Hypericin-mediated photodynamic therapy (HY-PDT) has become a potential treatment for tumors and nonmalignant disorders. Some studies reported that HY-PDT could lead to apoptosis in some carcinoma cells. However, the molecular mechanism of HY-PDT remains unknown. In this study, we evaluated the molecular mechanisms of hypericin associated with light-emitting diode irradiation on the poorly differentiated human nasopharyngeal carcinoma cell line CNE-2 in vitro. To comprehensively understand the effects of HY-PDT on CNE-2 cells, we detected cell viability, cell cycle, apoptosis, intracellular glutathione content, and intracellular caspase (caspase-9, caspase-3, and caspase-8) activity. Furthermore, we performed genome-wide expression analysis via microarrays at different time points in response to HY-PDT, and we found that differentially expressed genes were highly enriched in the pathways related to reactive oxygen species generation, mitochondrial activity, DNA replication and repair, cell cycle/proliferation, and apoptosis. These results were consistent with our cytology test results and demonstrated that caspase-dependent apoptosis occurred after HY-PDT. Taken together, both cellular and molecular data revealed that HY-PDT could inhibit the growth of CNE-2 cells and induce their apoptosis.
Photodynamic therapy (PDT) is one of the newest advancements in the management of different microbial, viral, fungal, and inflammatory disorders and a variety of cancers. Light-induced growth inhibition is used in this method. It involves the targeting of cells or tissues that have been sensitized to light by administration of a photosensitizing agent. One such agent is hypericin (HY; 1,3,4,6,8,13-hexahydroxy-10,11-dimethyl-phenanthro[1,10,9,8-opqra]perylene-7,14-dione; Falk, 1999), a secondary metabolite that can be isolated from the plant Hypericum performatum, commonly known as St. Johns wort. Because of its photoactive properties and low cytotoxicity, attention has been focused on its application in PDT (Okpanyi et al., 1990; Kersten et al., 1999; Agostinis et al., 2002; Roscetti et al., 2004; Kiesslich et al., 2006).
Apoptosis and necrosis are two kinds of PDT-induced cell death (Fiers et al., 1999). Which pathway is induced depends on the different properties of the photosensitizer, the type of cells, the density of population, and the experimental method. Furthermore, the method itself varies by photosensitizing agent concentration, light dose, and incubation time (Blank et al., 2002; Alvarez et al., 2003). Which pathway the cell takes to PDT-induced death is organelle-dependent as well. That is, plasma membrane and lysosome can lead to necrosis, whereas mitochondrial activity can lead to programmed cell death, including both caspase-dependent and -independent apoptosis (Chen et al., 2000). Caspase-dependent apoptosis includes two pathways, the extrinsic death pathway (death receptor-dependent) and the intrinsic death pathway (mitochondria-dependent). In the past decades, mitochondria has played an important role in initiating and executing apoptosis in several types of cells (Green and Kroemer, 2004; Bras et al., 2005; Zoratti et al., 2005).
Previous studies showed PDT associated with hypericin could lead to apoptosis in the human nasopharyngeal carcinoma cell line CNE-2 (Ali et al., 2001; Ali and Olivo, 2002), but others found it yielded necrosis (Du et al., 2003). Ali et al. (2002) reported photosensitization of HY could enhance CD95/CD95L expression and CD95 signaling-dependent cell death in all tumor cell lines. This was accomplished in poorly differentiated CNE-2 cells by measuring the change of membrane potential in mitochondria, the release of cytochrome c, the activity of caspases-3 and -8, the status of caspase-3-specific substrate poly(ADP-ribose) polymerase, and expression of CD95/CD95L. Thong et al. (2005) used PDT associated with hypericin-treated cells and reported the intracellular concentration of Ca2+ in experimental group to be significantly higher than in the control.
Furthermore, many other reports indicated HY-PDT could lead to apoptosis in the human laryngeal squamous cell carcinoma strain Hep-2 (Sun et al., 2005), hepatoblastoma, pediatric hepatocellular carcinoma cells (Seitz et al., 2008), GH4C1 rat pituitary tumors (Cole et al., 2008), childhood rhabdomyosarcoma (Seitz et al., 2007), and esophageal cancer cells (Höpfner et al., 2003). Nevertheless, these works lacked sufficient evidence regarding to the molecular mechanism for HY-PDT. In addition, some experiments demonstrated apoptosis induced by HY-PDT could be promoted by inhibiting p38 mitogen-activated protein kinases and that such cell demise could be stimulated by HY-PDT associated with some other drugs (Kocanova et al., 2007; Buytaert et al., 2008; Schneider-Yin et al., 2009).
Microarray analysis has been widely used in the detection of differentially expressed genes and the pathway analysis for potential molecular mechanisms (Watts et al., 2001; Sarközi et al., 2008). Recently, Sanovic et al (2009) detected an alteration of the gene expression in the human squamous cell carcinoma cell line A-431 after HY-PDT by cDNA microarray technique. A total of 168 genes were found to be differentially up-regulated and 45 were down-regulated. Because of the significant expression changes, the following could be concluded: 1) lipoprotein receptor-mediated endocytosis could play an important role in the uptake of lipophilic hypericin; and 2) cytoskeleton rearrangement and formation of apoptotic bodies occurred.
Although some studies showed apoptosis induced by HY-PDT, genome-wide expression profile studies or systematic molecular evidence could not reveal the mechanisms of apoptosis in CNE-2 cells subjected to HY-PDT. To gain insight into the complex molecular mechanisms of this therapy, we conducted both cytology tests and genome-wide expression analysis of hypericin associated with light-emitting diode (LED) irradiation of human CNE-2 cells line in vitro. We found numerous features with respect to molecular pathways that are involved in various aspects of cell proliferation, DNA repair, and apoptosis.
Materials and Methods
Human nasopharyngeal carcinoma cell line CNE-2 was purchased from Shanghai Cell Biology Institute (Chinese Academy of Science, Shanghai. China). Cells were grown at 37°C, 100% humidity, and 95% air, 5% CO2, and they were fed with 10% fetal bovine serum (FBS) and RPMI medium 1640 (Invitrogen, Carlsbad, CA). RPMI medium 1640 was supplemented with 1% l-glutamine, 100 μg/ml penicillin, and 100 μg/ml streptomycin.
In cell viability experiments, CNE-2 cells were seeded in 96-well plates (104cells/100 μl media/well) and cultured as described above. After 24 h, hypericin (Alexis Laboratories, San Diego, CA), which was dissolved in DMSO, was added to increasing concentrations (0.04, 0.08, 0.12, 0.16, and 0.20 μg/ml). Cells were incubated for 6 h in the dark and then exposed to yellow LED for hypericin and red LED for hematoporphyrin (HP) irradiation for 90 min PDT. The light energy was 5.67 J/cm2. After drug treatment, cells were incubated in the dark.
Afterward, we established the following experimental group and control groups: treatment of 0.20 μg/ml HY and light irradiation as the experimental group (group A) and treatment of 0.20 μg/ml HY without irradiation as the negative control group (group B). In addition, we added one or two extra negative controls in different experiments: treatment of irradiation without HY (group C) and treatment without HY or irradiation (group D).
After drug treatment, cells were incubated in the dark for an additional 20 h. Meanwhile, the group that contained only DMSO and the groups that contained HP in increasing concentrations (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 μg/ml) were designated as the blank control and positive control, respectively. Cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. After 20-h incubation, medium was removed, and cells were washed with PBS, pH 7.4. Then, an additional 100 μl of medium containing MTT (0.5 mg/ml) without FBS was added, and cells were incubated 4 h in the dark. Afterward, the medium was decanted carefully and dissolved in formazan in 100 μl of DMSO and absolute ethanol (1:1) with agitation for 15 min. Absorption was measured on a SpectraMax M2 microplate reader (Molecular Devices, Sunnyvale, CA) at 570 nm. Inhibition rate (IR) (%) = (1 − average A570 of the experimental group/average A570 of the control group) × 100%. IC50 was calculated using the Bliss method.
Cell cycle test kits (CycleTest Plus DNA Reagent kit; BD Biosciences, Franklin Lakes, NJ) were used according to the manufacturer's instructions at 20 h after light irradiation. Cells were collected by centrifugation at 400g for 5 min and then the supernatant was removed. We then resuspended the pellet in 250 μl of solution A, containing trypsin, and incubated it for 15 min. Next, we added 200 μl of solution B, containing trypsin inhibitor and RNase A, and then carefully mixed them. After 15-min incubation, 200 μl of solution C, containing propidium iodide, was added and incubated at 4°C for 15 min in the dark. Finally, each sample was filtered by 50-μm aperture nylon membrane. The results were detected by a FACSCalibur flow cytometer (BD Biosciences). After using CellQuest software to collect approximately 20,000 cells, the cell cycle was analyzed by ModFit LT 2.0 software (Verity Software House, Topsham, ME).
Cells in group A and B were incubated in the dark for an additional 18, 28, and 48 h. Then, apoptosis was determined with an apoptosis test kit (APO-BRDU kit; BD Biosciences) according to the manufacturer's instructions. Cells were collected and resuspended in 0.5 ml of 1× PBS. Next, we added 5 ml of 1% paraformaldehyde. Cells were then incubated on ice for 15 min. We then resuspended cells in 0.5 ml of 1× PBS and centrifuged at 400g for 5 min. After this, we resuspended cells in 0.5 ml of 1× PBS. Next, 70% ethanol was added, and cells were incubated at −20°C overnight. We then centrifuged cells and resuspended them in 1 ml of wash buffer. After another round of centrifugation, cells were resuspended in 50 μl of DNA marker solution and incubated at 37°C for 60 min. We next added 1 ml of RNase buffer, and each tube was incubated for 10 min and centrifuged at 300g for 5 min. We next removed supernatant and resuspended cells in 0.1 ml of fluorescent-labeled anti-5-bromo-2′-deoxyuridine antibody. After 30-min incubation at 37°C, we added 0.5 ml of propidium iodide (0.25%)/RNase A solution and incubated again at 37°C for 30 min in the dark. The results were detected by flow cytometry.
Intracellular Glutathione Content.
Cells in group A, B, C, and D were collected by centrifugation. Content of intracellular glutathione (GSH) was determined by test kit (ApoAlert Glutathione Detection kit; Clontech, Otsu, Japan) according to the manufacturer's instructions. Cells were collected and resuspended in 10 ml of fresh RPMI medium containing 10% FBS. Cells were collected by centrifugation at 700g. The pellet was resuspended in 1 ml of ice-cold 1× cell wash buffer. We then transferred resuspended pellet into a 1.5-ml microcentrifuge tube and centrifuged at 700g for 5 min. We then resuspended the pellet in 100 μl of ice-cold 1× cell lysis buffer and incubated for 10 min on ice and centrifuged at maximal speed using a tabletop centrifuge for 10 min. Next, we added 2 μl of 100 mM monochlorobimane (MCB) to each supernatant. We prepared a negative control sample by adding 2 μl of MCB to 100 μl of 1× cell lysis buffer. All samples were incubated at 37°C for 15 min. The fluorescence was detected with a fluorometer (Cary Eclipse fluorescence spectrophotometer; Varian, Inc., Palo Alto, CA) at 395 and 480 nm.
Intracellular Caspases, Caspase-9, Caspase-3, and Caspase-8 Activities.
Cells in group A, B, C, and D were collected by centrifugation. According to the manufacturer's instructions, activities of the overall caspases, caspase-9, caspase-3, and caspase-8 were determined by the appropriate caspase test kit (CaspGLOW Fluorescein Caspase Staining kit; BioVision, Mountain View, CA), respectively. Aliquots of 300 μl from cell culture from each group were transferred to Eppendorf tubes. We then added 1 μl of FITC-VAD-FMK, FITC-LEHD-FMK, FITC-DEVD-FMK, and FITC-IETD-FMK, respectively, into each tube and incubated them for 0.5 h at 37°C with 5% CO2. Cells were then centrifuged at 3000 rpm for 5 min, and the supernatant was removed. We then resuspended cells in 0.5 ml of wash buffer and centrifuged again. This step was repeated once. The results were detected by flow cytometry.
Transcriptional Analysis of Time Course in Response to HY-PDT.
After both treatment (0.20 μg/ml HY) and irradiation, cells were incubated in the dark for 0, 2, 6, 12, and 20 h as experimental groups. Cells in HY treatment without irradiation were incubated in the dark for 20 h as the control group. Total RNAs were isolated from the cultured cells in both experimental and control groups and hybridized to Illumina Sentrix Human WG-6_V2 expression BeadChip arrays (Illumina, San Diego, CA) separately according to the manufacturer's instructions.
Microarray Data Analysis.
Gene expressions measures were available at GEO (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE20134). The data were extracted using BeadArray scanner and analyzed by BeadStation software (both from Illumina) provided by the manufacturer. Genes, whose DiffScore was above 13 compared with the control, were defined as differentially expressed genes. The Cluster program (Eisen et al., 1998) was used to cluster the candidate genes into a hierarchical tree. Pathway analysis was performed with GenMAPP 2.0 software (Dahlquist et al., 2002; Doniger et al., 2003). Significantly altered pathways were defined when their Z scores were above 1.96.
Means and standard deviations of individual groups (n = 3) were calculated. P values were assessed by performing two-sided Student's t test.
Irradiated with LED light, the cell viability showed significant differences between the cells added with increasing concentrations of HY (0.04, 0.08, 0.12, 0.16, and 0.20 μg/ml) and blank control (two-sided t test, P < 0.01). When the final concentration of HY reached 0.16 μg/ml, IR was more than 90% (Fig. 1), with an IC50 value of 0.049 μg/ml. In the presence of HY without irradiation, cell viability was slightly inhibited (Fig. 1). However, there was a difference between treatment with irradiation and nonirradiation at the same concentration of HY (P < 0.01; Fig. 1). As illustrated, the HY-PDT was dose-dependent and the IR of the irradiation group was much more than the nonirradiation group. Furthermore, application of hematoporphyrin and irradiation with red LED light yielded inhibition of CNE-2 (P < 0.01; Fig. 2), with an IC50 value of 0.650 μg/ml. The IC50 value of HY was 13 times less than that of HP.
Our data detected by flow cytometry showed cell proportion at the G1 phase in the experimental groups was lower than that in the control groups. However, the cell proportions of S and G2 phase were higher in the experimental group than those in controls (Table 1).
Our data detected by flow cytometry showed there was a small amount of apoptotic cells in the group of HY without irradiation, and the proportion of apoptosis cells reached 22.37% after 48-h culture. However, the apoptosis ratio of the HY irradiation group was markedly higher than for the nonirradiation group. The ratios were 72.19 and 92.24%, respectively, after 28 and 48 h (Table 2). This outcome was consistent with our externalization of membrane phosphatidylserine test (data not show).
Intracellular GSH Content.
The glutathione content was markedly decreased in group A. In contrast, the content in groups B and C had slightly decreased ROS compared with group D (Fig. 3). Because GSH was depleted to reduce ROS, this result suggests ROS were largely generated during HY-PDT.
Intracellular Caspase Activity.
The activity of total caspases, caspase-9, caspase-3, and caspase-8 in the CNE-2 cells was detected by flow cytometry and activated only in group A. In contrast, there was no indication of total caspase, caspase-9, caspase-3, or caspase-8 activity in the other three controls (groups B, C, and D) (Table 3).
Differentially Expressed mRNAs.
The cellular responses of HY-PDT treatment suggested many genes contributed to these phenotypes. We followed the transcriptional profile of CNE-2 with HY-PDT through an extended time course, with samples taken from cultures 0, 2, 6, 12, and 20 h after 1.5 h exposed to LED irradiation.
Genes that differentially expressed in at least one time point in response to the HY-PDT treatment are defined as DE mRNAs. We obtained 5619 DE mRNAs, in which 2889 mRNAs were up-regulated and 2730 mRNAs were down-regulated. Meanwhile, 370 mRNAs remained differentially expressed throughout the entire time course, in which 140 genes were induced and 230 genes were repressed. Detailed gene information is listed in Supplemental Tables S1 and S2.
We have applied hierarchical clustering to the DE genes and samples separately (Fig. 4). The temporal expression at time point 0 (without incubation immediately after irradiation) is quite different from that in the subsequent incubations. Moreover, among all the time points, we observed the largest group of DE genes at the 0-h time point, 1775 genes up-regulated and 1451 genes down-regulated, and the second largest group is at the 20-h time point.
ROS Activation, Damage of Mitochondrial Membrane, and DNA.
Next, we used GeneMapp to analyze the pathway involved in HY-PDT treatment based on the DE gene at each time point (Table 4). Detailed pathway information is shown in Supplemental Figures S1 to S6 and Supplemental Tables S3 to S7. Noticeably, there were more altered pathways at the 0-h time point than those at the subsequent time points.
The oxidative stress pathway was significantly induced immediately after irradiation (0-h time point), consistent with glutathione test. We suggest ROS was produced in the presence of HY-PDT (Supplemental Fig. S3).
In addition, mitochondrial inner membrane proteins were induced to higher mRNA levels during the early time course (Supplemental Fig. S4). This is consistent with the theory that one target of HY-PDT is the mitochondrial electron transport chain and more precisely that the focus of damage is at the quinone reducing center (Qi) of complex III (Theodossiou et al., 2008, 2009).
Pathways involved in helicase activity, DNA replication, and DNA repair also were induced at time point 0. Helicase activity remained for a longer time to cause DNA unwinding and chromatin disassembling in the end of time course.
Cell Cycle and Cell Proliferation.
DNA microarray also revealed some interesting expression patterns of the cell cycle pathway. They were altered in the early time points in response to HY-PDT, consistent with the cell cycle test (Table 1). This suggests the cells were enriched in the S and G2 phases for repairing the damaged DNA (Supplemental Fig. S2). Meanwhile, cellular metabolism was negatively regulated.
The pathway of negative regulation of cell proliferation was significantly activated during the entire time course, confirming the result of MTT assay that HY-PDT can inhibit cell proliferation (Supplemental Fig. S1).
Apoptosis pathways were significantly altered in the entire time course. Change of mitochondrial membrane indicated that the intrinsic cell death pathway was activated. Furthermore, the Fas extrinsic cell death pathway was significantly activated during the early time course, in which FADD in death-inducing signal complex was up-regulated. Moreover, extrinsic cell death pathway modulation by HSP70 appeared markedly different at the 6-h time point, which is suggestive of extrinsic cell death pathway activation. These results were confirmed by detection of capase-8 activity (Table 3).
It should be noted that most of the caspases were not significantly induced in mRNA level during the treatment, whereas the caspase test showed the activation of caspases. Many cysteine-type endopeptidases involved in proteolysis were induced immediately after irradiation, such as members of ubiquitin-specific processing protease family (e.g., USP8, USP10, USP13, USP30, USP38, USP39, and USP49)., indicating cellular proteolysis was significantly promoted by HY-PDT.
Other Pathways Related with Different Cellular Behaviors.
HY-PDT also can induce an inflammatory response in the middle of the time course. Pathways related to intracellular structures, such as the lysosome, Golgi apparatus, and cytoskeleton, also showed alteration compared with the control, which indicated that HY-PDT might induce the instability of intracellular structure. Finally, G protein-mediated signaling pathways were altered at the 20-h time point.
Theoretically, HY-PDT treatment could result in both ROS overproduction and disruption of the homeostasis of the inner mitochondrial membrane, and then damage the outer membrane of mitochondria. This damage would decrease the membrane potential and change the permeability of the outer mitochondrial membrane, which is related to both apoptosis and necrosis. Reportedly, HY-PDT could induce apoptosis in several kinds of carcinoma cells (Ali et al., 2001; Ali and Olivo, 2002; Höpfner et al., 2003; Sun et al., 2005; Seitz et al., 2007, 2008; Cole et al., 2008). Apoptosis was detected in HY-PDT treatment cells and was promoted by using this therapy.
Although some reports showed there was an obvious effect on CNE-2 using PDT (Ali et al., 2001, 2002; Ali and Olivo, 2002), we have tried to explain the molecular mechanism of HY-PDT in the inhibition of viability and induction of apoptosis in vitro, by using LED light source to replace the expensive laser.
Here, we found a dose-dependent inhibition of CNE-2 cell proliferation by HY-PDT in vitro. It is important to note that HP has been shown to have more side effects such as retention in the body as long as 4 weeks. Thus, patients need to avoid light during this period, and higher concentrations of HP increase the photoallergic reaction. According to our data, HY as an ideal photosensitizer had more advantages than HP. The IC50 value of HY (0.049 μg/ml) was 13 times less than that of HP (0.650 μg/ml).
Furthermore, the apoptotic ratio significantly increased with prolonging time in the irradiation group. At 28 h there was 72.19% and at 48 h was 92.24% compared with the nonirradiation group. This result showed the significant inhibition of cell proliferation with irradiation in CNE-2 cells. Furthermore, it is in agreement with several reports (Seitz et al., 2008; Mikes et al., 2009; Ferenc et al., 2010), showing HY had the ability to inhibit biological activity with irradiation.
According to the previous studies, ROS were largely produced during PDT (Buytaert et al., 2007). With this in mind, we further tested the intracellular glutathione content. A large amount of GSH was depleted during this therapy, so we deduced ROS was induced and GSH was used to eliminate ROS. In this case, we hypothesized that the photogenerated ROS would induce release of cytochrome c and activation of the caspase cascade.
To understand whether or which phase cells were or were not arrested, we characterized the cell cycle and found the cells of S and G2 phase increased. According to previous studies, the S phase was a sensitive period for chemotherapeutics, and drugs could inhibit DNA synthesis and the growth of carcinoma cells by arresting this phase. Thus, we suggest HY-PDT probably affects DNA synthesis and replication.
To determine which kind of apoptosis pathway was stimulated, we tested the activation of overall caspases. Compared with the control group, caspases were markedly activated in the HY-PDT group. We found that cell death caused by HY-PDT therapy was caused by caspase-dependent apoptosis.
Caspase-dependent apoptosis signaling pathways have been found in two forms: mitochondria-dependent (intrinsic signal) and extrinsic signal (such as tumor necrosis factor and Fas ligand)-dependent. Some reports showed mitochondria were not only the target of HY but also the first target of photodynamic therapy (Theodossiou et al., 2008), acting on mitochondria, releasing cytochrome c, and changing DNA fragments and cell morphology.
We further detected the activity of caspase-3, -8, and -9, respectively. Results showed all of them were activated. The activated caspase-3 and -9 indicated that intrinsic cell death pathway was activated by HY-PDT. Unexpectedly caspase-8 also was activated during HY-PDT, which suggested that extrinsic cell death pathway also contributed to this therapy.
Analysis of the genes of HY-PDT induction should offers insight into the response of CNE-2 cells and resulting apoptosis. Therefore, we detected the gene expression profiling at the transcriptional level at five different time points in response to HY-PDT.
By analysis of DE genes related to HY-PDT and pathways involved in biological processes, we found that DE genes were highly enriched in the pathways involved in ROS, mitochondria, DNA replication and repair, cell cycle, cell proliferation, and apoptosis. Microarray analysis results were consistent with our cytology test results and evidently demonstrated mitochondria-dependent apoptosis occurs by HY-PDT. In addition, we detected the differential expression of genes in the FAS pathway and stress induction of HSP regulation, which confirmed the existence of extrinsic cell death (Supplemental Fig. S6). The reason for this phenomenon remains unknown. According to our detected FADD up-regulation and caspase-8 activation, we deduced the Fas pathway was not activated directly by Fas ligand but by amplification of internal signaling through the recruitment of more death domain-containing protein (FADD) and initiator caspase-8. Caspase-8 subsequently led to the proteolytic activation of the main effector caspases-3/7 and generated truncated Bid, which could, in turn, bind to Bcl-2, inhibiting its antiapoptotic function.
Interestingly, most caspases were not significantly induced in mRNA level during the treatment, whereas the caspase test showed that the caspase activities were activated. This phenomenon suggested that caspase-3, -8, and -9 were activated via promoting of the cleavage of inactive procaspases in response to HY-PDT induction.
Among all the time points, we observed that the DE gene at the 0-h time point was the largest, 1775 genes were up-regulated and 1451 genes were down-regulated. The reason was that the cells at the 0-h time point had been irradiated with HY-PDT for 90 min. During this period, cells dramatically responded to photodynamic pressure and had enough time to change their expression behavior to adapt to the environment rapidly. Supplemental Table S3 has detailed information on the 0-h time point pathway analysis. It is interesting to note that differentially expressed pathways in this time point included the majority of organelle pathways that were altered in other time points, such as helicase activity, DNA replication, response to DNA damage, cell proliferation, cell cycle, apoptosis to stimulus, oxidative stress, mitochondrial membrane, caspase, Fas pathway, stress induction of HSP regulation, and Golgi apparatus. With the deprivation of PDT and the prolonging of culture time, cells no longer yielded to the photodynamic pressure and became moderate gradually.
In conclusion, from the results of these experiments, HY-PDT induces the generation of ROS, which attacks the mitochondrial membrane and DNA in both direct and indirect ways. In addition, HY-PDT activates cysteine-type endopeptidase, which inhibits cell growth and induces apoptosis. We propose that the apoptosis induced by HY-PDT is subserved by both the mitochondria-dependent intrinsic pathway and the activation of the extrinsic pathway.
We thank Dr. Brian Giunta (Department of Psychiatry and Behavioral Medicine, University of South Florida, Tampa, FL) for critical corrections.
This work was supported by the Technology Fund of Shenzhen Bureau of Science Technology and Information [Grant 06KJP038] and was also a part of Project 30860081 supported by the National Natural Science Foundation of China.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
- photodynamic therapy
- hypericin-mediated photodynamic therapy
- light-emitting diode
- fetal bovine serum
- dimethyl sulfoxide
- methylthiazolyldiphenyl-tetrazolium bromide
- phosphate-buffered saline
- inhibition rate
- fluorescein isothiocyanate
- reactive oxygen species
- differentially expressed
- FAS-associated death domain-containing protein
- heat shock protein.
- Received March 31, 2010.
- Accepted June 11, 2010.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics