Differential responses of Mcl-1 in photosensitized epithelial vs lymphoid-derived human cancer cells

Target Prediction of 5,10,15,20-Tetrakis(4'-Sulfonatophenyl)-Porphyrin Using Molecular Docking

Photodynamic therapy has the potential to be a new and effective cancer treatment. Even if in vitro and in vivo research show promise, the molecular mechanism remains unclear. In this study, molecular docking simulations predict the binding affinity of the 5,10,15,20-tetrakis(4'-sulfonatophenyl)-porphyrin tetraammonium photosensitizer on several potential targets in photodynamic treatment. Our results indicate that this photosensitizer binds to several receptor targets, including B-cell lymphoma 2 (BCL-2) and other related proteins BCL-xL, MCL-1, or A1. The binding affinity of the porphyrin derivative with human serum albumin was determined using UV-vis absorption spectroscopy and predicted using molecular docking. We conclude that the studied porphyrin photosensitizer binds to human serum albumin and may inhibit the cancer cell line through its interactions with HIS and MET AA residues from BCL-2, MCL-1, and β-catenin receptors or through its low estimated free energy of binding when interacting with A1 and BCL-B receptors.

Deficient Nucleotide Excision Repair in Squamous Cell Carcinoma Cells

Squamous cell carcinomas (SCCs) are associated with ultraviolet radiation and multiple genetic changes, but the mechanisms leading to genetic instability are unclear. SCC cell lines were compared to normal keratinocytes for sensitivity to ultraviolet radiation, DNA repair kinetics and DNA repair protein expression. Relative to normal keratinocytes, four SCC cell lines were all variably sensitive to ultraviolet radiation and, except for the SCC25 cell line, were deficient in global repair of cyclobutane pyrimidine dimers, although not 6-4 photoproducts. Impaired DNA repair of cyclobutane pyrimidine dimers was associated with reduced mRNA expression from XPC but not DDB2 genes which each encode key DNA damage recognition proteins. However, levels of XPC or DDB2 proteins or both were variably reduced in repair-deficient SCC cell lines. p53 levels did not correlate with DNA repair activity or with XPC and DDB2 levels, but p63 levels were deficient in cell lines with reduced global repair. Repair-proficient SCC25 cells depleted of p63 lost XPC expression, early global DNA repair activity and UV resistance. These results demonstrate that some SCC cell lines are deficient in global nucleotide excision repair and support a role for p63 as a regulator of nucleotide excision repair in SCCs.

Enhanced apoptotic effects by downregulating Mcl-1: evidence for the improvement of photodynamic therapy with Celecoxib

Tumor cells exposed to sub-lethal photodynamic therapy (PDT) cause cellular rescue responses that lead to resistance to the therapy, including expression of angiogenic factors and survival molecules. However, the mechanisms contributing to the resistance are yet to be fully understood. Here, we show for the first time that Mcl-1, an anti-apoptotic protein, plays an important role in protecting cells from PDT-induced apoptosis. In contrast to the reduction in the anti-apoptotic proteins Bcl-2 and Bcl-xl, sub-lethal PDT induces an increase in Mcl-1 expression. Silencing Mcl-1 sensitizes tumor cells to PDT-induced apoptosis, and ectopic expression of Mcl-1 significantly delays Bax translocation to mitochondria and inhibits caspase-3 activity following PDT. Mcl-1 expression is associated closely with activated AKT signaling following PDT. AKT can regulate Mcl-1 expression through GSK-3β and NF-κB at the protein and transcriptional levels, respectively. Inhibition of AKT by Wortmannin or siRNA significantly reduces the levels of Mcl-1 mRNA and protein and enhances PDT-induced apoptosis. Treatment with Celecoxib, a non-steroidal anti-inflammatory drug (NSAID), is shown to downregulate Mcl-1 expression, and enhances PDT-induced apoptosis both in vitro and in vivo. This down-regulation is closely related to the inhibition effect of Celecoxib on the AKT/GSK-3β pathway, and was blocked upon addition of GSK-3β inhibitor LiCl or the proteasome inhibitor MG132. These results suggest that Mcl-1 is a potential target for improving the antitumor efficiency of PDT. A loss in Mcl-1 by inhibiting AKT promotes PDT-induced apoptosis through the mitochondrial pathway. This also provides a novel rationale for utilizing Celecoxib to improve the efficacy of PDT.

New insights into the mechanisms for photodynamic therapy-induced cancer cell death

Photodynamic therapy (PDT) is a promising therapeutic modality for cancer treatment; however, a more detailed understanding is needed to improve the clinical use of this therapy. PDT induces cancer cell death by apoptosis, necrosis, and autophagy, and these mechanisms can be concurrently occurred. PDT destroys cancer cells by inducing apoptosis through diverse signaling pathways coupled with Bcl-2 family members, caspases, and apopotosis-inducing factor. When the apoptotic pathway is unavailable, PDT can cause cancer cell death through induction of a necrotic or autophagic mechanism. Autophagy is occurred in a Bax-independent manner and can be stimulated in parallel with apoptosis. PDT directly destroys cancer cells by inducing either apoptotic or necrotic death. PDT also can induce autophagy as a death or a survival mechanism. These mechanisms are dependent on a variety of parameters including the nature of the photosensitizer, PDT dose, and cell genotype. Understanding the complex cross talk between these pathways may improve the effectiveness of PDT. Here, we discuss the interplay between these mechanisms based on recent evidence and suggest prospects with regard to advances in PDT.

Serine 162, an essential residue for the mitochondrial localization, stability and anti-apoptotic function of Mcl-1

Mcl-1 is an anti-apoptotic member of the Bcl-2 family that plays a key role in normal development, but also in pathologies such as cancer. It has some unusual properties compared to other anti-apoptotic members of the Bcl-2 family, and its expression and function are dynamically regulated by a variety of post-transcriptional and post-translational processes. Of note, Mcl-1 protein has a very short half life, and its stability and function may be regulated by reversible phosphorylation. There is also evidence to suggest that it may be localized to different subcellular compartments. The aim of this work was to determine whether residues within the PEST region of Mcl-1 that may undergo reversible phosphorylation, also regulate its subcellular distribution. We show that EGFP:Mcl-1 localizes mainly to the mitochondria of HeLa cells, with some additional cytoplasmic and nuclear localization. The mutations, S64A, S64E, S121A, S159A, T163A and T163E did not significantly affect the localization of Mcl-1. However, mutation of Ser162 to the phospho-null residue, Alanine resulted in an essentially nuclear localization, with some cytoplasmic but no mitochondrial localization. This mutant Mcl-1 protein, S162A, showed significantly decreased stability and it decreased the ability to protect against Bak-induced apoptosis. These data identify a new molecular determinant of Mcl-1 function, localization and stability that may be important for understanding the role of this protein in disease.

Promotion of PDT efficacy by a Bcl-2 antagonist

Photodynamic therapy (PDT) directed against the endoplasmic reticulum (ER) is also known to target antiapoptotic Bcl-2 family proteins. This effect is associated with the initiation of both apoptosis, a cell death pathway, and autophagy, an organelle recycling system that can lead to survival or cell death. In this study, we examined the ability of the Bcl-2 antagonist HA14-1 to promote the photodynamic efficacy of PDT directed at the ER. At concentrations that independently caused only a small loss of viability, HA14-1 markedly enhanced the proapoptotic and phototoxic effects of ER photodamage. These results provide additional evidence that the antiapoptotic properties of Bcl-2 constitute an important determinant of photokilling, and demonstrate that synergistic effects can result when PDT is coupled with pharmacologic suppression of Bcl-2 function.

Apoptosis mechanisms related to the increased sensitivity of Jurkat T-cells vs A431 epidermoid cells to photodynamic therapy with the phthalocyanine Pc 4

To examine the clinical applicability of Pc 4, a promising second-generation photosensitizer, for the photodynamic treatment of lymphocyte-mediated skin diseases, we studied the A431 and Jurkat cell lines, commonly used as surrogates for human keratinocyte-derived carcinomas and lymphocytes, respectively. As revealed by ethyl acetate extraction and absorption spectrophotometry, uptake of Pc 4 into the two cell lines was linear with Pc 4 concentration and similar on a per cell basis but greater in Jurkat cells on a per mass basis. Flow cytometry showed that uptake was linear at low doses; variations in the dose-response for uptake measured by fluorescence supported differential aggregation of Pc 4 in the two cell types. As detected by confocal microscopy, Pc 4 localized to mitochondria and endoplasmic reticulum in both cell lines. Jurkat cells were much more sensitive to the lethal effects of phthalocyanine photodynamic therapy (Pc 4-PDT) than were A431 cells, as measured by a tetrazolium dye reduction assay, and more readily underwent morphological apoptosis. In a search for molecular factors to explain the greater photosensitivity of Jurkat cells, the fate of important Bcl-2 family members was monitored. Jurkat cells were more sensitive to the induction of immediate photodamage to Bcl-2, but the difference was insufficient to account fully for their greater sensitivity. The antiapoptotic protein Mcl-1 was extensively cleaved in a dose- and caspase-dependent manner in Jurkat, but not in A431, cells exposed to Pc 4-PDT. Thus, the greater killing by Pc 4-PDT in Jurkat compared with A431 cells correlated with greater Bcl-2 photodamage and more strongly to the more extensive Mcl-1 degradation. Pc 4-PDT may offer therapeutic advantages in targeting inflammatory cells over normal keratinocytes in the treatment of T-cell-mediated skin diseases, such as cutaneous lymphomas, dermatitis, lichenoid tissue reactions and psoriasis, and it will be instructive to evaluate the role of Bcl-2 family proteins, especially Mcl-1, in the therapeutic response.

Photodynamic therapy with the phthalocyanine photosensitizer Pc 4: the case experience with preclinical mechanistic and early clinical-translational studies

Photodynamic therapy (PDT) is emerging as a promising non-invasive treatment for cancers. PDT involves either local or systemic administration of a photosensitizing drug, which preferentially localizes within the tumor, followed by illumination of the involved organ with light, usually from a laser source. Here, we provide a selective overview of our experience with PDT at Case Western Reserve University, specifically with the silicon phthalocyanine photosensitizer Pc 4. We first review our in vitro studies evaluating the mechanism of cell killing by Pc 4-PDT. Then we briefly describe our clinical experience in a Phase I trial of Pc 4-PDT and our preliminary translational studies evaluating the mechanisms behind tumor responses. Preclinical work identified (a) cardiolipin and the anti-apoptotic proteins Bcl-2 and Bcl-xL as targets of Pc 4-PDT, (b) the intrinsic pathway of apoptosis, with the key participation of caspase-3, as a central response of many human cancer cells to Pc 4-PDT, (c) signaling pathways that could modify apoptosis, and (d) a formulation by which Pc 4 could be applied topically to human skin and penetrate at least through the basal layer of the epidermis. Clinical-translational studies enabled us to develop an immunohistochemical assay for caspase-3 activation, using biopsies from patients treated with topical Pc 4 in a Phase I PDT trial for cutaneous T-cell lymphoma. Results suggest that this assay may be used as an early biomarker of clinical response.

Mitochondrial membrane permeabilization in cell death

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Effect of downregulation of survivin expression on radiosensitivity of human epidermoid carcinoma cells

PURPOSE

The expression of survivin, a member of the inhibitor-of-apoptosis protein family, is elevated in many types of human cancer. High survivin expression has been associated with poor patient prognosis and tumor resistance to chemotherapy and radiotherapy. The purpose of this study was to compare the radiosensitizing effects of five agents that target survivin on their relative ability to downregulate survivin expression.

METHODS AND MATERIALS

The human epidermoid carcinoma cell line A431 was treated with adenoviral-mediated wild-type p53, antisense to survivin, the mitogen-activated protein kinase inhibitor PD98059, the cyclin-dependent kinase inhibitor Purvalanol A, or the histone deacetylase inhibitor trichostatin A. The radiosensitizing effects of these treatments were determined by clonogenic survival curve analysis and their abilities to suppress survivin expression by Western blot analysis.

RESULTS

All the strategies were shown to radiosensitize A431 cells. This effect correlated with their abilities to downregulate survivin.

CONCLUSION

Expression of survivin appears to confer a radioresistant phenotype that can be overcome using several clinically achievable strategies that target survivin either specifically or nonspecifically.

Boronated protohaemins: synthesis and in vivo antitumour efficacy

The conjugates of porphyrin macrocycles with boron-containing polyhedra are under investigation as agents for binary treatment strategies of cancer. Aiming at the design of photoactive compounds with low-to-zero dark toxicity, we synthesized a series of carboranyl and monocarbon-carboranyl derivatives of protohaemin IX using the activation of porphyrin carboxylic groups with di-tert-butyl pyrocarbonate or pivaloyl chloride. The water-soluble 1,3,5,8-tetramethyl-2,4-divinyl-6(7)-[2'-(closo-monocarbon-carborane-1''-yl)methoxycarbonylethyl]-7(6)-(2'-carboxyethyl)porphyrin Fe(III) (compound 9) exerted no discernible cytotoxicity for cultured mammalian cells, nor did it cause general toxicity in rats. Importantly, 9 demonstrated dose-dependent activity as a phototoxin in photodynamic therapy of M-1 sarcoma-bearing rats. In animals injected with 20 mg kg(-1) of 9, the tumours shrank by day 3 after one single irradiation of the tumour with red laser light. Between 7 and 14 days post-irradiation, 88.9% of rats were tumour-free; no recurrence of the disease was detectable within at least 90 days. Protohaemin IX alone was without effect, indicating that boronation is important for the phototoxic activity of 9. This is the first study that presents the synthesis and preclinical in vivo efficacy of boronated derivatives of protohaemin as phototoxins. The applicability in photodynamic treatment broadens the therapeutic potential of boronated porphyrins beyond their conventional role as radiosensitizers in boron neutron capture therapy.

Ceramide response post-photodamage is absent after treatment with HA14-1

The oxidative stress induced by photodynamic therapy using the phthalocyanine Pc 4 (PDT) can lead to apoptosis, and is accompanied by photodamage to Bcl-2 and accumulation of de novo ceramide. Similar to PDT, the oxidative stress inducer and Bcl-2 inhibitor HA14-1 triggers apoptosis. To test the specificity of the ceramide response, Jurkat cells were exposed to an equitoxic dose of HA14-1. Unlike PDT, HA14-1 did not induce accumulation of de novo ceramide, although levels of sphingomyelin, phosphatidylserine and phosphatidylethanolamine were below control values after either treatment. In contrast to PDT, (i) the transient inhibition of serine palmitoyltransferase induced by HA14-1 was associated with the initial decrease in de novo ceramide, and (ii) HA14-1-initiated inhibition of sphingomyelin synthase and glucosylceramide synthase did not result in accumulation of de novo ceramide. These results show that the ceramide response to PDT is not induced by another pro-apoptotic stimulus, and may be unique to PDT as described here.