Compound C sensitizes Caki renal cancer cells to TRAIL-induced apoptosis through reactive oxygen species-mediated down-regulation of c-FLIPL and Mcl-1

Dorsomorphin attenuates ABCG2-mediated multidrug resistance in colorectal cancer

Colorectal cancer is a common malignant tumor with high mortality, for which chemotherapy resistance is one of the main reasons. The high expression of ABCG2 in the cancer cells and expulsion of anticancer drugs directly cause multidrug resistance (MDR). Therefore, the development of new ABCG2 inhibitors that block the active causes of MDR may provide a strategy for the treatment of colorectal cancer. In this study, we find that dorsomorphin (also known as compound C or BML-275) potently inhibits the transporter activity of ABCG2, thereby preserving the chemotherapeutic agents mitoxantrone and doxorubicin to antagonize MDR in ABCG2-overexpressing colorectal cancer cells. Additionally, dorsomorphin does not alter ABCG2 protein expression. The results of molecular docking studies show that dorsomorphin is bound stably to the ABCG2-binding pocket, suggesting that dorsomorphin is a potent ABCG2 inhibitor that attenuates ABCG2-mediated MDR in colorectal cancer.

AMPK inhibition induces MCL1 mRNA destabilization via the p38 MAPK/miR-22/HuR axis in chronic myeloid leukemia cells

The oncogenic and tumor-suppressive roles of AMPK in chronic myeloid leukemia (CML) are controvertible. This study aimed to investigate the cytotoxic effects of the AMPK inhibitor Compound C in the CML cell lines K562, KU812, and MEG-01. Compared to K562 cells, KU812 and MEG-01 cells were more sensitive to Compound C-mediated cytotoxicity. Moreover, Compound C induced SIRT3 upregulation in K562 cells but not in KU812 or MEG-01 cells. SIRT3 silencing increased the sensitivity of K562 cells to Compound C. Additionally; Compound C-induced autophagy attenuated its induced apoptosis in KU812 and MEG-01 cells. Compound C-induced ROS-mediated AMPKα inactivation resulted in the downregulation of apoptotic regulator MCL1 in KU812 and MEG-01 cells. Mechanistically, AMPK inhibition activated p38 MAPK-mediated miR-22 expression, which in turn inhibited HuR expression, thereby reducing MCL1 mRNA stability. Overexpression of constitutively active AMPKα1 and abolishment of the activation of p38 MAPK inhibited Compound C-induced cell death and MCL1 downregulation. Furthermore, Compound C synergistically enhanced the cytotoxicity of BCR-ABL inhibitors and the BCL2 inhibitor ABT-199. Collectively, this study indicates that Compound C induces MCL1 downregulation through the AMPK/p38 MAPK/miR-22/HuR pathway, thereby inducing apoptosis of KU812 and MEG-01 cells. Furthermore, our findings suggest that AMPK inhibition is a promising strategy for improving CML therapy.

Compound C Inhibits Renca Renal Epithelial Carcinoma Growth in Syngeneic Mouse Models by Blocking Cell Cycle Progression, Adhesion and Invasion

Compound C (CompC), an inhibitor of AMP-activated protein kinase, reduces the viability of various renal carcinoma cells. The molecular mechanism underlying anti-proliferative effect was investigated by flow cytometry and western blot analysis in Renca cells. Its effect on the growth of Renca xenografts was also examined in a syngeneic BALB/c mouse model. Subsequent results demonstrated that CompC reduced platelet-derived growth factor receptor signaling pathways and increased ERK1/2 activation as well as reactive oxygen species (ROS) production. CompC also increased the level of active Wee1 tyrosine kinase (P-Ser⁶⁴²-Wee1) and the inactive form of Cdk1 (P-Tyr¹⁵-Cdk1) while reducing the level of active histone H3 (P-Ser¹⁰-H3). ROS-dependent ERK1/2 activation and sequential alterations in Wee1, Cdk1, and histone H3 might be responsible for the CompC-induced G2/M cell cycle arrest and cell viability reduction. In addition, CompC reduced the adhesion, migration, and invasion of Renca cells in the in vitro cell systems, and growth of Renca xenografts in the BALB/c mouse model. Taken together, the inhibition of in vivo tumor growth by CompC may be attributed to the blockage of cell cycle progression, adhesion, migration, and invasion of tumor cells. These findings suggest the therapeutic potential of CompC against tumor development and progression.

Kidney cancer biomarkers and targets for therapeutics: survivin (BIRC5), XIAP, MCL-1, HIF1α, HIF2α, NRF2, MDM2, MDM4, p53, KRAS and AKT in renal cell carcinoma

The incidence of renal cell carcinoma (RCC) is increasing worldwide with an approximate 20% mortality rate. The challenge in RCC is the therapy-resistance. Cancer resistance to treatment employs multiple mechanisms due to cancer heterogeneity with multiple genetic and epigenetic alterations. These changes include aberrant overexpression of (1) anticancer cell death proteins (e.g., survivin/BIRC5), (2) DNA repair regulators (e.g., ERCC6) and (3) efflux pump proteins (e.g., ABCG2/BCRP); mutations and/or deregulation of key (4) oncogenes (e.g., MDM2, KRAS) and/or (5) tumor suppressor genes (e.g., TP5/p53); and (6) deregulation of redox-sensitive regulators (e.g., HIF, NRF2). Foci of tumor cells that have these genetic alterations and/or deregulation possess survival advantages and are selected for survival during treatment. We will review the significance of survivin (BIRC5), XIAP, MCL-1, HIF1α, HIF2α, NRF2, MDM2, MDM4, TP5/p53, KRAS and AKT in treatment resistance as the potential therapeutic biomarkers and/or targets in RCC in parallel with our analized RCC-relevant TCGA genetic results from each of these gene/protein molecules. We then present our data to show the anticancer drug FL118 modulation of these protein targets and RCC cell/tumor growth. Finally, we include additional data to show a promising FL118 analogue (FL496) for treating the specialized type 2 papillary RCC.

EGR-1 plays a protective role in AMPK inhibitor compound C-induced apoptosis through ROS-induced ERK activation in skin cancer cells

Skin cancer is caused by abnormal proliferation, gene regulation and mutation of epidermis cells. Compound C is commonly used as an inhibitor of AMP-activated protein kinase (AMPK), which serves as an energy sensor in cells. Recently, compound C has been reported to induce apoptotic and autophagic death in various skin cancer cell lines via an AMPK-independent pathway. However, the signaling pathways activated in compound C-treated cancer cells remain unclear. The present oligodeoxynucleotide-based microarray screening assay showed that the mRNA expression of the zinc-finger transcription factor early growth response-1 (EGR-1), which helps regulate cell cycle progression and cell survival, was significantly upregulated in compound C-treated skin cancer cells. Compound C was demonstrated to induce EGR-1 mRNA and protein expression in a time and dose-dependent manner. Confocal imaging showed that compound C-induced EGR-1 protein expression was localized in the nucleus. Compound C was demonstrated to activate extracellular signal-regulated kinase (ERK) phosphorylation. Inhibition of this compound C-induced ERK phosphorylation downregulated the mRNA and protein expression of EGR-1. In addition, removal of compound C-induced reactive oxygen species (ROS) not only decreased ERK phosphorylation, but also inhibited compound C-induced EGR-1 expression. A functional assay showed that knock down of EGR-1 expression in cancer cells decreased the survival rate while also increasing caspase-3 activity and apoptotic marker expression after compound C treatment. However, no difference in autophagy marker light chain 3-II protein expression was observed between compound C-treated control cells and EGR-1-knockdown cells. Thus, it was concluded that that EGR-1 may antagonize compound C-induced apoptosis but not compound C-induced autophagy through the ROS-mediated ERK activation pathway.

The X-linked trichothiodystrophy-causing gene RNF113A links the spliceosome to cell survival upon DNA damage

Prolonged cell survival occurs through the expression of specific protein isoforms generated by alternate splicing of mRNA precursors in cancer cells. How alternate splicing regulates tumor development and resistance to targeted therapies in cancer remain poorly understood. Here we show that RNF113A, whose loss-of-function causes the X-linked trichothiodystrophy, is overexpressed in lung cancer and protects from Cisplatin-dependent cell death. RNF113A is a RNA-binding protein which regulates the splicing of multiple candidates involved in cell survival. RNF113A deficiency triggers cell death upon DNA damage through multiple mechanisms, including apoptosis via the destabilization of the prosurvival protein MCL-1, ferroptosis due to enhanced SAT1 expression, and increased production of ROS due to altered Noxa1 expression. RNF113A deficiency circumvents the resistance to Cisplatin and to BCL-2 inhibitors through the destabilization of MCL-1, which thus defines spliceosome inhibitors as a therapeutic approach to treat tumors showing acquired resistance to specific drugs due to MCL-1 stabilization.

Alternate splicing of mRNA precursors has been linked to tumor development. Here the authors reveal a role of the E3 ligase RNF113A in spliceosome regulation affecting cell survival upon DNA damage.

Compound C enhances the anticancer effect of aspirin in HER-2-positive breast cancer by regulating lipid metabolism in an AMPK-independent pathway

Various clinical studies have determined that aspirin shows anticancer effects in many human malignant cancers, including human epidermal growth factor receptor-2 (HER-2)-positive breast cancer. However, the anti-tumor mechanism of aspirin has not been fully defined. The aim of this study was to determine the role of Compound C in enhancing the anticancer effect of aspirin. HER-2-positive breast cancer cell lines were treated with aspirin with or without Compound C pre-treatment; their phenotypes and mechanisms were then analyzed in vitro and in vivo. Aspirin exhibited anticancer effects in HER-2-positive breast cancer by inhibiting cell growth and inducing apoptosis through the activation of AMP-activated protein kinase (AMPK). Unexpectedly, pre-treatment with Compound C, a widely used AMPK inhibitor, induced robust anticancer effects in cells compared to aspirin monotherapy. This anticancer effect was not distinct in HER-2 negative breast cancer MDA-MB-231 cells and may be due to the inhibition of lipid metabolism mediated by c-myc. Besides, c-myc re-expression or palmitic acid supply could partially restored cell proliferation. Aspirin exhibits anticancer effects in HER-2-positive breast cancer by regulating lipid metabolism mediated by c-myc, and Compound C strengthens these effects in an AMPK-independent manner. Our results potentially provide a novel therapeutic strategy exploiting combined aspirin and Compound C therapy for HER-2-positive breast cancer, which acts by reducing de novo lipid synthesis.

The circular RNA-NRIP1 plays oncogenic roles by targeting microRNA-505 in the renal carcinoma cell lines

We explored the roles and regulatory mechanisms of the circular RNA (circRNA) nuclear receptor-interacting protein 1 (NRIP1; circNRIP1) in ACHN and CAKI-1 cells. ACHN and CAKI-1 cells were transfected with small-interfering-circNRIP1 (si-circNRIP1) and microRNA-505 (miR-505) inhibitor or the corresponding controls. Cell viability was detected with the Cell Counting Kit-8. The protein expression levels of Bcl-2, Bax, cleaved-caspase-3, matrix metalloproteinase (MMP)-2, MMP-9, adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), protein kinase B (AKT), phosphatidylinositol 3-kinase (PI3K), and mammalian target of rapamycin (mTOR) were individually determined via Western blot. Quantitative reverse transcription polymerase chain reaction was used to examine the expressions of circNRIP1 and miR-505 both in tumor cells and tissues. The apoptotic rate, the colony numbers, and the migration rate were separately determined by the Annexin V-fluorescein isothiocyanate/propidium iodide and flow cytometer, colony formation assay, and migration assay. We found that circNRIP1 was overexpressed in tumor tissue but miR-505 was overproduced. Silencing circZNF292 induced inhibition of cell viability, colony formation, and migration, as well as the activity of AMPK and PI3K/AKT/mTOR cascades but enhancement of apoptosis. si-circNRIP1 stimulated the upregulation of miR-505, whose silence abolished the effects of si-circNRIP1 on these elements mentioned above. In conclusion, the circNRIP1 played oncogenic roles in the ACHN and the CAKI-1 cell lines by targeting miR-505 via stimulating AMPK and PI3K/AKT/mTOR cascades.

AMPK contributes to autophagosome maturation and lysosomal fusion

AMP-activated protein kinase (AMPK) regulates autophagy initiation when intracellular ATP level decreases. However, the role of AMPK during autophagosome maturation is not fully understood. Here, we report that AMPK contributes to efficient autophagosome maturation and lysosomal fusion. Using CRISPR-Cas9 gene editing, we generated AMPK α1 knockout HEK293T cell lines, in which starvation-induced autophagy is impaired. Compound C, an AMPK-independent autophagy inducer, and trehalose, an mTOR-independent autophagy inducer were used to examine the role of AMPK in autophagosome maturation and lysosomal fusion. While the treatment of control cells with either compound C or trehalose induces activation of autophagosomes as well as autolysosomes, the treatment of AMPK α1 knockout cells with compound C or trehalose induces mainly activation of autophagosomes, but not autolysosomes. We demonstrate that this effect is due to interference with the fusion of autophagosomes with lysosomes in AMPK α1 knockout cells. The transient expression of AMPK α1 can rescue autophagosome maturation. These results indicate that AMPK α1 is required for efficient autophagosome maturation and lysosomal fusion.

Reactive oxygen species and cancer paradox: To promote or to suppress?

Reactive oxygen species (ROS), a group of highly reactive ions and molecules, are increasingly being appreciated as powerful signaling molecules involved in the regulation of a variety of biological processes. Indeed, their role is continuously being delineated in a variety of pathophysiological conditions. For instance, cancer cells are shown to have increased ROS levels in comparison to their normal counterparts. This is partly due to an enhanced metabolism and mitochondrial dysfunction in cancer cells. The escalated ROS generation in cancer cells contributes to the biochemical and molecular changes necessary for the tumor initiation, promotion and progression, as well as, tumor resistance to chemotherapy. Therefore, increased ROS in cancer cells may provide a unique opportunity to eliminate cancer cells via elevating ROS to highly toxic levels intracellularly, thereby, activating various ROS-induced cell death pathways, or inhibiting cancer cell resistance to chemotherapy. Such results can be achieved by using agents that either increase ROS generation, or inhibit antioxidant defense, or even a combination of both. In fact, a large variety of anticancer drugs, and some of those currently under clinical trials, effectively kill cancer cells and overcome drug resistance via enhancing ROS generation and/or impeding the antioxidant defense mechanism. This review focuses on our current understanding of the tumor promoting (tumorigenesis, angiogenesis, invasion and metastasis, and chemoresistance) and the tumor suppressive (apoptosis, autophagy, and necroptosis) functions of ROS, and highlights the potential mechanism(s) involved. It also sheds light on a very novel and an actively growing field of ROS-dependent cell death mechanism referred to as ferroptosis.

Compound C Increases Sestrin2 Expression via Mitochondria-Dependent ROS Production

Compound C is a widely used chemical inhibitor that down-regulates AMP-activated protein kinase (AMPK) activity. However, it has been suggested that compound C exerts AMPK-independent effects in various cells. Here, we investigated whether compound C induces Sestrin2 (SESN2), an antioxidant enzyme induced by diverse stress. In addition, the mechanism responsible for SESN2 induction by compound C was determined. Our results showed that compound C increased SESN2 protein expression in HepG2 cells in a concentration- and time-dependent manner. The induction of SESN2 mRNA was also observed in cells treated with compound C. Increase of SESN2 luciferase activity confirmed transcriptional regulation by compound C and this substance also increased nuclear factor erythroid 2 (NF-E2)-related factor-2 (Nrf2) phosphorylation, which implies that Nrf2 was involved in SESN2 induction. Next, we sought to demonstrate whether production of reactive oxygen species (ROS) accompanied SESN2 expression. Compound C increased ROS production, but this effect was prevented by pretreatment with antioxidants or the mitochondrial complex I inhibitor. Moreover, cyclosporin A, an inhibitor of pore formation in the mitochondrial membrane, attenuated compound C-induced SESN2 induction. However, overexpression of a constitutively active form of AMPK was not able to abolish SESN2 induction by compound C, which implies that its action is independent of AMPK inhibition. In conclusion, this is the first study demonstrating that compound C alters mitochondrial function and induces ROS production, which ultimately leads to phosphorylation of Nrf2 and induction of SESN2.

Berberine Regulated Lipid Metabolism in the Presence of C75, Compound C, and TOFA in Breast Cancer Cell Line MCF-7

Berberine interfering with cancer reprogramming metabolism was confirmed in our previous study. Lipid metabolism and mitochondrial function were also the core parts in reprogramming metabolism. In the presence of some energy-related inhibitors, including C75, compound C, and TOFA, the discrete roles of berberine in lipid metabolism and mitochondrial function were elucidated. An altered lipid metabolism induced by berberine was observed under the inhibition of FASN, AMPK, and ACC in breast cancer cell MCF-7. And the reversion of berberine-induced lipid suppression indicated that ACC inhibition might be involved in that process instead of FASN inhibition. A robust apoptosis induced by berberine even under the inhibition of AMPK and lipid synthesis was also indicated. Finally, mitochondrial function regulation under the inhibition of AMPK and ACC might be in an ACL-independent manner. Undoubtedly, the detailed mechanisms of berberine interfering with lipid metabolism and mitochondrial function combined with energy-related inhibitors need further investigation, including the potential compensatory mechanisms for ATP production and the upregulation of ACL.

6-Shogaol enhances renal carcinoma Caki cells to TRAIL-induced apoptosis through reactive oxygen species-mediated cytochrome c release and down-regulation of c-FLIP(L) expression

6-Shogaol, a potent bioactive compound in ginger (Zingiber officinale Roscoe), has been reported for anti-inflammatory and anti-cancer activity. In this study, we investigated the effect of 6-shogaol to enhance tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis. The combined treatment with 6-shogaol and TRAIL markedly induces apoptosis in various cancer cells (renal carcinoma Caki cells, breast carcinoma MDA-MB-231 cells and glioma U118MG cells), but not in normal mesangial cells and normal mouse kidney cells. 6-Shogaol reduced the mitochondrial membrane potential (MMP) and released cytochrome c from mitochondria to cytosol via Bax activation. Furthermore, we found that 6-shogaol induced down-regulation of c-FLIP(L) expression at the post-translational levels and the overexpression of c-FLIP(L) markedly inhibited 6-shogaol plus TRAIL-induced apoptosis. Moreover, 6-shogaol increased reactive oxygen species (ROS) production in Caki cells. Pretreatment with ROS scavengers attenuated 6-shogaol plus TRAIL-induced apoptosis through inhibition of MMP reduction and down-regulation of c-FLIP(L) expression. In addition, 6-gingerol, another phenolic alkanone isolated from ginger, did not enhance TRAIL-induced apoptosis and down-regulate c-FLIP(L) expression. Taken together, our results demonstrated that 6-shogaol enhances TRAIL-mediated apoptosis in renal carcinoma Caki cells via ROS-mediated cytochrome c release and down-regulation of c-FLIP(L) expression.

The Histone Deacetylase Inhibitor Trichostatin A Sensitizes Human Renal Carcinoma Cells to TRAIL-Induced Apoptosis through Down-Regulation of c-FLIPL

Histone acetylation plays a critical role in the regulation of transcription by altering the structure of chromatin, and it may influence the resistance of some tumor cells to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) by regulating the gene expression of components of the TRAIL signaling pathway. In this study, we investigated the effects and molecular mechanisms of trichostatin A (TSA), a histone deacetylase inhibitor, in sensitizing TRAIL-induced apoptosis in Caki human renal carcinoma cells. Our results indicate that nontoxic concentrations of TSA substantially enhance TRAIL-induced apoptosis compared with treatment with either agent alone. Cotreatment with TSA and TRAIL effectively induced cleavage of Bid and loss of mitochondrial membrane potential (MMP), which was associated with the activation of caspases (-3, -8, and -9) and degradation of poly (ADP-ribose) polymerase (PARP), contributing toward the sensitization to TRAIL. Combined treatment with TSA and TRAIL significantly reduced the levels of the cellular Fas-associated death domain (FADD)-like interleukin-1β-converting enzyme (FLICE) inhibitory protein (c-FLIP), whereas those of death receptor (DR) 4, DR5, and FADD remained unchanged. The synergistic effect of TAS and TRAIL was perfectly attenuated in c-FLIP_L-overexpressing Caki cells. Taken together, the present study demonstrates that down-regulation of c-FLIP contributes to TSA-facilitated TRAIL-induced apoptosis, amplifying the death receptor, as well as mitochondria-mediated apoptotic signaling pathways.

Targeting the Anti-Apoptotic Protein c-FLIP for Cancer Therapy

Cellular FLICE (FADD-like IL-1beta-converting enzyme)-inhibitory protein (c-FLIP) is a major resistance factor and critical anti-apoptotic regulator that inhibits tumor necrosis factor-alpha (TNF-alpha), Fas-L, and TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis as well as chemotherapy-triggered apoptosis in malignant cells. c-FLIP is expressed as long (c-FLIP(L)), short (c-FLIP(S)), and c-FLIP(R) splice variants in human cells. c-FLIP binds to FADD and/or caspase-8 or -10 in a ligand-dependent and-independent fashion, which in turn prevents death-inducing signaling complex (DISC) formation and subsequent activation of the caspase cascade. Moreover, c-FLIP(L) and c-FLIP(S) are known to have multifunctional roles in various signaling pathways, as well as activating and/or upregulating several cytoprotective signaling molecules. Upregulation of c-FLIP has been found in various tumor types, and its downregulation has been shown to restore apoptosis triggered by cytokines and various chemotherapeutic agents. Hence, c-FLIP is an important target for cancer therapy. For example, small interfering RNAs (siRNAs) that specifically knockdown the expression of c-FLIP(L) in diverse human cancer cell lines augmented TRAIL-induced DISC recruitment and increased the efficacy of chemotherapeutic agents, thereby enhancing effector caspase stimulation and apoptosis. Moreover, small molecules causing degradation of c-FLIP as well as decreasing mRNA and protein levels of c-FLIP(L) and c-FLIP(S) splice variants have been found, and efforts are underway to develop other c-FLIP-targeted cancer therapies. This review focuses on (1) the functional role of c-FLIP splice variants in preventing apoptosis and inducing cytokine and drug resistance; (2) the molecular mechanisms that regulate c-FLIP expression; and (3) strategies to inhibit c-FLIP expression and function.

BAI, a novel cyclin-dependent kinase inhibitor induces apoptosis in A549 cells through activation of caspases and inactivation of Akt

Previously, we have synthesized a novel cyclin-dependent kinase (CDK) inhibitor, 2-[1,1'biphenyl]-4-yl-N-[5-(1,1-dioxo-1λ(6) -isothiazolidin-2-yl)-1H-indazol-3-yl]acetamide (BAI) and reported its anti-cancer activity in head and neck cancer cells. In this study, we further evaluated the effect of BAI on growth of various human cancer cell lines, including A549 (nonsmall cell lung cancer), HCT116 (colon), and Caki (kidney). Profoundly, results of XTT and clonogenic assays demonstrated that BAI at nanomolar concentrations (20-60 nM) inhibited growth of A549, HCT116, and Caki cells, suggesting the anti-cancer potency. We show that BAI induced a dose-dependent apoptotic cell death in these human cancer cells, as measured by fluorescence-activated cell sorting (FACS). Interestingly, further biochemical analysis showed that treatment with BAI at 20 nM induced apoptosis in A549 cells in association with activation of caspases, cleavage of phospholipase C-γ1 (PLC-γ1), and inhibition of Akt in A549 cells. Importantly, pharmacological inhibition study revealed that pretreatment with z-VAD-fmk, a pan caspase inhibitor strongly blocked the BAI-induced apoptosis in A549 cells. Transfection analysis with Akt cDNA encoding constitutively active Akt further addressed the significance of Akt inhibition in the BAI-induced apoptosis in A549 cells. Notably, disruption of the PI3K/Akt pathway by LY294002, a PI3K/Akt inhibitor potentiated apoptosis in A549 cells by BAI at a subcytotoxic concentration. These findings collectively suggest that BAI potently inhibits growth of A549, HCT116, and Caki cells, and that the BAI-induced apoptosis in A549 cells is associated with activation of caspases, and inhibition of Akt.

Anisomycin treatment enhances TRAIL-mediated apoptosis in renal carcinoma cells through the down-regulation of Bcl-2, c-FLIP(L) and Mcl-1

Anisomycin is known to inhibit protein synthesis and induce ribotoxic stress. In this study, we investigated whether anisomycin treatment could modulate TRAIL-mediated apoptosis in human renal carcinoma Caki cells. We found that anisomycin treatment (10-15 nM) alone had no effect on the level of apoptosis, but a combination treatment of anisomycin and TRAIL significantly increased the level of apoptosis in human renal carcinoma (Caki, ACHN and A498), human glioma (U251MG), and human breast carcinoma (MDA-MB-361 and MCF7) cells. Anisomycin treatment led to the down-regulation of Bcl-2 expression at the transcriptional level, and the over-expression of Bcl-2 inhibited the apoptosis induced by the combination treatment of anisomycin and TRAIL. Furthermore, anisomycin treatment resulted in the down-regulation of c-FLIP(L) and Mcl-1 at the post-transcriptional level, and the over-expression of c-FLIP(L) and Mcl-1 blocked the induction of apoptosis caused by the combination treatment of anisomycin with TRAIL. In contrast, anisomycin treatment had no effect on the levels of TRAIL-mediated apoptosis in mouse kidney cells (TMCK-1) or normal human skin fibroblasts (HSF). Cumulatively, our study demonstrates that anisomycin treatment enhances TRAIL-mediated apoptosis through the down-regulation of Bcl-2, c-FLIP(L) and Mcl-1 at the transcriptional or post-transcriptional level.

BML-275, an AMPK inhibitor, induces DNA damage, G2/M arrest and apoptosis in human pancreatic cancer cells

Adenosine monophosphate-activated protein kinase (AMPK) is a principal intracellular energy sensor which regulates energy producing pathways and energy requiring pathways when the cellular AMP/ATP ratio is altered. BML-275 (compound C), a well-known inhibitor of AMPK, has been found to induce apoptosis in myeloma, glioma and prostate cancer cells. However, the mechanisms responsible for the selective apoptotic effect(s) by BML-275 in cancer cells remain unknown. In the present study, BML-275 was investigated for its antitumor effect(s) in human pancreatic cancer cell lines. BML-275 inhibited the cell proliferation of 4 human pancreatic cancer cell lines (MIA PaCa-2, Panc-1, Colo-357 and AsPC-1). In addition, BML-275 significantly increased the generation of intracellular reactive oxygen species (ROS), followed by induction of DNA damage signaling and apoptosis. Furthermore, BML-275 induced cell cycle arrest in the G2/M phase. The inhibition of ROS generation by N-acetyl cysteine (NAC) significantly prevented the induction of DNA damage and apoptosis, but failed to prevent the induction of G2/M arrest by BML-275. Small interfering RNA (siRNA)-mediated knockdown of AMPKα increased the generation of intracellular ROS, DNA damage signaling and apoptosis without cell cycle arrest at the G2/M phase. These findings suggest that BML-275 exerts its antitumor effects by inducing ROS generation, DNA damage and apoptosis via inhibition of the AMPK pathway and by inducing G2/M arrest via a pathway independent of AMPK, implicating its potential application as an antitumor agent for pancreatic cancer.

Dioscin sensitizes cells to TRAIL-induced apoptosis through downregulation of c-FLIP and Bcl-2

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has received attention as a potential anticancer drug, because it induces apoptosis in a wide variety of cancer cells but not in most normal human cell types. Here, we showed that co-treatment with subtoxic doses of dioscin and TRAIL-induced apoptosis in Caki human renal cancer cells. Treatment of Caki cells with dioscin downregulated c-FLIPL and Bcl-2 proteins in a dose-dependent manner. Dioscin-induced decrease in c-FLIPL protein levels may be caused by the increased protein instability. We also found that dioscin induced downregulation of Bcl-2 at the transcriptional level. Pretreatment with NAC slightly inhibited the expression levels of c-FLIPL downregulated by the treatment of dioscin, suggesting that dioscin is partially dependent on the generation of ROS for downregulation of c-FLIPL. Taken together, the present study demonstrates that dioscin enhances TRAIL-induced apoptosis in human renal cancer cells by downregulation of c-FLIPL and Bcl-2.

Antimycin A sensitizes cells to TRAIL-induced apoptosis through upregulation of DR5 and downregulation of c-FLIP and Bcl-2

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been the focus as a potential anticancer drug, because it induces apoptosis in a wide variety of cancer cells but not in most normal human cell types. In this study, we showed that combination treatment with sub-toxic doses of antimycin A (AMA), an inhibitor of electron transport, plus TRAIL induced apoptosis in human renal cancer cells, but not in normal tubular kidney cells. Treatment of Caki cells with AMA upregulated the death receptor 5 (DR5) protein and downregulated c-FLIP and Bcl-2 proteins in a dose-dependent manner. AMA-induced decrease of c-FLIPL and c-FLIPs protein levels which were caused by increased protein instability, which was confirmed by the result showing that treatment with a protein biosynthesis inhibitor, CHX, accelerated degradation of c-FLIPL and c-FLIPs proteins caused by AMA treatment. We also found that AMA induced upregulation of DR5 and downregulation of Bcl-2 at the transcriptional level. Pretreatment with N-acetyl-l-cysteine (NAC) partly recovered the expression levels of c-FLIPL and c-FLIPs proteins were downregulated by the AMA treatment, suggesting that AMA appears to be partially dependent on the generation of ROS for downregulation of c-FLIPL and c-FLIPs. Collectively, this study demonstrates that AMA enhances TRAIL-induced apoptosis in human renal cancer cells by upregulation of DR5 as well as downregulation of c-FLIP and Bcl-2. Furthermore, this study shows that AMA markedly increases sensitivity to cisplatin in Caki human renal cancer cells.

AMPK inhibitor compound C suppresses cell proliferation by induction of apoptosis and autophagy in human colorectal cancer cells

BACKGROUND AND OBJECTIVES

AMP-activated protein kinase (AMPK) is a main regulator of energy metabolism through the inhibition of biosynthetic pathways and enhancement of ATP-generating pathways. However, targeting AMPK as anti-tumor therapy remains controversial. In this study, we examined the effect of compound C, a small molecule inhibitor of AMPK, on the proliferation of several human colorectal cancer cell lines with diverse characteristics.

METHODS

Four human colorectal cancer cell lines (HCT116, DLD-1, SW480, and KM12C) were treated with compound C. Cell viability was determined by MTS assay. Cell cycle prolife was analyzed by flow cytometry. Acidic vesicular organelles were detected by acridine orange staining. Protein levels were measured by western blotting.

RESULTS

Compound C inhibited the growth of four cell lines in a dose-dependent manner and caused G(2) /M arrest. Compound C increased sub-G(1) cell population and induced chromatin condensation and cleavage of PARP in HCT116 and KM12C cells, while it induced acidic vesicular formation and conversion of LC3-I to autophagosome-associated LC3-II in DLD-1 and SW480 cells. Survivin, an anti-apoptotic protein, was down-regulated in all cell lines treated with compound C.

CONCLUSIONS

Compound C induces apoptotic or autophagic death in colorectal cancer cells and the preferred death mode is cell type-dependent.

TRAIL-activated EGFR by Cbl-b-regulated EGFR redistribution in lipid rafts antagonises TRAIL-induced apoptosis in gastric cancer cells

Most gastric cancer cells are resistant to tumour necrosis factor-related apoptosis-inducing ligand (TRAIL). Since TRAIL resistance is associated with lipid rafts, in which both death receptors and epidermal growth factor receptors (EGFR) are enriched, our aim is to identify how lipid raft-regulated receptor redistribution influences the sensitivity of TRAIL in gastric cancer cells. In TRAIL-resistant gastric cancer cells, TRAIL did not induce effective death-inducing signalling complex (DISC) formation in lipid rafts, accompanied with EGFR translocation into lipid rafts, and activation of EGFR pathway. Knockdown of casitas B-lineage lymphoma-b (Cbl-b) enhanced TRAIL-induced apoptosis by promoting DISC formation in lipid rafts. However, knockdown of Cbl-b also enhanced EGFR translocation into lipid rafts and EGFR pathway activation induced by TRAIL. Either using inhibitors of EGFR or depletion of EGFR with small interfering RNA (siRNA) prevented EGFR pathway activation, and thus increased TRAIL-induced apoptosis, especially in Cbl-b knockdown clones. Taken together, TRAIL-induced EGFR activation through Cbl-b-regulated EGFR redistribution in lipid rafts antagonised TRAIL-induced apoptosis. The contribution of DISC formation and the inhibition of EGFR signal triggered in lipid rafts are both essential for increasing the sensitivity of gastric cancer cells to TRAIL.

Effective delivery of anti-miRNA DNA oligonucleotides by functionalized gold nanoparticles

MicroRNAs (miRNAs) are gaining recognition as essential regulators involved in many biological processes, and they are emerging as therapeutic targets for treating disease. Here, we introduce a method for effective delivery of anti-miRNA oligonucleotides (AMOs) using functionalized gold nanoparticles (AuNPs). To demonstrate the ability of AMOs to silence miRNA, we selected miR-29b, which is known to downregulate myeloid cell leukemia-1 (MCL-1), a factor responsible for promoting cell survival. We first generated AuNPs coated with cargo DNA, which was then coupled to complementary DNA linked to an antisense miR-29b sequence. When the AuNPs were delivered into HeLa cells, MCL-1 protein and mRNA levels were increased significantly. Furthermore, apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) was inhibited, proving that AMOs targeting miR-29b were effectively delivered by our innovative AuNP. In addition, we provided evidence that AuNP could deliver other AMOs against miR-21 into two independent cell lines, KGN and 293T, suggesting that the AuNP conjugates can be versatile for any AMO and cell type.

Compound C independent of AMPK inhibits ICAM-1 and VCAM-1 expression in inflammatory stimulants-activated endothelial cells in vitro and in vivo

Activation of the NF-κB and mitogen activated protein (MAP) kinases plays an important role in the expression of inflammatory genes such as adhesion molecules. Although compound C is known as an AMPK inhibitor, AMPK-independent action of it has been recognized. Effects on the expression of ICAM-1 and VCAM-1 by compound C were investigated in TNF-α-activated human umbilical vein endothelial cells (HUVECs) in vitro and in thoracic aorta of rats treated with lipopolysaccharide (LPS) in vivo. Compound C inhibited ICAM-1 and VCAM-1 expression at the transcriptional as well as translational level in TNF-α-activated HUVECs. In both DN-AMPK- and AMPKα(1)-siRNA-transfected HUVECs, compound C still inhibited TNF-α-induced VCAM-1 and ICAM-1 expression, indicating that this is AMPK-independent action. Interestingly, compound C significantly inhibited NF-κB activity and translocation of p65 to nucleus in HUVECs when activated with TNF-α. Importantly, administration of compound C (0.2 mg/kg) significantly reduced expression of both ICAM-1 and VCAM-1 in LPS-treated rat thoracic aortas. In addition, compound C significantly inhibited iNOS and production of NO in both TNF-α- and LPS-activated RAW 264.7 cells. Finally, compound C significantly inhibited phosphorylation of Akt and p-38MAPK but not protein kinase c or ERK1/2 in HUVECs. Taken together, we conclude that adhesion molecules (ICAM-1, VCAM-1) are to be the novel targets of compound C in preventing inflammatory insult to endothelial cells independent of AMPK inhibition via inhibition of NF-κB activity along with inhibition of phosphorylation of PI3K and P38 MAPK.

TRAIL-mediated signaling in prostate, bladder and renal cancer

Tumor necrosis factor related apoptosis inducing ligand (TRAIL) is a death receptor ligand that has the ability to preferentially initiate apoptosis in malignant cells with minimal toxicity to normal cells. TRAIL-based therapeutics, including recombinant TRAIL, TRAIL-receptor agonistic antibodies and TRAIL gene therapy, have now entered clinical trials. Although these therapeutics are promising, concerns regarding TRAIL resistance are causing research efforts to shift towards the identification of effective combination therapies. Small-molecule inhibitors, natural compounds, and drugs approved for treatment of diseases other than cancer have been shown to affect TRAIL receptors, antiapoptotic proteins and survival pathways in prostate, bladder and renal cell lines and in preclinical models. Changes in endogenous TRAIL and TRAIL receptor expression during the development of genitourinary malignancies and the way in which the expression pattern is affected by treatment are of great interest, and understanding the biological consequences of such changes will be important to maximize the potential of TRAIL-based therapeutics.

Compound C stimulates heme oxygenase-1 gene expression via the Nrf2-ARE pathway to preserve human endothelial cell survival

We recently identified adenosine monophosphate-activated protein kinase (AMPK) as a novel inducer of heme oxygenase-1 (HO-1) and surprisingly found that compound C (6-[4-(2-piperidin-1-yl-ethoxy)-phenyl]-3-pyridin-4-yl-pyrazolo[1,5-a] pyrimidine), a cell-permeable inhibitor of AMPK, could also elevate HO-1 suggesting other AMPK-independent actions for this agent. In this study, we investigated the biochemical mechanism by which compound C stimulates HO-1 expression in human endothelial cells (ECs) and determined the biological significance of the induction of HO-1 by compound C in these cells. Compound C stimulated a concentration- and time-dependent increase in HO-1 expression and an increase in HO-1 promoter activity that was abrogated by mutating the antioxidant responsive elements (AREs) in the HO-1 promoter or by overexpressing a dominant negative mutant of NF-E2-related factor 2 (Nrf2). Compound C also stimulated Nrf2 expression this was associated with an increase in the production of reactive oxygen species and with a decline in intracellular glutathione levels. Interestingly, the glutathione donor N-acetyl-l-cysteine or the NADPH oxidase inhibitor apocynin blocked the induction of HO-1 by compound C. Finally, compound C stimulated EC death and this was potentiated by silencing HO-1 expression and reversed by the administration of CO, biliverdin, or bilirubin. In conclusion, this study demonstrates that compound C stimulates HO-1 gene expression in human vascular endothelium via the activation of the Nrf2/ARE signaling pathway to counteract compound C-mediated cell death. The ability of compound C to induce HO-1 expression may contribute to the pleiotropic actions of this agent and suggest caution when using compound C to probe for AMPK functions.

Compound C inhibits vascular smooth muscle cell proliferation and migration in an AMP-activated protein kinase-independent fashion

6-[4-(2-Piperidin-1-yl-ethoxy)-phenyl]-3-pyridin-4-yl-pyrazolo[1,5-a] pyrimidine (compound C) is a cell-permeable pyrrazolopyrimidine derivative that acts as a potent inhibitor of AMP-activated protein kinase (AMPK). Although compound C is often used to determine the role of AMPK in various physiological processes, it also evokes AMPK-independent actions. In the present study, we investigated whether compound C influences vascular smooth muscle cell (SMC) function through the AMPK pathway. Treatment of rat aortic SMCs with compound C (0.02-10 μM) inhibited vascular SMC proliferation and migration in a concentration-dependent fashion. These actions of compound C were not mimicked or affected by silencing AMPKα expression or infecting SMCs with an adenovirus expressing a dominant-negative mutant of AMPK. In contrast, the pharmacological activator of AMPK 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside inhibited the proliferation and migration of SMCs in a manner that was strictly dependent on AMPK activity. Flow cytometry experiments revealed that compound C arrested SMCs in the G(0)/G(1) phase of the cell cycle, and this was associated with a decrease in cyclin D1 and cyclin A protein expression and retinoblastoma protein phosphorylation and an increase in p21 protein expression. Finally, local perivascular delivery of compound C immediately after balloon injury of rat carotid arteries markedly attenuated neointima formation. These studies identify compound C as a novel AMPK-independent regulator of vascular SMC function that exerts inhibitory effects on SMC proliferation and migration and neointima formation after arterial injury. Compound C represents a potentially new therapeutic agent in treating and preventing occlusive vascular disease.

Putative mechanisms of antitumor activity of cyano-substituted heteroaryles in HeLa cells

Six recently synthesized cyano-substituted heteroaryles, which do not bind to DNA but are highly cytotoxic against the human tumor cell line HeLa, were analyzed for their antitumor mechanisms of action (MOA). They did not interfere with the expression of human papillomavirus oncogenes integrated in the HeLa cell genome, but they did induce strong G1 arrest and result in the activation of caspase-3 and apoptosis. A computational analysis was performed that compared the antiproliferative activities of our compounds in 13 different tumor cell lines with those of compounds listed in the National Cancer Institute database. The results indicate that interference with cytoskeletal function and inhibition of mitosis are the likely antitumor MOA. Furthermore, a second in silico investigation revealed that the tumor cells that are sensitive to the cyano-substituted compounds show differences in their expression of locomotion genes compared with that of insensitive cell lines, thus corroborating the involvement of the cytoskeleton. This MOA was also confirmed experimentally: the cyano-substituted heteroaryles disrupted the actin and the tubulin networks in HeLa cells and inhibited cellular migration. However, further analysis indicated that multiple MOA may exist that depend on the position of the cyano-group; while cyano-substituted naphthiophene reduced the expression of cytoskeletal proteins, cyano-substituted thieno-thiophene-carboxanilide inhibited the formation of cellular reactive oxygen species.