up to 0.5 Gy are related with cytokine cascades, while higher doses with ROS metabolism. We additionally identified distinct gene signatures for different types of radiation. Overall, our data suggest that different radiation types and doses can trigger distinct trajectories of cell-intrinsic and cell-extrinsic pathways that hold promise to be manipulated toward improving radiotherapy efficiency and reducing systemic radiotoxicities.

Aggregation-Induced Emission Photosensitizer Synergizes Photodynamic Therapy and the Inhibition of the NF-κB Signaling Pathway to Overcome Hypoxia in Breast Cancer

Triple-negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer, and TNBC patients often develop resistance to endocrine or molecular targeted therapy. Thus, a search for effective treatments is urgently required. Photodynamic therapy (PDT) has been verified to be a successful therapy for cancer. However, this treatment is oxygen-consuming, thus considerably limiting the PDT outcomes. The present study introduced a multistage drug delivery system to alleviate hypoxia and enhance PDT efficiency. Specifically, aggregation-induced emission luminogen (AIEgen) TPE-Py was first introduced to achieve PDT properties, and natural naphthohydroquinone dimer Rubioncolin C (RC), a blocker of mitochondria-associated oxidative phosphorylation (OXPHOS) and an NF-κB inhibitor, was applied to suppress the O₂ consumption of OXPHOS and mitigate hypoxia thereafter. Enhanced PDT efficiency was validated by in vitro and in vivo TNBC models. In terms of the mechanism, AIEgen-based PDT synergized with RC could induce a fatal burst of reactive oxygen species (ROS) and ROS-mediated apoptosis. Moreover, this combination promoted the effectiveness of PDT by inhibiting the NF-κB signaling pathway. All of these results demonstrated that the administration system not only achieved a synergistic anti-TNBC effect but also expanded the clinical application of AIEgen-based PDT by overcoming hypoxia and inhibiting the NF-κB signaling pathway.

Mito-Bomb: Targeting Mitochondria for Cancer Therapy

Cancer has been one of the most common life-threatening diseases for a long time. Traditional cancer therapies such as surgery, chemotherapy (CT), and radiotherapy (RT) have limited effects due to drug resistance, unsatisfactory treatment efficiency, and side effects. In recent years, photodynamic therapy (PDT), photothermal therapy (PTT), and chemodynamic therapy (CDT) have been utilized for cancer treatment owing to their high selectivity, minor resistance, and minimal toxicity. Accumulating evidence has demonstrated that selective delivery of drugs to specific subcellular organelles can significantly enhance the efficiency of cancer therapy. Mitochondria-targeting therapeutic strategies are promising for cancer therapy, which is attributed to the essential role of mitochondria in the regulation of cancer cell apoptosis, metabolism, and more vulnerable to hyperthermia and oxidative damage. Herein, the rational design, functionalization, and applications of diverse mitochondria-targeting units, involving organic phosphine/sulfur salts, quaternary ammonium (QA) salts, peptides, transition-metal complexes, guanidinium or bisguanidinium, as well as mitochondria-targeting cancer therapies including PDT, PTT, CDT, and others are summarized. This review aims to furnish researchers with deep insights and hints in the design and applications of novel mitochondria-targeting agents for cancer therapy.

Sunitinib with photoirradiation-mediated reactive oxygen species generation induces apoptosis of renal cell carcinoma cells

BACKGROUND

Photodynamic therapy is a clinically approved, minimally invasive,therapeutic procedure used for the treatment of several cancers. In recent years, sunitinib, one of the tyrosine kinase inhibitors, has also attracted attention as a novel photosensitizer. However, there is currently no data available on the combined cytotoxic effects of sunitinib and photoirradiation on renal cell carcinoma including how the treatment induced cellular toxicity.

METHODS

In the present study, we used sunitinib as a photosensitizer and evaluated the effects of sunitinib and photodynamic therapy treatment on renal cancer cell lines, including the induction of cell death.

RESULTS

Our study showed that treatment with sunitinib and photoirradiation at 8 mW/cm² for 30 min resulted in the production intracellular reactive oxygen species (ROS), which is indicated by the increase in mRNA expression levels of PAI-1, NF-κβ, and Caspase-3. An increase in rate of apoptotic reaction and increase in the expression level of apoptotic marker were also observed when cells undergo treatment with sunitinib and photoirradiation.

CONCLUSIONS

Our findings suggest that combining photodynamic therapy with sunitinib represents a minimally invasive therapeutic procedure with cancer selectivity for renal cell carcinoma.

Dihydroartemisinin inhibits activation of the AIM2 inflammasome pathway and NF-κB/HIF-1α/VEGF pathway by inducing autophagy in A431 human cutaneous squamous cell carcinoma cells

The therapeutic effect of dihydroartemisinin (DHA) against cutaneous squamous cell carcinoma (cSCC) has been previously demonstrated; however, the underlying mechanism remains unclear. This study sought to verify the therapeutic effect of DHA against cSCC and explore its underlying mechanism in A431 cSCC cells. This study reported that DHA inhibited A431 cells proliferation in a time- and concentration-dependent manner and promoted A431 cells apoptosis. Moreover, DHA inhibited the invasion and migration of A431 cells. Mechanistically, DHA promoted autophagy and inhibited activation of the absent in melanoma 2 (AIM2) inflammasome pathway and NF-κB/HIF-1α/VEGF pathway. Treatment of A431 cells with the mTOR inhibitor, and autophagy promoter, rapamycin also inhibited these two pathways. In conclusion, DHA inhibited activation of the AIM2 inflammasome pathway and NF-κB/HIF-1α/VEGF pathway by promoting autophagy in A431 cells, thus accounting for its therapeutic effect. Induction of autophagy by DHA may be mediated by inhibiting the mTOR pathway and promoting reactive oxygen species production.

Plasmonic Hot-Electron Reactive Oxygen Species Generation: Fundamentals for Redox Biology

For decades, the possibility to generate Reactive Oxygen Species (ROS) in biological systems through the use of light was mainly restricted to the photodynamic effect: the photoexcitation of molecules which then engage in charge- or energy-transfer to molecular oxygen (O2) to initiate ROS production. However, the classical photodynamic approach presents drawbacks, like per se chemical reactivity of the photosensitizing agent or fast molecular photobleaching due to in situ ROS generation, to name a few. Recently, a new approach, which promises many advantages, has entered the scene: plasmon-driven hot-electron chemistry. The effect takes advantage of the photoexcitation of plasmonic resonances in metal nanoparticles to induce a new cohort of photochemical and redox reactions. These metal photo-transducers are considered chemically inert and can undergo billions of photoexcitation rounds without bleaching or suffering significant oxidative alterations. Also, their optimal absorption band can be shape- and size-tailored in order to match any of the near infrared (NIR) biological windows, where undesired absorption/scattering are minimal. In this mini review, the basic mechanisms and principal benefits of this light-driven approach to generate ROS will be discussed. Additionally, some significant experiments in vitro and in vivo will be presented, and tentative new avenues for further research will be advanced.

Photodynamic Diagnosis and Therapy for Peritoneal Carcinomatosis from Gastrointestinal Cancers: Status, Opportunities, and Challenges

Selective accumulation of a photosensitizer and the subsequent response in only the light-irradiated target are advantages of photodynamic diagnosis and therapy. The limited depth of the therapeutic effect is a positive characteristic when treating surface malignancies, such as peritoneal carcinomatosis. For photodynamic diagnosis (PDD), adjunctive use of aminolevulinic acid- protoporphyrin IX-guided fluorescence imaging detects cancer nodules, which would have been missed during assessment using white light visualization only. Furthermore, since few side effects have been reported, this has the potential to become a vital component of diagnostic laparoscopy. A variety of photosensitizers have been examined for photodynamic therapy (PDT), and treatment protocols are heterogeneous in terms of photosensitizer type and dose, photosensitizer-light time interval, and light source wavelength, dose, and dose rate. Although several studies have suggested that PDT has favorable effects in peritoneal carcinomatosis, clinical trials in more homogenous patient groups are required to identify the true benefits. In addition, major complications, such as bowel perforation and capillary leak syndrome, need to be reduced. In the long term, PDD and PDT are likely to be successful therapeutic options for patients with peritoneal carcinomatosis, with several options to optimize the photosensitizer and light delivery parameters to improve safety and efficacy.

Oxidative Stress-Inducing Anticancer Therapies: Taking a Closer Look at Their Immunomodulating Effects

Cancer cells are characterized by higher levels of reactive oxygen species (ROS) compared to normal cells as a result of an imbalance between oxidants and antioxidants. However, cancer cells maintain their redox balance due to their high antioxidant capacity. Recently, a high level of oxidative stress is considered a novel target for anticancer therapy. This can be induced by increasing exogenous ROS and/or inhibiting the endogenous protective antioxidant system. Additionally, the immune system has been shown to be a significant ally in the fight against cancer. Since ROS levels are important to modulate the antitumor immune response, it is essential to consider the effects of oxidative stress-inducing treatments on this response. In this review, we provide an overview of the mechanistic cellular responses of cancer cells towards exogenous and endogenous ROS-inducing treatments, as well as the indirect and direct antitumoral immune effects, which can be both immunostimulatory and/or immunosuppressive. For future perspectives, there is a clear need for comprehensive investigations of different oxidative stress-inducing treatment strategies and their specific immunomodulating effects, since the effects cannot be generalized over different treatment modalities. It is essential to elucidate all these underlying immune effects to make oxidative stress-inducing treatments effective anticancer therapy.

Redox Potential of Antioxidants in Cancer Progression and Prevention

The benevolent and detrimental effects of antioxidants are much debated in clinical trials and cancer research. Several antioxidant enzymes and molecules are overexpressed in oxidative stress conditions that can damage cellular proteins, lipids, and DNA. Natural antioxidants remove excess free radical intermediates by reducing hydrogen donors or quenching singlet oxygen and delaying oxidative reactions in actively growing cancer cells. These reducing agents have the potential to hinder cancer progression only when administered at the right proportions along with chemo-/radiotherapies. Antioxidants and enzymes affect signal transduction and energy metabolism pathways for the maintenance of cellular redox status. A decline in antioxidant capacity arising from genetic mutations may increase the mitochondrial flux of free radicals resulting in misfiring of cellular signalling pathways. Often, a metabolic reprogramming arising from these mutations in metabolic enzymes leads to the overproduction of so called ’oncometabolites’ in a state of ‘pseudohypoxia’. This can inactivate several of the intracellular molecules involved in epigenetic and redox regulations, thereby increasing oxidative stress giving rise to growth advantages for cancerous cells. Undeniably, these are cell-type and Reactive Oxygen Species (ROS) specific, which is manifested as changes in the enzyme activation, differences in gene expression, cellular functions as well as cell death mechanisms. Photodynamic therapy (PDT) using light-activated photosensitizing molecules that can regulate cellular redox balance in accordance with the changes in endogenous ROS production is a solution for many of these challenges in cancer therapy.

Dihydroartemisinin administration improves the effectiveness of 5-aminolevulinic acid-mediated photodynamic therapy for the treatment of high-risk human papillomavirus infection

AIMS AND BACKGROUND

High-risk human papillomavirus (HR-HPV) infection has been confirmed to be highly related to diseases such as Bowenoid papulosis, cervical cancer, and cervical intraepithelial neoplasia. 5-aminolevulinic acid-mediated PDT (ALA-PDT) has been used in a variety of HR-HPV infection-related diseases. Dihydroartemisinin (DHA) is one of artemisinin derivatives, and has inhibitory effects on a variety of cancer cells. For now, there is no published study focusing on the combination use of ALA-PDT with DHA to improve clinical efficacy of HR-HPV infection-related diseases. So in this study, we will examine the effectiveness of combined treatment of ALA-PDT and DHA for HR-HPV infection as well as its underlying mechanism.

METHODS

The human cervical cancer cell line HeLa (containing whole genome of HR-HPV18) was treated with ALA-PDT or/and DHA, and cell viability, long proliferation, ROS production and apoptosis were evaluated by CCK8, colony-forming assay, immunofluorescence and flow cytometry, respectively. The protein expression of NF-κB-HIF-1α-VEGF pathway and NRF2-HO-1 pathway was examined by western blot.

RESULTS

The results showed that DHA could enhance the effect of ALA-PDT on cell viability long proliferation, ROS production and apoptosis in HeLa cells. We also found that DHA inhibited NF-κB-HIF-1α-VEGF pathway which was activated by ALA-PDT. Besides, ALA-PDT combined with DHA activated NRF2-HO-1 pathway.

CONCLUSION

Although the NRF2 - NO-1 pathway as a resistance mechanism remains unresolved, DHA has the potential to enhance the effect of ALA-PDT for HPV infection-related diseases through inhibiting NF-κB - HIF-1α - VEGF pathway.

Lifetime and diffusion distance of singlet oxygen in air under everyday atmospheric conditions

Singlet oxygen is a toxic chemical but powerful oxidant, exploited in many chemical and biological applications. However, the lifetime of singlet oxygen in air under atmospheric conditions is yet to be known. This has limited safe usage of singlet oxygen in air, despite being a strong antimicrobial agent with the unique property of relaxing to breathable oxygen after serving its purpose. Here, we solve this long-standing problem by combining experimental and theoretical research efforts; we generate singlet oxygen using a photosensitizer at a local source and monitor the time-dependent extent of singlet oxygen reaction with probe molecules at a detector, precisely controlling the detector distance from the source. To explain our experimental results, we employ a theoretical model that fully accounts for singlet oxygen diffusion, radiative and nonradiative relaxations, and the bimolecular reaction with probe molecules at the detector. For all cases investigated, our model, with only two adjustable parameters, provides an excellent quantitative explanation of the experiment. From this analysis, we extract the lifetime of singlet oxygen in the air to be 2.80 s at 23 °C under 1 atm, during which time singlet oxygen diffuses about 0.992 cm. The correctness of this estimation is confirmed by a simple mean-first-passage time analysis of the maximum distance singlet oxygen can reach from the source. We also confirm the sterilization effects of singlet oxygen for distances up to 0.6-0.8 cm, depending on the bacteria strain in question, between the bacteria and the singlet oxygen source.

The role of ABCG2 in modulating responses to anti-cancer photodynamic therapy

The ATP-binding cassette (ABC) superfamily G member 2 (ABCG2) transmembrane protein transporter is known for conferring resistance to treatment in cancers. Photodynamic therapy (PDT) is a promising anti-cancer method involving the use of light-activated photosensitisers to precisely induce oxidative stress and cell death in cancers. ABCG2 can efflux photosensitisers from out of cells, reducing the capacity of PDT and limiting the efficacy of treatment. Many studies have attempted to elucidate the relationship between the expression of ABCG2 in cancers, its effect on the cellular retention of photosensitisers and its impact on PDT. This review looks at the studies which investigate the effect of ABCG2 on a range of different photosensitisers in different pre-clinical models of cancer. This work also evaluates the approaches that are being investigated to address the role of ABCG2 in PDT with an outlook on potential clinical validation.

Cell death in photodynamic therapy: From oxidative stress to anti-tumor immunity

Photodynamic therapy is a promising approach for cancer treatment that relies on the administration of a photosensitizer followed by tumor illumination. The generated oxidative stress may activate multiple mechanisms of cell death which are counteracted by cells through adaptive stress responses that target homeostasis rescue. The present renaissance of PDT was leveraged by the acknowledgment that this therapy has an immediate impact locally, in the illumination volume, but that subsequently it may also elicit immune responses with systemic impact. The investigation of the mechanisms of cell death under the oxidative stress of PDT is of paramount importance to understand how the immune system is activated and, ultimately, to make PDT a more appealing/relevant therapeutic option.

Emerging Therapeutic Targets in Oncologic Photodynamic Therapy

Background:

Reactive oxygen species sustain tumorigenesis and cancer progression through deregulated redox signalling which also sensitizes cancer cells to therapy. Photodynamic therapy (PDT) is a promising anti-cancer therapy based on a provoked singlet oxygen burst, exhibiting a better toxicological profile than chemo- and radiotherapy. Important gaps in the knowledge on underlining molecular mechanisms impede on its translation towards clinical applications.

Aims and Methods:

The main objective of this review is to critically analyse the knowledge lately gained on therapeutic targets related to redox and inflammatory networks underlining PDT and its outcome in terms of cell death and resistance to therapy. Emerging therapeutic targets and pharmaceutical tools will be documented based on the identified molecular background of PDT.

Results:

Cellular responses and molecular networks in cancer cells exposed to the PDT-triggered singlet oxygen burst and the associated stresses are analysed using a systems medicine approach, addressing both cell death and repair mechanisms. In the context of immunogenic cell death, therapeutic tools for boosting anti-tumor immunity will be outlined. Finally, the transcription factor NRF2, which is a major coordinator of cytoprotective responses, is presented as a promising pharmacologic target for developing co-therapies designed to increase PDT efficacy.

Conclusion:

There is an urgent need to perform in-depth molecular investigations in the field of PDT and to correlate them with clinical data through a systems medicine approach for highlighting the complex biological signature of PDT. This will definitely guide translation of PDT to clinic and the development of new therapeutic strategies aimed at improving PDT.

Large-Pore Mesoporous-Silica-Coated Upconversion Nanoparticles as Multifunctional Immunoadjuvants with Ultrahigh Photosensitizer and Antigen Loading Efficiency for Improved Cancer Photodynamic Immunotherapy

Reported immunoadjuvants still have many limitations, such as inferior cellular uptake capacity and biocompatibility, overly large particle sizes, single function, and unsatisfactory therapeutic efficacy. Here, large-pore mesoporous-silica-coated upconversion nanoparticles (UCMSs) with a size of less than 100 nm are successfully prepared by a typical silica sol-gel reaction using mesitylene as a pore-swelling agent and are applied as a novel immunoadjuvant. The obtained UCMSs not only show significantly higher loadings for the photosensitizers merocyanine 540 (MC540), model proteins (chicken ovalbumin (OVA)), and tumor antigens (tumor cell fragment (TF)), but also are successfully employed for highly efficient in vivo vaccine delivery. The prepared UCMSs-MC540-OVA under 980 nm near-infrared irradiation shows the best synergistic immunopotentiation action, verified by the strongest Th1 and Th2 immune responses and the highest frequency of CD4⁺ , CD8⁺ , and effector-memory T cells. Additionally, nanovaccines UCMSs-MC540-TF can more effectively inhibit tumor growth and increase the survival of colon cancer (CT26)-tumor-bearing BALB/c mice compared with either photodynamic therapy or immunological therapy alone, suggesting the enhanced immunotherapy efficacy and clinical potential of UCMSs as immunoadjuvants for cancer immunotherapy.

Artemisinin and AIEgen Conjugate for Mitochondria-Targeted and Image-Guided Chemo- and Photodynamic Cancer Cell Ablation

Cell organelle targeting is a promising approach for cancer therapy. We herein report a light-up probe (tetraphenylethenethiophene (TPETH)-Mito-1ART) to co-deliver artemisinin (ART) and an aggregation-induced emission (AIE) photosensitizer to cancer cell mitochondria for image-guided combination cancer cell ablation. This probe contains a TPETH core, two mitochondria targeting arms with ART on one arm, which show high specificity toward cancer cells over normal ones, predominant accumulation, and fluorescence turn-on in mitochondria. The fresh heme produced in mitochondria quickly activates ART, and the direct generation of reactive oxygen species at mitochondria promotes photodynamic therapy (PDT) performance. The incorporation of ART and PDT leads to a largely improved cancer cell ablation efficacy with a synergistic effect, which could quickly depolarize mitochondrial membrane and largely reduce cancer migration activity. This co-delivery strategy provides great potentials for subcellular organelle-targeted and image-guided combination cancer cell ablation.

Nanoparticles of Titanium and Zinc Oxides as Novel Agents in Tumor Treatment: a Review

Cancer has become a global problem. On all continents, a great number of people are diagnosed with this disease. In spite of the progress in medical care, cancer still ends fatal for a great number of the ill, either as a result of a late diagnosis or due to inefficiency of therapies. The majority of the tumors are resistant to drugs. Thus, the search for new, more effective therapy methods continues. Recently, nanotechnology has been attributed with big expectations in respect of the cancer fight. That interdisciplinary field of science creates nanomaterials (NMs) and nanoparticles (NPs) that can be applied, e.g., in nanomedicine. NMs and NPs are perceived as very promising in cancer therapy since they can perform as drug carriers, as well as photo- or sonosensitizers (compounds that generate the formation of reactive oxygen species as a result of either electromagnetic radiation excitation with an adequate wavelength or ultrasound activation, respectively). Consequently, two new treatment modalities, the photodynamic therapy (PDT) and the sonodynamic therapy (SDT) have been created. The attachment of ligands or antibodies to NMs or to NPs improve their selective distribution into the targeted organ or cell; hence, the therapy effectiveness can be improved. An important advantage of the targeted tumor treatment is lowering the cyto- and genotoxicity of active substance towards healthy cells. Therefore, both PDT and SDT constitute a valuable alternative to chemo- or radiotherapy. The vital role in cancer eradication is attributed to two inorganic sensitizers in their nanosized scale: titanium dioxide and zinc oxide.

Photodynamic therapy by conjugation of cell-penetrating peptide with fluorochrome

Photodynamic therapy (PDT) is a promising alternative therapy that could be used as an adjunct to chemotherapy and surgery for cancer, and works by destroying tissue with visible light in the presence of a photosensitizer (PS) and oxygen. The PS should restrict tissue destruction only to the tumor and be activated by light of a specific wavelength; both of these properties are required. Arginine-rich peptides, such as cell-penetrating peptides, have membrane-translocating and nuclear-localizing activities, which have led to their application in various drug delivery modalities. Protamine (Pro) is an arginine-rich peptide with membrane-translocating and nuclear-localizing properties. The reaction of an N-hydroxysuccinimide (NHS) ester of rhodamine (Rho) and clinical Pro was carried out in this study to yield RhoPro, and a demonstration of its phototoxicity, wherein clinical Pro improved the effect of PDT, was performed. The reaction between Pro and the NHS ester of Rho is a solution-phase reaction that results in the complete modification of the Pro peptides, which feature a single reactive amine at the N-terminal proline and a single carboxyl group at the C-terminal arginine. This study aimed to identify a new type of PS for PDT by in vitro and in vivo experiments and to assess the antitumor effects of PDT, using the Pro-conjugated PS, on a cancer cell line. Photodynamic cell death studies showed that the RhoPro produced has more efficient photodynamic activities than Rho alone, causing rapid light-induced cell death. The attachment of clinical Pro to Rho, yielding RhoPro, confers the membrane-internalizing activity of its arginine-rich content on the fluorochrome Rho and can induce rapid photodynamic cell death, presumably owing to light-induced cell membrane rupture. PDT using RhoPro for HT-29 cells was very effective and these findings suggest that RhoPro is a suitable candidate as a PS for solid tumors.

Direct 1O2 optical excitation: A tool for redox biology

Molecular oxygen (O2) displays very interesting properties. Its first excited state, commonly known as singlet oxygen (1O2), is one of the so-called Reactive Oxygen Species (ROS). It has been implicated in many redox processes in biological systems. For many decades its role has been that of a deleterious chemical species, although very positive clinical applications in the Photodynamic Therapy of cancer (PDT) have been reported. More recently, many ROS, and also 1O2, are in the spotlight because of their role in physiological signaling, like cell proliferation or tissue regeneration. However, there are methodological shortcomings to properly assess the role of 1O2 in redox biology with classical generation procedures. In this review the direct optical excitation of O2 to produce 1O2 will be introduced, in order to present its main advantages and drawbacks for biological studies. This photonic approach can provide with many interesting possibilities to understand and put to use ROS in redox signaling and in the biomedical field.

Strategies for optimizing the delivery to tumors of macrocyclic photosensitizers used in photodynamic therapy (PDT)

This review briefly summaries the principles and mechanisms of action of photodynamic therapy (PDT) as concerns its application in the oncological field, highlighting its drawbacks and some of the strategies that have been or are being explored to overcome them. The major aim is to increase the efficiency and selectivity of the photosensitizer (PS) uptake in the cancer cells for optimizing the PDT effects on tumors while sparing normal cells. Some attempts to achieve this are based on the conjugation of the PS to biomolecules (small ligands, peptides) functioning as carriers with the ability to efficiently penetrate cells and/or specifically recognize and bind proteins/receptors overexpressed on the surface of cancer cells. Alternatively, the PS can be entrapped in nanocarriers derived from various types of materials that can target the tumor by exploiting the enhanced permeability and retention (EPR) effects. The use of nanocarriers is particularly attractive because it allows the simultaneous delivery of more than one drug with the possibility of combining PDT with other therapeutic modalities.

Brazilian Green Propolis Extract Synergizes with Protoporphyrin IX-mediated Photodynamic Therapy via Enhancement of Intracellular Accumulation of Protoporphyrin IX and Attenuation of NF-κB and COX-2

Brazilian green propolis (BGP) is noted for its impressive antitumor effects and has been used as a folk medicine in various cultures for many years. It has been demonstrated that BGP could enhance the cytotoxic effect of cytostatic drugs on tumor cells. Photodynamic therapy (PDT) is a therapeutic approach used against malignant cells. To assess the synergistic effect of BGP extract on protoporphyrin IX (PpIX)-mediated photocytotoxicity, MTT assays were performed using A431 and HeLa cells. TUNEL assay and Annexin V-FITC/PI staining were performed to confirm the induction of apoptosis. Western blotting analysis was performed to examine the pro-apoptotic proteins, anti-apoptotic proteins and inflammation related proteins in A431 cells. Intracellular accumulation of PpIX was examined by flow cytometry. The synergistic effect of BGP extract in PpIX-PDT was also evaluated with a xenograft model. Our findings reveal that BGP extract increased PpIX-mediated photocytotoxicity in A431 and HeLa cells. PpIX-PDT with BGP extract treatment resulted in a decrease in Bcl-xL and an increase in NOXA, Bax and caspase-3 cleavage. The protein expression levels of p-IKKα/β, NF-κB and COX-2 were upregulated by PpIX-PDT but significantly attenuated when in combination with BGP extract. BGP extract was also found to significantly enhance the intracellular accumulation of PpIX in A431 cells. BGP extract increased PpIX-mediated photocytotoxicity in a xenograft model as well. Our findings provide evidence for a synergistic effect of BGP extract in PpIX-PDT both in vitro and in vivo.

Temperature Sensitive Singlet Oxygen Photosensitization by LOV-Derived Fluorescent Flavoproteins

Optogenetic sensitizers that selectively produce a given reactive oxygen species (ROS) constitute a promising tool for studying cell signaling processes with high levels of spatiotemporal control. However, to harness the full potential of this tool for live cell studies, the photophysics of currently available systems need to be explored further and optimized. Of particular interest in this regard, are the flavoproteins miniSOG and SOPP, both of which (1) contain the chromophore flavin mononucleotide, FMN, in a LOV-derived protein enclosure, and (2) photosensitize the production of singlet oxygen, O₂(a¹Δ_g). Here we present an extensive experimental study of the singlet and triplet state photophysics of FMN in SOPP and miniSOG over a physiologically relevant temperature range. Although changes in temperature only affect the singlet excited state photophysics slightly, the processes that influence the deactivation of the triplet excited state are more sensitive to temperature. Most notably, for both proteins, the rate constant for quenching of ³FMN by ground state oxygen, O₂(X³Σ_g^-), increases ∼10-fold upon increasing the temperature from 10 to 43 °C, while the oxygen-independent channels of triplet state deactivation are less affected. As a consequence, this increase in temperature results in higher yields of O₂(a¹Δ_g) formation for both SOPP and miniSOG. We also show that the quantum yields of O₂(a¹Δ_g) production by both miniSOG and SOPP are mainly limited by the fraction of FMN triplet states quenched by O₂(X³Σ_g^-). The results presented herein provide a much-needed quantitative framework that will facilitate the future development of optogenetic ROS sensitizers.

Photodynamic therapy using chloro-aluminum phthalocyanine decreases inflammatory response in an experimental rat periodontal disease model

BACKGROUND AND OBJECTIVE

Emerging evidence suggests that photodynamic therapy (PDT) can exhibit immunomodulatory activity. The purpose of the present study was to analyse cytokine profiles after application of PDT in gingival tissues of rats with ligature-induced periodontal disease (PD).

STUDY DESIGN/MATERIAL AND METHODS

Periodontal disease was induced through the introduction of a cotton thread around the first left mandibular molar, while the right side molars did not receive ligatures. After 7days of PD evolution, ligatures were removed from the left side, and the animals were randomically divided into the following treatment groups: I, rats without treatment; II, rats received chloro-aluminum phthalocyanine (AlClPc); III, rats received low-level laser alone; and IV, rats received AlClPc associated with low-level laser (PDT). The animals were killed 7days after the treatments, and the mandibles were histologically processed to assess morphological and immunohistochemical profile, while gingival tissues were removed for quantification of tumor necrosis factor (TNF)-α, interleukin (IL-)1β and IL-10 expression (by ELISA).

RESULTS

Histomorphological analysis of periodontal tissues demonstrated that PDT-treated animals show tissue necrosis, as well as lower TNF- α expression, compared to ligatured animals treated with AlClPc alone.

CONCLUSIONS

It was concluded that PDT using AlClPc entrapped in a lipid nanoemulsion may be useful in therapies, because of immunomodulatory effects that decreased the inflammatory response and cause tissue destruction.

A photodynamic bifunctional conjugate for prostate cancer: an in vitro mechanistic study

Photodynamic therapy (PDT) has drawn considerable attention for its efficacy against certain types of cancers. It shows however limits in the case of deep cancers, favoring tumor recurrence under suboptimal conditions. More insight into the molecular mechanisms of PDT-induced cytotoxicity and cytoprotection is essential to extend and strengthen this therapeutic modality. As PDT induces iNOS/NO in both tumor and microenvironment, we examined the role of nitric oxide (NO) in cytotoxicity and cytoprotection. Our findings show that NO mediates its cellular effects by acting on the NF-κB/YY1/RKIP loop, which controls cell growth and apoptosis. The cytoprotective effect of PDT-induced NO is observed at low NO levels, which activate the pro-survival/anti-apoptotic NF-κB and YY1, while inhibiting the anti-survival/pro-apoptotic and metastasis suppressor RKIP. In contrast, high PDT-induced NO levels inhibit NF-κB and YY1 and induce RKIP, resulting in significant anti-tumor activity. These findings reveal a critical role played by NO in PDT and suggest that the use of bifunctional PDT agents composed of a photosensitizer and a NO-donor could enhance the photo-treatment effect. A successful application of NO in anticancer therapy requires control of its concentration in the target tissue. To address this issue we propose as PDT agent, a bimolecular conjugate called DR2, composed of a photosensitizer (Pheophorbide a) and a non-steroidal anti-androgen molecule capable of releasing NO under the exclusive control of light. The mechanism of action of DR2 in prostate cancer cells is reported and discussed.

The PARP inhibitor PJ-34 sensitizes cells to UVA-induced phototoxicity by a PARP independent mechanism

A combination of a photosensitizer with light of matching wavelength is a common treatment modality in various diseases including psoriasis, atopic dermatitis and tumors. DNA damage and production of reactive oxygen intermediates may impact pathological cellular functions and viability. Here we set out to investigate the role of the nuclear DNA nick sensor enzyme poly(ADP-ribose) polymerase 1 in photochemical treatment (PCT)-induced tumor cell killing. We found that silencing PARP-1 or inhibition of its enzymatic activity with Veliparib had no significant effect on the viability of A431 cells exposed to 8-methoxypsoralen (8-MOP) and UVA (2.5J/cm(2)) indicating that PARP-1 is not likely to be a key player in either cell survival or cell death of PCT-exposed cells. Interestingly, however, another commonly used PARP inhibitor PJ-34 proved to be a photosensitizer with potency equal to 8-MOP. Irradiation of PJ-34 with UVA caused changes both in the UV absorption and in the 1H NMR spectra of the compound with the latter suggesting UVA-induced formation of tautomeric forms of the compound. Characterization of the photosensitizing effect revealed that PJ-34+UVA triggers overproduction of reactive oxygen species, induces DNA damage, activation of caspase 3 and caspase 8 and internucleosomal DNA fragmentation. Cell death in this model could not be prevented by antioxidants (ascorbic acid, trolox, glutathione, gallotannin or cell permeable superoxide dismutase or catalase) but could be suppressed by inhibitors of caspase-3 and -8. In conclusion, PJ-34 is a photosensitizer and PJ-34+UVA causes DNA damage and caspase-mediated cell death independently of PARP-1 inhibition.