Ribavirin-induced resistance to heat shock, inhibition of the Ras-Raf-1 pathway and arrest in G(1)

Targeting EIF4E signaling with ribavirin in infant acute lymphoblastic leukemia

The poor outcomes in infant acute lymphoblastic leukemia (ALL) necessitate new treatments. Here we discover that EIF4E protein is elevated in most cases of infant ALL and test EIF4E targeting by the repurposed antiviral agent ribavirin, which has anticancer properties through EIF4E inhibition, as a potential treatment. We find that ribavirin treatment of actively dividing infant ALL cells on bone marrow stromal cells (BMSCs) at clinically achievable concentrations causes robust proliferation inhibition in proportion with EIF4E expression. Further, we find that ribavirin treatment of KMT2A-rearranged (KMT2A-R) infant ALL cells and the KMT2A-AFF1 cell line RS4:11 inhibits EIF4E, leading to decreases in oncogenic EIF4E-regulated cell growth and survival proteins. In ribavirin-sensitive KMT2A-R infant ALL cells and RS4:11 cells, EIF4E-regulated proteins with reduced levels of expression following ribavirin treatment include MYC, MCL1, NBN, BCL2 and BIRC5. Ribavirin-treated RS4:11 cells exhibit impaired EIF4E-dependent nuclear to cytoplasmic export and/or translation of the corresponding mRNAs, as well as reduced phosphorylation of the p-AKT1, p-EIF4EBP1, p-RPS6 and p-EIF4E signaling proteins. This leads to an S-phase cell cycle arrest in RS4:11 cells corresponding to the decreased proliferation. Ribavirin causes nuclear EIF4E to re-localize to the cytoplasm in KMT2A-AFF1 infant ALL and RS4:11 cells, providing further evidence for EIF4E inhibition. Ribavirin slows increases in peripheral blasts in KMT2A-R infant ALL xenograft-bearing mice. Ribavirin cooperates with chemotherapy, particularly L-asparaginase, in reducing live KMT2A-AFF1 infant ALL cells in BMSC co-cultures. This work establishes that EIF4E is broadly elevated across infant ALL and that clinically relevant ribavirin exposures have preclinical activity and effectively inhibit EIF4E in KMT2A-R cases, suggesting promise in EIF4E targeting using ribavirin as a means of treatment.

Ribavirin as a potential therapeutic for atypical teratoid/rhabdoid tumors

Atypical teratoid/rhabdoid tumors (AT/RT) are highly aggressive, malignant tumors and are the most common malignant brain tumor in children under 6 months of age. Currently, there is no standard treatment for AT/RT. Recent studies have reported potential anti-tumoral properties of ribavirin, a guanosine analog and anti-viral molecule approved by the Food and Drug Administration for treatment of hepatitis C. We previously demonstrated that ribavirin inhibited glioma cell growth in vitro and in vivo. Based on these results and the fact that no pre-clinical model of ribavirin in AT/RT exists, we decided to investigate the effect of ribavirin on several human AT/RT cell lines (BT12, BT16, and BT37) both in vitro and in vivo. We provide evidence that ribavirin has a significant impact on AT/RT cell growth and increases cell cycle arrest and cell death, potentially through modulation of the eIF4E and/or EZH2 pathways. Interestingly, using scratch wound and transwell Boyden chamber assays, we observed that ribavirin also impairs AT/RT cell migration, invasion, and adhesion. Finally, we demonstrate that ribavirin significantly improves the survival of mice orthotopically implanted with BT12 cells. Our work establishes that ribavirin is effective against AT/RT by decreasing tumoral cell growth and dissemination and could represent a new therapeutic option for children with this deadly disease.

Chromosomal instability and cytotoxicity induced by ribavirin: comparative analysis in cell lines with different drug-metabolizing profiles

Ribavirin is an important component of the treatment for hepatitis C virus (HCV) infection and, in combination with the new direct-acting antiviral (DAA) agents, comprises the major current therapeutic regimens. This study evaluated the cytotoxicity and chromosomal instability induced by ribavirin using the in vitro cytokinesis-block micronucleus cytome (CBMN-Cyt) assay in two cell lines with different expression levels of drug-metabolizing enzymes: human hepatocellular carcinoma cells (HepG2) and Chinese hamster ovary (CHO-K1) cells. HepG2 cells were treated with nine concentrations (from 15.3 μg/ml to 3.9 mg/ml) and CHO-K1 cells were exposed to eight concentrations (from 15.3 μg/ml to 1.9 mg/ml) of ribavirin for 24 h. Ribavirin inhibited cell proliferation in both cell lines, but at different concentrations: 3.9 mg/ml in HepG2 and 244.2 μg/ml in CHO-K1 cells. No significant differences were observed regarding aspects of cell death in HepG2 and CHO-K1 cells, reflecting the absence of cytotoxic effects associated to ribavirin. Ribavirin did not increase the frequency of nucleoplasmic bridges (NPBs) and nuclear bud (NBUD). However, when compared to the negative control, a significant increase in micronuclei (MNi) frequency was observed in both cell lines. However, chromosomal instability was induced by higher concentrations of ribavirin in HepG2 cells (from 61.1 to 976.8 μg/ml), compared with CHO-K1 cells (15.3 and 30.5 μg/ml). These results demonstrate the potential of ribavirin to promote chromosomal instability, and suggest that cells with different expressions of drug-metabolizing enzymes show different susceptibility to ribavirin effects.

Low-dose ribavirin treatments attenuate neuroinflammatory activation of BV-2 Cells by interfering with inducible nitric oxide synthase

Microglia play a key role in defending central nervous system from various internal and external threats. However, their excessive and/or chronic activation is associated with deleterious effects in a variety of neurodegenerative diseases. Previously, we have shown that ribavirin when applied in clinically relevant dosage (10 μM) modulates activated microglia in complex fashion inducing both anti- and proinflammatory effects, simultaneously causing cytotoxicity. Here, we examined potential of low-dose ribavirin (0.1 and 1 μM) to modulate activated BV-2 microglia. Morphological and functional activation of BV-2 cells was achieved with lipopolysaccharide (LPS) stimulation. Our results demonstrated that low-dose ribavirin did not induce cell death, while 10 μM ribavirin promoted LPS induced apoptosis. We determined that 1 μM ribavirin was equally efficient in deactivation of LPS induced morphological changes as 10 μM ribavirin treatment. Ribavirin showed halfway success in reducing markers of functional activation of microglia. Namely, none of the doses had effect on LPS triggered production of proinflammatory cytokine tumor necrosis factor alpha. On the other hand, low-dose ribavirin proved its effectiveness in reduction of another inflammatory mediator, nitric oxide, by inhibiting inducible form of nitric oxide synthase. Our results imply that low-dose ribavirin may alleviate nitrosative stress during neuroinflammation.

Efficacy of ribavirin against malignant glioma cell lines

Ribavirin (1-β-D-ribofuranosy-1,2,4-triazole-3-carboxamide) has been widely administered as an antiviral agent against RNA and DNA viruses. Ribavirin, in combination with interferon, has predominantly been applied in the treatment of the hepatitis C virus infection and its potential antitumor efficacy has recently become a point of interest. The aim of the present study was to evaluate the effect of ribavirin on the growth of malignant glioma cells, to identify novel predictive genes in malignant glioma cells (by analyzing gene expression profiles) and to assess the influence of ribavirin on the cell cycle of malignant glioma cells. The present study evaluated the antitumor efficacy of ribavirin against various malignant glioma cell lines (A-172, AM-38, T98G, U-87MG, U-138MG, U-251MG and YH-13). After culturing the cells in ribavirin-containing culture medium (final concentration, 0–1,000 μM) for 72 h, the viable proliferated cells were harvested and counted. The half maximal inhibitory concentration of ribavirin, with regard to the growth of the malignant glioma cell lines, was determined from the concentration of ribavirin required for 50% growth inhibition in comparison to the untreated control cells. Furthermore, the current study identified the genes in which the gene expression levels correlated with the ribavirin sensitivity of the malignant glioma cells lines, using a high-density oligonucleotide array. Finally, cell cycle analysis was performed on the U-87MG cell line. It was identified that ribavirin inhibited the growth of all of the malignant glioma cell lines in a dose-dependent manner, although the ribavirin sensitivity varied between each cell line. Of the extracted genes, PDGFRA demonstrated the strongest positive correlation between gene expression level and ribavirin sensitivity. Cell cycle analysis of the U-87MG cell line demonstrated that ribavirin treatment induces G0/G1 arrest and thus may be an effective agent for inhibiting malignant glioma cell growth. Therefore, the results of the current study indicate that ribavirin may have potential as a therapeutic agent in the treatment of malignant gliomas.

Interferon alpha and ribavirin collaboratively regulate p38 mitogen-activated protein kinase signaling in hepatoma cells

Signaling events triggered by interferon alpha (IFN-α) and ribavirin are involved in anti-hepatitis C virus (HCV) action. The p38 mitogen-activated protein kinase (MAPK) pathway plays an important role in HCV pathogenesis. Effects of IFN-α and ribavirin on p38 MAPK signaling were investigated in human hepatoma cells. Type I IFN receptor 2 (IFNAR2) mediated IFN-α-induced p38 MAPK phosphorylation. Also, p38 MAPK phosphorylation was enhanced by ribavirin. Treatment for 48 h with a combination of IFN-α and ribavirin increased p38 MAPK phosphorylation, whereas the treatment for 72 h reduced p38 MAPK phosphorylation. Cell culture-derived HCV (HCVcc) infection dramatically increased p38 MAPK phosphorylation and such phosphorylation was inhibited by IFN-α or ribavirin. Moreover, siRNA-mediated knockdown of p38 MAPK resulted in enhancement of ribavirin-dependent HCV RNA replication. These results suggest that regulation of p38 MAPK signaling by IFN-α and ribavirin might contribute to anti-HCV action.

Interference with ERK and STAT signaling pathways and inhibition of hepatitis C virus replication by ribavirin

Ribavirin in combination with interferon (IFN)-α is the approved treatment for hepatitis C virus (HCV) infection. Interference of ribavirin with signaling events is involved in its biological activities. However, little is known of signaling pathways induced by ribavirin following HCV infection. In human hepatoma cells, effects of ribavirin on ERK and signal transducers and activators of transcription (STAT) pathways, HCV replication, and antiviral gene expression were evaluated before and after cell culture-derived HCV infection. Ribavirin reduced phosphorylation of Raf, MEK, ERK, Tyk2, and STAT1, but selectively increased STAT3 phosphorylation. IFN-α synergistically regulated ERK and STAT3 phosphorylation with ribavirin, and up-regulated expression and phosphorylation of STAT1. Ribavirin dose-dependently decreased HCV RNA replication and HCV protein expression, with slight induction of IFN regulatory factor 9 and IFN-stimulated gene 15. Ribavirin and IFN-α exerted a synergetic inhibitory effect on HCV. ERK and STAT pathways were down-regulated by ribavirin following HCV infection. These results suggest that ribavirin may mediate anti-HCV activity through interference with ERK and STAT pathways.

Mycophenolic acid inhibits oleic acid-induced vascular smooth muscle cell activation by inhibiting cellular reactive oxygen species

BACKGROUND

Vascular smooth muscle cell (VSMC) proliferation and matrix protein accumulation play important roles in the development and progression of chronic allograft vasculopathy. Mycophenolic acid (MPA) inhibits various types of mesenchymal cell proliferation and cellular reactive oxygen species (ROS) are involved in the anti-proliferative effect of MPA. In this study, we investigated the effects of MPA on oleic acid (OA)-induced VSMC proliferation and the role of ROS in this process.

METHODS

Primary VSMCs from Sprague-Dawley rats were stimulated with 100 microM OA, with or without MPA (0.1- 10 microM) or 5 mM N-acetylcysteine (NAC) for one hour prior to the addition of OA. Cell proliferation was measured by methylthiazoletetrazolium (MTT) assays, proliferating cell nuclear antigen (PCNA) expression, and fibronectin secretion by Western blot analysis, and dichlorofluorescein (DCF)-sensitive cellular ROS by fluorescence-activated cell scanning (FACS).

RESULTS

OA (100 microM) increased cell proliferation, as measured by MTT (by 1.6-fold), PCNA expression, fibronectin secretion, and cellular ROS (by 1.6-fold). Treatment with MPA dose-dependently inhibited OA-induced VSMC proliferation, fibronectin secretion, and cellular ROS. Treatment with 5 mM NAC also inhibited OA-induced rat VSMC activation.

CONCLUSIONS

These results suggest that MPA inhibits OA-induced VSMC proliferation and matrix protein synthesis partially by inhibiting cellular ROS.

Downregulation of glial scarring after brain injury: the effect of purine nucleoside analogue ribavirin

The weak regenerative capacity of self-repair after injury to the adult brain is caused by the formation of glial scar due to reactive astrogliosis. In the present study the beginning of reactive astrogliosis in the adult, as shown immunocytochemically by upregulation of glial fibrillary acidic protein (GFAP) and vimentin, was seen two days after the left sensorimotor cortex lesion, being maximal during the first two weeks and declining by 30 days after the lesion. This was accompanied by intensive glial scarring. Conversely, after the neonatal lesion a lack of gliotic scar was seen until 30 days postsurgery, although the pattern of GFAP and vimentin expression during recovery period was the same. The aim of the study was to define an appropriate therapeutic intervention that could modulate astrocyte proliferation and diminish glial scar formation after adult brain lesion. For this purpose the effects of an antiproliferative agent, the purine nucleoside analogue ribavirin was examined. It was shown that daily injection of ribavirin for 5 and 10 days considerably decreased the number of reactive astrocytes, while slight GFAP labeling was restricted to the lesion site. Obtained results show that ribavirin treatment downregulates the process of reactive astrogliosis after adult brain injury, and thus may be a useful approach for improving neurological recovery from brain damage.

Mycophenolic acid inhibits mesangial cell activation through p38 MAPK inhibition

Mesangial cell (MC) proliferation and extracellular matrix (ECM) accumulation are major pathologic features of chronic renal disease including chronic allograft nephropathy (CAN). Mycophenolic acid (MPA), a potent immunosuppressant, has emerged as a treatment to prevent CAN because it inhibits MC proliferation and ECM synthesis, but the mechanism involved has not been clarified. The present study examined relative role of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (p38 MAPK) activation in inhibitory effect of MPA on MC activation. Growth arrested and synchronized primary rat MC (passages 7-11) were stimulated by PDGF 10 ng/ml in the presence and absence of clinically attainable dose of MPA (0-10 microM). Cell proliferation was assessed by [(3)H]thymidine incorporation, fibronectin and the activation of ERK and p38 MAPK by Western blot analysis, and total collagen by [(3)H]proline incorporation. PDGF increased cell proliferation by 4.6-fold, fibronectin secretion by 3.2-fold, total collagen synthesis by 1.8-fold, and the activation of ERK and 38 MAPK by 5.6-fold and 3.1-fold, respectively, compared to control. MPA, at doses inhibiting PDGF-induced MC proliferation and ECM synthesis, effectively blocked p38 MAPK activation but reduced ERK activation by 23% at maximal concentration tested (10 microM). Exogenous guanosine partially reversed the inhibition of MPA on p38 MAPK activation. Inhibitor of ERK or p38 MAPK suppressed PDGF-induced MC proliferation and ECM synthesis. In conclusion, MPA inhibits p38 MAPK activation leading to inhibiting proliferation and ECM synthesis in MC. Guanosine reduction is partially responsible for inhibitory effect of MPA on p38 MAPK activation in MC.

Therapeutic effect of nucleoside analogs on experimental autoimmune encephalomyelitis in dark agouti rats

Experimental autoimmune encephalomyelitis (EAE) is a commonly used animal model of the human neurological disorder multiple sclerosis. The purpose of the present study was to investigate the effect of combined treatment with two nucleoside analogs, ribavirin and tiazofurin, on development of EAE actively induced in highly susceptible dark agouti rats. The obtained results showed that ribavirin and tiazofurin applied either separately or in combination from the onset of the firstsymptoms of EAE after its induction (therapeutic treatment) significantly suppressed EAE?s clinical symptoms. However, the most pronounced effect was gained with combined treatment, probably as a result of synergistic/additive action.

p53-independent induction of p21(waf1/cip1) contributes to the activation of caspases in GTP-depletion-induced apoptosis of insulin-secreting cells

We investigated the role of some key regulators of cell cycle in the activation of caspases during apoptosis of insulin-secreting cells after sustained depletion of GTP by a specific inosine 5'-monophosphate dehydrogenase inhibitor, mycophenolic acid (MPA). p21(Waf1/Cip1) was significantly increased following MPA treatment, an event closely correlated with the time course of caspase activation under the same conditions. MPA-induced p21(Waf1/Cip1) was not mediated by p53, since p53 mass was gradually reduced over time of MPA treatment. The increment of p21(Waf1/Cip1) by MPA was further enhanced in the presence of a pan-caspase inhibitor, indicating that the increased p21(Waf1/Cip1) may occur prior to caspase activation. This notion of association of p21(Waf1/Cip1) accumulation with caspase activation and apoptosis was substantiated by using mimosine, a selective p21(Waf1/Cip1) inducer independent of p53. Mimosine, like MPA, also increased p21(Waf1/Cip1), promoted apoptosis and simultaneously increased the activity of caspases. Furthermore, knocking down of p21(Waf1/Cip1) transfection of siRNA duplex inhibited caspase activation and apoptosis due to GTP depletion. In contrast to p21(Waf1/Cip1), a reduction in p27(Kip1) occurred in MPA-treated cells. These results indicate that p21(Waf1/Cip1) may act as an upstream signal to block mitogenesis and activate caspases which in turn contribute to induction of apoptosis.

Mycophenolic acid inhibits activation of inducible nitric oxide synthase in rodent fibroblasts

Mycophenolate mofetil (MMF) is an immunosuppressive drug that acts as a selective inhibitor of inosine monophosphate dehydrogenase (IMPDH). MMF has recently been shown to inhibit the enzymatic activity of inducible NO synthase (iNOS) and subsequent production of the cytotoxic free radical nitric oxide (NO) in endothelial cells. We here investigated the effect of bioactive MMF compound mycophenolic acid (MPA) on iNOS-mediated NO synthesis in fibroblasts, which are important source of NO in rheumatoid arthritis and during rejection of solid organ transplants. MPA exerted dose-dependent inhibition of NO synthesis, measured as nitrite accumulation, in IFN-gamma + LPS-stimulated L929 mouse fibroblast cell line and rat primary fibroblasts. The effect of MPA was not mediated through interference with IMPDH-dependent synthesis of iNOS co-factor BH4 and subsequent suppression of iNOS enzymatic activity, as direct BH4 precursor sepiapterin failed to block the action of the drug. MPA suppressed the IFN-gamma + LPS-induced expression of fibroblast iNOS protein, as well as mRNA for iNOS and its transcription factor IRF-1, as assessed by cell-based ELISA and semiquantitative RT-PCR, respectively. MPA suppression of fibroblast NO release, iNOS, and IRF-1 activation, was efficiently prevented by exogenous guanosine, indicating that the drug acted through reduction of IMPDH-dependent synthesis of guanosine nucleotides. These results suggest that MPA inhibits NO production in fibroblasts by blocking guanosine nucleotide-dependent expression of iNOS gene, through mechanisms that might involve the interference with the induction of iNOS transcription factor IRF-1.

Immunosuppressants leflunomide and mycophenolic acid inhibit fibroblast IL-6 production by distinct mechanisms

Mycophenolic acid (MPA) and A77 1726, the active components of the immunosuppressants mycophenolate mophetil and leflunomide, respectively, in a dose-dependent manner inhibited interferon (IFN)-gamma/LPS-induced interleukin (IL)-6 release in confluent cultures of mouse L929 fibrosarcoma cells. In addition, both drugs markedly reduced the production of the free radical gas nitric oxide (NO), without affecting the viability of L929 cells. The inhibitors of NO synthase, aminoguanidine and L-NMMA, but not L-NMMA inactive counterpart D-NMMA, mimicked the effects of A77 1726 and MPA on IL-6 generation in L929 fibroblasts. Furthermore, NO-releasing substance SNP completely reverted IL-6 accumulation in L929 cultures treated with A77 1726, while only partial recovery of IL-6 production was observed in the presence of MPA. MPA, but not A77 1726, significantly suppressed NO-independent IL-6 release triggered by cAMP-elevating agent rolipram. Thus, while A77 1726 effect on IL-6 production was mediated through concomitant reduction of NO synthesis, MPA action was mainly independent of the interference with NO generation. Finally, both agents inhibited IFN-gamma/LPS-triggered IL-6 production in mouse primary fibroblasts, but not in mouse peritoneal macrophages, indicating cell-specificity of this novel anti-inflammatory action of A77 1726 and MPA.

Mycophenolic acid downregulates inducible nitric oxide synthase induction in astrocytes

Free radical nitric oxide (NO), generated by inducible nitric oxide synthase (iNOS) in astrocytes and macrophages, has been implicated in CNS inflammatory disorders such as multiple sclerosis and its animal model experimental autoimmune encephalomyelitis (EAE). Mycophenolic acid (MPA), a selective inhibitor of inosine monophosphate dehydrogenase (IMPDH), inhibited interferon-gamma (IFN-gamma) + lipopolysaccharide (LPS)-induced NO production dose-dependently in astrocytes, but not in macrophages. The effect of MPA was not mediated through interference with IMPDH-dependent synthesis of iNOS cofactor BH4 and subsequent suppression of iNOS enzymatic activity, as direct BH4 precursor sepiapterin failed to block the action of the drug. However, MPA markedly inhibited IFN-gamma + LPS-triggered astrocyte expression of mRNA for iNOS and its transcription factor IRF-1, while the expression of tumor necrosis factor-alpha (TNF-alpha) gene was not altered. The observed MPA suppression of NO release and iNOS and IRF-1 induction in astrocytes were efficiently prevented by exogenous guanosine, indicating that the drug acted through reduction of IMPDH-dependent synthesis of guanosine nucleotides. This IRF-1-dependent inhibition of iNOS activation might be partly responsible for the protective effect of MPA in EAE, prompting investigation of its potential use in multiple sclerosis.

Down-regulation of multiple low dose streptozotocin-induced diabetes by mycophenolate mofetil

The new immunosuppressive agent mycophenolate mofetil (MMF) has been shown recently to exert a protective effects in certain animal models of autoimmunity, including diabetes in diabetes-prone bio-breeding (BB) rats. In the present study, the immunomodulatory potential of MMF was investigated in autoimmune diabetes induced by multiple low doses of streptozotocin (MLD-STZ) in genetically susceptible DA rats 20 mg STZ/kg body weight (b.w.) for 5 days] and CBA/H mice (40 mg STZ/kg b.w. for 5 days). In both species, short time treatment of animals with MMF (25 mg/kg) during the early development of the disease, as well as continuous MMF treatment, prevented the appearance of hyperglycaemia and inflammatory infiltrates in the pancreatic tissue. Moreover, clinical manifestations of diabetes were suppressed by application of the drug after the onset of clinical symptoms. Treatment with guanosine (1 mg/kg) in parallel with MMF completely reversed MMF activity in vivo, indicating that inhibition of inosine monophosphate dehydrogenase (IMPDH) was responsible for the observed suppressive effects. MMF-mediated protection from diabetes correlated with reduced ex vivo spontaneous spleen mononuclear cell (MNC) proliferation and defective adhesive cell interactions. MMF-treated animals also had lower local production of IFN-gamma, as well as IL-12 and nitric oxide (NO) production by peripheral tissues (spleen and peritoneal cells), compared to that in control diabetic groups, while IL-10 level was elevated. Together, these data demonstrate that MMF interferes with autoimmune process in streptozotocin-induced diabetes at multiple levels, including lymphocyte proliferation and adhesion, as well as pro/anti-inflammatory cytokine balance.