In vitro and in vivo inhibition of epidermal growth factor receptor-tyrosine kinase pathway by photodynamic therapy

A Combination of EGFR Inhibitors and AE-PDT Could Synergistically Suppress Breast Cancer Progression

BACKGROUND

Breast cancer is the most frequently diagnosed malignancy and the leading cause of cancerrelated deaths in women. Activation of EGFR by EC-secreted EGFR ligands promotes breast cancer progression. Current treatments provide limited benefits in triple-negative breast cancer (TNBC). Photodynamic therapy (PDT) has been proven effective for the treatment of TNBC through the EGFR pathway, but the underlying mechanism is still unclear.

PURPOSE

The purpose of this study was to determine the role of the EGFR pathway in the treatment of PDT on TNBC in a co-culture system.

METHODS

MB-231 and HUVEC were co-cultured for experiments (HU-231). Cell viability and ROS production were detected after AE-PDT, a combination of EGFR inhibitors (AEE788)with PDT to test angiogenesis, apoptosis, and pyroptosis. WB detects expression of EGFR. EGFR, P-EGFR, VEGF, caspase-1, capase-3, and GSDMD .

RESULTS

AE-PDT inhibited HU-231 cell proliferation and tumor angiogenesis, and induced cell apoptosis and pyroptosis by promoting ROS production. AEE788, an inhibitor of the EGFR, enhanced HU-231 cell killing after AE-PDT.

CONCLUSION

Our study suggested that the combination of EGFR inhibitors and AE-PDT could synergistically suppress breast cancer progression, providing a new treatment strategy.

Advanced photodynamic therapy with an engineered M13 phage targeting EGFR: Mitochondrial localization and autophagy induction in ovarian cancer cell lines

Photodynamic therapy (PDT) is a potential synergistic approach to chemotherapy for treating ovarian cancer, the most lethal gynecologic malignancy. Here we used M13 bacteriophage as a targeted vector for the efficient photodynamic killing of SKOV3 and COV362 cells. The M13 phage was refactored (M13_r) to display an EGFR binding peptide in its tip that is frequently overexpressed in ovarian cancer. The refactored phage was conjugated with chlorin e6 (Ce6), one of the most widely used photosensitizers (M13_r-Ce6). The new platform, upon irradiation, generated ROS by type I mechanism and showed activity in killing SKOV3 and COV362 cells even at concentrations in which Ce6 alone was ineffective. A microscopy analysis demonstrated an enhanced cellular uptake of M13_r-Ce6 compared to free Ce6 and its mitochondrial localization. Western blot analysis revealed significant downregulation in the expression of EGFR in cells exposed to M13_r-Ce6 after PDT. Following PDT treatment, autophagy induction was supported by an increased expression of LC3II, along with a raised autophagic fluorescent signal, as observed by fluorescence microscopy analysis for autophagosome visualization. As a conclusion we have herein proposed a bacteriophage-based receptor targeted photodynamic therapy for EGFR-positive ovarian cancer.

Curcumin encapsulation in functional PLGA nanoparticles: A promising strategy for cancer therapies

Nanoparticles have emerged as promising drug delivery systems for the treatment of several diseases. Novel cancer therapies have exploited these particles as alternative adjuvant therapies to overcome the traditional limitations of radio and chemotherapy. Curcumin is a natural bioactive compound found in turmeric, that has been reported to show anticancer activity against several types of tumors. Despite some biological limitations regarding its absorption in the human body, curcumin encapsulation in poly(lactic-co-glycolic acid) (PLGA), a non-toxic, biodegradable and biocompatible polymer, represents an effective strategy to deliver a drug to a tumor site. Furthermore, PLGA nanoparticles can be engineered with targeting moieties to reach specific cancer cells, thus enhancing the antitumor effects of curcumin. We herein aim to bring an up-to-date summary of the recently developed strategies for curcumin delivery to different types of cancer cells through encapsulation in PLGA nanoparticles, correlating their effects with those of curcumin on the biological capabilities acquired by cancer cells (cancer hallmarks). We discuss the targeting strategies proposed for advanced curcumin delivery and the respective improvements achieved for each cancer cell analyzed, in addition to exploring the encapsulation techniques employed. The conjugation of correct encapsulation techniques with tumor-oriented targeting design can result in curcumin-loaded PLGA nanoparticles that can successfully integrate the elaborate network of development of alternative cancer treatments along with traditional ones. Finally, the current challenges and future demands to launch these nanoparticles in oncology are comprehensively examined.

Photoimmunotherapy of Ovarian Cancer: A Unique Niche in the Management of Advanced Disease

Ovarian cancer (OvCa) is the leading cause of gynecological cancer-related deaths in the United States, with five-year survival rates of 15-20% for stage III cancers and 5% for stage IV cancers. The standard of care for advanced OvCa involves surgical debulking of disseminated disease in the peritoneum followed by chemotherapy. Despite advances in treatment efficacy, the prognosis for advanced stage OvCa patients remains poor and the emergence of chemoresistant disease localized to the peritoneum is the primary cause of death. Therefore, a complementary modality that is agnostic to typical chemo- and radio-resistance mechanisms is urgently needed. Photodynamic therapy (PDT), a photochemistry-based process, is an ideal complement to standard treatments for residual disease. The confinement of the disease in the peritoneal cavity makes it amenable for regionally localized treatment with PDT. PDT involves photochemical generation of cytotoxic reactive molecular species (RMS) by non-toxic photosensitizers (PSs) following exposure to non-harmful visible light, leading to localized cell death. However, due to the complex topology of sensitive organs in the peritoneum, diffuse intra-abdominal PDT induces dose-limiting toxicities due to non-selective accumulation of PSs in both healthy and diseased tissue. In an effort to achieve selective damage to tumorous nodules, targeted PS formulations have shown promise to make PDT a feasible treatment modality in this setting. This targeted strategy involves chemical conjugation of PSs to antibodies, referred to as photoimmunoconjugates (PICs), to target OvCa specific molecular markers leading to enhanced therapeutic outcomes while reducing off-target toxicity. In light of promising results of pilot clinical studies and recent preclinical advances, this review provides the rationale and methodologies for PIC-based PDT, or photo-immunotherapy (PIT), in the context of OvCa management.

Vandetanib sensitizes head and neck squamous cell carcinoma to photodynamic therapy through modulation of EGFR-dependent DNA repair and the tumour microenvironment

BACKGROUND

Epidermal growth factor receptor (EGFR) overexpression is characteristic in head and neck cancers and is associated with tumour regrowth following photodynamic therapy (PDT).

PURPOSE

We investigated vandetanib, which selectively blocks EGFR and vascular endothelial growth factor receptor-2 (VEGFR-2), to enhance the efficacy of PDT.

METHODS

We assessed the in vitro therapeutic efficacy of: 1) vandetanib; 2) PDT with the photosensitizer Chlorin e6 (Fotolon®); and 3) combined PDT + vadetanib treatment in CAL-27 oral squamous cell carcinoma (OSCC) cell line by cell viability, γH2AX foci immunostaining, cell cycle arrest and western blot. We also performed in vivo tumour regression study and immunohistochemical staining of formalin-fixed paraffin-embedded (FFPE) regressed and regrown tumour tissues.

RESULTS

First, we observed significantly higher cytotoxicity and residual DNA damage in vandetanib + PDT-treated CAL-27 OSCC cells than tumour cells treated with PDT alone. This is due to impaired DNA DSB repair caused by downregulation of EGFR-mediated DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activation. Next, combined vandetanib and PDT resulted in significant tumour growth delay in vivo that is linked to reduction of PDT-induced EGFR phosphorylation and cellular proliferation, along with loss of tumour vasculature. In particular, we observed significant revascularisation of the microenvironment that is associated with upregulated ERK1/2 phosphorylation in regrown tumours post-vandetanib + PDT, thereby corroborating the importance of microenvironmental modification for the observed drug-PDT synergistic interaction.

CONCLUSION

Taken together, our data suggests that vandetanib enhances the efficacy of PDT through both direct and indirect effects on the cellular DNA repair machinery and tumour microenvironment, respectively.

Evaluation of targeted curcumin (CUR) loaded PLGA nanoparticles for in vitro photodynamic therapy on human glioblastoma cell line

In this study, antibody-conjugated biodegradable polymeric nanoparticles were developed to enhance the photodaynamic efficiency of curcumin (CUR) on glioblastoma tumor cells. Poly (D, l-lactic-co-glycolic acid) nanoparticles (PLGA NPs) were synthesized and stabilized by polyvinyl alcohol (PVA). Poly(ethylene-alt-maleic anhydride) (PEMA) was used to provide carboxyl groups on the surface of NPs. The CUR or FITC (fluorescein isothiocyanate) was encapsulated in PLGA NPs using the nanoprecipitation method. The carboxylic groups on the surface of the PLGA NPs were covalently conjugated to the amino groups of a monoclonal antibody against EGFRvIII (A-EGFRvIII-f). The prepared NPs were fully characterized by Zetasizer, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR), and then entrapment efficiency (EE), drug loading efficiency (DLE), CUR release, cell internalization, intrinsic cytotoxicity, and phototoxicity were evaluated. Furthermore, the effect of monoclonal antibody (MAb) on the tyrosine phosphorylation of EGFRvIII after photodynamic therapy (PDT) was assessed. The immunoreactivity of the antibody in MAb-PLGA NPs was preserved during the process of conjugation. The selective cellular internalization of MAb-PLGA NPs (FITC or CUR loaded) into the DKMG/EGFRvIII cells (EGFRvIII overexpressed human glioblastoma cell line) in comparison with DK-MG^low (human glioblastoma cell line with low level of EGFRvIII) was also confirmed. MAb-CUR-PLGA NPs were able to show more effective photodynamic toxicity (56% vs. 24%) on the DKMG/EGFRvIII cells compared to CUR-PLGA NPs. These results suggest that the anti-EGFRvIII MAb-CUR-PLGA NPs have potential of targeted drug delivery system for PDT in the overexpressed EGFRvIII tumor cells.

Influence and mechanism of 5-aminolevulinic acid-photodynamic therapy on the metastasis of esophageal carcinoma

BACKGROUD

Photodynamic therapy (PDT) for the treatment of esophageal cancer was more and more popularly used since it was approved for the treatment of advanced esophageal cancer in 1996. It has been reported to influence the tumor growth and metastasis via a variety of signaling pathways, but its mechanism remains to be further studied. This research studied the effects of ALA-PDT on esophageal carcinoma in vitro and in vivo, discovering its molecular regulating mechanism and the way to enhence the PDT effect.

METHODS

Eca-109 cells were incubated with a medium containing EGFR tyrphostin AG1478 or PI3K inhibitor LY294002, then with ALA, and the cells were irradiated with the laser 6h later. The cell viability was measured with MTT assay, and the migration ability was detected by transwell experiments 24h post-ALA-PDT. The gene and protein expression on EGFR/PI3K/AKT signaling pathway was analyzed by realtime PCR and Western blotting respectively. Then, RFP-Eca-109 burdened nude mice model was constructed, and were treated with ALA-PDT when the tumor volume reached 150-350mm³. The gene and protein expression were analyzed 24h and 50days post-ALA-PDT.

RESULTS

Our study showed that ALA-PDT respectively combined with AG1478, LY294002 could synergistically reduce the growth and migration ability of the Eca-109 cells in vitro and significantly down-regulate the protein expression of EGFR/PI3K and PI3K/AKT, meanwhile, significantly down-regulate the gene expression of EGFR when combining with AG1478. Forthermore, ALA-PDT could significantly decrease the tumor growth and metastasis and down-regulate the gene expression of EGFR and the protein expression of EGFR and PI3K in the tumor of mice.

CONCLUSION

This study revealed a molecular mechanism of ALA-PDT and developed a new modality application of therapy, by combining ALA-PDT with small molecular inhibitors, for better effect in the clinical practice of esophageal carcinoma.

Nimotuzumab increases the anti-tumor effect of photodynamic therapy in an oral tumor model

Oral squamous cell carcinoma (OSCC) represents 90% of all oral cancers and is characterized with poor prognosis and low survival rate. Epidermal growth factor receptor (EGFR) is highly expressed in oral cancer and is a target for cancer therapy and prevention. In this present work, we evaluate the efficacy of photodynamic therapy (PDT) in combination with an EGFR inhibitor, nimotuzumab in oral cancer cell lines and OSCC xenograft tumor model. PDT is a promising and minimally invasive treatment modality that involves the interaction of a photosensitizer, molecular oxygen and light to destroy tumors. We demonstrated that EGFR inhibitors nimotuzumab and cetuximab exhibits anti-angiogenic properties by inhibiting the migration and invasion of oral cancer cell lines and human endothelial cells. The EGFR inhibitors also significantly reduced tube formation of endothelial cells. Chlorin e6-PDT in combination with nimotuzumab and cetuximab reduced cell proliferation in different oral cancer and endothelial cells. Furthermore, our in vivo studies showed that the combination therapy of PDT and nimotuzumab synergistically delayed tumor growth when compared with control and PDT treated tumors. Downregulation of EGFR, Ki-67 and CD31 was observed in the tumors treated with combination therapy. Analysis of the liver and kidney function markers showed no treatment related toxicity. In conclusion, PDT outcome of oral cancer can be improved when combined with EGFR inhibitor nimotuzumab.

Fluence Rate Differences in Photodynamic Therapy Efficacy and Activation of Epidermal Growth Factor Receptor after Treatment of the Tumor-Involved Murine Thoracic Cavity

Photodynamic therapy (PDT) of the thoracic cavity can be performed in conjunction with surgery to treat cancers of the lung and its pleura. However, illumination of the cavity results in tissue exposure to a broad range of fluence rates. In a murine model of intrathoracic PDT, we studied the efficacy of 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH; Photochlor^®)-mediated PDT in reducing the burden of non-small cell lung cancer for treatments performed at different incident fluence rates (75 versus 150 mW/cm). To better understand a role for growth factor signaling in disease progression after intrathoracic PDT, the expression and activation of epidermal growth factor receptor (EGFR) was evaluated in areas of post-treatment proliferation. The low fluence rate of 75 mW/cm produced the largest reductions in tumor burden. Bioluminescent imaging and histological staining for cell proliferation (anti-Ki-67) identified areas of disease progression at both fluence rates after PDT. However, increased EGFR activation in proliferative areas was detected only after treatment at the higher fluence rate of 150 mW/cm. These data suggest that fluence rate may affect the activation of survival factors, such as EGFR, and weaker activation at lower fluence rate could contribute to a smaller tumor burden after PDT at 75 mW/cm.

Mechanisms in photodynamic therapy: part two-cellular signaling, cell metabolism and modes of cell death

Photodynamic therapy (PDT) has been known for over a hundred years, but is only now becoming widely used. Originally developed as a tumor therapy, some of its most successful applications are for non-malignant disease. In the second of a series of three reviews, we will discuss the mechanisms that operate in PDT on a cellular level. In Part I [Castano AP, Demidova TN, Hamblin MR. Mechanism in photodynamic therapy: part one-photosensitizers, photochemistry and cellular localization. Photodiagn Photodyn Ther 2004;1:279-93] it was shown that one of the most important factors governing the outcome of PDT, is how the photosensitizer (PS) interacts with cells in the target tissue or tumor, and the key aspect of this interaction is the subcellular localization of the PS. PS can localize in mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus and plasma membranes. An explosion of investigation and explorations in the field of cell biology have elucidated many of the pathways that mammalian cells undergo when PS are delivered in tissue culture and subsequently illuminated. There is an acute stress response leading to changes in calcium and lipid metabolism and production of cytokines and stress proteins. Enzymes particularly, protein kinases, are activated and transcription factors are expressed. Many of the cellular responses are centered on mitochondria. These effects frequently lead to induction of apoptosis either by the mitochondrial pathway involving caspases and release of cytochrome c, or by pathways involving ceramide or death receptors. However, under certain circumstances cells subjected to PDT die by necrosis. Although there have been many reports of DNA damage caused by PDT, this is not thought to be an important cell-death pathway. This mechanistic research is expected to lead to optimization of PDT as a tumor treatment, and to rational selection of combination therapies that include PDT as a component.

Cellular intrinsic factors involved in the resistance of squamous cell carcinoma to photodynamic therapy

Photodynamic therapy (PDT) is widely used to treat non-melanoma skin cancer. However, some patients affected with squamous cell carcinoma (SCC) do not respond adequately to PDT with methyl-δ-aminolevulinic acid (MAL-PDT) and the tumors acquire an infiltrative phenotype and became histologically more aggressive, less differentiated, and more fibroblastic. To search for potential factors implicated in SCC resistance to PDT, we have used the SCC-13 cell line (parental) and resistant SCC-13 cells obtained by repeated MAL-PDT treatments (5th and 10th PDT-resistant generations). Xenografts assays in immunodeficient mice showed that the tumors generated by resistant cells were bigger than those induced by parental cells. Comparative genomic hybridization array (aCGH) showed that the three cell types presented amplicons in 3p12.1 CADM2, 7p11.2 EFGR, and 11q13.3 CCND1 genes. The 5th and 10th PDT-resistant cells showed an amplicon in 5q11.2 MAP3K1, which was not present in parental cells. The changes detected by aCGH on CCND1, EFGR, and MAP3K1 were confirmed in extracts of SCC-13 cells by reverse-transcriptase PCR and by western blot, and by immunohistochemistry in human biopsies from persistent tumors after MAL-PDT. Our data suggest that genomic imbalances related to CCND1, EFGR, and particularly MAP3K1 seem to be involved in the development of the resistance of SCC to PDT.

Photodynamic therapy with 3-(1'-hexyloxyethyl) pyropheophorbide a for cancer of the oral cavity

PURPOSE

The primary objective was to evaluate safety of 3-(1'-hexyloxyethyl)pyropheophorbide-a (HPPH) photodynamic therapy (HPPH-PDT) for dysplasia and early squamous cell carcinoma of the head and neck (HNSCC). Secondary objectives were the assessment of treatment response and reporters for an effective PDT reaction.

EXPERIMENTAL DESIGN

Patients with histologically proven oral dysplasia, carcinoma in situ, or early-stage HNSCC were enrolled in two sequentially conducted dose escalation studies with an expanded cohort at the highest dose level. These studies used an HPPH dose of 4 mg/m(2) and light doses from 50 to 140 J/cm(2). Pathologic tumor responses were assessed at 3 months. Clinical follow up range was 5 to 40 months. PDT induced cross-linking of STAT3 were assessed as potential indicators of PDT effective reaction.

RESULTS

Forty patients received HPPH-PDT. Common adverse events were pain and treatment site edema. Biopsy proven complete response rates were 46% for dysplasia and carcinoma in situ and 82% for squamous cell carcinomas (SCC) lesions at 140 J/cm(2). The responses in the carcinoma in situ/dysplasia cohort are not durable. The PDT-induced STAT3 cross-links is significantly higher (P = 0.0033) in SCC than in carcinoma in situ/dysplasia for all light doses.

CONCLUSION

HPPH-PDT is safe for the treatment of carcinoma in situ/dysplasia and early-stage cancer of the oral cavity. Early-stage oral HNSCC seems to respond better to HPPH-PDT in comparison with premalignant lesions. The degree of STAT3 cross-linking is a significant reporter to evaluate HPPH-PDT-mediated photoreaction.

GRP78-targeting subtilase cytotoxin sensitizes cancer cells to photodynamic therapy

Glucose-regulated protein 78 (GRP78) is an endoplasmic reticulum (ER)-resident chaperone and a major regulator of the unfolded protein response (UPR). Accumulating evidence indicate that GRP78 is overexpressed in many cancer cell lines, and contributes to the invasion and metastasis in many human tumors. Besides, GRP78 upregulation is detected in response to different ER stress-inducing anticancer therapies, including photodynamic therapy (PDT). This study demonstrates that GRP78 mRNA and protein levels are elevated in response to PDT in various cancer cell lines. Stable overexpression of GRP78 confers resistance to PDT substantiating its cytoprotective role. Moreover, GRP78-targeting subtilase cytotoxin catalytic subunit fused with epidermal growth factor (EGF-SubA) sensitizes various cancer cells to Photofrin-mediated PDT. The combination treatment is cytotoxic to apoptosis-competent SW-900 lung cancer cells, as well as to Bax-deficient and apoptosis-resistant DU-145 prostate cancer cells. In these cells, PDT and EGF-SubA cytotoxin induce protein kinase R-like ER kinase and inositol-requiring enzyme 1 branches of UPR and also increase the level of C/EBP (CCAAT/enhancer-binding protein) homologous protein, an ER stress-associated apoptosis-promoting transcription factor. Although some apoptotic events such as disruption of mitochondrial membrane and caspase activation are detected after PDT, there is no phosphatidylserine plasma membrane externalization or DNA fragmentation, suggesting that in DU-145 cells the late apoptotic events are missing. Moreover, in SW-900 cells, EGF-SubA cytotoxin potentiates PDT-mediated cell death but attenuates PDT-induced apoptosis. In addition, the cell death cannot be reversed by caspase inhibitor z-VAD, confirming that apoptosis is not a major cell death mode triggered by the combination therapy. Moreover, no typical features of necrotic or autophagic cell death are recognized. Instead, an extensive cellular vacuolation of ER origin is observed. Altogether, these findings indicate that PDT and GRP78-targeting cytotoxin treatment can efficiently kill cancer cells independent on their apoptotic competence and triggers an atypical, non-apoptotic cell death.

Oncologic photodynamic therapy: clinical strategies that modulate mechanisms of action

Photodynamic therapy (PDT) is an elegant minimally invasive oncologic therapy. The clinical simplicity of photosensitizer (PS) drug application followed by appropriate illumination of target leading to the oxygen dependent tumor ablative Photodynamic Reaction (PDR) has gained this treatment worldwide acceptance. Yet the true potential of clinical PDT has not yet been achieved. This paper will review current mechanisms of action and treatment paradigms with critical commentary on means to potentially improve outcome using readily available clinical tools.

A new nanoconstruct for epidermal growth factor receptor-targeted photo-immunotherapy of ovarian cancer

Targeted photodynamic therapy (TPDT) involves the administration of a photosensitizer (PS) conjugated with a targeting moiety followed by light activation. The systemic toxicity associated with conventional therapy may thus be significantly reduced in TPDT due to the dual selectivity provided by the spatial localization of the illumination as well as the target-localizing ability of the conjugate. Herein, a photo-immuno-conjugate-associating-liposome (PICAL) for TPDT has been developed in which the FDA approved benzoporphyrin derivative monoacid A (BPD) and the Cetuximab antibody for epidermal growth factor receptor (EGFR) were associated into a stable Preformed Plain Liposome (PPL) by passive physical adsorption. Results have shown that the BPD molecules adsorbed into PICAL have stable optical behavior and a higher fluorescence quantum yield than free-BPD. The Cetuximab adsorbed into PPL selectively binds to cells that overexpress EGFR. The inhibition of EGFR signaling by PICAL has enhanced PDT-mediated ovarian cancer cell death.

FROM THE CLINICAL EDITOR

In this basic science study, a photo-immuno-conjugate-associating-liposome for targeted photodynamic therapy is investigated. The FDA-approved benzoporphyrin derivative monoacid A and an epidermal growth factor receptor antibody were assembed into a stable Preformed Plain Liposome (PPL) by passive physical adsorption. The authors demonstrate therapeutic efficacy of the above construct in an ovarian tumor system.

Photodynamic therapy activated signaling from epidermal growth factor receptor and STAT3: Targeting survival pathways to increase PDT efficacy in ovarian and lung cancer

Patients with serosal (pleural or peritoneal) spread of malignancy have few definitive treatment options and consequently have a very poor prognosis. We have previously shown that photodynamic therapy (PDT) can be an effective treatment for these patients, but that the therapeutic index is relatively narrow. Here, we test the hypothesis that EGFR and STAT3 activation increase survival following PDT, and that inhibiting these pathways leads to increased PDT-mediated direct cellular cytotoxicity by examining BPD-PDT in OvCa and NSCLC cells. We found that BPD-mediated PDT stimulated EGFR tyrosine phosphorylation and nuclear translocation, and that EGFR inhibition by erlotinib resulted in reduction of PDT-mediated EGFR activation and nuclear translocation. Nuclear translocation and PDT-mediated activation of EGFR were also observed in response to BPD-mediated PDT in multiple cell lines, including OvCa, NSCLC and head and neck cancer cells, and was observed to occur in response to porfimer sodium-mediated PDT. In addition, we found that PDT stimulates nuclear translocation of STAT3 and STAT3/EGFR association and that inhibiting STAT3 signaling prior to PDT leads to increased PDT cytotoxicity. Finally, we found that inhibition of EGFR signaling leads to increased PDT cytotoxicity through a mechanism that involves increased apoptotic cell death. Taken together, these results demonstrate that PDT stimulates the nuclear accumulation of both EGFR and STAT3 and that targeting these survival pathways is a potentially promising strategy that could be adapted for clinical trials of PDT for patients with serosal spread of malignancy.

Photoimmunotherapy and irradiance modulation reduce chemotherapy cycles and toxicity in a murine model for ovarian carcinomatosis: perspective and results

Significant toxicities from multiple cycles of chemotherapy often cause delays or early termination of treatment, leading to poor outcomes in ovarian cancer patients. Complementary modalities that potentiate the efficacy of traditional agents with fewer cycles and less toxicity are needed. Photodynamic therapy is a mechanistically-distinct modality that synergizes with chemo and biologic agents. A combination regimen with a clinically relevant chemotherapy cocktail (cisplatin + paclitaxel) and anti-EGFR targeted photoimmunotherapy (PIT) is evaluated in a murine model for ovarian carcinomatosis. Mice received either 1 or 2 chemotherapy cycles followed by PIT with a chlorine6-Erbitux photoimmunoconjugate and 25 J/cm2 light. PIT + 1 cycle of chemotherapy significantly reduced tumor burden, comparable to multiple chemotherapy cycles. Relative to 1 cycle of chemotherapy, the addition of PIT did not cause significant mouse weight loss, whereas 2 cycles of chemotherapy led to a significant reduction in weight. Irradiance-dependence on PIT efficacy was a function of the conjugation chemistry, providing an additional variable for optimization of PIT outcome.

Epidermal growth factor receptor-targeted photosensitizer selectively inhibits EGFR signaling and induces targeted phototoxicity in ovarian cancer cells

Targeted photosensitizer delivery to EGFR-expressing cells was achieved in the present study using a high purity, targeted photoimmunoconjugate (PIC). When the PDT agent, benzoporphyrin derivative monoacid ring A (BPD) was coupled to an EGFR-targeting antibody (cetuximab), we observed altered cellular localization and selective phototoxicity of EGFR-positive cells, but no phototoxicity of EGFR-negative cells. Cetuximab in the PIC formulation blocked EGF-induced activation of the EGFR and downstream signaling pathways. Our results suggest that photoimmunotargeting is a useful dual strategy for the selective destruction of cancer cells and also exerts the receptor-blocking biological function of the antibody.

Antiangiogenesis agents avastin and erbitux enhance the efficacy of photodynamic therapy in a murine bladder tumor model

BACKGROUND AND OBJECTIVE

Photodynamic therapy (PDT) has been established as an alternative therapy for the treatment of various types of malignant disorders, including oesophageal, lung, and bladder cancer. However, one of the limitations of PDT is treatment-induced hypoxia that triggers angiogenesis. The objective of this study was to evaluate the effects of combination therapy with PDT and an antiangiogenic protocol using monoclonal antibodies against both vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR).

MATERIALS AND METHODS

In vitro angiogenesis assays and in vivo matrigel assay were performed to understand the inhibitory effects of the antiangiogenic agents. Tumor bearing mice were assigned to six different categories: Control, PDT only, Avastin + Erbitux, PDT + Avastin, PDT + Erbitux, and PDT + Avastin and Erbitux. Treated and control tumors were monitored for recurrence for up to 90 days.

RESULTS

In vitro results provided valuable insight into the dynamics of endothelial cells in response to angiogenic stimulants and inhibitors to assess the angiogenesis processes. Addition of VEGF increased the migration of bladder cancer cells and addition of Avastin and Erbitux decreased cell migration significantly. Both inhibitors were also able to suppress invasion and tube formation in human umbilical vein endothelial cells (HUVEC). The in vivo tumor response for PDT with single inhibitor (Avastin or Erbitux) and double inhibitor (Avastin + Erbitux) was comparable; however, targeting both VEGF and EGFR pathways along with PDT resulted in more rapid response. Downregulation of VEGF and EGFR were observed in tumors treated with PDT in combination with Avastin and Erbitux respectively.

CONCLUSION

Our results show that blocking the VEGF or EGFR pathway along with PDT can effectively suppress tumor growth and the combination of both VEGF and EGFR inhibitors along with PDT could be used to treat more aggressive tumors to achieve rapid response.

Photodynamic therapy-induced angiogenic signaling: consequences and solutions to improve therapeutic response

Photodynamic therapy (PDT) can be a highly effective treatment for diseases ranging from actinic keratosis to cancer. While use of this therapy shows great promise in preclinical and clinical studies, understanding the molecular consequences of PDT is critical to designing better treatment protocols. A number of publications have documented alteration in angiogenic factors and growth factor receptors following PDT, which could abrogate treatment effect by inducing angiogenesis and re-establishment of the tumor vasculature. In response to these findings, work over the past decade has examined the efficacy of combining PDT with molecular targeting drugs, such as anti-angiogenic compounds, in an effort to combat these PDT-induced molecular changes. These combinatorial approaches increase rates of apoptosis, impair pro-tumorigenic signaling, and enhance tumor response. This report will examine the current understanding of PDT-induced angiogenic signaling and address molecular-based approaches to abrogate this signaling or its consequences thereby enhancing PDT efficacy.

Cutaneous epidermal growth factor receptor system following ultraviolet irradiation: exploring the role of molecular mechanisms

BACKGROUND/PURPOSE

The epidermal growth factor receptor (EGFR) pathway appears to be essential in many cutaneous disorders. It is well established that ultraviolet (UV) irradiation activates the EGFR in the animal and human skin; however, the molecular mechanisms involved in such activation remain unclear. Our aim is to review and analyse them.

METHODS

Computerized search and selection of original papers in the MEDLINE database (PubMed) from 1988 to 2009 were performed. Systematic analysis and breakdown of the information selected were carried out.

RESULTS

Full manuscripts were retrieved for 32 citations. It was proven that UV light acts directly and indirectly on EGFR (ErbB1/ErbB2) and on numerous intermediaries of extracellular and intracellular signalling. The most closely observed changes imply concentrations and/or molecular activity of the reactive oxygen species group, hydrogen peroxide, matrix metalloproteinases, p38MAPKinase, p21WAF1, p53, signal transducers and activators of transcription 3 and telomerase.

CONCLUSION

Our results help to clarify the working and importance of the UV-EGFR system in the human skin.

PDT-induced inflammatory and host responses

Photodynamic therapy (PDT) is used in the management of neoplastic and nonmalignant diseases. Its unique mechanisms of action include direct cytotoxic effects exerted towards tumor cells, destruction of tumor and peritumoral vasculature and induction of local acute inflammatory reaction. The latter develops in response to (1) damage to tumor and stromal cells that leads to the release of cell death-associated molecular patterns (CDAMs) or damage associated molecular patterns (DAMPs), (2) early vascular changes that include increased vascular permeability, vascular occlusion, and release of vasoactive and proinflammatory mediators, (3) activation of alternative pathway of complement leading to generation of potent chemotactic factors, and (4) induction of signaling cascades and transcription factors that trigger secretion of cytokines, matrix metalloproteinases, or adhesion molecules. The majority of studies indicate that induction of local inflammatory response contributes to the antitumor effects of PDT and facilitates development of systemic immunity. However, the degree of PDT-induced inflammation and its subsequent contribution to its antitumor efficacy depend on multiple parameters, such as chemical nature, concentration and subcellular localization of the photosensitizers, the spectral characteristics of the light source, light fluence and fluence rate, oxygenation level, and tumor type. Identification of detailed molecular mechanisms and development of therapeutic approaches modulating PDT-induced inflammation will be necessary to tailor this treatment to particular clinical conditions.

The role of epidermal growth factor receptor in photodynamic therapy: a review of the literature and proposal for future investigation

The epidermal growth factor receptor (EGFR) pathway seems to be an important contributor to the antiproliferative response to photodynamic therapy (PDT), in terms of cell death, apoptosis and tumour destruction. We reviewed all preclinical investigations in the scientific literature on the role of the EGFR pathway in PDT. A systematic search of Medline-indexed references up to March 2010 using the recommended strategies for Medline information retrieval and identifying relevant studies from systematic reviews, revealed 16 full articles that were exhaustively analysed. EGFR inhibition/degradation appeared to be a major effect of PDT in all investigations. PDT was found to result in a time-dependent reduction of EGFR expression, inhibition of tyrosine phosphorylation and induction of apoptosis during the regression of tumours. Within the time period of the PDT reaction, normal and malignant cells lose their responsiveness to EGF. The ERK1/2 and EGFR-PI3K-Akt pathways seem to be involved in cellular survival after PDT. Pharmacotherapy and immunotherapy to block EGFR activity combined with PDT seem to be very effective in reducing malignant tumours in vivo. The effect of PDT is associated with inactivation of the EGFR pathway, but biochemical and cellular phenomena are important and scarcely investigated. EGFR inhibitors and PDT act synergistically, and this is highly relevant for clinical use.

Targeted Therapy of Cancer Using Photodynamic Therapy in Combination with Multi-faceted Anti-Tumor Modalities

Photodynamic therapy (PDT) has emerged as one of the important therapeutic options in the management of cancer and other diseases. PDT involves a tumor-localized photosensitizer (PS), which when appropriately illuminated by visible light converts oxygen into cytotoxic reactive oxygen species (ROS), that attack key structural entities within the targeted cells, ultimately resulting in necrosis or apoptosis. Though PDT is a selective modality, it can be further enhanced by combining other targeted therapeutic strategies that include the use of synthetic peptides and nanoparticles for selective delivery of photosensitizers. Another potentially promising strategy is the application of targeted therapeutics that exploit a myriad of critical pathways involved in tumorigenesis and metastasis. Vascular disrupting agents that eradicate tumor vasculature during PDT and anti-angiogenic agents that targets specific molecular pathways and prevent the formation of new blood vessels are novel therapeutic approaches that have been shown to improve treatment outcome. In addition to the well-documented mechanisms of direct cell killing and damage to the tumor vasculature, PDT can also activate the body's immune response against tumors. Numerous pre-clinical studies and clinical observations have demonstrated the immuno-stimulatory capability of PDT. Herein, we aim to integrate the most important findings with regard to the combination of PDT and other novel targeted therapy approaches, detailing its potential in cancer photomedicine.

Targeted inhibition of the EGFR pathways enhances Zn-BC-AM PDT-induced apoptosis in well-differentiated nasopharyngeal carcinoma cells

Epidermal growth factor receptor (EGFR), a receptor often expressed in nasopharyngeal carcinoma (NPC) cells, is one of the recently identified molecular targets in cancer treatment. In the present study, the effects of combined treatment of Zn-BC-AM PDT with an EGFR inhibitor AG1478 were investigated. Well-differentiated NPC HK-1 cells were subjected to PDT with 1 microM of Zn-BC-AM and were irradiated at a light dose of 1 J/cm(2) in the presence or absence of EGFR inhibitor AG1478. Specific protein kinase inhibitors of downstream EGFR targets were also used in the investigation. EGFR, Akt, and ERK were found constitutively activated in HK-1 cells and the activities could be inhibited by the EGFR inhibitor AG1478. A sub-lethal concentration of AG1478 was found to further enhance the irreversible cell damage induced by Zn-BC-AM PDT in HK-1 cells. Pre-incubation of the cells with specific inhibitors of EGFR (AG1478), PI3k/Akt (LY294002), or MEK/ERK (PD98059) before light irradiation were found to enhance Zn-BC-AM PDT-induced formation of apoptotic cells. The efficacy of Zn-BC-AM PDT can be increased through the inhibition of EGFR/PI3K/Akt and EGFR/MEK/ERK signaling pathways in NPC cells. Combination therapy with Zn-BC-AM PDT and EGFR inhibitors may further be developed for the treatment of advanced NPC.

Synthesis, properties and in vitro photodynamic activity of water-soluble azaphthalocyanines and azanaphthalocyanines

In this work zinc azaphthalocyanines (AzaPcs) from the group of tetrapyrazinoporphyrazines and zinc azanaphthalocyanines from the group of tetra[6,7]quinoxalinoporphyrazines (TQP) with eight diethylaminoethylsulfanyl substituents were synthesized. Tertiary amines were later quaternized with ethyl iodide to obtain water-soluble photosensitizers (PSs). Quaternized compounds showed high singlet oxygen quantum yields as determined in DMF by monitoring decomposition of 1,3-diphenylisobenzofuran. In water medium, quaternized AzaPc derivatives appeared in monomeric form in a wide range of concentrations while quaternized TQP derivatives showed aggregation at higher concentrations (over 1 microM). Photodynamic activity was tested on Hep2 cells using light of lambda > 640 nm. Both quaternized dyes showed high photodynamic activity (IC(50) = 104 and 220 nm for AzaPc and TQP, respectively). Dark toxicity was not detected even at the highest concentration used in in vitro tests (200 microM) which indicates a promising therapeutic index of these new substances. Tested compounds localized inside the cells mainly within the lysosomes thus suggesting an endocytic mechanism of cellular uptake. No localization within mitochondria was detected. A great advantage of TQP derivatives over other PSs is their very strong absorption at 747 nm that allows activation at wavelengths penetrating deeper into human tissues.

Targeting EGFR with photodynamic therapy in combination with Erbitux enhances in vivo bladder tumor response

BACKGROUND

Photodynamic therapy (PDT) is a promising cancer treatment modality that involves the interaction of the photosensitizer, molecular oxygen and light of specific wavelength to destroy tumor cells. Treatment induced hypoxia is one of the main side effects of PDT and efforts are underway to optimize PDT protocols for improved efficacy. The aim of this study was to investigate the anti-tumor effects of PDT plus Erbitux, an angiogenesis inhibitor that targets epidermal growth factor receptor (EGFR), on human bladder cancer model. Tumor-bearing nude mice were assigned to four groups that included control, PDT, Erbitux and PDT plus Erbitux and tumor volume was charted over 90-day period.

RESULTS

Our results demonstrate that combination of Erbitux with PDT strongly inhibits tumor growth in the bladder tumor xenograft model when compared to the other groups. Downregulation of EGFR was detected using immunohistochemistry, immunofluorescence and western blotting. Increased apoptosis was associated with tumor inhibition in the combination therapy group. In addition, we identified the dephosphorylation of ErbB4 at tyrosine 1284 site to play a major role in tumor inhibition. Also, at the RNA level downregulation of EGFR target genes cyclin D1 and c-myc was observed in tumors treated with PDT plus Erbitux.

CONCLUSION

The combination therapy of PDT and Erbitux effectively inhibits tumor growth and is a promising therapeutic approach in the treatment of bladder tumors.

Ultrasound exposure in the presence of hematoporphyrin induced loss of membrane integral proteins and inactivity of cell proliferation associated enzymes in sarcoma 180 cells in vitro

Ultrasonically induced effects of hematoporphyrin (HPD) on cell damage and membrane protein alteration of S180 isolated tumor cells in vitro were investigated, and the potential mechanisms of sonodynamic therapy (SDT) inhibiting tumor growth were discussed. Tumor cells suspended in air-saturated PBS (pH 7.2) were exposed to ultrasound at 1.8 MHz for up to 180s in the presence and absence of HPD. The viability of cells was determined by a trypan blue exclusion test. To estimate the damage effects of SDT on plasma membrane of tumor cells primarily, membrane integral proteins (EGFR, Ras, Fas, FasL) and cell proliferation associated enzymes (adenylate cyclase and guanylate cyclase) were checked with immunochemical methods. The results indicated that the intensity threshold for ultrasonically induced cell damage at 1.8 MHz was 3 W/cm2. At this condition, the expression of the integral proteins was obviously inhibited and the activity of the enzymes was decreased post ultrasound treatment in the presence of 20 microg/ml HPD. Loss of the membrane proteins and inactivity of AC and GC post SDT was time-dependent. This paper reveals SDT can cause the loss of tumor cell membrane integral proteins and inactivity of the enzymes associated with cell proliferation which might be attributed to a sonochemical activation mechanism. The mechanisms by that tumor growth is inhibited by SDT can be understood as that the growth signaling pathway is partially interdicted and the resistance of tumor cells to the specifically activated immune cells is weakened.

Effect of photodynamic therapy on the extracellular matrix and associated components

In many countries, photodynamic therapy (PDT) has been recognized as a standard treatment for malignant conditions (for example, esophageal and lung cancers) and non-malignant ones such as age-related macular degeneration and actinic keratoses. The administration of a non-toxic photosensitizer, its selective retention in highly proliferating cells and the later activation of this molecule by light to form reactive oxygen species that cause cell death is the principle of PDT. Three important mechanisms are responsible for the PDT effectiveness: a) direct tumor cell kill; b) damage of the tumor vasculature; c) post-treatment immunological response associated with the leukocyte stimulation and release of many inflammatory mediators like cytokines, growth factors, components of the complement system, acute phase proteins, and other immunoregulators. Due to the potential applications of this therapy, many studies have been reported regarding the effect of the treatment on cell survival/death, cell proliferation, matrix assembly, proteases and inhibitors, among others. Studies have demonstrated that PDT alters the extracellular matrix profoundly. For example, PDT induces collagen matrix changes, including cross-linking. The extracellular matrix is vital for tissue organization in multicellular organisms. In cooperation with growth factors and cytokines, it provides cells with key signals in a variety of physiological and pathological processes, for example, adhesion/migration and cell proliferation/differentiation/death. Thus, the focus of the present paper is related to the effects of PDT observed on the extracellular matrix and on the molecules associated with it, such as, adhesion molecules, matrix metalloproteinases, growth factors, and immunological mediators.

Cross-linking of signal transducer and activator of transcription 3--a molecular marker for the photodynamic reaction in cells and tumors

PURPOSE

Photodynamic therapy (PDT) depends on the delivery of a photosensitizer to the target tissue that, under light exposure, produces singlet oxygen and other reactive oxygen species, which in turn cause the death of the treated cell. This study establishes a quantitative marker for the photoreaction that will predict the outcome of PDT.

EXPERIMENTAL DESIGN

Cells in tissue culture, murine s.c. tumors, and endobronchial carcinomas in patients were treated with PDT, and the noncleavable cross-linking of the latent signal transducer and activator of transcription 3 (STAT3) was determined.

RESULTS

Murine and human cancer cell lines reacted to PDT by an immediate covalent cross-linking of STAT3 to homodimeric and other complexes. The magnitude of this effect was strictly a function of the PDT reaction that is determined by the photosensitizer concentration and light dose. The cross-link reaction of STAT3 was proportional to the subsequent cytotoxic outcome of PDT. An equivalent photoreaction as detected in vitro occurred in tumors treated in situ with PDT. The light dose-dependent STAT3 cross-linking indicated the relative effectiveness of PDT as a function of the distance of the tissue to the treating laser light source. Absence of cross-links correlated with treatment failure.

CONCLUSIONS

The data suggest that the relative amount of cross-linked STAT3 predicts the probability for beneficial outcome, whereas absence of cross-links predicts treatment failure. Determination of STAT3 cross-links after PDT might be clinically useful for early assessment of PDT response.

Y1068 phosphorylation is the most sensitive target of disulfonated tetraphenylporphyrin-based photodynamic therapy on epidermal growth factor receptor

Photodynamic therapy (PDT) is an anticancer therapy that utilizes the cytotoxic properties of a photosensitizer (PS) when combined with exposure to light. Photochemical internalization (PCI) is a drug delivery method for macromolecules based on PDT with endo-lysosomal localizing PSs, and synergistic effects can be obtained by PCI of EGFR targeting drugs. In this report the effects of PDT with two endo-lysosomal localizing PSs on EGFR are described. The experiments were performed in EGFR-positive cell-lines in vitro and also in a subcutaneous tumour-model in mice. In PCI, the PSs are transported from the plasma membrane to endocytic vesicles by endocytosis and some of the PS can therefore be retained at the plasma membrane. Two distinct treatment conditions with different amounts of the PS on the plasma membrane were therefore studied in vitro. The expression of total and phosphorylated EGFR was analyzed on Western blots and EGF-binding to EGFR was evaluated by fluorescence microscopy of Alexa488-labelled EGF. The results showed that PDT, as utilized in PCI, caused inhibition of EGF-stimulated EGFR phosphorylation on Y1068 in NuTu-19 cells, but not in WiDr cells. PDT performed with more PS on the plasma membrane of NuTu-19 cells caused in addition inhibition of EGF binding and also lack of recognition by antibodies towards sequences in the intracellular domain of EGFR. In vivo, total EGFR was reduced 24h after PDT in WiDr tumours. This report indicates EGF-stimulated phosphorylation on Y1068 as the most sensitive target on EGFR to PDT with amphiphilic PSs.

Targeted Delivery and Enhanced Cytotoxicity of Cetuximab−Saporin by Photochemical Internalization in EGFR-Positive Cancer Cells

Photochemical internalization (PCI) is a novel technology of macromolecular delivery. By PCI, endocytosed membrane-impermeable therapeutic drugs are photochemically released from entrapment in endo-lysosomal compartments to the cytosol of target cells. In the present report, we describe the in vitro proof-of-concept for PCI of cetuximab-saporin, an immunotoxin targeting EGFR-expressing cells. This immunotoxin consists of the chimeric murine-human IgG1 monoclonal antibody cetuximab (C225 or Erbitux) bound to the type I ribosome-inactivating protein toxin saporin by a biotin-streptavidin linkage. The photochemical treatment enhanced the cytotoxicity of the immunotoxin in a synergistic manner in three different EGFR-expressing carcinoma cell lines derived from different tumor tissues (colorectal, HCT-116; prostate, DU-145; and epidermis, A-431). Both cytotoxicity of cetuximab-saporin and epifluorescence of Alexa488-cetuximab were evaluated by competition with cetuximab demonstrating specific binding and uptake of cetuximab-saporin in EGFR positive cells. In the EGFR-negative uterine sarcoma cell line MES-SA, neither binding nor preferential accumulation of Alexa488-cetuximab was detected. In addition, PCI enhanced the cytotoxicity of cetuximab-saporin to the same extent as streptavidin-saporin in the MES-SA cells. In conclusion, PCI enhances selectivity of the cytotoxicity of the immunotoxin cetuximab-saporin in EGFR-expressing cells.

Photodynamic therapy causes cross-linking of signal transducer and activator of transcription proteins and attenuation of interleukin-6 cytokine responsiveness in epithelial cells

Photodynamic therapy (PDT) is a local treatment of cancers. The principle of PDT is the production of reactive oxygen species, in particular singlet oxygen, by light activation of a photosensitizer introduced into the target cells. The direct photochemical and subsequent redox reactions can lead to cell death. This study sought to identify effects occurring during PDT and some of their consequences in surviving cells. Using epithelial cells in tissue culture and in tumors, several distinct PDT-mediated reactions were found, including global dephosphorylation of proteins, induced phosphorylation of a 71-kDa protein, initiation of cellular stress responses, structural modification and loss of epidermal growth factor receptor, and cross-linking of proteins. Specific covalent cross-linking of nonactivated signal transducer and activator of transcription (STAT)-3, and to a lesser extent of STAT1 and STAT4, correlated with PDT dose. Cross-linked STAT3 was primarily localized to the cytoplasm and failed to bind to DNA. The combination of STAT cross-linking and inactivation of receptor functions rendered PDT-treated cells refractory for at least 24 hours to interleukin-6 and oncostatin M, cytokines known to be elevated at site of tissue damage and inflammation. It is suggested that the loss of responsiveness to these inflammatory cytokines in the PDT-treated field assists tumor cells in evading the growth-suppressive activity of these mediators expected to be present at tissue sites after PDT.

Intracellular signaling mechanisms in photodynamic therapy

In photodynamic therapy (PDT) a sensitizer, light and oxygen are used to induce death of tumor cells and in the treatment of certain noncancerous conditions. Cell death in PDT may occur by apoptosis or by necrosis, depending on the sensitizer, on the PDT dose and on the cell genotype. Some sensitizers that have been used in PDT are accumulated in the mitochondria, and this may explain their efficiency in inducing apoptotic cell death, both in vitro and in vivo. In this review we will focus on the events that characterize apoptotic death in PDT and on the intracellular signaling events that are set in motion in photosensitized cells. Activation of phospholipases, changes in ceramide metabolism, a rise in the cytosolic free Ca2+ concentration, stimulation of nitric oxide synthase (NOS), changes in protein phosphorylation and alterations in the activity of transcription factors and on gene expression have all been observed in PDT-treated cells. Although many of these metabolic reactions contribute to the demise process, some of them may antagonize cell death. Understanding the signaling mechanisms in PDT may provide means to modulate the PDT effects at the molecular level and potentiate its antitumor effectiveness.

New advances on the functions of epidermal growth factor receptor and ceramides in skin cell differentiation, disorders and cancers

Recent advances in understanding of the biological functions of the epidermal growth factor and epidermal growth factor receptor (EGF-EGFR) system and ceramide production for the maintenance of skin integrity and barrier function are reported. In particular, the opposite roles of EGFR and ceramide cascades in epithelial keratinocyte proliferation, migration and terminal differentiation are described. Moreover, the functions of ceramides in the epidermal permeability barrier are reviewed. The alterations in EGFR signaling and ceramide metabolism, which might be involved in the etiopathogenesis of diverse skin disorders and cancers, are described. New progress in understanding of skin organization, which might provide the basis for the design of new transcutaneous drug delivery techniques as well as for the development of new therapies of skin disorders and cancers, are reported.

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Downregulation of epidermal growth factor receptor signaling by singlet oxygen through activation of caspase-3 and protein phosphatases

Downregulation of survival signaling pathways contributes to the cytotoxicity of reactive oxygen species (ROS) and may underlie certain therapies for hyperproliferative diseases. We have investigated the role of singlet oxygen, an ROS formed by photosensitization, in the regulation of survival signaling via the epidermal growth factor receptor (EGFR). Exposure of human keratinocytes to singlet oxygen resulted in rapid loss of EGFR, which was not blocked by either inhibition of receptor internalization or by interrupting the major proteolytic pathways (proteasome, lysosome or calpain). However, pretreatment with a caspase-3 inhibitor, DEVD-FMK, inhibited EGFR degradation. Caspase-3 cleavage was detected as early as 5 min after singlet oxygen treatment, and recombinant active caspase-3 completely cleaved EGFR in a keratinocyte membrane fraction. The singlet oxygen-induced loss of EGFR was accompanied by dephosphorylation of EGFR as well as of Akt and extracellular signal-regulated kinase 1/2 (ERK)1/2. Singlet oxygen-induced protein dephosphorylation was not dependent on activation of caspase-3. In contrast, inhibition of protein phosphatases (PPs) with okadaic acid completely blocked dephosphorylation of EGFR, ERK1/2 and Akt as well as degradation of EGFR. These results indicate that the oxidative stress produced by singlet oxygen rapidly disrupts EGFR-mediated signaling by decreasing both the protein level and its phosphorylation. These responses depended on intertwined activation of caspase-3 and PPs.