Photodynamic therapy: current status and future directions

Photodynamic effect of protoporphyrin IX in gliosarcoma 9l/lacZ cell line

Photodynamic Therapy (PDT) is an oncologic treatment, producing reactive oxygen species (ROS) to induce the death of cancer cells. This study aimed to evaluate the action of PDT on gliosarcoma cells, using protoporphyrin IX as PS by incubation with the precursor aminolevulinic acid (ALA). An LED device was used with a light dose of 10 J/cm². The success of the therapy proved to be dependent on the concentration of ALA, and an incubation time of 4 h required for an effective response. Cell death was prevalent due to necrosis when assessed 18 h post-PDT. ALA proved to be an option to PDT in cells of the 9 L/lacZ, with the protocol tested.

Nanoparticle-Mediated Delivery Systems in Photodynamic Therapy of Colorectal Cancer

Colorectal cancer (CRC) involving a malignant tumour remains one of the greatest contributing causes of fatal mortality and has become the third globally ranked malignancy in terms of cancer-associated deaths. Conventional CRC treatment approaches such as surgery, radiation, and chemotherapy are the most utilized approaches to treat this disease. However, they are limited by low selectivity and systemic toxicity, so they cannot completely eradicate this disease. Photodynamic therapy (PDT) is an emerging therapeutic modality that exerts selective cytotoxicity to cancerous cells through the activation of photosensitizers (PSs) under light irradiation to produce cytotoxic reactive oxygen species (ROS), which then cause cancer cell death. Cumulative research findings have highlighted the significant role of traditional PDT in CRC treatment; however, the therapeutic efficacy of the classical PDT strategy is restricted due to skin photosensitivity, poor cancerous tissue specificity, and limited penetration of light. The application of nanoparticles in PDT can mitigate some of these shortcomings and enhance the targeting ability of PS in order to effectively use PDT against CRC as well as to reduce systemic side effects. Although 2D culture models are widely used in cancer research, they have some limitations. Therefore, 3D models in CRC PDT, particularly multicellular tumour spheroids (MCTS), have attracted researchers. This review summarizes several photosensitizers that are currently used in CRC PDT and gives an overview of recent advances in nanoparticle application for enhanced CRC PDT. In addition, the progress of 3D-model applications in CRC PDT is discussed.

Biocompatible Nanocarriers for Enhanced Cancer Photodynamic Therapy Applications

In recent years, the role of nanotechnology in drug delivery has become increasingly important, and this field of research holds many potential benefits for cancer treatment, particularly, in achieving cancer cell targeting and reducing the side effects of anticancer drugs. Biocompatible and biodegradable properties have been essential for using a novel material as a carrier molecule in drug delivery applications. Biocompatible nanocarriers are easy to synthesize, and their surface chemistry often enables them to load different types of photosensitizers (PS) to use targeted photodynamic therapy (PDT) for cancer treatment. This review article explores recent studies on the use of different biocompatible nanocarriers, their potential applications in PDT, including PS-loaded biocompatible nanocarriers, and the effective targeting therapy of PS-loaded biocompatible nanocarriers in PDT for cancer treatment. Furthermore, the review briefly recaps the global clinical trials of PDT and its applications in cancer treatment.

Photochemical Internalization of Etoposide Using Dendrimer Nanospheres Loaded with Etoposide and Protoporphyrin IX on a Glioblastoma Cell Line

Glioblastoma multiforme (GBM) is the most common malignant primary neoplasm of the adult central nervous system originating from glial cells. The prognosis of those affected by GBM has remained poor despite advances in surgery, chemotherapy, and radiotherapy. Photochemical internalization (PCI) is a release mechanism of endocytosed therapeutics into the cytoplasm, which relies on the membrane disruptive effect of light-activated photosensitizers. In this study, phototherapy by PCI was performed on a human GBM cell-line using the topoisomerase II inhibitor etoposide (Etop) and the photosensitizer protoporphyrin IX (PpIX) loaded in nanospheres (Ns) made from generation-5 polyamidoamine dendrimers (PAMAM(G5)). The resultant formulation, Etop/PpIX-PAMAM(G5) Ns, measured 217.4 ± 2.9 nm in diameter and 40.5 ± 1.3 mV in charge. Confocal microscopy demonstrated PpIX fluorescence within the endo-lysosomal compartment, and an almost twofold increase in cellular uptake compared to free PpIX by flow cytometry. Phototherapy with 3 min and 5 min light illumination resulted in a greater extent of synergism than with co-administered Etop and PpIX; notably, antagonism was observed without light illumination. Mechanistically, significant increases in oxidative stress and apoptosis were observed with Etop/PpIX-PAMAM(G5) Ns upon 5 min of light illumination in comparison to treatment with either of the agents alone. In conclusion, simultaneous delivery and endo-lysosomal co-localization of Etop and PpIX by PAMAM(G5) Ns leads to a synergistic effect by phototherapy; in addition, the finding of antagonism without light illumination can be advantageous in lowering the dark toxicity and improving photo-selectivity.

Photodynamic Priming Improves the Anti-Migratory Activity of Prostaglandin E Receptor 4 Antagonist in Cancer Cells In Vitro

The combination of photodynamic agents and biological inhibitors is rapidly gaining attention for its promise and approval in treating advanced cancer. The activity of photodynamic treatment is mainly governed by the formation of reactive oxygen species upon light activation of photosensitizers. Exposure to reactive oxygen species above a threshold dose can induce cellular damage and cancer cell death, while the surviving cancer cells are "photodynamically primed", or sensitized, to respond better to other drugs and biological treatments. Here, we report a new combination regimen of photodynamic priming (PDP) and prostaglandin E2 receptor 4 (EP4) inhibition that reduces the migration and invasion of two human ovarian cancer cell lines (OVCAR-5 and CAOV3) in vitro. PDP is achieved by red light activation of the FDA-approved photosensitizer, benzoporphyrin derivative (BPD), or a chemical conjugate composed of the BPD linked to cetuximab, an anti-epithelial growth factor receptor (EGFR) antibody. Immunoblotting data identify co-inhibition of EGFR, cAMP-response element binding protein (CREB), and extracellular signal-regulated kinase 1/2 (ERK1/2) as key in the signaling cascades modulated by the combination of EGFR-targeted PDP and EP4 inhibition. This study provides valuable insights into the development of a molecular-targeted photochemical strategy to improve the anti-metastatic effects of EP4 receptor antagonists.

Self-Assembled Microporous M-HOFs Based on an Octahedral Rhenium Cluster with Benzimidazole

Substitution of apical halide ligands in [{Re₆Seⁱ₈}X^a₆]^3- (X = Cl, Br) by benzimidazole (bimzH) accompanied by a self-assembly process leads to the formation of microporous Re₆-based hydrogen-bonded organic frameworks (Re₆-HOFs) constructed on N-H···X hydrogen bonds and π-π-stacking interactions between bimzH ligands. Re₆-HOFs demonstrate sorption properties with a Brunauer-Emmett-Teller surface area of up to 443 m² g^-1 and luminescence with a quantum yield and an emission lifetime of up to 0.16 and 16 μs, respectively. The compounds obtained complement small groups of transition-metal cluster-based HOFs, which are a perspective for the development of multifunctional frameworks.

Visible-Light-Mediated Modification and Manipulation of Biomacromolecules

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

8,8'-(Benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(quinolin-4(1H)-one): a twisted photosensitizer with AIE properties

A new benzothiadiazole (BTZ) luminogen is prepared via the Suzuki-Miyaura Pd-catalysed C-C cross-coupling of 8-iodoquinolin-4(1H)-one and a BTZ bispinacol boronic ester. The rapid reaction (5 min) affords the air-, thermo-, and photostable product in 97% yield as a yellow precipitate that can be isolated by filtration. The luminogen exhibits aggregated-induced emission (AIE) properties, which are attributed to its photoactive BTZ core and nonplanar geometry. It also behaves as a molecular heterogeneous photosensitizer for the production of singlet oxygen under continuous flow conditions.

Substituted Dibenzodiazocines: Rapid Synthesis and Photochemical Properties

11,12-Dihydrodibenzo[c,g]-1,2-diazocines have been established as a viable alternative to azobenzene for photoswitching, in particular, as they show an inverted switching behavior: the ground state is the Z isomer. In this paper, we present an improved method to obtain dibenzodiazocine and its derivatives from the respective 2-nitrotoluenes in two reaction steps, each proceeding in minutes. This fast access to a variety of derivatives permitted the study of substitution effects on the synthesis and on the photochemical properties. With biochemical applications in mind, methanol was chosen as a protic solvent system for the photochemical investigations. In contrast to the azobenzene system, none of the tested substitution patterns resulted in more efficient switching or in significantly prolonged half-lives, showing that the system is dominated by the ring strain.

DNA-Triggered Enhancement of Singlet Oxygen Production by Pyridinium Alkynylanthracenes

There is an ongoing interest in ¹ O₂ sensitizers, whose activity is selectively controlled by their interaction with DNA. To this end, we synthesized three isomeric pyridinium alkynylanthracenes 2 o-p and a water-soluble trapping reagent for ¹ O₂ . In water and in the absence of DNA, these dyes show a poor efficiency to sensitize the photooxygenation of the trapping reagent as they decompose due to electron transfer processes. In contrast, in the presence of DNA ¹ O₂ is generated from the excited DNA-bound ligand. The interactions of 2 o-p with DNA were investigated by thermal DNA melting studies, UV/vis and fluorescence spectroscopy, and linear and circular dichroism spectroscopy. Our studies revealed an intercalative binding with an orientation of the long pyridyl-alkynyl axis parallel to the main axis of the DNA base pairs. In the presence of poly(dA : dT), all three isomers show an enhanced formation of singlet oxygen, as indicated by the reaction of the latter with the trapping reagent. With green light irradiation of isomer 2 o in poly(dA : dT), the conversion rate of the trapping reagent is enhanced by a factor >10. The formation of ¹ O₂ was confirmed by control experiments under anaerobic conditions, in deuterated solvents, or by addition of ¹ O₂ quenchers. When bound to poly(dG : dC), the opposite effect was observed only for isomers 2 o and 2 m, namely the trapping reagent reacted significantly slower. Overall, we showed that pyridinium alkynylanthracenes are very useful intercalators, that exhibit an enhanced photochemical ¹ O₂ generation in the DNA-bound state.

Design, Synthesis, and Utility of Defined Molecular Scaffolds

A growing theme in chemistry is the joining of multiple organic molecular building blocks to create functional molecules. Diverse derivatizable structures—here termed “scaffolds” comprised of “hubs”—provide the foundation for systematic covalent organization of a rich variety of building blocks. This review encompasses 30 tri- or tetra-armed molecular hubs (e.g., triazine, lysine, arenes, dyes) that are used directly or in combination to give linear, cyclic, or branched scaffolds. Each scaffold is categorized by graph theory into one of 31 trees to express the molecular connectivity and overall architecture. Rational chemistry with exacting numbers of derivatizable sites is emphasized. The incorporation of water-solubilization motifs, robust or self-immolative linkers, enzymatically cleavable groups and functional appendages affords immense (and often late-stage) diversification of the scaffolds. Altogether, 107 target molecules are reviewed along with 19 syntheses to illustrate the distinctive chemistries for creating and derivatizing scaffolds. The review covers the history of the field up through 2020, briefly touching on statistically derivatized carriers employed in immunology as counterpoints to the rationally assembled and derivatized scaffolds here, although most citations are from the past two decades. The scaffolds are used widely in fields ranging from pure chemistry to artificial photosynthesis and biomedical sciences.

Photosensitization With Supramolecular Arrays for Enhanced Antimicrobial Photodynamic Treatments

Microbial infections represent a silent threat to health that has worsened in recent decades due to microbial resistance to multiple drugs, preventing the fight against infectious diseases. Therefore, the current postantibiotic era forces the search for new microbial control strategies. In this regard, antimicrobial photodynamic therapy (aPDT) using supramolecular arrays with photosensitizing capabilities showed successful emerging applications. This exciting field makes it possible to combine applied aspects of molecular photochemistry and supramolecular chemistry, together with the development of nano- and biomaterials for the design of multifunctional or "smart" supramolecular photosensitizers (SPS). This minireview aims to collect the concepts of the photosensitization process and supramolecular chemistry applied to the development of efficient applications of aPDT, with a brief discussion of the most recent literature in the field.

Overcoming barriers in photodynamic therapy harnessing nano-formulation strategies

Photodynamic therapy (PDT) has been extensively investigated for decades for tumor treatment because of its non-invasiveness, spatiotemporal selectivity, lower side-effects, and immune activation ability. It can be a promising treatment modality in several medical fields, including oncology, immunology, urology, dermatology, ophthalmology, cardiology, pneumology, and dentistry. Nevertheless, the clinical application of PDT is largely restricted by the drawbacks of traditional photosensitizers, limited tissue penetrability of light, inefficient induction of tumor cell death, tumor resistance to the therapy, and the severe pain induced by the therapy. Recently, various photosensitizer formulations and therapy strategies have been developed to overcome these barriers. Significantly, the introduction of nanomaterials in PDT, as carriers or photosensitizers, may overcome the drawbacks of traditional photosensitizers. Based on this, nanocomposites excited by various light sources are applied in the PDT of deep-seated tumors. Modulation of cell death pathways with co-delivered reagents promotes PDT induced tumor cell death. Relief of tumor resistance to PDT with combined therapy strategies further promotes tumor inhibition. Also, the optimization of photosensitizer formulations and therapy procedures reduces pain in PDT. Here, a systematic summary of recent advances in the fabrication of photosensitizers and the design of therapy strategies to overcome barriers in PDT is presented. Several aspects important for the clinical application of PDT in cancer treatment are also discussed.

Possible Enhancement of Photodynamic Therapy (PDT) Colorectal Cancer Treatment when Combined with Cannabidiol

Colorectal Cancer (CRC) has a high mortality rate and is one of the most difficult diseases to manage due to tumour resistance and metastasis. The treatment of choice for CRC is reliant on the phase and time of diagnosis. Despite several conventional treatments available to treat CRC (surgical excision, chemo-, radiationand immune-therapy), resistance is a major challenge, especially if it has metastasized. Additionally, these treatments often cause unwanted adverse side effects and so it remains imperative to investigate alternative combination therapies. Photodynamic Therapy (PDT) is a promising treatment modality for the primary treatment of CRC, since it is non-invasive, has few side effects and selectively damages only cancerous tissues, leaving adjacent healthy structures intact. PDT involves three fundamentals: a Photosensitizer (PS) drug localized in tumour tissues, oxygen, and light. Upon PS excitation using a specific wavelength of light, an energy transfer cascade occurs, that ultimately yields cytotoxic species, which in turn induces cell death. Cannabidiol (CBD) is a cannabinoid compound derived from the Cannabis sativa plant, which has shown to exert anticancer effects on CRC through different pathways, inducing apoptosis and so inhibiting tumour metastasis and secondary spread. This review paper highlights current conventional treatment modalities for CRC and their limitations, as well as discusses the necessitation for further investigation into unconventional active nanoparticle targeting PDT treatments for enhanced primary CRC treatment. This can be administered in combination with CBD, to prevent CRC secondary spread and enhance the synergistic efficacy of CRC treatment outcomes, with less side effects.

Radiodynamic Therapy Using TAT Peptide-Targeted Verteporfin-Encapsulated PLGA Nanoparticles

Radiodynamic therapy (RDT) is a recent extension of conventional photodynamic therapy, in which visible/near infrared light irradiation is replaced by a well-tolerated dose of high-energy X-rays. This enables greater tissue penetration to allow non-invasive treatment of large, deep-seated tumors. We report here the design and testing of a drug delivery system for RDT that is intended to enhance intra- or peri-nuclear localization of the photosensitizer, leading to DNA damage and resulting clonogenic cell kill. This comprises a photosensitizer (Verteporfin, VP) incorporated into poly (lactic-co-glycolic acid) nanoparticles (PLGA NPs) that are surface-functionalized with a cell-penetrating HIV trans-activator of transcription (TAT) peptide. In addition to a series of physical and photophysical characterization studies, cytotoxicity tests in pancreatic (PANC-1) cancer cells in vitro under 4 Gy X-ray exposure from a clinical 6 MV linear accelerator (LINAC) showed that TAT targeting of the nanoparticles markedly enhances the effectiveness of RDT treatment, particularly when assessed by a clonogenic, i.e., DNA damage-mediated, cell kill.

Molecular dynamics simulations of the effects of lipid oxidation on the permeability of cell membranes

The formation of transient pores in their membranes is a well-known mechanism of permeabilization of cells exposed to high-intensity electric pulses. However, the formation of such pores is not able to explain all aspects of the so-called electroporation phenomenon. In particular, the reasons for sustained permeability of cell membranes, persisting long after the pulses' application, remain elusive. The complete resealing of cell membranes takes indeed orders of magnitude longer than the time for electropore closure as reported from molecular dynamics (MD) investigations. Lipid peroxidation has been suggested as a possible mechanism to explain the sustainable permeability of cell membranes. However, theoretical investigations of membrane lesions containing excess amounts of hydroperoxides have shown that the conductivities of such lesions were not high enough to account for the experimental measurements. Here, expanding on these studies, we investigate quantitatively the permeability of cell membrane lesions that underwent secondary oxidation. MD simulations and free energy calculations of lipid bilayers show that such lesions provide a better model of post-pulse permeable and conductive electropermeabilized cells. These results are further discussed in the context of sonoporation and ferroptosis, respectively a procedure and a phenomenon, among others, in which, alike electroporation, substantial lipid oxidation might be triggered.

Photostable Platinated Bacteriochlorins as Potent Photodynamic Agents

Photodynamic therapy (PDT) is used to treat various cancerous diseases. Recently, we have demonstrated that platinated pyridyl-substituted porphyrins are potent agents for PDT with very high phototoxicity (IC₅₀ down to 17 nM) and excellent phototoxic indices of higher than 5800 (p.i. = IC₅₀(dark)/IC₅₀(light)) [Rubbiani, R. et al., Chem. Commun. 2020, 56, 14373]. However, the absorption of porphyrins is not ideal for the treatment of larger tumors because they essentially do not absorb light between 650 and 850 nm. Herein, we report stable conjugates of a novel bacteriochlorin with cisplatin and transplatin. They exhibit extremely high phototoxicity (IC₅₀ values down to 6 nM, irradiated with a 750 nm LED at a fluence of 5 J/cm²), very low dark toxicity, and thereby extremely high phototoxic indices up to 8300. Based on these exciting results, we believe that platinated bacteriochlorins are promising candidates for further investigation as novel PDT anticancer agents.

Biocompatible hole scavenger-assisted graphene oxide dots for photodynamic cancer therapy

Photodynamic therapy (PDT) receives scholarly attention for its low invasiveness and mild adverse effects. Among the reactive oxygen species for PDT, H2O2 is advantageous for achieving long life and low cytotoxicity. Nitrogen-doped graphene oxide dots (NGODs), which are small (∼4.4 nm) and highly biocompatible, can serve as a photosensitizer for PDT. The charge transfer in NGODs is efficient because the NGOD structure is highly crystalline and its carbon-π orbitals are extensively conjugated with nitrogen-nonbonding orbitals. In the presence of ascorbic acid (AA), to scavenge photogenerated holes, NGODs effectively produce H2O2 under white-light irradiation and their H2O2 rate is proportional to the AA concentration. This AA-supplemented PDT effectively kills lung, head and neck, colon, and oral cancer cells and it is highly safe for normal cells. During PDT, the NGODs are uptaken into the cell body and they produce concentrated H2O2 and subsequently induce both the apoptosis and necrosis pathways for cell death. The unique structure of NGODs confines the transfer of the photogenerated electrons for H2O2 production. This study demonstrates the high potential for efficacious and accurate deployment of the proposed NGOD-AA combination in PDT.

Novel fluorinated ring-fused chlorins as promising PDT agents against melanoma and esophagus cancer

Investigation of novel 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused chlorins, derived from 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, as PDT agents against melanoma and esophagus cancer is disclosed. Diol and diester fluorinated ring-fused chlorins, including derivatives with 2-(2-hydroxyethoxy)ethanamino groups at the phenyl rings, were obtained via a two-step methodology, combining SNAr and [8π + 2π] cycloaddition reactions. The short-chain PEG groups at the para-position of the phenyl rings together with the diol moiety at the fused pyrazole ring promote a red-shift of the Soret band, a decrease of the fluorescence quantum yield and an increase of the singlet oxygen formation quantum yield, improving the photophysical characteristics required to act as a photosensitizer. Introduction of these hydrophilic groups also improves the incorporation of the sensitizers by the cells reaching cellular uptake values of nearly 50% of the initial dose. The rational design led to a photosensitizer with impressive IC50 values, 13 and 27 nM against human melanoma and esophageal carcinoma cell lines, respectively.

Ascorbate-dependent and ascorbate-independent Mn porphyrin cytotoxicity: anticancer activity of Mn porphyrin-based SOD mimics through ascorbate-dependent and -independent routes

Objective

The aim of this study was to investigate how modifications at the periphery of the porphyrin ring affect the anticancer activity of Mn porphyrins (MnPs)-based SOD mimics.

Methods

Six compounds: MnTE-2-PyP with a short ethyl chain on the pyridyl ring; MnTnHexOE-2-PyP and MnTnOct-2-PyP with linear 8-atom alkyl chains, but the former with an oxygen atom within the alkyl chain; MnTE-2-PyPhP and MnTPhE-2-PyP with pyridyl and phenyl substituents, were investigated. Cytotoxicity was studied using pII and MDA-MB-231 cancer cell lines. Viability was assessed by the MTT (3-[4,5-dimethylthiazol-2-yl)]-2,5-diphenyltetrazolium bromide) assay and cell proliferation was determined by the sulforhodamine B assay.

Results

Cellular uptake was increased with the increase of the lipophilicity of the compounds, whereas reduction potential (E_½) of the Mn(III)/Mn(II) redox couple shifted away from the optimal value for efficient redox cycling with ascorbate, necessary for ROS production. Amphiphilic MnPs, however, exerted anticancer activity by a mechanism not involving ROS.

Conclusion

Two different processes account for MnPs cytotoxicity. MnPs with appropriate E_½ act via a ROS-dependent mechanism. Amphiphilic MnPs with suitable structure damage sensitive cellular constituents, leading to the suppression of proliferation and loss of viability. Design of compounds interacting directly with sensitive cellular targets is highly promising in the development of anticancer drugs with high selectivity and specificity.

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.

H2O2 enhances the anticancer activity of TMPyP4 by ROS-mediated mitochondrial dysfunction and DNA damage

Cancer is one of the diseases that threatens human health and is a leading cause of mortality worldwide. High levels of reactive oxygen species (ROS) have been observed in cancer tissues compared with normal tissues in vivo, and it is not yet known how this influences chemotherapeutic drug action. Cationic porphyrin 5,10,15,20-tetra-(N-methyl-4-pyridyl) porphyrin (TMPyP4) is a photosensitizer used in photodynamic therapy (PDT) and a telomerase inhibitor used in the treatment of telomerase-positive cancer. Here, we investigated the anticancer activity of TMPyP4 in A549 and PANC cells cultured in H₂O₂. The results showed that compared to TMPyP4 alone, the combination of TMPyP4 and H₂O₂ exhibited sensitization effects on cell viability and colony formation inhibition and apoptosis in A549 and PANC cells, but had no effect in human normal MIHA cells. Mechanistically, the combination of TMPyP4 and H₂O₂ activates high ROS and mitochondrial membrane potential in A549 and PANC cells, resulting in intense DNA damage and DNA damage responses. Consequently, compared to TMPyP4 alone, TMPyP4 and H₂O₂ combined treatment upregulates the expression of BAX, cleaved caspase 3, and p-JNK and downregulates the expression of Bcl-2 in A549 and PANC cells. Taken together, these data suggested that H₂O₂ enhanced the anticancer activity of TMPyP4-mediated ROS-dependent DNA damage and related apoptotic protein regulation, revealing that the high ROS tumor microenvironment plays an important role in chemotherapeutic drug action.

Photodynamic Therapy for Biomodulation and Disinfection in Implant Dentistry: Is It Feasible and Effective?

Dental implants are the most common rehabilitation and restorative treatment used to replace missing teeth. Biofilms adhere to implant surfaces to trigger implant-associated infection and inflammatory response. Clinically, the biofilm induces a local host response with the infiltration of phagocytic immune cells. The pro-inflammatory surroundings set off osteoclastogenesis, which leads to the septic loosening of the implant. The standard of dental care for implant-associated infection relies on a combination of surgery and antimicrobial therapy. Antimicrobial photodynamic therapy is a noninvasive and photochemistry-based approach capable of reducing bacterial load and modulating inflammatory responses. In this review, we explore the photobiomodulation and disinfection outcomes promoted by photodynamic therapy for implant infections, highlighting the quality of evidence on the most up-to-date studies, and discuss the major challenges on the advance of these therapeutic strategies.

Studying the "Rigid-Flexible" Properties of Polymeric Micelle Core-Forming Segments with a Hydrophobic Phthalocyanine Probe Using NMR and UV Spectroscopy

The aim of the performed studies was to thoroughly examine the internal structure of self-assembled nanocarriers (i.e., polymeric micelles-PMs) by means of a hydrophobic phthalocyanine probe in order to identify the crucial features that are required to enhance the photoactive probe stability and reactivity. PMs of hydrophilic poly(ethylene glycol) and hydrophobic poly(ε-caprolactone) (PCL) or poly(d,l-lactide) (PDLLA) were fabricated and loaded with tetra tert-butyl zinc(II) phthalocyanine (ZnPc-t-but₄), a multifunctional spectroscopic probe with a profound ability to generate singlet oxygen upon irradiation. The presence of subdomains, comprising "rigid" and "flexible" regions, in the studied block copolymers' micelles as well as their interactions with the probe molecules, were assessed by various high-resolution NMR measurements [e.g., through-space magnetic interactions by the 1D NOE effect, pulsed field gradient spin-echo, and spin-lattice relaxation time (T₁) techniques]. The studies of the impact of the core-type microenvironment on the ZnPc-t-but₄ photochemical performance also included photobleaching and reactive oxygen species measurements. ZnPc-t-but₄ molecules were found to exhibit spatial proximity effects with both (PCL and PDLLA) hydrophobic polymer chains and interact with both subdomains, which are characterized by different rigidities. It was deduced that the interfaces between particular subdomains constitute an optimal host space for probe molecules, especially in the context of photochemical stability, photoactivity (i.e., for significant enhancement of singlet oxygen generation rates), and aggregation prevention. The present contribution proves that the combination of an appropriate probe, high-resolution NMR techniques, and UV-vis spectroscopy enables one to gain complex information about the subtle structure of PMs essential for their application as nanocarriers for photoactive compounds, for example, in photodynamic therapy, nanotheranostics, combination therapy, or photocatalysis, where the micelles constitute the optimal microenvironment for the desired photoreactions.

Photodynamic effect of TPP encapsulated in polystyrene nanoparticles toward multi-resistant pathogenic bacterial strains: AFM evaluation

Photodynamic inactivation (PDI) is a promising approach for the efficient killing of pathogenic microbes. In this study, the photodynamic effect of sulfonated polystyrene nanoparticles with encapsulated hydrophobic 5,10,15,20-tetraphenylporphyrin (TPP-NP) photosensitizers on Gram-positive (including multi-resistant) and Gram-negative bacterial strains was investigated. The cell viability was determined by the colony forming unit method. The results showed no dark cytotoxicity but high phototoxicity within the tested conditions. Gram-positive bacteria were more sensitive to TPP-NPs than Gram-negative bacteria. Atomic force microscopy was used to detect changes in the morphological properties of bacteria before and after the PDI treatment.

The effect of two porphyrine photosensitizers TMPyP and ZnTPPS4 for application in photodynamic therapy of cancer cells in vitro

Photodynamic therapy (PDT) is one of the treatments for cancer. This therapy uses a combination of a photosensitizer (PS), light irradiation, and oxygen O₂, which is converted to cytotoxic ¹O₂ and other forms of reactive oxygen species (ROS), causing selective damage to the target tissue. In this work, we studied effect of two porphyrin photosensitizers TMPyP and ZnTPPS₄ at three different concentrations (0.25, 0.5, 5μM) after two irradiation doses (5 and 25 J/cm²). Photodynamic efect of TMPyP and ZnTPPS₄ were confirmed by a battery of in vitro tests including MTT, reactive oxygen species (ROS) production and mitochondrial membrane potential test (MMP). Morphological changes of the cells before and after treatment were imaged by atomic force microscopy (AFM). The most effective combination of irradiation dose and concentration for both PSs showed a concentration of 5 μM and a irradiation dose of 25 J/cm² in both cell cultures.

Nanomedicine-Based Strategies Assisting Photodynamic Therapy for Hypoxic Tumors: State-of-the-Art Approaches and Emerging Trends

Since the first clinical cancer treatment in 1978, photodynamic therapy (PDT) technologies have been largely improved and approved for clinical usage in various cancers. Due to the oxygen-dependent nature, the application of PDT is still limited by hypoxia in tumor tissues. Thus, the development of effective strategies for manipulating hypoxia and improving the effectiveness of PDT is one of the most important area in PDT field. Recently, emerging nanotechnology has benefitted progress in many areas, including PDT. In this review, after briefly introducing the mechanisms of PDT and hypoxia, as well as basic knowledge about nanomedicines, we will discuss the state of the art of nanomedicine-based approaches for assisting PDT for treating hypoxic tumors, mainly based on oxygen replenishing strategies and the oxygen dependency diminishing strategies. Among these strategies, we will emphasize emerging trends about the use of nanoscale metal-organic framework (nMOF) materials and the combination of PDT with immunotherapy. We further discuss future perspectives and challenges associated with these trends in both the aspects of mechanism and clinical translation.

Non-Oncologic Applications of Nanomedicine-Based Phototherapy

Phototherapy is widely applied to various human diseases. Nanomedicine-based phototherapy can be classified into photodynamic therapy (PDT) and photothermal therapy (PTT). Activated photosensitizer kills the target cells by generating radicals or reactive oxygen species in PDT while generating heat in PTT. Both PDT and PTT have been employed for treating various diseases, from preclinical to randomized controlled clinical trials. However, there are still hurdles to overcome before entering clinical practice. This review provides an overview of nanomedicine-based phototherapy, especially in non-oncologic diseases. Multiple clinical trials were undertaken to prove the therapeutic efficacy of PDT in dermatologic, ophthalmologic, cardiovascular, and dental diseases. Preclinical studies showed the feasibility of PDT in neurologic, gastrointestinal, respiratory, and musculoskeletal diseases. A few clinical studies of PTT were tried in atherosclerosis and dry eye syndrome. Although most studies have shown promising results, there have been limitations in specificity, targeting efficiency, and tissue penetration using phototherapy. Recently, nanomaterials have shown promising results to overcome these limitations. With advanced technology, nanomedicine-based phototherapy holds great potential for broader clinical practice.

Visible Light Photochemical Reactions for Nucleic Acid-Based Technologies

The expanding scope of chemical reactions applied to nucleic acids has diversified the design of nucleic acid-based technologies that are essential to medicinal chemistry and chemical biology. Among chemical reactions, visible light photochemical reaction is considered a promising tool that can be used for the manipulations of nucleic acids owing to its advantages, such as mild reaction conditions and ease of the reaction process. Of late, inspired by the development of visible light-absorbing molecules and photocatalysts, visible light-driven photochemical reactions have been used to conduct various molecular manipulations, such as the cleavage or ligation of nucleic acids and other molecules as well as the synthesis of functional molecules. In this review, we describe the recent developments (from 2010) in visible light photochemical reactions involving nucleic acids and their applications in the design of nucleic acid-based technologies including DNA photocleaving, DNA photoligation, nucleic acid sensors, the release of functional molecules, and DNA-encoded libraries.

Multifunctional system for combined chemodynamic–photodynamic therapy employing the endothelin axis based on conjugated polymer nanoparticles

Most nanomedicines that attack tumors by Reactive Oxygen Species (ROS) based on lipid peroxidation mechanisms require external activation to work.

NIR-Absorbing RuII Complexes Containing α-Oligothiophenes for Applications in Photodynamic Therapy

The design of near-infrared (NIR)-active photosensitizers (PSs) for light-based cancer treatments such as photodynamic therapy (PDT) has been a challenge. While several NIR-RuII scaffolds have been reported, this approach has not been proven in cells. This is the first report of NIR-RuII PSs that are phototoxic to cancer cells, including highly pigmented B16F10 melanoma cells. The PS family incorporated a bis(1,8-naphthyridine)-based ligand (tpbn), a bidentate thiophene-based ligand (nT; n=0-4), and a monodentate 4-picoline ligand (4-pic). All compounds absorbed light >800 nm with maxima near 730 nm. Transient absorption (TA) measurements indicated that n=4 thiophene rings (4T) positioned the PDT-active triplet intraligand charge transfer (3 ILCT) excited state in energetic proximity to the lowest-lying triplet metal-to-ligand charge transfer (3 MLCT). 4T had low-micromolar phototoxicity with PIvis and PI733nm values as large as 90 and 12, respectively. Spectroscopic studies suggested that the longer-lived (τTA =3-6 μs) 3 ILCT state was accessible from the 3 MLCT state, but energetically uphill in the overall photophysics. The study highlights that phototoxic effects can be achieved with NIR-absorbing RuII PSs as long as the reactive 3 ILCT states are energetically accessible from the low-energy 3 MLCT states. It also demonstrates that tissue-penetrating NIR light can be used to activate the PSs in highly pigmented cells where melanin attenuates shorter wavelengths of light.

Smart Dual-Functionalized Gold Nanoclusters for Spatio-Temporally Controlled Delivery of Combined Chemo- and Photodynamic Therapy

We report the preparation of gold nanoclusters (AuNCs) as a delivery vehicle for the clinically approved photodynamic and chemotherapeutic agents Protoporphyrin IX (PpIX) and doxorubicin (DOX), respectively, and their effect on tumor cells. DOX was attached to the gold nanoclusters through a singlet oxygen-cleavable linker and was therefore released after PpIX irradiation with red light, contributing, synergistically with singlet oxygen, to induce cell death. The doubly functionalized AuNCs proved more effective than a combination of individually functionalized AuNCs. Unlike free DOX, the photoactive nanosystem was non-toxic in the absence of light, which paves the way to introduce a spatiotemporal control of the anticancer therapy and could contribute to reducing the undesirable side effects of DOX.

Biophysical Characterization and Anticancer Activities of Photosensitive Phytoanthraquinones Represented by Hypericin and Its Model Compounds

Photosensitive compounds found in herbs have been reported in recent years as having a variety of interesting medicinal and biological activities. In this review, we focus on photosensitizers such as hypericin and its model compounds emodin, quinizarin, and danthron, which have antiviral, antifungal, antineoplastic, and antitumor effects. They can be utilized as potential agents in photodynamic therapy, especially in photodynamic therapy (PDT) for cancer. We aimed to give a comprehensive summary of the physical and chemical properties of these interesting molecules, emphasizing their mechanism of action in relation to their different interactions with biomacromolecules, specifically with DNA.

Os(II) Oligothienyl Complexes as a Hypoxia-Active Photosensitizer Class for Photodynamic Therapy

Hypoxia presents a challenge to anticancer therapy, reducing the efficacy of many available treatments. Photodynamic therapy is particularly susceptible to hypoxia, given that its mechanism relies on oxygen. Herein, we introduce two new osmium-based polypyridyl photosensitizers that are active in hypoxia. The lead compounds emerged from a systematic study of two Os(II) polypyridyl families derived from 2,2'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (dmb) as coligands combined with imidazo[4,5-f][1,10]phenanthroline ligands tethered to n = 0-4 thiophenes (IP-nT). The compounds were characterized and investigated for their spectroscopic and (photo)biological activities. The two hypoxia-active Os(II) photosensitizers had n = 4 thiophenes, with the bpy analogue 1-4T being the most potent. In normoxia, 1-4T had low nanomolar activity (half-maximal effective concentration (EC50) = 1-13 nM) with phototherapeutic indices (PI) ranging from 5500 to 55 000 with red and visible light, respectively. A sub-micromolar potency was maintained even in hypoxia (1% O2), with light EC50 and PI values of 732-812 nM and 68-76, respectively -currently among the largest PIs for hypoxic photoactivity. This high degree of activity coincided with a low-energy, long-lived (0.98-3.6 μs) mixed-character intraligand charge-transfer (3ILCT)/ligand-to-ligand charge-transfer (3LLCT) state only accessible in quaterthiophene complexes 1-4T and 2-4T. The coligand identity strongly influenced the photophysical and photobiological results in this study, whereby the bpy coligand led to longer lifetimes (3.6 μs) and more potent photo-cytotoxicity relative to those of dmb. The unactivated compounds were relatively nontoxic both in vitro and in vivo. The maximum tolerated dose for 1-4T and 2-4T in mice was greater than or equal to 200 mg kg-1, an excellent starting point for future in vivo validation.

Metallodrugs are unique: opportunities and challenges of discovery and development

Metals play vital roles in nutrients and medicines and provide chemical functionalities that are not accessible to purely organic compounds. At least 10 metals are essential for human life and about 46 other non-essential metals (including radionuclides) are also used in drug therapies and diagnostic agents. These include platinum drugs (in 50% of cancer chemotherapies), lithium (bipolar disorders), silver (antimicrobials), and bismuth (broad-spectrum antibiotics). While the quest for novel and better drugs is now as urgent as ever, drug discovery and development pipelines established for organic drugs and based on target identification and high-throughput screening of compound libraries are less effective when applied to metallodrugs. Metallodrugs are often prodrugs which undergo activation by ligand substitution or redox reactions, and are multi-targeting, all of which need to be considered when establishing structure-activity relationships. We focus on early-stage in vitro drug discovery, highlighting the challenges of evaluating anticancer, antimicrobial and antiviral metallo-pharmacophores in cultured cells, and identifying their targets. We highlight advances in the application of metal-specific techniques that can assist the preclinical development, including synchrotron X-ray spectro(micro)scopy, luminescence, and mass spectrometry-based methods, combined with proteomic and genomic (metallomic) approaches. A deeper understanding of the behavior of metals and metallodrugs in biological systems is not only key to the design of novel agents with unique mechanisms of action, but also to new understanding of clinically-established drugs.

BODIPY-Based Photosensitizers as Potential Anticancer and Antibacterial Agents: Role of the Positive Charge and the Heavy Atom Effect

Boron-dipyrromethene derivatives, including cationic and iodinated analogs, were obtained and subjected to physicochemical and in vitro photodynamic activity studies. Iodinated derivatives revealed a substantial heavy atom effect manifested by a bathochromic shift of the absorption band by about 30 nm and fluorescence intensity reduced by about 30-35 times, compared to that obtained for non-iodinated ones. In consequence, singlet oxygen generation significantly increased with Φ_Δ values in the range 0.69-0.97. The in vitro photodynamic activity was evaluated on Gram-positive Staphylococcus aureus, Gram-negative Escherichia coli, and on human androgen-sensitive prostate adenocarcinoma cells (LNCaP). The novel cationic, iodinated BODIPY, demonstrated the highest activity toward all studied cells. An excellent cytotoxic effect was found against LNCaP cells with an IC₅₀ value of 19.3 nM, whereas the viability of S. aureus was reduced by >5.6 log₁₀ at 0.25 μM concentration and by >5.3 log₁₀ in the case of E. coli at 5 μM. Thus, this analog seems to be a very promising candidate for the application in both anticancer and antimicrobial photodynamic therapy.

meso-Thiophenium Porphyrins and Their Zn(II) Complexes: A New Category of Cationic Photosensitizers

A new category of cationic meso-thiophenium porphyrins are introduced as possible alternatives to the popular meso-pyridinium porphyrins. Combinations of cationic porphyrins bearing meso-2-methylthiophenium and meso-4-hydroxyphenyl moieties T₂(OH)₂M (A₂B₂ type) and T(OH)₃M (AB₃ type) along with their zinc(II) complexes T₂(OH)₂MZn and T(OH)₃MZn, are reported. The increase in the number of thienyl groups attached to the meso-positions of the porphyrin derivatives (A₂B₂ frame) has been shown to impart longer fluorescence lifetimes and stronger photocytotoxicity toward A549 lung cancer cells, as evident with T₂(OH)₂M and its corresponding diamagnetic metal complex T₂(OH)₂MZn. The photoactivated T₂(OH)₂MZn imparts an early stage reactive oxygen species (ROS) upregulation and antioxidant depletion in A549 cells and contributes to the strongest oxidative stress-induced cell death mechanism in the series. The DFT calculations of the singlet-triplet energy gap (ΔE) of all the four hydrophilic thiophenium porphyrin derivatives establish the potential applicability of these cationic photosensitizers as PDT agents.

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.

Breaking the barrier: an osmium photosensitizer with unprecedented hypoxic phototoxicity for real world photodynamic therapy

Hypoxia presents a two-fold challenge in the treatment of cancer, as low oxygen conditions induce biological changes that make malignant tissues simultaneously more aggressive and less susceptible to standard chemotherapy. This paper reports the first metal-based photosensitizer that approaches the ideal properties for a phototherapy agent. The Os(phen)2-based scaffold was combined with a series of IP-nT ligands, where phen = 1,10-phenanthroline and IP-nT = imidazo[4,5-f][1,10]phenanthroline tethered to n = 0-4 thiophene rings. Os-4T (n = 4) emerged as the most promising complex in the series, with picomolar activity and a phototherapeutic index (PI) exceeding 106 in normoxia. The photosensitizer exhibited an unprecedented PI > 90 (EC50 = 0.651 μM) in hypoxia (1% O2) with visible and green light, and a PI > 70 with red light. Os-4T was also active with 733 nm near-infrared light (EC50 = 0.803 μM, PI = 77) under normoxia. Both computation and spectroscopic studies confirmed a switch in the nature of the lowest-lying triplet excited state from triplet metal-to-ligand charge transfer (3MLCT) to intraligand charge transfer (3ILCT) at n = 3, with a lower energy and longer lifetime for n = 4. All compounds in the series were relatively nontoxic in the dark but became increasingly phototoxic with additional thiophenes. These normoxic and hypoxic activities are the largest reported to date, demonstrating the utility of osmium for phototherapy applications. Moreover, Os-4T had a maximum tolerated dose (MTD) in mice that was >200 mg kg-1, which positions this photosensitizer as an excellent candidate for in vivo applications.

Near-infrared absorbing Ru(ii) complexes act as immunoprotective photodynamic therapy (PDT) agents against aggressive melanoma

Mounting evidence over the past 20 years suggests that photodynamic therapy (PDT), an anticancer modality known mostly as a local treatment, has the capacity to invoke a systemic antitumor immune response, leading to protection against tumor recurrence. For aggressive cancers such as melanoma, where chemotherapy and radiotherapy are ineffective, immunomodulating PDT as an adjuvant to surgery is of interest. Towards the development of specialized photosensitizers (PSs) for treating pigmented melanomas, nine new near-infrared (NIR) absorbing PSs based on a Ru(ii) tris-heteroleptic scaffold [Ru(NNN)(NN)(L)]Cl_n, were explored. Compounds 2, 6, and 9 exhibited high potency toward melanoma cells, with visible EC₅₀ values as low as 0.292–0.602 μM and PIs as high as 156–360. Single-micromolar phototoxicity was obtained with NIR-light (733 nm) with PIs up to 71. The common feature of these lead NIR PSs was an accessible low-energy triplet intraligand (³IL) excited state for high singlet oxygen (¹O₂) quantum yields (69–93%), which was only possible when the photosensitizing ³IL states were lower in energy than the lowest triplet metal-to-ligand charge transfer (³MLCT) excited states that typically govern Ru(ii) polypyridyl photophysics. PDT treatment with 2 elicited a pro-inflammatory response alongside immunogenic cell death in mouse B16F10 melanoma cells and proved safe for in vivo administration (maximum tolerated dose = 50 mg kg⁻¹). Female and male mice vaccinated with B16F10 cells that were PDT-treated with 2 and challenged with live B16F10 cells exhibited 80 and 55% protection from tumor growth, respectively, leading to significantly improved survival and excellent hazard ratios of ≤0.2.

Ru(ii) photosensitizers (PSs) destroy aggressive melanoma cells, triggering an immune response that leads to protection against tumor challenge and mouse survival.

Tolerability of Photodynamic Therapy Using 10% 5-Aminolevulinic Acid Hydrochloride Gel for Treating Actinic Keratoses on Surface Areas Larger than 75cm2

BACKGROUND: Photodynamic therapy (PDT) is a well-known treatment modality for actinic keratosis (AK). The largest surface area approved by the FDA is 20cm² with 10% 5-aminolevulinic acid hydrochloride gel (10% ALA gel). OBJECTIVE: This retrospective study assessed the tolerability of PDT with 10% ALA gel in areas ranging from 75cm² to 300cm². METHODS: The medical records of 203 patients with AKs treated with 376 PDT sessions using 10% ALA gel were reviewed. Face and ears were incubated with 10% ALA gel for 60 minutes without occlusion while all other areas were incubated for 90 minutes with plastic wrap occlusion followed by 10J/cm² blue light. Patients were given specific post-PDT care directions. Patient outcomes data was collected. RESULTS: Skin irritation was reported in 27 (7%) PDT sessions in 25 patients (12%). These occurred primarily on the face (n=17), hands (n=4,) and scalp (n=3). Of the 349 PDT treatments (93%) without irritation, these subjects reported adherence to a specific post-PDT regimen using zinc oxide and healing creams for 48 hours. LIMITATIONS: This was a retrospective study observing safety and tolerability. Clearance data was not collected. CONCLUSION: Based on this retrospective observational case series, PDT with ALA gel appears to be safe for treating patients with AKs covering surface areas 75 to 300cm². Irritation might be mitigated by post-PDT care regimens.

The role of autofluorescence, photodynamic diagnosis and Photodynamic therapy in malignant tumors of the duodenum

This article presents the current state of knowledge and a review of the literature in terms of the prevalence, etiopathogenesis, differential diagnosis, management, prognosis, and treatment of malignant tumors of the duodenum. The role of autofluorescence and photodynamic diagnosis as an emerging treatment method for rarely o ccurring duodenal malignant neoplasms .. We selected publications which can be found in databases such as The National Center for Biotechnology Information, U.S. National Library of Medicine (PubMed), The American Chemical Society, The American Association of Pharmaceutical Sciences and The American Society for Photobiology and The Canada Institute for Scientific and Technical Information.