Inhibition of calcium-independent phospholipase A2 activates p38 MAPK signaling pathways during cytostasis in prostate cancer cells

iPLA2β-Null Mice Show HCC Protection by an Induction of Cell-Cycle Arrest after Diethylnitrosamine Treatment

Group VIA phospholipase A2 (iPLA2β) play diverse biological functions in epithelial cells and macrophages. Global deletion in iPLA2β-null (KO) mice leads to protection against hepatic steatosis in non-alcoholic fatty liver disease, in part, due to the replenishment of the loss of hepatocellular phospholipids. As the loss of phospholipids also occurs in hepatocellular carcinoma (HCC), we hypothesized that global deletion in KO mice may lead to protection against HCC. Here, HCC induced by diethylnitrosamine (DEN) was chosen because DEN causes direct injury to the hepatocytes. Male wild-type (WT) and KO mice at 3-5 weeks of age (12-13 mice/group) were subjected to a single intraperitoneal treatment with 10 mg/kg DEN, and mice were killed 12 months later. Analyses of histology, plasma cytokines, and gene expression were performed. Due to the low-dose DEN used, we observed a liver nodule in 3 of 13 WT and 2 of 12 KO mice. Only one DEN-treated WT mouse was confirmed to have HCC. DEN-treated KO mice did not show any HCC but showed suppressed hepatic expression of cell-cycle cyclinD2 and BCL2 as well as inflammatory markers IL-1β, IL-10, and VCAM-1. Notably, DEN-treated KO mice showed increased hepatic necrosis and elevated levels of plasma lactate dehydrogenase suggesting an exacerbation of liver injury. Thus, global iPLA2β deficiency in DEN-treated mice rendered HCC protection by an induction of cell-cycle arrest. Our results suggest the role of iPLA2β inhibition in HCC treatment.

Phospholipase A2 superfamily in cancer

Phospholipase A2 enzymes (PLA₂s) comprise a superfamily that is generally divided into six subfamilies known as cytosolic PLA₂s (cPLA₂s), calcium-independent PLA₂s (iPLA₂s), secreted PLA₂s (sPLA₂s), lysosomal PLA₂s, platelet-activating factor (PAF) acetylhydrolases, and adipose specific PLA₂s. Each subfamily consists of several isozymes that possess PLA₂ activity. The first three PLA₂ subfamilies play important roles in inflammation-related diseases and cancer. In this review, the roles of well-studied enzymes sPLA₂-IIA, cPLA₂α and iPLA₂β in carcinogenesis and cancer development were discussed. sPLA₂-IIA seems to play conflicting roles and can act as a tumor suppressor or a tumor promoter according to the cancer type, but cPLA₂α and iPLA₂β play protumorigenic role in most cancers. The mechanisms of PLA₂-mediated signal transduction and crosstalk between cancer cells and endothelial cells in the tumor microenvironment are described. Moreover, the mechanisms by which PLA₂s mediate lipid reprogramming and glycerophospholipid remodeling in cancer cells are illustrated. PLA₂s as the upstream regulators of the arachidonic acid cascade are generally high expressed and activated in various cancers. Therefore, they can be considered as potential pharmacological targets and biomarkers in cancer. The detailed information summarized in this review may aid in understanding the roles of PLA₂s in cancer, and provide new clues for the development of novel agents and strategies for tumor prevention and treatment.

Hydrazinocurcumin Induces Apoptosis of Hepatocellular Carcinoma Cells Through the p38 MAPK Pathway

Hydrazinocurcumin (HZC), a synthetic derivative of curcumin (CUR), has been documented to show anticancer potential in impeding tumor growth in several cancers, including hepatocellular carcinoma (HCC). However, the underlying molecular mechanisms remain unclear. This study aimed to explore the function and underlying mechanisms of HZC on HCC cells, which may involve the p38 mitogen activated protein kinase (MAPK) pathway. HZC was first purified and identified. HepG2 cells were then subjected to treatment with HZC or CUR of different concentrations and p38 MAPK signaling inhibitor (SB203580) to verify their effects on HCC cell apoptosis and proliferation. Furthermore, the functional relevance between HZC and the p38 MAPK pathway in HCC was examined. It was observed that 40 μM HZC exhibited the best pro-apoptosis effect in HCC cells. HZC was found to inhibit HCC cell proliferation and promote apoptosis, the effect of which was stronger than 5-fluorouracil (5-FU). More importantly, the anti-oncogenic effect of HZC and 5-FU was implicated with activation of the p38 MAPK pathway. In vivo experimental results showed that HZC inhibited tumor growth more effectively than 5-FU through the p38 MAPK pathway. These results provide evidence that HZC exerted anti-oncogenic and pro-apoptosis effects in HCC cells through activation of the p38 MAPK pathway.

Inhibition of the key metabolic pathways, glycolysis and lipogenesis, of oral cancer by bitter melon extract

BACKGROUND

Metabolic reprogramming is one of the hallmarks of cancer which favours rapid energy production, biosynthetic capabilities and therapy resistance. In our previous study, we showed bitter melon extract (BME) prevents carcinogen induced mouse oral cancer. RNA sequence analysis from mouse tongue revealed a significant modulation in "Metabolic Process" by altering glycolysis and lipid metabolic pathways in BME fed group as compared to cancer group. In present study, we evaluated the effect of BME on glycolysis and lipid metabolism pathways in human oral cancer cells.

METHODS

Cal27 and JHU022 cells were treated with BME. RNA and protein expression were analysed for modulation of glycolytic and lipogenesis genes by quantitative real-time PCR, western blot analyses and immunofluorescence. Lactate and pyruvate level was determined by GC/MS. Extracellular acidification and glycolytic rate were measured using the Seahorse XF analyser. Shotgun lipidomics in Cal27 and JHU022 cell lines following BME treatment was performed by ESI/ MS. ROS was measured by FACS.

RESULTS

Treatment with BME on oral cancer cell lines significantly reduced mRNA and protein expression levels of key glycolytic genes SLC2A1 (GLUT-1), PFKP, LDHA, PKM and PDK3. Pyruvate and lactate levels and glycolysis rate were reduced in oral cancer cells following BME treatment. In lipogenesis pathway, we observed a significant reduction of genes involves in fatty acid biogenesis, ACLY, ACC1 and FASN, at the mRNA and protein levels following BME treatment. Further, BME treatment significantly reduced phosphatidylcholine, phosphatidylethanolamine, and plasmenylethanolamine, and reduced iPLA2 activity. Additionally, BME treatment inhibited lipid raft marker flotillin expression and altered its subcellular localization. ER-stress associated CHOP expression and generation of mitochondrial reactive oxygen species were induced by BME, which facilitated apoptosis.

CONCLUSION

Our study revealed that bitter melon extract inhibits glycolysis and lipid metabolism and induces ER and oxidative stress-mediated cell death in oral cancer. Thus, BME-mediated metabolic reprogramming of oral cancer cells will have important preventive and therapeutic implications along with conventional therapies.

The involvement of FBP1 in prostate cancer cell epithelial mesenchymal transition, invasion and metastasis by regulating the MAPK signaling pathway

Prostate cancer (PCa) is a frequently occurring malignancy in males, and epithelial mesenchymal transition (EMT) plays a critical role in PCa metastasis. Thus, developing biomarkers inhibiting EMT may provide significance for treatment of PCa. Hence, the aim of the current study was to investigate the mechanism by which FBP1 gene silencing influences PCa cell EMT, invasion and metastasis by mediating the MAPK pathway. PCa cell lines exhibiting the highest FBP1 expression were selected and treated with plasmids of siRNA-FBP1 sequence 1 and 2, pcDNA3.1-Flag-FBP1 (over-expression plasmid of FBP1), U0126 (an inhibitor of the ERK signaling pathway) and PD98059 (an inhibitor of the MEK signaling pathway). Cell proliferation, migration and invasion were detected by MTT assay, wound healing assay and Transwell assay, respectively. The mRNA and protein expression of related factors of EMT and MAPK signaling were determined by RT-qPCR and western blot analysis, respectively. Xenograft tumor growth after inoculation of DU145 cells was regularly analyzed in the nude mice. The positive expression of EMT markers was determined by immunohistochemistry. DU-145 and PC-3 cells displaying the highest FBP1 expression were selected for further analysis. The PCa cells treated with siRNA-FBP1 exhibited increased proliferation, migration rate and invasion, in addition to facilitated xenograft tumor growth. Notably, siRNA-FBP1 was identified to accelerate PCa cell EMT by elevating the expression of Vimentin and N-cadherin while diminishing E-cadherin expression via activation of the MAPK signaling pathway. The aforementioned results were reversed in PCa cells treated by pcDNA3.1-Flag-FBP1. Evidence has been provided in this study that FBP1 gene silencing activates the MAPK pathway, which ultimately promotes cell EMT, invasion and metastasis in PCa.

Bromoenol Lactone Attenuates Nicotine-Induced Breast Cancer Cell Proliferation and Migration

Objectives

Calcium independent group VIA phospholipase A₂ (iPLA₂β) and Matrix Metalloproteinase-9 (MMP-9) are upregulated in many disease states; their involvement with cancer cell migration has been a recent subject for study. Further, the molecular mechanisms mediating nicotine-induced breast cancer cell progression have not been fully investigated. This study aims to investigate whether iPLA₂β mediates nicotine-induced breast cancer cell proliferation and migration through both in-vitro and in-vivo techniques. Subsequently, the ability of Bromoenol Lactone (BEL) to attenuate the severity of nicotine-induced breast cancer was examined.

Method and Results

We found that BEL significantly attenuated both basal and nicotine-induced 4T1 breast cancer cell proliferation, via an MTT proliferation assay. Breast cancer cell migration was examined by both a scratch and transwell assay, in which, BEL was found to significantly decrease both basal and nicotine-induced migration. Additionally, nicotine-induced MMP-9 expression was found to be mediated in an iPLA₂β dependent manner. These results suggest that iPLA₂β plays a critical role in mediating both basal and nicotine-induced breast cancer cell proliferation and migration in-vitro. In an in-vivo mouse breast cancer model, BEL treatment was found to significantly reduce both basal (p<0.05) and nicotine-induced tumor growth (p<0.01). Immunohistochemical analysis showed BEL decreased nicotine-induced MMP-9, HIF-1alpha, and CD31 tumor tissue expression. Subsequently, BEL was observed to reduce nicotine-induced lung metastasis.

Conclusion

The present study indicates that nicotine-induced migration is mediated by MMP-9 production in an iPLA₂β dependent manner. Our data suggests that BEL is a possible chemotherapeutic agent as it was found to reduce both nicotine-induced breast cancer tumor growth and lung metastasis.

Synthetic and natural inhibitors of phospholipases A2: their importance for understanding and treatment of neurological disorders

Phospholipases A2 (PLA2) are a diverse group of enzymes that hydrolyze membrane phospholipids into arachidonic acid and lysophospholipids. Arachidonic acid is metabolized to eicosanoids (prostaglandins, leukotrienes, thromboxanes), and lysophospholipids are converted to platelet-activating factors. These lipid mediators play critical roles in the initiation, maintenance, and modulation of neuroinflammation and oxidative stress. Neurological disorders including excitotoxicity; traumatic nerve and brain injury; cerebral ischemia; Alzheimer's disease; Parkinson's disease; multiple sclerosis; experimental allergic encephalitis; pain; depression; bipolar disorder; schizophrenia; and autism are characterized by oxidative stress, inflammatory reactions, alterations in phospholipid metabolism, accumulation of lipid peroxides, and increased activities of brain phospholipase A2 isoforms. Several old and new synthetic inhibitors of PLA2, including fatty acid trifluoromethyl ketones; methyl arachidonyl fluorophosphonate; bromoenol lactone; indole-based inhibitors; pyrrolidine-based inhibitors; amide inhibitors, 2-oxoamides; 1,3-disubstituted propan-2-ones and polyfluoroalkyl ketones as well as phytochemical based PLA2 inhibitors including curcumin, Ginkgo biloba and Centella asiatica extracts have been discovered and used for the treatment of neurological disorders in cell culture and animal model systems. The purpose of this review is to summarize information on selective and potent synthetic inhibitors of PLA2 as well as several PLA2 inhibitors from plants, for treatment of oxidative stress and neuroinflammation associated with the pathogenesis of neurological disorders.

Calcium-independent phospholipases A2 and their roles in biological processes and diseases

Among the family of phospholipases A2 (PLA2s) are the Ca(2+)-independent PLA2s (iPLA2s) and they are designated group VI iPLA2s. In relation to secretory and cytosolic PLA2s, the iPLA2s are more recently described and details of their expression and roles in biological functions are rapidly emerging. The iPLA2s or patatin-like phospholipases (PNPLAs) are intracellular enzymes that do not require Ca(2+) for activity, and contain lipase (GXSXG) and nucleotide-binding (GXGXXG) consensus sequences. Though nine PNPLAs have been recognized, PNPLA8 (membrane-associated iPLA2γ) and PNPLA9 (cytosol-associated iPLA2β) are the most widely studied and understood. The iPLA2s manifest a variety of activities in addition to phospholipase, are ubiquitously expressed, and participate in a multitude of biological processes, including fat catabolism, cell differentiation, maintenance of mitochondrial integrity, phospholipid remodeling, cell proliferation, signal transduction, and cell death. As might be expected, increased or decreased expression of iPLA2s can have profound effects on the metabolic state, CNS function, cardiovascular performance, and cell survival; therefore, dysregulation of iPLA2s can be a critical factor in the development of many diseases. This review is aimed at providing a general framework of the current understanding of the iPLA2s and discussion of the potential mechanisms of action of the iPLA2s and related involved lipid mediators.

Cell mechanisms of gustatory lipids perception and modulation of the dietary fat preference

Dietary lipids are usually responsible of several metabolic disorders. Recent compelling evidences suggest that there is a sixth taste modality, destined for the detection of oro-gustatory fats. The lipid-binding glycoprotein CD36, expressed by circumvallate papillae (CVP) of the mouse tongue, has been shown to be implicated in oro-gustatory perception of dietary lipids. We demonstrate that linoleic acid (LA) by activating sPLA2, cPLA2 and iPLA2 via CD36, produced arachidonic acid (AA) and lyso-phosphatidylcholine (Lyso-PC) which triggered Ca(2+) influx in CD36-positive taste bud cells (TBC), purified from mouse CVP. LA induced the production of Ca(2+) influx factor (CIF). CIF, AA and Lyso-PC exerted different actions on the opening of store-operated Ca2+ (SOC) channels, constituted of Orai proteins and regulated by STIM1, a sensor of Ca(2+) depletion in the endoplasmic reticulum. We observed that CIF and Lyso-PC opened Orai1 channels whereas AA-opened Ca(2+) channels were composed of Orai1/Orai3. STIM1 was found to regulate LA-induced CIF production and opening of both kinds of Ca(2+) channels. Furthermore, Stim1(-/-) mice lost the spontaneous preference for fat, observed in wild-type animals. Our results suggest that fatty acid-induced Ca(2+) signaling, regulated by STIM1 via CD36, might be implicated in oro-gustatory perception of dietary lipids and the spontaneous preference for fat. Other cell types are involved in, and external factors can influence this preference.

Dual specificity phosphatase 1 expression inversely correlates with NF-κB activity and expression in prostate cancer and promotes apoptosis through a p38 MAPK dependent mechanism

Dual specificity phosphatase 1 (DUSP1) and the transcription factor NF-κB are implicated in prostate cancer since their expression levels are altered along this disease, although there are no evidences up to date demonstrating a crosstalk between them. In this report, we show for the first time that DUSP1 over-expression in DU145 cells promotes apoptosis and decreases NF-κB activity by blocking p65/NF-κB nuclear translocation. Moreover, although DUSP1 impairs TNF-α-induced p38 MAPK and JNK activation, only the specific inhibition of p38 MAPK exerts the same effects than DUSP1 over-expression on both apoptosis and NF-κB activity. Consistently, DUSP1 promotes apoptosis and decreases NF-κB activity in cells in which p38 MAPK is induced by TNF-α treatment. These results demonstrate that p38 MAPK is specifically involved in DUSP1-mediated effects on both apoptosis and NF-κB activity. Interestingly, we show an inverse correlation between DUSP1 expression and activation of both p65/NF-κB and p38 MAPK in human prostate tissue specimens. Thus, most of apparently normal glands, benign prostatic hyperplasia and low-grade prostatic intraepithelial neoplasia samples show high DUSP1 expression and low levels of both nuclear p65/NF-κB and activated p38 MAPK. By contrast, DUSP1 expression levels are low or even absent in high-grade prostatic intraepithelial neoplasia and prostatic adenocarcinoma samples, whereas nuclear p65/NF-κB and activated p38 MAPK are highly expressed in the same samples. Overall, our results provide evidence for a role of DUSP1 in the apoptosis of prostate cancer cells, through a mechanism involving the inhibition of p38 MAPK and NF-κB. Furthermore, our findings suggest that the ratio between DUSP1 and p65/NF-κB expression levels, rather than the individual expression of both molecules, is a better marker for diagnostic purposes in prostate cancer.

Targeting 3-phosphoinositide-dependent protein kinase 1 by N-acetyl-cysteine through activation of peroxisome proliferators activated receptor alpha in human lung cancer cells, the role of p53 and p65

Background

N-Acetyl-Cysteine (NAC), a natural sulfur-containing amino acid derivative, and peroxisome proliferators activated receptor alpha (PPARα) ligand have been shown to have anticancer properties. However, the mechanisms by which these agents inhibit human non-small cell lung carcinoma (NSCLC) cell growth have not been well elucidated.

Methods

Small interfering RNAs (siRNAs) were used to knockdown 3-phosphoinositide-dependent protein kinase 1 (PDK1), PPARα, p65 and p53 genes; Western Blot was performed to detect the protein expression of PDK1, PPARα, p65 and p53; Cell viability and MTT assays were carried out to determine the cell proliferation; Transient transfection and Dual-Luciferase Reporter assays were used to transfect siRNAs or exogenous expression vectors, and to measure the gene promoter activity.

Results

We showed that NAC inhibited NSCLC cell proliferation through reduction of PDK1 expression. NAC also induced the protein expression of PPARα. While PPARα ligand enhanced, PPARα antagonist and siRNA abrogated the effect of NAC on PDK1 promoter activity, protein expression and cell growth. Overexpression of PDK1 diminished the inhibitory effect of NAC on cell proliferation. NAC induced p53 and reduced p65 protein expression through activation of PPARα. Silencing of p53 and overexpression of p65 blocked the effect of NAC on PDK1 promoter activity and protein expression.

Conclusion

Our results show that NAC inhibits PDK1 expression through PPARα-mediated induction of p53 and inhibition of p65 protein expression. PPARα ligand enhances the effect of NAC. This ultimately inhibits NSCLC cell growth. This study unveils a novel mechanism by which NAC in combination with PPARα ligand inhibits growth of human lung carcinoma cells.

Prostate cancer chemoprevention in men of African descent: current state of the art and opportunities for future research

Prostate cancer is the most frequently diagnosed malignancy in men. However, African American/Black men are 60 % more likely to be diagnosed with and 2.4 times more likely to die from prostate cancer, compared to Non-Hispanic White men. Despite the increased burden of this malignancy, no evidence-based recommendation regarding prostate cancer screening exists for the high-risk population. Moreover, in addition to screening and detection, African American men may constitute a prime population for chemoprevention. Early detection and chemoprevention may thus represent an integral part of prostate cancer control in this population. Importantly, recent research has elucidated biological differences in the prostate tumors of African American compared to European American men. The latter may enable a more favorable response in African American men to specific chemopreventive agents that target relevant signal transduction pathways. Based on this evolving evidence, the aims of this review are threefold. First, we aim to summarize the biological differences that were reported in the prostate tumors of African American and European American men. Second, we will review the single- and multi-target chemopreventive agents placing specific emphasis on the pathways implicated in prostate carcinogenesis. And lastly, we will discuss the most promising nutraceutical chemopreventive compounds. Our review underscores the promise of chemoprevention in prostate cancer control, as well as provides justification for further investment in this filed to ultimately reduce prostate cancer morbidity and mortality in this high-risk population of African American men.

Fluoroketone inhibition of Ca(2+)-independent phospholipase A2 through binding pocket association defined by hydrogen/deuterium exchange and molecular dynamics

The mechanism of inhibition of group VIA Ca²⁺-independent phospholipase A₂ (iPLA₂) by fluoroketone (FK) ligands is examined by a combination of deuterium exchange mass spectrometry (DXMS) and molecular dynamics (MD). Models for iPLA₂ were built by homology with the known structure of patatin and equilibrated by extensive MD simulations. Empty pockets were identified during the simulations and studied for their ability to accommodate FK inhibitors. Ligand docking techniques showed that the potent inhibitor 1,1,1,3-tetrafluoro-7-phenylheptan-2-one (PHFK) forms favorable interactions inside an active-site pocket, where it blocks the entrance of phospholipid substrates. The polar fluoroketone headgroup is stabilized by hydrogen bonds with residues Gly486, Gly487, and Ser519. The nonpolar aliphatic chain and aromatic group are stabilized by hydrophobic contacts with Met544, Val548, Phe549, Leu560, and Ala640. The binding mode is supported by DXMS experiments showing an important decrease of deuteration in the contact regions in the presence of the inhibitor. The discovery of the precise binding mode of FK ligands to the iPLA₂ should greatly improve our ability to design new inhibitors with higher potency and selectivity.

Haloenol pyranones and morpholinones as antineoplastic agents of prostate cancer

Haloenol pyran-2-ones and morpholin-2-ones were synthesized and evaluated as inhibitors of cell growth in two different prostate human cancer cell lines (PC-3 and LNCaP). Analogs derived from L- and D-phenylglycine were found to be the most effective antagonists of LNCaP and PC-3 cell growth. Additional studies reveal that the inhibitors induced G2/M arrest and the (S)-enantiomer of the phenylglycine-based derivatives was a more potent inhibitor of cytosolic iPLA(2)β.

Maintenance of synaptic stability requires calcium-independent phospholipase A₂ activity

Phospholipases A₂ (PLA₂s) represent one of the largest groups of lipid-modifying enzymes. Over the years, significant advances have been made in understanding their potential physiological and pathological functions. Depending on their calcium requirement for activation, PLA₂s are classified into calcium dependent and independent. This paper mainly focuses on brain calcium-independent PLA₂ (iPLA₂) and on the mechanisms by which they influence neuronal function and regulate synaptic plasticity. Particular attention will be given to the iPLA₂γ isoform and its role in the regulation of synaptic glutamate receptors. In particular, the paper discusses the possibility that brain iPLA₂γ deficiencies could destabilise normal synaptic operation and might contribute to the aetiology of some brain disorders. In this line, the paper presents new data indicating that iPLA₂γ deficiencies accentuate AMPA receptor destabilization and tau phosphorylation, which suggests that this iPLA₂ isoform should be considered as a potential target for the treatment of Tau-related disorders.

Group VIA PLA2 (iPLA2β) is activated upstream of p38 mitogen-activated protein kinase (MAPK) in pancreatic islet β-cell signaling

Group VIA phospholipase A(2) (iPLA(2)β) in pancreatic islet β-cells participates in glucose-stimulated insulin secretion and sarco(endo)plasmic reticulum ATPase (SERCA) inhibitor-induced apoptosis, and both are attenuated by pharmacologic or genetic reductions in iPLA(2)β activity and amplified by iPLA(2)β overexpression. While exploring signaling events that occur downstream of iPLA(2)β activation, we found that p38 MAPK is activated by phosphorylation in INS-1 insulinoma cells and mouse pancreatic islets, that this increases with iPLA(2)β expression level, and that it is stimulated by the iPLA(2)β reaction product arachidonic acid. The insulin secretagogue D-glucose also stimulates β-cell p38 MAPK phosphorylation, and this is prevented by the iPLA(2)β inhibitor bromoenol lactone. Insulin secretion induced by d-glucose and forskolin is amplified by overexpressing iPLA(2)β in INS-1 cells and in mouse islets, and the p38 MAPK inhibitor PD169316 prevents both responses. The SERCA inhibitor thapsigargin also stimulates phosphorylation of both β-cell MAPK kinase isoforms and p38 MAPK, and bromoenol lactone prevents both events. Others have reported that iPLA(2)β products activate Rho family G-proteins that promote MAPK kinase activation via a mechanism inhibited by Clostridium difficile toxin B, which we find to inhibit thapsigargin-induced β-cell p38 MAPK phosphorylation. Thapsigargin-induced β-cell apoptosis and ceramide generation are also prevented by the p38 MAPK inhibitor PD169316. These observations indicate that p38 MAPK is activated downstream of iPLA(2)β in β-cells incubated with insulin secretagogues or thapsigargin, that this requires prior iPLA(2)β activation, and that p38 MAPK is involved in the β-cell functional responses of insulin secretion and apoptosis in which iPLA(2)β participates.

Enhanced antitumor activity of low-dose continuous administration schedules of topotecan in prostate cancer

PURPOSE

The objective of this study was to determine the antitumor effects of alternate dosing schedules of topotecan in prostate cancer.

RESULTS

A concentration-dependent increase in cytotoxicity was observed in PC-3 and LNCaP cells after topotecan treatment using conventional and metronomic protocols. A significant increase in potency (2.4-18 fold, after 72 hr) was observed following metronomic dosing compared to conventional dosing administration in both cell lines. Metronomic dosing also increased the percentage of PC-3 cells in the G2/M, compared to control, but did not alter LNCaP cell cycle distribution. Metronomic dosing increased p21 protein expression in LNCaP and PC-3 cells compared to conventional dosing. The observed in vitro activity was confirmed using an in vivo model of human prostate cancer. Metronomic dosing and continuous infusion decreased tumor volume significantly (p < 0.05) compared to control and conventional topotecan treatment, but had no effect on tumor vascular staining.

METHODS

The cytotoxicity of topotecan after conventional or metronomic dosing was determined by examining cellular morphology, mitochondrial enzymatic activity (MTT), total cellular protein (SRB), annexin V and propidium iodine (PI) staining, cell cycle and western blot analysis in human prostate cancer cell lines (PC-3 and LNCaP) and the effects metronomic or continuous infusion on tumor growth in an in vivo tumor xenograft model.

CONCLUSIONS

These data support the hypothesis that low-dose continuous administration of topotecan increases potency compared to conventional dosing in prostate cancer. These data also suggest the novel finding that the enhanced antitumor activity of topotecan following low-dose exposure correlates to alterations in cell cycle and increased p21 expression.

PEDF inhibits IL8 production in prostate cancer cells through PEDF receptor/phospholipase A2 and regulation of NFκB and PPARγ

Interleukin-8 (IL8/CXCL8) has been described as a key effector in prostate cancer progression and resistance to standard chemotherapeutic drugs. In the present study, we investigated the effect of the natural, angio-inhibitory and anti-tumoral Pigment Epithelium-Derived Factor (PEDF) on the expression of IL8 cytokine by prostate cancer cells. Using a cytokine antibody array and ELISA, in addition to IL8 quantitative RT PCR, we showed that PEDF inhibits the production of IL8 in human hormone-refractory prostate cancer cells, and delays the growth of these cells in vitro. IL8 reduction was mimicked in cancer cells treated with PPARγ agonist and NFκB-specific inhibitors. Accordingly, PPARγ expression increased in response to PEDF, whereas RelA/p65 expression and nuclear localization, and NFκB transcriptional activity decreased. NFκB deactivation was reversed by the PPARγ antagonist GW9662 and PPARγ (Leu(468)/Glu(471)) dominant negative suggesting a PPARγ-dependent process. We also investigated PEDF Receptor/PLA2 as key player in this pathway by small interference RNA. PEDFR knock down in prostate cancer cells reversed PEDF-induced PPARγ up-regulation, and NFκB and IL8 inhibition compared to non-targeting control siRNA. We conclude that by binding to PEDFR, PEDF up-regulates PPARγ, leading subsequently to suppressed NFκB-mediated transcriptional activation, reduced production of IL8 and limited proliferation of prostate cancer cells. These results reinforce PEDF's therapeutic potential and imply that blocking IL8 could represent a novel alternative for prostate cancer treatment.

Platelet-activating factor and metastasis: calcium-independent phospholipase A2β deficiency protects against breast cancer metastasis to the lung

We determined the contribution of calcium-independent phospholipase A(2)β (iPLA(2)β) to lung metastasis development following breast cancer injection into wild-type (WT) and iPLA(2)β-knockout (iPLA(2)β-KO) mice. WT and iPLA(2)β-KO mice were injected in the mammary pad with 200,000 E0771 breast cancer cells. There was no difference in primary tumor size between WT and iPLA(2)β-KO mice at 27 days postinjection. However, we observed an 11-fold greater number of breast cancer cells in the lungs of WT mice compared with iPLA(2)β-KO animals (P < 0.05). Isolated WT lung endothelial cells demonstrated a significant increase in platelet-activating factor (PAF) production when stimulated with thrombin [1 IU/ml, 10 min, 4,330 ± 555 vs. 15,227 ± 1,043 disintegrations per minute (dpm), P < 0.01] or TNF-α (10 ng/ml, 2 h, 16,532 ± 538 dpm, P < 0.01). Adherence of E0771 cells to WT endothelial cells was increased by thrombin (4.8 ± 0.3% vs. 70.9 ± 6.3, P < 0.01) or TNF-α (60.5 ± 4.3, P < 0.01). These responses were blocked by pretreatment with the iPLA(2)β-selective inhibitor (S)-bromoenol lactone and absent in lung endothelial cells from iPLA(2)β-KO mice. These data indicate that endothelial cell iPLA(2)β is responsible for PAF production and adherence of E0771 cells and may play a role in cancer cell migration to distal locations.

Cadmium suppresses the proliferation of piglet Sertoli cells and causes their DNA damage, cell apoptosis and aberrant ultrastructure

OBJECTIVE

Very little information is known about the toxic effects of cadmium on somatic cells in mammalian testis. The objective of this study is to explore the toxicity of cadmium on piglet Sertoli cells.

METHODS

Sertoli cells were isolated from piglet testes using a two-step enzyme digestion and followed by differential plating. Piglet Sertoli cells were identified by oil red O staining and Fas ligand (FasL) expression as assayed by immunocytochemistry and expression of transferrin and androgen binding protein by RT-PCR. Sertoli cells were cultured in DMEM/F12 supplemented with 10% fetal calf serum in the absence or presence of various concentrations of cadmium chloride, or treatment with p38 MAPK inhibitor SB202190 and with cadmium chloride exposure. Apoptotic cells in seminiferous tubules of piglets were also performed using TUNEL assay in vivo.

RESULTS

Cadmium chloride inhibited the proliferation of Piglet Sertoli cells as shown by MTT assay, and it increased malondialdehyde (MDA) but reduced superoxide dismutase (SOD) and Glutathione peroxidase (GSH-Px) activity. Inhibitor SB202190 alleviated the proliferation inhibition of cadmium on piglet Sertoli cells. Comet assay revealed that cadmium chloride caused DNA damage of Piglet Sertoli cells and resulted in cell apoptosis as assayed by flow cytometry. The in vivo study confirmed that cadmium induced cell apoptosis in seminiferous tubules of piglets. Transmission electronic microscopy showed abnormal and apoptotic ultrastructure in Piglet Sertoli cells treated with cadmium chloride compared to the control.

CONCLUSION

cadmium has obvious adverse effects on the proliferation of piglet Sertoli cells and causes their DNA damage, cell apoptosis, and aberrant morphology. This study thus offers novel insights into the toxicology of cadmium on male reproduction.