Photofrin® photodynamic therapy with intratumor photosensitizer injection provides similar tumor response while reducing systemic skin photosensitivity: Pilot murine study

Nanoparticle-mediated Photodynamic Therapy as a Method to Ablate Oral Cavity Squamous Cell Carcinoma in Preclinical Models

Photodynamic therapy (PDT) is a tissue ablation technique able to selectively target tumor cells by activating the cytotoxicity of photosensitizer dyes with light. PDT is nonsurgical and tissue sparing, two advantages for treatments in anatomically complex disease sites such as the oral cavity. We have previously developed PORPHYSOME (PS) nanoparticles assembled from chlorin photosensitizer-containing building blocks (∼94,000 photosensitizers per particle) and capable of potent PDT. In this study, we demonstrate the selective uptake and curative tumor ablation of PS-enabled PDT in three preclinical models of oral cavity squamous cell carcinoma (OCSCC): biologically relevant subcutaneous Cal-33 (cell line) and MOC22 (syngeneic) mouse models, and an anatomically relevant orthotopic VX-2 rabbit model. Tumors selectively uptake PS (10 mg/kg, i.v.) with 6-to 40-fold greater concentration versus muscle 24 hours post-injection. Single PS nanoparticle-mediated PDT (PS-PDT) treatment (100 J/cm2, 100 mW/cm2) of Cal-33 tumors yielded significant apoptosis in 65.7% of tumor cells. Survival studies following PS-PDT treatments demonstrated 90% (36/40) overall response rate across all three tumor models. Complete tumor response was achieved in 65% of Cal-33 and 91% of MOC22 tumor mouse models 14 days after PS-PDT, and partial responses obtained in 25% and 9% of Cal-33 and MOC22 tumors, respectively. In buccal VX-2 rabbit tumors, combined surface and interstitial PS-PDT (200 J total) yielded complete responses in only 60% of rabbits 6 weeks after a single treatment whereas three repeated weekly treatments with PS-PDT (200 J/week) achieved complete ablation in 100% of tumors. PS-PDT treatments were well tolerated by animals with no treatment-associated toxicities and excellent cosmetic outcomes.

SIGNIFICANCE

PS-PDT is a safe and repeatable treatment modality for OCSCC ablation. PS demonstrated tumor selective uptake and PS-PDT treatments achieved reproducible efficacy and effectiveness in multiple tumor models superior to other clinically tested photosensitizer drugs. Cosmetic and functional outcomes were excellent, and no clinically significant treatment-associated toxicities were detected. These results are enabling of window of opportunity trials for fluorescence-guided PS-PDT in patients with early-stage OCSCC scheduled for surgery.

Structure and functions of Aggregation-Induced Emission-Photosensitizers in anticancer and antimicrobial theranostics

Photosensitizers with Aggregation-Induced Emission (AIE) can allow the efficient light-mediated generation of Reactive Oxygen Species (ROS) based on their complex molecular structure, while interacting with living cells. They achieve better tissue targeting and allow penetration of different wavelengths of Ultraviolet-Visible-Infrared irradiation. Not surprisingly, they are useful for fluorescence image-guided Photodynamic Therapy (PDT) against cancers of diverse origin. AIE-photosensitizers can also function as broad spectrum antimicrobials, capable of destroying the outer wall of microbes such as bacteria or fungi without the issues of drug resistance, and can also bind to viruses and deactivate them. Often, they exhibit poor solubility and cellular toxicity, which compromise their theranostic efficacy. This could be circumvented by using suitable nanomaterials for improved biological compatibility and cellular targeting. Such dual-function AIE-photosensitizers nanoparticles show unparalleled precision for image-guided detection of tumors as well as generation of ROS for targeted PDT in living systems, even while using low power visible light. In short, the development of AIE-photosensitizer nanoparticles could be a better solution for light-mediated destruction of unwanted eukaryotic cells and selective elimination of prokaryotic pathogens, although, there is a dearth of pre-clinical and clinical data in the literature.

4'-Nitrobiphenyl thioglucoside as the Smallest, fluorescent photosensitizer with cancer targeting ligand

We have previously developed a glucose-linked biphenyl photosensitizer that can pass through glucose transporters, aiming for cancer-selective photodynamic therapy (PDT). Its small size (MW: 435) will allow oral administration and a fast clearance avoiding photosensitivity. However, its fluorescence efficiency was quite low, causing difficulty in monitoring cellular uptake. We thus synthesized a series of monosaccharide-linked biphenyl derivatives with a sulfur atom replacing an oxygen atom, in search of a photosensitizer with a brighter fluorescence. Among them, 4'-nitrobiphenyl thioglucoside showed a fluorescence emission extending to near infra-red region with a strength three times greater than that of the previous compound. This compound was found to have a higher ¹O₂-producing efficiency (Φ_Δ: 0.75) than the previous compound (Φ_Δ: 0.65). The thioglucoside indicated a significant photodamaging effect (IC₅₀: 250 μM) against cancer cells. Although the galactose and mannose analogs exerted similar photodamaging effects, they were moderately toxic in the dark at a concentration of 300 μM. The thioglucoside and thiomannoside were at least partially uptaken through glucose transporters as demonstrated by inhibition with cytochalasin B, whereas no inhibition was observed for the galactoside. The behavior of d-glucose toward the cellular uptakes of these photosensitizers was bipolar: inhibitory at a low concentration and recovery or acceleratory at a higher concentration. These results indicate that 4'-nitrobiphenyl thioglucoside is the smallest (MW: 393) cancer-targeting photosensitizer with a trackable fluorescence property.

Quantitative Structure-Property Relationship Modelling for the Prediction of Singlet Oxygen Generation by Heavy-Atom-Free BODIPY Photosensitizers*

Heavy-atom-free sensitizers forming long-living triplet excited states via the spin-orbit charge transfer intersystem crossing (SOCT-ISC) process have recently attracted attention due to their potential to replace costly transition metal complexes in photonic applications. The efficiency of SOCT-ISC in BODIPY donor-acceptor dyads, so far the most thoroughly investigated class of such sensitizers, can be finely tuned by structural modification. However, predicting the triplet state yields and reactive oxygen species (ROS) generation quantum yields for such compounds in a particular solvent is still very challenging due to a lack of established quantitative structure-property relationship (QSPR) models. In this work, the available data on singlet oxygen generation quantum yields (ΦΔ ) for a dataset containing >70 heavy-atom-free BODIPY in three different solvents (toluene, acetonitrile, and tetrahydrofuran) were analyzed. In order to build reliable QSPR model, a series of new BODIPYs were synthesized that bear different electron donating aryl groups in the meso position, their optical and structural properties were studied along with the solvent dependence of singlet oxygen generation, which confirmed the formation of triplet states via the SOCT-ISC mechanism. For the combined dataset of BODIPY structures, a total of more than 5000 quantum-chemical descriptors was calculated including quantum-chemical descriptors using density functional theory (DFT), namely M06-2X functional. QSPR models predicting ΦΔ values were developed using multiple linear regression (MLR), which perform significantly better than other machine learning methods and show sufficient statistical parameters (R=0.88-0.91 and q2 =0.62-0.69) for all three solvents. A small root mean squared error of 8.2 % was obtained for ΦΔ values predicted using MLR model in toluene. As a result, we proved that QSPR and machine learning techniques can be useful for predicting ΦΔ values in different media and virtual screening of new heavy-atom-free BODIPYs with improved photosensitizing ability.

Characterization of radical types, penetration profile and distribution pattern of the topically applied photosensitizer THPTS in porcine skin ex vivo

The topical photodynamic therapy (PDT) is mainly used in the treatment of dermato-oncological diseases. The distribution and functionality of the photosensitizer Tetrahydroporphyrin-Tetratosylat (THPTS) was investigated using microscopic and spectroscopic methods after topical application to excised porcine skin followed by irradiation. The distribution of THPTS was determined by two-photon tomography combined with fluorescence lifetime imaging (TPT/FLIM) and confocal Raman microspectroscopy (CRM). The radicals were quantified and characterized by electron paramagnetic resonance (EPR) spectroscopy. Results show a penetration depth of THPTS into the skin down to around 12 ± 5 µm. A penetration of THPTS through the stratum corneum was not clearly observable after 1 h penetration time, but cannot be excluded. The irradiation within the phototherapeutic window (spectral range of visible and near infrared light in the range ≈ 650-850 nm) is needed to activate THPTS. An incubation time of 10 min showed the highest radical production. A longer incubation time affected the functionality of THPTS, whereby significant less radicals were detectable. During PDT mainly reactive oxygen species (ROS) and lipid oxygen species (LOS) are produced. Overall, the irradiation dose per se influences the radical types formed in skin. While ROS are always prominent at low doses, LOS increase at high doses, independent of previous skin treatment and the irradiation wavelength used.

Novel sulfonamide porphyrin TBPoS-2OH used in photodynamic therapy for malignant melanoma

The application of photodynamic therapy (PDT) for the treatment of skin diseases has been receiving much attention. Here, we examined the anti-tumor effect of a novel porphyrin-based photosensitizer TBPoS-2OH in the malignant melanoma A375 and B16 cells. TBPoS-2OH has obvious cell photo-cytotoxicity, but it has low cell dark-cytotoxicity. Further research showed that TBPoS-2OH is enriched in lysosomes after being taken up by cells. Subsequently, the apoptotic rates were significantly increased in TBPoS-2OH-treated A375 and B16 cells. The specific mechanism may be that after receiving light stimulation, TBPoS-2OH could effectively increase the level of intracellular reactive oxygen species (ROS), thereby activating mitochondrial apoptosis pathway-related proteins in A375 and B16 cells. We found an increase in the content of cytochrome C in the cytoplasm, and the levels of related proteins, such as cleaved caspase-3, cleaved caspase-9, and cleaved PARP1, were significantly increased in TBPoS-2OH-treated cells. These results indicated that the new compound TBPoS-2OH could be developed and become an alternative drug for the treatment of melanoma. Some reference ideas for the development of new photosensitizers are also provided.

Enhancement of Photodynamic Cancer Therapy by Physical and Chemical Factors

The viable use of photodynamic therapy (PDT) in cancer therapy has never been fully realized because of its undesirable effects on healthy tissues. Herein we summarize some physicochemical factors that can make PDT a more viable and effective option to provide future oncological patients with better-quality treatment options. These physicochemical factors include light sources, photosensitizer (PS) carriers, microwaves, electric fields, magnetic fields, and ultrasound. This Review is meant to provide current information pertaining to PDT use, including a discussion of in vitro and in vivo studies. Emphasis is placed on the physicochemical factors and their potential benefits in overcoming the difficulty in transitioning PDT into the medical field. Many advanced techniques, such as employing X-rays as a light source, using nanoparticle-loaded stem cells and bacteriophage bio-nanowires as a photosensitizer carrier, as well as integration with immunotherapy, are among the future directions.

A Twist-Assisted Biphenyl Photosensitizer Passable Through Glucose Channel

While the development of low-molecular-weight drugs is saturating, agents for photodynamic therapies (PDTs) may become alternative seeds in pharmaceutical industry. Among them, orally administrative, cancer-selective, and side effect-free photosensitizers (PSs) that can be activated by tissue-penetrative near-infrared (NIR) lights are strongly demanded. We discovered such a PS from scratch by focusing on a twist-assisted spin-orbit charge transfer intersystem crossing (ISC) mechanism in a biphenyl derivative, which was demonstrated by thorough photophysical studies. The unique ISC mechanism enables the PS to be small and slim so as to pass through glucose transporters and exert a PDT effect selectively on a cancer cell line. The smallness will allow for oral administration and fast clearance, which have been agenda of approved PSs with larger molecular weights. We also demonstrated that our PS was able to be activated with an NIR pulse laser through two-photon excitation.