Inhibition of proteasomal degradation of Mcl-1 by cobalt chloride suppresses cobalt chloride-induced apoptosis in HCT116 colorectal cancer cells

Molecular and Cellular Response of Co-cultured Cells toward Cobalt Chloride (CoCl2)-Induced Hypoxia

Cobalt chloride (CoCl₂) is a well-known hypoxia mimetic mediator that induces hypoxia-like responses. CoCl₂, a mediator confirmed to alleviate hypoxia-inducible factor-1 (HIF-1), has been associated with a variety of hypoxic responses. HIF-1 is the foremost transcriptionfactor that is particularly activated during hypoxia and regulates various genes. Therefore, this study aimed to investigate the cellular and molecular responses of the co-cultured cells under the influence of the CoCl₂-induced hypoxic condition. Mono- and co-cultured C2C12 and 3T3-L1 cells were exposed to CoCl₂, and a significant induction in HIF-1, reactive oxygen species and lipid peroxidase and a reduction in glutathione and catalase were observed. The expressions of proapoptotic genes like Bax, p53, caspase-9, and caspase-3 were notably increased, whereas the antiapoptotic gene, i.e., Bcl2, was downregulated during hypoxia in mono- as well as co-cultured C2C12 cells. However, the co-cultured C2C12 cells show significantly lower induction in oxidative stress and expression of apoptotic genes in comparison to monocultured C2C12 cells. Whereas, the co-cultured 3T3-L1 cells show comparatively higher oxidative stress and apoptotic event in comparison to monocultured 3T3-L1 cells. The reason may be the communication between the cells and some soluble factors that help in cell survival/death from hypoxia. Moreover, it may also be due to the fact that fat and muscle cells interact and communicate via proximity and mutual ability when growing together. Therefore, the co-culture system provides a unique approach to intercellular communication between the two different cell types.

Cobalt Chloride Induced Apoptosis by Inhibiting GPC3 Expression via the HIF-1α/c-Myc Axis in HepG2 Cells

Purpose

To investigate the role of glypican-3 (GPC3) in cobalt chloride (CoCl₂)-induced cell apoptosis in hepatocellular carcinoma.

Methods

HepG2 cells were treated with CoCl₂ in the absence or presence of GPC3 plasmid transfection. Cell viability and apoptosis were assessed by MTT assay and flow cytometry, respectively. The expression of GPC3, hypoxia-inducible factor 1α (HIF-1α), c-myc, sp1, poly-ADP-ribose polymerase (PARP) and caspase-3 was determined by real-time PCR, Western blotting, and immunofluorescence after the cells were treated with different concentrations of CoCl₂ or siRNA targeting HIF-1α.

Results

CoCl₂ significantly inhibited the proliferation of HepG2 cells and induced apoptosis. Additionally, the expression of GPC3 mRNA and protein was decreased, and overexpression of GPC3 attenuated the tumour inhibiting effects. Further studies showed that CoCl₂ increased the expression of HIF-1α while reducing the expression of sp1 and c-myc; knockdown of HIF-1α elevated the expression of GPC3, sp1, and c-myc.

Conclusion

CoCl₂ inhibited the growth of HepG2 cells through downregulation of GPC3 expression via the HIF-1α/c-myc axis.

Chloramphenicol Induces Autophagy and Inhibits the Hypoxia Inducible Factor-1 Alpha Pathway in Non-Small Cell Lung Cancer Cells

Chloramphenicol is an inexpensive and excellent bactericidal antibiotic. It is used to combat anaerobic infections in the Third World countries, whereas its systemic application has been abandoned in developed countries. However, in recent years, clinicians have reintroduced chloramphenicol in clinical practice. In this study, chloramphenicol was found to repress the oxygen-labile transcription factor, hypoxia inducible factor-1 alpha (HIF-1α), in hypoxic A549 and H1299 cells. Furthermore, it suppressed the mRNA levels of vascular endothelial growth factor (VEGF) and glucose transporter 1, eventually decreasing VEGF release. Chloramphenicol initiated the autophagy pathway in treated cells, as observed by the increase in formation of Atg12-Atg5 conjugates, and in beclin-1 and LC3-II levels. The chloramphenicol-mediated HIF-1α degradation was completely reverted by autophagic flux blockage. In HIF-1α-overexpressing cells, the formation of HIF-1α/SENP-1 (Sentrin/SUMO-specific protease 1) protein complex seemed to facilitate the escape of HIF-1α from degradation. Chloramphenicol inhibited HIF-1α/SENP-1 protein interaction, thereby destabilizing HIF-1α protein. The enhancement in HIF-1α degradation due to chloramphenicol was evident during the incubation of the antibiotic before hypoxia and after HIF-1α accumulation. Since HIF-1α plays multiple roles in infections, inflammation, and cancer cell stemness, our findings suggest a potential clinical value of chloramphenicol in the treatment of these conditions.

Synthesis of novel 10,11-methylenedioxy-camptothecin glycoside derivatives and investigation of their anti-tumor effects in vivo

10,11-Methylenedioxy-camptothecin (FL118) is a novel camptothecin analogue that possesses exceptional antitumor efficacy in human tumor xenograft models. The aim of the current study was to develop novel 20-substituted FL118 derivatives coupled with glycosyl-succinic acid esters with improved antitumor efficacy. These FL118 glycoside derivatives were designed, synthesized and their cytotoxicity evaluated in three tumor cell lines (A-549, MDA-MB-231 and RM-1). All of the derivatives showed superior in vitro cytotoxic activity and were more potent than irinotecan in A549 and MDA-MB-231 cells. In mouse prostate cancer cells RM-1, 10,11-methylenedioxy-camptothecin rhamnoside 11b displayed significant activities with IC₅₀ of 48.27 nM. Western blot analysis demonstrated that 11b inhibited survivin expression and induced cancer cells apoptosis. Further cell cycle analyses clearly showed 11b induced G2/M phase cell cycle arrest. Molecule docking studies suggested that the binding mode of 11b was different from that of the crystal complex of ligand topotecan in Top1/DNA. Importantly, 11b showed high in vivo antitumor efficacy in the RM-1 mouse model with transplantation of prostate cancer (TGI = 44.9%) at dose of 9 mg kg⁻¹ without apparent toxicity.

In a RM-1 xenograft model, 11b had superior in vivo antitumor efficacy (TGI = 44.9%) at a dose of 9 mg kg⁻¹.

Misoprostol regulates Bnip3 repression and alternative splicing to control cellular calcium homeostasis during hypoxic stress

The cellular response to hypoxia involves the activation of a conserved pathway for gene expression regulated by the transcription factor complex called hypoxia-inducible factor (HIF). This pathway has been implicated in both the adaptive response to hypoxia and in several hypoxic-ischemic-related pathologies. Perinatal hypoxic injury, often associated with prematurity, leads to multi-organ dysfunction resulting in significant morbidity and mortality. Using a rodent model of neonatal hypoxia and several representative cell lines, we observed HIF1α activation and down-stream induction of the cell death gene Bnip3 in brain, large intestine, and heart which was mitigated by administration of the prostaglandin E1 analog misoprostol. Mechanistically, we determined that misoprostol inhibits full-length Bnip3 (Bnip3-FL) expression through PKA-mediated NF-κB (P65) nuclear retention, and the induction of pro-survival splice variants. We observed that the dominant small pro-survival variant of Bnip3 in mouse cells lacks the third exon (Bnip3ΔExon3), whereas human cells produce a pro-survival BNIP3 variant lacking exon 2 (BNIP3ΔExon2). In addition, these small Bnip3 splice variants prevent mitochondrial dysfunction, permeability transition, and necrosis triggered by Bnip3-FL by blocking calcium transfer from the sarco/endoplasmic reticulum to the mitochondria. Furthermore, misoprostol and Bnip3ΔExon3 promote nuclear calcium accumulation, resulting in HDAC5 nuclear export, NFAT activation, and adaptive changes in cell morphology and gene expression. Collectively, our data suggests that misoprostol can mitigate the potential damaging effects of hypoxia on multiple cell types by activating adaptive cell survival pathways through Bnip3 repression and alternative splicing.

Alterations in blood pressure, antioxidant status and caspase 8 expression in cobalt chloride-induced cardio-renal dysfunction are reversed by Ocimum gratissimum and gallic acid in Wistar rats

The protective abilities of the chloroform extract of Ocimum gratissimum (COG) and gallic acid against cobalt chloride (CoCl2) - induced cardiac and renal toxicity were evaluated. Rats were exposed to CoCl2 (350ppm) for 7 days, either alone, or in combination with COG (100 and 200mg/kg) or gallic acid (120mg/kg). CoCl2 given alone, caused significant increases (p<0.05) in oxidative stress parameters (hydrogen peroxide, H2O2 and malondialdehyde, MDA) and increased expression of the apoptotic initiator caspase 8 in the heart and kidneys. There was significant reduction (p<0.05) in reduced glutathione (GSH) in cardiac and renal tissues; reduction in superoxide dismutase (SOD) activity in the kidneys and adaptive increases in Glutathione S-transferase (GST) and catalase (CAT). CoCl2 also produced significant reduction (p<0.05) in systolic (SBP), diastolic (DBP) and mean arterial (MAP) blood pressures. Oral COG and gallic acid treatment significantly reduced (p<0.05) the levels of H2O2 and MDA; with reduced expression of caspase 8 and restoration of GSH levels, GPx, SOD and CAT activities, howbeit, to varying degrees in the heart and kidneys. COG (200mg/kg) was most effective in restoring the blood pressures in the rats to near control levels. CoCl2-induced histopathological lesions including myocardial infarction and inflammation and renal tubular necrosis and inflammation were effectively ameliorated by the treatments administered. This study provides evidence for the protective roles of O. gratissimum and gallic acid by modulation of CoCl2-induced alterations in blood pressure, antioxidant status and pro-apoptotic caspase 8 in Wistar rats.

MCL-1, BCL-XL and MITF Are Diversely Employed in Adaptive Response of Melanoma Cells to Changes in Microenvironment

Melanoma cells can switch their phenotypes in response to microenvironmental insults. Heterogeneous melanoma populations characterized by long-term growth and a high self-renewal capacity can be obtained in vitro in EGF(+)bFGF(+) medium whilst invasive potential of melanoma cells is increased in serum-containing cultures. In the present study, we have shown that originally these patient-derived melanoma populations exhibit variable expression of pro-survival genes from the BCL-2 family and inhibitors of apoptosis (IAPs), and differ in the baseline MCL-1 transcript stability as well. While being transferred to serum-containing medium, melanoma cells are well protected from death. Immediate adaptive response of melanoma cells selectively involves a temporary MCL-1 increase, both at mRNA and protein levels, and BCL-X_L can complement MCL-1, especially in MITF_low populations. Thus, the extent of MCL-1 and BCL-XL contributions seems to be cell context-dependent. An increase in MCL-1 level results from a transiently enhanced stability of its transcript, but not from altered protein turnover. Inhibition of MCL-1 preceding transfer to serum-containing medium caused the induction of cell death in a subset of melanoma cells, which confirms the involvement of MCL-1 in melanoma cell survival during the rapid alteration of growth conditions. Additionally, immediate response to serum involves the transient increase in MITF expression and inhibition of ERK-1/2 activity. Uncovering the mechanisms of adaptive response to rapid changes in microenvironment may extend our knowledge on melanoma biology, especially at the stage of dissemination.

Preconditioning with cobalt chloride modifies pain perception in mice

Cobalt chloride (CoCl₂) modifies mitochondrial permeability and has a hypoxic-mimetic effect; thus, the compound induces tolerance to ischemia and increases resistance to a number of injury types. The aim of the present study was to investigate the effects of CoCl₂ hypoxic preconditioning for three weeks on thermonociception, somatic and visceral inflammatory pain, locomotor activity and coordination in mice. A significant pronociceptive effect was observed in the hot plate and tail flick tests after one and two weeks of CoCl₂ administration, respectively (P<0.001). Thermal hyperalgesia (Plantar test) was present in the first week, but recovered by the end of the experiment. Contrary to the hyperalgesic effect on thermonociception, CoCl₂ hypoxic preconditioning decreased the time spent grooming the affected area in the second phase of the formalin test on the orofacial and paw models. The first phase of formalin-induced pain and the writhing test were not affected by CoCl₂ preconditioning. Thus, the present study demonstrated that CoCl₂ preconditioning has a dual effect on pain, and these effects should be taken into account along with the better-known neuro-, cardio- and renoprotective effects of CoCl₂.

Ursodeoxycholyl lysophosphatidylethanolamide inhibits cholestasis- and hypoxia-induced apoptosis by upregulating antiapoptosis proteins

An increase of toxic bile acids such as glycochenodeoxycholic acid occurs during warm ischemia reperfusion causing cholestasis and damage in hepatocytes and intrahepatic biliary epithelial cells. We aim to test antiapoptosis effects of ursodeoxycholyl lysophosphatidylethanolamide under cholestatic induction by glycochenodeoxycholic acid treatment of mouse hepatocytes and hypoxia induction by cobalt chloride treatment of intrahepatic biliary epithelial cancer Mz-ChA-1cell line. Such treatments caused marked increases in apoptosis as evidenced by activation of caspase 3, caspase 8 and poly (ADP-ribose) polymerase-1. Co-treatment with ursodeoxycholyl lysophosphatidylethanolamide significantly inhibited these increases. Interestingly, ursodeoxycholyl lysophosphatidylethanolamide was able to increase expression of antiapoptotic cellular FLICE-inhibitory protein in both cell types. Ursodeoxycholyl lysophosphatidylethanolamide also prevented the decreases of myeloid cell leukemia sequence-1 protein in both experimental systems, and this protection was due to ursodeoxycholyl lysophosphatidylethanolamide's ability to inhibit ubiquitination-mediated degradation of myeloid cell leukemia sequence-1, and to increase the phosphorylation of GSK-3β. In addition, ursodeoxycholyl lysophosphatidylethanolamide was able to prevent the decreased expression of another antiapoptotic cellular inhibitor of apoptosis 2 in cobalt chloride-treated Mz-ChA-1 cells. Hence, ursodeoxycholyl lysophosphatidylethanolamide mediated cytoprotection against apoptosis during toxic bile-acid and ischemic stresses by a mechanism involving accumulation of cellular FLICE-inhibitory protein, myeloid cell leukemia sequence-1 and cellular inhibitor of apoptosis 2 proteins. Ursodeoxycholyl lysophosphatidylethanolamide may thus be used as an agent to prevent hepatic ischemia reperfusion.

Antitumor activity of FL118, a survivin, Mcl-1, XIAP, and cIAP2 selective inhibitor, is highly dependent on its primary structure and steric configuration

We recently reported the identification and characterization of a novel small chemical molecule designated FL118. FL118 selectively inhibits multiple cancer survival and proliferation-associated antiapoptotic proteins (survivin, Mcl-1, XIAP, cIAP2) and eliminates small and large human tumor xenografts in animal models (Ling et al., PLoS One 2012, 7, e45571). Here, we report a follow-up study on the structure-activity relationship (SAR) of the hydroxyl group in the lactone ring of FL118. We found that the superior antitumor efficacy of FL118 heavily depends on its steric configuration through comparing the antitumor activity of FL118 with FL113 (the racemic mixture of FL118). Consistently, FL118 proved much more effective in inhibiting the expression of survivin, Mcl-1, and cIAP2, both in vitro and in vivo, compared to FL113. Additionally, Tet-on controlled induction of survivin or forced expression of Mcl-1 protects cancer cells from FL118-mediated growth inhibition and cell death. To further explore the SAR, we synthesized seven position 20-esterifiable FL118 and FL113 derivatives. Studies on these seven new compounds revealed that keeping a free hydroxyl group of FL118 is also important for high antitumor efficacy. Together, these studies confirm the superior anticancer activity of FL118 and narrow the window for further SAR studies to generate novel analogues based on FL118 core structure on its other potential chemical positions.

Autophagy takes place in mutated p53 neuroblastoma cells in response to hypoxia mimetic CoCl(2)

Solid tumors like neuroblastoma exhibit hypoxic areas, which can lead both to cell death or aggressiveness increase. Hypoxia is a known stress able to induce stabilization of p53, implicated in cell fate regulation. Recently, p53 appeared to be involved in autophagy in an opposite manner, depending on its location: when nuclear, it enhanced transcription of pro-autophagic genes whereas when cytoplasmic, it inhibited the autophagic process. Today, we used cobalt chloride, a hypoxia mimetic that inhibits proteasomal HIF-1 degradation and generates reactive oxygen species (ROS). We focused on CoCl2-induced cell death in a DNA-binding mutated p53 neuroblastoma cell line (SKNBE(2c)). An autophagic signaling was evidenced by an increase of Beclin-1, ATG 5-12, and LC3-II expression whereas the p53(mut) presence decreased with CoCl2 time exposure. Activation of the pathway seemed to protect cells from ROS production and, at least in part, from death. The autophagic inhibitors activated the apoptotic signaling and the death was enhanced. To delineate the eventual implication of the p53(mut) in the autophagic process in response to hypoxia, we monitored signaling in p53(WT)SHSY5Y cells, after either shRNA-p53 down-regulation or transcriptional activity inhibition by pifithrin alpha. We did not detect autophagy neither with p53(wt) nor when p53 was lacking whereas such a response was effective with a mutated or inactivated p53. To conclude, mutated p53 in neuroblastoma cells could be linked with the switch between apoptotic response and cell death by autophagy in response to hypoxic mimetic stress.

A novel small molecule FL118 that selectively inhibits survivin, Mcl-1, XIAP and cIAP2 in a p53-independent manner, shows superior antitumor activity

Drug/radiation resistance to treatment and tumor relapse are major obstacles in identifying a cure for cancer. Development of novel agents that address these challenges would therefore be of the upmost importance in the fight against cancer. In this regard, studies show that the antiapoptotic protein survivin is a central molecule involved in both hurdles. Using cancer cell-based survivin-reporter systems (US 7,569,221 B2) via high throughput screening (HTS) of compound libraries, followed by in vitro and in vivo analyses of HTS-derived hit-lead compounds, we identified a novel anticancer compound (designated FL118). FL118 shows structural similarity to irinotecan. However, while the inhibition of DNA topoisomerase 1 activity by FL118 was no better than the active form of irinotecan, SN-38 at 1 µM, FL118 effectively inhibited cancer cell growth at less than nM levels in a p53 status-independent manner. Moreover, FL118 selectively inhibited survivin promoter activity and gene expression also in a p53 status-independent manner. Although the survivin promoter-reporter system was used for the identification of FL118, our studies revealed that FL118 not only inhibits survivin expression but also selectively and independently inhibits three additional cancer-associated survival genes (Mcl-1, XIAP and cIAP2) in a p53 status-independent manner, while showing no inhibitory effects on control genes. Genetic silencing or overexpression of FL118 targets demonstrated a role for these targets in FL118's effects. Follow-up in vivo studies revealed that FL118 exhibits superior antitumor efficacy in human tumor xenograft models in comparison with irinotecan, topotecan, doxorubicin, 5-FU, gemcitabine, docetaxel, oxaliplatin, cytoxan and cisplatin, and a majority of mice treated with FL118 showed tumor regression with a weekly × 4 schedule. FL118 induced favorable body-weight-loss profiles (temporary and reversible) and was able to eliminate large tumors. Together, the molecular targeting features of FL118 plus its superior antitumor activity warrant its further development toward clinical trials.