Even Angell-Petersen

Porphyrin‐related photosensitizers for cancer imaging and therapeutic applications

A photosensitizer is defined as a chemical entity, which upon absorption of light induces a chemical or physical alteration of another chemical entity. Some photosensitizers are utilized therapeutically such as in photodynamic therapy (PDT) and for diagnosis of cancer (fluorescence diagnosis, FD). PDT is approved for several cancer indications and FD has recently been approved for diagnosis of bladder cancer. The photosensitizers used are in most cases based on the porphyrin structure. These photosensitizers generally accumulate in cancer tissues to a higher extent than in the surrounding tissues and their fluorescing properties may be utilized for cancer detection. The photosensitizers may be chemically synthesized or induced endogenously by an intermediate in heme synthesis, 5‐aminolevulinic acid (5‐ALA) or 5‐ALA esters. The therapeutic effect is based on the formation of reactive oxygen species (ROS) upon activation of the photosensitizer by light. Singlet oxygen is assumed to be the most important ROS for the therapeutic outcome. The fluorescing properties of the photosenisitizers can be used to evaluate their intracellular localization and treatment effects. Some photosensitizers localize intracellularly in endocytic vesicles and upon light exposure induce a release of the contents of these vesicles, including externally added macromolecules, into the cytosol. This is the basis for a novel method for macromolecule activation, named photochemical internalization (PCI). PCI has been shown to potentiate the biological activity of a large variety of macromolecules and other molecules that do not readily penetrate the plasma membrane, including type I ribosome‐inactivating proteins, immunotoxins, gene‐encoding plasmids, adenovirus, peptide‐nucleic acids and the chemotherapeutic drug bleomycin. The background and present status of PDT, FD and PCI are reviewed.

Photodynamic Therapy of Superficial Basal Cell Carcinoma with 5-Aminolevulinic Acid with Dimethylsulfoxide and Ethylendiaminetetraacetic Acid: A Comparison of Two Light Sources

Abstract The aim of this prospective randomized study was to compare the clinical and cosmetic outcome of superficial basal cell carcinomas (BCC), using either laser or broadband halogen light, in photodynamic therapy with topical 5-aminolevulinic acid (ALA). A total of 83 patients with 245 superficial BCC were included in the study. Standard treatment involved 15 min of local pretreatment with 99% dimethylsulfoxide (DMSO) before topical application of 20% ALA with DMSO (2%) and ethylendiaminetetraacetic acid (2%) as cofactors for 3 h before light exposure with either laser or a broadband lamp (BL). A complete response was achieved in 95 lesions (86%) in the laser group and 110 lesions (82%) in the BL group 6 months after treatment. Of these, 80 lesions (84%) in the laser group and 101 lesions (92%) in the lamp group were independently evaluated to have an excellent or good cosmetic post-treatment score. No serious adverse events were reported. This study shows that there is no statistical significant difference in cure the rate (P = 0.49) and the cosmetic outcome (P = 0.075) with topical application of a modified ALA-cream between light exposure from a simple BL with continuous spectrum (570–740 nm) or from a red-light laser (monochromatic 630 nm). Cost and safety are further elements in favor of the BL in this setting.

Disulfonated tetraphenyl chlorin (TPCS2a), a novel photosensitizer developed for clinical utilization of photochemical internalization

Photochemical internalisation (PCI) is a novel technology for release of endocytosed macromolecules into the cytosol. The technology is based on the use of photosensitizers that locate in endocytic vesicles, and that upon activation by light induce a release of macromolecules from the endocytic vesicles. PCI has been shown to stimulate delivery of a large variety of macromolecules and other molecules that do not readily penetrate the plasma membrane. The preclinical evaluation of PCI has been performed with aluminum phthalocyanine disulfonate (AlPcS(2a)) as photosensitizer. AlPcS(2a), due to its large number of isomers potentially with batch-to-batch ratio variations, is not an optimal photosenstizer for clinical use. Disulfonated tetraphenyl chlorin (TPCS(2a)) has therefore been developed by di-imide reduction of disulfonated tetraphenyl porphine (TPPS(2a)). The synthesized TPCS(2a) contains 3 isomers as shown by HPLC with low (<4%) inter-batch variation with respect to isomer formation, less than 0.5% (w/w) of the starting material TPPS(2a) and absorbs light at 652 nm. As prerequisites for a PCI photosensitizer TPCS(2a) was found to localize in intracellular granules assumed to be endocytic vesicles. In cells in culture TPCS(2a)-PCI induced activation of gelonin as seen by enhanced cytotoxicity, increased transfection efficacy by an enhanced green fluorescence protein (EGFP)-encoding plasmid, induced gene silencing by siRNA towards EGFP and induced in a synergistic manner tumor growth delay by TPCS(2a)-mediated PCI of bleomycin in CT26.CL25 carcinomas growing subcutaneously in athymic mice. TPCS(2a)-PCI of bleomycin was found superior to meso-tetraphenyl chlorin-based photodynamic therapy (mTHPC-PDT) with respect to inhibition of tumor growth. The tumor growth delay by PCI of bleomycin was independent of the time of bleomycin administration between 3 h prior to light to immediately after light, while bleomycin administered 24 h prior to or 24 h after the light exposure induced suboptimal or only additive effects on tumor growth delay respectively. TPCS(2a)-PDT and -PCI induced indistinguishably strong edema the first 3-4 days after TPCS(2a)-administration and only weak erythema the first day after TPCS(2a) administration. In contrast, mTHPC-PDT induced moderate edema the first 7 days after mTHPC administration, but strong erythema resulting in open wounds and escar formation the first 2-3 days after mTHPC administration. The pharmacokinetic properties of TPCS(2a) were evaluated in athymic mice. The plasma pharmacokinetics was best fit to a 2-compartment model with half-lives of 0.78 and 36 hrs. TPCS(2a) was found to be a clinically suitable PCI photosensitizer for photochemical activation of molecules that do not readily penetrate the cellular plasma membrane.

Photochemical Internalization of Bleomycin is Superior to Photodynamic Therapy Due to the Therapeutic Effect in the Tumor Periphery

Photochemical internalization (PCI) is under development for clinical use in treatment of soft tissue sarcomas and other solid tumors. PCI may release endocytosed bleomycin (BLM) into the cytosol by photochemical rupture of the endocytic vesicles. In this study, the human fibrosarcoma xenograft HT1080 was transplanted into the leg muscle of athymic mice. The photosensitizer disulfonated aluminum phthalocyanine (AlPcS2a) and BLM were systemically administrated 48 h and 30 min, respectively, prior to light exposure at 670 nm (30 J cm−2). The purposes of this study were to evaluate the treatment response to AlPcS2a‐photodynamic therapy (PDT) and AlPcS2a‐PDT in combination with BLM (i.e. PCI of BLM) in an orthotopic, invasive and clinically relevant tumor model and to explore the underlying response mechanisms caused by PDT and PCI of BLM. The treatment response was evaluated by measuring tumor growth, contrast‐enhanced magnetic resonance imaging (CE‐MRI), histology and fluorescence microscopy. The results show that PCI of BLM is superior to PDT in inducing tumor growth retardation and acts synergistically as compared to the individual treatment modalities. The CE‐MRI analyses 2 h after AlPcS2a‐PDT and PCI of BLM identified a treatment‐induced nonperfused central zone of the tumor and a well‐perfused peripheral zone. While there were no differences in the vascular response between PDT and PCI, the histological analyses showed that PDT caused necrosis in the tumor center and viable tumor cells were found in the tumor periphery. PCI caused larger necrotic areas and the regrowth in the peripheral zone was almost completely inhibited after PCI. The results indicate that PDT is less efficient in the tumor periphery than in the tumor center and that the treatment effect of PCI is superior to PDT in the tumor periphery.

The effects of ultra low fluence rate single and repetitive photodynamic therapy on glioma spheroids.

Achieving local control of gliomas with photodynamic therapy (PDT) requires the delivery of adequate light fluences to depths of 1–2 cm in the resection margin where the majority of local recurrences originate. This is clinically impractical with current single‐shot, intraoperative PDT treatments due to the length of time required to deliver adequate fluences. Multiple or extended treatment protocols would therefore seem to be required. The response of human glioma spheroids to 5‐aminolevulinic acid (ALA)‐mediated PDT using single or, repetitive light delivery protocols was investigated at both low and ultra low fluence rates.

Bystander Effects in Cell Death Induced by Photodynamic Treatment, UVA Radiation and Inhibitors of ATP Synthesis¶

Abstract Confluent layers of MDCK II cells were treated with four different photosensitizers (a purified version of hematoporphyrin derivative [Photofrin], tetra(3-hydroxyphenyl)porphine [3-THPP], meso-tetra(4-sulphonatophenyl)porphine [TPPS4] and ALA-induced Protoporphyrin IX) and irradiated with blue light, with UVA without exogenous photosensitizers, or incubated with the metabolic inhibitors carbonyl cyanide m-chlorophenylhydrazone and 2-deoxy-d-glucose. Necrotic and apoptotic cells were detected about 4 h later by fluorescence microscopy. Dead cells appeared in distinct clusters in the confluent layers. The number of dead cells in these clusters was determined by manual counting and image analysis. Forty-one of the 43 experimental distributions of dead cells in clusters were found to be significantly different from a Monte Carlo simulation of the distribution of independently inactivated cells. However, a Monte Carlo simulation model, assuming that each dead cell increased the probability of inactivation of adjacent cells, fitted 34 of the 43 observed distributions of dead cells in clusters, indicating a significant bystander effect for all the investigated treatments. The bystander-effect model parameter, defined as a cells increase in probability of dying when it has dead neighbors, was significantly lower for 3-THPP-PDT and TPPS4-PDT than for Photofrin-PDT, ALA-PDT and treatment with metabolic inhibitors.

Photodynamic treatment of oral lichen planus

OBJECTIVES The aim of this study was to examine the clinical behavior and response to topical methyl 5-aminolevulinate (MAL) photodynamic therapy (PDT) of oral lichen planus and to describe the buildup and biodistribution of photoactive porphyrins in normal and lichen planus-affected oral mucosa after MAL application. STUDY DESIGN The difference in clinical expression in 14 patients with buccal oral lichen planus was compared before and after treatment. MAL-induced photoactive porphyrins were monitored using noninvasive in situ fluorescence measurements. Microfluorometry was used to study the biodistribution. RESULTS The absorption and conversion of protoporphyrin IX (PpIX) in epithelial and subepithelial T cells was demonstrated in histologic sections. As a result of 1 treatment session, there was a significant improvement of oral lichen planus after 6 months (P = 0.02) and during a 4-year follow-up period. CONCLUSIONS MAL is absorbed and converted to PpIX in T cells. Oral lichen planus treated with MAL-PDT showed lasting improvement after a single treatment.

Determination of fluence rate and temperature distributions in the rat brain; implications for photodynamic therapy.

Light and heat distributions are measured in a rat glioma model used in photodynamic therapy. A fiber delivering 632-nm light is fixed in the brain of anesthetized BDIX rats. Fluence rates are measured using calibrated isotropic probes that are positioned stereotactically. Mathematical models are then used to derive tissue optical properties, enabling calculation of fluence rate distributions for general tumor and light application geometries. The fluence rates in tumor-free brains agree well with the models based on diffusion theory and Monte Carlo simulation. In both cases, the best fit is found for absorption and reduced scattering coefficients of 0.57 and 28 cm(-1), respectively. In brains with implanted BT(4)C tumors, a discrepancy between diffusion and Monte Carlo-derived two-layer models is noted. Both models suggest that tumor tissue has higher absorption and less scattering than normal brain. Temperatures are measured by inserting thermocouples directly into tumor-free brains. A model based on diffusion theory and the bioheat equation is found to be in good agreement with the experimental data and predict a thermal penetration depth of 0.60 cm in normal rat brain. The predicted parameters can be used to estimate the fluences, fluence rates, and temperatures achieved during photodynamic therapy.

Interstitial light application for photodynamic therapy in a rat brain tumor model

The usefulness of repetitive ALA mediated PDT is being evaluated in a rat brain tumor model. In preliminary experiments an optical fiber was repeatedly introduced directly into the brain to apply light, requiring multiple surgical procedures. In an attempt to refine the animal model, an indwelling light applicator, using a modified microdialysis guide cannula has been developed. The cannula is fixed to the scull and can remain in the rat brain for several weeks without complications. In studies of repetitive PDT the need for repeated mounting in a stereotactic frame and surgical procedures can be eliminated. The applicator also makes it feasible to employ low fluence rates with long treatment times, which correspond to future clinically relevant protocols. The fluence rate distribution was measured in vivo and compared to diffusion theory and Monte Carlo simulations to estimate the tissue optical properties of the rat brain for light at 632 nm. The modeling suggested a reduced scattering coefficient 38 cm-1, an absorption coefficient 0.46 cm-1 and a penetration depth 0.14 cm.

Repetitive 5-aminolevulinic acid mediated photodynamic therapy of rat glioma

The probability of achieving local control with current single-shot, intraoperative PDT treatments of intracerebral gliomas seems improbable due to the length of time required to deliver adequate light fluences to depths of 1 - 2 cm in the resection margin. The results of in vitro experiments indicated that PDT, repeated at weekly intervals, was substantially more effective at inhibiting glioma spheriod growth than single treatment regimes. This prompted the initiation of in vivo studies of repetitive PDT in a rat glioma model. BT4C cell line tumors were established in the brains of inbred BD-IX rats. Three days following tumor induction, the animals were injected with 250 mg/kg ALA i.p. and four hours later, after the introduction of an optical fiber, light treatment at various radiant energies was given over a 10- to 30-minute interval. Two additional treatments were given at weekly intervals. In vitro experiments verified that spheroids derived from the cell line were sensitive to ALA PDT. Microfluorometry of frozen tissue sections showed that PpIX is produced with a 10 - 20:1 tumor to normal tissue selectivity ratio four hours after 250 mg/kg ALA i.p. Toxic radiant energy levels for ALA PDT have been determined.