Short Drug-light Interval Research Articles

Vascular-targeted photodynamic therapy with glucose-conjugated chlorin e6 for dogs with spontaneously occurring tumours.

Photodynamic therapy (PDT) using photosensitisers is a minimally invasive treatment for malignant tumours. However, ideal photosensitisers are not yet established. Recently, we developed a new photosensitiser, glucose-conjugated chlorin e6 (G-Ce6). To evaluate the clinical efficacy of vascular-targeted PDT (VTP), a type of PDT utilising a short drug-light interval, using G-Ce6 to treat spontaneously occurring tumours in dogs. Five dogs with spontaneously occurring tumours (malignant melanoma: three; haemangiopericytoma: two; and squamous cell carcinoma: one) were subjected to VTP. These dogs were intravenously injected with G-Ce6 at doses of 1-3mg/kg 5min before laser irradiation. Tumours were superficially or interstitially irradiated using a 677-nm diode laser. Repeated VTP decreased tumour size, yielding complete remission in three dogs. Complications such as oedema surrounding normal tissues and fistulae were observed, and the oedema was self-limiting. The fistula was cured by debriding the necrotic tissues formed after VTP. Our findings demonstrate that VTP using G-Ce6 had antitumour effects in dogs with spontaneously occurring tumours.

Development of a Clinically Viable Strategy for Nanoparticle‐Based Photodynamic Therapy of Colorectal Cancer

AbstractPhotodynamic therapy (PDT) is an anticancer treatment modality that is poorly adopted into clinical practice for a variety of factors. Though fundamental studies supporting its utility abound, few clinical trials are performed on its use. This may be due to failures in the translation of treatment protocols used in fundamental studies into clinically viable protocols. This study seeks to develop a clinically viable protocol for the treatment of colorectal cancer using nanoparticle‐based PDT by using three complementary animal models. Using the porphysome nanoparticle as a model photosensitizer, several theoretical and practical challenges to the clinical delivery of PDT are addressed including the required drug‐light interval (DLI), the route of administration, and the method of light irradiation delivery. This study finds that nanoparticle‐based PDT can effectively ablate colorectal cancer tumors, that PDT can be effectively delivered after a relatively short DLI, and that safety concerns related to off‐target effects can be mitigated through the peritumoral administration of the photosensitizer and the transanal intraluminal placement of light irradiation. These findings lay the framework for future clinical trials investigating the use of PDT as a component of the multi‐modal approach to the treatment of colorectal cancer.

Pharmacokinetics and pharmacodynamics of liposomal chemophototherapy with short drug-light intervals

Chemophototherapy (CPT) merges photodynamic therapy with chemotherapy and can substantially enhance drug delivery. Using a singular liposomal formulation for CPT, we describe a semi-mechanistic pharmacokinetic-pharmacodynamic (PK/PD) model to investigate observed antitumor effects. Long-circulating, sterically-stabilized liposomes loaded with doxorubicin (Dox) stably incorporate small amounts of a porphyrin-phospholipid (PoP) photosensitizer in the bilayer. These were administered intravenously to mice bearing low-passage, patient-derived pancreatic cancer xenografts (PDX). Dox PK was described with a two-compartment model and tumor drug disposition kinetics were modeled with first-order influx and efflux rates. Tumor irradiation with 665 nm laser light (200 J/cm2) 1 h after liposome administration increased tumor vascular permeabilization and drug accumulation, which was accounted for in the PK/PD model with increased tumor influx and efflux rates by approximately 12- and 4- fold, respectively. This modeling approach provided an overall 7-fold increase in Dox area under the curve in the tumor, matching experimental data (7.4-fold). A signal transduction model based on nonlinear direct cell killing accounted for observed tumor growth patterns. This PK/PD model adequately describes the CPT anti-PDX tumor response based on enhanced drug delivery at the short drug-light interval used.

Highly Selective Photodynamic Therapy with a Short Drug-Light Interval Using a Cytotoxic Photosensitizer Porphyrus Envelope for Drug-Resistant Prostate Cancer Cells

Background: Photodynamic therapy (PDT) is a less invasive cancer treatment using photochemical reactions induced by light irradiation to a photosensitizer (PS). Highly selective PDT with fast accumulation of the PS in target site might be a promising treatment option for drug-resistant prostate cancer facing high incidence rate of elderly men who have no effective treatment options and require a minimally invasive treatment. Hemagglutinating virus of Japan envelope (HVJ-E) allows selective and fast drug delivery to the drug-resistant prostate cancer cells via rapid cell membrane fusion. PS named porphyrus envelope (PE) has been developed by insertion of lipidated protoporphyrin IX (PpIX lipid) into HVJ-E. In this study, we investigated the optimal conditions for PE preparation and laser irradiation for highly selective PDT using PE with a short drug-light interval. Materials and Methods: Human hormon refractory prostate cancer cell line PC-3 and human normal prostate epithelial cell line PNT2 were cultured. PpIX lipid uptake and cytotoxicity of PDT in the cells incubated with PE for 10 min were evaluated by measuring fluorescence intensity and by using a cell counting reagent 24 h after PDT, respectively. Results: PpIX lipid uptake and cytotoxicity of PDT were increased with PpIX lipid concentration. Cytotoxicity of PDT using PE was more than 9 times as strong as that with PpIX lipid and PpIX induced by 5-aminolevulinic acid. Much stronger cytotoxicity was induced in PC-3 cells than PNT2 cells with the ratio of cell death rate for cancer to normal cells up to 4.64 ± 0.09. Conclusions: Fast PS delivery with HVJ-E allows highly selective PDT with a short drug-light interval. Therefore, PDT using PE has a potential to shorten treatment period and reduce side effects of PDT.

Temperature Influence on Myocardial Cell Cytotoxicity of the Extracellular Photosensitization Reaction with Talaporfin Sodium and Serum Proteins at 17°-37°C.

We investigated the binding of talaporfin sodium with albumin and its photocytotoxicity during temperature changes by measuring absorbance spectra. The targeted tissue temperature differs according to the procedure. The photocytotoxicity efficiency should be investigated quantitatively because efficiency changes arising from temperature changes are expected. The temperature dependence of talaporfin sodium binding with human serum albumin (0-20 mg/mL), high-density lipoprotein (0-0.04 mg/mL), and low-density lipoprotein (0-0.14 mg/mL) was investigated at 17°C, 27°C, and 37°C by measurement of absorbance spectra. Cell lethality was measured using a water-soluble tetrazolium-8 assay at 2 h after the photosensitization reaction at 17°C and 37°C. The binding ratios of talaporfin sodium with high-density lipoprotein decreased by 6.3% and those with low-density lipoprotein decreased by 12.8% when the temperature increased from 17°C to 37°C. Cell lethality increased significantly with a temperature rise from 17°C to 37°C at irradiation exposure of 20 and 40 J/cm2 and talaporfin sodium concentration of 20 μg/mL. From our in vitro data, we can predict that the change in photocytotoxicity efficiency would be negligible with a temperature decrease of <5°C from the body temperature in the case of photodynamic ablation with a short drug-light interval.

Myocardial necrosis depth prediction during extracellular photosensitization reaction of talaporfin sodium by defined index using fluorescence measurement

An application of photodynamic therapy for myocardial ablation, which would induce myocardial electrical conduction block, is proposed. For the proposed application, an extracellular photosensitization reaction (PR) is performed while photosensitizer is distributed in myocardial interstitial space by employing a short drug-light interval. Because the myocardial necrosis depth must be accurately controlled to prevent surrounding tissue injury during the myocardial ablation procedure, the necrosis depth during PR needs to be predicted. The purpose of this study is to investigate the availability of predicting PR-induced myocardial necrosis depth (d(nec)) using a defined fluorescence-fall amount (FA), which is the calculated result of fluorescence intensity decrease from the start of the PR multiplied by irradiation duration and corresponds to photosensitizer consumption amount under an assumption that the photosensitizer consumption rate is faster than the photosensitizer supply rate. The correlation between FA and d nec was experimentally investigated in vivo using an open-chested canine heart model with 2.5 and 5.0 mg/kg of talaporfin sodium at an irradiance of 5-20 W/cm(2) for 5-20 s. The fluorescence measurement was performed at a wavelength of 710 nm during the PR to derive FA. One week after the PR, a uniform necrosis depth was measured histopathologically as d(mnec). A logarithmic correlation between d(mnec) and FA was confirmed with R(2) = 0.69-0.80 and a d(mnec) range of 0.2-7.1 mm. The defined FA might be useful for predicting d nec for the extracellular PR in myocardium when using talaporfin sodium.

Cellular and vascular effects of the photodynamic agent temocene are modulated by the delivery vehicle

The effects of the drug delivery system on the PDT activity, localization, and tumor accumulation of the novel photosensitizer temocene (the porphycene analogue of temoporfin or m-tetrahydroxyphenyl chlorin) were investigated against the P815 tumor, both in vitro and in DBA/2 tumor bearing mice. Temocene was administered either free (dissolved in PEG400/EtOH mixture), or encapsulated in Cremophor EL micelles or in DPPC/DMPG liposomes, chosen as model delivery vehicles. The maximum cell accumulation and photodynamic activity in vitro was achieved with the free photosensitizer, while temocene in Cremophor micelles hardly entered the cells. Notwithstanding, the micellar formulation showed the best in vivo response when used in a vascular regimen (short drug light interval), whereas liposomes were found to be an efficient drug delivery system for a tumor cell targeting strategy (long drug–light interval). PEG/EtOH formulation was discarded for further in vivo experiments as it provoked lethal toxic effects caused by photosensitizer aggregation. These results demonstrate that drug delivery systems modulate the vascular and cellular outcomes of photodynamic treatments with temocene.

Photodynamic therapy for prostate cancer-an emerging approach for organ-confined disease

Since the first report of the use of photodynamic therapy (PDT) for prostate cancer in 1990 it has been investigated as a primary and a salvage treatment, using either whole gland or focal approaches. Since 1990 advances in the transperineal approach to the prostate, coupled with photosensitizers which have a short drug-light interval and minimal skin phototoxicity, have resulted in major advances in the field. This review will look at the work done to date, and the ongoing studies which help to define the place of PDT as a useful treatment modality for organ-confined prostate cancer.

Mechanism of cell death mediated by a BF2‐chelated tetraaryl‐azadipyrromethene photodynamic therapeutic: Dissection of the apoptotic pathway in vitro and in vivo

Photodynamic therapy (PDT) is an established treatment modality for cancer. ADPM06 is an emerging non-porphyrin PDT agent which has been specifically designed for therapeutic application. Recently, we have demonstrated that ADPM06-PDT is well tolerated in vivo and elicits impressive complete response rates in various models of cancer when a short drug-light interval is applied. Herein, the mechanism of action of ADPM06-PDT in vitro and in vivo is outlined. Using a drug and light combination that reduces the clonogenicity of MDA-MB-231 cells by >90%, we detected a well-orchestrated apoptotic response accompanied by the activation of various caspases in vitro. The generation of reactive oxygen species (ROS) upon photosensitizer irradiation was found to be the key instigator in the observed apoptotic response, with the endoplasmic reticulum (ER) found to be the intracellular site of initial PDT damage, as determined by induction of a rapid ER stress response post-PDT. PDT-induced apoptosis was also found to be independent of p53 tumor suppressor status. A robust therapeutic response in vivo was demonstrated, with a substantial reduction in tumor proliferation observed, as well as a rapid induction of apoptosis and initiation of ER stress, mirroring numerous aspects of the mechanism of action of ADPM06 in vitro. Finally, using a combination of (18) F-labeled 3'-deoxy-3'-fluorothymidine ((18) F-FLT) nuclear and optical imaging, a considerable decrease in tumor proliferation over 24-hr in two models of human cancer was observed. Taken together, this data clearly establishes ADPM06 as an exciting novel PDT agent with significant potential for further translational development.

Increasing Damage to Tumor Blood Vessels during Motexafin Lutetium-PDT through Use of Low Fluence Rate

Photodynamic therapy (PDT) with low light fluence rate has rarely been studied in protocols that use short drug-light intervals and thus deliver illumination while plasma concentrations of photosensitizer are high, creating a prominent vascular response. In this study, the effects of light fluence rate on PDT response were investigated using motexafin lutetium (10 mg/kg) in combination with 730 nm light and a 180-min drug-light interval. At 180 min, the plasma level of photosensitizer was 5.7 ng/microl compared to 3.1 ng/mg in RIF tumor, and PDT-mediated vascular effects were confirmed by a spasmodic decrease in blood flow during illumination. Light delivery at 25 mW/cm(2) significantly improved long-term tumor responses over that at 75 mW/cm(2). This effect could not be attributed to oxygen conservation at low fluence rate, because 25 mW/cm(2) PDT provided little benefit to tumor hemoglobin oxygen saturation. However, 25 mW/cm(2) PDT did prolong the duration of ischemic insult during illumination and was correspondingly associated with greater decreases in perfusion immediately after PDT, followed by smaller increases in total hemoglobin concentration in the hours after PDT. Increases in blood volume suggest blood pooling from suboptimal vascular damage; thus the smaller increases after 25 mW/cm(2) PDT provide evidence of more widespread vascular damage, which was accompanied by greater decreases in clonogenic survival. Further study of low fluence rate as a means to improve responses to PDT under conditions designed to predominantly damage vasculature is warranted.

Intratumor Administration of the Photosensitizer Pc 4 Affords Photodynamic Therapy Efficacy and Selectivity at Short Drug-Light Intervals

We evaluated intratumor (IT) versus intravenous (IV) administration of the photosensitizer Pc 4 with respect to tumor photosensitizer concentration, specificity, and responses to irradiation. BALB/c mice bearing intradermal EMT6 tumors were given 0.3 mg/kg Pc 4 injected IT or IV through the tail vein. Photosensitizer concentration was evaluated by chloroform extraction and localization assessed by fluorescence imaging and spectroscopy in vivo. Tumors were irradiated at 667 nm, 50 mW/cm2, and 100 J/cm2. Cures were defined as no palpable tumor 90 days after irradiation. Tumor Pc 4 concentrations 1 hour after IT administration were 35,000-fold higher than measured 24 hours after IV administration (0.112 vs 0.317 x 10-5µg Pc 4/mg tumor). Exquisite tumor selectivity was observed 1 hour after IT injection. Fluorescence imaging of freshly sectioned tumors revealed no regions devoid of sensitizer at this time point, with pixel intensities in a midline section within a factor of 3 of the peak intensity. For identical photosensitizer doses, IT administration significantly improved tumor responses to irradiation, with more than 70% of tumors cured with IT-Pc 4-PDT. In this model, IT-Pc 4 administration provides improved tumor control, greater selectivity, and opportunity for a short drug-light interval.

Effect of drug–light interval on the mode of action of Photofrin photodynamic therapy in a mouse tumor model

Our objective was to examine the effect of time intervals between Photofrin injection and laser irradiation [i.e., drug-light interval (DLI)] on the mode of action of Photofrin photodynamic therapy (PDT). Kunming mice transplanted with sarcoma-180 cells were used as an animal model. The tumor-bearing mice in the control group were given neither photosensitizer nor laser irradiation. PDT groups were given intravenous (i.v.) injection of Photofrin (7.5 mg/kg) prior to being irradiated with a 630 nm laser at 120 J/cm(2) at different DLIs (1 min-48 h). Tumors and overlying skin were visually examined daily. Histopathological and electron microscopic examinations were carried out 48 h after PDT. Survival rates were recorded. The mice in the groups that had experienced short DLIs (<60 min) showed stronger skin reactions than the groups subjected to long DLIs (>6 h). Histological examination showed that antitumor effects were achieved mainly by the destruction of tumor blood vessels and the formation of thrombosis at short DLIs, whereas, at long DLIs, the tumor cells were killed directly by PDT-mediated cytotoxicity. Electron microscopy revealed various degrees of mitochondrial swelling. The survival rate of the mice subjected to long DLIs was slightly higher than that of the mice subjected to short DLIs. Both vascular (e.g., tumor vessel destruction) and cellular (e.g., cytotoxicity) effects contributed to Photofrin PDT-induced tumor ablation.

Molecular profiling of angiogenesis in hypericin mediated photodynamic therapy

BackgroundPhotodynamic therapy (PDT) involves the administration of a tumor-localizing photosensitizing drug, which is activated by light of specific wavelength in the presence of molecular oxygen thus generating reactive oxygen species that is toxic to the tumor cells. PDT selectively destroys photosensitized tissue leading to various cellular and molecular responses. The present study was designed to examine the angiogenic responses at short (0.5 h) and long (6 h) drug light interval (DLI) hypericin-PDT (HY-PDT) treatment at 24 h and 30 days post treatment in a human bladder carcinoma xenograft model. As short DLI targets tumor vasculature and longer DLI induces greater cellular damage, we hypothesized a differential effect of these treatments on the expression of angiogenic factors.ResultsImmunohistochemistry (IHC) results showed minimal CD31 stained endothelium at 24 h post short DLI PDT indicating extensive vascular damage. Angiogenic proteins such as vascular endothelial growth factor (VEGF), tumor necrosis growth factor-α (TNF-α), interferon-α (IFN-α) and basic fibroblast growth factor (bFGF) were expressed to a greater extent in cellular targeting long DLI PDT compared to vascular mediated short DLI PDT. Gene expression profiling for angiogenesis pathway demonstrated downregulation of adhesion molecules – cadherin 5, collagen alpha 1 and 3 at 24 h post treatment. Hepatocyte growth factor (HGF) and Ephrin-A3 (EFNA3) were upregulated in all treatment groups suggesting a possible activation of c-Met and Ephrin-Eph signaling pathways.ConclusionIn conclusion, long DLI HY-PDT induces upregulation of angiogenic proteins. Differential expression of genes involved in the angiogenesis pathway was observed in the various groups treated with HY-PDT.

Photodynamic Therapy Using Verteporfin Photosensitization in the Pancreas and Surrounding Tissues in the Syrian Golden Hamster

Background/Aim: Photodynamic therapy (PDT) is a potential treatment for locally advanced pancreatic cancer. We aimed to assess the safety of interstitial PDT using verteporfin (benzoporphyrin derivative monoacid A – a novel photosensitizer with a short drug-light interval and limited cutaneous photosensitivity) in the Syrian golden hamster, and compare it to meso-tetrahydroxyphenylchlorin (mTHPC) which we have previously evaluated in preclinical and clinical studies. Methods: Verteporfin (2 mg/kg) was administered at laparotomy by inferior vena caval injection (n = 57), with plasma levels quantified at 5, 15, 30, 60 and 240 min, and 24 h. 15 min after photosensitization, tissues (liver, pancreas, duodenum, colon, aorta) were illuminated with 690 nm red laser light (150 mW), at a range of light doses (1–100 J/cm²). The PDT effects on the targeted organ and adjacent structures were assessed at post-mortem on days 3 and 21, or at the time of death. Results: The elimination half-life of verteporfin was 4–5 h. Light doses of 10, 25 and 50 J/cm² were safe in the hamster pancreas, liver and colon, respectively, and produced coagulative necrotic lesions of 3 (range 3–4), 10 (9–10) and 7 (7–8) mm diameter. Collagen was resistant to damage and lesions healed mainly by regeneration of normal tissue. At higher light doses, necrosis extended to the edge of organs, sometimes causing sealed duodenal perforations as seen with mTHPC. Conclusion: The safety profile of verteporfin is very similar to mTHPC, with the advantages of a shorter drug-light interval and drug elimination time. Phase I clinical studies using this photosensitizer in pancreatic cancer should be feasible.

VASCULAR-TARGETED PHOTODYNAMIC THERAPY IN ORGAN CONFINED PROSTATE CANCER -REPORT OF A NOVEL PHOTOSENSITISER

Introduction & Objectives Photodynamic Therapy (PDT) uses a photosensitising drug, activated by single wavelength light from a laser to cause localised necrosis. Tookad is a vascular acting photosensitiser which is activated by 763 nm light. It has a short drug light interval, so that both drug and light are given in a single session. Due to rapid clearance, it has no skin phototoxicity after 3 hours. Vascular-Targeted Photodynamic therapy (VTP) with Tookad (WST09) has been evaluated in patients with post-radiotherapy prostate cancer recurrence. Here we report the use of Tookad VTP in the previously untreated prostate. The effect of different light doses with a constant drug dose was evaluated using gadolinium-enhanced MRI at 1 week. Material & Methods Under general anaesthetic, using transrectal ultrasound guidance and a perineal template, two hollow, clear plastic needles were inserted into each of the right and left lobes of the prostate. On each side, the needles held one optical delivery fibre, and one optical detection fibre. Optical detectors were also placed within catheters in the urethra and rectum to monitor light levels throughout the light delivery phase. Once needle positions were finalised, an infusion of 2 mg/kg Tookad was given over 20 minutes. After the infusion began, the light dose was given. The light dose was escalated throughout the study, with a minimum of 50 J/cm, and a maximum of 300 J/cm at a power of either 150 or 200 mW. The active length of the diffuser was chosen to leave a 5 mm margin at the base and apex of the prostate. A dynamic gadolinium-enhanced MRI was performed prior to and 1 week after the VTP procedure. PSA was measured prior to and at 1, 3 and 6 months after VTP. Results Eleven men have undergone the Tookad VTP procedure and 1 week MRI to date. Prostate tissue necrosis, seen as absence of uptake of gadolinium, was observed in men receiving a light dose of 150 J/cm or more. The volume of necrosis varied with the light dose per cm, and the total light dose, but all patients had a PSA reduction at 1 or 3 months. All patients had a successful catheter removal the day after Tookad VTP, with four experiencing transient irritative urinary symptoms. Nine patients had a transient elevation of gamma GT and transaminases which resolved spontaneously within two weeks. Conclusions The Tookad VTP procedure is a promising minimally invasive treatment for prostate cancer. It can cause necrosis, as shown by lack of uptake of gadolinium on dynamic MRI at 1 week. This is accompanied by a PSA reduction. The procedure itself is safe and well tolerated. The study will continue using multiple optical fibres in each lobe.

Clinical Pharmacokinetics of Anti-angiogenic Photodynamic Therapy with Benzoporphyrin Derivative Monoacid Ring-A in Dogs Having Naturally Occurring Neoplasms

The aim of this study was to examine the pharmacokinetics of clinically applied benzoporphyrin derivative monoacid ring-A (BPD-MA; Verteporfin), a second-generation photosensitizer, during a trial of photodynamic therapy (PDT) in nine dogs having naturally occurring neoplasms. After injecting BPD-MA at 0.5 mg/kg intravenously, its mean half-life (t1/2) was found to be 8.14 +/- 5.34 h, mean clearance (Cl) 35.13 +/- 9.62 ml/(h kg), the mean value of the volume of distribution (Vc) 0.08 +/- 0.01 l/kg and the mean steady state volume of distribution (Vss) 0.38 +/- 0.31 l/kg respectively. With the exception of a transitional increase in serum alkaline phosphatase activity, no other clinical abnormalities were observed. The t1/2 in dogs with naturally occurring tumours was longer than that in humans, but similar to that in rats. The values of Cl and Vss in dogs having naturally occurring neoplasms were lower than those in humans. It is suggested that the pharmacokinetics of BPD-MA in tumour-bearing dogs would be helpful in determining the protocol of a short drug-light interval PDT with BPD-MA that mainly targets the tumour vasculature.

A green fluorescent protein-expressing murine tumour but not its wild-type counterpart is cured by photodynamic therapy

The ideal cancer treatment should both destroy the primary tumour and at the same time educate the immune system to recognise the tumour as foreign so that distant metastases will also be eradicated. Photodynamic therapy (PDT) involves the i.v. administration of photosensitisers followed by illumination of the tumour with red light producing reactive oxygen species that eventually cause vascular shutdown and tumour cell death by apoptosis and necrosis. Anti-tumour immunity is stimulated after PDT due to the acute inflammatory response, generation of tumour-specific antigens, and induction of heat-shock proteins. Green fluorescent protein (GFP) is used as an optical reporter to noninvasively image the progression of mouse tumours, and in addition, may act as a foreign (jellyfish) antigen. We asked whether GFP-expressing tumours could be used to monitor the response of tumour-bearing mice to PDT, and whether the tumour response differed when a nonimmunogenic tumour cell line was transduced with GFP. We injected RIF-1 or RIF-1 EGFP (stably transduced with a retroviral vector) cells in the leg of C3H/HeN mice and both the cells and tumour grew equally well. We used PDT with benzoporphyrin derivative and a short drug-light interval. There were complete cures and 100% mouse survival of RIF-1 EGFP while RIF-1 wild-type tumours all recurred. Cured mice were resistant to rechallenge with RIF-1 EGFP cells and a rechallenge with wild-type RIF-1 cells grew significantly slower. There was also slower RIF-1 EGFP rechallenge growth but no rejection when RIF-1 EGFP tumours were surgically removed. There was a low rate of PDT cure of tumours when RIF-1 cells were transduced with an empty retroviral vector. The presence of antibodies against EGFP in mouse serum suggests EGFP can act as a foreign antigen and PDT can then stimulate a long-term memory immune response.

Photodynamic therapy with WST09 (Tookad): Quantitative studies in normal colon and transplanted tumours

Photodynamic therapy (PDT) is attracting increasing interest for the safe destruction of localised tumours in a range of organs. However, most photosensitising drugs require a delay of hours to days between drug administration and light activation with skin photosensitivity that may last for weeks. WST09 (Tookad) is a new faster acting photosensitiser that clears within a few hours. In normal rat colon, after sensitisation with an intravenous bolus of WST09, light was delivered to a single point on the mucosa and the extent of PDT necrosis measured 3 days later. The lesion diameter was greatest with the highest dose of drug and light and the shortest drug light interval (DLI), falling rapidly with a DLI more than 5 min. In tumours transplanted subcutaneously or into the colon, the extent of necrosis only started falling with a DLI greater than 15 min, suggesting a possible window for tumour selectivity. Histological changes 3 days after PDT were essentially the same as those seen with longer acting photosensitisers. The lesion dimensions were comparable to the largest ones seen with other photosensitisers under similar experimental conditions. We conclude that WST09 is a powerful photosensitiser that produces PDT effects similar to those seen with longer acting drugs, but with the major advantages of a short DLI and rapid clearance.

Doppler optical coherence tomography to monitor the effect of photodynamic therapy on tissue morphology and perfusion

We investigated the feasibility of using optical coherence tomography (OCT) for noninvasive real-time visualization of the vascular effects of photodynamic therapy (PDT) in normal and tumor tissue in mice. Perfusion control measurements were initially performed after administrating vaso-active drugs or clamping of the subcutaneous tumors. Subsequent measurements were made on tumor-bearing mice before and after PDT using the photosensitizer meta-tetrahydroxyphenylchlorin (mTHPC). Tumors were illuminated using either a short drug light interval (D-L, 3 h), when mTHPC is primarily located in the tumor vasculature or a long D-L interval (48 h), when the drug is distributed throughout the whole tumor. OCT enabled visualization of the different layers of tumor, and overlying skin with a maximal penetration of < or =0.5-1 mm. PDT with a short D-L interval resulted in a significant decrease of perfusion in the tumor periphery, to 20% of pre-treatment values at 160 min, whereas perfusion in the skin initially increased by 10% (at 25 min) and subsequently decreased to 60% of pre-treatment values (at 200 min). PDT with a long D-L interval did not induce significant changes in perfusion. The concept of using noninvasive OCT measurements for monitoring early, treatment-related changes in morphology and perfusion may have applications in evaluating effects of anti-angiogenic or antivascular (cancer) therapy.

Perylenequinones in Photodynamic Therapy: Cellular versus Vascular Response

Photodynamic therapy (PDT) is a promising new modality in the treatment of cancers, which employs the interaction between a tumor-localizing photosensitizer and light of an appropriate wavelength to bring about molecular oxygen-induced cell death. We have investigated the efficacy of photosensitizers from the family perylenequinone, namely Hypericin, Hypocrellin A and B, in the treatment of cancer. These photosensitizers are known as potent second generation natural photosensitizers that have phototherapeutic advantages over the presently used porphyrins. We have studied the in vitro signaling mechanism involved in the photodynamic action following PDT in various human carcinoma cell lines. The difference of tumor cell death between two modes of action i.e., vascular- and cellular-mediated cell death, were evaluated in order to compare treatments that can efficaciously eradicate tumor in xenografts model. The antivascular effect of PDT was demonstrated in the chick chorioallantoic membrane (CAM) model. Tumor therapy based on targeting the vasculature of the tumor is indeed promising as demonstrated in the higher relative regression percentage of treated tumor compared to cellular targeted PDT. The favorable tumor response derived from short drug-light interval mediated PDT was primarily based on the differential uptake of the photosensitizer into tumor-associated vasculature as opposed to the cellular compartments of the tumor.