Development of amidine-based sphingosine kinase 1 nanomolar inhibitors and reduction of sphingosine 1-phosphate in human leukemia cells

Sphingosine 1-phosphate (S1P) is a bioactive lipid that has been identified as an accelerant of cancer progression. The sphingosine kinases (SphKs) are the sole producers of S1P, and thus, SphK inhibitors may prove effective in cancer mitigation and chemosensitization. Of the two SphKs, SphK1 overexpression has been observed in a myriad of cancer cell lines and tissues and has been recognized as the presumptive target over that of the poorly characterized SphK2. Herein, we present the design and synthesis of amidine-based nanomolar SphK1 subtype-selective inhibitors. A homology model of SphK1, trained with this library of amidine inhibitors, was then used to predict the activity of additional, more potent, inhibitors. Lastly, select amidine inhibitors were validated in human leukemia U937 cells, where they significantly reduced endogenous S1P levels at nanomolar concentrations.     

Inhibition of mitogen-activated protein kinase kinase enhances apoptosis induced by arsenic trioxide in human breast cancer MCF-7 cells

Arsenic trioxide (As2O3) has recently been used to treat acute promyelocytic leukaemia and has activity in vitro against several solid tumour cell lines where the induction of differentiation and apoptosis are the prime effects. The mechanism of As2O3-induced cell death has yet to be clarified, especially in solid cancers. In the present study, the human breast cancer cell line MCF-7 was examined as a cellular model for As2O3 treatment. The involvement of extracellular signal-regulated kinase (ERK), p38 and c-Jun N-terminal kinase (JNK) was investigated in As2O3-induced cell death. 3. It was found that As2O3 activates the prosurvival mitogen-activated protein kinase kinase (MEK)/ERK pathway in MCF-7 cells, which, conversely, may compromise the efficacy of As2O3. Hence, a combination treatment of As2O3 and MEK inhibitors was investigated to determine whether this treatment could lead to enhanced growth inhibition and apoptosis in MCF-7 cells. 4. Inhibition of MEK/ERK with the pharmacological inhibitors U0126 (10 micromol/L) or PD98059 (20 micromol/L) together with As2O3 (2 and 5 micromol/L) resulted in a significant enhancement of growth inhibition in breast cancer MCF-7 cells as determined by the 3-(4,5-dimethyl-2 thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide assay and [Methyl-3H]-thymidine incorporation. Furthermore, the results demonstrated that combined treatment with As2O3 and the MEK1/2 inhibitor U0126 could augment breast cancer MCF-7 cell apoptosis approximately twofold compared with the effects of the two drugs alone, as determined by Hoechst 33258 or annexin V/propidium iodide (PI) staining and flow cytometry. 5. In addition, As2O3 activated p38 in a dose-dependent manner, but had no effect on JNK1/2. Treatment with a p38 inhibitor did not prevent As2O3-induced apoptosis. 6. In conclusion, the results of the present study showed that enhanced apoptosis is detected in breast cancer MCF-7 cells in the presence of As2O3 and an MEK inhibitor, which may be a new promising adjuvant to current breast cancer treatments.     

鞘氨醇激酶1抑制剂和5-FU联合应用对体外胃癌细胞增殖与凋亡的影响

目的观察鞘氨醇激酶1(SphK1)抑制剂二甲基鞘氨醇(DMS)与化疗药物5-氟尿嘧啶(5-FU)联合应用对体外胃癌细胞SGC7901增殖与凋亡的影响。方法体外培养人胃癌细胞株SGC7901,分别单用不同浓度5-FU(1、5、25μg/ml)或5-FU与DMS(1μmol/L)联合应用。MTT比色法检测各组细胞生长抑制率,光镜下观察细胞形态变化,流式细胞术检测各组细胞凋亡率。通过SAS软件进行反应曲面分析,分析两药之间的关系。结果不同浓度的5-FU单用组及联用DMS组的抑制率差异有统计学意义(P<0.05),联用组抑制率均高于单用组,两者具有协同作用。单用DMS组及5-FU组的胃癌细胞凋亡率较空白对照组明显增高,联用组凋亡率较单用组明显增加(P<0.05)。结论 DMS可抑制SGC7901细胞的增殖;DMS和5-FU联用显示了较好的协同作用,提示抑制SphK1活性能够提高胃癌细胞对于化疗药物的敏感性。     

Thioredoxin reductase 1 knockdown enhances selenazolidine cytotoxicity in human lung cancer cells via mitochondrial dysfunction

Thioredoxin reductase (TR1) is a selenoprotein that is involved in cellular redox status control and deoxyribonucleotide biosynthesis. Many cancers, including lung, overexpress TR1, making it a potential cancer therapy target. Previous work has shown that TR1 knockdown enhances the sensitivity of cancer cells to anticancer treatments, as well as certain selenocompounds. However, it is unknown if TR1 knockdown produces similar effect on the sensitivity of human lung cancer cells. To further elucidate the role of TR1 in the mechanism of selenocompounds in lung cancer, a lentiviral microRNA delivery system to knockdown TR1 expression in A549 human lung adenocarcinoma cells was utilized. Cell viability was assessed after 48 hr treatment with the selenocysteine prodrug selenazolidines 2-butylselenazolidine-4(R)-carboxylic acid (BSCA) and 2-cyclohexylselenazolidine-4-(R)-carboxylic acid (ChSCA), selenocystine (SECY), methylseleninic acid (MSA), 1,4-phenylenebis(methylene)selenocyanate (p-XSC), and selenomethionine (SEM). TR1 knockdown increased the cytotoxicity of BSCA, ChSCA, and SECY but did not sensitize cells to MSA, SEM, or p-XSC. GSH and TR1 depletion together decreased cell viability, while no change was observed with GSH depletion alone. Reactive oxygen species generation was induced only in TR1 knockdown cells treated with the selenazolidines or SECY. These three compounds also decreased total intracellular glutathione levels and oxidized thioredoxin, but in a TR1 independent manner. TR1 knockdown increased selenazolidine and SECY-induced mitochondrial membrane depolarization, as well as DNA strand breaks and AIF translocation from the mitochondria. These results indicate the ability of TR1 to modulate the cytotoxic effects of BSCA, ChSCA and SECY in human lung cancer cells through mitochondrial dysfunction.     

Inhibition of the unfolded protein response by ricin a-chain enhances its cytotoxicity in Mammalian cells

Ricin is a highly toxic type II ribosome-inactivating protein that has potential as a biochemical weapon and as the toxic component of immunotoxins. The unfolded protein response (UPR) is a survival response that helps cells to recover from endoplasmic reticulum (ER) stress. Failure to recover from ER stress leads to apoptosis. In yeast, ricin-A-chain (RTA), the enzymatic component of ricin, inhibits UPR. Our goals were to determine if RTA inhibits UPR in two epithelial cell lines and if this affects RTA cytotoxicity. RTA alone did not induce UPR. However, RTA inhibited both phosphorylation of inositol-requiring enzyme 1 (IRE1) and splicing of X-box binding protein1 mRNA by the UPR-inducing agent tunicamycin (Tm). The ability of dithiothreitol (DTT) to activate eukaryotic translation initiation factor 2 alpha (eIF2α), a component of the PERK pathway, was also inhibited by RTA. Treatment with RTA in combination with Tm or DTT inhibited protein synthesis more than either agent did alone in one cell line, while caspase cleavage was enhanced by the treatment combination in both cell lines. These data indicate that RTA is more cytotoxic when UPR is inhibited. This ability to inhibit UPR may enhance the potential of RTA as a therapeutic immunotoxin in solid tumors.     

Oligomeric proanthocyanidins alleviate hexabromocyclododecane-induced cytotoxicity in HepG2 cells through regulation on ROS formation and mitochondrial pathway

Hexabromocyclododecane (HBCD), a type of brominated flame retardants (BFR), has become ubiquitous organic contaminants in recent years. However, studies on HBCD toxicity and the related molecular mechanisms are so far limited. The objective of the present study was to investigate the effects of oligomeric proanthocyanidins (OPCs) on cytotoxicity induced by HBCD and the underlying molecular mechanisms. HepG2 cells were treated with HBCD and/or OPCs at different concentrations, and cell viability, cell apoptosis, reactive oxygen species (ROS) production, cellular Ca²⁺ level, mitochondrial membrane potential (ΔΨ), cytochrome C (Cyt-c) release, and nuclear factor-erythroid 2-related factor 2 (Nrf2) proteins expression were evaluated. Results showed that HBCD induced toxic effects in HepG2 cells in a concentration-dependent manner. HBCD at high concentrations (40 and 60 μM) caused a significant decrease of cell viability and led to elevated cell apoptosis ratio, intracellular Ca²⁺ level, cytoplasmic Cyt-c level, and ROS production, together with a loss of ΔΨ and mobilization of Nrf2. Pretreatment with OPCs effectively attenuated the cytotoxic effects and ROS production, as well as mitochondrial responses induced by HBCD. Thus, OPCs could alleviate cytotoxicity in HepG2 cells induced by HBCD through regulation on intracellular Ca²⁺ level and ROS formation in a mitochondrial pathway.     

Pemetrexed downregulates ERCC1 expression and enhances cytotoxicity effected by resveratrol in human nonsmall cell lung cancer cells

The multitargeted antifolate pemetrexed has demonstrated certain clinical activities against nonsmall cell lung cancer (NSCLC). Resveratrol (3,5,4-trihydroxy-trans-stilbene) is a polyphenol found in grapes and other plants and has great potential as a preventative and therapeutic agent due to its anticarcinogenic activity. The efficacy of adding resveratrol to pemetrexed to prolong the survival of patients with NSCLC still remains unclear. The excision repair cross-complementation 1 (ERCC1) is a DNA repair gene coding 5′ endonuclease in nucleotide excision repair and is overexpressed in chemo- or radioresistant carcinomas. In this study, resveratrol (10–50 μM) inhibited cell survival in two NSCLC cells, H520 and H1975. Treatment with resveratrol increased ERCC1 messenger RNA and protein levels in a MKK3/6-p38 MAPK signal activation-dependent manner. Furthermore, blocking p38 MAPK activation by SB202190 or knocking down ERCC1 expression by transfection with small interfering RNA of ERCC1 enhanced the cytotoxicity of resveratrol. Combining resveratrol with pemetrexed resulted in a synergistic cytotoxic effect, accompanied with the reduction of phospho-p38 MAPK and ERCC1 protein levels, and a DNA repair capacity. Expression of constitutively active MKK6 (MKK6E) or HA-p38 MAPK vectors significantly rescued the decreased p38 MAPK activity, and restored ERCC1 protein levels and cell survival in resveratrol and pemetrexed cotreated NSCLC cells. In this study, for the first time, we have demonstrated the synergistic effect of combined treatment with resveratrol and pemetrexed in human NSCLC cells through downregulation of the MKK3/6-p38 MAPK-ERCC1 signal, suggesting a potential benefit of combining resveratrol and pemetrexed to treat lung cancer in the future.     

Inhibition of Hec1 expression enhances the sensitivity of human ovarian cancer cells to paclitaxel

Aim:

Hec1, a member of the Ndc80 kinetochore complex, is highly expressed in cancers. The aim of this study was to explore the role and mechanism of action of Hec1 with respect to the cytotoxicity of paclitaxel in ovarian cancer.

Methods:

Thirty ovarian cancer samples and 6 normal ovarian samples were collected. Hec1 expression in these samples was determined with immunohistochemistry. Ovarian cancer cell lines A2780, OV2008, C13K, SKOV3, and CAOV3 and A2780/Taxol were examined. Cell apoptosis and cell cycle analysis were detected with flow cytometric technique. siRNA was used to delete Hec1 in the cells. The expression of related mRNAs and proteins was measured using RT-PCR and Western blot analysis, respectively.

Results:

Hec1 expression was significantly higher in ovarian cancer samples than in normal ovarian samples, and was associated with paclitaxel-resistance and poor prognosis. Among the 6 ovarian cancer cell lines examined, Hec1 expression was highest in paclitaxel-resistant A2780/Taxol cells, and lowest in A2780 cells. Depleting Hec1 in A2780/Taxol cells with siRNA decreased the IC₅₀ value of paclitaxel by more than 10-fold (from 590±26.7 to 45.6±19.4 nmol/L). Depleting Hec1 in A2780 cells had no significant effect on the paclitaxel sensitivity. In paclitaxel-treated A2780/Taxol cells, depleting Hec1 significantly increased the cleaved PARP and Bax protein levels, and decreased the Bcl-xL protein level.

Conclusion:

Hec1 overexpression is associated with the progression and poor prognosis of ovarian cancer. Inhibition of Hec1 expression can sensitize ovarian cancer cells to paclitaxel.     

5,7-二甲氧基黄酮增强TRAIL诱导肝癌干细胞凋亡的研究

目的研究天然源性化合物5,7-二甲氧基黄酮(5,7-dimethoxyfl avone,5,7-DMF)是否具有增强肿瘤坏死因子相关凋亡诱导配体(TNF related apoptosis inducing ligand,TRAIL)诱导肝癌干细胞(liver cancer stem cells,LCSCs)凋亡的作用。方法采用干细胞条件培养基超低黏附板悬浮培养得到肝癌肿瘤球形成细胞;Western blot检测肿瘤干细胞标志物CD133、CD44和ALDH1蛋白表达状态;ELISA和Annexin V/PI染色流式细胞术检测肝癌球形成细胞凋亡率。结果第3代肿瘤球细胞的单个细胞成球的百分率(73.4%)相对第5代原代培养细胞的肿瘤球形成百分率(18.7%)显著提高,且其肿瘤球大小亦有差异。源自复发性肝细胞癌的第3代球细胞高表达肿瘤干细胞标志物CD133、CD44和Oct4。亚细胞毒性浓度5,7-DMF(1.0μmol·L-1)明显增强TRAIL(10.0 ng·m L-1)诱导LCSCs的凋亡作用。结论本研究证明,5,7-DMF具有增强TRAIL诱导LCSCs凋亡的作用。     

Enhanced cell death effects of MAP kinase inhibitors in propyl gallate-treated lung cancer cells are related to increased ROS levels and GSH depletion

Propyl gallate (PG) has an anti-growth effect in lung cancer cells. The present study investigated the effects of mitogen-activated protein kinase (MAPK; MEK, JNK, and p38) inhibitors on PG-treated Calu-6 and A549 lung cancer cells in relation to cell death as well as reactive oxygen species (ROS) and glutathione (GSH) levels. PG induced cell death in both Calu-6 and A549 lung cancer cells at 24 h, which was accompanied by loss of mitochondrial membrane potential (MMP; ΔΨ_m). All of the tested MAPK inhibitors increased cell death in both PG-treated lung cancer cell lines. In particular, MEK inhibitor strongly enhanced cell death and MMP (ΔΨ_m) loss in PG-treated Calu-6 cells and p38 inhibitor had the same effects in A549 cells as well. PG increased ROS levels and caused GSH depletion in both cell lines at 24 h. MAPK inhibitors increased O₂^•- levels and GSH depletion in PG-treated Calu-6 cells, and JNK and p38 inhibitors increased ROS levels and GSH depletion in PG-treated A549 cells. In conclusion, MAPK inhibitors increased cell death in PG-treated Calu-6 and A549 lung cancer cells. Enhanced cell death and GSH depletion in Calu-6 cells caused by the MEK inhibitor were related to increased O₂^•- levels, and the effects of the p38 inhibitor in A549 cells were correlated with increased general ROS levels.     

p38 MAPK激酶抑制剂增强二烯丙基二硫化物诱导CNE2细胞凋亡

目的　研究二烯丙基二硫化物 (DADS)诱导CNE2细胞凋亡及 p38MAPK信号转导通路对此过程的作用。 方法　DADS处理CNE2细胞 2 4h后 ,荧光显微镜下观察形态学变化及凋亡细胞计数 ,MTT法测定细胞活性 ,流式细胞仪检测凋亡细胞 ,蛋白质印迹法检测磷酸化p38MAPK表达。结果　在培养的CNE2细胞中 ,DADS(50～ 1 50 μmol·L- 1 )作用 2 4h后 ,DADS诱导CNE2细胞产生典型的凋亡细胞形态学变化 (核浓染 ,核碎裂 ) ,流式细胞仪结果显示 ,随着DADS给药剂量增加 ,细胞周期中各期细胞所占百分率的变化无规律 ,细胞凋亡呈剂量依赖性 ,DADS(50～ 1 50 μmol·L- 1 )浓度依赖性刺激磷酸化p38MAPK的表达 ,p38MAPK抑制剂SB2 0 3580明显增强DADS致凋亡作用。结论　DADS诱导CNE2细胞凋亡时激活磷酸化 p38MAPK表达 ,磷酸化p38MAPK抑制剂增强DADS诱导CNE2细胞凋亡效应     

miR-205 impairs the autophagic flux and enhances cisplatin cytotoxicity in castration-resistant prostate cancer cells

Compelling evidence suggests that epithelial-to-mesenchymal transition is involved in the resistance of human cancer cells to chemotherapy. We previously reported that the expression of miR-205, a miRNA down-regulated in prostate cancer, is further repressed in prostate cancer cells undergoing epithelial-to-mesenchymal transition, suggesting a possible involvement of the miRNA in the acquisition of the chemoresistant phenotype. In the present study, we show that miR-205 replacement in castration-resistant mesenchymal prostate cancer cells caused an enhancement of cisplatin cytotoxic activity in vitro and in vivo, as a consequence of autophagy impairment. Specifically, the constraints on the autophagic flux were associated to the miRNA-dependent down-regulation of the lysosome-associated proteins RAB27A and LAMP3. These findings suggest that miR-205-mediated impairment of the autophagic pathway may interfere with the detoxifying capabilities of prostate cancer cells in their attempt to cope with cisplatin-induced detrimental effects. Overall, our data indicate that (i) loss of miR-205 may indeed contribute to acquire mesenchymal tracts and concomitantly establish a permissive autophagic milieu that confers a chemotherapy resistant phenotype to prostate cancer cells, and (ii) strategies aimed at restoring miR-205 expression levels may represent a successful approach to overcome resistance of prostate cancer to platinum compounds.     

Ferric iron increases ROS formation, modulates cell growth and enhances genotoxic damage by 4-hydroxynonenal in human colon tumor cells.

Iron is a relevant risk factor for colorectal cancer due to its genotoxic properties. Here we hypothesised that iron-overload causes other toxic effects, which contribute to carcinogenesis. For this, we investigated formation of reactive oxygen species (ROS), DNA repair, cell growth and glutathione (GSH) in human colon tumor cells (HT29 clone 19A) treated with ferric nitrilotriacetate (Fe-NTA, 0-2000 microM). Intracellular formation of ROS was analysed with the peroxide-labile fluorescent dye carboxy-dichlorodihydrofluorescine-diacetate. DNA repair, reflected as the persistency of DNA damage induced by selected genotoxins, was determined with the Comet assay. Cell growth and GSH were measured by fluorimetrical analysis. Key findings were that ROS formation increased with time (1000 microM Fe-NTA, p < 0.001). DNA damage was largely repaired after 120 min, but was not affected by 10 microM Fe-NTA. In contrast, 10 microM Fe-NTA significantly increased DNA damage induced by 4-hydroxynonenal. Doses of 25 microM Fe-NTA increased cell growth (p < 0.05), whereas high concentrations (2000 microM) resulted in growth arrest (p < 0.05), that was accompanied by increased GSH levels (p < 0.01). In conclusion, high concentrations of Fe-NTA caused cellular effects, which reflect a stress response, and resulted in formation of ROS. Carcinogenic risks from ferric iron could be derived also from lower concentrations, which enhance tumor cell growth and cause progenotoxic effects.     

Astaxanthin enhances pemetrexed-induced cytotoxicity by downregulation of thymidylate synthase expression in human lung cancer cells

Pemetrexed, a multitargeted antifolate agent, has demonstrated clinical activity in non-small cell lung cancer (NSCLC) cells. Increased expression of thymidylate synthase (TS) is thought to be associated with resistance to pemetrexed. Astaxanthin exhibits a wide range of beneficial effects including anti-cancer and anti-inflammatory properties. In this study, we showed that down-regulating of TS expression in two NSCLC cell lines, human lung adenocarcinoma H1650 and squamous cell carcinoma H1703 cells, with astaxanthin were associated with decreased MKK1/2-ERK1/2 activity. Enforced expression of constitutively active MKK1 (MKK1-CA) vector significantly rescued the decreased TS mRNA and protein levels in astaxanthin-treated NSCLC cells. Combined treatment with a MKK1/2 inhibitor (U0126 or PD98059) further decreased the TS expression in astaxanthin-exposed NSCLC cells. Knockdown of TS using small interfering RNA (siRNA) or inhibiting ERK1/2 activity enhanced the cytotoxicity and cell growth inhibition of astaxanthin. Combination of pemetrexed and astaxanthin resulted in synergistic enhancing cytotoxicity and cell growth inhibition in NSCLC cells, accompanied with reduced activation of phospho-MKK1/2, phopho-ERK1/2, and TS expression. Overexpression of MKK1/2-CA reversed the astaxanthin and pemetrexed-induced synergistic cytotoxicity. Our findings suggested that the down-regulation of MKK1/2-ERK1/2-mediated TS expression by astaxanthin is an important regulator of enhancing the pemetrexed-induced cytotoxicity in NSCLC cells.     

Inhibition of glycyrrhizic acid on aflatoxin B1-induced cytotoxicity in hepatoma cells

Aflatoxin B(1) (AFB(1)) causes oxidative stress and ROS formation via metabolic activation of AFB(1). Glycyrrhizic acid (GA) has been reported to have antioxidative properties. The present study was to investigate the effect of GA, a major component of licorice on AFB(1)-induced cytotoxicity in human hepatoma cell line (HepG2). GA displayed protective effects against AFB(1) treatment. Both CYP1A1, and glutathione S-transferase (GST) activities were increased in cells after treatment with the GA, while CYP1A2 did not seem to be affected by GA. For cells without GA pre-treatment, cell injury was implicated as indicated by the decrease in cell viability. The time-course study of GA showed pretreatment of cells with GA for 24 h was effective. The treatment of cells with GA and AFB(1) enhanced the detoxifying enzyme activity. The pre-treatment of cells with GA provides protective effects in terms of the enzyme activity and increase in cell viability. The results suggest that GA protects against aflatoxin-induced oxidative stress. This may contribute to its anticarcinogenic capability. The protective effect is likely due to its capacity to inhibit the metabolic activation of hepato-toxin, a critical factor in the pathogenesis of chemical-induced carcinogenicity.     

Effects of triptolide on the sphingosine kinase – Sphingosine-1-phosphate signaling pathway in colitis-associated colon cancer

BackgroundsTriptolide (TP) exhibits effective activity against colon cancer in multiple preclinical models, but the mechanisms underlying the observed effects are not fully understood. Sphingosine-1-phosphate (S1P) is a potent bioactive sphingolipid involved in the regulation of colon cancer progression. The aim of this study was to investigate the effect of TP on the sphingosine kinase (SPHK)-S1P signaling pathway in colitis-associated colon cancer.MethodsAn azoxymethane (AOM)/dextran sulfate sodium (DSS) mouse model and the THP-1 cell line were used to evaluate the therapeutic effects and mechanisms of TP in colitis-associated colon cancer (CACC). Various molecular cell biology experiments, including Western blotting, real-time PCR and immunofluorescence, were used to obtain relevant experimental data. A liquid chromatography–tandem mass spectrometry (LC-MS/MS) method was also established to detect the levels of S1P in tissue and plasma.ResultsIn the AOM/DSS mouse model, TP treatment induced a dose-dependent decrease in tumor incidence and inhibited macrophage recruitment and M2 polarization in the tumors. TP also efficiently decreased the S1P levels and SPHK1/S1PR1/S1PR2 expression and significantly inhibited activation of the S1P-mediated phosphorylation of ERK protein in macrophages.ConclusionsThe results indicated that TP might influence the recruitment and polarization of tumor-associated macrophages by suppressing the SPHK-S1P signaling pathway.