A review of progress in clinical photodynamic therapy

Photodynamic therapy of tumors can lead to development of systemic antigen-specific immune response

Background

The mechanism by which the immune system can effectively recognize and destroy tumors is dependent on recognition of tumor antigens. The molecular identity of a number of these antigens has recently been identified and several immunotherapies have explored them as targets. Photodynamic therapy (PDT) is an anti-cancer modality that uses a non-toxic photosensitizer and visible light to produce cytotoxic reactive oxygen species that destroy tumors. PDT has been shown to lead to local destruction of tumors as well as to induction of anti-tumor immune response.

Methodology/Principal Findings

We used a pair of equally lethal BALB/c colon adenocarcinomas, CT26 wild-type (CT26WT) and CT26.CL25 that expressed a tumor antigen, β-galactosidase (β-gal), and we treated them with vascular PDT. All mice bearing antigen-positive, but not antigen-negative tumors were cured and resistant to rechallenge. T lymphocytes isolated from cured mice were able to specifically lyse antigen positive cells and recognize the epitope derived from beta-galactosidase antigen. PDT was capable of destroying distant, untreated, established, antigen-expressing tumors in 70% of the mice. The remaining 30% escaped destruction due to loss of expression of tumor antigen. The PDT anti-tumor effects were completely abrogated in the absence of the adaptive immune response.

Conclusion

Understanding the role of antigen-expression in PDT immune response may allow application of PDT in metastatic as well as localized disease. To the best of our knowledge, this is the first time that PDT has been shown to lead to systemic, antigen- specific anti-tumor immunity.

Quenching enhancement of the singlet excited state of pheophorbide-a by DNA in the presence of the quinone carboquone

Changes in the emission fluorescence intensity of pheophorbide-a (PHEO) in the presence of carboquone (CARBOQ) were used to obtain the association constant, the number of CARBOQ molecules interacting with PHEO, and the fluorescence quantum yield of the complex. Excitation spectra of mixtures of PHEO and CARBOQ in ethanol (EtOH) show an unresolved doublet in the red-most excitation band of PHEO, indicating the formation of a loose ground-state complex. The 1:1 CARBOQ-PHEO complex shows a higher fluorescence quantum yield in EtOH (0.41 ± 0.02) than in buffer solution (0.089 ± 0.002), which is also higher than that of the PHEO monomer (0.28). Quenching of the PHEO fluorescence by DNA nucleosides and double-stranded oligonucleotides was also observed and the bimolecular quenching rate constants were determined. The quenching rate constant increase as the oxidation potential of the DNA nucleoside increases. Larger quenching constants were obtained in the presence of CARBOQ suggesting that CARBOQ enhances DNA photo-oxidation, presumably by inhibiting the back-electron-transfer reaction from the photoreduced PHEO to the oxidized base. Thus, the enhanced DNA-base photosensitized oxidation by PHEO in the presence of CARBOQ may be related to the large extent by which this quinone covalently binds to DNA, as previously reported.

Effects of photodynamic exposure on endothelial cells in vitro

Experiments on cultured human umbilical vein endotheliocytes showed that accumulation of photosensitive dye (aluminum phthalocyanin; PHOTOSENSE) in cells and laser exposure alone were inessential for the viability of endothelial cells. Contrary to this, exposure of the cells which have accumulated aluminum phthalocyanin (an average of 111.1 ng/mg protein) to low-intensity laser (λ=675 nm) led to a dose-dependent reduction of endotheliocyte viability. Hence, cultured endothelial cells can be used for screening of various photosensitizers and preliminary optimization of photodynamic therapy.

In-body optical stimulation formed connective tissue vascular grafts, "biotubes," with many capillaries and elastic fibers

The autologous biotube, developed by using in-body tissue architecture technology, is one of the most promising small-diameter vascular grafts in regenerative medicine. The walls of the biotubes obtained by a traditional silicone mold-based method were very thin, and this is still the primary obstacle while handling anastomosis, even though these biotubes have adequate pressure resistance ability. This pilot study showed the effect of optical stimulation of subcutaneous tissue formation in the body during the preparation of the biotubes. A blue light-emitting diode (LED) was embedded into a silicone rod as a mold. The biotube was prepared by placing the luminescent molds into the dorsal subcutaneous pouches of a pair of beagles (each weighing ~10 kg) for 2 weeks under photoirradiation. The wall thickness of the obtained biotubes was 506.9 ± 185.7 μm, which was remarkably more than that of the previous biotubes prepared by 2 months of embedding similarly in beagles' subcutaneous pouches (thickness, 77.2 ± 14.8 μm). Many capillaries with smooth muscle cells were infiltrated into the wall and concentrated in the internal layer. Interestingly, the formation of elastic fibers had already started along with collagen fibers, mostly with a regular circumferential orientation. The short-term in-body optical stimulation resulted in the rapid formation of a biotube. These phenomena will allow easy surgical handling and may induce vascular maturation in histology during the acute phase after implantation.

Photodynamic therapy-generated cancer vaccines

Eradication of cancer by an intervention producing a potent immune response capable of rejecting both primary and metastatic deposits remains the most pragmatic approach in cancer therapy. Cancer vaccine generated by photodynamic therapy (PDT) is therefore of considerable interest, particularly as it is becoming increasingly clear that it holds unique prospects for optimally presenting tumor antigens and because of emerging indications that its efficacy can be further potentiated by continued development. The present report dissects the preparation of PDT vaccine in a mouse model of squamous cell carcinoma.

Fluorescent proteins and their applications in imaging living cells and tissues

Green fluorescent protein (GFP) from the jellyfish Aequorea victoria and its homologs from diverse marine animals are widely used as universal genetically encoded fluorescent labels. Many laboratories have focused their efforts on identification and development of fluorescent proteins with novel characteristics and enhanced properties, resulting in a powerful toolkit for visualization of structural organization and dynamic processes in living cells and organisms. The diversity of currently available fluorescent proteins covers nearly the entire visible spectrum, providing numerous alternative possibilities for multicolor labeling and studies of protein interactions. Photoactivatable fluorescent proteins enable tracking of photolabeled molecules and cells in space and time and can also be used for super-resolution imaging. Genetically encoded sensors make it possible to monitor the activity of enzymes and the concentrations of various analytes. Fast-maturing fluorescent proteins, cell clocks, and timers further expand the options for real time studies in living tissues. Here we focus on the structure, evolution, and function of GFP-like proteins and their numerous applications for in vivo imaging, with particular attention to recent techniques.

The role of porphyrin chemistry in tumor imaging and photodynamic therapy

In recent years several review articles and books have been published on the use of porphyrin-based compounds in photodynamic therapy (PDT). This critical review is focused on (i) the basic concept of PDT, (ii) advantages of long-wavelength absorbing photosensitizers (PS), (iii) a brief discussion on recent advances in developing PDT agents, and (iv) the various synthetic strategies designed at the Roswell Park Cancer Institute, Buffalo, for developing highly effective long-wavelength PDT agents and their utility in constructing the conjugates with tumor-imaging and therapeutic potential (Theranostics). The clinical status of certain selected PDT agents is also summarized (205 references).

Photodynamic therapy: superficial and interstitial illumination

Photodynamic therapy (PDT) is reviewed using the treatment of skin tumors as an example of superficial lesions and prostate cancer as an example of deep-lying lesions requiring interstitial intervention. These two applications are among the most commonly studied in oncological PDT, and illustrate well the different challenges facing the two modalities of PDT-superficial and interstitial. They thus serve as good examples to illustrate the entire field of PDT in oncology. PDT is discussed based on the Lund University group's over 20 yr of experience in the field. In particular, the interplay between optical diagnostics and dosimetry and the delivery of the therapeutic light dose are highlighted. An interactive multiple-fiber interstitial procedure to deliver the required therapeutic dose based on the assessment of light fluence rate and sensitizer concentration and oxygen level throughout the tumor is presented.

Polymeric micelle nanoparticles for photodynamic treatment of head and neck cancer cells

Objective: To encapsulate 5,10,15,20-tetrakis( meso-hydroxyphenyl)porphyrin (mTHPP), a photosensitizer, into polymeric micelles; characterize the micelles; and test in vitro photodynamic therapy efficacy against human head and neck cancer cells.

Study Design: A nanoparticle design, fabrication, and in vitro testing study.

Setting: Polymer chemistry laboratory.

Subjects and Methods: Micelles encapsulating mTHPP were produced, and micellar size was measured. Ultraviolet visible spectra and fluorescence spectroscopy were used to characterize the mTHPP-loaded micelles. In vitro cell culture using HSC-3 and HN-5 cancer cells was performed to test the photodynamic therapy efficacy of the micelles using confocal microscopy and method of transcriptional and translational (MTT) assay.

Results: mTHPP was encapsulated with high loading efficiency (> 85%) and density (up to 17%) into micelles. Micelle size was 30.6 ± 3.3 nm by transmission electron microscopy and 30.8 ± 0.6 nm by dynamic light scattering. The absorption maximum for each sample was 418 nm, and fluorescent spectroscopy revealed quenching with maximal fluorescence at five percent loading. Significant cytotoxicity was observed with confocal microscopy when HSC-3 cells were treated with 10 percent mTHPP micelles, with 100 percent cytotoxicity within the zone of laser light exposure at 420 nm. Phototoxicity and dark toxicity against HSC-3 and HN-5 cells measured using the MTT assay with five and 10 percent loaded mTHPP micelles demonstrated greater than 90 percent cytotoxicity with photodynamic therapy and less than 10 percent dark toxicity at a micelle concentration of 25 μg/mL for both cell lines.

Conclusion: Micelles were able to encapsulate and solubilize mTHPP at high loading densities with uniform size distribution. These micelles exhibit fluorescence and photodynamic therapy mediated cytotoxicity against head and neck cancer cells in vitro.

In vivo study of photosensitizer pharmacokinetics by fluorescence transillumination imaging

The possibility of in vivo investigation of the pharmacokinetics of photosensitizers by means of fluorescence transillumination imaging is demonstrated. An animal is scanned in the transilluminative configuration by a single source and detector pair. Transillumination is chosen as an alternative approach to reflection imaging. In comparison with the traditional back-reflection technique, transillumination is preferable for photosensitizer detection due to its higher sensitivity to deep-seated fluorophores. The experiments are performed on transplantable mouse cervical carcinomas using three drugs: photosens, alasens, and fotoditazin. For quantitative evaluation of the photosensitizer concentration in tumor tissue the fluorescence signal is calibrated using tissue phantoms. We show that the kinetics of photosensitizer tumor uptake obtained by transillumination imaging in vivo agree with data of standard ex vivo methods. The described approach enables rapid and cost-effective study of newly developed photosensitizers in small animals.

A telemetric light delivery system for metronomic photodynamic therapy (mPDT) in rats

Light delivery and monitoring during photodynamic therapy (PDT) is often limited by the need for a physical link between the light source, detectors and the treatment volume. This paper reports on the first in vivo experiments performed with a fully implantable telemetric system, designed for a rat glioblastoma model. In this system, light delivery is performed using a solid state optode containing 2 LEDs, and 4 photodiodes which will be used to monitor light delivery in future experiments. Powering and communication is achieved by means of an inductive link. The implant may remain in the animal for extended time periods, making it particularly interesting for performing metronomic PDT. In this paper, we demonstrate the feasibility of in vivo light delivery and biocompatibility of the device.. Activation of the inductive link as well as illumination of the brain by the LED did not influence animal behavior during or after treatment. We show that the implant can remain in the animal for two weeks without causing serious biological reactions.

One pot synthesis of new hybrid versatile nanocarrier exhibiting efficient stability in biological environment for use in photodynamic therapy

A new versatile hybrid nanocarrier has been designed using a "soft chemistry" synthesis, to efficiently encapsulate a photosensitizer - the protoporphyrin IX (Pp IX) - while preserving its activity intact in biological environment for advantageous use in photodynamic therapy (PDT). The synthesized Pp IX silica-based nanocarriers show to be spherical in shape and highly monodisperse with size extending from 10 nm up to 200 nm according to the synthesis procedure. Upon laser irradiation, the entrapped Pp IX shows to efficiently deliver reactive oxygen species (ROS) which are responsible for damaging tumor tissues. The ability of Pp IX silica-based nanocarriers to induce tumor cell death has been tested successfully in vitro. The stability of the Pp IX silica-based nanocarriers has been followed by UV-vis absorption and fluorescence emission in aqueous media and in 100% mouse serum media. The flexibility of the nanocarrier silica core has been examined as the key parameter to tune the Pp IX stability in biological environment. Indeed, an additional biocompatible inorganic surface coating performed on the Pp IX silica-based nanocarriers to produce an optimized bilayer coating demonstrates to significantly enhance the Pp IX stabilization in biological environments. Such versatile hybrid nanocarriers open new perspectives for PDT.

Oral mucous squamous cell carcinoma-an anticipated consequence of autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED)

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a rare autosomal recessive disease caused by mutations in the AIRE gene. We report the case of a female patient with a 967-979del13 mutation in the AIRE gene. Her medical history included autoimmune hypoparathyroidism, Addison disease, and chronic mucocutaneous candidiasis. At the age of 40, she developed multiple white verrucous plaques on the oral mucosa. Histologically, the lesions appeared as moderately differentiated squamous cell carcinomas. The patient subsequently developed multiple local recurrences and therefore required repeated surgery. Notably, a higher incidence rate of oral and esophageal squamous cell carcinoma has been observed in this syndrome. However, the critical pathogenetic pathways implicated in squamous cell carcinoma development in APECED are far from being well understood.

Exploitation of immune response-eliciting properties of hypocrellin photosensitizer SL052-based photodynamic therapy for eradication of malignant tumors

A diaminophenyl derivative of hypocrellin B (SL052) has been developed as a photosensitizer for use in photodynamic therapy (PDT) of solid tumors. Testing SL052-PDT on mouse carcinoma and fibrosarcoma models revealed a typical response seen with clinically established photosensitizers featuring initial rapid tumor ablation with ensuing recurrence at rates dependent on photosensitizer/light doses. Elevated numbers of immune cells were found in lymph nodes draining SCCVII mouse squamous cell carcinomas treated by SL052-PDT (in particular T cells), and the accumulation of degranulating cytotoxic T cells was detected at the tumor-treated site. This indicates that a significant contribution to tumor cures is elicited by an antitumor adaptive immune response. Two different immunotherapy agents, gamma-interferon and antibody blocking inhibitory FcgammaRIIB receptor, were both found to be highly effective in potentiating the curative effect of SL052-PDT with SCCVII tumors. Combining SL052-PDT with FcgammaRIIB-blocking antibody treatment caused a further increase in the number of cells in tumor-draining lymph nodes and in degranulating CD8+ cells, suggesting the amplification of the immune response induced by PDT. Vaccines consisting of SCCVII cells treated with SL052-PDT in vitro were effective in reducing growth of established subcutaneous SCCVII tumors. In conclusion, PDT mediated by SL052 is suitable to be integrated with various immunotherapy protocols.

Imaging tumor variation in response to photodynamic therapy in pancreatic cancer xenograft models

PURPOSE

A treatment monitoring study investigated the differential effects of orthotopic pancreatic cancer models in response to interstitial photodynamic therapy (PDT), and the validity of using magnetic resonance imaging as a surrogate measure of response was assessed.

METHODS AND MATERIALS

Different orthotopic pancreatic cancer xenograft models (AsPC-1 and Panc-1) were used to represent the range of pathophysiology observed in human beings. Identical dose escalation studies (10, 20, and 40J/cm) using interstitial verteporfin PDT were performed, and magnetic resonance imaging with T2-weighted and T1-weighted contrast were used to monitor the total tumor volume and the vascular perfusion volume, respectively.

RESULTS

There was a significant amount of necrosis in the slower-growing Panc-1 tumor using high light dose, although complete necrosis was not observed. Lower doses were required for the same level of tumor kill in the faster-growing AsPC-1 cell line.

CONCLUSIONS

The tumor growth rate and vascular pattern of the tumor affect the optimal PDT treatment regimen, with faster-growing tumors being relatively easier to treat. This highlights the fact that therapy in human beings shows a heterogeneous range of outcomes, and suggests a need for careful individualized treatment outcomes assessment in clinical work.

Photoactivated chemotherapy (PACT): the potential of excited-state d-block metals in medicine

The fields of phototherapy and of inorganic chemotherapy both have long histories. Inorganic photoactivated chemotherapy (PACT) offers both temporal and spatial control over drug activation and has remarkable potential for the treatment of cancer. Following photoexcitation, a number of different decay pathways (both photophysical and photochemical) are available to a metal complex. These pathways can result in radiative energy release, loss of ligands or transfer of energy to another species, such as triplet oxygen. We discuss the features which need to be considered when developing a metal-based anticancer drug, and the common mechanisms by which the current complexes are believed to operate. We then provide a comprehensive overview of PACT developments for complexes of the different d-block metals for the treatment of cancer, detailing the more established areas concerning Ti, V, Cr, Mn, Re, Fe, Ru, Os, Co, Rh, Pt, and Cu and also highlighting areas where there is potential for greater exploration. Nanoparticles (Ag, Au) and quantum dots (Cd) are also discussed for their photothermal destructive potential. We also discuss the potential held in particular by mixed-metal systems and Ru complexes.

Apoptosis of vascular smooth muscle cells induced by photodynamic therapy with protoporphyrin IX

Photodynamic therapy (PDT) had been shown effective in the treatment of intimal hyperplasia, which contributes to restenosis, by eradicating cells in the vessel wall. This study is designed to evaluate the effects of PDT with protoporphyrin IX (PpIX) on the viability of vascular smooth muscle cells (SMCs) and to define the cell-death pathway. Fluorescence microscopy and laser-induced fluorescence spectroscopic detection showed that SMCs selectively uptake PpIX, and the intracellular PpIX concentration increases with the amount of PpIX in the incubation solution. PDT with PpIX impaired cellular viability from 93+/-3.4% to 36+/-3.9% when the light intensity increases from 2 to 9J/cm(2) and intracellular PpIX concentration increases from 0.5 to 20 microg/ml. Although PDT induced both apoptosis and necrosis, the ratio of apoptotic cells increased with light dosage or intracellular PpIX concentration. The loss of mitochondrial membrane potential coincided with the apoptotic ratio. Our results indicated that the induction of apoptosis of SMCs may be one of the mechanisms by which PDT inhibits restenosis in vivo.

Evaluating the antitumor activity of combined photochemotherapy mediated by a meso-substituted tetracationic porphyrin and adriamycin

The combined anticancer modality comprising porphyrins as photodynamic sensitizers and anticancer drugs has been an interesting subject for many researchers. In this study, the photochemotherapeutic effect mediated by simultaneous photoactivation of tetracationic meso-tetrakis(N-methyl-4-pyridyl) porphine tetratosylate (TMPyP) and adriamycin (ADM) were explored using human hepatocellular carcinoma cell line (HePG2). The efficiency of TMPyP acting in concert with ADM in the dark and in the presence of photoirradiation was evaluated, by studying cell viability, caspase-3 activity and ultrastructural changes in the cells after incubation with each of the two agents, separately, or simultaneously as a co-mixture. Under dark conditions, the simultaneous incubation of cells with TMPyP and ADM significantly enhanced cell death by 1.8 folds and 1.3 folds, compared with TMPyP or ADM treatment, respectively. After photoirradiation, the antiproliferative effect of the co-treatment with TMPyP and ADM increased further by 2 folds. Transmission electron microscopy and the measurements of caspase-3 levels in treated cells revealed that the co-treatment of cells with ADM and TMPyP followed by light irradiation directed the cell death towards necrosis and abrogated the apoptotic cell death pathway, which was exhibited in cells treated with ADM in absence and in presence of photoirradiation.

Effective photoreduction of a Pt(IV) complex with quantum dots: a feasible new light-induced method of releasing anticancer Pt(II) drugs

Irradiation of CdSe-ZnS quantum dots (QDs) with visible light in the presence of [PtCl(4)(bpy)] (1) (bpy = 2,2'-bipyridine) produced with high efficiency [PtCl(2)(bpy)] (2) by photoinduced electron transfer; a reaction and strategy which opens up new opportunities for cancer therapy.

Photosensitizing action of isomeric zincN-methylpyridylporphyrins in human carcinoma cells

The success of photodynamic therapy (PDT), as a minimally invasive approach, in treating both neoplastic and non-neoplastic diseases has stimulated the search for new compounds with potential application in PDT. We have previously reported that Zn(II) N-alkylpyridylporphyrins (ZnTM-2(3,4)-PyP(4+) and ZnTE-2-PyP(4+)) can act as photosensitizers and kill antibiotic-resistant bacteria. This study investigated the photosensitizing effects of the isomers of ZnTMPyP(4+) (ZnTM-2(3,4)-PyP(4+)) and respective ligands on a human colon adenocarcinoma cell line. At 10 microM and 30 min of illumination the isomeric porphyrins completely inhibited cell growth, and at 20 microM killed approximately 50% of the cancer cells. All these effects were entirely light-dependent. The isomers of the ZnTMPyP(4+) and the respective ligands show high photosensitizing efficiency and no toxicity in the dark. Their efficacy as photosensitizers is comparable to that of hematoporphyrin derivative (HpD).

Effect of photodynamic therapy on the healing of cutaneous third-degree-burn: histological study in rats

The aim of this study was to conduct a histological assessment of the effect of photodynamic therapy (PDT) on the repairing of third-degree-burn wounds made on the backs of rats with a heated scalpel. Ninety-six rats were divided into groups: G1, control (n = 24), cold scalpel; G2, burned, heated scalpel (n = 24); G3, low-level laser therapy (LLLT) (n = 24), on burns; and G4, photodynamic therapy (PDT) (n = 24), toluidine-O blue (100 microg/ml) and LLLT treatment on burns. The laser (685 nm) was applied in continuous mode, 50 mW, 4.5 J/cm(2), contact mode at nine points (9 s/point). Eight animals in each group were killed at 3 days, 7 days or 14 days after surgery, and tissue specimens containing the whole wounded area were removed and processed for histological analysis; the results were statistically analyzed with Kruskal-Wallis and Dunn's tests (P < 0.05). The results demonstrated significant differences between G2 and G3, and between G2 and G4, at both 3 days and 7 days, with regard to acute inflammation scores; G1 and G2 showed significant differences when compared with G4 at 3 days, with regard to neo-angiogenesis scores; G1 and G2 were statistically different from G3 and G4 at both 3 days and 7 days, with regard to re-epithelization scores; G2 showed statistically significant differences when compared with G3 and G4 with regard to collagen fiber scores at 7 days. LLLT and PDT acted as a biostimulating coadjuvant agent, balancing the undesirable effect of the burn on the wound healing process, acting mainly in the early healing stages, hastening inflammation and increasing collagen deposition.

The relationship of phthalocyanine 4 (pc 4) concentrations measured noninvasively to outcome of pc 4 photodynamic therapy in mice

The ability to noninvasively measure photosensitizer concentration at target tissues will allow optimization of photodynamic therapy (PDT) and could improve outcome. In this study, we evaluated whether preirradiation tumor phthalocyanine 4 (Pc 4) concentrations, measured noninvasively by the optical pharmacokinetic system (OPS), correlated with tumor response to PDT. Mice bearing human breast cancer xenografts were treated with 2 mg kg(-1) Pc 4 iv only, laser irradiation (150 J cm(-2)) only, Pc 4 followed by fractionated irradiation or Pc 4 followed by continuous irradiation. Laser irradiation treatment was initiated when the tumor to skin ratio of Pc 4 concentration reached a maximum of 2.1 at 48 h after administration. Pc 4 concentrations in tumor, as well as in Intralipid in vitro, decreased monoexponentially with laser fluence. Pc 4-PDT resulted in significant tumor regression, and tumor response was similar in the groups receiving either fractionated or continuous irradiation treatment after Pc 4. Tumor growth delay following Pc 4-PDT correlated with OPS-measured tumor Pc 4 concentrations at 24 h prior to PDT (R2=0.86). In excised tumors, OPS-measured Pc 4 concentrations were similar to the HPLC-measured concentrations. Thus, OPS measurements of photosensitizer concentrations can be used to assist in the scheduling of Pc 4-PDT.

Self-expandable metal stents and trans-stent light delivery: are metal stents and photodynamic therapy compatible?

BACKGROUND AND OBJECTIVES

Obstructive non-small cell lung cancer and obstructive esophageal cancer are US FDA approved indications of photodynamic therapy (PDT). The usefulness of PDT for the treatment of cholangiocarcinoma is currently under clinical investigation. Endoscopic stenting for lumen restoration is a common palliative intervention for those indications. It is important to assess whether self-expandable metal stents are compatible with trans-stent PDT light delivery.

STUDY DESIGN/MATERIALS AND METHODS

Direct effects of various components of metal biliary (n = 2), esophageal (n = 2), and bronchial (n = 1) stents on PDT light transmittance and distribution were examined using a point or linear light source (630 or 652 nm diode laser). Resected pig biliary duct and esophageal wall tissues were used to examine the feasibility of PDT light delivery through the fully expanded metal stents.

RESULTS

While using a point light source, the metal components (thread and joint) of the stent could cause a significant shadow effect. The liner material (polytetrafluoroethylene or polyurethane) could cause various degrees of light absorption. When the stent was covered with a thin layer of biliary duct and esophageal tissues containing all wall layers, the shadow effect could be mitigated due to tissue scattering.

CONCLUSIONS

This study clearly demonstrates that it is feasible to combine stenting and PDT for the treatment of luminal lesions. PDT light dose should be adjusted to counteract the reduction of light transmittance caused by the metal and liner materials of stent.

A heterogeneous algorithm for PDT dose optimization for prostate

The object of this study is to develop optimization procedures that account for both the optical heterogeneity as well as photosensitizer (PS) drug distribution of the patient prostate and thereby enable delivery of uniform photodynamic dose to that gland. We use the heterogeneous optical properties measured for a patient prostate to calculate a light fluence kernel (table). PS distribution is then multiplied with the light fluence kernel to form the PDT dose kernel. The Cimmino feasibility algorithm, which is fast, linear, and always converges reliably, is applied as a search tool to choose the weights of the light sources to optimize PDT dose. Maximum and minimum PDT dose limits chosen for sample points in the prostate constrain the solution for the source strengths of the cylindrical diffuser fibers (CDF). We tested the Cimmino optimization procedures using the light fluence kernel generated for heterogeneous optical properties, and compared the optimized treatment plans with those obtained using homogeneous optical properties. To study how different photosensitizer distributions in the prostate affect optimization, comparisons of light fluence rate and PDT dose distributions were made with three distributions of photosensitizer: uniform, linear spatial distribution, and the measured PS distribution. The study shows that optimization of individual light source positions and intensities are feasible for the heterogeneous prostate during PDT.

Combination of photodynamic therapy and immunomodulation: current status and future trends

Photodynamic therapy (PDT) has been used for the treatment of nonmalignant and malignant diseases from head to toe. Over the last decade its clinical application has gained increasing acceptance around the world. Pre-clinical studies demonstrate that, in addition to the direct local cytotoxicity and vascular effects, PDT can induce various host immune responses. Recent clinical data also show that improved clinical outcomes are obtained through the combination of PDT and immunomodulation. This review will summarize and discuss recent progress in developing innovative regimen of PDT combined with immunomodulation for the treatment of both nonmalignant and malignant diseases.

Photodynamic therapy for treatment of solid tumors--potential and technical challenges

Photodynamic therapy (PDT) involves the administration of photosensitizer followed by local illumination with visible light of specific wavelength(s). In the presence of oxygen molecules, the light illumination of photosensitizer can lead to a series of photochemical reactions and consequently the generation of cytotoxic species. The quantity and location of PDT-induced cytotoxic species determine the nature and consequence of PDT. Much progress has been seen in both basic research and clinical application in recent years. Although the majority of approved PDT clinical protocols have primarily been used for the treatment of superficial lesions of both malignant and non-malignant diseases, interstitial PDT for the ablation of deep-seated solid tumors are now being investigated worldwide. The complexity of the geometry and non-homogeneity of solid tumor pose a great challenge on the implementation of minimally invasive interstitial PDT and the estimation of PDT dosimetry. This review will discuss the recent progress and technical challenges of various forms of interstitial PDT for the treatment of parenchymal and/or stromal tissues of solid tumors.

Modeling of Photochemical Reactions in a Focused Laser Beam, II

A method is described for obtaining the rate constant of the photodegradation process of fluorophores illuminated by a focused laser beam. The explicit kinetic equations, describing the population dynamics of excited singlet and triplet states, are averaged over the illuminated volume to describe the resulting fluorescence signal. The illumination is modulated at frequencies from 1 Hz to 100 Hz. Synchronous detection of the resulting fluorescence yields in-phase and quadrature components. The measurement of the ratio of quadrature to in-phase components at several power levels yields information on the photodegradation rate. Specifically it is shown that the data can be interpreted in a manner which yields the value of the photodegradation rate independently of other parameters entering the model. Experiments are performed with erythrosine B which has a large intersystem crossing rate to the triplet state. Measurements in solutions with different viscosities show that the photodegradation rate depends on the viscosity. This is interpreted as evidence for an intermolecular interaction mechanism. We explore the uncertainty of the estimated photodegradation constant taking into account the uncertainties of the measurements used in the synchronous detection technique.