Oltipraz and dithiolethione congeners inhibit hypoxia-inducible factor-1α activity through p70 ribosomal S6 kinase-1 inhibition and H 2 O 2 -scavenging effect

STC2 is a potential biomarker of hepatocellular carcinoma with its expression being upregulated in Nrf1α-deficient cells, but downregulated in Nrf2-deficient cells

Nrf1 (encoded by Nfe2l1) and Nrf2 (encoded by Nfe2l2), as two key members of the CNC-bZIP transcription factor, exhibit significant functional differences in their pathophysiology. Our previous findings demonstrated that loss of Nrf1α (i.e., a full-length isoform of Nrf1) promotes HepG2-derived tumor growth in xenograft mice, but malgrowth of the xenograft tumor is significantly suppressed by knockout of Nrf2. To gain insights into the mechanism underlying such marked distinctions in their pathologic phenotypes, we mined transcriptome data from liver cancer in the TCGA database to establish a prognostic model and calculate predicted risk scores for each cell line. The results revealed that knockout of Nrf1α markedly increased the risk score in HepG2 cells, whereas the risk score was reduced by knockout of Nrf2. Notably, stanniocalcin 2 (STC2), a biomarker associated with liver cancer, that is upexpressed in hepatocellular carcinoma (HCC) tissues with a reduction in the overall survival ratio of those patients. We observed increased expression levels of STC2 in Nrf1α-/- cells but decreased expression in Nrf2-/- cells. These findings suggested that STC2 may play a role in mediating the distinction between Nrf1α-/- and Nrf2-/-. Such potential function of STC2 was further corroborated through a series of experiments combined with transcriptomic sequencing. The results revealed that STC2 functions as a dominant tumor-promoter, because the STC2-leading increases in clonogenicity of hepatoma cells and malgrowth of relevant xenograft tumor were almost completely abolished in STC2-/- cells. Together, these demonstrate that STC2 could be paved as a potential therapeutic target, albeit as a diagnostic marker, for HCC.

Synthesis of 4,5-Dihydro-1H-[1,2]dithiolo[3,4-c]quinoline-1-thione Derivatives and Their Application as Protein Kinase Inhibitors

This study represents the design and synthesis of a new set of hybrid and chimeric derivatives of 4,5-dihydro-4,4-dimethyl-1H-[1,2]dithiolo[3,4-c]quinoline-1-thiones, the structure of which the tricyclic fragment linearly bound or/and condensed with another heterocyclic fragment. Using the PASS Online software, among the previously synthesized and new derivatives of 1,2-dithiolo[3,4-c]quinoline-1-thione we identified 12 substances with pleiotropic activity, including chemoprotective and antitumor activity. All the synthesized derivatives were screened for their inhibitory assessment against a number of kinases. Compounds which exhibited prominent inhibition percentage in cells (>85%) were also examined for their inhibitory efficiency on human kinases via ELISA utilizing sorafenib as a reference standard to estimate their IC50 values. It was revealed that compounds 2a, 2b, 2c, and 2q displayed a significant inhibition JAK3 (IC50 = 0.36 μM, 0.38 μM, 0.41 μM, and 0.46 μM, respectively); moreover, compounds 2a and 2b displayed excellent activities against NPM1-ALK (IC50 = 0.54 μM, 0.25 μM, respectively), against cRAF[Y340D][Y341D], compound 2c showed excellent activity, and compound 2q showed weak activity (IC50 = 0.78 μM, 5.34 μM, respectively) (sorafenib IC50 = 0.78 μM, 0.43 μM, 1.95 μM, respectively). Thus, new promising preferred structures for the creation of drugs for the treatment of cancer and other multifactorial diseases in the future have been found.

Inhibition of p70 ribosomal S6 kinase 1 (S6K1) by PF-4708671 decreased infarct size in early cerebral ischemia-reperfusion with decreased BBB permeability

It is not clear whether inhibition of p70 ribosomal S6 kinase 1 (S6K1) is neuroprotective in cerebral ischemia-reperfusion. Decreasing blood-brain barrier (BBB) disruption has been associated with a better neuronal outcome in cerebral ischemia. We hypothesized that inhibition of S6K1 would decrease BBB disruption and infarct size in the early stage of cerebral ischemia-reperfusion. Middle cerebral artery occlusion (MCAO) was performed in rats under isoflurane anesthesia with controlled ventilation. 75 mg/kg of PF-4708671, an S6K1 inhibitor, was administered intraperitoneally 15 min after MCAO. After 1 h of MCAO and 2 h of reperfusion, the transfer coefficient (K_i) of ¹⁴C-α-aminoisobutyric acid and the volume of ³H-dextran distribution were determined to assess the degree of BBB disruption. At the same time point, phosphorylated Rictor (pT1135) and the infarct size were measured to evaluate S6K1 activity. In the PF-4708671 treated rats, the K_i of the ischemic-reperfused cortex was lower than the untreated rats (-22%, P < 0.05) and the volume of dextran distribution was significantly lower in most brain regions. With PF-4708671, a significant decrease in pT1135 Rictor was observed and the percentage of cortical infarct out of total cortical area was decreased (11.6 ± 2.0% vs 7.2 ± 1.1%, P < 0.0001). Our data demonstrate that PF-4708671 decreased the size of the cortical infarct in the ischemic-reperfused cortex with a decrease in BBB disruption suggesting that inhibition of S6K1 may induce neuronal survival in early cerebral ischemia-reperfusion and that a decrease of BBB disruption could be one of the contributing factors.

Environmental hypoxia favors myoblast differentiation and fast phenotype but blunts activation of protein synthesis after resistance exercise in human skeletal muscle

We hypothesized that a single session of resistance exercise performed in moderate hypoxic (FiO₂: 14%) environmental conditions would potentiate the anabolic response during the recovery period spent in normoxia. Twenty subjects performed a 1-leg knee extension session in normoxic or hypoxic conditions. Muscle biopsies were taken 15 min and 4 h after exercise in the vastus lateralis of the exercised and the nonexercised legs. Blood and saliva samples were taken at regular intervals before, during, and after the exercise session. The muscle fractional-protein synthetic rate was determined by deuterium incorporation into proteins, and the protein-degradation rate was determined by methylhistidine release from skeletal muscle. We found that: 1) hypoxia blunted the activation of protein synthesis after resistance exercise; 2) hypoxia down-regulated the transcriptional program of autophagy; 3) hypoxia regulated the expression of genes involved in glucose metabolism at rest and the genes involved in myoblast differentiation and fusion and in muscle contraction machinery after exercise; and 4) the hypoxia-inducible factor-1α pathway was not activated at the time points studied. Contrary to our hypothesis, environmental hypoxia did not potentiate the short-term anabolic response after resistance exercise, but it initiated transcriptional regulations that could potentially translate into satellite cell incorporation and higher force production in the long term.-Gnimassou, O., Fernández-Verdejo, R., Brook, M., Naslain, D., Balan, E., Sayda, M., Cegielski, J., Nielens, H., Decottignies, A., Demoulin, J.-B., Smith, K., Atherton, P. J., Fancaux, M., Deldicque, L. Environmental hypoxia favors myoblast differentiation and fast phenotype but blunts activation of protein synthesis after resistance exercise in human skeletal muscle.

Isorhamnetin Inhibits Reactive Oxygen Species-Dependent Hypoxia Inducible Factor (HIF)-1α Accumulation

Isorhamnetin is a flavonoid metabolite of quercetin and isolated from water dropwort (Oenanthe javanica, Umbelliferae). It has been reported that isorhamnetin exerts beneficial effects including antioxidant, anti-inflammatory, and anti-proliferative activities. The present study investigated whether the antioxidant activity of isorhamnetin is correlated with its anti-cancer effects on colorectal cancer cells. Isorhamnetin significantly repressed cobalt chloride (CoCl₂)- or hypoxia-induced hypoxia inducible factor-1α (HIF-1α) accumulation in HCT116 and HT29 cells. When compared with quercetin, isorhamnetin showed potent inhibition of HIF-1α. Moreover, it inhibited CoCl₂-induced activity of hypoxia response element reporter gene and HIF-1α-dependent transcription of genes such as glucose transporter 1, lactate dehydrogenase A, carbonic anhydrase-IX, and pyruvate dehydrogenase kinase 1. Isorhamnetin also blocked hydrogen peroxide (H₂O₂)-induced HIF-1α accumulation. The antioxidant effects of isorhamnetin were confirmed by observation of CoCl₂- or H₂O₂-induced reactive oxygen species (ROS) production. Consistently, overexpressed HIF-1α was decreased by isorhamnetin or N-acetyl-L-cysteine in HEK293 cells. In vitro migration and invasion assay further confirmed the inhibitory effects of isorhamnetin on cancer cells. Collectively, these results demonstrate that isorhamnetin inhibits ROS-mediated HIF-1α accumulation, which contributes to its anti-metastatic efficacy.

5-Fluorouracil inhibits cell migration by induction of Sestrin2 in colon cancer cells

5-Fluorouracil (5-FU) is a chemotherapeutic agent used in the treatment of colorectal cancer. In this study, we investigated whether 5-FU induces Sestrin2 (SESN2), an antioxidant enzyme, and the role of SESN2 in 5-FU action in colon cancer cells. We found that 5-FU upregulated SESN2 protein expression in both HCT116 and HT29 cells. It also increased transcripts of SESN1 and SESN2, but not of SESN3. Furthermore, we investigated whether production of reactive oxygen species (ROS) was involved in 5-FU-induced SESN2 expression. 5-FU did not increase ROS production nor affect Nrf2 phosphorylation and expression levels. Moreover, SESN2 upregulation by 5-FU was not prevented by pretreatment with antioxidants. Next, we investigated p53 levels after 5-FU treatment to elucidate the regulation of SESN2 by 5-FU. An increase in p53 levels was detected following 5-FU treatment; pifithrin-α, an inhibitor of p53 activation, reversed 5-FU-induced SESN2 expression. 5-FU prevented serum-induced in vitro cell migration, but knockdown of SESN2 or treatment with pifithrin-α reversed a 5-FU-mediated decrease in cell migration. Taken together, our results suggest that 5-FU increases SESN2 levels via a p53-dependent pathway, which contributes to inhibition of cancer cell migration in vitro.

Sestrin2 inhibits hypoxia-inducible factor-1α accumulation via AMPK-mediated prolyl hydroxylase regulation

Sestrin2 (SESN2) is an antioxidant protein that modulates cellular redox homeostasis through regeneration of peroxiredoxins. It has beneficial effects in oxidative or metabolic stress conditions as an upstream regulator of AMP-activated protein kinase (AMPK). Since hypoxia causes oxidative and metabolic stress, this study investigated the effect of SESN2 on signaling pathways altered by hypoxia in colon cancer cells. SESN2 overexpression in HEK293 cells inhibited hypoxia-inducible factor-1α (HIF-1α), which plays a crucial role in tumor growth and development in hypoxia. Moreover, infection with adenovirus-SESN2 (Ad-SESN2) decreased hypoxia or CoCl₂-induced HIF-1α accumulation in colorectal cancer cells. Ad-SESN2 also reduced CoCl₂-induced hypoxia response element (HRE)-luciferase activity and mRNA level of HIF-1α-driven genes. Furthermore, Ad-SESN2 infected cells showed anti-metastatic effects in serum-induced cell migration and invasion in vitro. Ad-SESN2 facilitated the ubiquitination of HIF-1α protein and increased hydroxyl-HIF-1α (OH-HIF-1α) level. In contrast, treatment with dimethyloxalylglycine (DMOG), an inhibitor of prolyl hydroxylase (PHD), reversed Ad-SESN2-induced OH-HIF-1α and subsequently suppressed HIF-1α level. The inhibitory effects of SESN2 on the serum-induced in vitro cell migration and invasion were also abrogated by DMOG treatment. Furthermore, knockdown of AMPKα reversed Ad-SESN2-mediated increase of OH-HIF-1α and inhibition of HIF-1α. Dominant-negative form of AMPK also restored the Ad-SESN2 mediated decrease in HIF-1α accumulation. Lastly, Ad-SESN2 suppressed tumor growth in a mouse xenograft model. Taken together, these results suggest that SESN2 increases degradation of HIF-1α via AMPK-PHD regulation that contributes to inhibition of in vitro and in vivo tumorigenesis.

Synthesis and biological evaluation of 1,2-dithiol-3-thiones and pyrrolo[1,2-a]pyrazines as novel hypoxia inducible factor-1 (HIF-1) inhibitor

Hypoxia-inducible factor-1 (HIF-1) is a key transcription factor which is strongly associated with tumor survival, progression, and therapeutic resistance. Accordingly, it has been suggested that the inhibition of the HIF-1 pathway can suppress tumor, and it has become an important therapeutic target. In present study, oltipraz, its metabolite M2, and their derivatives were synthesized and evaluated as HIF-1α inhibitors. Among the synthesized, benzyl-substituted pyrrolo[1,2-a]pyrazine 2g most potently inhibited HIF-1α protein accumulation (81% at 10μM) and VEGF, GLUT-1 transcription (77% and 92% at 10μM, respectively).

p70 Ribosomal protein S6 kinase (Rps6kb1): an update

The Rps6kb1 gene encodes the 70 kDa ribosomal protein S6 kinase (p70S6K), which is a serine/threonine kinase regulated by phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway. p70S6K plays a crucial role in controlling cell cycle, growth and survival. The PI3K/mTOR signalling pathway is one of the major mechanisms for controlling cell survival, proliferation and metabolism and is the central regulator of translation of some components of protein synthesis system. Upon activation, this kinase phosphorylates S6 protein of ribosomal subunit 40S resulting in selective translation of unique family of mRNAs that contain oligopyrimidine tract on 5' transcriptional site (5'TOP). 5'TOP mRNAs are coding the components of translational apparatus including ribosomal proteins and elongation factors. Due to the role of p70S6K in protein synthesis and also its involvement in a variety of human diseases ranging from diabetes and obesity to cancer, p70S6K is now being considered as a new therapeutic target for drug development. Furthermore, p70S6K acts as a biomarker for response to immunosuppressant as well as anticancer effects of inhibitors of the mTOR. Because of the narrow therapeutic index of mTOR inhibitors, drug monitoring is essential, and this is usually done by measuring blood drug levels, therapeutic response and drug-induced adverse effects. Recent studies have suggested that plasma p70S6K is a reliable index for the monitoring of patient response to mTOR inhibitors. Therefore, a better understanding of p70S6K and its role in various pathological conditions could enable the development of strategies to aid diagnosis, prognosis and treatment schedules.

Targeting GRP78 and antiestrogen resistance in breast cancer

Breast cancer is the most prevalent cancer in women, with over 200,000 new cases diagnosed each year. Over 70% of breast cancers express the estrogen receptor-α, and drugs targeting these receptors such as tamoxifen or Faslodex(®) often fail to cure these patients. Many estrogen receptor-positive tumors lose drug sensitivity, making endocrine resistance a major clinical problem. Recently, investigation into the molecular mechanisms of endocrine resistance has highlighted a causative role of the unfolded protein response in antiestrogen resistance. In particular, the master regulator of the unfolded protein response, GRP78, was observed to be elevated in endocrine-resistant breast cancer and directly affected antiestrogen therapy responsiveness. GRP78 was found to impact many different cellular processes that may affect breast cancer survival. Recently, various compounds have been reported to affect GRP78 activity and it may be advantageous to combine these drugs with antiestrogens to overcome endocrine therapy resistance.

Curcumin attenuates radiation-induced inflammation and fibrosis in rat lungs

A beneficial radioprotective agent has been used to treat the radiation-induced lung injury. This study was performed to investigate whether curcumin, which is known to have anti-inflammatory and antioxidant properties, could ameliorate radiation-induced pulmonary inflammation and fibrosis in irradiated lungs. Rats were given daily doses of intragastric curcumin (200 mg/kg) prior to a single irradiation and for 8 weeks after radiation. Histopathologic findings demonstrated that macrophage accumulation, interstitial edema, alveolar septal thickness, perivascular fibrosis, and collapse in radiation-treated lungs were inhibited by curcumin administration. Radiation-induced transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF) expression, and collagen accumulation were also inhibited by curcumin. Moreover, western blot analysis revealed that curcumin lowered radiation-induced increases of tumor necrosis factor-α (TNF-α), TNF receptor 1 (TNFR1), and cyclooxygenase-2 (COX-2). Curcumin also inhibited the nuclear translocation of nuclear factor-κ B (NF-κB) p65 in radiation-treated lungs. These results indicate that long-term curcumin administration may reduce lung inflammation and fibrosis caused by radiation treatment.

Effect of acute environmental hypoxia on protein metabolism in human skeletal muscle

Hypoxia-induced muscle wasting has been observed in several environmental and pathological conditions. However, the molecular mechanisms behind this loss of muscle mass are far from being completely elucidated, certainly in vivo. When studying the regulation of muscle mass by environmental hypoxia, many confounding factors have to be taken into account, such as decreased protein ingestion, sleep deprivation or reduced physical activity, which make difficult to know whether hypoxia per se causes a reduction in muscle mass.

AIM

We hypothesized that acute exposure to normobaric hypoxia (11% O2 ) would repress the activation of the mTOR pathway usually observed after a meal and would activate the proteolytic pathways in skeletal muscle.

METHODS

Fifteen subjects were exposed passively for 4 h to normoxic and hypoxic conditions in a random order after consumption of a light breakfast. A muscle biopsy and a blood sample were taken before, after 1 and 4 h of exposure.

RESULTS

After 4 h, plasma insulin concentration and the phosphorylation state of PKB and S6K1 in skeletal muscle were higher in hypoxia than in normoxia (P < 0.05). At the same time, Redd1 mRNA level was upregulated (P < 0.05), whilst MAFbx mRNA decreased (P < 0.05) in hypoxia compared with normoxia. Proteasome, cathepsin L and calpain activities were not altered by environmental hypoxia.

CONCLUSION

Contrary to our hypothesis and despite an increase in the mRNA level of Redd1, an inhibitor of the mTORC1 pathway, short-term acute environmental hypoxia induced a higher response of PKB and S6K1 to a meal, which may be due to increased plasma insulin concentration.

Apolipoprotein A-I mimetic peptides inhibit expression and activity of hypoxia-inducible factor-1α in human ovarian cancer cell lines and a mouse ovarian cancer model

Our previous results demonstrated that the apolipoprotein A-I (apoA-I) mimetic peptides L-4F and L-5F inhibit vascular endothelial growth factor production and tumor angiogenesis. The present study was designed to test whether apoA-I mimetic peptides inhibit the expression and activity of hypoxia-inducible factor-1α (HIF-1α), which plays a critical role in the production of angiogenic factors and angiogenesis. Immunohistochemistry staining was used to examine the expression of HIF-1α in tumor tissues. Immunoblotting, real-time polymerase chain reaction, immunofluorescence, and luciferase activity assays were used to determine the expression and activity of HIF-1α in human ovarian cancer cell lines. Immunohistochemistry staining demonstrated that L-4F treatment dramatically decreased HIF-1α expression in mouse ovarian tumor tissues. L-4F inhibited the expression and activity of HIF-1α induced by low oxygen concentration, cobalt chloride (CoCl(2), a hypoxia-mimic compound), lysophosphatidic acid, and insulin in two human ovarian cancer cell lines, OV2008 and CAOV-3. L-4F had no effect on the insulin-induced phosphorylation of Akt, but inhibited the activation of extracellular signal-regulated kinase and p70s6 kinase, leading to the inhibition of HIF-1α synthesis. Pretreatment with L-4F dramatically accelerated the proteasome-dependent protein degradation of HIF-1α in both insulin- and CoCl(2)-treated cells. The inhibitory effect of L-4F on HIF-1α expression is in part mediated by the reactive oxygen species-scavenging effect of L-4F. ApoA-I mimetic peptides inhibit the expression and activity of HIF-1α in both in vivo and in vitro models, suggesting the inhibition of HIF-1α may be a critical mechanism responsible for the suppression of tumor progression by apoA-I mimetic peptides.