Photodynamic therapy: a review

Photodynamic therapy for Barrett's esophagus with high-grade dysplasia: a cost-effectiveness analysis

OBJECTIVES

To assess the cost-effectiveness of photodynamic therapy (PDT) and esophagectomy (ESO) relative to surveillance (SURV) for patients with Barrett's esophagus (BE) and high-grade dysplasia (HGD).

METHODS

A Markov decision tree was constructed to estimate costs and health outcomes of PDT, ESO and SURV in a hypothetical cohort of male patients, 50 years of age, with BE and HGD. Outcomes included unadjusted life-years (LYs) and quality-adjusted LYs (QALYs). Direct medical costs (2003 CDN$) were measured from the perspective of a provincial ministry of health. The time horizon for the model was five years (cycle length three months), and costs and outcomes were discounted at 3%. Model parameters were assigned unique distributions, and a probabilistic analysis with 10,000 Monte Carlo simulations was performed.

RESULTS

SURV was the least costly strategy, followed by PDT and ESO, but SURV was also the least effective. In terms of LYs, the incremental cost-effectiveness ratios were 814 dollars/LY for PDT versus SURV and 3,397 dollars/LY for ESO versus PDT. PDT dominated ESO for QALYs in the base-case. The incremental cost-effectiveness ratio of PDT versus SURV was 879 dollars/QALY. In probabilistic analysis, PDT was most likely to be cost-effective at willingness-to-pay (WTP) values between 100 dollars/LY and 3,500 dollars/LY, and ESO was most likely to be cost-effective for WTP values over 3500 dollars/LY. For quality-adjusted survival, PDT was most likely to be cost-effective for all WTP thresholds above 1,000 dollars/QALY. The likelihood that PDT was the most cost-effective strategy reached 0.99 at a WTP ceiling of 25,000 dollars/QALY.

CONCLUSIONS

In male patients with BE and HGD, PDT and ESO are cost-effective alternatives to SURV.

Novel flexible light diffuser and irradiation properties for photodynamic therapy

Many current light diffusers for photodynamic therapy are inflexible, and the applied light dose is difficult to adjust during treatment, especially on complex body surfaces. A thin and flexible luminous textile is developed using plastic optical fibers as a light distributor. The textile diffuser is evaluated for flexibility, irradiance, brightness distribution, and temperature rise with a 652-nm laser set to 100 mW. The bending force of the textile diffuser resembles a defined optical film. On the textile surface, an average output power of 3.6+/-0.6 mWcm(2) is measured, corresponding to a transmission rate of 40+/-3.8% on an area of 11 cm(2). Aluminum backing enhances the irradiance to the face (treatment side). The measured brightness distribution seems to lie within a range similar to other photodynamic therapy (PDT) devices. A power setting of 100 mW increases the temperature of the textile diffuser surface of up to 27 degrees C, and 1 W raises the temperature above 40 degrees C. Results confirm that the flexible textile diffuser supplies suitable radiation for low fluence rate photodynamic therapy on an area of several cm(2).

Photodynamic therapy for pancreatic cancer

OBJECTIVES

This study examined the status of photodynamic therapy (PDT) in the treatment of cancers of the pancreas.

METHODS

Original and review articles, editorials, and case reports published primarily in English and listed in Medline/ISI up to October 2006 or identified by a manual search have been reviewed in an attempt to provide a comprehensive overview of the mechanisms of PDT action and clinical application of PDT in the treatment of pancreatic cancers.

RESULTS

Photodynamic therapy represents a novel treatment of pancreatic malignancy; it produces local necrosis of tissue with light after administration of a photosensitizing agent. Evidences from in vivo and in vitro results have shown that PDT significantly decreases pancreatic cancer cell growth, destroys pancreatic carcinoma, and prolongs the survival of patients with unresectable pancreatic malignancy, and also show that PDT has disadvantages and limitations for the treatment of pancreatic cancer.

CONCLUSIONS

Photodynamic therapy can be an effective treatment of patients with pancreatic cancer, but more extensive preclinical and clinical trials are needed for further improvement in the clinical application of PDT, especially in avoidance of complications during PDT.

Receptor-mediated DNA-targeted photoimmunotherapy

We show the efficacy of a therapeutic strategy that combines the potency of a DNA-binding photosensitizer, UV(A)Sens, with the tumor-targeting potential of receptor-mediated endocytosis. The photosensitizer is an iodinated bibenzimidazole, which, when bound in the minor groove of DNA and excited by UV(A) irradiation, induces cytotoxic lesions attributed to a radical species resulting from photodehalogenation. Although reminiscent of photochemotherapy using psoralens and UV(A) irradiation, an established treatment modality in dermatology particularly for the treatment of psoriasis and cutaneous T-cell lymphoma, a critical difference is the extreme photopotency of the iodinated bibenzimidazole, approximately 1,000-fold that of psoralens. This feature prompted consideration of combination with the specificity of receptor-mediated targeting. Using two in vitro model systems, we show the UV(A) cytotoxicity of iodo ligand/protein conjugates, implying binding of the conjugate to cell receptors, internalization, and degradation of the conjugate-receptor complex, with release and translocation of the ligand to nuclear DNA. For ligand-transferrin conjugates, phototoxicity was inhibited by coincubation with excess native transferrin. Receptor-mediated UV(A)-induced cytotoxicity was also shown with the iodo ligand conjugate of an anti-human epidermal growth factor receptor monoclonal antibody, exemplifying the potential application of the strategy to other cancer-specific targets to thus improve the specificity of phototherapy of superficial lesions and for extracorporeal treatments.

Review of photodynamic therapy

INTRODUCTION

Photodynamic Therapy (PDT) is an emerging treatment for a variety of conditions including ocular and extra ocular diseases. The porphyrins have been used extensively, as dyes, which are laser-activated to achieve desired clinical effects. Commonly used agents are verteporfin and porfimer sodium.

METHODS

We performed a literature search of the PubMed database using the medical search headings: photodynamic therapy, photosensitizer verteporfin, visudyne, porfimer sodium and photofrin. We also performed a manual search using references from these articles, review articles and manufacturers' product monographs.

RESULTS

Verteporfin and porfimer sodium are commonly used photosensitizing agents with their wide applications in different fields of medicine. Both have well established safety profiles. They are most commonly used in wet age-related macular degeneration, gastrointestinal diseases and bronchial cancers.

CONCLUSION

PDT is a well established treatment entity in ophthalmology and other medical fields. In ophthalmology, it has rekindled interest and hopes in the common yet sight-threatening problem of age-related macular degeneration (AMD). This problem is still considered to be a serious issue as far as management is concerned. However in selective cases of AMD, it has shown success in restoring sight, especially in the 'classic' form of the disease. PDT is also being used to treat a range of solid cancers and non malignant conditions

Pretreatment photosensitizer dosimetry reduces variation in tumor response

PURPOSE

To compensate for photosensitizer uptake variation in photodynamic therapy (PDT), via control of delivered light dose through photodynamic dose calculation based on online dosimetry of photosensitizer in tissue before treatment.

METHODS AND MATERIALS

Photosensitizer verteporfin was quantified via multiple fluorescence microprobe measurements immediately before treatment. To compensate individual PDT treatments, photodynamic doses were calculated on an individual animal basis, by matching the light delivered to provide an equal photosensitizer dose multiplied by light dose. This was completed for the lower quartile, median, and upper quartile of the photosensitizer distribution. PDT-induced tumor responses were evaluated by the tumor regrowth assay.

RESULTS

Verteporfin uptake varied considerably among tumors and within a tumor. The coefficient of variation in the surviving fraction was found significantly decreased in groups compensated to the lower quartile (CL-PDT), the median (CM-PDT), and the upper quartile (CU-PDT) of photosensitizer distribution. The CL-PDT group was significantly less effective compared with NC-PDT (Noncompensated PDT), CM-PDT, and CU-PDT treatments. No significant difference in effectiveness was observed between NC-PDT, CM-PDT, and CU-PDT treatment groups.

CONCLUSIONS

This research suggests that accurate quantification of tissue photosensitizer levels and subsequent adjustment of light dose will allow for reduced subject variation and improved treatment consistency.

Sensitivity of Candida albicans germ tubes and biofilms to photofrin-mediated phototoxicity

Treatment of mucocutaneous and cutaneous Candida albicans infections with photosensitizing agents and light, termed photodynamic therapy (PDT), offers an alternative to conventional treatments. Initial studies using the clinically approved photosensitizer Photofrin demonstrated the susceptibility of C. albicans to its photodynamic effects. In the present study, we have further refined parameters for Photofrin-mediated photodynamic action against C. albicans and examined whether mechanisms commonly used by microorganisms to subvert either antimicrobial oxidative defenses or antimicrobial therapy, including biofilm formation, were operative. In buffer and defined medium, germ tubes preloaded with Photofrin retained their photosensitivity for up to 2 hours, indicating the absence of degradation or export of Photofrin by the organism. The addition of serum resulted in a gradual loss of photosensitivity over 2 hours. In contrast to an adaptive response by germ tubes to oxidative stress by hydrogen peroxide, there was no adaptive response to singlet oxygen-mediated stress by photodynamic action. C. albicans biofilms were sensitive to Photofrin-mediated phototoxicity in a dose-dependent manner. Finally, the metabolic activity of C. albicans biofilms following photodynamic insult was significantly lower than that of biofilms treated with amphotericin B for the same time period. These results demonstrate that several of the mechanisms microorganisms use to subvert either antimicrobial oxidative defenses or antimicrobial therapy are apparently not operative during Photofrin-mediated photodynamic treatment of C. albicans. These observations provide support and rationale for the continued investigation of PDT as an adjunctive, or possibly alternative, mode of therapy against cutaneous and mucocutaneous candidiasis.

MACULAR THICKNESS MAPPING IN EXUDATIVE AGE-RELATED MACULAR DEGENERATION

PURPOSE

To report the feasibility of retinal thickness mapping for evaluating thickness differences in retinal areas with and without leakage shown by fluorescein angiography for patients who have age-related macular degeneration with choroidal neovascularization.

METHODS

A custom-built version of the retinal thickness analyzer was used for thickness mapping. Retinal thickness was defined as the separation between vitreoretinal and pigment epithelium-choroid interfaces. Imaging was performed in 1 eye of 10 patients with the clinical diagnoses of age-related macular degeneration and choroidal neovascularization. Patients either had never undergone photodynamic therapy at the time of measurement (untreated) or had received one or more photodynamic therapy treatments (treated). Average retinal thicknesses in selected areas with and without the presence of leakage shown by fluorescein angiography were calculated and compared statistically.

RESULTS

Retinal thickness (mean +/- SD) in areas with leakage (315 +/- 54 microm) was significantly greater than that in areas without leakage (280 +/- 28 microm) (P = 0.03). In untreated patients, areas with leakage (345 +/- 45 microm) were significantly thicker than areas without leakage (289 +/- 23 microm) (P = 0.02). In treated patients, retinal thickness in areas with leakage (271 +/- 33 microm) and without leakage (267 +/- 34 microm) was similar.

CONCLUSION

Retinal thickness mapping may prove to be useful as an adjunct to fluorescein angiography to monitor choroidal neovascularization and its treatment.

Physical and chemical properties of pyropheophorbide-a methyl ester in ethanol, phosphate buffer and aqueous dispersion of small unilamellar dimyristoyl-l-α-phosphatidylcholine vesicles

The aggregation process of pyropheophorbide-a methyl ester (PPME), a second-generation photosensitizer, was investigated in various solvents. Absorption and fluorescence spectra showed that the photosensitizer was under a monomeric form in ethanol as well as in dimyristoyl-L-alpha-phosphatidylcholine liposomes while it was strongly aggregated in phosphate buffer. A quantitative determination of reactive oxygen species production by PPME in these solvents has been undertaken by electron spin resonance associated with spin trapping technique and absorption spectroscopy. In phosphate buffer, both electron spin resonance and absorption measurements led to the conclusion that singlet oxygen production was not detectable while hydroxyl radical production was very weak. In liposomes and ethanol, singlet oxygen and hydroxyl radical production increased highly; the singlet oxygen quantum yield was determined to be 0.2 in ethanol and 0.13 in liposomes. The hydroxyl radical production origin was also investigated. Singlet oxygen was formed from PPME triplet state deactivation in the presence of oxygen. Indeed, the triplet state formation quantum yield of PPME was found to be about 0.23 in ethanol, 0.15 in liposomes (too small to be measured in PBS).

Solubilization of poorly soluble PDT agent, meso-tetraphenylporphin, in plain or immunotargeted PEG-PE micelles results in dramatically improved cancer cell killing in vitro

Poorly soluble photodynamic therapy (PDT) agent, meso-tetratphenylporphine (TPP), was effectively solubilized using non-targeted and tumor-targeted polymeric micelles prepared of polyethylene glycol/phosphatidyl ethanolamine conjugate (PEG-PE). Encapsulation of TPP into PEG-PE-based micelles and immunomicelles (bearing an anti-cancer monoclonal 2C5 antibody) resulted in significantly improved anticancer effects of the drug at PDT conditions against murine (LLC, B16) and human (MCF-7, BT20) cancer cells in vitro. For this purpose, the cells were incubated for 6 or 18 h with the TPP or TPP-loaded PEG-PE micelles/immunomicelles and then light-irradiated for 30 min. The phototoxic effect depended on the TPP concentration and specific targeting by immunomicelles. An increased level of apoptosis was shown in the PDT-treated cultures. The attachment of the anti-cancer 2C5 antibodies to TPP-loaded micelles provided the maximum level of cell killing at a given time. The results of this study showed that TPP-containing PEG-PE micelles may represent a useful formulation of the photosensitizer for practical PDT.

Photodynamic damages induced by a monocationic porphyrin derivative in a human carcinoma cell line

The photokilling activity of 5-(4-trimethylammoniumphenyl)-10,15,20-tris(2,4,6-trimethoxyphenyl)porphyrin (CP) was evaluated on a Hep-2 human larynx-carcinoma cell line. Cell treatment was carried out with 5 microM CP incorporated into liposomal vesicles. Under violet-blue exciting light, the red fluorescence of CP was mainly detected as a filamentous pattern characteristic of mitochondrial localization. Similar pattern was also observed using rhodamine 123 in Hep-2 cells. No dark cytotoxicity was observed using 5 microM CP concentration and long incubation time (24 h). Using Hoechst-33258 and caspase-3 immunostaining methods, cell cultures treated for 24 h with CP and exposed to light for 7.5 min (27 J/cm2) showed a great amount of apoptotic cells (40%). In contrast, necrotic cells (58%) were observed using the same drug concentration but irradiated for 15 min (54 J/cm2). The results show that CP can induce different mechanisms of cell death depending on irradiation doses in the photodynamic treatments, which makes this agent an interesting sensitizer with potential application in photodynamic tumor therapy.

Endoscopic ablation of dysplastic Barrett's oesophagus comparing argon plasma coagulation and photodynamic therapy: a randomized prospective trial assessing efficacy and cost-effectiveness

OBJECTIVE

Endoscopic mucosal ablation is a promising technique that is used to treat dysplastic Barrett's oesophagus. The purpose of this study was to investigate the efficacy and cost-effectiveness of two promising techniques, argon plasma coagulation (APC) and photodynamic therapy (PDT), in the ablation of dysplastic Barrett's oesophagus.

MATERIALS AND METHODS

Twenty-six patients with dysplastic Barrett's oesophagus (21 M, median age 60 years, median length 4 cm, 23 low-grade dysplasia (LGD), 3 high-grade dysplasia (HGD)) were randomized to APC: 13 patients, PDT: 13 patients. APC was performed at a power setting of 65 W and argon gas flow at 1.8 l/min in 1-6 sessions (mean 5). PDT was performed 48 h after intravenous injection of Photofrin 2 mg/kg with a 630 nm red laser light, 200 J/cm through a PDT balloon in one session. All patients received treatment with high-dose proton pump inhibitors. Cost analysis was undertaken and the results were assessed by endoscopy and biopsies at 4 months and 12 months after therapy.

RESULTS

All patients in both groups showed a reduction in the length of Barrett's oesophagus. The median length of Barrett's oesophagus eradicated at the 4-month follow-up: APC 65%, PDT 57% and at the 12-month follow-up: APC 56%, PDT 60%. Dysplasia eradication at 4 months: APC 62%, PDT 77%, p = 0.03 (95% CI 0.66-0.96) and at 12 months APC 67%, PDT 77%. Buried columnar glands with intestinal metaplasia were seen in both groups, with one patient in the PDT arm developing adenocarcioma under the neo-squamous epithelium. Severe adverse events included APC 2/13 (15%) stricture, 1/13 (8%) odynophagia, chest pain and fever; PDT 2/13 (15%) photosensitivity, 2/13 (15%) stricture. PDT would cost an additional 266 pounds sterling for every percentage reduction in Barrett's length and 146 pounds sterling per percentage reduction in dysplasia compared with APC treatment.

CONCLUSIONS

APC and PDT are equally effective in eradicating Barrett's mucosa, with PDT being the more expensive treatment. However, PDT is more effective in eradicating dysplasia and the extra benefits of PDT are generated at an extra cost. The occurrence of buried columnar glands and carcinoma warrants caution. Long-term follow-up is needed to assess cancer prevention and the durability of the neo-squamous epithelium to justify these interventions.

Involvement of both endoplasmic reticulum and mitochondria in photokilling of nasopharyngeal carcinoma cells by the photosensitizer Zn-BC-AM

Photodynamic therapy (PDT) is recently developed as an effective treatment for malignant disease. In PDT, the photosensitizer eradicates tumour by induction of apoptosis. In this study, we investigated the mechanistic actions of a recently developed second generation photosensitizer, Zn-BC-AM, on nasopharyngeal carcinoma (NPC) cells. Zn-BC-AM was found to localize in the mitochondria, endoplasmic reticulum (ER), and golgi body. Photoactivation of Zn-BC-AM loaded NPC cells resulted in a rapid collapse of mitochondrial membrane potential (Deltapsim) (15 min), followed by the release of cytochrome c (1 h), and activation of caspases-9 and -3 (4 h). Expression of ER chaperones Bip/Grp78 and Grp94, and ER resident lectin-like chaperone calnexin (CNX) was also enhanced in PDT-stressed NPC cells. Caspase-12, an important caspase involved in ER stress-induced apoptosis, was also activated. Inhibition of Ca2+ uptake into mitochondria by ruthenium red (RR) or loading the cells with EGTA-AM, an agent that buffers intracellular Ca2+ released from ER, resulted in a significant reduction of Zn-BC-AM PDT-induced cell death. These observations suggest that both ER and mitochondria are the subcellular targets of Zn-BC-AM. Effective activation of ER- and mitochondria-mediated apoptotic pathways is responsible for Zn-BC-AM PDT-induced NPC cell death.

Pharmacokinetic and phototherapeutic studies of monocationic methoxyphenylporphyrin derivative

BACKGROUND AND OBJETIVE

Photodynamic therapy, a novel treatment for cancer, works through photoactivation of a tumor-localized photosensitive drug, and localized through oxidative damage to kill cells and ablate tumors. Pharmacokinetic and phototherapeutic properties of a cationic porphyrin were assayed in a Balb/c mouse cancer model in order to evaluate its efficiency as photosensitizer.

METHODS

Biodistribution studies were carried out by intraperitoneal injection of 5mg/kg CP incorporated into a liposome solution. CP was recovered from serum and organs at various times after treatment. The serum biochemical parameters and histological studies were used to test hepatic and renal functionality. For phototherapeutic studies, the light source used was a slide projector (360J/cm(2)). The efficiency of CP was evaluated by following tumor growth curves for 10 days after PDT doses. Immunohistochemical detection was carried out to evaluate caspase-3 activation in CP-PDT-treated tumors.

RESULTS AND CONCLUSIONS

The photosensitizer distribution suggests that CP is mainly eliminated from the organism via the bile-gut pathway, and that neurotoxic and cutaneous photosensitivity effects are reduced or absent. The porphyrin distribution from bloodstream to tissue began at 24h of drug administration. CP did not affect the hepatic and renal functionality, as was demonstrated by the physiological parameters. PDT-treated tumors showed delay in growth rate as compared to untreated control mice. Biochemical studies showed that the efficient tumor regression is dependent on caspase-3 activity signaling response associated with apoptosis. The results obtained suggest that the porphyrin CP may be a promising candidate for further use in PDT treatments.

DNA binding and photocleavage in vitro by new dirhodium(II) dppz complexes: correlation to cytotoxicity and photocytotoxicity

Two new dirhodium(II) complexes possessing the intercalating dppz ligand (dppz = dipyrido[3,2-a:2',3'-c]phenazine), cis-[Rh(2)(mu-O(2)CCH(3))(2)(dppz)(eta(1)-O(2)CCH(3))(CH(3)OH)](+) (1) and cis-[Rh(2)(mu-O(2)CCH(3))(2)(dppz)(2)](2+) (2), were synthesized and characterized as potential agents for photochemotherapy. Various techniques show that 1 binds to DNA through intercalation, although some aggregation of the complex on the DNA surface is also present. In contrast, 2 does not intercalate between the DNA bases; however, strong hypochromic behavior is observed in the presence of DNA, which can be attributed to intermolecular pi-stacking of 2 enhanced by the polyanion. The apparent DNA binding constants determined using optical titrations are compared to those from dialysis experiments. Both complexes photocleave pUC18 plasmid in vitro under irradiation with visible light (lambda(irr) >or= 395 nm, 15 min), resulting in the nicked, circular form. Greater photocleavage is observed for 1 relative to 2, which may be due to the ability of 1 to intercalate between the DNA bases. The cytotoxicity toward human skin cells (Hs-27) measured as the concentration at which 50% cell death is recorded, LC(50), was found to be 135 +/- 8 microM for 2 in the dark (30 min), which is significantly lower than those of 1 (LC(50) = 27 +/- 2 microM) and Rh(2)(O(2)CCH(3))(4) (LC(50) = 15 +/- 2 microM). Irradiation of cell cultures containing 1 and Rh(2)(O(2)CCH(3))(4) with visible light (400-700 nm, 30 min) has little effect on their cytotoxicity, with LC(50) values of 21 +/- 3 and 13 +/- 2 microM, respectively. Interestingly, a 3.4-fold increase in the toxicity of 2 is observed when the cell cultures are irradiated (400-700 nm, 30 min), resulting in LC(50) = 39 +/- 1 microM. The greater toxicity of 1 compared to 2 in the dark may be related to the ability of the former compound to intercalate between the DNA bases. The lower cytotoxicity of 2, together with its significantly greater photocytotoxicity, makes this complex a potential agent for photodynamic therapy (PDT). These results suggest that intercalation or strong DNA binding may not be a desirable property of a potential PDT agent.

Photodynamic therapy of head and neck basal cell carcinoma according to different clinicopathologic features

BACKGROUND AND OBJECTIVES

We aimed to treat different pathologic types of basal cell carcinomas (BCCs) using photodynamic therapy (PDT).

STUDY DESIGN/MATERIALS AND METHODS

Thirty lesions in six patients underwent PDT. The photosensitizer used was Photoheme, a hematoporphyrin derivative IX. It was injected intravenously at the dose of 2-3.25 mg/kg. After 24 hours, the lesions were illuminated by laser light (lambda = 632 nm, light exposure dose = 100-200 J/cm2). Lesions were evaluated pre and post-operatively and at follow-up sessions (of up to 6 months).

RESULTS

After a single session of PDT, the average response rate in different histopathologic kinds of basal cell carcinoma (e.g., ulcerative, superficial, nodular, and pigmented forms) were 100%, 62%, 90%, and 14%, respectively. In patients who responded completely, the cosmetic results were excellent and there were no recurrence at 6th month of follow-up.

CONCLUSION

Although PDT seems to be an effective treatment modality for superficial, ulcerative, and nodular BCCs, it is not recommended for pigmented lesions.

Susceptibility of Candida species to photodynamic effects of photofrin

The in vitro susceptibility of pathogenic Candida species to the photodynamic effects of the clinically approved photosensitizing agent Photofrin was examined. Internalization of Photofrin by Candida was confirmed by confocal fluorescence microscopy, and the degree of uptake was dependent on incubation concentration. Uptake of Photofrin by Candida and subsequent sensitivity to irradiation was influenced by culture conditions. Photofrin uptake was poor in C. albicans blastoconidia grown in nutrient broth. However, conversion of blastoconidia to filamentous forms by incubation in defined tissue culture medium resulted in substantial Photofrin uptake. Under conditions where Photofrin was effectively taken up by Candida, irradiated organisms were damaged in a drug dose- and light-dependent manner. Uptake of Photofrin was not inhibited by azide, indicating that the mechanism of uptake was not dependent on energy provided via electron transport. Fungal damage induced by Photofrin-mediated photodynamic therapy (PDT) was determined by evaluation of metabolic activity after irradiation. A strain of C. glabrata took up Photofrin poorly and was resistant to killing after irradiation. In contrast, two different strains of C. albicans displayed comparable levels of sensitivity to PDT. Furthermore, a reference strain of C. krusei that is relatively resistant to fluconazole compared to C. albicans was equally sensitive to C. albicans at Photofrin concentrations of >/=3 microg/ml. The results indicate that photodynamic therapy may be a useful adjunct or alternative to current anti-Candida therapeutic modalities, particularly for superficial infections on surfaces amenable to illumination.

Photodynamic activity of monocationic and non-charged methoxyphenylporphyrin derivatives in homogeneous and biological media

A novel 5-[4-(trimethylammonium)phenyl]-10,15,20-tris(2,4,6-trimethoxyphenyl)porphyrin iodide (2) has been synthesized. A positive charge was incorporated at a peripheral position to increase the amphiphilic character of the structure. The photodynamic effect of the cationic porphyrin 2 was compared with that of non-charged 5-(4-aminophenyl)-10,15,20-tris(2,4,6-trimethoxyphenyl)porphyrin (1), both in a homogeneous medium bearing photooxidizable substrates and in vitro on the Hep-2 human larynx carcinoma cell line. Absorption and fluorescence spectroscopic studies in different media show that 2 is essentially unaggregated in solution, and also in human cells. The singlet molecular oxygen, O2(1delta(g)), production was evaluated using 9,10-dimethylanthracene in N,N-dimethylformamide, yielding phi(delta) values of approximately 0.66 for both porphyrins. The addition of beta-carotene suppresses the O2(1delta(g))-mediated photooxidation. L-Tryptophan and guanosine 5'-monophosphate were used as biological substrate models. Porphyrin 2 sensitizes the decomposition of both compounds faster than does 1. In the biological medium, no dark cytotoxicity was observed, even though a high porphyrin concentration (10 microM) and a long incubation time (24 h) were employed. Cell treatments were performed with 5 microM of porphyrin for 24 h. Under these conditions, the uptake of porphyrin 2 into Hep-2 was about 3 times higher than that of 1. Cell survival after irradiation with visible light was dependent upon both the light exposure level and intracellular sensitizer concentration. Thus, a higher photocytotoxic effect was found for porphyrin 2 in comparison to 1. These results show that the amphiphilic monocationic porphyrin 2 could be a promising model for phototherapeutic agents with potential applications in tumor cell inactivation by photodynamic therapy.

Topical methyl aminolevulinate

Methyl aminolevulinate (MAL), an ester of aminolevulinic acid, has been used effectively as a topical photosensitizing agent in the photodynamic therapy (PDT) of epidermal lesions such as actinic keratosis (AK) and basal cell carcinoma (BCC). The optimal regimen for MAL-PDT (as used in all clinical trials) is MAL 160 mg/g applied for 3 hours before illumination with red light (570-670 nm) at a total light dose of 75 J/cm(2), as determined in dose-finding trials. In randomized, multicenter, phase III clinical trials, treatment with MAL-PDT resulted in a complete response (i.e. complete disappearance) in up to 91% of AK lesions and up to 97% of BCC lesions. With regard to lesion response rates, MAL-PDT was superior to placebo-PDT (in AK or BCC), and at least as effective as cryotherapy (in AK or BCC) or excision surgery (in BCC). Cosmetic outcome with MAL-PDT was excellent to good in the vast majority of patients, and was judged by investigators to be better than with cryotherapy (in AK or BCC) or surgery (in BCC). black triangle Over 75% of BCC lesions treated with MAL-PDT, including difficult-to-treat BCC, were still in remission 12-24 months after the last treatment. MAL-PDT was generally well tolerated in clinical trials. The most frequently reported adverse events were local phototoxicity reactions, most of which were of mild to moderate intensity, resolved rapidly and were rarely treatment limiting.

Photodynamic therapy for peripheral lung cancer

Photodynamic therapy (PDT) has now achieved the status of a standard treatment modality for centrally located early-stage lung cancer. In the last decade, CT screening for lung cancer has attracted much attention for its ability to detect early peripheral lung cancer. Extremely recently, treatment using PDT has been introduced for the first time in patients with peripheral lung cancer, who did not meet the previous criteria for surgery. The procedure was carried out with local anesthesia with xylocain infiltrated into the chest wall, 48 h after Photofrin administration. Needles (19 gauge) containing an internal catheter were inserted percutaneously under CT guidance. The needles were then extracted and a diffuser fiber with a 2 cm long tip for light delivery was positioned in the tumor through the catheter. Of the nine patients enrolled in this trial, seven achieved partial remission (PR). No serious complications, except for two cases of pneumothorax, were noted. As an increasing number of patients consider quality of life after therapy, the indications for PDT are expected to expand. We conclude that PDT is a promising new technique for curative treatment of localized, peripheral lung cancer less than 1cm in size in patients who are unfit for surgery or radiotherapy.

Photodynamic therapy for human oral squamous cell carcinoma and xenografts using a new photosensitizer, PAD-S31

BACKGROUND AND OBJECTIVES

Photodynamic therapy (PDT) is a novel and promising cancer treatment that employs a combination of photosensitizer and visible light. We examined the effect of PDT using a new photosensitizer, PAD-S31, and the 670-nm diode laser in human oral squamous cell carcinomas (SCC).

STUDY DESIGN/MATERIALS AND METHODS

SAS and HSC-4 cell lines were used in all the experiments. Cell viability was determined by a modified MTT assay. Two methods were used for the determination of apoptosis in human oral SCC cells: TUNEL assay and detection of fragmented mono- and oligo-nucleosomes by ELISA. Xenografts of human oral SCC cells were generated in KSN S1c nude mice.

RESULTS

In vitro PDT using PAD-S31 and the 670-nm diode laser showed cytotoxicity that was a function of laser energy, drug concentration, and time to the SAS and HSC-4 cell lines. On the other hand, PAD-S31 without irradiation had no effect on cell viability. The combinated use of PAD-S31 and the laser irradiation showed excellent anti-tumor activity against tumor xenografts without severe side effects. PDT-mediated cell death occurred predominantly by apoptosis in vitro and in vivo.

CONCLUSIONS

The present study demonstrates that PAD-S31 may serve as a potent photosensitizer for PDT. Furthermore, it is expected that this therapy will be clinically useful for the treatment of patients with oral carcinoma.

Liposomal photofrin enhances therapeutic efficacy of photodynamic therapy against the human gastric cancer

Photodynamic therapy (PDT) has been established as a potent and less invasive treatment for gastrointestinal tumors. The aim of the present study was to investigate whether or not liposomalization of the photosensitizer enhanced the therapeutic efficacy of PDT. Photofrin (PF) was entrapped in multilammelar liposomes. Mice implanted with a human gastric cancer xenograft, were divided into a PF group and a liposomal photofrin (LPF) group and intravenously administered 10 mg/kg of PF or LPF (as a dose of PF), respectively. At 8 h after injection PF level in tumor tissue in the LPF group was significantly higher level by 2.4-fold of that in the PF group, whereas the PF levels in the skin were almost equal. Irradiation was performed with the excimer dye laser at 150 mW/cm(2), total dose 40 J, at 8 h after PF or LPF administration. The results revealed that the volume of necrotic tumor tissue was significantly higher in the LPF group than in the PF group. The apoptotic index of the tumor was also significantly higher in the LPF group. In conclusion, the liposomalization of the photosensitizer increased its tumor accumulation, with a resulting enhancement of the therapeutic effect of PDT.

Photodynamic toxicity and its prevention by antioxidative agents in Bufo arenarum embryos

In this work we describe an experimental model to evaluate the photodynamic toxicity on amphibian embryos, as well as the protective effect of antioxidants against the lethal oxidative stress induced by photosensitization. Bufo arenarum embryos were treated with 10 mg/l methylene blue (MB) in AMPHITOX solution for 72 h and then irradiated with a red laser or white light for variable times. Both light sources affected the survival of MB-treated animals and lethal effects occurred within the initial 12 h post-irradiation. For white light irradiation, the most effective phototoxic condition in our study, the LD10, 50 and 90 at 6 h post-irradiation corresponded to 13.57, 19.87 and 29.10 J/cm2, respectively. To explore the action of antioxidants against the photogenerated oxidative stress, MB-treated embryos were incubated with 1mM glutathione (GSH) or ascorbic acid (AA) during 48 h before irradiation. For GSH and 21.6 J/cm2 irradiation, the survival increased from 20 to 90%, whereas 100% survival was achieved with AA even after 43.2 J/cm2 irradiation. These results indicate that both the lethal photodynamic effect and its prevention by antioxidants can be evaluated by means of a simple toxicity test employing amphibian embryos.

Activation of the stress-activated JNK and p38 MAP kinases in human cells by Photofrin-mediated photodynamic therapy

We have examined the possible role of the stress-activated JNK and p38 protein kinases in cellular sensitivity following Photofrin-mediated photodynamic therapy (PDT). Previously we reported that immortalized Li-Fraumeni syndrome (LFS) cells are more resistant to Photofrin-mediated PDT compared to normal human fibroblasts (NHF) at equivalent cellular Photofrin levels. In the current work we report that Photofrin-mediated PDT increased the activity of JNK1 and p38 within 30 min in both cell types. However, the increased activity of JNK1 and p38 was transient in the sensitive NHF cells and returned back to near basal levels by 3 h after PDT. In contrast, the resistant LFS cells exhibited a more prolonged activation of JNK and p38, which lasted for at least 11 h and 7 h after PDT, respectively. Blocking of the p38 pathway in LFS cells by transient infection with a recombinant adenovirus expressing a dominant negative mutant of p38 or in HeLa cells by stable transfection with a dominant negative mutant of p38 had no effect on cell survival following PDT. These data suggest that although Photofrin-mediated PDT is able to induce JNK1 and p38 in human cells, the p38 pathway alone does not play a major role in the sensitivity of LFS cells to Photofrin-mediated PDT.

The Influence of Depleted Glutathione Levels on the Photodynamic Action of Zinc Phthalocyanine in CHO K1 Cells

OBJECTIVE

The current study focuses on any influence that depletion of endogenous glutathione in CHO K1 cells may have on the photodynamic action of zinc phthalocyanine (ZnPc).

MATERIALS AND METHODS

Two lasers--a HeNe laser, 632.5 nm, maximum power output 3.5 mW, and a Toshiba semiconducting laser, 670 nm, maximum power of 7 mW--were used. Chinese Hamster Ovary cells (CHO K1) were exposed to light, 2-10 J. Cellular reduced glutathione levels [GSH] were depressed prior to exposure to ZnPc and laser light, using buthionine sulphoximine, a potent inhibitor of gamma-glutamylcysteine synthetase. The influence of hypoxic intracellular conditions was studied by reduction of oxygen content of cells by 80% following purging of cell cultures with nitrogen.

RESULTS

In well-aerated cells, doubling times are reduced by the photodynamic action of ZnPc by 29 +/- 6%, fig 2 (p = 0.01). Cells with lowered [GSH] do not show this effect (p = 0.1). When hypoxic cells are studied at normal [GSH], no photodynamic effect is observed (p = 0.1). When cell viability is studied, using the 670-nm laser, a photodynamic effect is observed, (80% fall from controls, p < 0.001), irrespective of the cellular [GSH] level for a single dose of 6 J. This effect is observed in cells with normal [GSH], for varied doses of 2 J and higher (63% fall at 2 J, p < 0.001).

CONCLUSIONS

Lowered [GSH] was observed to depress the photodynamic effect of ZnPc when cell-doubling times were the endpoint. The photostimulating effect of ZnPc was similarly suppressed by hypoxic conditions. When cell viability was the endpoint, then a photodynamic effect of ZnPc was observed irrespective of the endogenous [GSH] values.

The physiology and pharmacology of singlet oxygen

Reactive oxygen species (ROS) are generated by many different cells. Singlet oxygen (1O(2)) and a reaction product of it, excited carbonyls (C=O*), are important ROS. 1O(2) and C=O* are nonradicalic and emit light (one photon/molecule) when returning to ground state oxygen. Especially activated polymorphonuclear neutrophil granulocytes (PMN) produce large amounts of 1O(2). Via activation of the respiratory burst (NADPH oxidase and myeloperoxidase) they synthesize hypochlorite (NaOCl) and chloramines (in particular N-chlorotaurine). Chloramines are selective and stable chemical generators of 1O(2). In the human organism, 1O(2) is both a signal and a weapon with therapeutic potency against very different pathogens, such as microbes, virus, cancer cells and thrombi. Chloramines at blood concentrations between 1 and 2 mmol/L inactivate lipid enveloped virus and chloramines at blood concentrations below 0.5 mmol/L, i.e. at oxidant concentrations that do not affect thrombocytes or hemostasis factors, act antithrombotically by activation of the physiologic PMN mediated fibrinolysis; this thrombolysis is of selective nature, i.e. it does not impair the hemostasis system of the patient allowing the antithrombotic treatment in patients where the current risky thrombolytic treatment is contraindicated. The action of 1O(2) might be compared to the signaling and destroying gunfire of soldiers directed against bandits at night, resulting in an autorecruitment of the physiological inflammatory response. Chloramines (such as the mild and untoxic oxidant chloramine T (N-chloro-p-toluene-sulfonamide)) and their signaling and destroying reaction product 1O(2) might be promising new therapeutic agents against a multitude of up to now refractory diseases.

COX-2 inhibitors for the prevention of breast cancer

The inducible prostaglandin synthase cyclooxygenase-2 (COX-2) is normally expressed predominantly in kidney and brain, and also has important roles in reproduction and inflammation. COX-2 misexpression has been observed in numerous human cancers, including the majority of colorectal cancers. Recently, COX-2 overexpression has been described in human breast cancer. COX-2 is present in about 40% of invasive breast carcinomas, particularly those that overexpress HER2/neu, and COX-2 expression correlates with poor patient prognosis. Manipulation of Cox-2 gene dosage by using transgenic overexpression and knockout approaches has revealed an important role for Cox-2 in tumorigenesis. Furthermore, translational experiments using rodent breast cancer models suggest COX-2 inhibition to be an effective strategy for both prevention and treatment of experimental breast cancers. Since COX-2 can contribute to multiple facets of tumorigenesis, including angiogenesis, several mechanisms are likely to underlie the anticancer action of COX inhibitors. Thus, selective COX-2 inhibitors offer considerable promise for the prevention and treatment of human breast cancer.

Photodynamic therapy with pyropheophorbide-a methyl ester in human lung carcinoma cancer cell: efficacy, localization and apoptosis

Pyropheophorbide-a methyl ester (MPPa) is a semisynthetic photosensitizer derived from chlorophyll a. The absorption peak of MPPa in organic solvent and in cells was at 667 and 674 nm, respectively. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay showed that MPPa had no dark cytotoxicity. In vitro photodynamic activity was extensively evaluated using a human lung carcinoma cancer cell line (NCI-h446). MPPa exhibited no genotoxicity, as assayed by single-cell gel electrophoresis. Using confocal laser scanning microscopy and organelle-specific fluorescent probes, MPPa was found to localize in the intracellular membrane system, namely the endoplasmic reticulum, Golgi apparatus, lysosomes and mitochondria, in the NCI-h446 cells. Furthermore, nuclear staining and DNA gel electrophoresis revealed that DNA condensation and fragmentation occurred post-photodynamic therapy, indicating the cell death was in the apoptotic mode.

Photodynamic therapy for companion animals with cancer

Photodynamic therapy is an emerging form of cancer therapy in veterinary medicine, which capitalizes on a photochemical reaction to kill malignant cells. Photodynamic therapy has been used to successfully treat a variety of veterinary cancers, with documented efficacy similar to radiation therapy. However, equipment expense and availability of photosensitizer have limited the widespread use of photodynamic therapy by veterinarians.

Protoporphyrin IX photodynamic therapy for synovitis

OBJECTIVE

To determine the conditions for synovial accumulation of protoporphyrin IX (PpIX) and photodynamic therapy (PDT)-induced synovial cytotoxicity in vitro and in vivo.

METHODS

Synovial tissues were obtained from mice with antigen-induced arthritis (AIA) and incubated with different concentrations of 5-aminolevulinic acid hexyl ester (h-ALA), a PpIX precursor. Following photoexcitation, cell death in synovial tissues was evaluated by Sytox green fluorescence. PDT was performed after intraarticular injection of h-ALA into the knee joints of mice with AIA, and its effect on joint inflammation was assessed by technetium scintigraphy and histology. Synovial biopsy samples were obtained from patients with osteoarthritis (OA; n = 9) and rheumatoid arthritis (RA; n = 7) and studied for PDT-induced cytotoxicity in vitro.

RESULTS

Conversion of h-ALA to PpIX was observed in inflamed synovium in mice and humans. Cytotoxicity was confirmed by Sytox green staining in samples subjected to PDT. In the AIA model, injection of affected knees with h-ALA prior to PDT led to a statistically significant reduction of joint damage in the irradiated joints. The preferential transformation of h-ALA to PpIX in inflammatory tissues was confirmed in human synovial biopsy tissues, where RA samples showed higher tissue concentrations of PpIX following incubation with h-ALA than did OA samples. Fluorescence microscopy showed that PpIX was localized to the synovial lining layer, endothelial cells, and macrophages and induced cell death after PDT.

CONCLUSION

Our findings suggest that PDT based on the accumulation of PpIX in the synovial membrane may be a rational basis for photodynamic synovectomy in arthritic diseases.

Genetic rescue of Leishmania deficiency in porphyrin biosynthesis creates mutants suitable for analysis of cellular events in uroporphyria and for photodynamic therapy

Leishmania was found deficient in at least five and most likely seven of the eight enzymes in the heme biosynthesis pathway, accounting for their growth requirement for heme compounds. The xenotransfection of this trypanosomatid protozoan led to their expression of the mammalian genes encoding delta-aminolevulinate (ALA) dehydratase and porphobilinogen deaminase, the second and the third enzymes of the pathway, respectively. These transfectants still require hemin or protoporphyrin IX for growth but produce porphyrin when ALA was supplied exogenously. Leishmania is thus deficient in all first three enzymes of the pathway. Uroporphyrin I was produced as the sole intermediate by these transfectants, further indicating that they are also deficient in at least two porphyrinogen-metabolizing enzymes downstream of porphobilinogen deaminase, i.e. uroporphyrinogen III co-synthase and uroporphyrinogen decarboxylase. Pulsing the transfectants with ALA induced their transition from aporphyria to uroporphyria. Uroporphyrin I emerged in these cells initially as diffused throughout the cytosol, rendering them sensitive to UV irradiation. The porphyrin was subsequently sequestered in cytoplasmic vacuoles followed by its release and accumulation in the extracellular milieu, concomitant with a reduced photosensitivity of the cells. These events may represent cellular mechanisms for disposing soluble toxic waste from the cytosol. Monocytic tumor cells were rendered photosensitive by infection with uroporphyric Leishmania, suggestive of their potential application for photodynamic therapy.

Photodynamic effects of mTHPC on human colon adenocarcinoma cells: photocytotoxicity, subcellular localization and apoptosis

The photodynamic properties of meta-tetra(hydroxyphenyl)chlorin (mTHPC), a promising second-generation photosensitizer, were investigated using a human colon adenocarcinoma cell line (Colo 201 cells). The study on photocytotoxicity using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay showed that mTHPC was an effective photosensitizer on Colo 201 cells. The photocytotoxicity of mTHPC showed both drug and light dose-dependent characteristics. To reach LD50, namely, the dose at which 50% of the cells were killed, only 0.45+/-0.15 microg/mL of mTHPC and 3 J/cm2 of light dose were required. The presence of 10% fetal calf serum in culture medium significantly decreased the incorporation of mTHPC into cells and resulted in the reduction of photodynamic efficacy. Using confocal laser scanning microscopy, mTHPC was first shown to localize in lysosomes rather than in mitochondria. Furthermore, nuclear stainings demonstrated that photodynamic therapy with mTHPC induced apoptosis in Colo 201 cells.

Platelet adhesion to photodynamic therapy-treated extracellular matrix proteins

Photodynamic therapy (PDT) produces reactive species that alter vascular wall biology and vessel wall proteins. In this study, we examined platelet adhesion to PDT-treated (photosensitizer = Photofrin; fluence 100 J/cm2; lambda = 630 nm) extracellular matrix (ECM), fibrinogen, von Willebrand factor (vWF) and collagen Types I and III, under flow conditions in a recirculating perfusion chamber. Platelet adhesion was quantified by image analysis. The effect of PDT on vWF was assessed by measuring the binding of domain-specific antibodies to treated vWF. PDT significantly decreased platelet adhesion to the ECM, fibrinogen and vWF. However, PDT of collagen resulted in significantly increased platelet adhesion, with large aggregate formation. PDT affected mostly the A1 (glycoprotein [GP]-Ib-binding site), A2 and A3 (collagen-binding site) domains of vWF but not the D'-D3 (factor VIII-binding site) and B-C1 (GP-IIb/IIIa-binding site) domains. In conclusion, PDT can alter the ECM, resulting in decreased platelet adhesion. However, vessels with high collagen content, such as veins and small arteries, may become increasingly prone to thrombosis. The results of this study may thus play a role in understanding the thrombogenic properties and mechanisms of vascular PDT.

Designing peptide-based scaffolds as drug delivery vehicles

Methods for delivering drugs into cells remain an important part of the process of designing drugs. One promising approach is the concept of loligomers, synthetic peptides composed of a branched polylysine core harboring identical arms. Loligomers are typically synthesized with eight arms, each carrying peptide signals guiding their import and localization into cells. The most important advantage of loligomers is the multivalent presentation of targeting signals resulting from a tentacular arrangement. Multivalency increases the efficiency of import and intracellular routing signals as compared to similar linear peptides. Secondly, it reduces and delays the impact of peptide degradation in terms of cellular processing and compartmentalization. The vectorial delivery of nucleus-directed loligomers into cells has recently been confirmed by microscopy and flow cytometry studies. Practical uses of loligomers as intracellular vehicles include the import of plasmid DNA into cells, the conjugation of chemical groups, such as photosensitizers for use in photodynamic therapy, and the incorporation of cytotoxic T-lymphocyte (CTL) epitopes with a view to creating synthetic vaccines. Branched peptides such as loligomers represent simple and versatile molecular vehicles with potential applications in a wide variety of drug design approaches.

Topical 5-aminolevulinic acid and photodynamic therapy in dermatology: a minireview

Photodynamic therapy (PDT) is a treatment modality using a photosensitizer, light and oxygen to cause photochemically induced selective cell death. When exposed to light with the proper wavelength, the topically applied photosensitizer or photosensitizer precursor can activate a biomolecule through electron transfer to yield free radicals or produce singlet oxygen from energy transferred from the excited sensitizer to molecular oxygen. The tissue damage is the result of the activation of reactive singlet oxygen or free radical production. Photodynamic therapy with topical application of 5-aminolevulinic acid (ALA) is a new technique and although it remains largely experimental, it has potential application for treatment of malignant skin tumors, various precancerous and selected benign skin diseases. This technique yields not only a high percentage of good therapeutic results but also excellent cosmetic outcome. This paper reviews the recently published data on clinical ALA-based PDT in dermatology.

Synthesis and biological evaluation of methoxyphenyl porphyrin derivatives as potential photodynamic agents

A new meso-2,4,6-trimethoxyphenyl porphyrin covalently linked to a 2',6'-dinitro-4'-trifluoromethylphenyl group by an amine bond 5 and its metal complex with Cd(II) 6 was prepared. The photodynamic activities of 5 and 6 were evaluated in vitro on Hep-2 cells. A considerable increase in the photocytotoxic effect was found for 6, which has higher singlet molecular oxygen, O(2)((1)Delta(g)), production.

Photodynamic studies of metallo 5,10,15,20-tetrakis(4-methoxyphenyl) porphyrin: photochemical characterization and biological consequences in a human carcinoma cell line

The photodynamic activities of the free-base 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (TMP) and their metal complexes with zinc(II) (ZnTMP), copper(II) (CuTMP) and cadmium(II) (CdTMP) have been compared in two systems: reverse micelle of n-heptane/sodium bis(2-ethylhexyl)sulfosuccinate/water bearing photooxidizable substrates and Hep-2 human larynx carcinoma cell line. The quantum yields of singlet molecular oxygen, O2(1 delta g), production (phi delta) of TMP, ZnTMP and CdTMP in tetrahydrofuran, were determined yielding values of 0.65, 0.73 and 0.73, respectively, while O2(1 delta g) formation was not detected for CuTMP. In the reverse micellar system, the amino acid L-tryptophan (Trp) was used as biological substrate to analyze the O2(1 delta g)-mediated photooxidation. The observed rate constants for Trp photooxidation (kobsTrp) were proportional to the sensitizer quantum yield of O2(1 delta g). A value of approximately 2 x 10(7) s-1 M-1 was found for the second-order rate constant of Trp (krTry) in this system. The response of Hep-2 cells to cytotoxicity photoinduced by these agents in a biological medium was studied. The Hep-2 cultures were treated with 1 microM of porphyrin for 24 h at 37 degrees C and the cells exposed to visible light. The cell survival at different light exposure levels was dependent on phi delta. Under these conditions, the cytotoxic effect increases in the order: Cu-TMP << TMP < ZnTMP approximately CdTMP, correlating with the production of O2(1 delta g). A similar behavior was observed in both the chemical and biological media indicating that the O2(1 delta g) mediation appears to be mainly responsible for the cell inactivation.

Photodynamic therapy and the alimentary tract

Photodynamic therapy offers the possibility of relatively selective tumour necrosis and normal tissue healing. It has many potential applications but as yet no clear role. Articles, editorials and case reports published primarily in English and listed in Medline/ISI up to April 2000 or identified by a manual search have been reviewed in an attempt to provide a comprehensive overview of the use of photodynamic therapy in the alimentary tract. It is concluded that photodynamic therapy can be an effective treatment for superficial pre-malignant mucosal lesions and early cancers, especially in diffuse disease. Suitable patients include those wishing to avoid surgery, high risk subjects or those in whom other forms of treatment have failed. Superiority over other methods of ablation has not so far been demonstrated. Cheaper and more effective photosensitizers and improved techniques of light delivery are likely to increase the application of photodynamic therapy.

Photodynamic activity of 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin on the Hep-2 human carcinoma cell line: effect of light dose and wavelength range

The photodynamic activity of 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (TMP) has been investigated in two systems: reverse micelles of n-heptane/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water-bearing photooxidizable substrates and on a Hep-2 human carcinoma cell line. The effect of variation in the light dose and wavelength range (360-800, 455-800, and 590-800 nm) was compared in both media. The aerobic singlet oxygen-mediated photooxidation of L-tryptophan (Trp) was used as a model of biological substrate in a micellar system. A considerable increase of the observed rate constants of Trp (k(Trp)(obs)) was noted, increasing the irradiated area of the TMP spectrum. In vitro, the survival curves of Hep-2 cells, treated with TMP, were markedly dependent on the light wavelength ranges used for irradiation. A linear behavior between k(Trp)(obs) and the photoinactivation rate of Hep-2 cells was found, indicating that the singlet oxygen (1O2 ) is the main species responsible for cell inactivation. These results contributed to an understanding of the photodynamic process yielded by this porphyrin in vitro and the sensitivity of Hep-2 cells to photodamage.

Even after UVA-exposure will nitric oxide protect cells from reactive oxygen intermediate-mediated apoptosis and necrosis

Reactive oxygen species (ROS) play a pivotal role in UVA-induced cell damage. As expression of the inducible nitric oxide synthase (iNOS) is a normal response of human skin to UV radiation we examined the role of nitric oxide (NO) as a protective agent during or even after UVA1- or ROS-exposure against apoptosis or necrosis of rat endothelial cells. When added during or up to 2 h subsequent to UVA1 or ROS exposure the NO-donor S-nitroso-cysteine (SNOC) at concentrations from 100-1000 microM significantly protects from both apoptosis as well as necrosis. The NO-mediated protection strongly correlates with complete inhibition of lipid peroxidation (sixfold increase of malonedialdehyde formation in untreated versus 1.2-fold with 1 mM SNOC). NO-mediated protection of membrane function was also shown by the inhibition of cytochrome c leakage in UVA1 treated cells, a process not accompanied by alterations in Bax and Bcl-2 protein levels. Thus, the experiments presented demonstrate that NO exposure during or even after a ROS-mediated toxic insult fully protects from apoptosis or necrosis by maintaining membrane integrity and function.