Fluorinated Photodynamic Therapy Device Tips and their Resistance to Fouling for In Vivo Sensitizer Release

We describe progress on a one‐step photodynamic therapy (PDT) technique that is simple: device tip delivery of sensitizer, oxygen and light simultaneously. Control is essential for their delivery to target sites to generate singlet oxygen. One potential problem is the silica device tip may suffer from biomaterial fouling and the pace of sensitizer photorelease is slowed. Here, we have used biomaterial (e.g. proteins, cells, etc.) from SQ20B head and neck tumors and whole blood for an assessment of fouling of the silica tips by adsorption. It was shown that by exchanging the native silica tip for a fluorinated tip, a better nonstick property led to an increased sensitizer output by ~10%. The fluorinated tip gave a sigmoidal photorelease where singlet oxygen is stabilized to physical quenching, whereas the native silica tip with unprotected SiO–H groups gave a slower (pseudolinear) photorelease. A further benefit from fluorinated silica is that 15% less biomaterial adheres to its surface compared to native silica based on a bicinchoninic acid assay (BCA) and X‐ray photoelectron spectroscopy (XPS) measurements. We discuss how the fluorination of the device tip increases biofouling resistance and can contribute to a new pointsource PDT tool.     

Gold Nanorod–Photosensitizer Complex Obtained by Layer‐by‐Layer Method for Photodynamic/Photothermal Therapy In Vitro

Gold nanorod (GNR)–photosensitizer (PS) complex was prepared using anionic PS (sodium salt of purpurin‐18) and cationic poly(allylamine hydrochloride) by layer‐by‐layer method, and was characterized by transmission electron microscopy, UV‐vis spectroscopy, and zeta potential. The GNR–PS complex is a promising agent for synergistic (photothermal and photodynamic) therapy (PTT/PDT), in which PTT generates heat as well as operates the PS release which maximize the following PDT activity. The combined dual therapy, PTT followed by PDT, exhibits a significantly higher photocytotoxicity result based on synergistic effect of hyperthermia from PTT as well as singlet oxygen photogeneration from PDT.     

Cellular Uptake and Photodynamic Activity of Protein Nanocages Containing Methylene Blue Photosensitizing Drug

This study reports that photosensitizers encapsulated in supramolecular protein cages can be internalized by tumor cells and can deliver singlet oxygen intracellularly for photodynamic therapy (PDT). As an alternative to other polymeric and/or inorganic nanocarriers and nanoconjugates, which may also deliver photosensitizers to the inside of the target cells, protein nanocages provide a unique vehicle of biological origin for the intracellular delivery of photosensitizing molecules for PDT by protecting the photosensitizers from reactive biomolecules in the cell membranes, and yet providing a coherent, critical mass of destructive power (by way of singlet oxygen) upon specific light irradiation for photodynamic therapy of tumor cells. As a model, we demonstrated the successful encapsulation of methylene blue (MB) in apoferritin via a dissociation–reassembly process controlled by pH. The resulting MB-containing apoferritin nanocages show a positive effect on singlet oxygen production, and cytotoxic effects on MCF-7 human breast adenocarcinoma cells when irradiated at the appropriate wavelength (i.e. 633 nm).     

Photodynamic Therapy Efficacy Enhanced by Dynamics: The Role of Charge Transfer and Photostability in the Selection of Photosensitizers

Progress in the photodynamic therapy (PDT) of cancer should benefit from a rationale to predict the most efficient of a series of photosensitizers that strongly absorb light in the phototherapeutic window (650–800 nm) and efficiently generate reactive oxygen species (ROS=singlet oxygen and oxygen‐centered radicals). We show that the ratios between the triplet photosensitizer–O₂ interaction rate constant (k_D) and the photosensitizer decomposition rate constant (k_d), k_D/k_d, determine the relative photodynamic activities of photosensitizers against various cancer cells. The same efficacy trend is observed in vivo with DBA/2 mice bearing S91 melanoma tumors. The PDT efficacy intimately depends on the dynamics of photosensitizer–oxygen interactions: charge transfer to molecular oxygen with generation of both singlet oxygen and superoxide ion (high k_D) must be tempered by photostability (low k_d). These properties depend on the oxidation potential of the photosensitizer and are suitably combined in a new fluorinated sulfonamide bacteriochlorin, motivated by the rationale.     

Multifunctional Logic in a Photosensitizer with Triple‐Mode Fluorescent and Photodynamic Activity

Herein we describe a photosensitizer (PS) with the capacity to perform multiple logic operations based on a pyrene‐containing phthalocyanine (Pc) derivative. The system presents three output signals (fluorescence at 377 and 683 nm, and singlet oxygen (¹O₂) production), which are dependent on three inputs: two chemical (concentration of dithiothreitol (DTT) and acidic pH) and one physical (visible light above 530 nm for ¹O₂ sensitization). The multi‐input/multioutput nature of this PS leads to single‐, double‐, and triple‐mode activation pathways of its fluorescent and photodynamic functions, through the interplay of various interrelated AND, ID, and INHIBIT gates. Dual fluorescence emissions are potentially useful for orthogonal optical imaging protocols while ¹O₂ is the main reactive species in photodynamic therapy (PDT). We thus expect that this kind of PS logic system will be of great interest for multimodal cellular imaging and therapeutic applications.     

H2S‐Activable MOF Nanoparticle Photosensitizer for Effective Photodynamic Therapy against Cancer with Controllable Singlet‐Oxygen Release

Photodynamic therapy (PDT) has emerged as an important minimally invasive tumor treatment technology. The search for an effective photosensitizer to realize selective cancer treatment has become one of the major foci in recent developments of PDT technology. Controllable singlet‐oxygen release based on specific cancer‐associated events, as another major layer of selectivity mode, has attracted great attention in recent years. Here, for the first time, we demonstrated that a novel mixed‐metal metal–organic framework nanoparticle (MOF NP) photosensitizer can be activated by a hydrogen sulfide (H₂S) signaling molecule in a specific tumor microenvironment for PDT against cancer with controllable singlet‐oxygen release in living cells. The effective removal of tumors in vivo further confirmed the satisfactory treatment effect of the MOF NP photosensitizer.     

Development of a Novel Covalent Folate‐Albumin‐Photosensitizer Conjugate

There is considerable interest in the development of novel and more efficient delivery systems for improving the efficacy of photodynamic therapy (PDT). The authors in this highlighted issue describe the synthesis and the photobiological characterizations of two photosensitizer (PS) conjugates based on β‐carboline derivatives covalently conjugated to folic acid (FA) coupled to bovine serum albumin (BSA) as a carrier system specifically targeting cancer cells overexpressing FA receptor alpha (FRα). Accordingly, only the FA–BSA–β‐carboline conjugates are internalized specifically in FRα‐positive cells and are proved to be phototoxic. On the other hand, albumin–β‐carboline conjugates without FA or β‐carboline derivatives alone are not internalized and nontoxic. This conjugate is among the first to produce a conjugate composed of a PS and FA molecules that are directly conjugated to BSA. In addition, the in vitro studies are the first evidence that directly conjugated FA‐BSA can be used as carriers to selectively enhance cytotoxicity by PDT relative to unmodified PS or nontargeted BSA‐PS. This strategy is a positive step forward for the covalent design and construction of a photodynamic nanomedicine for FR‐positive tumors.     

Synthesis of a Photostable Near‐Infrared‐Absorbing Photosensitizer for Selective Photodamage to Cancer Cells

A new class of near‐infrared (NIR)‐absorptive (>900 nm) photosensitizer based on a phenothiazinium scaffold is reported. The stable solid compound, o‐DAP, the oxidative form of 3,7‐bis(4‐methylaminophenyl)‐10H‐phenothiazine, can generate reactive oxygen species (ROS, singlet oxygen and superoxide) under appropriate irradiation conditions. After biologically evaluating the intracellular uptake, localization, and phototoxicity of this compound, it was concluded that o‐DAP is photostable and a potential selective photodynamic therapy (PDT) agent under either NIR or white light irradiation because its photodamage is more efficient in cancer cells than in normal cells and is without significant dark toxicity. This is very rare for photosensitizers in PDT applications.     

Immobilized phthalocyanines of magnesium,aluminum, and zinc in photodynamic treatment of mesenchymal stromal cells

Phthalocyanines of magnesium, aluminum, and zinc immobilized on nano-sized silica and poly-N-vinylpyrrolidone in aqueous solutions were synthesized. Photochemical activity of the immobilized metal complexes was assessed by generation of singlet oxygen. Nontoxic concentrations of the new photosensitizers were determined in vitro. A comparative analysis of the efficiency of photodynamic therapy (PDT) was performed for immobilized phthalocyanines using mesenchymal stromal cells as a cell model. Aluminum phthalocyanine immobilized on nano-sized silica displayed the highest cell tropism. Irradiation of phthalocyanine-loaded cells resulted in generation of active singlet oxygen and subsequent apoptotic cell death. The use of immobilized phthalocyanines allowed decreasing the effective concentration (dose) of photosensitizer and enhancing the PDT cytotoxicity.     

Synthesis and Photochemical Evaluation of Iodinated Squarylium Cyanine Dyes

Several (multiply) iodinated squarylium cyanine dyes of type 1 and 8 (see Scheme and Table), derived from 1,3‐benzothiazole and 6‐iodo‐1,3‐benzothiazole, were synthesized as potential new photosensitizers, with absorptions in the 700‐nm region. Their ability to generate singlet oxygen (¹O₂) was assessed by luminescence‐decay measurement in the near‐IR. Some of these new dyes show interesting photophysical properties, and may be potentially used in photodynamic therapy (PDT).     

Multifunctional Nano‐Bioprobes Based on Rattle‐Structured Upconverting Luminescent Nanoparticles

Lanthanide‐doped upconversion nanoparticles (UCNPs) have shown great promise in versatile bioapplications. For the first time, organosilica‐shelled β‐NaLuF₄:Gd/Yb/Er nanoprobes with a rattle structure have been designed for dual‐modal imaging and photodynamic therapy (PDT). Benefiting from the unique rattle structure and aromatic framework, these nanoprobes are endowed with a high loading capacity and the disaggregation effect of photosensitizers. After loading of β‐carboxyphthalocyanine zinc or rose Bengal into the nanoprobes, we achieved higher energy transfer efficiency from UCNPs to photosensitizers as compared to those with conventional core–shell structure or with pure‐silica shell, which facilitates a large production of singlet oxygen and thus an enhanced PDT efficacy. We demonstrated the use of these nanoprobes in proof‐of‐concept X‐ray computed tomography (CT) and UC imaging, thus revealing the great potential of this multifunctional material as an excellent nanoplatform for cancer theranostics.     

A Comparison of Dose Metrics to Predict Local Tumor Control for Photofrin‐mediated Photodynamic Therapy

This preclinical study examines light fluence, photodynamic therapy (PDT) dose and “apparent reacted singlet oxygen,” [¹O₂]_rx, to predict local control rate (LCR) for Photofrin‐mediated PDT of radiation‐induced fibrosarcoma (RIF) tumors. Mice bearing RIF tumors were treated with in‐air fluences (50–250 J cm^?2) and in‐air fluence rates (50–150 mW cm^?2) at Photofrin dosages of 5 and 15 mg kg^?1 and a drug‐light interval of 24 h using a 630‐nm, 1‐cm‐diameter collimated laser. A macroscopic model was used to calculate [¹O₂]_rx and PDT dose based on in vivo explicit dosimetry of the drug concentration, light fluence and tissue optical properties. PDT dose and [¹O₂]_rx were defined as a temporal integral of drug concentration and fluence rate, and singlet oxygen concentration consumed divided by the singlet oxygen lifetime, respectively. LCR was stratified for different dose metrics for 74 mice (66 + 8 control). Complete tumor control at 14 days was observed for [¹O₂]_rx ≥ 1.1 mm or PDT dose ≥1200 μm J cm^?2 but cannot be predicted with fluence alone. LCR increases with increasing [¹O₂]_rx and PDT dose but is not well correlated with fluence. Comparing dosimetric quantities, [¹O₂]_rx outperformed both PDT dose and fluence in predicting tumor response and correlating with LCR.     

Hypoxia Induced by Upconversion‐Based Photodynamic Therapy: Towards Highly Effective Synergistic Bioreductive Therapy in Tumors

Local hypoxia in tumors is an undesirable consequence of photodynamic therapy (PDT), which will lead to greatly reduced effectiveness of this therapy. Bioreductive pro‐drugs that can be activated at low‐oxygen conditions will be highly cytotoxic under hypoxia in tumors. Based on this principle, double silica‐shelled upconversion nanoparticles (UCNPs) nanostructure capable of co‐delivering photosensitizer (PS) molecules and a bioreductive pro‐drug (tirapazamine, TPZ) were designed (TPZ‐UC/PS), with which a synergetic tumor therapeutic effect has been achieved first by UC‐based (UC‐) PDT under normal oxygen environment, immediately followed by the induced cytotoxicity of activated TPZ when oxygen is depleted by UC‐PDT. Treatment with TPZ‐UC/PS plus NIR laser resulted in a remarkably suppressed tumor growth as compared to UC‐PDT alone, implying that the delivered TPZ has a profound effect on treatment outcomes for the much‐enhanced cytotoxicity of TPZ under PDT‐induced hypoxia.     

GSH and H2O2 Co‐Activatable Mitochondria‐Targeted Photodynamic Therapy under Normoxia and Hypoxia

Currently, photosensitizers (PSs) that are microenvironment responsive and hypoxia active are scarcely available and urgently desired for antitumor photodynamic therapy (PDT). Presented herein is the design of a redox stimuli activatable metal‐free photosensitizer (aPS), also functioning as a pre‐photosensitizer as it is converted to a PS by the mutual presence of glutathione (GSH) and hydrogen peroxide (H₂O₂) with high specificity on a basis of domino reactions on the benzothiadiazole ring. Superior to traditional PSs, the activated aPS contributed to efficient generation of reactive oxygen species including singlet oxygen and superoxide ion through both type 1 and type 2 pathways, alleviating the aerobic requirement for PDT. Equipped with a triphenylphosphine ligand for mitochondria targeting, ^mito aPS showed excellent phototoxicity to tumor cells with low light fluence under both normoxic and hypoxic conditions, after activation by intracellular GSH and H₂O₂. The ^mito aPS was also compatible to near infrared PDT with two photon excitation (800 nm) for extensive bioapplications.     

Self‐Amplified Photodynamic Therapy through the 1O2‐Mediated Internalization of Photosensitizers from a Ppa‐Bearing Block Copolymer

Nanocarriers are employed to deliver photosensitizers for photodynamic therapy (PDT) through the enhanced penetration and retention effect, but disadvantages including the premature leakage and non‐selective release of photosensitizers still exist. Herein, we report a ¹O₂‐responsive block copolymer (POEGMA‐b‐P(MAA‐co‐VSPpaMA) to enhance PDT via the controllable release of photosensitizers. Once nanoparticles formed by the block copolymer have accumulated in a tumor and have been taken up by cancer cells, pyropheophorbide a (Ppa) could be controllably released by singlet oxygen (¹O₂) generated by light irradiation, enhancing the photosensitization. This was demonstrated by confocal laser scanning microscopy and in vivo fluorescence imaging. The ¹O₂‐responsiveness of POEGMA‐b‐P(MAA‐co‐VSPpaMA) block copolymer enabled the realization of self‐amplified photodynamic therapy by the regulation of Ppa release using NIR illumination. This may provide a new insight into the design of precise PDT.     

A Comparison of the Photodynamic Effects of Temoporfin (mTHPC) and MC540 on Leukemia Cells: Efficacy and Apoptosis

The photodynamic effects of temoporfin (meso-tetrahy-droxyphenylchlorin, mTHPC) and merocyanine 540 (MC540) in murine myeloid leukemia M1 and WEHI 3B (JCS) cells were compared. The mTHPC was found to be more potent and selective. At a lethal dosage of 90% killing (LD90), only 1.3 μM of mTHPC and 4.2 kj/m2 of light irradiation was required, which was a 20-fold lower drug concentration and 11-fold smaller light dose than that required when using MC540. Meanwhile, three times less, or 15%, of the coincubated erythrocytes were destroyed by mTHPC than by MC540. Confocal micrographs showed that both drugs accumulated diffusely inside the cytoplasm in a very similar fashion, but mTHPC induced a more extensive apoptosis in photosensitized JCS cells. For example, at LD90, mTHPC practically killed all JCS cells via apoptosis and cleaved the DNA to extremely small 150 base-pair fragments. In contrast, among the JCS cells killed by MC540, about 88% died via apoptosis and large DNA fragments were abundant. Relative to MC540, the ability of mTHPC to trigger large-scale and thorough apoptosis in leukemia cells may help explain its potency and selectivity.     

The Photosensitizer Temoporfin (mTHPC) – Chemical,Pre-clinical and Clinical Developments in the Last Decade†‡

This review follows the research, development and clinical applications of the photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (mTHPC, temoporfin) in photodynamic (cancer) therapy (PDT) and other medical applications. Temoporfin is the active substance in the medicinal product Foscan® authorized in the EU for the palliative treatment of head and neck cancer. Chemistry, biochemistry and pharmacology, as well as clinical and other applications of temoporfin are addressed, including the extensive work that has been done on formulation development including liposomal formulations. The literature has been covered from 2009 to early 2022, thereby connecting it to the previous extensive review on this photosensitizer published in this journal [Senge, M. O. and J. C. Brandt (2011) Photochem. Photobiol. 87, 1240–1296] which followed its way from initial development to approval and clinical application.     

Clinical Evaluation of the Cutaneous Phototoxicity of 5,10,15,20-Tetra (m-hydroxyphenyl)chlorin

The cutaneous phototoxic reaction induced by intravenous injection of 5,-10,-15,-20-tetra(m-hydroxyphenyl)chlorin (mTHPC) has been clinically evaluated in patients undergoing photodynamic therapy. These tests were performed on the backs of 23 patients with a solar simulator at various times after drug administration ranging from 5 h to 57 days. The mTHPC doses ranged from 0.1 to 0.3 mg/kg, and the illuminations lasted from 30 s up to 8 min. These tests have shown that the duration of the skin photosensitization induced after a typical therapeutic dose of mTHPC (0.15 mg/kg) is less important than with Photofrin®(2 mg/kg). The level of mTHPC in the skin was also assessed in vivo and at times corresponding to the irradiations using an optical fiber-based spectrofiuorometer. This study indicates that the light-induced fluorescence spectroscopy of mTHPC enables prediction of the degree of photosensitivity of the skin.     

A Bifunctional Photosensitizer for Enhanced Fractional Photodynamic Therapy: Singlet Oxygen Generation in the Presence and Absence of Light

The photosensitized generation of singlet oxygen within tumor tissues during photodynamic therapy (PDT) is self‐limiting, as the already low oxygen concentrations within tumors is further diminished during the process. In certain applications, to minimize photoinduced hypoxia the light is introduced intermittently (fractional PDT) to allow time for the replenishment of cellular oxygen. This condition extends the time required for effective therapy. Herein, we demonstrated that a photosensitizer with an additional 2‐pyridone module for trapping singlet oxygen would be useful in fractional PDT. Thus, in the light cycle, the endoperoxide of 2‐pyridone is generated along with singlet oxygen. In the dark cycle, the endoperoxide undergoes thermal cycloreversion to produce singlet oxygen, regenerating the 2‐pyridone module. As a result, the photodynamic process can continue in the dark as well as in the light cycles. Cell‐culture studies validated this working principle in vitro.     

Membrane‐Anchoring Photosensitizer with Aggregation‐Induced Emission Characteristics for Combating Multidrug‐Resistant Bacteria

Traditional photosensitizers (PSs) show reduced singlet oxygen (¹O₂) production and quenched fluorescence upon aggregation in aqueous media, which greatly affect their efficiency in photodynamic therapy (PDT). Meanwhile, non‐targeting PSs generally yield low efficiency in antibacterial performance due to their short lifetimes and small effective working radii. Herein, a water‐dispersible membrane anchor (TBD‐anchor) PS with aggregation‐induced emission is designed and synthesized to generate ¹O₂ on the bacterial membrane. TBD‐anchor showed efficient antibacterial performance towards both Gram‐negative (Escherichia coli) and Gram‐positive bacteria (Staphylococcus aureus). Over 99.8 % killing efficiency was obtained for methicillin‐resistant S. aureus (MRSA) when they were exposed to 0.8 μm of TBD‐anchor at a low white light dose (25 mW cm^?2) for 10 minutes. TBD‐anchor thus shows great promise as an effective antimicrobial agent to combat the menace of multidrug‐resistant bacteria.