Rational drug design and synthesis of new α-Santonin derivatives as potential COX-2 inhibitors.

Sesquiterpene compounds are widely known for their numerous pharmacological activities. Herein the focus of the authors was on α-Santonin, a sesquiterpene lactone from the Artemisia genus: the aim was to determine whether α-Santonin could be considered in the treatment of inflammation and pain. To this purpose, a small series of derivatives was designed and screened in silico against the enzyme COX-2 along with the parent compound. Drug-likeness parameters were also assessed. The compounds were eventually synthesized, and few were tested to determine their efficacy in the inhibition of COX-2 activity and expression. Overall, compound A2 was the only one with a detectable inhibitory potential of COX-2 activity whilst two of its ether derivatives demonstrated improved ability in the inhibition of COX-2 expression.

Targeting Survivin Enhances Chemosensitivity in Retinoblastoma Cells and Orthotopic Tumors.

Treatments for retinoblastoma (Rb) vary depending on the size and location of the intraocular lesions and include chemotherapy and radiation therapy. We examined whether agents used to treat Rb induce a pro-survival phenotype associated with increased expression of survivin, a member of the inhibitor of apoptosis family of proteins. We document that exposure to carboplatin, topotecan or radiation resulted in elevated expression of survivin in two human Rb cell lines but not in normal retinal pigmented epithelial (RPE) cells. Cellular levels of survivin were attenuated in Rb cells exposed to an imidazolium-based survivin suppressant, Sepantronium bromide (YM155). Protein expression patterns of survivin in RPE cells were not altered following treatment protocols involving exposure to YM155. Including YM155 with chemotherapy or radiation increased levels of apoptosis in Rb cells but not in RPE cells. Intraocular luciferase expressing Rb tumors were generated from the Rb cell lines and used to evaluate the effects of carboplatin and YM155 on in-vivo survivin expression and tumor growth. Carboplatin induced expression of survivin while carboplatin combined with YM155 reduced survivin expression in tumor bearing eyes. The combination protocol was also most effective in reducing the rate of tumor regrowth. These results indicate that targeted inhibition of the anti-apoptotic protein survivin provides a therapeutic advantage for Rb cells and tumors treated with chemotherapy.

Pro-apoptotic and anti-inflammatory properties of the green tea constituent epigallocatechin gallate increase photodynamic therapy responsiveness.

BACKGROUND: A polyphenol constituent of green tea, epigallocatechin gallate (EGCG), has anti-carcinogenic properties. A growing number of studies document EGCG-mediated induction of apoptotic pathways and inhibition of pro-survival factors when combined with chemotherapy or radiation. We evaluated the efficacy of EGCG in modulating photofrin (PH)-mediated photodynamic therapy (PDT) responses. METHODS: Mouse mammary carcinoma (BA) cells and transplanted BA tumors growing in C3H mice were treated with PH-mediated PDT. Select groups of treated cells and mice also received EGCG and then cytotoxicity, tumor response, and expression of survival molecules were evaluated in all experimental groups. RESULTS: EGCG increased apoptosis and cytotoxicity in BA cells exposed to PH-mediated PDT. The initial pro-survival phase of the unfolded protein response (UPR), characterized by increased expression of the 78 kDa glucose-regulated protein (GRP-78), was induced by PDT. The second pro-apoptotic phase of the UPR, characterized by phospho-c-Jun N-terminal kinase (p-JNK) expression, activation of caspases-3 and 7, poly ADP ribose polymerase (PARP) cleavage, and expression of C/EBP homologous protein was observed when PDT was combined with EGCG. EGCG also decreased the expression of the pro-survival proteins GRP-78 and survivin, and attenuated PDT-induced prostaglandin E2 (PGE2 ) expression in PDT-treated cells. Comparable responses also were observed when BA tumors were treated with PDT and EGCG. In addition, PDT-induced expression of metalloproteinases (MMPs) and vascular endothelial growth factor (VEGF) was down-regulated in treated tumor tissue by EGCG. CONCLUSIONS: The polyphenol EGCG improves PDT efficacy by increasing tumor apoptosis and decreasing expression of pro-survival and angiogenic molecules within the tumor microenvironment.

Enhancement of photodynamic therapy by 2,5-dimethyl celecoxib, a non-cyclooxygenase-2 inhibitor analog of celecoxib.

Photodynamic therapy (PDT) effectiveness can be improved by employing combined modality approaches involving pharmaceuticals targeting the tumor microenvironment and/or tumor cell death pathways. In one approach, combining PDT with celecoxib improves long-term tumoricidal activity without increasing normal tissue photosensitization. However, side effects arising from the use of coxib based cyclooxygenase-2 (COX-2) inhibitors, including cardiovascular injury, decreases the clinical applications of this class of compounds. A growing number of studies demonstrate that the tumoricidal actions of coxibs such as celecoxib involve non-COX-2 mediated mechanisms. The celecoxib analog, 2,5-dimethyl celecoxib (DMC), lacks COX-2 inhibitory activity but exhibits cytotoxic properties comparable to the COX-2 inhibitor celecoxib. We compared the effectiveness of DMC and celecoxib in modulating PDT response at both the in vitro and in vivo level using a C3H/BA murine mammary carcinoma model. Both DMC and celecoxib blocked PDT induced expression of the pro-survival protein survivin, enhanced the endoplasmic reticulum stress (ERS) response of PDT, and increased both apoptosis and cytotoxicity in BA cells exposed to combination protocols. DMC enhanced the in vivo tumoricidal responsiveness of PDT without altering PGE2 levels. Our data demonstrates that DMC improved PDT by increasing apoptosis and tumoricidal activity without modulating COX-2 catalytic activity. Our results also suggest that celecoxib mediated enhancement of PDT may involve both COX-2 dependent and independent mechanisms.

Identification of MAP kinase pathways involved in COX-2 expression following photofrin photodynamic therapy.

Photodynamic therapy (PDT) using the photosensitizer Photofrin is approved for the clinical treatment of solid tumors. PDT causes cytotoxic oxidative stress, but additionally induces prosurvival molecules such as cyclooxygenase-2 (COX-2). Combining PDT with COX-2 inhibitors increases the efficacy of in vivo treatment. Understanding mechanisms leading to prosurvival molecule induction is relevant to the design of more effective treatments. Using COX-2 promoter constructs, transcription factor-binding assays, identification of protein kinase activation, and inhibitors of transcription factor binding we were able to determine that COX-2 expression following PDT involves the p38 MAP kinase pathway.

Cyclooxygenase-2 expression induced by photofrin photodynamic therapy involves the p38 MAPK pathway.

Photodynamic therapy (PDT), using the porphyrin photosensitizer Photofrin (PH), is approved for the clinical treatment of solid tumors. In addition to the direct cytotoxic responses of PH-PDT-mediated oxidative stress, this procedure also induces expression of angiogenic and prosurvival molecules including cyclooxygenase-2 (COX-2). In vivo treatment efficacy is improved when PH-PDT is combined with inhibitors of COX-2. In the current study we evaluated the signaling pathways involved with PH-PDT-mediated COX-2 expression in a mouse fibrosarcoma cell line. COX-2 promoter reporter constructs with mutated transcription elements documented that the nuclear factor kappa B (NFkappaB) element, cyclic-AMP response element 2 (CRE-2), CCAAT/enhancer binding protein (C/EBP) element and activator binding protein-1 (AP-1) element were responsive to PH-PDT. Transcription factor binding assays demonstrated that nuclear protein binding to NFkappaB, CRE-2, c-fos and c-jun elements were elevated following PH-PDT. Kinase phosphorylation upstream of COX-2 expression was also examined following PH-PDT. Stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) and c-Jun were phosphorylated following PH-PDT but the SAPK/JNK inhibitor SP600125 failed to attenuate COX-2 expression. In contrast, p38 mitogen-activated protein kinase (MAPK), which activates CRE-2 binding, was phosphorylated following PH-PDT and inhibitors of p38 MAPK, SB203580 and SB202190, decreased PH-PDT-induced COX-2 expression at both the mRNA and protein levels. Extracellular signal-regulated kinase (ERK1/2) phosphorylation, which also increases CRE-2 binding activity, was initially high in untreated cells, decreased immediately following PH-PDT and then rapidly increased. MEK1/2 is immediately upstream of ERK1/2 and the MEK1 inhibitor PD98059 failed to attenuate COX-2 expression while the MEK1/2 inhibitor U0126 induced a slight decrease in COX-2 expression. The NFkappaB inhibitor SN50 failed to reduce COX-2 expression. These results demonstrate that multiple protein kinase cascades can be activated by oxidative stress and that the p38 MAPK signaling pathway and CRE-2 binding are involved in COX-2 expression following PH-PDT.

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.

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.

Photodynamic therapy: combined modality approaches targeting the tumor microenvironment.

BACKGROUND AND OBJECTIVES: Photodynamic therapy causes direct cytotoxicity to malignant cells within a tumor. Photodynamic therapy (PDT) can also have both direct and indirect effects upon various non-malignant components of the tumor microenvironment. This action can lead to PDT-mediated angiogenesis and inflammation, which are emerging as important determinants of PDT responsiveness. STUDY DESIGN/MATERIALS AND METHODS: Preclinical studies have been performed to document how PDT modulates the tumor microenvironment. The expression, function, and treatment relevance of angiogenic growth factors, proteinases, and inflammatory molecules have been monitored following PDT using mouse tumor models. RESULTS: Photofrin-mediated PDT was shown to be a strong activator of VEGF, MMPs, and COX-2 derived prostaglandins within the tumor microenvironment. Inhibitors that target these angiogenic and pro-survival molecules can enhance the effectiveness of PDT. CONCLUSIONS: Improvements in PDT tumor responsiveness may be achieved by employing combined modality regimens targeting malignant cells as well as treatment-induced angiogenesis and/or inflammation.

CHOP activation by photodynamic therapy increases treatment induced photosensitization.

BACKGROUND AND OBJECTIVES: C/EBP homologous protein (CHOP) is an endoplasmic reticulum (ER) stress inducible transcription factor involved in the development of apoptosis, growth arrest, and differentiation. CHOP deficient (chop - / - ) mouse embryonic fibroblasts (MEFs) exposed to ER stresses such as tunicamycin exhibit decreased apoptosis and reduced toxicity when compared to chop + / + control cells. Overexpression of the 70 kDa heat shock stress protein (HSP-70) can inhibit apoptotic pathways. The biological significance of photodynamic therapy (PDT) protocols that induce cellular damage resulting in differential CHOP and stress protein expression patterns was examined. STUDY DESIGN/MATERIALS AND METHODS: Wild type mouse radiation induced fibrosarcoma (RIF) cells as well as MEFs with chop + / + and chop - / - genotypes were used with either a mitochondrial and ER localizing porphyrin (PH) photosensitizer or a lysosomal localizing chlorin (NPe6) photosensitizer. PDT induced cytotoxicity, apoptosis, and stress protein expression patterns were determined as a function of cell type and photosensitizer. RESULTS: PH mediated PDT induced expression of CHOP and 78 kDa glucose regulated protein (GRP-78), but not HSP-70 while NPe6 mediated PDT induced protein expression of HSP-70 but did not activate CHOP or GRP-78 expression. Enhanced apoptosis and toxicity were observed in chop + / + cells following exposure to tunicamycin or PH mediated PDT when compared to identical treatments in chop - / - cells. NPe6 mediated PDT induced minimally detectable apoptosis in both chop + / + and chop - / - cells and only a modest increase in survival for chop - / - cells. CONCLUSIONS: These results demonstrate that PDT activation of CHOP, GRP-78, and HSP-70 varied as a function of photosensitizer subcellular localization and that a single oxidative stress response was not observed following PDT. We also show that CHOP expression increased apoptosis following PH mediated PDT and that increased CHOP expression is associated with enhanced PDT photosensitization.

Spontaneous and controllable activation of suicide gene expression driven by the stress-inducible grp78 promoter resulting in eradication of sizable human tumors.

GRP78 is a stress-inducible chaperone protein with antiapoptotic properties that is overexpressed in transformed cells and cells under glucose starvation, acidosis, and hypoxic conditions that persist in poorly vascularized tumors. Previously we demonstrated that the Grp78 promoter is able to eradicate tumors using murine cells in immunocompetent models by driving expression of the HSV-tk suicide gene. Here, through the use of positron emission tomography (PET) imaging, we provide direct evidence of spontaneous in vivo activation of the HSV-tk suicide gene driven by the Grp78 promoter in growing tumors and its activation by photodynamic therapy (PDT) in a controlled manner. In this report, we evaluated whether this promoter can be applied to human cancer therapy. We observed that the Grp78 promoter, in the context of a retroviral vector, was highly activated by stress and PDT in three different types of human breast carcinomas independent of estrogen receptor and p53. Complete regression of sizable human tumors was observed after prodrug ganciclovir treatment of the xenografts in immunodeficient mice. In addition, the Grp78 promoter-driven suicide gene is strongly expressed in a variety of human tumors, including human osteosarcoma. In contrast, the activity of the murine leukemia virus (MuLV) long-terminal repeat (LTR) promoter varied greatly in different human breast carcinoma cell lines, and in some cases, stress resulted in partial suppression of the LTR promoter activity. In transgenic mouse models, the Grp78 promoter-driven transgene is largely quiescent in major adult organs but highly active in cancer cells and cancer-associated macrophages, which can diffuse to tumor necrotic sites devoid of vascular supply and facilitate cell-based therapy. Thus, transcriptional control through the use of the Grp78 promoter offers multiple novel approaches for human cancer gene therapy.

Cyclooxygenase-2 inhibitor treatment enhances photodynamic therapy-mediated tumor response.

Photodynamic therapy (PDT) continues to be used in the treatment of solid tumors. Clinical results are promising, but the therapy has not been optimized, and tumor recurrences can occur. Recently, it has been shown that inhibitors of cyclooxygenase (COX)-2 can be effective in combination with conventional chemotherapy and radiation therapy. In the current study, we examined the parameters of PDT-mediated activation of COX-2 expression. We also examined the tumoricidal effectiveness of combining PDT with the selective COX-2 inhibitor NS-398. PDT induced the transcriptional activation of COX-2. Prolonged expression of COX-2 protein was observed in PDT-treated mouse sarcoma and carcinoma cell lines, whereas COX-1 was not inducible by PDT. Prostaglandin (PG) E2 synthesis was also increased in PDT-treated cells, and PGE2 levels were attenuated in cells coincubated with NS-398, indicating that PDT induced the expression of biologically active COX-2. Both porphyrin- and chlorin-based photosensitizers were able to elicit PDT-mediated COX-2 expression. COX-2 was also elevated in radiation-induced fibrosarcoma (RIF) tumors after treatment with PDT. We also observed that systemic administration of NS-398 decreased PDT induction of both PGE2 and vascular endothelial growth factor in treated RIF tumors. Additionally, we demonstrated that NS-398 enhanced PDT responsiveness in RIF tumors without increasing toxicity to normal tissue. These results provide strong evidence that combination procedures involving selective COX-2 inhibitors may improve the therapeutic effectiveness of PDT.

Enhanced photodynamic therapy efficacy with inducible suicide gene therapy controlled by the grp promoter.

Photodynamic therapy (PDT) is a promising cancer treatment involving the administration of a tumor-localizing photosensitizer followed by the photochemical generation of cytotoxic singlet oxygen. PDT elicits strong transcriptional activation of a variety of genes including stress response genes belonging to the glucose-regulated protein (grp) family. Oxidative stress and hypoxia can activate GRP-78, and both of these physiological insults occur in treated tissue during and/or after PDT. In the current study, we evaluated the grp promoter as a PDT-inducible molecular switch for controlled expression of the herpes simplex virus-thymidine kinase (HSV-tk) suicide gene in mouse mammary adenocarcinoma (TSA) cells and tumors stably transduced with the G1NaGrpTk retroviral expression vector. We also examined whether PDT-inducible expression of HSV-tk, together with systemic administration of ganciclovir, could enhance the tumoricidal responsiveness of PDT. Inducible expression of HSV-tk was observed after PDT in stably transduced TSA cells grown in culture and in TSA tumors growing in BALB/c mice. We also observed enhanced tumoricidal activity in mice with TSA tumors containing the G1NaGrpTk expression vector treated with PDT plus ganciclovir when compared with either treatment alone. Our results confirm that the grp promoter was able to effectively function as a molecular switch for the inducible expression of the HSV-tk gene after exposure to PDT.