Induction of apoptosis in human cancer cells by candidaspongiolide, a novel sponge polyketide

Prospects of marine-derived compounds as potential therapeutic agents for glioma

CONTEXT

Glioma, the most common primary malignant brain tumour, is a grave health concern associated with high morbidity and mortality. Current treatments, while effective to some extent, are often hindered by factors such as the blood-brain barrier and tumour microenvironment. This underscores the pressing need for exploring new pharmacologically active anti-glioma compounds.

METHODS

This review synthesizes information from major databases, including Chemical Abstracts, Medicinal and Aromatic Plants Abstracts, ScienceDirect, SciFinder, Google Scholar, Scopus, PubMed, Springer Link and relevant books. Publications were selected without date restrictions, using terms such as 'Hymenocrater spp.,' 'phytochemical,' 'pharmacological,' 'extract,' 'essential oil' and 'traditional uses.' General web searches using Google and Yahoo were also performed. Articles related to agriculture, ecology, synthetic work or published in languages other than English or Chinese were excluded.

RESULTS

The marine environment has been identified as a rich source of diverse natural products with potent antitumour properties.

CONCLUSIONS

This paper not only provides a comprehensive review of marine-derived compounds but also unveils their potential in treating glioblastoma multiforme (GBM) based on functional classifications. It encapsulates the latest research progress on the regulatory biological functions and mechanisms of these marine substances in GBM, offering invaluable insights for the development of new glioma treatments.

Cancer and apoptosis: The apoptotic activity of plant and marine natural products and their potential as targeted cancer therapeutics

Cancer is a multifactorial, multi-stage disease, including complex cascades of signaling pathways—the cell growth governed by dysregulated and abrupt cell division. Due to the complexity and multi-regulatory cancer progression, cancer is still a challenging disease to treat and survive. The screening of extracts and fractions from plants and marine species might lead to the discovery of more effective compounds for cancer therapeutics. The isolated compounds and reformed analogs were known as future prospective contenders for anti-cancer chemotherapy. For example, Taxol, a potent mitotic inhibitor discovered from Taxus brevifolia, suppresses cell growth and arrest, induces apoptosis, and inhibits proliferation. Similarly, marine sponges show remarkable tumor chemo preventive and chemotherapeutic potential. However, there is limited research to date. Several plants and marine-derived anti-cancer compounds having the property to induce apoptosis have been approved for clinical trials. The anti-cancer activity kills the cell and slows the growth of cancer cells. Among cell death mechanisms, apoptosis induction is a more profound mechanism of cell death triggered by naturally isolated anti-cancer agents. Evading apoptosis is the major hurdle in killing cancer cells, a mechanism mainly regulated as intrinsic and extrinsic. However, it is possible to modify the apoptosis-resistant phenotype of the cell by altering many of these mechanisms. Various extracts and fractions successfully induce apoptosis, cell-cycle modulation, apoptosis, and anti-proliferative activity. Therefore, there is a pressing need to develop new anti-cancer drugs of natural origins to reduce the effects on normal cells. Here, we’ve emphasized the most critical elements: i) A better understanding of cancer progression and development and its origins, ii) Molecular strategies to inhibit the cell proliferation/Carcino-genesis, iii) Critical regulators of cancer cell proliferation and development, iv) Signaling Pathways in Apoptosis: Potential Targets for targeted therapeutics, v) Why Apoptosis induction is mandatory for effective chemotherapy, vi) Plants extracts/fractions as potential apoptotic inducers, vii) Marine extracts as Apoptotic inducers, viii) Marine isolated Targeted compounds as Apoptotic inducers (FDA Approved/treatment Phase). This study provides a potential therapeutic option for cancer, although more clinical studies are needed to verify its efficacy in cancer chemotherapy.

Natural Marine Products: Anti-Colorectal Cancer In Vitro and In Vivo

Colorectal cancer, a malignant tumor with high mortality, has a poor prognosis due to drug resistance and toxicity in clinical surgery and chemotherapy. Thus, finding safer and more efficient drugs for clinical trials is vital and urgent. Natural marine compounds, with rich resources and original chemical structures, are applied widely in anticancer treatments. We provide a systematic overview of recently reported marine compounds such as alkaloids, peptides, terpenoids, polysaccharides, and carotenoids from in vitro, in vivo, and clinical studies. The in vitro studies summarized the marine origins and pharmacological mechanisms, including anti-proliferation, anti-angiogenesis, anti-migration, anti-invasion, the acceleration of cycle arrest, and the promotion of tumor apoptosis, of various compounds. The in vivo studies outlined the antitumor effects of marine compounds on colorectal cancer model mice and evaluated their efficacy in terms of tumor inhibition, hepatotoxicity, and nephrotoxicity. The clinical studies summarized the major chemical classifications and targets of action of the clinical drugs that have entered clinical approval and completed approval for marine anticancer. In summary, we present the current situation regarding the application of natural anti-colorectal cancer marine compounds and prospects for their clinical application.

Synthetic and Naturally Occurring Heterocyclic Anticancer Compounds with Multiple Biological Targets

Cancer is a complex group of diseases initiated by abnormal cell division with the potential of spreading to other parts of the body. The advancement in the discoveries of omics and bio- and cheminformatics has led to the identification of drugs inhibiting putative targets including vascular endothelial growth factor (VEGF) family receptors, fibroblast growth factors (FGF), platelet derived growth factors (PDGF), epidermal growth factor (EGF), thymidine phosphorylase (TP), and neuropeptide Y4 (NY4), amongst others. Drug resistance, systemic toxicity, and drug ineffectiveness for various cancer chemo-treatments are widespread. Due to this, efficient therapeutic agents targeting two or more of the putative targets in different cancer cells are proposed as cutting edge treatments. Heterocyclic compounds, both synthetic and natural products, have, however, contributed immensely to chemotherapeutics for treatments of various diseases, but little is known about such compounds and their multimodal anticancer properties. A compendium of heterocyclic synthetic and natural product multitarget anticancer compounds, their IC50, and biological targets of inhibition are therefore presented in this review.

Impedance analysis of adherent cells after in situ electroporation-mediated delivery of bioactive proteins, DNA and nanoparticles in µL-volumes

Specific intracellular manipulation of animal cells is a persistent goal in experimental cell biology. Such manipulations allow precise and targeted interference with signaling cascades, metabolic pathways, or bi-molecular interactions for subsequent tracking of functional consequences. However, most biomolecules capable of molecular recognition are membrane impermeable. The ability to introduce these molecules into the cytoplasm and then to apply appropriate readouts to monitor the corresponding cell response could prove to be an important research tool. This study describes such an experimental approach combining in situ electroporation (ISE) as a means to efficiently deliver biomolecules to the cytoplasm with an impedance-based, time-resolved analysis of cell status using electric cell-substrate impedance sensing (ECIS). In this approach, gold-film electrodes, deposited on the bottom of regular culture dishes, are used for both electroporation and monitoring. The design of the electrode layout and measurement chamber allows working with sample volumes as small as 10 µL. A miniaturized setup for combined electroporation and impedance sensing (µISE-ECIS) was applied to load different adherent cells with bioactive macromolecules including enzymes, antibodies, nucleic acids and quantum dot nanoparticles. The cell response after loading the cytoplasm with RNase A or cytochrome c (in the presence or absence of caspase inhibitors) was tracked by non-invasive impedance readings in real-time.

Natural Products from Sponges

The sponge is one of the oldest multicellular invertebrates in the world. Marine sponges represent one of the extant metazoans of 700–800 million years. They are classified in four major classes: Calcarea, Demospongiae, Hexactinellida, and Homoscleromorpha. Among them, three genera, namely, Haliclona, Petrosia, and Discodemia have been identified to be the richest source of biologically active compounds. So far, 15,000 species have been described, and among them, more than 6000 species are found in marine and freshwater systems throughout tropical, temperate, and polar regions. More than 5000 different compounds have been isolated and structurally characterized to date, contributing to about 30% of all marine natural products. The chemical diversity of sponge products is high with compounds classified as alkaloids, terpenoids, peptides, polyketides, steroids, and macrolides, which integrate a wide range of biological activities, including antibacterial, anticancer, antifungal, anti-HIV, anti-inflammatory, and antimalarial. There is an open debate whether all natural products isolated from sponges are produced by sponges or are in fact derived from microorganisms that are inhaled though filter-feeding or that live within the sponges. Apart from their origin and chemoecological functions, sponge-derived metabolites are also of considerable interest in drug development. Therefore, development of recombinant microorganisms engineered for efficient production of sponge-derived products is a promising strategy that deserves further attention in future investigations in order to address the limitations regarding sustainable supply of marine drugs.

Anticancer Activity of Gukulenin A Isolated from the Marine Sponge Phorbas gukhulensis In Vitro and In Vivo

Gukulenin A is a bis-tropolone tetraterpenoid isolated from the marine sponge Phorbas gukhulensis. In this study, we examined the anticancer activities of gukulenin A in ovarian cancer cell lines (A2780, SKOV3, OVCAR-3, and TOV-21G) and in an ovarian cancer mouse model generated by injecting A2780 cells. We found that gukulenin A suppressed tumor growth in A2780-bearing mice. Gukulenin A markedly inhibited cell viability in four ovarian cancer cell lines, including the A2780 cell line. Gukulenin A treatment increased the fraction of cells accumulated at the sub G1 phase in a dose-dependent manner and the population of annexin V-positive cells, suggesting that gukulenin A induces apoptotic cell death in ovarian cancer cells. In addition, gukulenin A triggered the activation of caspase-3, -8, and -9, and caspase inhibitors attenuated gukulenin A-induced A2780 cell death. The results suggest that gukulenin A may be a potential therapeutic agent for ovarian cancer.

New Drugs from the Sea: Pro-Apoptotic Activity of Sponges and Algae Derived Compounds

Natural compounds derived from marine organisms exhibit a wide variety of biological activities. Over the last decades, a great interest has been focused on the anti-tumour role of sponges and algae that constitute the major source of these bioactive metabolites. A substantial number of chemically different structures from different species have demonstrated inhibition of tumour growth and progression by inducing apoptosis in several types of human cancer. The molecular mechanisms by which marine natural products activate apoptosis mainly include (1) a dysregulation of the mitochondrial pathway; (2) the activation of caspases; and/or (3) increase of death signals through transmembrane death receptors. This great variety of mechanisms of action may help to overcome the multitude of resistances exhibited by different tumour specimens. Therefore, products from marine organisms and their synthetic derivates might represent promising sources for new anticancer drugs, both as single agents or as co-adjuvants with other chemotherapeutics. This review will focus on some selected bioactive molecules from sponges and algae with pro-apoptotic potential in tumour cells.

Diclofenac induced apoptosis via altering PI3K/Akt/MAPK signaling axis in HCT 116 more efficiently compared to SW480 colon cancer cells

Diclofenac is a preferential cyclooxygenase 2 inhibitor (COX-2) and member of non-steroidal anti-inflammatory drugs (NSAIDs). Inflammation is one of the main reason of poor prognosis of colon cancer cases; thereby NSAIDs are potential therapeutic agents in colon cancer therapy. In this study, our aim to understand the potential molecular targets of diclofenac, which may propose new therapeutic targets in HCT 116 (wt p53) and SW480 (mutant p53R273H) colon cancer cells. For this purpose, we identified different response against diclofenac treatment through expression profiles of PI3K/Akt/MAPK signaling axis. Our hypothesis was diclofenac-mediated apoptosis is associated with inhibition of PI3K/Akt/MAPK signaling axis. We found that sub-cytotoxic concentration of diclofenac (400 µM) promoted further apoptosis in HCT 116 cells compared to SW480 colon cancer cells. Diclofenac triggered dephosphorylation of PTEN, PDK, Akt, which led to inhibition of PI3K/Akt survival axis in HCT 116 colon cancer cells. However, diclofenac showed lesser effect in SW480 colon cancer cells. In addition, diclofenac further activated p44/42, p38 and SAPK/JNK in HCT 116 cells compared to SW480 cells.

Investigations on the mode of action of gephyronic acid, an inhibitor of eukaryotic protein translation from myxobacteria

The identification of inhibitors of eukaryotic protein biosynthesis, which are targeting single translation factors, is highly demanded. Here we report on a small molecule inhibitor, gephyronic acid, isolated from the myxobacterium Archangium gephyra that inhibits growth of transformed mammalian cell lines in the nM range. In direct comparison, primary human fibroblasts were shown to be less sensitive to toxic effects of gephyronic acid than cancer-derived cells. Gephyronic acid is targeting the protein translation system. Experiments with IRES dual luciferase reporter assays identified it as an inhibitor of the translation initiation. DARTs approaches, co-localization studies and pull-down assays indicate that the binding partner could be the eukaryotic initiation factor 2 subunit alpha (eIF2α). Gephyronic acid seems to have a different mode of action than the structurally related polyketides tedanolide, myriaporone, and pederin and is a valuable tool for investigating the eukaryotic translation system. Because cancer derived cells were found to be especially sensitive, gephyronic acid could potentially find use as a drug candidate.

Sponges: A Reservoir of Genes Implicated in Human Cancer

Recently, it was shown that the majority of genes linked to human diseases, such as cancer genes, evolved in two major evolutionary transitions—the emergence of unicellular organisms and the transition to multicellularity. Therefore, it has been widely accepted that the majority of disease-related genes has already been present in species distantly related to humans. An original way of studying human diseases relies on analyzing genes and proteins that cause a certain disease using model organisms that belong to the evolutionary level at which these genes have emerged. This kind of approach is supported by the simplicity of the genome/proteome, body plan, and physiology of such model organisms. It has been established for quite some time that sponges are an ideal model system for such studies, having a vast variety of genes known to be engaged in sophisticated processes and signalling pathways associated with higher animals. Sponges are considered to be the simplest multicellular animals and have changed little during evolution. Therefore, they provide an insight into the metazoan ancestor genome/proteome features. This review compiles current knowledge of cancer-related genes/proteins in marine sponges.

Marine Sponge Natural Products with Anticancer Potential: An Updated Review

Despite the huge investment into research and the significant effort and advances made in the search for new anticancer drugs in recent decades, cancer cure and treatment continue to be a formidable challenge. Many sources, including plants, animals, and minerals, have been explored in the oncological field because of the possibility of identifying novel molecular therapeutics. Marine sponges are a prolific source of secondary metabolites, a number of which showed intriguing tumor chemopreventive and chemotherapeutic properties. Recently, Food and Drug Administration-approved drugs derived from marine sponges have been shown to reduce metastatic breast cancer, malignant lymphoma, and Hodgkin's disease. The chemopreventive and potential anticancer activity of marine sponge-derived compounds could be explained by multiple cellular and molecular mechanisms, including DNA protection, cell-cycle modulation, apoptosis, and anti-inflammatory activities as well as their ability to chemosensitize cancer cells to traditional antiblastic chemotherapy. The present article aims to depict the multiple mechanisms involved in the chemopreventive and therapeutic effects of marine sponges and critically explore the limitations and challenges associated with the development of marine sponge-based anticancer strategy.

Blue-Print Autophagy: Potential for Cancer Treatment

The marine environment represents a very rich source of biologically active compounds with pharmacological applications. This is due to its chemical richness, which is claiming considerable attention from the health science communities. In this review we give a general overview on the marine natural products involved in stimulation and inhibition of autophagy (a type of programmed cell death) linked to pharmacological and pathological conditions. Autophagy represents a complex multistep cellular process, wherein a double membrane vesicle (the autophagosome) captures organelles and proteins and delivers them to the lysosome. This natural and destructive mechanism allows the cells to degrade and recycle its cellular components, such as amino acids, monosaccharides, and lipids. Autophagy is an important mechanism used by cells to clear pathogenic organism and deal with stresses. Therefore, it has also been implicated in several diseases, predominantly in cancer. In fact, pharmacological stimulation or inhibition of autophagy have been proposed as approaches to develop new therapeutic treatments of cancers. In conclusion, this blue-print autophagy (so defined because it is induced and/or inhibited by marine natural products) represents a new strategy for the future of biomedicine and of biotechnology in cancer treatment.

Selective Toxicity of Persian Gulf Sea Cucumber (Holothuria parva) and Sponge (Haliclona oculata) Methanolic Extracts on Liver Mitochondria Isolated from an Animal Model of Hepatocellular Carcinoma

BACKGROUND

Natural products isolated from marine environments are well known for their pharmacodynamic potential in diverse disease treatments, such as for cancer or inflammatory conditions. Sea cucumbers are marine animals of the phylum Echinoderm and the class Holothuroidea, with leathery skin and gelatinous bodies. Sponges are important components of Persian Gulf animal communities, and the marine sponges of the genus Haliclona have been known to display broad-spectrum biological activity. Many studies have shown that sea cucumbers and sponges contain antioxidants and anti-cancer compounds.

OBJECTIVES

This study was designed to determine the selective toxicity of Persian Gulf sea cucumber (Holothuria parva) and sponge (Haliclona oculata) methanolic extracts on liver mitochondria isolated from an animal model of hepatocellular carcinoma, as part of a national project that hopes to identify novel potential anticancer candidates among Iranian Persian Gulf flora and fauna.

MATERIALS AND METHODS

To induce hepatocarcinogenesis, rats were given diethylnitrosamine (DEN) injections (200 mg/kg i.p. by a single dose), and then the cancer was promoted with 2-acetylaminofluorene (2-AAF) (0.02 w/w) for two weeks. Histopathological evaluations were performed, and levels of liver injury markers and a specific liver cancer marker (alpha-fetoprotein), were determined for confirmation of hepatocellular carcinoma induction. Finally, mitochondria were isolated from cancerous and non-cancerous hepatocytes.

RESULTS

Our results showed that H. parva methanolic extracts (250, 500, and 1000 µg/mL) and H. oculata methanolic extracts (200, 400, and 800 µg/mL) increased reactive oxygen species (ROS) formation, mitochondrial membrane potential (MMP), mitochondrial swelling, and cytochrome c release in the mitochondria obtained from cancerous hepatocytes, but not in mitochondria obtained from non-cancerous liver hepatocytes. These extracts also induced caspase-3 activation, which is known as a final mediator of apoptosis, in the hepatocytes obtained only from cancerous, not non-cancerous, rat livers.

CONCLUSIONS

Our results suggest that H. parva and H. oculata may be promising therapeutic candidates for the treatment of HCC, following further confirmatory in vivo experiments and clinical trials.

A novel copper(I) complex induces ER-stress-mediated apoptosis and sensitizes B-acute lymphoblastic leukemia cells to chemotherapeutic agents

A phosphine copper(I) complex [Cu(thp)₄][PF₆] (CP) was recently identified as an efficient in vitro antitumor agent. In this study, we evaluated the antiproliferative activity of CP in leukemia cell lines finding a significant efficacy, especially against SEM and RS4;11 cells. Immunoblot analysis showed the activation of caspase-12 and caspase-9 and of the two effector caspase-3 and -7, suggesting that cell death occurred in a caspase-dependent manner. Interestingly we did not observe mitochondrial involvement in the process of cell death. Measures on semipurified proteasome from RS4;11 and SEM cell extracts demonstrated that chymotrypsin-, trypsin- and caspase-like activity decreased in the presence of CP. Moreover, we found an accumulation of ubiquitinated proteins and a remarkable increase of ER stress markers: GRP78, CHOP, and the spliced form of XBP1. Accordingly, the protein synthesis inhibitor cycloheximide significantly protected cancer cells from CP-induced cell death, suggesting that protein synthesis machinery was involved. In well agreement with results obtained on stabilized cell lines, CP induced ER-stress and apoptosis also in primary cells from B-acute lymphoblastic leukemia patients. Importantly, we showed that the combination of CP with some chemotherapeutic drugs displayed a good synergy that strongly affected the survival of both RS4;11 and SEM cells.

Mitochondrial superoxide mediates mitochondrial and endoplasmic reticulum dysfunctions in TRAIL-induced apoptosis in Jurkat cells

Reactive oxygen species (ROS), such as superoxide (O2(•-)) and hydrogen peroxide (H2O2), have been reported to be important mediators of the apoptosis induced by death ligands, including Fas, tumor necrosis factor-α, and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Conversely, there is evidence that H2O2 and prooxidative conditions are protective. Therefore, the roles of ROS in death ligand-induced apoptosis are a matter of debate. In this study, we attempted to define the oxidant species mediating TRAIL-induced apoptosis in human tumor cells. The generation of intracellular O2(•-), but not H2O2, was correlated with apoptosis in the cells. TRAIL treatment resulted in increased mitochondrial O2(•-) generation and the oxidation of cardiolipin. The O2(•-)-selective scavenger MnTBaP [Mn(III) tetrakis (4-benzoic acid) porphyrin chloride] specifically blocked TRAIL-induced apoptosis and proapoptotic events including mitochondrial membrane collapse and caspase-3/7 activation. TRAIL also induced endoplasmic reticulum (ER) stress responses including caspase-12 activation, while inhibition of caspase-12 prevented the apoptosis. In addition, increased mitochondrial O2(•-) generation by uncoupling of oxidative phosphorylation or inhibition of the electron transport chain amplified the TRAIL-induced apoptosis and proapoptotic events. This amplification was also significantly abolished by MnTBaP treatment. Our data indicate that mitochondrial O2(•-) mediates mitochondrial and ER dysfunctions during TRAIL-induced apoptosis in Jurkat cells. The present findings suggest that pharmacological agents increasing mitochondrial O2(•-) may serve as clinical drugs that amplify TRAIL effectiveness toward cancer cells.

Arsenic trioxide induced endoplasmic reticulum stress in laryngeal squamous cell line Hep-2 cells

Arsenic trioxide (As2O3) has been used in the treatment of acute promyelocytic leukemia (APL) and many malignant solid tumors. Recently, endoplasmic reticulum (ER) stress plays an important role in As2O3-treated laryngeal squamous cell line Hep-2 cells. In the present work, the expression of ER stress-related proteins was investigated in As2O3-treated Hep-2 cells. The results showed that As2O3 increased the expression of GRP78, CHOP, phosphorylated eIF2α and ATF4, all of which are the molecule of ER stress. Therefore, As2O3 induced ER stress in Hep-2 cells.

Hydrogen peroxide induces cell death in human TRAIL-resistant melanoma through intracellular superoxide generation

Intracellular reactive oxygen species (ROS) such as hydrogen peroxide (H(2)O2()) are thought to mediate apoptosis induced by death receptor ligands, including tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). However, the role of H(2)O(2) is controversial, since some evidence suggests that H(2)O(2) acts as an anti-apoptotic factor. Here, we show that exogenously applied H(2)O(2) (30-100 µM) induces cell death in TRAIL-resistant human melanoma cells via intracellular superoxide (O(2)-) generation. H(2)O(2) induced apoptotic or necrotic cell death, depending on the concentration of the oxidant applied; low concentrations of H(2)O(2) preferentially activated the caspase-dependent apoptotic pathway, while high concentrations of H(2)O(2) induced apoptotic and necrotic cell death in a caspase-independent manner. The H(2)O(2)-induced cell death was associated with increased mitochondrial membrane potential collapse and caspase-3/7 activation and ER stress responses including caspase-12 and X-box-binding protein-1 (XBP-1) activation. H(2)O(2) induced intracellular O2- generation even within the mitochondria, while TRAIL did not. The superoxide dismutase mimetic antioxidant MnTBaP [Mn (III) tetrakis (4-benzonic acid) porphyrin chloride] inhibited the H(2)O(2)-induced O(2)- generation, apoptosis and XBP-1 and caspase-12 activation at comparable concentrations. Importantly, H(2)O(2) treatment caused minimal O(2)- generation and apoptosis in normal primary melanocytes. These data show that H(2)O(2) induces endoplasmic reticulum-associated cell death via intracellular O(2)- generation and that malignant melanoma cells are more susceptible than normal cells to this oxidative cell death. The findings suggest that H(2)O(2) has therapeutic potential in the treatment of TRAIL-resistant melanoma.

Depolarization potentiates TRAIL-induced apoptosis in human melanoma cells: role for ATP-sensitive K+ channels and endoplasmic reticulum stress

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is promising for cancer treatment owing to its selective cytotoxicity against malignant cells. However, some cancer cell types, including malignant melanoma cells, are resistant to TRAIL-induced apoptosis. Therefore, drugs that can amplify TRAIL cytotoxicity are urgently required. Depolarization of the plasma membrane potential is associated with apoptosis induced by a variety of death-inducing agents but its role in apoptosis remains a matter of debate. We found that TRAIL treatment resulted in robust depolarization in human melanoma cells with a considerable lag (2-4 h). Moreover, membrane-depolarizing agents, including K+ and ATP-sensitive K+ (KATP) channel inhibitors glibenclamide and U37883A enhanced TRAIL-induced apoptosis. On the contrary, inhibitors of calcium- and voltage-dependent K+ channels and mitochondrial KATP channels had no such effects. Melanocytes were insensitive to TRAIL-induced depolarization and apoptosis as well as to the sensitization by membrane-depolarizing agents despite their substantial surface expression of death receptors. TRAIL induced robust activation of X-box-binding protein-1 and caspase-12, both of which were enhanced by the K+ and KATP channel inhibitors, but not by other K+ channel inhibitors. Finally, caspase-12-selective inhibitor completely abolished the amplification of apoptosis. These findings suggest that depolarization promotes endoplasmic reticulum stress-mediated death pathway, thereby amplifying TRAIL cytotoxicity. Thus, membrane-depolarizing agents such as KATP channel inhibitors may have therapeutic potential in the treatment of TRAIL-resistant cancer cells without impairing tumor-selectivity.

Stereochemically versatile synthesis of the C1-C12 fragment of tedanolide C

A flexible synthesis of the C1-C12 fragment of Tedanolide C has been accomplished in eight steps from 2-methyl-2,4-pentadienal. Asymmetric hydroformylation of a 1,3-diene allows for the late-stage generation of either C10 epimer with complete catalyst control. Diastereoselective addition of an isobutyryl β-ketoester dianion to an α,β-disubstituted chiral aldehyde sets the C5 stereochemistry while installing the geminal dimethyl unit. Differential protection of a syn-1,3-diol is performed as a highly efficient single-pot operation.

The role of PKR/eIF2α signaling pathway in prognosis of non-small cell lung cancer

BACKGROUND

In this study, we investigated whether PKR protein expression is correlated with mRNA levels and also evaluated molecular biomarkers that are associated with PKR, such as phosphorylated PKR (p-PKR) and phosphorylated eIF2α (p-eIF2α).

METHODOLOGY AND FINDINGS

We determined the levels of PKR protein expression and mRNA in 36 fresh primary lung tumor tissues by using Western blot analysis and real-time reverse-transcriptase PCR (RT-PCR), respectively. We used tissue microarrays for immunohistochemical evaluation of the expression of p-PKR and p-eIF2α proteins. We demonstrated that PKR mRNA levels are significantly correlated with PKR protein levels (Spearman's rho = 0.55, p<0.001), suggesting that PKR protein levels in tumor samples are regulated by PKR mRNA. We also observed that the patients with high p-PKR or p-eIF2α expression had a significantly longer median survival than those with little or no p-PKR or p-eIF2α expression (p = 0.03 and p = 0.032, respectively). We further evaluated the prognostic effect of combined expression of p-PKR plus PKR and p-eIF2α plus PKR and found that both combinations were strong independent prognostic markers for overall patient survival on stage I and all stage patients.

CONCLUSIONS

Our findings suggest that PKR protein expression may controlled by transcription level. Combined expression levels of PKR and p-PKR or p-eIF2α can be new markers for predicting the prognosis of patients with NSCLC.

Recently confirmed apoptosis-inducing lead compounds isolated from marine sponge of potential relevance in cancer treatment

Despite intense efforts to develop non-cytotoxic anticancer treatments, effective agents are still not available. Therefore, novel apoptosis-inducing drug leads that may be developed into effective targeted cancer therapies are of interest to the cancer research community. Targeted cancer therapies affect specific aberrant apoptotic pathways that characterize different cancer types and, for this reason, it is a more desirable type of therapy than chemotherapy or radiotherapy, as it is less harmful to normal cells. In this regard, marine sponge derived metabolites that induce apoptosis continue to be a promising source of new drug leads for cancer treatments. A PubMed query from 01/01/2005 to 31/01/2011 combined with hand-curation of the retrieved articles allowed for the identification of 39 recently confirmed apoptosis-inducing anticancer lead compounds isolated from the marine sponge that are selectively discussed in this review.

Cellular and biomolecular responses of human ovarian cancer cells to cytostatic dinuclear platinum(II) complexes

Polynuclear platinum(II) complexes represent a class of potential anticancer agents that have shown promising pharmacological properties in preclinical studies. The nature of cellular responses induced by these complexes, however, is poorly understood. In this research, the cellular responses of human ovarian cancer COC1 cells to dinuclear platinum(II) complexes {[cis-Pt(NH₃)₂Cl]₂L¹}(NO₃)₂ (1) and {[cis-Pt(NH₃)₂Cl]₂L²}(NO₃)₂ (2) (L¹ = α,α'-diamino-p-xylene, L² = 4,4'-methylenedianiline) has been studied using cisplatin as a reference. The effect of platinum complexes on the proliferation, death mode, mitochondrial membrane potential, and cell cycle progression has been examined by MTT assay and flow cytometry. The activation of cell cycle checkpoint kinases (CHK1/2), extracellular signal-regulated kinases (ERK1/2), and p38 mitogen-activated protein kinase (p38 MAPK) of the cells by the complexes has also been analyzed using phospho-specific flow cytometry. Complex 1 is more cytotoxic than complex 2 and cisplatin at most concentrations; complex 2 and cisplatin are comparably cytotoxic. These complexes kill the cells through an apoptotic or apoptosis-like pathway characterized by exposure of phosphatidylserine and dissipation of mitochondrial membrane potential. Complex 1 shows the strongest inductive effect on the morphological changes of the cells, followed by cisplatin and complex 2. Complexes 1 and 2 arrest the cell cycle in G2 or M phase, while cisplatin arrests the cell cycle in S phase. The influence of these complexes on CHK1/2, ERK1/2, and p38 MAPK varies with the dose of the drugs or reaction time. Activation of phospho-ERK1/2 and phospho-p38 MAPK by these complexes is closely related to the cytostatic activity. The results demonstrate that dinuclear platinum(II) complexes can induce some cellular responses different from those caused by cisplatin.

Two new cytotoxic candidaspongiolides from an indonesian sponge

Marine sponges have been recognized as potentially rich sources of various bioactive molecules. In our continuing search for new secondary metabolites from Indonesian marine invertebrates, we collected a sponge, whose extract showed cytotoxicity against cultured cells at 0.1 μg/mL. Purification of the extract yielded two new macrolides 2 and 3 along with known candidaspongiolide (1). The structures for compounds 2 and 3 were elucidated by spectral analysis (¹H, ¹³C, COSY, HMQC, HMBC) and by comparison of their NMR data with those of 1. Compounds 2 and 3 exhibited a little more potent cytotoxicity (IC₅₀ 4.7 and 19 ng/mL) than that (IC₅₀ 37 ng/mL) of candidaspongiolide (1) against NBT-T2 cells.

New candidaspongiolides, tedanolide analogues that selectively inhibit melanoma cell growth

Extracts of the sponge genus Candidaspongia showed selective cytotoxicity toward melanoma cells in the NCI 60-cell-line screen. Continued investigation of the Candidaspongia sp. extracts led to the isolation of three new tedanolide analogues, precandidaspongiolides A (1) and B (2) and candidaspongiolide B (4), as well as candidaspongiolide A (3) and tedanolide (5). Semisynthetic derivatives were also generated to develop SAR. Candidaspongiolides A/B were the most potent and showed low nanomolar activity against several melanoma cell lines.

Role of the hypoxic tumor microenvironment in the resistance to anti-angiogenic therapies

Angiogenesis, a key process for the growth of human cancers, has recently been exploited for the development of a novel class of cancer therapeutics that was thought to have wide applications and not to induce resistance in the clinical setting. Indeed, anti-angiogenic therapy has become an important option for the management of several human malignancies. However, a significant number of patients either do not respond to anti-angiogenic agents or fairly rapidly develop resistance. In addition, the benefit of anti-angiogenic therapy is relatively short-lived and the majority of patients eventually relapses and progresses. Several mechanisms of resistance to anti-angiogenic therapy have been recently proposed. The current review focuses on the role of intra-tumor hypoxia as a mechanism of resistance to anti-angiogenic agents and speculates on therapeutic approaches that might circumvent resistance and thereby improve clinical outcome.