5-Aminolevulinic acid-based photodynamic therapy: principles and experimental research

5-aminolevulinic acid induced photodynamic reactions in diagnosis and therapy for female lower genital tract diseases

Since the patients suffering from female lower genital tract diseases are getting younger and younger and the human papilloma virus (HPV) infection is becoming more widespread, the novel non-invasive precise modalities of diagnosis and therapy are required to remain structures of the organ and tissue, and fertility as well, by which the less damage to normal tissue and fewer adverse effects are able to be achieved. In all nucleated mammalian cells, 5-Aminolevulinic acid (5-ALA) is an amino acid that occurs spontaneously, which further synthesizes in the heme biosynthetic pathway into protoporphyrin IX (PpIX) as a porphyrin precursor and photosensitizing agent. Exogenous 5-ALA avoids the rate-limiting step in the process, causing PpIX buildup in tumor tissues. This tumor-selective PpIX distribution after 5-ALA application has been used successfully for tumor photodynamic diagnosis (PDD) and photodynamic therapy (PDT). Several ALA-based drugs have been used for ALA-PDD and ALA-PDT in treating many (pre)cancerous diseases, including the female lower genital tract diseases, yet the ALA-induced fluorescent theranostics is needed to be explored further. In this paper, we are going to review the studies of the mechanisms and applications mainly on ALA-mediated photodynamic reactions and its effectiveness in treating female lower genital tract diseases.

Upregulation of iNOS/NO in Cancer Cells That Survive a Photodynamic Challenge: Role of No in Accelerated Cell Migration and Invasion

Anti-tumor photodynamic therapy (PDT) is a unique modality that employs a photosensitizer (PS), PS-exciting light, and O2 to generate cytotoxic oxidants. For various reasons, not all malignant cells in any given tumor will succumb to a PDT challenge. Previous studies by the authors revealed that nitric oxide (NO) from inducible NO synthase (iNOS/NOS2) plays a key role in tumor cell resistance and also stimulation of migratory/invasive aggressiveness of surviving cells. iNOS was the only NOS isoform implicated in these effects. Significantly, NO from stress-upregulated iNOS was much more important in this regard than NO from preexisting enzymes. Greater NO-dependent resistance, migration, and invasion was observed with at least three different cancer cell lines, and this was attenuated by iNOS activity inhibitors, NO scavengers, or an iNOS transcriptional inhibitor. NO diffusing from PDT-targeted cells also stimulated migration/invasion potency of non-targeted bystander cells. Unless counteracted by appropriate measures, all these effects could seriously compromise clinical PDT efficacy. Here, we will review specific examples of these negative side effects of PDT and how they might be suppressed by adjuvants such as NO scavengers or inhibitors of iNOS activity or expression.

Fagopyrin F fraction from Fagopyrum tataricum demonstrates photodynamic inactivation of skin infecting bacterium and squamous cell carcinoma (A431) cells

Photodynamic therapy (PDT) stands out as a noteworthy development as an alternative targeted treatment against skin ailments. While PDT has advanced significantly, research into photo-activatable "Green drugs" derived from plants which are less toxic than the synthetic drugs has not kept pace. This study investigates the potential of Fagopyrin F Containing Fraction (FCF) derived from Fagopyrum tataricum in mediating PDT against Staphylococcus aureus and skin cancer cells (A431). FCF was isolated from the plant extract using thin-layer chromatography, followed by identification of the compound through high-performance liquid chromatography and high-resolution liquid chromatography-mass spectrometry. FCF was tested to determine its antibacterial and anticancer efficacy. Results revealed that FCF-mediated PDT exhibited potent action against S. aureus, significantly reducing bacterial viability (MIC 19.5 μg/100 μL). Moreover, FCF-mediated PDT showed good efficacy against A431 cells, resulting in a notable reduction in cell viability (IC50 29.08 μg/mL). Given the known association between S. aureus and squamous cell carcinoma (SCC), FCF shows the potential to effectively target and eradicate both SCC and the related S. aureus present within the lesions. In silico study reveals that Fagopyrin F effectively binds with the epidermal growth factor (EGFR), one among the highly expressed proteins in the A431 cells, with a binding energy of - 9.6 kcal/mol. The affinity of Fagopyrin F for EGFR on A431 cancer cells along with its cytotoxicity against skin cancer cells while safeguarding the normal cells (L929) plays a major part in the way it targets cancer cells. However, its safety, efficacy, and long-term advantages in treating skin conditions require more investigation, including in vivo investigations and clinical trials.

Novel Iron-Chelating Prodrug Significantly Enhanced Fluorescence-Mediated Detection of Glioma Cells Experimentally In Vitro

(1) Background: The protoporphyrin IX (PpIX)-mediated fluorescence-guided resection and interoperative photodynamic therapy (PDT) of remaining cells may be effective adjuvants to the resection of glioma. Both processes may be enhanced by increasing intracellular PpIX concentrations, which can be achieved through iron chelation. AP2-18 is a novel combinational drug, which ester-links a PpIX precursor (aminolaevulinic acid; ALA) to an iron-chelating agent (CP94). (2) Methods: Human glioma U-87 MG cells were cultured in 96-well plates for 24 h and incubated for 3 or 6 h with various test compound combinations: ALA (±) CP94, methyl aminolevulinate (MAL) (±) CP94 and AP2-18. PpIX fluorescence was measured at 0, 3 or 6 h with a Bio-tek Synergy HT plate reader, as well as immediately after irradiation with a 635 nm red light (Aktilite CL16 LED array), representing the PDT procedure. Cell viability post-irradiation was assessed using the neutral red assay. (3) Results: AP2-18 significantly increased PpIX fluorescence compared to all other test compounds. All treatment protocols effectively achieved PDT-induced cytotoxicity, with no significant difference between test compound combinations. (4) Conclusions: AP2-18 has potential to improve the efficacy of fluorescence-guided resection either with or without the subsequent intraoperative PDT of glioma. Future work should feature a more complex in vitro model of the glioma microenvironment.

Pro-Tumor Activity of Endogenous Nitric Oxide in Anti-Tumor Photodynamic Therapy: Recently Recognized Bystander Effects

Various studies have revealed that several cancer cell types can upregulate inducible nitric oxide synthase (iNOS) and iNOS-derived nitric oxide (NO) after moderate photodynamic treatment (PDT) sensitized by 5-aminolevulinic acid (ALA)-induced protoporphyrin-IX. As will be discussed, the NO signaled cell resistance to photokilling as well as greater growth and migratory aggressiveness of surviving cells. On this basis, it was predicted that diffusible NO from PDT-targeted cells in a tumor might enhance the growth, migration, and invasiveness of non- or poorly PDT-targeted bystander cells. This was tested using a novel approach in which ALA-PDT-targeted cancer cells on a culture dish were initially segregated from non-targeted bystander cells of the same type via impermeable silicone-rimmed rings. Several hours after LED irradiation, the rings were removed, and both cell populations were analyzed in the dark for various responses. After a moderate extent of targeted cell killing (~25%), bystander proliferation and migration were evaluated, and both were found to be significantly enhanced. Enhancement correlated with iNOS/NO upregulation in surviving PDT-targeted cancer cells in the following cell type order: PC3 > MDA-MB-231 > U87 > BLM. If occurring in an actual PDT-challenged tumor, such bystander effects might compromise treatment efficacy by stimulating tumor growth and/or metastatic dissemination. Mitigation of these and other negative NO effects using pharmacologic adjuvants that either inhibit iNOS transcription or enzymatic activity will be discussed.

Photodynamic Therapy, Probiotics, Acetic Acid, and Essential Oil in the Treatment of Chronic Wounds Infected with Pseudomonas aeruginosa

As a prevalent medical problem that burdens millions of patients across the world, chronic wounds pose a challenge to the healthcare system. These wounds, often existing as a comorbidity, are vulnerable to infections. Consequently, infections hinder the healing process and complicate clinical management and treatment. While antibiotic drugs remain a popular treatment for infected chronic wounds, the recent rise of antibiotic-resistant strains has hastened the need for alternative treatments. Future impacts of chronic wounds are likely to increase with aging populations and growing obesity rates. With the need for more effective novel treatments, promising research into various wound therapies has seen an increased demand. This review summarizes photodynamic therapy, probiotics, acetic acid, and essential oil studies as developing antibiotic-free treatments for chronic wounds infected with Pseudomonas aeruginosa. Clinicians may find this review informative by gaining a better understanding of the state of current research into various antibiotic-free treatments. Furthermore. this review provides clinical significance, as clinicians may seek to implement photodynamic therapy, probiotics, acetic acid, or essential oils into their own practice.

5-Aminolevulinic Acid as a Theranostic Agent for Tumor Fluorescence Imaging and Photodynamic Therapy

5-Aminolevulinic acid (ALA) is a naturally occurring amino acid synthesized in all nucleated mammalian cells. As a porphyrin precursor, ALA is metabolized in the heme biosynthetic pathway to produce protoporphyrin IX (PpIX), a fluorophore and photosensitizing agent. ALA administered exogenously bypasses the rate-limit step in the pathway, resulting in PpIX accumulation in tumor tissues. Such tumor-selective PpIX disposition following ALA administration has been exploited for tumor fluorescence diagnosis and photodynamic therapy (PDT) with much success. Five ALA-based drugs have now received worldwide approval and are being used for managing very common human (pre)cancerous diseases such as actinic keratosis and basal cell carcinoma or guiding the surgery of bladder cancer and high-grade gliomas, making it the most successful drug discovery and development endeavor in PDT and photodiagnosis. The potential of ALA-induced PpIX as a fluorescent theranostic agent is, however, yet to be fully fulfilled. In this review, we would like to describe the heme biosynthesis pathway in which PpIX is produced from ALA and its derivatives, summarize current clinical applications of ALA-based drugs, and discuss strategies for enhancing ALA-induced PpIX fluorescence and PDT response. Our goal is two-fold: to highlight the successes of ALA-based drugs in clinical practice, and to stimulate the multidisciplinary collaboration that has brought the current success and will continue to usher in more landmark advances.

Evaluation of the Effect of Photodynamic Therapy on CAM-Grown Sarcomas

Resection margin adequacy plays a critical role in the local control of sarcomas. Fluorescence-guided surgery has increased complete resection rates and local recurrence-free survival in several oncological disciplines. The purpose of this study was to determine whether sarcomas exhibit sufficient tumor fluorescence (photodynamic diagnosis (PDD)) after administration of 5-aminolevulinic acid (5-ALA) and whether photodynamic therapy (PDT) has an impact on tumor vitality in vivo. Sixteen primary cell cultures were derived from patient samples of 12 different sarcoma subtypes and transplanted onto the chorio-allantoic membrane (CAM) of chick embryos to generate 3-dimensional cell-derived xenografts (CDXs). After treatment with 5-ALA, the CDXs were incubated for another 4 h. Subsequently accumulated protoporphyrin IX (PPIX) was excited by blue light and the intensity of tumor fluorescence was analyzed. A subset of CDXs was exposed to red light and morphological changes of both CAMs and tumors were documented. Twenty-four hours after PDT, the tumors were excised and examined histologically. High rates of cell-derived engraftments on the CAM were achieved in all sarcoma subtypes and an intense PPIX fluorescence was observed. PDT of CDXs resulted in a disruption of tumor-feeding vessels and 52.4% of CDXs presented as regressive after PDT treatment, whereas control CDXs remained vital in all cases. Therefore, 5-ALA mediated PDD and PDT appear to be promising tools in defining sarcoma resection margins (PDD) and adjuvant treatment of the tumor bed (PDT).

Photodynamic Effects with 5-Aminolevulinic Acid on Cytokines and Exosomes in Human Peripheral Blood Mononuclear Cells from Patients with Crohn's Disease

Photodynamic therapy (PDT) using 5-aminolevulinic acid (ALA) which is the precursor of the photosensitizer protoporphyrin IX (PpIX) is an available treatment for several diseases. ALA-PDT induces the apoptosis and necrosis of target lesions. We have recently reported the effects of ALA-PDT on cytokines and exosomes of human healthy peripheral blood mononuclear cells (PBMCs). This study has investigated the ALA-PDT-mediated effects on PBMC subsets from patients with active Crohn's disease (CD). No effects on lymphocyte survival after ALA-PDT were observed, although the survival of CD3^-/CD19⁺ B-cells seemed slightly reduced in some samples. Interestingly, ALA-PDT clearly killed monocytes. The subcellular levels of cytokines and exosomes associated with inflammation were widely downregulated, which is consistent with our previous findings in PBMCs from healthy human subjects. These results suggest that ALA-PDT may be a potential treatment candidate for CD and other immune-mediated diseases.

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.

Amplifying the efficacy of ALA-based prodrugs for photodynamic therapy using nanotechnology

5-aminolevulinic acid (ALA) is a clinically approved prodrug involved in intracellular Heme biosynthesis to produce the natural photosensitizer (PS) Protoporphyrin IX (PpIX). ALA based photodynamic therapy (PDT) has been used to treat various malignant and non-malignant diseases. However, natural ALA has disadvantages such as weak lipophilicity, low stability and poor bioavailability, greatly reducing its clinical performance. The emerging nanotechnology is expected to address these limitations and thus improve the therapeutic outcomes. Herein, we summarized important recent advances in the design of ALA-based prodrugs using nanotechnology to improve the efficacy of PDT. The potential limitations and future perspectives of ALA-based nanomedicines are also briefly presented and discussed.

Hyper-Aggressiveness of Bystander Cells in an Anti-Tumor Photodynamic Therapy Model: Role of Nitric Oxide Produced by Targeted Cells

When selected tumor cells in a large in vitro population are exposed to ionizing radiation, they can send pro-survival signals to non-exposed counterparts (bystander cells). If there is no physical contact between irradiated and bystander cells, the latter respond to mediators from targeted cells that diffuse through the medium. One such mediator is known to be nitric oxide (NO). It was recently discovered that non-ionizing anti-tumor photodynamic therapy (PDT) can also elicit pro-survival/expansion bystander effects in a variety of human cancer cells. A novel silicone ring-based approach was used for distinguishing photodynamically-targeted cells from non-targeted bystanders. A key finding was that NO from upregulated iNOS in surviving targeted cells diffused to the bystanders and caused iNOS/NO upregulation there, which in turn stimulated cell proliferation and migration. The intensity of these responses depended on the extent of iNOS/NO induction in targeted cells of different cancer lines. Moreover, the responses could be replicated using NO from the chemical donor DETA/NO. This review will focus on these and related findings, their negative implications for clinical PDT, and how these might be averted by using pharmacologic inhibitors of iNOS activity or transcription.

5-aminolevulinic acid and sodium ferrous citrate decreased cell viability of gastric cancer cells by enhanced ROS generation through improving COX activity

BACKGROUND

Mitochondrial dysfunctions are related to cancer development.. 5-aminolevulinic acid (ALA) is used for photodynamic therapy (PDT). In this PDT, protoporphyrin IX (PpIX), which is converted from ALA, can generate reactive oxygen species (ROS) that kill the cancer cell. ALA is also reported to promote cytochrome c oxidase (COX) activity, which can generate ROS itself. Therefore, this study focused on the effect of ALA during PDT. In addition, in the previous study, sodium ferrous citrate (SFC) is reported to increase COX activity. So, this study also aims to improve the COX activity by the addition of SFC that can promote ROS generation, which has a cytotoxic effect.

METHODS

In this study, we used ALA and SFC, then evaluated the effects of the treatment on the human gastric cancer cell line MKN45, including the induction of cell death.

RESULTS

This study showed that treatment with ALA and SFC increases intracellular heme and heme proteins. Moreover, COX activity was promoted, resulting in the production of intracellular reactive oxygen species (ROS), which eventually reduced the cell viability in human gastric cancer cell line MKN45.

CONCLUSION

Our study can detect ROS generation with ALA and SFC. Furthermore, we found this generation of ROS has a cytotoxic effect. Therefore, this phenomenon contributes to the effect of PDT.

Role of nitric oxide in hyper-aggressiveness of tumor cells that survive various anti-cancer therapies

Low level nitric oxide (NO) produced by inducible NO synthase (iNOS) in many malignant tumors is known to play a key role in the survival and proliferation of tumor cells. NO can also induce or augment resistance to anti-tumor treatments such as platinum-based chemotherapy (CT), ionizing radiotherapy (RT), and non-ionizing photodynamic therapy (PDT). In each of these treatments, tumor cells that survive the challenge may exhibit a striking increase in NO-dependent proliferative, migratory, and invasive aggressiveness compared with non-challenged controls. Moreover, NO from cells directly targeted by PDT can often stimulate aggressiveness in non- or poorly targeted bystander cells. Although NO-mediated resistance to many of these therapies is fairly-well recognized by now, the hyper-aggressiveness of surviving cells and bystander counterparts is not. We will focus on these negative aspects in this review, citing examples from the PDT, CT, and RT publications. Increased aggressiveness of cells that escape therapeutic elimination is a concern because it could enhance tumor progression and metastatic dissemination. Pharmacologic approaches for suppressing these negative responses will also be discussed, e.g., administering inhibitors of iNOS activity or iNOS expression as therapeutic adjuvants.

Suppression of resistance to aminolevulinic acid-based photodynamic therapy in esophageal cell lines by administration of iron chelators in collagen type I matrices

PURPOSE

Photodynamic therapy (PDT) utilizes visible light to activate the cytotoxic effects of photosensitizing drugs. PDT protocols require optimization to overcome treatment resistance and induce a beneficial anti-tumor immune response. The aim of this study was to examine the possibility to suppress the resistance of esophageal cell lines to aminolevulinic acid (ALA)-PDT by administration of iron chelators to induce sufficient cell cytotoxicity under pathophysiologically relevant conditions, mimicking the advanced stages of cancer.

MATERIALS AND METHODS

Effects of ALA-PDT in combination with iron chelators were compared in three esophageal cell lines in conventional monolayers and in 3 D cultures based on collagen type I. Modified colony assay and fluorescence-based live cell imaging, respectively were applied. The latter was used also to test the capability of pre-polarized macrophages to interact with cancer cells subjected to ALA-PDT with or without iron chelators.

RESULTS

Iron chelators were effective in the enhancement of ALA-PDT in all cell lines under both culture conditions. Fluorescence evaluation of cell viability in 3 D cultures indicated the contribution of apoptotic cell death after ALA-PDT, both with and without iron chelators. Engulfment of remnants of dead cancer cells by macrophages in 2 D cultures was indicated, however, the interaction between macrophages and cancer cells in 3 D cultures subjected to ALA-PDT with or without iron chelators was not present.

CONCLUSIONS

The potential of iron chelators to enhance ALA-PDT was maintained in 3 D collagen matrices. Although PDT dose (ALA concentration, light exposure time) required modification in a cell line-dependent manner to achieve a comparable effect of PDT alone in conventional monolayers and in collagen matrices, the potential of iron chelators to suppress the resistance of esophageal cells to ALA-PDT was not influenced by a fibrillar collagen matrix.

Evolutionary Trend Analysis of Research on 5-ALA Delivery and Theranostic Applications Based on a Scientometrics Study

5-aminolevulinic acid (5-ALA) has been extensively studied for its sustainability and broad-spectrum applications in medical research and theranostics, as well as other areas. It’s a precursor of protoporphyrin IX (PpIX), a sustainable endogenous and naturally-existing photosensitizer. However, to the best of our knowledge, a scientometrics study based on the scientific knowledge assay of the overall situation on 5-ALA research has not been reported so far, which would be of major importance to the relevant researchers. In this study, we collected all the research articles published in the last two decades from the Web of Science Core Collection database and employed bibliometric methods to comprehensively analyze the dataset from different perspectives using CiteSpace. A total of 1595 articles were identified. The analysis results showed that China published the largest number of articles, and SBI Pharmaceuticals Co., Ltd. was the most productive institution that sponsored several of the most productive authors. The cluster analysis and burst detections indicated that the improvement of photodynamic efficacy theranostics is the up-to-date key direction in 5-ALA research. Furthermore, we emphatically studied nanotechnology involvement in 5-ALA delivery and theranostics research. We envision that our results will be beneficial for researchers to have a panorama of and deep insights into this area, thus inspiring further exploitations, especially of the nanomaterial-based systems for 5-ALA delivery and theranostic applications.

Identification and pharmacological modification of resistance mechanisms to protoporphyrin-mediated photodynamic therapy in human cutaneous squamous cell carcinoma cell lines

BACKGROUND

Photodynamic therapy (PDT) is clinically approved to treat neoplastic skin diseases such as precursors of cutaneous squamous cell carcinoma (cSCC). In PDT, 5-aminolevulinic acid (5-ALA) drives the selective formation of the endogenous photosensitizer protoporphyrin IX (PpIX). Although 5-ALA PDT is clinically highly effective, resistance might occur due to decreased accumulation of PpIX in certain tumors. Such resistance may be caused by any fundamental step of PpIX accumulation: 5-ALA uptake, PpIX synthesis and PpIX efflux.

METHODS

We investigated PpIX accumulation and photodynamically induced cell death in PDT refractory SCC-13, PDT susceptible A431, and normal human epidermal keratinocytes (NHEK). Expression of genes associated with cellular PpIX kinetics was investigated on mRNA and protein level. PpIX accumulation and cell death upon illumination were pharmacologically manipulated using drugs targeting 5-ALA uptake, PpIX synthesis or efflux.

RESULTS

The experiments indicate that taurine transporter (SLC6A6) is the major pathway for 5-ALA uptake in cSCC cells, while being less important in NHEK. Downregulation of PpIX synthesis enzymes in SCC-13 was counteracted by methotrexate (MTX) treatment, which restored PpIX formation and cell death. PpIX efflux inhibitors targeting ABC transporters led to significantly increased PpIX accumulation in SCC-13, thereby fully overcoming resistance.

CONCLUSIONS

The results indicate a conserved threshold for PpIX accumulation with respect to PDT-resistance. Cells showed increased viability after PDT at PpIX concentrations below 1.5 nM. Selective uptake of 5-ALA via taurine transporter SLC6A6 in cutaneous tumor cells is novel but unrelated to resistance. MTX can partially abrogate resistance by PpIX synthesis enzyme induction, while efflux mechanisms via ABC transporters seem the main driving force and promising drug targets.

Photodynamic therapy with 5-aminolevulinic acid: A new diagnostic, therapeutic, and surgical aid for neuroblastoma

BACKGROUND

5-Aminolevulinic acid (ALA)-based photodynamic therapy (PDT) is widely used in cancer therapy because of the tumor-specific accumulation of photosensitizing protoporphyrin IX (PpIX). We aimed to assess the susceptibility of human neuroblastoma cell lines to ALA-PDT and determine the mechanism of PDT.

METHODS

We used four human neuroblastoma cell lines (GOTO, NB9, IMR32, and NB1) and a gastric cancer cell line (MKN45) as a positive control. Cells were treated with increasing concentrations of ALA, and the ALA-induced production of PpIX in tumor cells was quantified using fluorescence spectrophotometry. PDT photocytotoxicity was measured by exposing the cells to a 630-nm irradiation for 10 min, and apoptotic cells stained with phosphatidylserine (PS) and propidium iodide (PI) were detected through flow cytometry.

RESULTS

ALA cytotoxicity was not observed in any cell line. The intracellular concentration of PpIX increased in an ALA dose-dependent manner, and intracellular fluorescence of PpIX increased in a time-dependent manner. The viability of NB-1 cells treated with 250 μM 5-ALA rapidly decreased to 5%. Photocytotoxicity was observed in the following order: NB1, IMR32, NB-9, and GOTO. Photocytotoxicity was positively correlated with intracellular PpIX concentrations. PS+/PI- cells increased up to 21% after 12 h, and PS+/PI+ cells accounted for 35% of all cells after 24 h, which suggests that ALA-PDT induced apoptotic cell death.

CONCLUSION

This study shows that neuroblastoma cell lines were susceptible to 5-ALA-PDT, resulting in persistent apoptotic cell death.

LEVELS OF EVIDENCE

N/A for basic study.

Photodynamic Effects with 5-Aminolevulinic Acid on Cytokines and Exosomes in Human Peripheral Blood Mononuclear Cells

Photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA), a precursor to the potent photosensitizer, protoporphyrin IX (PpIX), is an established modality for several malignant and premalignant diseases. This treatment is based on the light-activated PpIX in targeted lesions. Although numerous studies have confirmed the necrosis and apoptosis involved in the mechanism of action of this modality, little information is available for the change of exosome levels after treatment. We report from the first study on the effects of ALA-PDT on cytokines and exosomes of human healthy peripheral blood mononuclear cells (PBMCs). The treatment reduced the cytokines and exosomes studied, although there was variation among individual PBMC samples. This reduction is consistent with PDT-mediated survivals of subsets of PBMCs. More specifically, the ALA-PDT treatment apparently decreased all pro-inflammatory cytokines included, suggesting that this treatment may provide a strong anti-inflammatory effect. In addition, the treatment has decreased the levels of different types of exosomes, the HLA-DRDPDQ exosome in particular, which plays an important role in the rejection of organ transplantation as well as autoimmune diseases. These results may suggest future therapeutic strategies of ALA-PDT.

Analysis of Factors Affecting 5-ALA Fluorescence Intensity in Visualizing Glial Tumor Cells-Literature Review

Glial tumors are one of the most common lesions of the central nervous system. Despite the implementation of appropriate treatment, the prognosis is not successful. As shown in the literature, maximal tumor resection is a key element in improving therapeutic outcome. One of the methods to achieve it is the use of fluorescent intraoperative navigation with 5-aminolevulinic acid. Unfortunately, often the level of fluorescence emitted is not satisfactory, resulting in difficulties in the course of surgery. This article summarizes currently available knowledge regarding differences in the level of emitted fluorescence. It may depend on both the histological type and the genetic profile of the tumor, which is reflected in the activity and expression of enzymes involved in the intracellular metabolism of fluorescent dyes, such as PBGD, FECH, UROS, and ALAS. The transport of 5-aminolevulinic acid and its metabolites across the blood–brain barrier and cell membranes mediated by transporters, such as ABCB6 and ABCG2, is also important. Accompanying therapies, such as antiepileptic drugs or steroids, also have an impact on light emission by tumor cells. Accurate determination of the factors influencing the fluorescence of 5-aminolevulinic acid-treated cells may contribute to the improvement of fluorescence navigation in patients with highly malignant gliomas.

5-ALA-mediated fluorescence of musculoskeletal tumors in a chick chorio-allantoic membrane model: preclinical in vivo qualification analysis as a fluorescence-guided surgery agent in Orthopedic Oncology

Background

Fluorescence-guided surgery (FGS) with 5-aminolevulinic acid (5-ALA) and other contrast agents has shown its efficacy in improving resection margins, local recurrence and survival rates in several medical disciplines. It is the objective of this study to analyze the engraftment rate of musculoskeletal tumor specimens on the chick chorio-allantoic membrane (CAM), the rate of tumor fluorescence (PDD), and the effects of photodynamic therapy (PDT) after exposure of tumors to 5-ALA in an in vivo environment.

Methods

A total of 486 CAMs were inoculated with macroscopic tumor grafts (n = 26; n = 478 eggs) and primary cell culture suspensions (n = 2; n = 8 eggs) from 26 patients on day 10 of egg development. On day 16, 2 mg/200 µl 5-ALA were topically applied per egg. After 4 h of incubation, Protoporphyrin IX was excited using blue light (420 ± 10 nm). Tumor fluorescence (PDD) was photo-documented. A subgroup of specimens was additionally exposed to red light (635 nm ± 10 nm; PDT). After the termination of the experiment, CAM-grown tumors were histopathologically analyzed.

Results

Benign and borderline tumors (chondroblastoma, giant cell tumor of bone and atypical chondrogenic tumor) presented with high rates of detectable fluorescence. Comparable results were found for chondrosarcoma, osteosarcoma and Ewing’s sarcoma among bone and dedifferentiated liposarcoma, myxofibrosarcoma and undifferentiated pleomorphic sarcoma among soft tissue sarcomas. Overall, tumor fluorescence was negative for 20.2%, single-positive (+) for 46.9% and double-positive (++) for 32.9% of macroscopic xenografts, and negative in 20% and (+) in 80% of primary cell culture tumors. Macroscopic tumor xenografts (n = 478) were identified as viable in 14.8%, partially viable in 2.9% and partially to completely regressive in 45.2%. All (n = 8) tumors grown from primary cell culture were viable. After PDT, tumor samples were found viable in 5.5%, partially viable in 5.5% and partially to completely regressive in 68%. Egg survival increased with decreasing PDT doses.

Conclusions

The CAM model proves to be a suitable in vivo model for the investigation of short-term observation questions in musculoskeletal tumors. The findings of this study warrant further investigation of PDT effects on musculoskeletal tumors and a possible incorporation of 5-ALA FGS in clinical Orthopedic Oncology care.

Mesoporous Silica-Coated Upconversion Nanoparticles Assisted Photodynamic Therapy Using 5-Aminolevulinic Acid: Mechanistic and In Vivo Studies

Exclusively red-emitting upconversion nanoparticles (UCNPs) with the composition NaErF₄:0.5%Tm as a core and NaYF₄ as a shell were synthesized for performing photodynamic therapy (PDT). A possible mechanism was proposed for core-shell UCNPs formation. For loading a maximum amount of 5-aminolevulinic acid (5-ALA), mesoporous silica coating was performed on UCNPs. Studies under dark conditions confirmed the biocompatibility of 5-ALA-loaded UCNPs formulation (UCNPs-5-ALA) with MCF-7 cells. Meanwhile, studies under light-exposed conditions exhibited effective cytotoxicity against MCF-7 cells. Studies employing D₂O-based cell cultured media and addition of DABCO in cell culture established that the cell death was due to oxidation of cellular components by reactive oxygen species (ROS) triggering the apoptosis. The formation of ROS was confirmed by DCF(H)DA-based ROS analysis via fluorescence microscopy to demonstrate the ROS production, which mediates the programmed cell death. Additionally, we have validated the apoptosis in MCF-7 cells with flow cytometry analyses. This was further confirmed by an electrophoretic mobility shift assay on nuclear extract and measurement of mitochondrial membrane potential. In the case of animal model studies, the formulation UCNPs-5-ALA without irradiation (980 nm) did not possess any in vivo cytotoxicity on tumor-induced SCID mice and there was a minimum migration of UCNPs-5-ALA to the vital organs but maximum retention at the tumor site only. Meanwhile, only the mice treated with UCNPs-5-ALA and irradiated on the tumor region with 980 nm laser (500 mW) for 20 min possessed a tumor with a size reduced to about 75% as compared with the corresponding control groups. To the best of our knowledge, this type of study was conducted for the first time employing exclusively red-emitting phosphors for effective PDT.

Disulfur-bridged polyethyleneglycol/DOX nanoparticles for the encapsulation of photosensitive drugs: a case of computational simulations on the redox-responsive chemo-photodynamic drug delivery system

Tumor redox stimulus-responsive nanoparticulate drug delivery systems (nano-DDSs) have attracted considerable attention due to their thermodynamically stable microstructures and well-controlled drug release properties. However, drug-loading nanoparticle conformation and redox-triggered drug release mechanisms at the molecular level remain unclear. Herein, doxorubicin-conjugated polymers were constructed using disulfide bonds as linkages (PEG-SS-DOX), which loaded photosensitizer chlorin e6 (Ce6). We integrated multiple scale dynamic simulations (density functional theory (DFT) calculation, atomistic molecular dynamics (MD) simulation and dissipative particle dynamics (DPD) simulations) to elucidate the assembly/drug release dynamic processing. First, it was revealed that the emergence of the calculated bond flexible angle of disulfide bonds facilitated the assembly behavior and improved the stability of conformation. Sorted by the binding model, hydrogen bonding accounted for the major interactions between polymers and photosensitive drugs. DPD simulations were further delved into to acquire knowledge regarding the drug-free self-aggregation and Ce6-loaded assembly mechanism. The results show that nano-assembly conformation not only depended on the concentration of polymers, but also were associated with the polymer-drug ratio. Different from dicarbon bond-bridging polymers, disulfide bonds would contribute to the breakage of the polymer and the rapid release of DOX and Ce6. Our findings provide deep insights into the influence of redox-responsive chemical linkages and offer theoretical guidance to the rational design of specific stimulus-responsive nano-DDSs for cancer therapy.

Implications of photodynamic cancer therapy: an overview of PDT mechanisms basically and practically

BACKGROUND

Tumor eradication is one of the most important challengeable categories in oncological studies. In this account, besides the molecular genetics methods including cell therapy, gene therapy, immunotherapy, and general cancer therapy procedures like surgery, radiotherapy, and chemotherapy, photodynamic adjuvant therapy is of great importance. Photodynamic therapy (PDT) as a relatively noninvasive therapeutic method utilizes the irradiation of an appropriate wavelength which is absorbed by a photosensitizing agent in the presence of oxygen. In this procedure, a series of events lead to the direct death of malignant cells such as damage to the microvasculature and also the induction of a local inflammatory function. PDT has participated with other treatment modalities especially in the early stage of malignant tumors and has resulted in decreasing morbidity besides improving survival rate and quality of life. High spatial resolution of PDT has attracted considerable attention in the field of image-guided photodynamic therapy combined with chemotherapy of multidrug resistance cancers. Although PDT outcomes vary across the different tumor types, minimal natural tissue toxicity, minor systemic effects, significant reduction in long-term disease, lack of innate or acquired resistance mechanisms, and excellent cosmetic effects, as well as limb function, make it a valuable treatment option for combination therapies.

SHORT CONCLUSION

In this review article, we tried to discuss the potential of PDT in the treatment of some dermatologic and solid tumors, particularly all its important mechanisms.

Chitosan-tripolyphosphate nanoparticles-mediated co-delivery of MTHFD1L shRNA and 5-aminolevulinic acid for combination photodynamic-gene therapy in oral cancer

BACKGROUND

Rationally designed nanostructured materials can produce improved drug carriers that play an increasingly important role in cancer treatment. In comparison with conventional drug combination approaches, using co-delivery systems of multiple drugs achieves sophisticated targeting strategies and multifunctionality.

METHODS

First, a nano-co-delivery of chitosan/tripolyphosphate (CS-TPP) was synthesized and characterized combining 5-aminolevulinic acid photodynamic therapy (ALA-PDT) with methylenetetrahydrofolate dehydrogenase 1-like (MTHFD1L) shRNA. In this report, we investigated the efficacy of the simultaneous delivery of shRNA/photosensitizer on the gene expression of oral squamous cell carcinoma (OSCC) cells. The efficacy of CS-TPP-(shMTHFD1L-ALA)-PDT in inducing apoptosis and in generating of reactive oxygen species (ROS) in vitro was then assessed by Annexin V-PI and DCFH-DA assays respectively. In vivo therapeutic experiments were conducted in well-established orthotopic animal models of HNSCC.

RESULTS

The results showed that the CS-TPP-(shMTHFD1L-ALA) nanoparticles (NPs) were approximately 145 nm in size. The cytotoxicity of OSCC cells was significantly increased by co-delivery of MTHFD1L shRNA and ALA-PDT compared with other groups. Furthermore, individual and combined therapies revealed remarkable pro-apoptotic, ROS and anti-tumorigenesis effects, and CS-TPP-(shMTHFD1L-ALA)-PDT had additive effects in vitro and in vivo.

CONCLUSION

These observations indicate that CS-TPP-(shMTHFD1L-ALA) NPs may be an ideal candidate for gene/photosensitizer delivery.

Challenges and opportunities of bioprocessing 5-aminolevulinic acid using genetic and metabolic engineering: a critical review

5-Aminolevulinic acid (5-ALA), a non-proteinogenic five-carbon amino acid, has received intensive attentions in medicine due to its approval by the US Food and Drug Administration (FDA) for cancer diagnosis and treatment as photodynamic therapy. As chemical synthesis of 5-ALA performed low yield, complicated processes, and high cost, biosynthesis of 5-ALA via C4 (also called Shemin pathway) and C5 pathway related to heme biosynthesis in microorganism equipped more advantages. In C4 pathway, 5-ALA is derived from condensation of succinyl-CoA and glycine by 5-aminolevulic acid synthase (ALAS) with pyridoxal phosphate (PLP) as co-factor in one-step biotransformation. The C5 pathway involves three enzymes comprising glutamyl-tRNA synthetase (GltX), glutamyl-tRNA reductase (HemA), and glutamate-1-semialdehyde aminotransferase (HemL) from α-ketoglutarate in TCA cycle to 5-ALA and heme. In this review, we describe the recent results of 5-ALA production from different genes and microorganisms via genetic and metabolic engineering approaches. The regulation of different chassis is fine-tuned by applying synthetic biology and boosts 5-ALA production eventually. The purification process, challenges, and opportunities of 5-ALA for industrial applications are also summarized.

Clinical Pharmacokinetics and Safety of a 10% Aminolevulinic Acid Hydrochloride Nanoemulsion Gel (BF-200 ALA) in Photodynamic Therapy of Patients Extensively Affected With Actinic Keratosis: Results of 2 Maximal Usage Pharmacokinetic Trials

The nanoemulsion‐based 10% aminolevulinic acid (ALA) hydrochloride gel BF‐200 ALA optimizes epidermal penetration of its active ingredient and is approved for topical photodynamic therapy (PDT) for the treatment of actinic keratosis in the United States and Europe. To characterize systemic absorption from dermal application during PDT, ALA and its key active metabolite protoporphyrin IX (PpIX) were analyzed in 2 maximal usage pharmacokinetic trials (MUsT) in patients severely affected with actinic keratosis. The primary objective of both MUsTs was to assess baseline‐adjusted plasma concentration–time curves for ALA and PpIX after a single PDT treatment applying either 2 g (1 tube) of BF‐200 ALA on the face (MUsT‐1) or applying 6 g (3 tubes) of BF‐200 ALA on the face/scalp or body periphery (MUsT‐2), to 20 or 60 cm², respectively. All PDTs were performed using red light at around 635 nm wavelength. Safety and tolerability were documented along with pharmacokinetics. In both MUsTs, ALA plasma concentrations were transiently increased to a maximum concentration at about 2.5 to 3.3 times above endogenous baseline with time to maximum concentration at ≈3 hours after dosing. Plasma levels subsequently returned to baseline within 10 hours after dosing. Overall baseline‐adjusted mean area under the baseline‐adjusted plasma concentration‐time curve from time zero to the last sampling time point at which the concentration was at or above the lower limit of quantification ranged from 142.8 to 146.2, indicating that a similar, minor fraction of topical ALA is systemically absorbed under both dosing regimens. Systemic PpIX exposure after administration of either dose of BF‐200 ALA was equally minimal. Application site skin reactions were treatment area size‐related, albeit transient and consistent with the known safety profile of BF‐200 ALA.

Application of Photodynamic Therapy with 5-Aminolevulinic Acid to Extracorporeal Photopheresis in the Treatment of Patients with Chronic Graft-versus-Host Disease: A First-in-Human Study

Extracorporeal photopheresis (ECP), an immunomodulatory therapy for the treatment of chronic graft-versus-host disease (cGvHD), exposes isolated white blood cells to photoactivatable 8-methoxypsoralen (8-MOP) and UVA light to induce the apoptosis of T-cells and, hence, to modulate immune responses. However, 8-MOP-ECP kills diseased and healthy cells with no selectivity and has limited efficacy in many cases. The use of 5-aminolevulinic acid (ALA) and light (ALA-based photodynamic therapy) may be an alternative, as ex vivo investigations show that ALA-ECP kills T-cells from cGvHD patients more selectively and efficiently than those treated with 8-MOP-ECP. The purpose of this phase I-(II) study was to evaluate the safety and tolerability of ALA-ECP in cGvHD patients. The study included 82 treatments in five patients. One patient was discharged due to the progression of the haematological disease. No significant persistent changes in vital signs or laboratory values were detected. In total, 62 adverse events were reported. Two events were severe, 17 were moderate, and 43 were mild symptoms. None of the adverse events evaluated by the internal safety review committee were considered to be likely related to the study medication. The results indicate that ALA-ECP is safe and is mainly tolerated well by cGvHD patients.

Nanocarriers for Photodynamic Therapy Intended to Cutaneous Tumors

Photodynamic Therapy (PDT) is a therapeutic modality used for several malignant and premalignant skin disorders, including Bowen's disease skin cancers and Superficial Basal Cell Carcinoma (BCC). Several photosensitizers (PSs) have been explored for tumor destruction of skin cancers, after their activation by a light source of appropriate wavelength. Topical release of PSs avoids prolonged photosensitization reactions associated with systemic administration; however, its clinical usefulness is influenced by its poor tissue penetration and the stability of the active agent. Nanotechnology-based drug delivery systems are promising tool to enhance the efficiency for PDT of cancer. This review focuses on PSs encapsulated in nanocarriers explored for PDT of skin tumors.

Experimental investigation of a combinational iron chelating protoporphyrin IX prodrug for fluorescence detection and photodynamic therapy

Photodynamic therapy (PDT) is an oxygen-dependent, light-activated, and locally destructive drug treatment of cancer. Protoporphyrin IX (PpIX)-induced PDT exploits cancer cells' own innate heme biosynthesis to hyper-accumulate the naturally fluorescent and photoactive precursor to heme, PpIX. This occurs as a result of administering heme precursors (e.g., aminolevulinic acid; ALA) because the final step of the pathway (the insertion of ferrous iron into PpIX by ferrochelatase to form heme) is relatively slow. Separate administration of an iron chelating agent has previously been demonstrated to significantly improve dermatological PpIX-PDT by further limiting heme production. A newly synthesized combinational iron chelating PpIX prodrug (AP2-18) has been assessed experimentally in cultured primary human cells of bladder and dermatological origin, as an alternative photosensitizing agent to ALA or its methyl or hexyl esters (MAL and HAL respectively) for photodetection/PDT. Findings indicated that the technique of iron chelation (either through the separate administration of the established hydroxypyridinone iron chelator CP94 or the just as effective combined AP2-18) did not enhance either PpIX fluorescence or PDT-induced (neutral red assessed) cell death in human primary normal and malignant bladder cells. However, 500 µM AP2-18 significantly increased PpIX accumulation and produced a trend of increased cell death within epithelial squamous carcinoma cells. PpIX accumulation destabilized the actin cytoskeleton in bladder cancer cells prior to PDT and resulted in caspase-3 cleavage/early apoptosis afterwards. AP2-18 iron chelation should continue to be investigated for the enhancement of dermatological PpIX-PDT applications but not bladder photodetection/PDT.

Efficacy of 5-aminolevulinic acid-based photodynamic therapy in different subtypes of canine mammary gland cancer cells

Canine mammary gland tumors (CMGTs) are heterogeneous disease and subclassified [sarcomas (S), carcinomas (C), and carcinosarcomas (CS)] according to histopathological differentiation. Photodynamic therapy (PDT) is a promising treatment strategy based on the use of a photosensitizer (PS) activated by light. However, the therapeutic potential of PDT in the treatment of CMGTs has not been investigated, yet. Therefore, the aim of this study was to determine the in vitro protocol of 5-ALA-based-PDT for the treatment of three subtypes of CMGTs, for the first time. The intracellular PpIX florescence intensity was measured for 5-ALA (0.5 and 1 mM). After irradiation with different light doses (6, 9, 12, 18, and 24 J/cm²) for two different modes [continuous wave (CW) and pulse radiation (PR)], the cytotoxic effects of 5-ALA (0.5 and 1 mM) on the subtypes (C, S, and CS) of CMGTs were analyzed by WST-1. Finally, the optimal PDT treatment protocol was validated through Annexin V and AO/EtBr staining. Our results showed that 1 mM 5-ALA for 4-h incubation was the best treatment condition in all subtypes of CMGTs due to higher intracellular PpIX level. After irradiation with different light doses, PR mode was more effective in S primary cells at 9 J/cm². However, a significant decrease in the viability of C and CS cells was detected at 12 /cm² in CW mode (p < 0.05). Additionally, 1 mM 5-ALA induced apoptotic cell death in each subtype of CMGTs. Our preliminary findings suggest that (i) each subtype of CMGTs differentially responds to PDT and (ii) the light dose and mode could play an important role in the effective PDT treatment. However, further studies are needed to investigate the role of the different light sources and PDT-based apoptotic cell death in CMGTs cells.

Development of a high payload, cancer-targeting liposomes of methyl aminolevulinate for intraoperative photodynamic diagnosis/therapy of peritoneal carcinomatosis

Methyl aminolevulinate (MAL) is a photosensitizer topically used for photodynamic diagnosis (PDD) and photodynamic therapy (PDT) of skin pre-cancers and cancers. In this study, our goal is to expand the application of MAL to dual intraoperative PDD and PDT of peritoneal carcinomatosis. A new liposomal MAL formulation (lipMAL) designed for systemic or intraperitoneal administration was developed. LipMALs prepared by ammonium sulfate gradient technique achieved MAL payload up to 18% (w/w) with drug encapsulation efficiency in the range of 15.1-31.5%. All lipMALs demonstrated controlled MAL release behavior, and achieved strong fluorescence in cancer cells (SKOV3) but minimal fluorescence in non-cancer peritoneal cells (B14FAF28-G3). LipMALs led to significantly higher fluorescence levels than free MAL groups (P < 0.05), up to 6.8-fold of the free MAL fluorescence levels in SKOV3 cells. The PDD performance of lipMALs was also compared with free MAL in SKOV3/ B14FAF28-G3 co-cultures simulating ovarian cancer micrometastases on peritoneal surface. The lipMAL-treated cancer colonies glew more brightly than the free MAL treated colonies and were clearly distinguishable from the dim peritoneum background with unaided eyes. LipMAL also achieved significantly stronger anticancer PDT effects than free MAL both in terms of cell viability and colony-formation (P < 0.05) while demonstrating minimal dark toxicity. To conclude, a new promising aid for the surgeons to achieve more complete resection of tumors and PC micrometastases and clean up any residual cancer cells undetected was developed.

Photodynamic Therapy as an Oxidative Anti-Tumor Modality: Negative Effects of Nitric Oxide on Treatment Efficacy

Anti-tumor photodynamic therapy (PDT) is a unique oxidative stress-based modality that has proven highly effective on a variety of solid malignancies. PDT is minimally invasive and generates cytotoxic oxidants such as singlet molecular oxygen (¹O₂). With high tumor site-specificity and limited off-target negative effects, PDT is increasingly seen as an attractive alternative or follow-up to radiotherapy or chemotherapy. Nitric oxide (NO) is a short-lived bioactive free radical molecule that is exploited by many malignant tumors to promote cell survival, proliferation, and metastatic expansion. Typically generated endogenously by inducible nitric oxide synthase (iNOS/NOS2), low level NO can also antagonize many therapeutic interventions, including PDT. In addition to elevating resistance, iNOS-derived NO can stimulate growth and migratory aggressiveness of tumor cells that survive a PDT challenge. Moreover, NO from PDT-targeted cells in any given population is known to promote such aggressiveness in non-targeted counterparts (bystanders). Each of these negative responses to PDT and their possible underlying mechanisms will be discussed in this chapter. Promising pharmacologic approaches for mitigating these NO-mediated responses will also be discussed.

Nitric Oxide-elicited Resistance to Antitumor Photodynamic Therapy via Inhibition of Membrane Free Radical-mediated Lipid Peroxidation

This review focuses on the ability of nitric oxide (NO) to antagonize antitumor photodynamic therapy (PDT). NO's anti-PDT effects were recognized relatively recently and require a better mechanistic understanding for developing new strategies to improve PDT efficacy. Many PDT sensitizers (PSs) are amphiphilic and tend to localize in membrane compartments of tumor cells. Unsaturated lipids in these compartments can undergo peroxidative degradation after PS photoactivation. Primary Type I (free radical) vs. Type II (singlet oxygen) photochemistry of lipid peroxidation is discussed, along with light-independent turnover of primary lipid hydroperoxides to free radical species. Chain lipid peroxidation mediated by the latter exacerbates membrane damage and cytotoxicity after a PDT challenge. Our studies have shown that NO from chemical donors can suppress chain peroxidation by intercepting lipid-derived free radical intermediates, thereby protecting cancer cells against photokilling. More recent evidence has revealed that inducible NO synthase (iNOS) is dramatically upregulated in several cancer cell types after a photodynamic challenge, and that iNOS-derived NO enhances resistance as well as growth and migratory aggressiveness of surviving cells. Chain breaking by NO and other possible NO-based resistance mechanisms are discussed, along with novel pharmacologic approaches for overcoming these negative effects.

Integrated photodynamic Raman theranostic system for cancer diagnosis, treatment, and post-treatment molecular monitoring

Theranostics, the combination of diagnosis and therapy, has long held promise as a means to achieving personalised precision cancer treatments. However, despite its potential, theranostics has yet to realise significant clinical translation, largely due the complexity and overriding toxicity concerns of existing theranostic nanoparticle strategies. Methods: Here, we present an alternative nanoparticle-free theranostic approach based on simultaneous Raman spectroscopy and photodynamic therapy (PDT) in an integrated clinical platform for cancer theranostics. Results: We detail the compatibility of Raman spectroscopy and PDT for cancer theranostics, whereby Raman spectroscopic diagnosis can be performed on PDT photosensitiser-positive cells and tissues without inadvertent photosensitiser activation/photobleaching or impaired diagnostic capacity. We further demonstrate that our theranostic platform enables in vivo tumour diagnosis, treatment, and post-treatment molecular monitoring in real-time. Conclusion: This system thus achieves effective theranostic performance, providing a promising new avenue towards the clinical realisation of theranostics.

Negative effects of tumor cell nitric oxide on anti-glioblastoma photodynamic therapy

Glioblastomas are highly aggressive brain tumors that can persist after exposure to conventional chemotherapy or radiotherapy. Nitric oxide (NO) produced by inducible NO synthase (iNOS/NOS2) in these tumors is known to foster malignant cell proliferation, migration, and invasion as well as resistance to chemo- and radiotherapy. Minimally invasive photodynamic therapy (PDT) sensitized by 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) is a highly effective anti-glioblastoma modality, but it is also subject to NO-mediated resistance. Studies by the authors have revealed that glioblastoma U87 and U251 cells use endogenous iNOS/NO to not only resist photokilling after an ALA/light challenge, but also to promote proliferation and migration/invasion of surviving cells. Stress-upregulated iNOS/NO was found to play a major role in these negative responses to PDT-like treatment. Our studies have revealed a tight network of upstream signaling events leading to iNOS induction in photostressed cells and transition to a more aggressive phenotype. These events include activation or upregulation of pro-survival/ pro-expansion effector proteins such as NF-κB, phosphoinositide-3-kinase (PI3K), protein kinase-B (Akt), p300, Survivin, and Brd4. In addition to this upstream signaling and its regulation, pharmacologic approaches for directly suppressing iNOS at its activity vs. transcriptional level are discussed. One highly effective agent in the latter category is bromodomain and extra-terminal (BET) inhibitor, JQ1, which was found to minimize iNOS upregulation in photostressed U87 cells. By acting similarly at the clinical level, a BET inhibitor such as JQ1 should markedly improve the efficacy of anti-glioblastoma PDT.

Daylight Photodynamic Therapy: An Update

Daylight photodynamic therapy (dPDT) uses sunlight as a light source to treat superficial skin cancer. Using sunlight as a therapeutic device has been present for centuries, forming the basis of photodynamic therapy in the 20th century. Compared to conventional PDT, dPDT can be a less painful, more convenient and an effective alternative. The first clinical uses of dPDT on skin cancers began in Copenhagen in 2008. Currently, aminolevulinic acid-mediated dPDT has been approved to treat actinic keratosis patients in Europe. In this review article, we introduce the history and mechanism of dPDT and focus on the pros and cons of dPDT in treating superficial skin cancers. The future applications of dPDT on other skin diseases are expected to expand as conventional PDT evolves.

Phototherapy Combined with Carbon Nanomaterials (1D and 2D) and their Applications in Cancer Therapy

Carbon-based materials have attracted research interest worldwide due to their physical and chemical properties and wide surface area, rendering them excellent carrier molecules. They are widely used in biological applications like antimicrobial activity, cancer diagnosis, bio-imaging, targeting, drug delivery, biosensors, tissue engineering, dental care, and skin care. Carbon-based nanomaterials like carbon nanotubes and graphene have drawn more attention in the field of phototherapy due to their unique properties such as thermal conductivity, large surface area, and electrical properties. Phototherapy is a promising next-generation therapeutic modality for many modern medical conditions that include cancer diagnosis, targeting, and treatment. Phototherapy involves the major administration of photosensitizers (PSs), which absorb light sources and emit reactive oxygen species under cellular environments. Several types of nontoxic PSs are functionalized on carbon-based nanomaterials and have numerous advantages in cancer therapy. In this review, we discuss the potential role and combined effect of phototherapy and carbon nanomaterials, the mechanism and functionalization of PSs on nanomaterials, and their promising advantages in cancer therapy.

Hydroxypyridinone-Based Iron Chelators with Broad-Ranging Biological Activities

Iron plays an essential role in all living cells because of its unique chemical properties. It is also the most abundant trace element in mammals. However, when iron is present in excess or inappropriately located, it becomes toxic. Excess iron can become involved in free radical formation, resulting in oxidative stress and cellular damage. Iron chelators are used to treat serious pathological disorders associated with systemic iron overload. Hydroxypyridinones stand out for their outstanding chelation properties, including high selectivity for Fe³⁺ in the biological environment, ease of derivatization, and good biocompatibility. Herein, we overview the potential for multifunctional hydroxypyridinone-based chelators to be used as therapeutic agents against a wide range of diseases associated either with systemic or local elevated iron levels.

Modulation of aminolevulinic acid-based photoinactivation efficacy by iron in vitro is cell type dependent

Iron availability to cells may be modified in the tumour microenvironment, which may be involved in treatment response. Iron availability affects the conversion of protoporphyrin IX to heme, which likely determines the efficacy of aminolevulinic acid-based photodynamic therapy (ALA-based PDT). We compared photoinactivation efficacy in three oesophageal cell lines in culture media differing in iron content, DMEM and RPMI 1640, and in RPMI 1640 supplemented with iron to understand the importance of iron presence for ALA-based PDT outcome. ALA-based PDT was more efficacious in DMEM than in RPMI 1640 in all tested cell lines. Consistently, the highest protoporphyrin IX fluorescence signals, indicating the highest level of protoporphyrin IX production, were detected from cell colonies incubated in DMEM compared to those incubated in RPMI 1640 irrespective of iron presence. Components in the culture media other than iron ions are likely to be responsible for the observed differences in two culture media. Nevertheless, iron supplementation to RPMI 1640 showed that the presence of ferric ions in the concentration range 0-8 mg/l affected ALA-based PDT efficacy in a cell type-dependent manner. In poorly differentiated carcinoma cells, the increased efficacy of ALA-induced photoinactivation in the presence of 0.1 mg/l of supplemented iron was found. At the same iron concentration, the slightly different mitochondrial potential at no modifications of the iron labile pool was observed. The efficacy of ALA-based PDT in vitro depends on the choice of culture medium and the presence of iron ions in culture medium depending on intrinsic properties of cells.

Zika Virus Infection Results in Biochemical Changes Associated With RNA Editing, Inflammatory and Antiviral Responses in Aedes albopictus

Rapid and significant range expansion of both the Zika virus (ZIKV) and its Aedes vector species has resulted in the declaration of ZIKV as a global health threat. Successful transmission of ZIKV by its vector requires a complex series of interactions between these entities including the establishment, replication and dissemination of the virus within the mosquito. The metabolic conditions within the mosquito tissues play a critical role in mediating the crucial processes of viral infection and replication and represent targets for prevention of virus transmission. In this study, we carried out a comprehensive metabolomic phenotyping of ZIKV infected and uninfected Ae. albopictus by untargeted analysis of primary metabolites, lipids and biogenic amines. We performed a comparative metabolomic study of infection state with the aim of understanding the biochemical changes resulting from the interaction between the ZIKV and its vector. We have demonstrated that ZIKV infection results in changes to the cellular metabolic environment including a significant enrichment of inosine and pseudo-uridine (Ψ) levels which may be associated with RNA editing activity. In addition, infected mosquitoes demonstrate a hypoglycemic phenotype and show significant increases in the abundance of metabolites such as prostaglandin H2, leukotriene D4 and protoporphyrinogen IX which are associated with antiviral activity. These provide a basis for understanding the biochemical response to ZIKV infection and pathology in the vector. Future mechanistic studies targeting these ZIKV infection responsive metabolites and their associated biosynthetic pathways can provide inroads to identification of mosquito antiviral responses with infection blocking potential.

Nitric oxide-elicited resistance to anti-glioblastoma photodynamic therapy

Glioblastoma multiforme is a highly aggressive primary brain malignancy that resists most conventional chemoand radiotherapeutic interventions. Nitric oxide (NO), a short lived free radical molecule produced by inducible NO synthase (iNOS) in glioblastomas and other tumors, is known to play a key role in tumor persistence, progression, and chemo/radiotherapy resistance. Site-specific and minimally invasive photodynamic therapy (PDT), based on oxidative damage resulting from non-ionizing photoactivation of a sensitizing agent, is highly effective against glioblastoma, but resistance also exists in this case. Studies in the authors' laboratory have shown that much of the latter is mediated by iNOS/NO. For example, when glioblastoma U87 or U251 cells sensitized in mitochondria with 5-aminolevulinic acid -induced protoporphyrin IX were exposed to a moderate dose of visible light, the observed apoptosis was strongly enhanced by an iNOS activity inhibitor or NO scavenger, indicating that iNOS/NO had increased cell resistance to photokilling. Moreover, cells that survived the photochallenge proliferated, migrated, and invaded more aggressively than controls, and these responses were also driven predominantly by iNOS/NO. Photostress-upregulated iNOS rather than basal enzyme was found to be responsible for all the negative effects described. Recognition of NO-mediated hyper-resistance/hyper-aggression in PDT-stressed glioblastoma has stimulated interest in how these responses can be prevented or at least minimized by pharmacologic adjuvants such as inhibitors of iNOS activity or transcription. Recent developments along these lines and their clinical potential for improving anti-glioblastoma PDT are discussed.

Radiodynamic therapy using 15-MV radiation combined with 5-aminolevulinic acid and carbamide peroxide for prostate cancer in vivo

Photodynamic therapy has been clinically proven to be effective, but its effect is limited to relatively shallow tumors because of its use of visible light. Radiodynamic therapy (RDT) has therefore been investigated as a means to treat deep-seated tumors. In this study, the treatment effect of a novel form of RDT consisting of radiation combined with 5-aminolevulinic acid (5-ALA) and carbamide peroxide was investigated using a mouse model. Male nude mice were injected bilaterally and subcutaneously with human prostate cancer (PC-3) cells and randomized into 8 treatment groups, consisting of various combinations of 15-MV radiotherapy (RT), 5-ALA, and carbamide peroxide. The treatment effect of a single fraction of treatment was measured by calculating tumor growth delay, monitored using weekly MR scans. The ability of the drugs to be delivered to the tumors was qualitatively measured using ¹⁸ F-FDG PET/CT scans. RDT was shown to significantly delay the tumor growth for the mouse model and tumor cell line investigated in this work. Tumors treated with RDT showed a decrease in tumor growth of 24 ± 9% and 21 ± 8% at one and two weeks post-treatment, respectively. Peroxide and 5-ALA did not contribute significantly to tumor growth delay when administered alone or separately with RT. Blood perfusion was shown to be able to deliver agents to the tumors investigated in this work, although uptake of ¹⁸ F-FDG was shown to be non-uniform.

Amylase-Protected Ag Nanodots for in vivo Fluorescence Imaging and Photodynamic Therapy of Tumors

BACKGROUND

Fluorescent metallic nanodots (NDs) have become a promising nanoprobe for a wide range of biomedical applications. Because Ag NDs have a high tendency to be oxidized, their synthesis and storage are a big challenge. Thus, the method for preparing stable Ag NDs is urgently needed. Surface modification and functionalization can enrich the capability of Ag NDs.

METHODS

In this work, fluorescent Ag NDs were synthesized in deoxygenated water by using porcine pancreatic α-amylase (PPA) as the stabilizing/capping agent. The absorption and fluorescence of PPA-protected Ag NDs (PPA@AgNDs) were measured with a spectrophotometer and a spectrofluorometer, respectively. The morphology of PPA@AgNDs was characterized by high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM). The biocompatibility of PPA@AgNDs was evaluated by tetrazolium (MTT)-based assay. PolyLys-Cys-SH (sequence: KKKKKKC) peptides were conjugated to PPA@AgNDs via heterobifunctional crosslinkers. PolyLys-Cys-linked PPA@AgNDs absorbed 5-aminolevulinic acid (ALA) by electrostatic interaction at physiological pH. The capability of tumor targeting was evaluated by intravenously injecting PPA@AgND-ALA into 4T1 breast cancer xenograft mouse models. Photodynamic therapy (PDT) against tumors was performed under 635 nm laser irradiation.

RESULTS

PPA@AgNDs emitted at 640 nm with quantum yield of 2.1%. The Ag NDs exhibited strong photostability over a long period and a fluorescence lifetime of 5.1 ns. PPA@AgNDs easily entered the cells to stain the nuclei, showing the capabilities of living cell imaging with negligible cytotoxicity. ALA-loaded PPA@AgNDs (PPA@AgND-ALA) presented the superiority of passive tumor targeting via the enhanced permeability and retention (EPR) effect. Tumors were visualized in the near-infrared (NIR) region with reduced background noise. ALA molecules released from PPA@AgND-ALA was converted into the photosensitizer (PS) of protoporphyrin IX (PpIX) intracellularly and intratumorally, which greatly improved the PDT efficacy.

CONCLUSION

Our approach opens a new way to design a novel theranostic nanoplatform of PPA@AgND-ALA for effective tumor targeting and fluorescence image-guided PDT.

Nitric Oxide-Mediated Resistance to Antitumor Photodynamic Therapy

As an antitumor modality based on sensitizer photoexcitation by tumor-directed light, photodynamic therapy (PDT) has the advantage of being site-specific compared with conventional chemotherapy or radiotherapy. Like these other therapies, however, PDT is often limited by pre-existing or acquired resistance. One type of resistance, discovered in the author's laboratory, involves nitric oxide (NO) generated by inducible nitric oxide synthase (iNOS) in tumor cells. Using human breast, prostate and brain cancer cell lines, we have shown that iNOS is dramatically upregulated after a moderate PDT challenge sensitized by 5-aminolevulinic acid-induced protoporphyrin IX. The elevated NO not only elicited a greater resistance to cell photokilling, but also an increase in the growth and migration/invasion rate of surviving cells. Greater iNOS/NO-based resistance was also demonstrated at the in vivo level using a breast tumor xenograft model. More recent studies have shown that NO from PDT-targeted cells can stimulate a progrowth/promigration response in non-targeted bystander cells. These novel effects of NO, their negative impact on PDT efficacy and possible mitigation thereof by anti-iNOS/NO pharmacologic agents will be discussed.

Nitric Oxide Inhibition of Chain Lipid Peroxidation Initiated by Photodynamic Action in Membrane Environments

Iron-catalyzed, free radical-mediated lipid peroxidation may play a major role in tumor cell killing by photodynamic therapy (PDT), particularly when membrane-localizing photosensitizers are employed. Many cancer cells exploit endogenous iNOS-generated NO for pro-survival/expansion purposes and for hyper-resistance to therapeutic modalities, including PDT. In addition to inhibiting the pro-oxidant activity of Fe(II) via nitrosylation, NO may intercept downstream lipid oxyl and peroxyl radicals, thereby acting as a chain-breaking antioxidant. We investigated this for the first time in the context of PDT by using POPC/Ch/PpIX (100:80:0.2 by mol) liposomes (LUVs) as a model system. Cholesterol (Ch or [¹⁴C]Ch) served as an in-situ peroxidation probe and protoporphyrin IX (PpIX) as photosensitizer. PpIX-sensitized lipid peroxidation was monitored by two analytical methods that we developed: HPLC-EC(Hg) and HPTLC-PI. 5α-hydroperoxy-Ch (5α-OOH) accumulated rapidly and linearly with irradiation time, indicating singlet oxygen (¹O₂) intermediacy. When ascorbate (AH^-) and trace lipophilic iron [Fe(HQ)₃] were included, 7α/7β-hydroperoxy-Ch (7-OOH) accumulated exponentially, indicating progressively greater membrane-damaging chain lipid peroxidation. With AH^-/Fe(HQ)₃ present, the NO donor SPNO had no effect on 5α-OOH formation, but dose-dependently inhibited 7-OOH formation due to NO interception of chain-carrying oxyl and peroxyl radicals. Similar results were obtained when cancer cells were PpIX/light-treated, using SPNO or activated macrophages as the NO source. These findings implicate chain lipid peroxidation in PDT-induced cytotoxicity and NO as a potent antagonist thereof by acting as a chain-breaking antioxidant. Thus, unless NO formation in aggressive tumors is suppressed, it can clearly compromise PDT efficacy.