CHOP activation by photodynamic therapy increases treatment induced photosensitization

Development of a multifunctional luciferase reporters system for assessing endoplasmic reticulum-targeting photosensitive compounds

Photodynamic therapy (PDT) is a recently developed antitumor modality utilizing the generation of reactive oxygen species (ROS), through light irradiation of photosensitizers (PSs) localized in tumor. Interference with proper functioning of endoplasmic reticulum (ER) by ER-targeting PDT is a newly proposed strategy to achieve tumor cell death. The aim of this study is to establish a multifunctional model to screen and assess ER-targeting PSs based on luciferase reporters system. Upregulation of GRP78 is a biomarker for the onset of ER stress. CHOP is a key initiating player in ER stress-induced cell death. Here, the most sensitive fragments of GRP78 and CHOP promoters responding to ER-targeting PDT were mapped and cloned into pGL3-basic vector, forming -702/GRP78-Luc and -443/CHOP-Luc construct, respectively. We demonstrated that -702/GRP78-Luc expression can be used to indicate the ER-targeting of PSs, meanwhile estimate the ROS level induced by low-dose ER-targeting PDT. Moreover, the luciferase signaling of -443/CHOP-Luc showed highly consistence with apoptosis rate caused by ER-targeting PDT, suggesting that -443/CHOP-Luc can evaluate the antitumor properties of PSs. Hypericin, Foscan® and methylene blue were applied to verify the sensitivity and reliability of our model. These results proved that GRP78-CHOP model may be suitable to screen ER-targeting photosensitive compounds with lower cost and higher sensitivity than traditional ways.

Role of ER stress response in photodynamic therapy: ROS generated in different subcellular compartments trigger diverse cell death pathways

We have analyzed the molecular mechanisms of photoinduced cell death using porphyrins with similar structure differing only in the position of the ethylene glycol (EG) chain on the phenyl ring. Meta- and para-positioned EG chains targeted porphyrins to different subcellular compartments. After photoactivation, both types of derivatives induced death of tumor cells via reactive oxygen species (ROS). Para derivatives pTPP(EG)4 and pTPPF(EG)4 primarily accumulated in lysosomes activated the p38 MAP kinase cascade, which in turn induced the mitochondrial apoptotic pathway. In contrast, meta porphyrin derivative mTPP(EG)4 localized in the endoplasmic reticulum (ER) induced dramatic changes in Ca(2+) homeostasis manifested by Ca(2+) rise in the cytoplasm, activation of calpains and stress caspase-12 or caspase-4. ER stress developed into unfolded protein response. Immediately after irradiation the PERK pathway was activated through phosphorylation of PERK, eIF2α and induction of transcription factors ATF4 and CHOP, which regulate stress response genes. PERK knockdown and PERK deficiency protected cells against mTPP(EG)4-mediated apoptosis, confirming the causative role of the PERK pathway.

Hydroxypheophorbide-α-mediated photodynamic therapy augmented by pretreatment with genistein inCaSkicervical cancer cells

Photodynamic therapy (PDT) is a treatment for cancer involving three key components — a sensitizing compound (light) tissue, and oxygen. In this study we applied phototreatment to cancer cells with 2 J.cm-2of red light after sensitizing with 9-hydroxypheophorbide-α (9-HpbD-α), a new chlorophyll-derived photosensitizer. We have investigated the cytotoxic and apoptotic effects of 9-HpbD-α-induced PDT in cervical cancer cells, the enhancing effect of genistein in PDT, and explored the molecular mechanisms of E6 or E7 oncogenes, apoptotic signaling molecules, and ER stress. Co-treatment downregulated the transcripts of the E6*I, E6*II, and E7 oncogenes. Combined treatment with PDT and genistein showed typical apoptotic features, i.e. apoptotic bodies. To elucidate the mechanism of combination treatment-induced apoptosis, various mediators of apoptosis were investigated. Activation of caspase-8, caspase-3, and PARP were distinct after combination treatment. Furthermore, ER stress-related proteins, such as CHOP and GRP78, were activated after combination treatment. We conclude that genistein sensitizes CaSki cells to apoptosis treated with PDT by 9-HpbD-α (0.59 μg/mL) through mechanisms that involve downregulation of the E6*I, E6*II, and E7 oncogenes, activation of caspase-8 or caspase-3, and ER stress.

Molecular effectors and modulators of hypericin-mediated cell death in bladder cancer cells

Photodynamic therapy (PDT) is an anticancer approach utilizing a light-absorbing molecule and visible light irradiation to generate, in the presence of O(2), cytotoxic reactive oxygen species, which cause tumor ablation. Given that the photosensitizer hypericin is under consideration for PDT treatment of bladder cancer we used oligonucleotide microarrays in the T24 bladder cancer cell line to identify differentially expressed genes with therapeutic potential. This study reveals that the expression of several genes involved in various metabolic processes, stress-induced cell death, autophagy, proliferation, inflammation and carcinogenesis is strongly affected by PDT and pinpoints the coordinated induction of a cluster of genes involved in the unfolded protein response pathway after endoplasmic reticulum stress and in antioxidant response. Analysis of PDT-treated cells after p38(MAPK) inhibition or silencing unraveled that the induction of an important subset of differentially expressed genes regulating growth and invasion, as well as adaptive mechanisms against oxidative stress, is governed by this stress-activated kinase. Moreover, p38(MAPK) inhibition blocked autonomous regrowth and migration of cancer cells escaping PDT-induced cell death. This analysis identifies new molecular effectors of the cancer cell response to PDT opening attractive avenues to improve the therapeutic efficacy of hypericin-based PDT of bladder cancer.

Multiple Components of Photodynamic Therapy Can Phosphorylate Akt?

A growing number of clinically relevant molecular and cellular responses are observed following photodynamic therapy (PDT). PDT-mediated oxidative stress and PDT-induced tissue hypoxia can elicit the transcriptional and/or translational expression of genes associated with cellular stress, inflammation, angiogenesis, immuno-modulation, apoptosis and signal transduction. One of the signaling molecules activated by oxidative stress is Akt/protein kinase B. Phosphorylation of Akt/protein kinase B activates this signaling molecule and induces a survival response in effected cells and tissue. We hypothesized that PDT using Photofrin (PH) as the photosensitizer could also induce increased levels of Akt phosphorylation. Results from our initial set of experiments demonstrated that in vitro and in vivo PDT treatments induced Akt phosphorylation. Interestingly, incubation of mouse and human breast cancer cells with the porphyrin-based photosensitizer, PH, increased the expression of Akt phosphorylation in the absence of light. Exposure of the corresponding mouse and human-derived breast cancer tumors growing in mice to 630 nm light in the absence of PH administration also induced Akt phosphorylation. These results demonstrate that individual components of the PDT process, photosensitizer alone and light alone, as well as the complete PDT procedure can activate the Akt signaling pathway.

Molecular effectors of multiple cell death pathways initiated by photodynamic therapy

Photodynamic therapy (PDT) is a recently developed anticancer modality utilizing the generation of singlet oxygen and other reactive oxygen species, through visible light irradiation of a photosensitive dye accumulated in the cancerous tissue. Multiple signaling cascades are concomitantly activated in cancer cells exposed to the photodynamic stress and depending on the subcellular localization of the damaging ROS, these signals are transduced into adaptive or cell death responses. Recent evidence indicates that PDT can kill cancer cells directly by the efficient induction of apoptotic as well as non-apoptotic cell death pathways. The identification of the molecular effectors regulating the cross-talk between apoptosis and other major cell death subroutines (e.g. necrosis, autophagic cell death) is an area of intense research in cancer therapy. Signaling molecules modulating the induction of different cell death pathways can become useful targets to induce or increase photokilling in cancer cells harboring defects in apoptotic pathways, which is a crucial step in carcinogenesis and therapy resistance. This review highlights recent developments aimed at deciphering the molecular interplay between cell death pathways as well as their possible therapeutic exploitation in photosensitized cells.

Survivin, a member of the inhibitor of apoptosis family, is induced by photodynamic therapy and is a target for improving treatment response

We observed that photodynamic therapy (PDT) induces the expression and phosphorylation of the inhibitor of apoptosis (IAP) protein survivin in murine and human cancer cells and tumors. Survivin inhibits caspase-9, blocks apoptosis, and is associated with resistance to chemotherapy and radiation. Survivin is a client protein for the 90-kDa heat shock protein (Hsp-90), and the binding of survivin to Hsp-90 assists in the maturation, proper folding, assembly, and transport of this IAP protein. A derivative of the antibiotic geldanamycin, 17-allylamino-17-demethoxygeldanamycin (17-AAG), interferes with proper binding of client proteins, such as survivin, to Hsp-90 and leads to misfolding of client proteins, ubiquination, and proteasome degradation. We hypothesized that PDT efficacy may be reduced by treatment-mediated expression and phosphorylation of survivin, and therefore, targeting the survivin pathway could increase PDT responsiveness. To address this hypothesis, we examined cellular and molecular responses following exposure to PDT, 17-AAG, and the combination of PDT plus 17-AAG in human BT-474 breast cancer cells using Photofrin and NPe6 as photosensitizers. Cells treated with the combination of PDT and 17-AAG exhibited decreased expression of the Hsp-90 client proteins phosphorylated survivin, phosphorylated Akt, and Bcl-2. The decreased expression of these client proteins was accompanied by higher apoptotic indexes and increased cytotoxicity. To confirm a specific role for survivin in modulating PDT, we used a human melanoma cell line, YUSAC2/T34A-C4, stably transfected with an inducible dominant-negative survivin gene under the control of a tetracycline-regulated (tet-off) promoter. PDT treatment of melanoma cells expressing the dominant-negative survivin resulted in increased cleavage of the caspase substrate poly(ADP-ribose) polymerase, apoptosis, and cytotoxicity when compared with results following PDT of the same melanoma cell line expressing wild-type survivin. These results show for the first time that targeting survivin and possibly other Hsp-90 client proteins improves in vitro PDT responsiveness and suggest that manipulation of the antiapoptotic pathway maintained by survivin may enhance PDT-mediated cancer therapy.

Relationship between subcellular localisation of Foscan and caspase activation in photosensitised MCF-7 cells

The present study investigates the relationship between the subcellular localisation of Foscan® and intrinsic apoptotic pathway post Foscan®-based photodynamic therapy (PDT). With this purpose, mammary carcinoma MCF-7 cells were incubated with Foscan® for 3 or 24 h and then subjected to equitoxic light doses. Fluorescence microscopy revealed very good Foscan® co-localization to endoplasmic reticulum (ER) and Golgi apparatus after 3 h incubation with MCF-7 cells. Progressive increase in incubation time shows leakage of Foscan® from Golgi apparatus. Twenty-four hours incubation yielded a fluence-dependent enhanced induction of the ER-resident glucose-regulated protein 78 (Bip/GRP78), along with a weak mitochondrial damage, thus underscoring the ER as the main site of photodamage after prolonged incubation. Analysis of events implicated in apoptotic pathway after 24 h incubation demonstrated photodamage to Bcl-2 protein in total cellular extract, but not in the mitochondrial fraction. We further determined an increase in caspases-7 and -6 activation, which was strongly related to the expression of GRP78. The above findings demonstrate that Foscan® localisation in ER improves the photoactivation of the caspase-7 apoptotic pathway, which is poorly related to mitochondrial damage.

Optical properties of adenocarcinoma and squamous cell carcinoma of the gastroesophageal junction

Photodynamic therapy (PDT) is an alternative to radical surgical resection for T1a or nonresectable carcinomas of the gastroesophageal junction. Besides the concentration of the photosensitizer, the light distribution in tissue is responsible for tumor destruction. For this reason, knowledge about the behavior of light in healthy and dysplastic tissue is of great interest for careful irradiation scheduling. The aim of this study is to determine the optical parameters (OP) of healthy and carcinomatous tissue of the gastroesophageal junction in vitro to provide reproducible parameters for optimal dosimetry when applying PDT. A total of 36 tissue samples [adenocarcinoma tissue (n=21), squamous cell tissue (n=15)] are obtained from patients with carcinomas of the gastroesophageal junction. The optical parameters are measured in 10-nm steps using new integrating sphere spectrometers in the PDT-relevant wavelength range of 300 to 1140 nm and evaluated by inverse Monte-Carlo simulation. Additional examinations are done in healthy tissue from the surgical safety margin. In the wavelength range of frequently applied photosensitizers at 330, 630, and 650 nm, the absorption coefficient in tumor tissue (adenocarcinoma 1.22, 0.16, and 0.15 mm(-1); squamous cell carcinoma 1.48, 0.13, and 0.11 mm(-1)) is significantly lower than in healthy tissue (stomach 3.34, 0.26, and 0.20 mm(-1); esophagus 2.47, 0.21, and 0.18 mm(-1)). The scattering coefficient of all tissues decreases continuously with increasing wavelength (adenocarcinoma 22.8, 12.99, and 12.52 mm(-1); squamous cell carcinoma 19.44, 9.35, and 8.98 mm(-1); stomach 20.55, 13.96, and 13.94 mm(-1); esophagus 20.34, 12.56, and 12.22 mm(-1). All tissues show an anisotropy factor between 0.80 and 0.94 over the entire spectrum. The maximum optical penetration depth for all tissues is achieved in the range of 800 to 1100 nm. At the wavelength range of 330, 630, and 650 nm, the optical penetration depth is significantly higher in carcinoma tissue (adenocarcinoma 0.27, 1.54, and 1.66 mm; squamous cell carcinoma 0.23, 1.71, and 1.84 mm) than in healthy tissue (stomach 0.16, 1.10, and 1.26 mm; esophagus 0.17, 1.47, and 1.65 mm; p<0.05). Above 1000 nm, a higher absorption coefficient of tumor tissue results in a lower optical penetration depth than in healthy tissue (p<0.05). The higher absorption and scattering of the tumor tissue in the wavelength range of available photosensitizer is associated with a low optical penetration depth. This necessitates higher energy doses and long application times or repeated applications to effectively treat large tumor volumes. Photosensitizers optimized for larger wavelength range need to be developed to increase the efficacy of PDT.

Transcriptome changes in a colon adenocarcinoma cell line in response to photochemical treatment as used in photochemical internalisation (PCI)

The photochemical internalisation (PCI) technology liberates endocytosed macromolecules like transgenes from endocytic vesicles in response to photochemical treatment. Thereby PCI improves gene transfection and is suggested for use in gene therapy. It has been proposed that PCI might also stimulate transcription of internalised transgenes, especially if they are controlled by photochemically inducible promoters (transcriptional targeting). In order to identify inducible promoters, and to evaluate the treatments influence on cellular transcriptional activity, the effect of the photochemical treatment as used in PCI (with the photosensitizer disulfonated meso-tetraphenylporphin followed by illumination) on gene transcription in WiDr adenocarcinoma cells was evaluated using microarrays. The expression of 390 genes were identified significantly changed (89% were up-regulated), of which genes associated with DNA binding and transcriptional functions were the most represented. This may be important for the expression of a photochemically internalised transgene under a specific promoter control. Real-time PCR verified photochemical up-regulation of the HSP family genes, as well as down-regulation of EGR-1 at 2-10h post-treatment, suggesting that the HSP (particularly HSP70), in addition to the microarray-identified metallothioneins, but not the EGR-1 promoters, could be relevant promoter candidates for transcriptional targeting via PCI. The resulting overview of gene expression changes in WiDr cells exposed to the PCI-relevant photochemical treatment also provide a basis for the design of new PCI-based strategies with respect of transcriptional targeting.

Photochemical Internalization of Transgenes Controlled by the Heat-shock Protein 70 Promoter

Photochemical internalization (PCI) is a targeting technique that facilitates endosomal escape of macromolecules, such as transgenes, in response to photochemical treatment with endosome/lysosome-localized photosensitizers, such as disulfonated meso-tetraphenylporphine (TPPS(2a)). In gene therapy this leads to enhanced transgene expression. Moreover, photochemical treatment generally activates transcription of stress-response genes, such as heat-shock proteins (HSPs), via stimulation of corresponding promoters. Therefore, we used HSP70 (HSPp; a promoter from the HSP family gene) and investigated whether the PCI stimulus could also activate HSPp and thereby stimulate transcription (expression) of the HSPp-controlled transgene internalized via PCI. Using human colorectal carcinoma and hepatoma cell lines in vitro, we showed that TPPS(2a)-based photochemical treatment enhances expression of cellular HSP70, which correlated with a photochemically enhanced expression (approximately 2-fold, at PCI-optimal doses) of the HSPp-controlled transgene integrated in the genome. Furthermore, PCI enhanced expression of the HSPp-controlled episomal transgene delivered as a plasmid. However, in plasmid-based transfection, PCI-mediated enhancement with HSPp did not exceed the enhancement achieved with the constitutive active CMV promoter. In conclusion, we demonstrated that the PCI-relevant treatment initiates HSP70 response and that the HSP70 promoter can be used in combination with PCI, leading to PCI-enhanced expression of the HSPp-controlled transgene.

Celecoxib and NS-398 enhance photodynamic therapy by increasing in vitro apoptosis and decreasing in vivo inflammatory and angiogenic factors

Photodynamic therapy (PDT) elicits both apoptotic and necrotic responses within treated tumors and produces microvascular injury leading to inflammation and hypoxia. PDT also induces expression of angiogenic and survival molecules including vascular endothelial growth factor, cyclooxygenase-2 (COX-2), and matrix metalloproteinases. Adjunctive administration of inhibitors to these molecules improves PDT responsiveness. In the current study, we examined how the combination of PDT and COX-2 inhibitors improve treatment responsiveness. Photofrin-mediated PDT combined with either celecoxib or NS-398 increased cytotoxicity and apoptosis in mouse BA mammary carcinoma cells. Immunoblot analysis of protein extracts from PDT-treated cells also showed poly(ADP-ribose) polymerase cleavage and Bcl-2 degradation, which were further enhanced following combined therapy. Tumor-bearing mice treated with PDT and either celecoxib or NS-398 exhibited significant improvement in long-term tumor-free survival when compared with PDT or COX-2 inhibitor treatments alone. The combined procedures did not increase in vivo tumor-associated apoptosis. Administration of celecoxib or NS-398 attenuated tissue levels of prostaglandin E2 and vascular endothelial growth factor induced by PDT in treated tumors and also decreased the expression of proinflammatory mediators interleukin-1beta and tumor necrosis factor-alpha. Increased tumor levels of the antiinflammatory cytokine, interleukin 10, were also observed following combined treatment. This study documents for the first time that adjunctive use of celecoxib enhances PDT-mediated tumoricidal action in an in vivo tumor model. Our results also show that administration of COX-2 inhibitors enhance in vitro photosensitization by increasing apoptosis and improve in vivo PDT responsiveness by decreasing expression of angiogenic and inflammatory molecules.