Optimizing the antitumor selectivity of PVP-Hypericin re A549 cancer cells and HLF normal cells through pulsed blue light

Photoactivity of hypericin: from natural product to antifungal application

Considering the multifaceted and increasing application of photodynamic therapy (PDT), in recent years the antimicrobial employment of this therapy has been highlighted, because of the antiviral, antibacterial, antiparasitic, and antifungal activities that have already been demonstrated. In this context, research focussed on antimycological action, especially for treatment of superficial infections, presents promising growth due to the characteristics of these infections that facilitate PDT application as new therapeutic options are needed in the field of medical mycology. Among the more than one hundred classes of photosensitizers the antifungal action of hypericin (Hyp) stands out due to its ability to permeate the lipid membrane and accumulate in different cytoplasmic organelles of eukaryotic cells. In this review, we aim to provide a complete overview of the origin, physicochemical characteristics, and optimal alternative drug deliveries that promote the photodynamic action of Hyp (Hyp-PDT) against fungi. Furthermore, considering the lack of a methodological consensus, we intend to compile the best strategies to guide researchers in the antifungal application of Hyp-PDT. Overall, this review provides a future perspective of new studies and clinical possibilities for the advances of such a technique in the treatment of mycoses in humans.

Photodynamic therapy of prostate cancer using porphyrinic formulations

Prostate cancer (PCa) is the second most frequent cancer diagnosed in men worldwide. Among the common treatment options, photodynamic therapy (PDT) is being considered a promising local therapy to treat this cancer. Although PDT is an established treatment modality approved for several types of cancer, the low solubility, the reduced tumor selectivity, the absorption in the therapeutic window and the poor clearance from the body of the currently approved photosensitizers (PS) hampers its wide clinical application. In this regard, herein we synthesized three fluorinated porphyrinoid derivatives and entrapped them into polyvinylpyrrolidone (PVP) to prevent their aggregation and preserve their desirable photophysical properties under the physiological environment. In vitro studies revealed the negligible dark cytotoxicity of all PVP formulations (PS1@PVP, PS2@PVP and PS3@PVP) at the tested concentrations (5.0 to 20 μM), but also confirmed the significant photodynamic effect of PS2@PVP and PS3@PVP towards the PCa cell line PC-3, upon red light irradiation at an irradiance of 17.6 mW.cm^-2. To provide insight into the underlying mechanisms of cell death under PDT treatment induced by PS2@PVP and PS3@PVP, their intracellular localization in PC-3 cells was firstly investigated by confocal microscopy. Since both PS2@PVP and PS3@PVP nanoparticles were mainly localized in mitochondria, the involvement of this organelle in PDT-induced apoptosis mediated by both formulations was further explored. Western blot analysis revealed that PDT treatment of PC-3 cells with either PS2@PVP or PS3@PVP resulted in the reduction of the expression level of the anti-apoptotic protein Bcl-2. As the photodamage to Bcl-2 after PDT with PS2@PVP and PS3@PVP was accompanied by the further activation of pro-caspase-3, we assumed that upon irradiation the photogenerated reactive oxygen species (ROS) were able to activate a caspase-dependent apoptotic response as a consequence of a post-mitochondrial event. Taken together, these findings demonstrate that among the tested fluorinated porphyrinoids, PS2@PVP and, particularly, PS3@PVP, are significantly more effective in overall PC-3 cell killing than PS1@PVP, thus highlighting their great potential as therapeutic agents for PCa.

Hypericin in photobiological assays: An overview

Hypericin is considered a potent photosensitizer for use in antitumor and antimicrobial photodynamic therapy (PDT). This review presents the primary biological results obtained with hypericin in photodynamic therapy applications, such as photodynamic cancer treatment, photoinactivation of microorganisms (PDI), tissue scarring, and photo diagnosis. We present a compilation of in vitro results that have been published thus far; for these studies, we highlight the hypericin concentration, light dose, and other experimental conditions to evaluate the efficiency of photodynamic treatment like cell death, cell viability, or cell proliferation. The results indicate that different hypericin phototoxicity levels can be observed according to the specific light dose and concentration. Furthermore, it was shown that cellular localization and cell death mechanisms (apoptosis and necrosis) are dependent on the cell type.

Hypericin-mediated photodynamic therapy for the treatment of cancer: a review

OBJECTIVES

Hypericin is a polycyclic aromatic naphthodianthrone that occurs naturally. It is also an active ingredient in some species of the genus Hypericum. Emerging evidence suggests that hypericin has attracted great attention as a potential anticancer drug and exhibits remarkable antiproliferative effect upon irradiation on various tumour cells. This paper aims to summarise the anticancer effect and molecular mechanisms modulated by hypericin-medicated photodynamic therapy and its potential role in the cancer treatment.

KEY FINDINGS

Hypericin-medicated photodynamic therapy could inhibit the proliferation of various tumour cells including bladder, colon, breast, cervical, glioma, leukaemia, hepatic, melanoma, lymphoma and lung cancers. The effect is primarily mediated by p38 mitogen-activated protein kinase (MAPK), JNK, PI3K, CCAAT-enhancer-binding protein homologous protein (CHOP)/TRIB3/Akt/mTOR, TRAIL/TRAIL-receptor, c-Met and Ephrin-Eph, the mitochondria and extrinsic signalling pathways. Furthermore, hypericin-medicated photodynamic therapy in conjunction with chemotherapeutic agents or targeted therapies is more effective in inhibiting the growth of tumour cells.

SUMMARY

During the past few decades, the anticancer properties of photoactivated hypericin have been extensively investigated. Hypericin-medicated photodynamic therapy can modulate a variety of proteins and genes and exhibit a great potential to be used as a therapeutic agent for various types of cancer.

Pharmaceutical assessment of polyvinylpyrrolidone (PVP): As excipient from conventional to controlled delivery systems with a spotlight on COVID-19 inhibition

Polyvinylpyrrolidone (PVP) is a water-soluble polymer obtained by polymerization of monomer N-vinylpyrrolidone. PVP is an inert, non-toxic, temperature-resistant, pH-stable, biocompatible, biodegradable polymer that helps to encapsulate and cater both hydrophilic and lipophilic drugs. These advantages enable PVP a versatile excipient in the formulation development of broad conventional to novel controlled delivery systems. PVP has tunable properties and can be used as a brace component for gene delivery, orthopedic implants, and tissue engineering applications. Based on different molecular weights and modified forms, PVP can lead to exceptional beneficial features with varying chemical properties. Graft copolymerization and other techniques assist PVP to conjugate with poorly soluble drugs that can inflate bioavailability and even introduces the desired swelling tract for their control or sustained release. The present review provides chemistry, mechanical, physicochemical properties, evaluation parameters, dewy preparation methods of PVP derivatives intended for designing conventional to controlled systems for drug, gene, and cosmetic delivery. The past and growing interest in PVP establishes it as a promising polymer to enhance the trait and performance of current generation pharmaceutical dosage forms. Furthermore, the scrutiny explores existing patents, marketed products, new and futuristic approaches of PVP that have been identified and scope for future development, characterization, and its use. The exploration spotlights the importance and role of PVP in the design of Povidone-iodine (PVP-I) and clinical trials to assess therapeutic efficacy against the COVID-19 in the current pandemic scenario.

The application of aluminium phthalocyanine AlPs-4-mediated photodynamic therapy against human soft tissue sarcoma (RMS) cell line

The main challenge in the cancer treatment is the on-target drug delivery to the affected cells. Various therapies have been designed to target the affected cells efficiently but still the success is awaited. An iron and cobalt nanocomposite for the effective drug delivery to target cells was designed. The photodynamic effect of anticancer drugs loaded with iron oxide and cobalt ferrite nanomaterials coated with polyvinyl alcohol (PVA) was studied. The iron oxide nanoparticles (IONPs) and cobalt ferrite (CF) NPs without the loaded drugs were characterized by UV, XRD, FTIR, SEM and EDX techniques. The photodynamic effect of the photosensitizer, doxorubicin, and dacarbazine loaded nanomaterials were screened against human rhabdomyosarcoma (RMS) cells after incubation for 3 h, 24 h, and 48 h using MTT assay. The combination of photodynamic therapy (PDT) with chemo drugs is studied over different doses. When RMS cells were exposed to nanomaterials loaded with chemo drugs and PDT alone, it resulted in less cell killing compared to chemo drugs followed by PDT. These results revealed that in the case of combined treatment (combination therapy) the cell viability decreases as compared to individual treatment (monotherapy). The in vitro studies showed positive results which give a new pathway for the in vivo studies.

Antibody-Based Immunotherapy: Alternative Approaches for the Treatment of Metastatic Melanoma

Melanoma is the least common form of skin cancer and is associated with the highest mortality. Where melanoma is mostly unresponsive to conventional therapies (e.g., chemotherapy), BRAF inhibitor treatment has shown improved therapeutic outcomes. Photodynamic therapy (PDT) relies on a light-activated compound to produce death-inducing amounts of reactive oxygen species (ROS). Their capacity to selectively accumulate in tumor cells has been confirmed in melanoma treatment with some encouraging results. However, this treatment approach has not reached clinical fruition for melanoma due to major limitations associated with the development of resistance and subsequent side effects. These adverse effects might be bypassed by immunotherapy in the form of antibody–drug conjugates (ADCs) relying on the ability of monoclonal antibodies (mAbs) to target specific tumor-associated antigens (TAAs) and to be used as carriers to specifically deliver cytotoxic warheads into corresponding tumor cells. Of late, the continued refinement of ADC therapeutic efficacy has given rise to photoimmunotherapy (PIT) (a light-sensitive compound conjugated to mAbs), which by virtue of requiring light activation only exerts its toxic effect on light-irradiated cells. As such, this review aims to highlight the potential clinical benefits of various armed antibody-based immunotherapies, including PDT, as alternative approaches for the treatment of metastatic melanoma.

1O2 determined from the measured PDT dose and 3O2 predicts long-term response to Photofrin-mediated PDT

Photodynamic therapy (PDT) that employs the photochemical interaction of light, photosensitizer and oxygen is an established modality for the treatment of cancer. However, dosimetry for PDT is becoming increasingly complex due to the heterogeneous photosensitizer uptake by the tumor, and complicated relationship between the tissue oxygenation ([³O₂]), interstitial light distribution, photosensitizer photobleaching and PDT effect. As a result, experts argue that the failure to realize PDT's true potential is, at least partly due to the complexity of the dosimetry problem. In this study, we examine the efficacy of singlet oxygen explicit dosimetry (SOED) based on the measurements of the interstitial light fluence rate distribution, changes of [³O₂] and photosensitizer concentration during Photofrin-mediated PDT to predict long-term control rates of radiation-induced fibrosarcoma tumors. We further show how variation in tissue [³O₂] between animals induces variation in the treatment response for the same PDT protocol. PDT was performed with 5 mg kg^-1 Photofrin (a drug-light interval of 24 h), in-air fluence rates (ϕ _air) of 50 and 75 mW cm^-2 and in-air fluences from 225 to 540 J cm^-2. The tumor regrowth was tracked for 90 d after the treatment and Kaplan-Meier analyses for local control rate were performed based on a tumor volume  ⩽100 mm³ for the two dosimetry quantities of PDT dose and SOED. Based on the results, SOED allowed for reduced subject variation and improved treatment evaluation as compared to the PDT dose.

Reactive oxygen species explicit dosimetry to predict local tumor control for Photofrin-mediated photodynamic therapy

Although photodynamic therapy (PDT) is an established modality for cancer treatment, current dosimetric quantities, such as light fluence and PDT dose, do not account for the differences in PDT oxygen consumption for different fluence rates (ϕ). A macroscopic model was adopted to calculate reactive oxygen species concentration ([ROS]_rx) to predict Photofrin-PDT outcome in mice bearing radiation-induced fibrosarcoma (RIF) tumors. Singlet oxygen is the primary cytotoxic species for ROS, which is responsible for cell death in type II PDT, although other type I ROS is included in the parameters used in our model. Using a combination of fluences (50-250 J/cm²) and ϕ (50 - 150 mW/cm²), tumor regrowth rate, k, was determined for each condition by fitting the tumor volume vs. time to V₀*exp(k*t). Treatment was delivered with a collimated laser beam of 1 cm diameter at 630 nm. Explicit dosimetry of initial tissue oxygen concentration, tissue optical properties, and Photofrin concentration was used to calculate [ROS]_rx,cal. ϕ was determined for the treatment volume based on Monte-Carlo simulations and measured tissue optical properties. Tissue oxygenation is measured using an oxylite oxygen probe to throughout the treatment to calculate the measured [ROS]_rx,mea. Cure index, CI = 1-k/k _ctr , for tumor gowth up to 14 days were determined as an endpoint using five dose metrics: light fluence, PDT dose, and [ROS]_rx,cal, and [ROS]_rx,mea. PDT dose was defined as the product of the time-integral of photosensitizer concentration and ϕ at a 3 mm tumor depth. Preliminary studies show that [ROS]_rx,mea best correlates with CI and is an effective dosimetric quantity that can predict treatment outcome.

Thermosensitive, fast gelling, photoluminescent, highly flexible, and degradable hydrogels for stem cell delivery

Stem cell therapy is a promising approach to regenerate ischemic cardiovascular tissues yet experiences low efficacy. One of the major causes is inferior cell retention in tissues. Injectable cell carriers that can quickly solidify upon injection into tissues so as to immediately increase viscosity have potential to largely improve cell retention. A family of injectable, fast gelling, and thermosensitive hydrogels were developed for delivering stem cells into heart and skeletal muscle tissues. The hydrogels were also photoluminescent with low photobleaching, allowing for non-invasively tracking hydrogel biodistribution and retention by fluorescent imaging. The hydrogels were polymerized by N-isopropylacrylamide (NIPAAm), 2-hydroxyethyl methacrylate (HEMA), 1-vinyl-2-pyrrolidinone (VP), and acrylate-oligolactide (AOLA), followed by conjugation with hypericin (HYP). The hydrogel solutions had thermal transition temperatures around room temperature, and were readily injectable at 4 °C. The solutions were able to quickly solidify within 7 s at 37 °C. The formed gels were highly flexible possessing similar moduli as the heart and skeletal muscle tissues. In vitro, hydrogel fluorescence intensity decreased proportionally to weight loss. After being injected into thigh muscles, the hydrogel can be detected by an in vivo imaging system for 4 weeks. The hydrogels showed excellent biocompatibility in vitro and in vivo, and can stimulate mesenchymal stem cell (MSC) proliferation and paracrine effects. The fast gelling hydrogel remarkably increased MSC retention in thigh muscles compared to slow gelling collagen, and non-gelling PBS. These hydrogels have potential to efficiently deliver stem cells into tissues. Hydrogel degradation can be non-invasively and real-time tracked. STATEMENT OF SIGNIFICANCE: Low cell retention in tissues represents one of the major causes for limited therapeutic efficacy in stem cell therapy. A family of injectable, fast gelling, and thermosensitive hydrogels that can quickly solidify upon injection into tissues were developed to improve cell retention. The hydrogels were also photoluminescent, allowing for non-invasively and real-time tracking hydrogel biodistribution and retention by fluorescent imaging.

Blue light-induced apoptosis of human promyelocytic leukemia cells via the mitochondrial-mediated signaling pathway

Acute promyelocytic leukemia is frequently associated with dizziness, fever, nausea, hematochezia and anemia. Blue light, or light with wavelengths of 400–480 nm, transmits high levels of energy. The aim of the present study was to determine the pro-apoptotic effects of blue light (wavelength, 456 nm; radiation power, 0.25 mW/cm²) and the underlying mechanisms in a human promyelocytic leukemia cell line (HL60). Blue light reduced the viability and enhanced the mortality of HL60 cells in a time-dependent manner. Exposure to blue light for 24 h caused depolarization of the mitochondrial membrane potential and the overproduction of reactive oxygen species in HL60 cells. In a nude mouse model, 9-day exposure to blue light markedly suppressed the growth of HL60-xenografted tumors; however, it had no effect on hepatic and renal tissues. In addition, blue light abrogated the expression of B-cell lymphoma (Bcl)-2 and Bcl extra-long, while enhancing the levels of Bcl-2-associated X protein, cytochrome c, and cleaved caspases-3 and −9 in tumor tissues. The results suggested that the pro-apoptotic effects of blue light in human promyelocytic leukemia cells may be associated with the mitochondrial apoptosis signaling pathway.

Investigating the effect of poly-l-lactic acid nanoparticles carrying hypericin on the flow-biased diffusive motion of HeLa cell organelles

OBJECTIVES

In this study, we investigate in human cervical epithelial HeLa cells the intracellular dynamics and the mutual interaction with the organelles of the poly-l-lactic acid nanoparticles (PLLA NPs) carrying the naturally occurring hydrophobic photosensitizer hypericin.

METHODS

Temporal and spatiotemporal image correlation spectroscopy was used for the assessment of the intracellular diffusion and directed motion of the nanocarriers by tracking the hypericin fluorescence. Using image cross-correlation spectroscopy and specific fluorescent labelling of endosomes, lysosomes and mitochondria, the NPs dynamics in association with the cell organelles was studied. Static colocalization experiments were interpreted according to the Manders' overlap coefficient.

KEY FINDINGS

Nanoparticles associate with a small fraction of the whole-organelle population. The organelles moving with NPs exhibit higher directed motion compared to those moving without them. The rate of the directed motion drops substantially after the application of nocodazole. The random component of the organelle motions is not influenced by the NPs.

CONCLUSIONS

Image correlation and cross-correlation spectroscopy are most appropriate to unravel the motion of the PLLA nanocarrier and to demonstrate that the rate of the directed motion of organelles is influenced by their interaction with the nanocarriers. Not all PLLA-hypericin NPs are associated with organelles.

Vascular-targeted photodynamic therapy of gastric antral vascular ectasia (GAVE)

BACKGROUND AND STUDY AIM

Vascular-targeted photodynamic therapy (V-PDT) has been used for several benign vascular diseases. The aim of this pilot study was to demonstrate the potential benefits of VPDT in the treatment of gastric antral vascular ectasia (GAVE).

PATIENTS AND METHODS

Data from patients with GAVE (n=5) who underwent endoscopic V-PDT were analyzed retrospectively. Pre- and post-V-PDT clinical and endoscopic features, hemoglobin levels, and transfusion requirement were compared.

RESULTS

The five GAVE patients received one to four sessions of V-PDT. The hemoglobin levels of all five patients increased steadily following V-PDT. Within 6-48months of follow-up, gastrointestinal bleeding and melena disappeared in all five patients and none of the patients needed a transfusion. Endoscopy examinations showed that the dilated vessels had disappeared without scar formation. No significant side effects or adverse reactions were reported.

CONCLUSION

This preliminary study indicates the good selectivity, safety, and efficacy of V-PDT in the treatment of patients with GAVE. Larger prospective studies are needed to further confirm the feasibility of using V-PDT to treat patients with GAVE.

Evaluation of the 2-(1-Hexyloxyethyl)-2-devinyl pyropheophorbide (HPPH) mediated photodynamic therapy by macroscopic singlet oxygen modeling

Photodynamic therapy (PDT) is known as a non-invasive treatment modality that is based on photochemical reactions between oxygen, photosensitizer, and a special wavelength of light. However, a dosimetric predictor for PDT outcome is still elusive because current dosimetric quantities do not account for the differences in the PDT oxygen consumption rate for different fluence rates. In this study, we evaluate several dose metrics, total fluence, photobleaching ratio, PDT dose, and mean reacted singlet oxygen (mean [1 O2 ]rx ) for predicting the PDT outcome and a clinically relevant tumor re-growth endpoint. For this reason, radiation-induced fibrosarcoma (RIF) mice tumors are treated with 2-(1-Hexyloxyethyl)-2-devinyl pyropheophorbide (HPPH) and different in-air fluences (30 J/cm2 , 50 J/cm2 , 135 J/cm2 , 250 J/cm2 , and 350 J/cm2 ) and in-air fluence rates (20, 50, 75, 150 mW/cm2 ). Explicit measurements of HPPH and oxygen concentration as well as tissue optical properties are performed pre- and post-treatment. Then, this information is incorporated into a macroscopic model to calculate the photobleaching, PDT dose, and mean [1 O2 ]rx . Changes in tumor volume are tracked following the treatment and compared with the dose metrics. The correlation demonstrates that mean [1 O2 ]rx  serves as a better dosimetric quantity for predicting treatment outcome and a clinically relevant tumor re-growth endpoint.

Conservation Strategies in the Genus Hypericum via Cryogenic Treatment

In the genus Hypericum, cryoconservation offers a strategy for maintenance of remarkable biodiversity, emerging from large inter- and intra-specific variability in morphological and phytochemical characteristics. Long-term cryostorage thus represents a proper tool for preservation of genetic resources of endangered and threatened Hypericum species or new somaclonal variants with unique properties. Many representatives of the genus are known as producers of pharmacologically important polyketides, namely naphthodianthrones and phloroglucinols. As a part of numerous in vitro collections, the nearly cosmopolitan Hypericum perforatum - Saint John's wort - has become a suitable model system for application of biotechnological approaches providing an attractive alternative to the traditional methods for secondary metabolite production. The necessary requirements for efficient cryopreservation include a high survival rate along with an unchanged biochemical profile of plants regenerated from cryopreserved cells. Understanding of the processes which are critical for recovery of H. perforatum cells after the cryogenic treatment enables establishment of cryopreservation protocols applicable to a broad number of Hypericum species. Among them, several endemic taxa attract a particular attention due to their unique characteristics or yet unrevealed spectrum of bioactive compounds. In this review, recent advances in the conventional two-step and vitrification-based cryopreservation techniques are presented in relation to the recovery rate and biosynthetic capacity of Hypericum spp. The pre-cryogenic treatments which were identified to be crucial for successful post-cryogenic recovery are discussed. Being a part of genetic predisposition, the freezing tolerance as a necessary precondition for successful post-cryogenic recovery is pointed out. Additionally, a beneficial influence of cold stress on modulating naphthodianthrone biosynthesis is outlined.

PDT Dose Dosimeter for Pleural Photodynamic Therapy

PDT dose is the product of the photosensitizer concentration and the light fluence in the target tissue. For improved dosimetry during plural photodynamic therapy (PDT), a PDT dose dosimeter was developed to measure both the light fluence and the photosensitizer concentration simultaneously in the same treatment location. Light fluence and spectral data were rigorously compared to other methods of measurement (e.g. photodiode, multi-fiber spectroscopy contact probe) to assess the accuracy of the measurements as well as their uncertainty. Photosensitizer concentration was obtained by measuring the fluorescence of the sensitizer excited by the treatment light. Fluence rate based on the intensity of the laser spectrum was compared to the data obtained by direct measurement of fluence rate by a fiber-coupled photodiode. Phantom studies were done to obtain an optical property correction for the fluorescence signal. Measurements were performed in patients treated Photofrin for different locations in the pleural cavity. Multiple sites were measured to investigate the heterogeneity of the cavity and to provide cross-validation via relative dosimetry. This novel method will allow for accurate real-time determination of delivered PDT dose and improved PDT dosimetry.

Deformable medical image registration of pleural cavity for photodynamic therapy by using finite-element based method

When the pleural cavity is opened during the surgery portion of pleural photodynamic therapy (PDT) of malignant mesothelioma, the pleural volume will deform. This impacts the delivered dose when using highly conformal treatment techniques. To track the anatomical changes and contour the lung and chest cavity, an infrared camera-based navigation system (NDI) is used during PDT. In the same patient, a series of computed tomography (CT) scans of the lungs are also acquired before the surgery. The reconstructed three-dimensional contours from both NDI and CTs are imported into COMSOL Multiphysics software, where a finite element-based (FEM) deformable image registration is obtained. The CT contour is registered to the corresponding NDI contour by overlapping the center of masses and aligning their orientations. The NDI contour is considered as the reference contour, and the CT contour is used as the target one, which will be deformed. Deformed Geometry model is applied in COMSOL to obtain a deformed target contour. The distortion of the volume at X, Y and Z is mapped to illustrate the transformation of the target contour. The initial assessment shows that FEM-based image deformable registration can fuse images acquired by different modalities. It provides insights into the deformation of anatomical structures along X, Y and Z-axes. The deformed contour has good matches to the reference contour after the dynamic matching process. The resulting three-dimensional deformation map can be used to obtain the locations of other critical anatomic structures, e.g., heart, during surgery.

Investigating the impact of oxygen concentration and blood flow variation on photodynamic therapy

Type II photodynamic therapy (PDT) is used for cancer treatment based on the combined action of a photosensitizer, a special wavelength of light, oxygen (³O₂) and generation of singlet oxygen (¹O₂). Intra-patient and inter-patient variability of oxygen concentration ([³O₂]) before and after the treatment as well as photosensitizer concentration and hemodynamic parameters such as blood flow during PDT has been reported. Simulation of these variations is valuable, as it would be a means for the rapid assessment of treatment effect. A mathematical model has been previously developed to incorporate the diffusion equation for light transport in tissue and the macroscopic kinetic equations for simulation of [³O₂], photosensitizers in ground and triplet states and concentration of the reacted singlet oxygen ([¹O₂]_rx) during PDT. In this study, the finite-element based calculation of the macroscopic kinetic equations is done for 2-(1-Hexyloxyethyl)-2-devinyl pyropheophorbide (HPPH)-mediated PDT by incorporating the information of the photosensitizer photochemical parameters as well as the tissue optical properties, photosensitizer concentration, initial oxygen concentration ([³O₂]₀), blood flow changes and ϕ that have been measured in mice bearing radiation-induced fibrosarcoma (RIF) tumors. Then, [¹O₂]_rx calculated by using the measured [³O₂] during the PDT is compared with [¹O₂]_rx calculated based on the simulated [³O₂]; both calculations showed a reasonably good agreement. Moreover, the impacts of the blood flow changes and [³O₂]₀ on [¹O₂]_rx have been investigated, which showed no pronounced effect of the blood flow changes on the long-term ¹O₂ generation. When [³O₂]₀ becomes limiting, small changes in [³O₂] have large effects on [¹O₂]_rx.

In-vivo outcome study of HPPH mediated PDT using singlet oxygen explicit dosimetry (SOED)

Type II photodynamic therapy (PDT) is based on the use of photochemical reactions mediated through an interaction between a tumor-selective photosensitizer, photoexcitation with a specific wavelength of light, and production of reactive singlet oxygen. However, the medical application of this technique has been limited due to inaccurate PDT dosimetric methods. The goal of this study is to examine the relationship between outcome (in terms of tumor growth rate) and calculated reacted singlet oxygen concentration ([¹O₂]_rx) after HPPH-mediated PDT to compare with other PDT dose metrics, such as PDT dose or total light fluence. Mice with radiation-induced fibrosarcoma (RIF) tumors were treated with different light fluence and fluence rate conditions. Explicit measurements of photosensitizer drug concentration and tissue optical properties via fluorescence and absorption measurement with a contact probe before and after PDT were taken to then quantify total light fluence, PDT dose, and [¹O₂]_rx based on a macroscopic model of singlet oxygen. In addition, photobleaching of photosenitizer were measured during PDT as a second check of the model. Changes in tumor volume were tracked following treatment and compared to the three calculated dose metrics. The correlations between total light fluence, PDT dose, reacted [¹O₂]_rx and tumor growth demonstrate that [¹O₂]_rx serves as a better dosimetric quantity for predicting treatment outcome and a clinically relevant tumor growth endpoint.

Explicit dosimetry for 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a-mediated photodynamic therapy: macroscopic singlet oxygen modeling

Type II photodynamic therapy (PDT) is based on the photochemical reactions mediated through an interaction between a photosensitizer, ground-state oxygen ([(3)O2]), and light excitation at an appropriate wavelength, which results in production of reactive singlet oxygen ([(1)O2]rx). We use an empirical macroscopic model based on four photochemical parameters for the calculation of [(1)O2]rx threshold concentration ([(1)O2]rx,sh) causing tissue necrosis in tumors after PDT. For this reason, 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH)-mediated PDT was performed interstitially on mice with radiation-induced fibrosarcoma (RIF) tumors. A linear light source at 665 nm with total energy released per unit length of 12 to 100  J/cm and source power per unit length (LS) of 12 to 150  mW/cm was used to induce different radii of necrosis. Then the amount of [(1)O2]rx calculated by the macroscopic model incorporating explicit PDT dosimetry of light fluence distribution, tissue optical properties, and HPPH concentration was correlated to the necrotic radius to obtain the model parameters and [(1)O2]rx,sh. We provide evidence that [(1)O2]rx is a better dosimetric quantity for predicting the treatment outcome than PDT dose, which is proportional to the time integral of the products of the photosensitizer concentration and light fluence rate.