Ceramide regulates gemcitabine-induced senescence and apoptosis in human pancreatic cancer cell lines

In Vitro Investigation of Therapy-Induced Senescence and Senescence Escape in Breast Cancer Cells Using Novel Flow Cytometry-Based Methods

Although cellular senescence was originally defined as an irreversible form of cell cycle arrest, in therapy-induced senescence models, the emergence of proliferative senescence-escaped cancer cells has been reported by several groups, challenging the definition of senescence. Indeed, senescence-escaped cancer cells may contribute to resistance to cancer treatment. Here, to study senescence escape and isolate senescence-escaped cells, we developed novel flow cytometry-based methods using the proliferation marker Ki-67 and CellTrace CFSE live-staining. We investigated the role of a novel senescence marker (DPP4/CD26) and a senolytic drug (azithromycin) on the senescence-escaping ability of MCF-7 and MDA-MB-231 breast cancer cells. Our results show that the expression of DPP4/CD26 is significantly increased in both senescent MCF-7 and MDA-MB-231 cells. While not essential for senescence induction, DPP4/CD26 contributed to promoting senescence escape in MCF-7 cells but not in MDA-MB-231 cells. Our results also confirmed the potential senolytic effect of azithromycin in senescent cancer cells. Importantly, the combination of azithromycin and a DPP4 inhibitor (sitagliptin) demonstrated a synergistic effect in senescent MCF-7 cells and reduced the number of senescence-escaped cells. Although further research is needed, our results and novel methods could contribute to the investigation of the mechanisms of senescence escape and the identification of potential therapeutic targets. Indeed, DPP4/CD26 could be a promising marker and a novel target to potentially decrease senescence escape in cancer.

Natural Products and Small Molecules Targeting Cellular Ceramide Metabolism to Enhance Apoptosis in Cancer Cells

Molecular targeting strategies have been used for years in order to control cancer progression and are often based on targeting various enzymes involved in metabolic pathways. Keeping this in mind, it is essential to determine the role of each enzyme in a particular metabolic pathway. In this review, we provide in-depth information on various enzymes such as ceramidase, sphingosine kinase, sphingomyelin synthase, dihydroceramide desaturase, and ceramide synthase which are associated with various types of cancers. We also discuss the physicochemical properties of well-studied inhibitors with natural product origins and their related structures in terms of these enzymes. Targeting ceramide metabolism exhibited promising mono- and combination therapies at preclinical stages in preventing cancer progression and cemented the significance of sphingolipid metabolism in cancer treatments. Targeting ceramide-metabolizing enzymes will help medicinal chemists design potent and selective small molecules for treating cancer progression at various levels.

Chemotherapy-Induced Senescence Reprogramming Promotes Nasopharyngeal Carcinoma Metastasis by circRNA-Mediated PKR Activation

Senescence is associated with tumor metastasis and chemotherapy resistance, yet the mechanisms remain elusive. Here, it is identified that nasopharyngeal carcinoma (NPC) patients who developed distant metastasis are characterized by senescence phenotypes, in which circWDR37 is a key regulator. CircWDR37 deficiency limits cisplatin or gemcitabine-induced senescent NPC cells from proliferation, migration, and invasion. Mechanistically, circWDR37 binds to and dimerizes double-stranded RNA-activated protein kinase R (PKR) to initiate PKR autophosphorylation and activation. Independent of its kinase activity, phosphorylated PKR induces I-kappaB kinase beta (IKKβ) phosphorylation, binds to and releases RELA from NF-κB inhibitor alpha (IκBα) to trigger nuclear factor kappa B (NF-κB) activation, thereby stimulating cyclin D1 (CCND1) and senescence-associated secretory phenotype component gene transcription in a circWDR37-dependent manner. Low circWDR37 levels correlate with chemotherapy response and favorable survival in NPC patients treated with gemcitabine or cisplatin induction chemotherapy. This study uncovers a new mechanism of circWDR37 activated PKR in senescence-driven metastasis and provides appealing therapeutic targets in NPC.

Targeting chemoresistant senescent pancreatic cancer cells improves conventional treatment efficacy

Pancreatic cancer is one of the deadliest cancers owing to its late diagnosis and of the strong resistance to available treatments. Despite a better understanding of the disease in the last two decades, no significant improvement in patient care has been made. Senescent cells are characterized by a stable proliferation arrest and some resistance to cell death. Increasing evidence suggests that multiple lines of antitumor therapy can induce a senescent-like phenotype in cancer cells, which may participate in treatment resistance. In this study, we describe that gemcitabine, a clinically-used drug against pancreatic cancer, induces a senescent-like phenotype in highly chemoresistant pancreatic cancer cells in vitro and in xenografted tumors in vivo. The use of ABT-263, a well-described senolytic compound targeting Bcl2 anti-apoptotic proteins, killed pancreatic gemcitabine-treated senescent-like cancer cells in vitro. In vivo, the combination of gemcitabine and ABT-263 decreased tumor growth, whereas their individual administration had no effect. Together these data highlight the possibility of improving the efficacy of conventional chemotherapies against pancreatic cancer by eliminating senescent-like cancer cells through senolytic intervention. Further studies testing different senolytics or their combination with available treatments will be necessary to optimize preclinical data in mouse models before transferring these findings to clinical trials.

Targeting Src reactivates pyroptosis to reverse chemoresistance in lung and pancreatic cancer models

Pancreatic and lung cancers frequently develop resistance to chemotherapy-induced cell apoptosis during the treatment, indicating that targeting nonapoptotic-related pathways, such as pyroptosis, can be an alternative cancer treatment strategy. Pyroptosis is a gasdermin-driven lytic programmed cell death triggered by inflammatory caspases when initiated by canonical or noncanonical pathways that has been recently seen as a potential therapeutic target in cancer treatment. However, overcoming chemoresistance in cancers by modulating pyroptosis has not been explored. Here, we demonstrate that β5-integrin represses chemotherapy-induced canonical pyroptosis to confer cancer chemoresistance through ASAH2-driven sphingolipid metabolic reprogramming. Clinically, high β5-integrin expression associates with poor patient prognosis and chemotherapeutic responses in cancers. In addition, chemoresistant cells in vitro fail to undergo chemotherapy-induced pyroptosis, which is controlled by β5-integrin. Mechanistically, proteomic and lipidomic analyses indicate that β5-integrin up-regulates sphingolipid metabolic enzyme ceramidase (ASAH2) expression through Src-signal transducer and activator of transcription 3 (STAT3) signaling, which then reduces the metabolite ceramide concentration and subsequent ROS production to prohibit chemotherapy-induced canonical pyroptosis. Using cancer cell lines, patient-derived tumor organoids, and orthotopic lung and pancreatic animal models, we show that administration of a Src or ceramidase inhibitor rescues the response of chemoresistant pancreatic and lung cancer cells to chemotherapy by reactivating pyroptosis in vitro and in vivo. Overall, our results suggest that pyroptosis-based therapy is a means to improve cancer treatment and warrants further investigation.

Targeting senescence as an anticancer therapy

Cellular senescence is a stress response elicited by different molecular insults. Senescence results in cell cycle exit and is characterised by multiple phenotypic changes such as the production of a bioactive secretome. Senescent cells accumulate during ageing and are present in cancerous and fibrotic lesions. Drugs that selectively kill senescent cells (senolytics) have shown great promise for the treatment of age-related diseases. Senescence plays paradoxical roles in cancer. Induction of senescence limits cancer progression and contributes to therapy success, but lingering senescent cells fuel progression, recurrence, and metastasis. In this review, we describe the intricate relation between senescence and cancer. Moreover, we enumerate how current anticancer therapies induce senescence in tumour cells and how senolytic agents could be deployed to complement anticancer therapies. "One-two punch" therapies aim to first induce senescence in the tumour followed by senolytic treatment to target newly exposed vulnerabilities in senescent tumour cells. "One-two punch" represents an emerging and promising new strategy in cancer treatment. Future challenges of "one-two punch" approaches include how to best monitor senescence in cancer patients to effectively survey their efficacy.

Polymolecular botanical drug of Orthosiphon stamineus extract (C5OSEW5050ESA) as a complementary therapy to overcome gemcitabine resistance in pancreatic cancer cells

Background and aim

Gemcitabine remains the cornerstone of pancreatic cancer treatment, despite exhibiting a modest effect on patient survival due to the development of drug resistance. Nuvastatic™ polymolecular botanical drug Orthosiphon stamineus (O. stamineus) is a folklore Asian herbal medicine that is used for the treatment of a variety of ailments. However, little is known about the mechanism of actions of the Nuvastatic™ polymolecular botanical drug of O. stamineus as a complementary therapy in resistant pancreatic cancer. It is postulated that the proprietary O. stamineus extract formulation (ID: C5EOSEW5050ESA) in Nuvastatic™ may sensitise resistant pancreatic cancer cells to gemcitabine. This study was conducted to assess the cytotoxic activity and synergistic effects of C5EOSEW5050ESA in gemcitabine-resistant pancreatic cancer cells.

Experimental procedure

The effects of C5EOSEW5050ESA treatment on cell viability, multidrug-resistant genes, epithelial-mesenchymal transition, cellular senescence, cell death, and Notch signalling pathway were evaluated in gemcitabine-resistant Panc-1 cells.

Results and conclusion

C5EOSEW5050ESA sensitised gemcitabine resistant cells towards C5EOSEW5050ESA-gemcitabine combination treatment by reducing the expression of multidrug-resistant genes and epithelial-mesenchymal transition markers in gemcitabine-resistant cells compared to the control group, possibly through the inhibition of Notch signalling. This study provides valuable insight into using C5EOSEW5050ESA as a potential complementary treatment for resistant pancreatic cancer.

Sphingolipids and Lymphomas: A Double-Edged Sword

Lymphomas are a highly heterogeneous group of hematological neoplasms. Given their ethiopathogenic complexity, their classification and management can become difficult tasks; therefore, new approaches are continuously being sought. Metabolic reprogramming at the lipid level is a hot topic in cancer research, and sphingolipidomics has gained particular focus in this area due to the bioactive nature of molecules such as sphingoid bases, sphingosine-1-phosphate, ceramides, sphingomyelin, cerebrosides, globosides, and gangliosides. Sphingolipid metabolism has become especially exciting because they are involved in virtually every cellular process through an extremely intricate metabolic web; in fact, no two sphingolipids share the same fate. Unsurprisingly, a disruption at this level is a recurrent mechanism in lymphomagenesis, dissemination, and chemoresistance, which means potential biomarkers and therapeutical targets might be hiding within these pathways. Many comprehensive reviews describing their role in cancer exist, but because most research has been conducted in solid malignancies, evidence in lymphomagenesis is somewhat limited. In this review, we summarize key aspects of sphingolipid biochemistry and discuss their known impact in cancer biology, with a particular focus on lymphomas and possible therapeutical strategies against them.

Ceramide-1-Phosphate Is Involved in Therapy-Induced Senescence

Sphingolipids are key signaling lipids and their dysregulation has been associated with various cellular processes. We have previously shown significant changes in sphingolipids in therapy-induced senescence, a state of cell cycle arrest as a response to chemotherapy, including the accumulation of ceramides, and provided evidence suggesting that ceramide processing is important for this process. Herein, we conducted a focused small molecule inhibitor screen targeting the sphingolipid pathway, which highlighted a new lipid regulator of therapy-induced senescence. Among the inhibitors tested, the inhibition of ceramide kinase by NVP-231 reduced the levels of senescent cells. Ceramide kinase knockdown exhibited similar effects, strongly supporting the involvement of ceramide kinase during this process. We showed that ceramide-1-phosphate was upregulated in therapy-induced senescence and that NVP-231 reduced ceramide-1-phosphate levels in different cell line models of therapy-induced senescence. Finally, ceramide-1-phosphate addition to NVP-231-treated cells reversed the effects of NVP-231 during senescence. Overall, our results identify a previously unknown lipid player in therapy-induced senescence and highlight a potential targetable enzyme to reduce the levels of therapy-induced senescent cells.

Lipids as Regulators of Cellular Senescence

Lipids are key macromolecules that perform a multitude of biological functions ranging from maintaining structural integrity of membranes, energy storage, to signaling molecules. Unsurprisingly, variations in lipid composition and its levels can influence the functional and physiological state of the cell and its milieu. Cellular senescence is a permanent state of cell cycle arrest and is a hallmark of the aging process, as well as several age-related pathologies. Senescent cells are often characterized by alterations in morphology, metabolism, chromatin remodeling and exhibit a complex pro-inflammatory secretome (SASP). Recent studies have shown that the regulation of specific lipid species play a critical role in senescence. Indeed, some lipid species even contribute to the low-grade inflammation associated with SASP. Many protein regulators of senescence have been well characterized and are associated with lipid metabolism. However, the link between critical regulators of cellular senescence and senescence-associated lipid changes is yet to be elucidated. Here we systematically review the current knowledge on lipid metabolism and dynamics of cellular lipid content during senescence. We focus on the roles of major players of senescence in regulating lipid metabolism. Finally, we explore the future prospects of lipid research in senescence and its potential to be targeted as senotherapeutics.

Sphingolipid metabolism in the development and progression of cancer: one cancer's help is another's hindrance

Cancer development is a multistep process in which cells must overcome a series of obstacles before they can become fully developed tumors. First, cells must develop the ability to proliferate unchecked. Once this is accomplished, they must be able to invade the neighboring tissue, as well as provide themselves with oxygen and nutrients. Finally, they must acquire the ability to detach from the newly formed mass in order to spread to other tissues, all the while evading an immune system that is primed for their destruction. Furthermore, increased levels of inflammation have been shown to be linked to the development of cancer, with sites of chronic inflammation being a common component of tumorigenic microenvironments. In this Review, we give an overview of the impact of sphingolipid metabolism in cancers, from initiation to metastatic dissemination, as well as discussing immune responses and resistance to treatments. We explore how sphingolipids can either help or hinder the progression of cells from a healthy phenotype to a cancerous one.

Mechanisms of Hydroxyurea-Induced Cellular Senescence: An Oxidative Stress Connection?

Hydroxyurea (HU) is a water-soluble antiproliferative agent used for decades in neoplastic and nonneoplastic conditions. HU is considered an essential medicine because of its cytoreduction functions. HU is an antimetabolite that inhibits ribonucleotide reductase, which causes a depletion of the deoxyribonucleotide pool and dramatically reduces cell proliferation. The proliferation arrest, depending on drug concentration and exposure, may promote a cellular senescence phenotype associated with cancer cell therapy resistance and inflammation, influencing neighboring cell functions, immunosuppression, and potential cancer relapse. HU can induce cellular senescence in both healthy and transformed cells in vitro, in part, because of increased reactive oxygen species (ROS). Here, we analyze the main molecular mechanisms involved in cytotoxic/genotoxic HU function, the potential to increase intracellular ROS levels, and the principal features of cellular senescence induction. Understanding the mechanisms involved in HU's ability to induce cellular senescence may help to improve current chemotherapy strategies and control undesirable treatment effects in cancer patients and other diseases.

AMPK Is the Crucial Target for the CDK4/6 Inhibitors Mediated Therapeutic Responses in PANC-1 and MIA PaCa-2 Pancreatic Cancer Cell Lines

The survival rate of pancreatic ductal adenocarcinoma (PDAC) patients is short, and PDAC is a cancer type that ranks fourth in the statistics regarding death due to cancer. Mutation in the KRAS gene, which plays a role in pancreatic cancer development, activates the PI3K/AKT/mTOR signaling pathway. The activity of the AMPK as a cellular energy sensor is one of the fundamental mechanisms that can induce effective therapeutic responses against CDK4/6 inhibitors via adjusting the cellular and tumor microenvironment stress management. The phosphorylation of AMPKα at the different phosphorylation residues such as Thr172 and Ser 377 causes metabolic differentiation in the cells following CDK4/6 inhibitor treatment in accordance with an increased cell cycle arrest and senescence under the control of different cellular players. In this study, we examined the competencies of the CDK4/6 inhibitors LY2835219 and PD-0332991 on the mechanism of cell survival and death based on AMPK signaling. Both CDK4/6 inhibitors LY2835219 and PD-0332991 modulated different molecular players on the PI3K/AKT/mTOR and AMPK signaling axis in different ways to reduce cell survival in a cell type dependent manner. These drugs are potential inducers of apoptosis and senescence that can alter the therapeutic efficacy cells.

Targeting sphingosine kinase 1 (SK1) enhances oncogene-induced senescence through ceramide synthase 2 (CerS2)-mediated generation of very-long-chain ceramides

Senescence is an antiproliferative mechanism that can suppress tumor development and can be induced by oncogenes such as genes of the Ras family. Although studies have implicated bioactive sphingolipids (SL) in senescence, the specific mechanisms remain unclear. Here, using MCF10A mammary epithelial cells, we demonstrate that oncogenic K-Ras (Kirsten rat sarcoma viral oncogene homolog) is sufficient to induce cell transformation as well as cell senescence-as revealed by increases in the percentage of cells in the G1 phase of the cell cycle, p21WAF1/Cip1/CDKN1A (p21) expression, and senescence-associated β-galactosidase activity (SA-β-gal). Furthermore, oncogenic K-Ras altered SL metabolism, with an increase of long-chain (LC) C18, C20 ceramides (Cer), and very-long-chain (VLC) C22:1, C24 Cer, and an increase of sphingosine kinase 1 (SK1) expression. Since Cer and sphingosine-1-phosphate have been shown to exert opposite effects on cellular senescence, we hypothesized that targeting SK1 could enhance oncogenic K-Ras-induced senescence. Indeed, SK1 downregulation or inhibition enhanced p21 expression and SA-β-gal in cells expressing oncogenic K-Ras and impeded cell growth. Moreover, SK1 knockdown further increased LC and VLC Cer species (C18, C20, C22:1, C24, C24:1, C26:1), especially the ones increased by oncogenic K-Ras. Fumonisin B1 (FB1), an inhibitor of ceramide synthases (CerS), reduced p21 expression induced by oncogenic K-Ras both with and without SK1 knockdown. Functionally, FB1 reversed the growth defect induced by oncogenic K-Ras, confirming the importance of Cer generation in the senescent phenotype. More specifically, downregulation of CerS2 by siRNA blocked the increase of VLC Cer (C24, C24:1, and C26:1) induced by SK1 knockdown and phenocopied the effects of FB1 on p21 expression. Taken together, these data show that targeting SK1 is a potential therapeutic strategy in cancer, enhancing oncogene-induced senescence through an increase of VLC Cer downstream of CerS2.

Bioactive sphingolipids: Advancements and contributions from the laboratory of Dr. Lina M. Obeid

Sphingolipids and their synthetic enzymes have emerged as critical mediators in numerous diseases including inflammation, aging, and cancer. One enzyme in particular, sphingosine kinase (SK) and its product sphingosine-1-phosphate (S1P), has been extensively implicated in these processes. SK catalyzes the phosphorylation of sphingosine to S1P and exists as two isoforms, SK1 and SK2. In this review, we will discuss the contributions from the laboratory of Dr. Lina M. Obeid that have defined the roles for several bioactive sphingolipids in signaling and disease with an emphasis on her work defining SK1 in cellular fates and pathobiologies including proliferation, senescence, apoptosis, and inflammation.

Convergence of therapy-induced senescence (TIS) and EMT in multistep carcinogenesis: current opinions and emerging perspectives

Drug induced resistance is a widespread problem in the clinical management of cancer. Cancer cells, when exposed to cytotoxic drugs, can reprogram their cellular machinery and resist cell death. Evasion of cell death mechanisms, such as apoptosis and necroptosis, are part of a transcriptional reprogramming that cancer cells utilize to mediate cytotoxic threats. An additional strategy adopted by cancer cells to resist cell death is to initiate the epithelial to mesenchymal transition (EMT) program. EMT is a trans-differentiation process which facilitates a motile phenotype in cancer cells which can be induced when cells are challenged by specific classes of cytotoxic drugs. Induction of EMT in malignant cells also results in drug resistance. In this setting, therapy-induced senescence (TIS), an enduring "proliferative arrest", serves as an alternate approach against cancer because cancer cells remain susceptible to induced senescence. The molecular processes of senescence have proved challenging to understand. Senescence has previously been described solely as a tumor-suppressive mechanism; however, recent evidences suggest that senescence-associated secretory phenotype (SASP) can contribute to tumor progression. SASP has also been identified to contribute to EMT induction. Even though the causes of senescence and EMT induction can be wholly different from each other, a functional link between EMT and senescence is still obscure. In this review, we summarize the evidence of potential cross-talk between EMT and senescence while highlighting some of the most commonly identified molecular players. This review will shed light on these two intertwined and highly conserved cellular process, while providing background of the therapeutic implications of these processes.

Cellular Senescence-Inducing Small Molecules for Cancer Treatment

Recently, the chemotherapeutic drug-induced cellular senescence has been considered a promising anti-cancer approach. The drug-induced senescence, which shows both similar and different hallmarks from replicative and oncogene-induced senescence, was regarded as a key determinant of tumor response to chemotherapy in vitro and in vivo. To date, an amount of effective chemotherapeutic drugs that can evoke senescence in cancer cells have been reported. The targets of these drugs differ substantially, including senescence signaling pathways, DNA replication process, DNA damage pathways, epigenetic modifications, microtubule polymerization, senescence-associated secretory phenotype (SASP), and so on. By summarizing senescence-inducing small molecule drugs together with their specific traits and corresponding mechanisms, this review is devoted to inform scientists to develop novel therapeutic strategies against cancer through inducing senescence.

Therapy-Induced Senescence: An "Old" Friend Becomes the Enemy

For the past two decades, cellular senescence has been recognized as a central component of the tumor cell response to chemotherapy and radiation. Traditionally, this form of senescence, termed Therapy-Induced Senescence (TIS), was linked to extensive nuclear damage precipitated by classical genotoxic chemotherapy. However, a number of other forms of therapy have also been shown to induce senescence in tumor cells independently of direct genomic damage. This review attempts to provide a comprehensive summary of both conventional and targeted anticancer therapeutics that have been shown to induce senescence in vitro and in vivo. Still, the utility of promoting senescence as a therapeutic endpoint remains under debate. Since senescence represents a durable form of growth arrest, it might be argued that senescence is a desirable outcome of cancer therapy. However, accumulating evidence suggesting that cells have the capacity to escape from TIS would support an alternative conclusion, that senescence provides an avenue whereby tumor cells can evade the potentially lethal action of anticancer drugs, allowing the cells to enter a temporary state of dormancy that eventually facilitates disease recurrence, often in a more aggressive state. Furthermore, TIS is now strongly connected to tumor cell remodeling, potentially to tumor dormancy, acquiring more ominous malignant phenotypes and accounts for several untoward adverse effects of cancer therapy. Here, we argue that senescence represents a barrier to effective anticancer treatment, and discuss the emerging efforts to identify and exploit agents with senolytic properties as a strategy for elimination of the persistent residual surviving tumor cell population, with the goal of mitigating the tumor-promoting influence of the senescent cells and to thereby reduce the likelihood of cancer relapse.

A Humanized Yeast Phenomic Model of Deoxycytidine Kinase to Predict Genetic Buffering of Nucleoside Analog Cytotoxicity

Knowledge about synthetic lethality can be applied to enhance the efficacy of anticancer therapies in individual patients harboring genetic alterations in their cancer that specifically render it vulnerable. We investigated the potential for high-resolution phenomic analysis in yeast to predict such genetic vulnerabilities by systematic, comprehensive, and quantitative assessment of drug–gene interaction for gemcitabine and cytarabine, substrates of deoxycytidine kinase that have similar molecular structures yet distinct antitumor efficacy. Human deoxycytidine kinase (dCK) was conditionally expressed in the Saccharomyces cerevisiae genomic library of knockout and knockdown (YKO/KD) strains, to globally and quantitatively characterize differential drug–gene interaction for gemcitabine and cytarabine. Pathway enrichment analysis revealed that autophagy, histone modification, chromatin remodeling, and apoptosis-related processes influence gemcitabine specifically, while drug–gene interaction specific to cytarabine was less enriched in gene ontology. Processes having influence over both drugs were DNA repair and integrity checkpoints and vesicle transport and fusion. Non-gene ontology (GO)-enriched genes were also informative. Yeast phenomic and cancer cell line pharmacogenomics data were integrated to identify yeast–human homologs with correlated differential gene expression and drug efficacy, thus providing a unique resource to predict whether differential gene expression observed in cancer genetic profiles are causal in tumor-specific responses to cytotoxic agents.

Exogenous C₈-Ceramide Induces Apoptosis by Overproduction of ROS and the Switch of Superoxide Dismutases SOD1 to SOD2 in Human Lung Cancer Cells

Ceramides, abundant sphingolipids on the cell membrane, can act as signaling molecules to regulate cellular functions including cell viability. Exogenous ceramide has been shown to exert potent anti-proliferative effects against cancer cells, but little is known about how it affects reactive oxygen species (ROS) in lung cancer cells. In this study, we investigated the effect of N-octanoyl-D-erythro-sphingosine (C₈-ceramide) on human non-small-cell lung cancer H1299 cells. Flow cytometry-based assays indicated that C₈-ceramide increased the level of endogenous ROS in H1299 cells. Interestingly, the ratio of superoxide dismutases (SODs) SOD1 and SOD2 seem to be regulated by C₈-ceramide treatment. Furthermore, the accumulation of cell cycle G1 phase and apoptotic populations in C₈-ceramide-treated H1299 cells was observed. The results of the Western blot showed that C₈-ceramide causes a dramatically increased protein level of cyclin D1, a critical regulator of cell cycle G1/S transition. These results suggest that C₈-ceramide acts as a potent chemotherapeutic agent and may increase the endogenous ROS level by regulating the switch of SOD1 and SOD2, causing the anti-proliferation, and consequently triggering the apoptosis of NSCLC H1299 cells. Accordingly, our works may give a promising strategy for lung cancer treatment in the future.

Consequences of blunting the mevalonate pathway in cancer identified by a pluri-omics approach

We have previously shown that the combination of statins and taxanes was a powerful trigger of HGT-1 human gastric cancer cells’ apoptosis¹. Importantly, several genes involved in the “Central carbon metabolism pathway in cancer”, as reported in the Kyoto Encyclopedia of Genes and Genomes, were either up- (ACLY, ERBB2, GCK, MYC, PGM, PKFB2, SLC1A5, SLC7A5, SLC16A3,) or down- (IDH, MDH1, OGDH, P53, PDK) regulated in response to the drug association. In the present study, we conducted non-targeted metabolomics and lipidomics analyses by complementary methods and cross-platform initiatives, namely mass spectrometry (GC-MS, LC-MS) and nuclear magnetic resonance (NMR), to analyze the changes resulting from these treatments. We identified several altered biochemical pathways involved in the anabolism and disposition of amino acids, sugars, and lipids. Using the Cytoscape environment with, as an input, the identified biochemical marker changes, we distinguished the functional links between pathways. Finally, looking at the overlap between metabolomics/lipidomics and transcriptome changes, we identified correlations between gene expression modifications and changes in metabolites/lipids. Among the metabolites commonly detected by all types of platforms, glutamine was the most induced (6–7-fold), pointing to an important metabolic adaptation of cancer cells. Taken together, our results demonstrated that combining robust biochemical and molecular approaches was efficient to identify both altered metabolic pathways and overlapping gene expression alterations in human gastric cancer cells engaging into apoptosis following blunting the cholesterol synthesis pathway.

Role of sphingolipids in senescence: implication in aging and age-related diseases

Aging is defined as the progressive deterioration of physiological function with age. Incidence of many pathologies increases with age, including neurological and cardiovascular diseases and cancer. Aging tissues become less adaptable and renewable, and cells undergo senescence, a process by which they "irreversibly" stop dividing. Senescence has been shown to serve as a tumor suppression mechanism with clear desirable effects. However, senescence also has deleterious consequences, especially for cardiovascular, metabolic, and immune systems. Sphingolipids are a major class of lipids that regulate cell biology, owing to their structural and bioactive properties and diversity. Their involvement in the regulation of aging and senescence has been demonstrated and studied in multiple organisms and cell types, especially that of ceramide and sphingosine-1-phosphate; ceramide induces cellular senescence and sphingosine-1-phosphate delays it. These discoveries could be very useful in the future to understand aging mechanisms and improve therapeutic interventions.

Inducers of Senescence, Toxic Compounds, and Senolytics: The Multiple Faces of Nrf2-Activating Phytochemicals in Cancer Adjuvant Therapy

The reactivation of senescence in cancer and the subsequent clearance of senescent cells are suggested as therapeutic intervention in the eradication of cancer. Several natural compounds that activate Nrf2 (nuclear factor erythroid-derived 2-related factor 2) pathway, which is involved in complex cytoprotective responses, have been paradoxically shown to induce cell death or senescence in cancer. Promoting the cytoprotective Nrf2 pathway may be desirable for chemoprevention, but it might be detrimental in later stages and advanced cancers. However, senolytic activity shown by some Nrf2-activating compounds could be used to target senescent cancer cells (particularly in aged immune-depressed organisms) that escape immunosurveillance. We herein describe in vitro and in vivo effects of fifteen Nrf2-interacting natural compounds (tocotrienols, curcumin, epigallocatechin gallate, quercetin, genistein, resveratrol, silybin, phenethyl isothiocyanate, sulforaphane, triptolide, allicin, berberine, piperlongumine, fisetin, and phloretin) on cellular senescence and discuss their use in adjuvant cancer therapy. In light of available literature, it can be concluded that the meaning and the potential of adjuvant therapy with natural compounds in humans remain unclear, also taking into account the existence of few clinical trials mostly characterized by uncertain results. Further studies are needed to investigate the therapeutic potential of those compounds that display senolytic activity.

Metabolic biomarker signature to differentiate pancreatic ductal adenocarcinoma from chronic pancreatitis

OBJECTIVE

Current non-invasive diagnostic tests can distinguish between pancreatic cancer (pancreatic ductal adenocarcinoma (PDAC)) and chronic pancreatitis (CP) in only about two thirds of patients. We have searched for blood-derived metabolite biomarkers for this diagnostic purpose.

DESIGN

For a case-control study in three tertiary referral centres, 914 subjects were prospectively recruited with PDAC (n=271), CP (n=282), liver cirrhosis (n=100) or healthy as well as non-pancreatic disease controls (n=261) in three consecutive studies. Metabolomic profiles of plasma and serum samples were generated from 477 metabolites identified by gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry.

RESULTS

A biomarker signature (nine metabolites and additionally CA19-9) was identified for the differential diagnosis between PDAC and CP. The biomarker signature distinguished PDAC from CP in the training set with an area under the curve (AUC) of 0.96 (95% CI 0.93-0.98). The biomarker signature cut-off of 0.384 at 85% fixed specificity showed a sensitivity of 94.9% (95% CI 87.0%-97.0%). In the test set, an AUC of 0.94 (95% CI 0.91-0.97) and, using the same cut-off, a sensitivity of 89.9% (95% CI 81.0%-95.5%) and a specificity of 91.3% (95% CI 82.8%-96.4%) were achieved, successfully validating the biomarker signature.

CONCLUSIONS

In patients with CP with an increased risk for pancreatic cancer (cumulative incidence 1.95%), the performance of this biomarker signature results in a negative predictive value of 99.9% (95% CI 99.7%-99.9%) (training set) and 99.8% (95% CI 99.6%-99.9%) (test set). In one third of our patients, the clinical use of this biomarker signature would have improved diagnosis and treatment stratification in comparison to CA19-9.

Small molecule compounds that induce cellular senescence

To date, dozens of stress‐induced cellular senescence phenotypes have been reported. These cellular senescence states may differ substantially from each other, as well as from replicative senescence through the presence of specific senescence features. Here, we attempted to catalog virtually all of the cellular senescence‐like states that can be induced by low molecular weight compounds. We summarized biological markers, molecular pathways involved in senescence establishment, and specific traits of cellular senescence states induced by more than fifty small molecule compounds.

Combination of carbon ion beam and gemcitabine causes irreparable DNA damage and death of radioresistant pancreatic cancer stem-like cells in vitro and in vivo

We try to elucidate whether a carbon ion beam alone or in combination with gemcitabine has advantages over X-ray in targeting putative pancreatic cancer stem-like cells (CSCs) in vitro and in vivo. Colony, spheroid formation and tumorigenicity assays confirmed that CD44+/ESA+ cells sorted from PANC1 and PK45 cells have more CSC properties than CD44−/ESA− cells. The number of colonies and spheroids formed from CSCs after carbon ion beam irradiation was significantly reduced compared to after X-ray irradiation, and they were extremely highly suppressed when carbon ion beam combined with gemcitabine. The relative biological effectiveness (RBE) values for the carbon ion beam relative to X-ray at the D10 levels for CSCs were 2.23-2.66. Expressions of multiple cell death-related genes were remarkably highly induced, and large numbers of γH2AX foci in CSCs were formed after carbon ion beam combined with gemcitabine. The highly expressed CSC markers were significantly inhibited after 30 Gy of carbon ion beam and almost lost after 25 Gy carbon ion beam combined with 50 mg/kg gemcitabine. In conclusion, a carbon ion beam combined with gemcitabine has superior potential to kill pancreatic CSCs via irreparable clustered DSB compared to a carbon ion alone or X-rays combined with gemcitabine.

Novel mechanisms of action of classical chemotherapeutic agents on sphingolipid pathways

The prevailing mechanisms of action of traditional chemotherapeutic agents have been challenged by sphingolipid cancer research. Many studies have shown that ceramide generation in response to cytotoxic agents is central to tumor cell death. Ceramide can be generated either via hydrolysis of cell-membrane sphingomyelin by sphingomyelinases, hydrolysis of cerebrosides, or via de novo synthesis by ceramide synthases. Ceramide can act as a second messenger for apoptosis, senescence or autophagy. Inherent or acquired alterations in the sphingolipid pathway can account for resistance to the classic chemotherapeutic agents. In particular, it has been shown that activation of the acid ceramidase can lead to the formation of sphingosine 1-phosphate, which then antagonizes ceramide signaling by initiating a pro-survival signaling pathway. Furthermore, ceramide glycosylation catalyzed by glucosylceramide synthase converts ceramide to glucosylceramide, thus eliminating ceramide and consequently protecting cancer cells from apoptosis. In this review, we describe the effects of some of the most commonly used chemotherapeutic agents on ceramide generation, with a particular emphasis on strategies used to enhance the efficacy of these agents.

Tumor suppressive functions of ceramide: evidence and mechanisms

Studies over the past two decades have identified ceramide as a multifunctional central molecule in the sphingolipid biosynthetic pathway. Given its diverse tumor suppressive activities, molecular understanding of ceramide action will produce fundamental insights into processes that limit tumorigenesis and may identify key molecular targets for therapeutic intervention. Ceramide can be activated by a diverse array of stresses such as heat shock, genotoxic damage, oxidative stress and anticancer drugs. Ceramide triggers a variety of tumor suppressive and anti-proliferative cellular programs such as apoptosis, autophagy, senescence, and necroptosis by activating or repressing key effector molecules. Defects in ceramide generation and metabolism in cancer contribute to tumor cell survival and resistance to chemotherapy. The potent and versatile anticancer activity profile of ceramide has motivated drug development efforts to (re-)activate ceramide in established tumors. This review focuses on our current understanding of the tumor suppressive functions of ceramide and highlights the potential downstream targets of ceramide which are involved in its tumor suppressive action.

Methamphetamine accelerates cellular senescence through stimulation of de novo ceramide biosynthesis

Methamphetamine is a highly addictive psychostimulant that causes profound damage to the brain and other body organs. Post mortem studies of human tissues have linked the use of this drug to diseases associated with aging, such as coronary atherosclerosis and pulmonary fibrosis, but the molecular mechanism underlying these findings remains unknown. Here we used functional lipidomics and transcriptomics experiments to study abnormalities in lipid metabolism in select regions of the brain and, to a greater extent, peripheral organs and tissues of rats that self-administered methamphetamine. Experiments in various cellular models (primary mouse fibroblasts and myotubes) allowed us to investigate the molecular mechanisms of systemic inflammation and cellular aging related to methamphetamine abuse. We report now that methamphetamine accelerates cellular senescence and activates transcription of genes involved in cell-cycle control and inflammation by stimulating production of the sphingolipid messenger ceramide. This pathogenic cascade is triggered by reactive oxygen species, likely generated through methamphetamine metabolism via cytochrome P450, and involves the recruitment of nuclear factor-κB (NF-κB) to induce expression of enzymes in the de novo pathway of ceramide biosynthesis. Inhibitors of NF-κB signaling and ceramide formation prevent methamphetamine-induced senescence and systemic inflammation in rats self-administering the drug, attenuating their health deterioration. The results suggest new therapeutic strategies to reduce the adverse consequences of methamphetamine abuse and improve effectiveness of abstinence treatments.

Evolving concepts in cancer therapy through targeting sphingolipid metabolism

Traditional methods of cancer treatment are limited in their efficacy due to both inherent and acquired factors. Many different studies have shown that the generation of ceramide in response to cytotoxic therapy is generally an important step leading to cell death. Cancer cells employ different methods to both limit ceramide generation and to remove ceramide in order to become resistant to treatment. Furthermore, sphingosine kinase activity, which phosphorylates sphingosine the product of ceramide hydrolysis, has been linked to multidrug resistance, and can act as a strong survival factor. This review will examine several of the most frequently used cancer therapies and their effect on both ceramide generation and the mechanisms employed to remove it. The development and use of inhibitors of sphingosine kinase will be focused upon as an example of how targeting sphingolipid metabolism may provide an effective means to improve treatment response rates and reduce associated treatment toxicity. This article is part of a Special Issue entitled Tools to study lipid functions.

Potential role of acid ceramidase in conversion of cytostatic to cytotoxic end-point in pancreatic cancer cells

PURPOSE

Acid ceramidase (AC) occupies an important place in the control of cancer cell proliferation. We tested the influence of AC inhibition on the effects of PSC 833, a P-glycoprotein antagonist with potent ceramide-generating capacity, to determine whether AC could be a therapeutic target in pancreatic cancer.

METHODS

Ceramide metabolism was followed using (3)H-palmitate, and molecular species were determined by mass spectroscopy. Apoptosis was measured by DNA fragmentation, autophagy by acridine orange staining, and cell cycle was assessed by flow cytometry and RB phosphorylation. AC was measured in intact cells using fluorescent substrate.

RESULTS

Exposure of human PANC-1 or MIA-PaCa-2 cells to PSC 833 promoted increases in de novo (dihydro)ceramides, (dihydro)glucosylceramides, and (dihydro)sphingomyelins, demarking ceramide generation and robust metabolism. Despite the multifold increases in (dihydro)ceramide levels, cells were refractory to PSC 833. However, PSC 833 produced a dose-dependent decrease in DNA synthesis and dose- and time-dependent decreases in RB phosphorylation, consistent with cell cycle arrest as demonstrated at G1. Cytostatic effects of PSC 833 were converted to cytotoxic end-point by acid ceramidase inhibition. Cytotoxicity was accompanied by formation of acridine orange-stained acidic vesicles and an increase in LC3 expression, indicative of autophagic response. Cell death was not reversed by preexposure to myriocin, which blocks PSC 833-induced ceramide generation.

CONCLUSION

Although the role of ceramide in end-point cytotoxicity is unclear, our results suggest that acid ceramidase is a viable target in pancreatic cancer. We propose that AC inhibition will be effective in concert with other anticancer therapies.

LCL124, a cationic analog of ceramide, selectively induces pancreatic cancer cell death by accumulating in mitochondria

Treatment of pancreatic cancer that cannot be surgically resected currently relies on minimally beneficial cytotoxic chemotherapy with gemcitabine. As the fourth leading cause of cancer-related death in the United States with dismal survival statistics, pancreatic cancer demands new and more effective treatment approaches. Resistance to gemcitabine is nearly universal and appears to involve defects in the intrinsic/mitochondrial apoptotic pathway. The bioactive sphingolipid ceramide is a critical mediator of apoptosis initiated by a number of therapeutic modalities. It is noteworthy that insufficient ceramide accumulation has been linked to gemcitabine resistance in multiple cancer types, including pancreatic cancer. Taking advantage of the fact that cancer cells frequently have more negatively charged mitochondria, we investigated a means to circumvent resistance to gemcitabine by targeting delivery of a cationic ceramide (l-t-C6-CCPS [LCL124: ((2S,3S,4E)-2-N-[6'-(1″-pyridinium)-hexanoyl-sphingosine bromide)]) to cancer cell mitochondria. LCL124 was effective in initiating apoptosis by causing mitochondrial depolarization in pancreatic cancer cells but demonstrated significantly less activity against nonmalignant pancreatic ductal epithelial cells. Furthermore, we demonstrate that the mitochondrial membrane potentials of the cancer cells were more negative than nonmalignant cells and that dissipation of this potential abrogated cell killing by LCL124, establishing that the effectiveness of this compound is potential-dependent. LCL124 selectively accumulated in and inhibited the growth of xenografts in vivo, confirming the tumor selectivity and therapeutic potential of cationic ceramides in pancreatic cancer. It is noteworthy that gemcitabine-resistant pancreatic cancer cells became more sensitive to subsequent treatment with LCL124, suggesting that this compound may be a uniquely suited to overcome gemcitabine resistance in pancreatic cancer.

Role of mitochondrial uncoupling protein 2 in cancer cell resistance to gemcitabine

Cancer cells exhibit an endogenous constitutive oxidative stress higher than that of normal cells, which renders tumours vulnerable to further reactive oxygen species (ROS) production. Mitochondrial uncoupling protein 2 (UCP2) can mitigate oxidative stress by increasing the influx of protons into the mitochondrial matrix and reducing electron leakage and mitochondrial superoxide generation. Here, we demonstrate that chemical uncouplers or UCP2 over-expression strongly decrease mitochondrial superoxide induction by the anticancer drug gemcitabine (GEM) and protect cancer cells from GEM-induced apoptosis. Moreover, we show that GEM IC(50) values well correlate with the endogenous level of UCP2 mRNA, suggesting a critical role for mitochondrial uncoupling in GEM resistance. Interestingly, GEM treatment stimulates UCP2 mRNA expression suggesting that mitochondrial uncoupling could have a role also in the acquired resistance to GEM. Conversely, UCP2 inhibition by genipin or UCP2 mRNA silencing strongly enhances GEM-induced mitochondrial superoxide generation and apoptosis, synergistically inhibiting cancer cell proliferation. These events are significantly reduced by the addition of the radical scavenger N-acetyl-l-cysteine or MnSOD over-expression, demonstrating a critical role of the oxidative stress. Normal primary fibroblasts are much less sensitive to GEM/genipin combination. Our results demonstrate for the first time that UCP2 has a role in cancer cell resistance to GEM supporting the development of an anti-cancer therapy based on UCP2 inhibition associated to GEM treatment.

2-Hydroxyoleate, a nontoxic membrane binding anticancer drug, induces glioma cell differentiation and autophagy

Despite recent advances in the development of new cancer therapies, the treatment options for glioma remain limited, and the survival rate of patients has changed little over the past three decades. Here, we show that 2-hydroxyoleic acid (2OHOA) induces differentiation and autophagy of human glioma cells. Compared to the current reference drug for this condition, temozolomide (TMZ), 2OHOA combated glioma more efficiently and, unlike TMZ, tumor relapse was not observed following 2OHOA treatment. The novel mechanism of action of 2OHOA is associated with important changes in membrane-lipid composition, primarily a recovery of sphingomyelin (SM) levels, which is markedly low in glioma cells before treatment. Parallel to membrane-lipid regulation, treatment with 2OHOA induced a dramatic translocation of Ras from the membrane to the cytoplasm, which inhibited the MAP kinase pathway, reduced activity of the PI3K/Akt pathway, and downregulated Cyclin D-CDK4/6 proteins followed by hypophosphorylation of the retinoblastoma protein (RB). These regulatory effects were associated with induction of glioma cell differentiation into mature glial cells followed by autophagic cell death. Given its high efficacy, low toxicity, ease of oral administration, and good distribution to the brain, 2OHOA constitutes a new and potentially valuable therapeutic tool for glioma patients.

Kinetic tracking of therapy-induced senescence using the real-time cell analyzer single plate system

In recent years, terminal growth arrest, that is, senescence, especially therapy-induced senescence (TIS), has become a major subject in cancer research and several fields of life sciences. Senescence is characterized by a specific set of morphological and biochemical changes. However, methods that evidence senescence induction are still very limited and show large variation between individual examiners. Most notably, these assays are classical endpoint assays, and, therefore, screening for senescence is time consuming and expensive. Here, we describe an efficient, simple, and objective method to screen for TIS over time by modifying the Real-Time Cell Analyzer SP system, thus enabling to pin point the induction of senescence. This method continuously detects the cell's impedance in each well of a 96-microwell plate that allows to observe increment of cell size, a hallmark feature of cellular senescence. This technique is suitable for high-throughput TIS screening by measuring several compounds, small molecules, and/or cell lines simultaneously.

Combinatorial therapies improve the therapeutic efficacy of nanoliposomal ceramide for pancreatic cancer

Poor prognosis cancers, such as pancreatic cancer, represent inherent challenges for ceramide-based nanotherapeutics due to metabolic pathways, which neutralize ceramide to less toxic or pro-oncogenic metabolites. We have recently developed a novel 80 nanometer diameter liposomal formulation that incorporates 30 molar percent C6-ceramide, a bioactive lipid that is pro-apoptotic to many cancer cells, but not to normal cells. In this manuscript, we evaluated the efficacy of combining nanoliposomal C6-ceramide (Lip-C6) with either gemcitabine or an inhibitor of glucosylceramide synthase. We first assessed the biological effect of Lip-C6 in PANC-1 cells, a gemcitabine-resistant human pancreatic cancer cell line, and found that low doses alone did not induce cell toxicity. However, cytotoxicity was achieved by combining Lip-C6 with either non-toxic sub-therapeutic concentrations of gemcitabine or with the glucosylceramide synthase inhibitor D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP). Furthermore, these combinations with Lip-C6 cooperatively inhibited PANC-1 tumor growth in vivo. Mechanistically, Lip-C6 inhibited pro-survival Akt and Erk signaling, whereas the nucleoside analog gemcitabine did not. Furthermore, by including PDMP within the nanoliposomes, which halted ceramide neutralization as evidenced by LC-MS3, the cytotoxic effects of Lip-C6 were enhanced. Collectively, we have demonstrated that nanoliposomal ceramide can be an effective anti-pancreatic cancer therapeutic in combination with gemcitabine or an inhibitor of ceramide neutralization.

3,4-Disubstituted oxazolidin-2-ones as constrained ceramide analogs with anticancer activities

Heterocyclic analogs of ceramide as 3-alkanoyl or benzoyl-4-(1-hydroxy-2-enyl)-oxazolidin-2-ones were designed by binding of primary alcohol and amide in sphinogosine backbone as a carbamate. They were synthesized by addition of acyl halide to the common ring 4-(1-t-butyldimethylsilyloxyhexadec-2-enyl)-oxazolidin-2-one which was elaborated from chiral aziridine-2-carboxylate including stereoselective reduction and ring opening reactions as key steps. Other analogs with different carbon frame at C4 position which is corresponding to the sphingoid backbone were prepared from 3-cyclopentanecarbonyl-4-(1-t-butyldimethylsilyloxybut-2-enyl)-oxazolidin-2-one and straight and cyclic alkenes by cross metathesis. All compounds were tested as antileukemic drugs against human leukemia HL-60 cells. Many of them including propionyl, cyclopentanoyl and p-nitrobenzoyl-4-(1-hydroxyhexadec-2-enyl)-oxazolidin-2-ones showed better antileukemic activities than natural C2-ceramide with good correlation between cell death and DNA fragmentation. There is a drastic change of the activities by the carbon chain lengths at C4 position. Cytotoxicity was induced by caspase activation without significant accumulation of endogenous ceramide concentration or any perturbation of ceramide metabolism.

Discovery and evaluation of inhibitors of human ceramidase

The ceramide/sphingosine-1-phosphate (S1P) rheostat has been hypothesized to play a critical role in regulating tumor cell fate, with elevated levels of ceramide inducing death and elevated levels of S1P leading to survival and proliferation. Ceramidases are key enzymes that control this rheostat by hydrolyzing ceramide to produce sphingosine and may also confer resistance to drugs and radiation. Therefore, ceramidase inhibitors have excellent potential for development as new anticancer drugs. In this study, we identify a novel ceramidase inhibitor (Ceranib-1) by screening a small molecule library and describe the synthesis of a more potent analogue (Ceranib-2). In a cell-based assay, both compounds were found to inhibit cellular ceramidase activity toward an exogenous ceramide analogue, induce the accumulation of multiple ceramide species, decrease levels of sphingosine and S1P, inhibit the proliferation of cells alone and in combination with paclitaxel, and induce cell-cycle arrest and cell death. In vivo, Ceranib-2 was found to delay tumor growth in a syngeneic tumor model without hematologic suppression or overt signs of toxicity. These data support the selection of ceramidases as suitable targets for anticancer drug development and provide the first nonlipid inhibitors of human ceramidase activity.

Combination of salinomycin and gemcitabine eliminates pancreatic cancer cells

Previous research has documented that a subpopulation of pancreatic cancer cells, named cancer stem cells (CSCs), harbor stem cell-like properties. Here, we examined the efficacy of combined treatments of salinomycin and gemcitabine in human pancreatic cancer cells. Salinomycin inhibited the growth of CSCs, while gemcitabine suppressed the viability of non-CSCs. Consistently, in vivo studies showed that salinomycin combined with gemcitabine could eliminate the engraftment of human pancreatic cancer more effectively than the individual agents. These data indicated that administration of salinomycin, which targets CSCs, may constitute a potential therapeutic strategy for improving the efficacy of gemcitabine to eradicate pancreatic cancer.

Gemcitabine response in pancreatic adenocarcinoma cells is synergistically enhanced by dithiocarbamate derivatives

Pancreatic adenocarcinoma is a common malignancy that remains refractory to all available therapies, including the gold standard drug gemcitabine (GEM). We investigated the effect of the combination of GEM and each of the ionophore compounds pyrrolidine dithiocarbamate (PDTC) and disulfiram [DSF; 1-(diethylthiocarbamoyldisulfanyl)-N,N-diethylmethanethioamide] on p53(-/-) pancreatic adenocarcinoma cell growth. PDTC or DSF synergistically inhibited cell proliferation when used in combination with GEM by inducing apoptotic cell death. This effect was associated with an increased mitochondrial O(2)(•-) production and was further enhanced by zinc ions. Basal levels of mitochondrial O(2)(•-) or manganese superoxide dismutase (MnSOD) strictly correlated with the IC(50) for GEM or the percentage of synergism. Thus, the most relevant values of the antiproliferative synergism were obtained in GEM-resistant pancreatic adenocarcinoma cell lines. Interestingly, the GEM-sensitive T3M4 cells transfected with MnSOD expression vector showed mitochondrial O(2)(•-) and IC(50) for GEM similar to those of resistant cell lines. In vivo experiments performed on nude mice xenotransplanted with the GEM-resistant PaCa44 cell line showed that only the combined treatment with GEM and DSF/Zn completely inhibited the growth of the tumoral masses. These results and the consideration that DSF is already used in clinics strongly support the GEM and DSF/Zn combination as a new approach to overcoming pancreatic cancer resistance to standard chemotherapy.

Involvement of the sphingolipid ceramide in heat-shock-induced apoptosis of bovine oocytes

Programmed cell death via the sphingomyelin pathway has been suggested to underlie heat-shock disturbance of oocyte developmental competence. A series of experiments were performed to characterise the role of the sphingolipid ceramide in heat-shock-induced apoptosis, and to determine whether ceramide formation can be regulated. Bovine cumulus–oocyte complexes (COCs) were aspirated from ovaries collected in the cold season (November–April), in vitro-matured, fertilised and cultured for 8 days. Exposure of COCs to heat shock (41°C) during maturation reduced cleavage rate and blastocyst formation relative to the control group (38.5°C). Annexin-V binding (V-FITC assay), which is associated with the early apoptotic event of membrane phosphatidylserine turnover, was higher in oocytes exposed to short-term versus long-term heat shock, suggesting that heat-shock-induced apoptosis involves membrane alterations. Similar to heat exposure, oocyte maturation with C2-ceramide had a dose-dependent deleterious effect on the first cleavages and subsequent embryonic development in association with increased annexin-V binding. Blocking endogenous ceramide generation with fumonisin B1, a specific inhibitor of dihydroceramide synthase (i.e. de novo formation), moderated, to some extent, the effects of heat shock on oocyte developmental competence, suggesting that ceramide plays an important role in heat-shock-induced apoptosis.

Sphingolipid metabolism and analysis in metabolic disease

Sphingolipids are an important class of structural and signaling molecules within the cell. As sphingolipids have been implicated in the development and pathogenesis of insulin resistance and the metabolic syndrome, it is important to understand their regulation and metabolism. Although these lipids are initially produced through a common pathway, there is no "generic" sphingolipid. Indeed, the biophysical and signaling properties of lipids may be manipulated by the subunit composition or isoform of their synthetic enzymes, via regulation of substrate integration. Functionally distinct pools of chemically-equivalent lipids may also be generated by de novo synthesis and recycling of existing complex sphingolipids. The highly integrated metabolism of the many bioactive sphingolipids means that manipulation of one enzyme or metabolite can result in a ripple effect, causing unforeseen changes in metabolite levels, enzyme activities, and cellular programmes. Fortunately, a suite of techniques, ranging from thin-layer chromatography to liquid chromatography-mass spectrometry approaches, allows investigators to undertake a functional characterization of all or part of the sphingolipidome in their systems of interest.

Cytotoxic responses to N-(4-hydroxyphenyl)retinamide in human pancreatic cancer cells

PURPOSE

Although fenretinide (4-HPR) has been studied in breast cancer and in neuroblastoma, little is known regarding its activity in pancreatic cancer, a neoplasm for which there are few therapeutic options. Since pancreatic cancer cells are susceptible to reactive oxygen species (ROS) and ceramide, two hallmarks of 4-HPR cytotoxicity, we investigated the effect of 4-HPR on human pancreatic cancer cells.

METHODS

Human pancreatic cancer cell lines MIA PaCa-2 and PANC-1 were treated with 4-HPR, followed by measurement of viability, proliferation, ROS and ceramide production, and Western blotting.

RESULTS

At the measured IC(50) of 10 μM, 4-HPR led to a 44-68% reduction in [(3)H]thymidine incorporation, a >3-fold increase in de novo ceramide levels, a 2.7-fold increase in ROS, and minor increases in markers of apoptosis. 4-HPR induced a robust, sustained increase in LC3 II expression and enhanced formation of acridine orange-stained acidic vesicles that are markers of autophagy. In addition, sustained, dose-dependent increases in JNK and p38 phosphorylation and decreased ERK phosphorylation were observed following treatment. Pretreatment with vitamin E, a ROS scavenger, and 3-methyladenine, an autophagy inhibitor, individually led to decreased sensitivity to 4-HPR; however, the de novo ceramide inhibitor myriocin had no effect.

CONCLUSIONS

These data show that 4-HPR triggers pancreatic cancer cell death by apoptosis and autophagy and that sensitivity appears to be mediated by ROS and not ceramide. This study is the first to characterize the response of human pancreatic cancer cells to 4-HPR and opens the door to investigations into this compound in pancreatic adenocarcinomas.

Study of apoptosis induction and deoxycytidine kinase/cytidine deaminase modulation in the synergistic interaction of a novel ceramide analog and gemcitabine in pancreatic cancer cells

This study investigated the interaction between the novel ceramide analog AL6 and gemcitabine in MIA PaCa-2 and PANC-1 pancreatic cancer cell lines, harboring different polymorphic variants of the gemcitabine catabolism enzyme cytidine deaminase (CDA). AL6 dose-dependently inhibited cell growth, induced apoptosis and synergistically enhanced the cytotoxic activity of gemcitabine. Moreover, it triggered apoptosis, which was significantly enhanced by the combination, and increased the ratio between gene expression of the activating enzyme deoxycytidine kinase (dCK) and CDA, potentially favoring gemcitabine activity. In conclusion, AL6 displays synergistic cytotoxic activity, enhances apoptosis, and favorably modulates enzymes involved in gemcitabine metabolism, supporting future investigation of this combination in pancreatic cancer.

Additive effects of C(2)-ceramide on paclitaxel-induced premature senescence of human lung cancer cells

AIMS

the aims of the study are to investigate the additive effect of exogenous short-carbon chain phospholipids, C(2)-ceramide, on an anti-cancer drug paclitaxel (PTX)-induced senescence of human non-small cell lung cancer (NSCLC) cells deficient in functional p53 and p16, and to examine whether mitogen-activated protein kinase (MAPK) plays a role in ceramide-sensitized senescence of NSCLC cells.

MAIN METHODS

to determine whether exogenous C(2)-ceramide renders lung cancer cells more sensitive to PTX treatment, techniques employing a flow cytometry-based cell cycle analysis and acidic β-galactosidase staining for senescent cells were used. Furthermore, to elucidate the role of MAPK proteins in modulating senescence, assays for protein levels of selective MAPKs and Bcl-2 family members, and detection of transcriptional levels senescence-associated genes were used in the study.

KEY FINDINGS

a sub-lethal dose of C(2)-ceramide sensitized the NSCLC H1299 cells to PTX treatment. The additive effects of C(2)-ceramide and PTX resulted in proliferative inhibition, G(2)-phase arrest of cell cycle, activation of p38 and eventually premature senescence. Importantly, neither p53, p21(waf1/cip1) nor p16(ink4) was shown to be involved in C(2)-ceramide-sensitized proliferative inhibition and senescence of H1299 cells by PTX in our study.

SIGNIFICANCE

our study demonstrates that the short-carbon chain C(2)-ceramide can effectively sensitize PTX-induced senescence of H1299 cells via both p21(waf1/cip1)- and p16(ink4)-independent pathways.