Mechanism Of Photodynamic Therapy Research Articles

Molecular mechanism of photodynamic therapy

Despite its more than 100-year history in experimental and clinical use, photodynamic therapy (PDT) is only starting to be appreciated for its full potential. PDT combines a photosensitizer and light in the presence of oxygen to treat cancer and other disorders. This paper reviews the molecular mechanism of PDT at the cellular level as well as in therapeutic settings in vivo. The availability of multiple photosensitizers with different structures and functional properties makes PDT an extremely versatile and, conversely, a challenging approach to cancer therapy. The advancing understanding of molecular pathways helps to design improved regimens. As most cancers are being treated with combined therapies, PDT is being integrated into rationally designed regimens that exploit molecular responses to PDT for improved efficacy.

ZnO:Er,Yb,Gd Particles Designed for Magnetic-Fluorescent Imaging and Near-Infrared Light Triggered Photodynamic Therapy

In this paper, fluorescent and magnetic bifunctional ZnO:Er,Yb,Gd particles were synthesized via a simple homogeneous precipitation method. The morphology, size, fluorescent properties, and magnetic properties of the particles can be readily modified by doping with Er3+, Yb3+, and Gd3+. The results revealed that the ZnO:Er,Yb,Gd particles have both down-conversion and up-conversion fluorescence after calcination at high temperatures (>700 °C). The products successfully labled the human hepatocellular carcinoma (HepG2) cells and presented low toxicity even at a high concentration of 2 mg/mL. Being upconverting nanoparticles (UCNPs), the prepared ZnO:Er,Yb,Gd particles exposed to 980 nm near-infrared (NIR) laser light emitted up-conversion fluorescence which could be absorbed by a photodynamic therapy (PDT) drug, methylene blue (MB), and then killed the HepG2 cells via PDT mechanism. In vitro therapeutic investigation evidenced the prominent PDT effects of MB-loaded ZnO:Er,Yb,Gd UCNPs upon NIR light irradia...

Bisanthracene Bis(dicarboxylic imide)s as Potential Photosensitizers in Photodynamic Therapy: A Theoretical Investigation

The electronic structures and spectroscopic properties of four bisanthracene bis(dicarboxylic imide)s (M1-M4) have been investigated theoretically by using density functional theory (DFT) and its time-dependent extension (TDDFT) in view of their potential use as photosensitizers in photodynamic therapy (PDT). The optimized geometries, electronic absorption transitions, singlet-triplet energy gaps, spin-orbit matrix elements, ionization potentials, and electron affinities have been determined in gas phase and in solvent. Both type I and II PDT mechanisms have been considered. In addition, the variation of a series of relevant properties upon heavy atom substitution (Br and I) have been determined and discussed. Results show that only M4 is able to support the type I reaction, and one of its brominated and iodinated derivatives can produce cytotoxic singlet oxygen (type II reaction).

In vitroandin vivoclearance of Rose Bengal Acetate-PhotoDynamic Therapy-induced autophagic and apoptotic cells

This study focuses on the clearance of Rose Bengal Acetate (RBAc)-PhotoDynamic Therapy (PDT)-generated apoptotic and autophagic HeLa cells by murine and human macrophages. Indeed, phagocytosis of dead cells drives the therapeutic efficacy of PDT through both efficient removal of dead/dying cells and macrophages response evoked during engulfment and, up to now, clearance of dying photosensitized cells has been less investigated than PDT mechanisms of cell death induction. RBAc-PDT ensures a long onset of cytotoxicity and a time-related cell death of HeLa cells by signals originating from or converging on almost all intracellular organelles. On this basis, to clarify whether the efficacious cell death commitment is followed by an efficient clearance mechanism, we primarily focused on the analysis of 'eat me' signals exposure and 'find me' signals release, and then investigated the migration, recognition, engulfment and response of murine Raw 264.7 and human blood isolated macrophages. Dead cells secreted 'find me' signals, i.e. fractalkine and Heat Shock Protein 70 (HSP 70), to recruit macrophages and promote their fast phagocytosis. Macrophages phagocytosed apoptotic and autophagic PDT-treated cells more efficiently than the respective positive controls, i.e. puromycin-induced apoptotic and Earle's balanced salt solution-starved autophagic cells. Phagocytosis depends on the glycans exposed on dead cells. The macrophages internalization of photokilled cells elicits the production of Interleukin-10, Transforming Growth Factor-β and Tumour Necrosis Factor-α by macrophages. TNFα production, along with HSP70 release and plasma membrane translocation on dead cells, suggest an immunogenic impact of RBAc-PDT. In fact, macrophages, activated fibroblasts and endothelial cells colonized the inoculum site of photosensitized cells in rat calf muscles, endorsing the hypothesis of immunogenic elicitation of RBAc-PDT.

Photodynamic Therapy (PDT) Utilizing Multiple Light Sources Significantly Improves Clinical Efficacy and Subject Satisfaction with a Review of PDT Mechanisms of Action

Introduction: Many topically applied devices and medicaments have been developed to give hope to people who want to reduce the signs of visible aging. All modalities have benefits and risks, and no single modality produces complete resolution of photoaging. Although approved by the US Food and Drug Administration for treatment of epithelial neoplasia, photodynamic therapy (PDT) is also reported to produce significant benefits in reducing photoaging. The goal of this study was to determine if clinical response and subject satisfaction can be improved for PDT while reducing downtime and increasing activation of the photosensitizer. Materials and Methods: In a regimen administered monthly for 3 treatments, 14 subjects participated in a prospective intervention pilot trial using an 830 nm light-emitting diode (LED), a 540 nm advanced fluorescence technology laser, a 570 nm advanced fluorescence technology laser, and a 633 nm LED. The photoactivation phase was initiated with the 830 nm LED 10 minutes after application of 20% 5-aminolevulinic acid, followed by each modality in listed order. Baseline global extrinsic aging scores were compared with scores 1 month after the final treatment. Subject satisfaction scores were also obtained 1 month after the final treatment. Results: Twelve subjects completed this trial. The global extrinsic aging score improved from a baseline of 3.3 to 1.0. Of these 12 subjects, 10 (84%) indicated that they were satisfied or very satisfied with the results 1 month after completion of the treatment. Conclusions: This photodynamic therapy regimen is very effective while being better tolerated and involving less downtime. The treatment can also be completed in a shorter time than regimens requiring a longer incubation time.

Chloride intracellular channel 4 involves in the reduced invasiveness of cancer cells treated by photodynamic therapy

The mechanisms of photodynamic therapy (PDT) have been studied on the cellular and tissue levels. However, the cellular behaviors of cancer cells survived from PDT are still not clear. Previously, we have found that PDT-derived variants A375/3A5 and A375/6A5 have reduced invasion ability. This study attempted to further elucidate the possible molecules associated with the altered invasiveness in the PDT-derived variants and cancer cells treated with PDT. Scratch wound healing assay and invasion assay were performed to evaluate the migration and invasion ability of human A375 melanoma and MDA-MB-231 breast adenocarcinoma cells. Single colony selection and microarray analysis were performed to examine the differentially expressed transcripts in parental A375 and PDT-derived variants. RT-PCR and Western blots analysis were performed to examine the expression levels of matrix metalloproteinase 9 (MMP9) and chloride intracellular channel 4 (CLIC4). The MMP9 activity was examined by Zymography assay. CLIC4 expressing construct was used to examine the influence on MMP9 expression and invasion ability of cancer cells treated with PDT. Correlated with the reduced invasiveness, we found that A375/3A5 and A375/6A5 cells have decreased production of MMP9. Microarray analysis and RT-PCR showed CLIC4 was down-regulated in the PDT-derived variants. Furthermore, down-regulation of CLIC4 and MMP9 was found in cancer cells treated with PDT. Transfection of surviving cancer cells with a plasmid vector encoding CLIC4 increased MMP9 expression and cell invasion. Furthermore, overexpression of CLIC4 in A375 and MDA-MB-231 cancer cells constrains PDT-induced suppression of invasiveness. Our results showed that the reduced expression of CLIC4 could further down-regulate MMP9 and result in the suppression of invasion in cancer cells treated with PDT. These results provide an insight into a new mechanism by which PDT affects the metastatic potential of cancer cells through down-regulation of MMP9 by CLIC4.

Photodynamic Therapy (PDT): PDT Mechanisms

Photodynamic therapy (PDT) is a light based therapy used to ablate tumors. As practiced in oncology a photosensitizing agent is applied and then activated by a specific wavelength and energy of light. This light energy in the presence of oxygen will lead to the creation of the photodynamic reaction which is cyto and vasculo toxic. This paper will review the mechanisms of action of PDT and how they may be manipulated to improve clinical outcome in cancer patients.

Bacteriophage bionanowire as a carrier for both cancer-targeting peptides and photosensitizers and its use in selective cancer cell killing by photodynamic therapy.

A photosensitizer, pyropheophorbid-a (PPa), is conjugated to SKBR-3 breast cancer cell-specific biological nanowire phage, to form a novel PPa-phage complex, which is further successfully used in selectively killing SKBR-3 breast cancer cells by the mechanism of photodynamic therapy (PDT).

Dosimetry in Pleural Photodynamic Therapy

Photodynamic therapy (PDT) centers on the photochemical interaction of 3 principal components: light, photosensitizer, and oxygen. Over the past 25 years, much has been learned about the basic biophysical mechanisms of PDT, and in the future, a clearer understanding of the physics of PDT will make it possible to translate this science into improved clinical treatments. This article explores the role of explicit dosimetry in PDT and the need for individualized determination of dosimetric parameters based on the heterogeneity of optical properties and photosensitizer drug concentration. In addition, the use of a navigation system to help deliver uniform light for pleural PDT is briefly discussed.

The Effect of Tissue Inhibitors on the Antibacterial Activity of Chitosan Nanoparticles and Photodynamic Therapy

Newer antibacterial alternatives such as chitosan nanoparticles (CSnps) and photodynamic therapy (PDT) have been investigated to achieve effective root canal disinfection. The current study aims to assess the effect of various tissue inhibitors such as dentin, dentin matrix, pulp tissue, bacterial lipopolysaccharides (LPSs), and bovine serum albumin (BSA) on the antibacterial activity of CSnps and PDT. The antibacterial effect of CSnps and PDT using photosensitizers, rose bengal (RB), and methylene blue (MB) were tested on planktonic Enterococcus faecalis American Type Culture Collection 29212 with or without pretreatment using different tissue inhibitors for an hour. Bacterial survival was assessed after 1, 8, and 24 hours of incubation with CSnps and after PDT using RB and MB. Pulp and BSA inhibited the antibacterial effect of CSnps significantly (P < .05). The antibacterial effect of CSnps was not affected by dentin, dentin matrix, or LPSs. The antibacterial activity of PDT using MB and RB was inhibited in a decreasing order by dentin matrix, BSA, pulp, dentin, and LPSs (P < .05). The effect of tissue inhibitors was higher in the case of PDT with RB. Depending on the antibacterial mechanism of CSnps and PDT, different inhibitory patterns were observed with different tissue inhibitors. The tissue inhibitors existing within the root canal affected the antibacterial activity of CSnps and PDT at varying degrees. Further research is required to enhance their antimicrobial efficacy in an endodontic environment.

Abstract 2839: Antitumor activity on colorectal and pancreatic tumors of a new strategy based on ROS generation by non-thermal plasma

Abstract Background. Local treatments of tumors are mainly based on surgical resection and/or treatment such as photodynamic therapy (PDT) or ionizing radiation (IR). Action mechanisms of IR and PDT are based on the generation of ROS in the vicinity of the cells. In this context, cold or Non Thermal Plasma (NTP), a new technology which can generate in situ ROS, is currently under investigations. NTP is a cold (&amp;lt;40°C) ionized gas (air or noble gas) thank to an electric discharge. It contains free charges (electrons, ions), free radicals and excited molecules. NTP can be generated at the end of a catheter (plasma jet) allowing a local treatment that is compatible with usual endoscopes for dysplasia or non resecable tumors. Previous studies have shown an in vitro antitumor activity of NTP on various cells lines and in vivo on subcutaneous xenografts. The aim of this work was to assess the antitumor potential of fibred NTP when applied directly on in situ orthotopic human pancreatic or colorectal carcinoma xenografts. Methods. For in vitro experiments, HCT116-Luc and Mia Paca-Luc cells were seeded in 24-well plate and then treated with a plasma jet device called plasma gun. The effects on cells were assessed by bioluminescence imaging (BLI). For in vivo experiments, HCT116-Luc cells were xenografted in the caecum wall of nude mice and tumors were treated by a single NTP exposure 7 days post-induction. Concerning pancreatic tumors, MIA PaCa2-Luc cells were injected in the pancreas head and NTP treatments were started 4 days after implantation. Two others exposures were performed on D14 and D24. For both models, tumor growth was monitored by BLI once a week. Results and Discussion. NTP treatment showed a significant antitumor effect on HCT116 and Mia Paca cells in vitro and in vivo. In vitro plasma induced a decrease of BLI resulting from a massive cell death. Localized treatments of tumor using plasma gun induced significant tumor stabilization. On colorectal tumors, a BLI difference of 90% between treated and CTRL tumors were observed at D22. This effect was confirmed by tumor weight measurement. Moreover, a significant metastasis decrease was observed. Similar results were observed on pancreatic tumors with also a stabilization of tumor growth and a BLI decrease following each treatment leading finally at D36 to a significant difference of tumor volume (84%). Comparison of NTP with the references drug of these pathologies is ongoing. The results obtained on two different tumor types show the potential antitumor activity of NTP on implanted small tumors. These effects were linked to a high rate generation of ROS in the vicinity of tumors, inducing lethal DNA damages, a multiphase cell cycle arrest and finally apoptosis. Such results demonstrate the interest of NTP for treatment of dysplasia and non-resecable tumors that could be associated to real time per operative near infrared fluorescence imaging via fibro/coelioscopy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2839. doi:1538-7445.AM2012-2839

In vitro study of cell death with 5-aminolevulinic acid based photodynamic therapy to improve the efficiency of cancer treatment

Photodynamic therapy (PDT) is a kind of photochemo therapeutic treatment that exerts its effect mainly through the induction of cell death. Distinct types of cell death may be elicited by different PDT regimes. In this study, efforts are underway to optimize PDT protocols for improved efficacy and combination of all three PDT mechanisms involved in the different human carcinomas cell narcosis. Our in vitro cell culture experiments with 5-aminolevulanic acid (ALA) a clinically approved photiosensitizer (PS) and 635 nm laser light have yielded promising results, as follow: (1) (human cervical cancer (HeLa) cell line incubated, for 18 h, with 30 μg/ml of 5-ALA, treated with laser light dose of 50 J/cm2 can produce 85% of cell killing (2) human larynx carcinoma (Hep2c) cell line incubated, for 7 h, with 55 μg/ml of 5-ALA, treated with laser light dose of 85 J/cm2 can produce 75% of cell killing (3) human liver cancer (HepG2) cell line incubated, for 22–48 h, with 262 μg/ml of 5-ALA, treated with laser light dose of 120 J/cm2 can produce 95% of cell killing (4) human muscle cancer (RD) cell line incubated, for 47 h, with 250 μg/ml of 5-ALA, treated with laser light dose of 80 J/cm2 can produce 76% of cell killing (5) Human embryonic kidney (HEK293T) cell line incu-bated, for 18 h, with 400 μg/ml of 5-ALA, treated with laser light dose of 40 J/cm2 can produce 82% of cell killing confirming the efficacy of photodynamic therapy.

The activity of G-ROS and the predominant role of Type II reaction in the photodynamic therapy using 9-hydroxypheophorbide-α for HeLa cell lines

Photodynamic therapy (PDT) is a treatment modality that destroys the tumor. It activates the photosensitizer with the light of a specific wavelength, where the light is well absorbed by the photosensitizer, thus causing a fatal injury and thereby leading to a tumor necrosis. To date, a hematoporphyrin-derived photosensitizer has been widely used. It is disadvantageous, however, in that it causes a long-term photo-toxicity and has a poor selectivity for the tumor. This had led to the development of a chlorophyll-derived photosensitizer. We conducted this study to elucidate the mechanisms by which the activity of ROS is involved in the PDT using a novel type of chlorophyll-derived photosensitizer, 9-hydroxypheophorbide-α (9-HpbD-α), for the HeLa cell lines. Besides, we also attempted to determine which reaction plays a predominant role in the synthesis of ROS, either Type I reaction or Type II one, when both reactions are involved in the synthesis of ROS during the PDT using 9-HpbD-α. Our results showed not only that the activity of ROS is involved in the PDT using 9-HpbD-α in human uterine cervical cancer cell lines but also that the mechanisms of PDT are based on Type II reaction where the singlet oxygen is involved.

Photodynamic therapy leads to death of C6 glioma cells partly through AMPAR

Glioma cells release glutamate during growth, which promotes proliferation and migration of itself and causes excitotoxicity to the surrounding neurons by Ca 2+ influx through glutamate receptors. However, the role of glutamate and its receptors in the photodynamic therapy (PDT) on glioma cells is still unclear. Here we administered α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptor (AMPAR) antagonist prior to PDT on C6 glioma cells. The changes of glutamate release, expression of AMPAR, apoptosis of C6 cells, and intracellular free calcium ([Ca 2+] i) were examined after PDT. We found that PDT increased extracellular glutamate and expression of AMPAR subunit GluR1 and GluR2, which might result in Ca 2+ influx and apoptosis of C6 cells. When AMPAR antagonist was added, intracellular free calcium reduced and apoptosis rate of C6 cells decreased. These results indicate that PDT may lead to death of C6 glioma cells partly through glutamate and its receptors AMPAR, which induces Ca 2+ influx and then cells apoptosis. This study allows us to further understand the effects and molecular mechanism of PDT on glioma.

Photodynamic therapy with Pc 4 induces apoptosis of Candida albicans.

The high prevalence of drug resistance necessitates the development of novel antifungal agents against infections caused by opportunistic fungal pathogens, such as Candida albicans. Elucidation of apoptosis in yeast-like fungi may provide a basis for future therapies. In mammalian cells, photodynamic therapy (PDT) has been demonstrated to generate reactive oxygen species, leading to immediate oxidative modifications of biological molecules and resulting in apoptotic cell death. In this report, we assess the in vitro cytotoxicity and mechanism of PDT, using the photosensitizer Pc 4, in planktonic C. albicans. Confocal image analysis confirmed that Pc 4 localizes to cytosolic organelles, including mitochondria. A colony formation assay showed that 1.0 μM Pc 4 followed by light at 2.0 J cm(-2) reduced cell survival by 4 logs. XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxyanilide) assay revealed that Pc 4-PDT impaired fungal metabolic activity, which was confirmed using the FUN-1 (2-chloro-4-[2,3-dihydro-3-methyl-(benzo-1,3-thiazol-2-yl)-methylidene]-1-phenylquinolinium iodide) fluorescence probe. Furthermore, we observed changes in nuclear morphology characteristic of apoptosis, which were substantiated by increased externalization of phosphatidylserine and DNA fragmentation following Pc 4-PDT. These data indicate that Pc 4-PDT can induce apoptosis in C. albicans. Therefore, a better understanding of the process will be helpful, as PDT may become a useful treatment option for candidiasis.

Targets and Mechanisms of Photodynamic Therapy in Lung Cancer Cells: A Brief Overview

Lung cancer remains one of the most common cancer-related causes of death. This type of cancer typically develops over a period of many years, and if detected at an early enough stage can be eliminated by a variety of treatments including photodynamic therapy (PDT). A critical discussion on the clinical applications of PDT in lung cancer is well outside the scope of the present report, which, in turn focuses on mechanistic and other aspects of the photodynamic action at a molecular and cellular level. The knowledge of these issues at pre-clinical levels is necessary to develop, check and adopt appropriate clinical protocols in the future. This report, besides providing general information, includes a brief overview of present experimental PDT and provides some non-exhaustive information on current strategies aimed at further improving the efficacy, especially in regard to lung cancer cells.

Studies on preparation and photodynamic mechanism of chlorin P6-13,15- N-(cyclohexyl)cycloimide (Chlorin-H) and its antitumor effect for photodynamic therapy in vitro and in vivo

Photodynamic therapy (PDT) represents a promising method for treatment of cancerous tumors. The chemical and physical properties of used photosensitizer play key roles in the treatment efficacy. In this study, a novel photosensitizer, Chlorin-H [-13,15- N-(cyclohexyl)cycloimide] which displayed a characteristic long wavelength absorption peak at 698 nm was synthesized. Following flash photolysis with 355 nm laser, Chlorin-H is potent to react with O 2 and then produce 1O 2. This finding indicates that Chlorin-H takes its effects through type II mechanism in PDT. Generally, Chlorin-H is localized in mitochondria and nucleus of cell. After light irradiation with 698 nm laser, it can kill many types of cell, inhibit cell proliferation and colony formation, suppress cancer cell invasiveness and trigger apoptosis via the mitochondrial pathway in A549 cells in vitro. In addition, Chlorin-H–PDT can destroy A549 tumor in nude mice and a necrotic scab was formed eventually. The expression levels of many genes which regulated cell growth and apoptosis were determined by RT-PCR following Chlorin-H–PDT. The results showed that it either increased or decrease. Among which, the expression level of TNFSF13, a member of tumor necrosis factor superfamily, increased significantly. Silencing of TNFSF13 caused by RNA interference decreased the susceptibility of A549 cells to Chlorin-H–PDT. In general, Chlorin-H is an effective antitumor photosensitizer in vitro and in vivo and is worthy of further study as a new drug candidate. TNFSF13 will be an important molecular target for the discovery of new photosensitizers.

Photodynamic therapy with 9-hydroxypheophorbide α on AMC-HN-3 human head and neck cancer cells: Induction of apoptosis via photoactivation of mitochondria and endoplasmic reticulum

Skin phototoxicity is the main side effect of photodynamic therapy (PDT). To overcome this problem, some new photosensitizers have been developed with longer absorbance wavelengths and shorter half-life in the body. In this study, we investigated the mechanism of PDT mediated by a new chlorophyll derivative photosensitizer, 9-hydroxypheophorbide α (9-HPbD), on AMC-HN-3 cancer cells. Phototoxicity and apoptosis on AMC-HN-3 cells induced by 9-HPbD was exhibited in a time- and dose-dependent manner. Mitochondria and endoplasmic reticulum (ER) were observed as preferential sites of 9-HPbD accumulation. Photoactivation of 9-HPbD-loaded AMC-HN-3 cells led to a rapid generation of reactive oxygen species (ROS) at 30 min, followed by a loss of mitochondrial membrane potential (MMP) at 2 h, translocation of apoptosis-inducing factor (AIF) at 2 h, and the release of cytochrome c at 3 h following PDT. Caspase-12, an important caspase involved in ER-induced apoptosis, and C/EBP homologous protein (CHOP), an ER stress inducible transcription factor, were also up-regulated after PDT (3-12 h and 6-12 h, respectively). Subsequently, activation of caspase-9 at 6 h, caspase-3 and PARP at 12 h also occurred in PDT-treated AMC-HN-3 cells. The above observations demonstrate that both mitochondria and ER serve not only as the sites of sensitizer binding, but also the subcellular targets of 9-HPbD-PDT, effective activation of which is responsible for 9-HPbD PDT-induced apoptosis in AMC-HN-3 cells.

The molecular mechanism of photodynamic therapy to fibrosis: Regulation on the pyridinoline cross-link formation in collagen

Fibrotic processes in tissues are characterised by an excessive accumulation of collagen containing increased levels of pyridinoline cross-links, which has been taken as an important criterion to diagnose the fibrosis. Hypocrellin B (HB) is a natural photosensitizer with excellent photodynamic activity but very low dark-toxicity. In the current work, main purpose was to clarify if photodynamic action of HB could be applied to regulating the level of pyridinoline cross-link in collagen. To use gelatin as a model collagen, it was observed that the pyridinoline cross-link formation was effectively degraded by HB photodynamic action in the gelatin, suggesting the level of pyridinoline cross-link formation in collagen may be photodynamically regulated to a normal level. Furthermore, mechanism of the photodynamic action of HB was studied.

9-hydroxypheophorbide-a와 660 nm 다이오드 레이저를 이용한 광역학치료의 항암효과와 치료기전에 대한 연구

녹조류인 Spirulina platensis에서 추출하여 만든 새로운 광감작제와 660 nm의 다이오드 레이저를 이용한 광역학치료의 항암효과와 치료기전을 알아보았다. 세포 독성능은 MTT assay를 이용하였고, 세포사멸기전은 propidium iodide과 Hoechst 33342 염색법과 투과전자현미경으로 확인하였다. 또한 암세포가 이종 이식된 누드마우스 모델에서 광역학치료를 시행하여 항암효과를 확인하였다. 3종류의 클로로필 유도체 중 9-hydroxypheophorbide-a (9-HpbD-a)의 세포 독성능이 가장 우수하였고, 9-HpbD-a의 적정 레이저조사 시간은 30분 (3.2 J/<TEX>$cm^{2}$</TEX>), 광감작제를 투여하고 레이저조사시간까지의 배양시간은 최소 6시간 이상임을 확인하였다. 광역학치료의 세포사멸기전은 낮은 9-HpbD-a 농도에서 세포고사가 주된 세포사멸기전이었고, 높은 농도의 9-HpbD-a에서는 세포괴사에 의한 세포사멸이 주된 기전임을 확인하였다. 투과전자현미경 하에서도 같은 양상을 관찰하였다. 그리고 암세포가 이종 이식된 누드마우스 모델에서의 광역학치료는 제1군 정상대조군과 제2군 9-HpbD-a만을 투여한 종양조직모두 지속적인 종양의 성장(100% )을 보였고, 제3군인 레이저만을 종양조직에 조사한 실험군에서는 3 마리는 치료가 되지 않았고(75.0%), 1 마리는 재발(25.0%) 하였다. 제4군 광역학치료군에서 총16 마리의 종양에서 10 마리는 완치(62.5%), 4 마리는 재발(25.0%), 2 마리는 치유되지 않았음(12.5% )을 확인하였다. 9-HpbD-a와 660 nm 다이오드 레이저를 이용한 광역학치료는 유의한 항암효과를 나타내었고 9-HpbD-a를 이용한 광역학치료는 새로운 치료방법으로서 향후 암치료의 유용한 치료방법으로 기대된다. A new photosensitizer, 9-Hydroxypheophorbide-a (9-HpbD-a), was derived from Spirulina platensis. We conducted a series of experiments, in vitro and in vivo, to evaluate the anticancer effect and mechanism of photodynamic therapy using 9-HpbD-a and 660 nm diode lasers on a squamous carcinoma cell line. We studied the cytotoxic effects of pheophytin-a, 9-HpbD-a, 9-HpbD-a red and 660 nm diode lasers in a human head and neck cancer cell line (SNU-1041). Cell growth inhibition was determined by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay. The effects of 9-HpbD was higher than those of 9-HpbD-a red or pheophytin-a in PDT. We then tested the cytotoxic effects of 9-hydroxypheophorbide-a (9-HpbD-a) in vitro. The cultured SNU-I041 cells were treated with serial concentrations of 9-HpbD-a followed by various energy doses (0, 0.1, 0.5, 3.2 J/<TEX>$cm^{2}$</TEX>) and by various interval times (0, 3, 6, 9, 12 hr) until laser irradiation, then MTT assay was applied to measure the relative inhibitory effects of photodynamic therapy (PDT). Optimal laser irradiation time was 30 minutes and the cytotoxic effects according to incubation time after 9-HpbD-a treatment increased until 6 hours, after which it then showed no increase. To observe the cell death mechanism after PDT, SUN-I041 cells were stained by Hoechst 33342 and propidium iodide after PDT, and observed under transmission electron microscopy (TEM). The principal mechanism of PDT at a low dose of 9-HpbD-a was apoptosis, and at a high dose of 9-HpbD-a it was necrosis. PDT effects were also observed in a xenografted nude mouse model. Group I (no 9-HpbD-a, no laser irradiation) and Group II (9-HpbD-a injection only) showed no response (4/4, 100%), and Group III (laser irradiation only) showed recurrence (1/4,25%) or no response (3/4, 75 %). Group IV (9-HpbD-a + laser irradiation) showed complete response (10/16, 62.5%), recurrence (4/16, 25%) or no response (2/16, 12.5%). Group IV showed a significant remission rate compared to other groups (p<0.05). These results suggest that 9-HpbD-a is a promising photosensitizer for the future and that further studies on biodistribution, toxicity and mechanism of action would be needed to use 9-HpbD-a as a photosensitizer in the clinical setting.