Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Onconase, a protein with anti-tumor activity, causes potent inhibition of protein synthesis in the rabbit reticulocyte lysate (IC50 10(-11) M) and when microinjected into Xenopus oocytes (IC50 10(-10) M). Onconase is a member of the RNase A superfamily; however, unlike RNase A, the mechanism of protein synthesis inhibition does not involve apparent degradation of lysate or cellular ribosomal RNAs. Rather, reticulocyte and oocyte tRNA is hydrolyzed after Onconase treatment. Furthermore, re-addition of tRNA to Onconase pretreated lysates or oocytes restores the translational capacity of the system. Taken together these results suggest that Onconase causes potent protein synthesis inhibition by a mechanism involving inactivation of cellular tRNA.
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PMID:Characterization of the mechanism of cellular and cell free protein synthesis inhibition by an anti-tumor ribonuclease. 794 54

Onconase (ONC) a ribonuclease from amphibian oocytes is cytostatic and cytotoxic to many human tumor lines, shows in vivo antitumor activity in mouse tumor models and is in Phase III clinical trials. The mechanism of antitumor activity of ONC is presumed to be due to its internalization, degradation of intracellular RNA and suppression of protein synthesis. Since apoptosis triggered by TNF-alpha is known to be potentiated by inhibitors of protein synthesis, we have hypothesized that it also may be potentiated by ONC. Indeed, preincubation of U-937 or HL-60 leukemic cells with 0.17 microM ONC rendered them more sensitive to induction of apoptosis by TNF-alpha or antibody to CD95 (Fas). The mechanism by which ONC amplifies the effect of TNF-alpha may involve suppression of induction of the survival genes whose expression is triggered by activation of NFkB by this factor.
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PMID:Potentiation of tumor necrosis factor induced apoptosis by onconase. 962 97

In proliferating cells the turnover rate of proteins responsible for regulation of the cell cycle progression, namely cyclins and inhibitors of the cyclin-dependent kinases (CDKs) and phosphatases, is rapid and their cellular level is modulated at the transcriptional, translational and/or degradation (via proteasome pathway) stages. Inhibition of proteasome function results in accumulation of rapidly turning over proteins and, thus, causes an imbalance of the cell cycle regulatory components, and loss of their regulatory function. Indeed, it has been shown that proteasome inhibitors perturb the cell cycle progression. Onconase, a novel RNase which has anti-tumor activity and is in clinical trials, has previously been shown to suppress protein synthesis, presumably by degradation of intracellular RNA, preferentially tRNA. By interfering with regulation of expression of cyclins and/or CDK-inhibitors, onconase also may induce the imbalance of these proteins and potentiate the effect of proteasome inhibitors. In the present study, we observed that the combinations of onconase with peptide-aldehyde inhibitors of calpain and proteasome such as the N-acetyl-leucinyl-leucinyl-norleucinal (LLnL) and the N-acetyl-leucinyl-valinyl-phenylalaninal (LVP), but not N-acetyl-leucinyl-leucinyl-methioninal (LLM), were synergistic in suppressing cell proliferation and inducing apoptosis in three human tumor cell lines: A-549 lung adenocarcinoma, DU-145 prostatic carcinoma, and MDA-MB-231 breast carcinoma. The observed cytotoxicity may also be a result of prevention of the induction of the 'survival' genes by the nuclear factor kappaB (NFkappaB) by onconase and proteasome inhibitors. The data indicate that such combinations should be further tested as potential anti-cancer regimens.
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PMID:Enhanced in vitro cytotoxicity and cytostasis of the combination of onconase with a proteasome inhibitor. 973 89

Microinjection of Onconase or RNase A into NIH/3T3 cells was used to study the intracellular actions of these two proteins. Onconase preferentially killed actively growing cells in both microinjection and cell culture experiments. Moreover, agents that increased the number of cells in S phase such as serum or microinjected signal transduction mediators (Ras, protein kinase C, and mitogen-activated protein kinase) enhanced Onconase cytotoxicity. Conversely, agents that decreased these proliferative pathways (dibutyryl cAMP and protein kinase A) correspondingly diminished Onconase cytotoxicity in microinjection experiments. These results were also mimicked in cell culture experiments since log-phase v-ras-transformed NIH/3T3 cells were more sensitive to Onconase (IC50 of 7 microg/ml) than parental NIH/3T3 fibroblasts (IC50 of 40 microg/ml). Based on those data we postulated that Onconase-mediated cell death in NIH/3T3 cells was related to events occurring at two or more points in the cell cycle preferentially associated with late G1/S and S phases. In contrast, quiescent NIH/3T3 cells were more sensitive to microinjected RNase A than log phase cells and positive mediators of proliferative signal transduction did not enhance RNase A-mediated cytotoxicity. Taken together, these results demonstrate that these two RNases use different pathways and/or mechanisms to elicit cytotoxic responses in NIH/3T3 cells. Predictions formulated from these studies can be tested for relevance to RNase actions in different target tumor cells.
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PMID:Cell cycle-related differences in susceptibility of NIH/3T3 cells to ribonucleases. 1004 64

Onconase, an anticancer ribonuclease, damages cellular tRNA and causes caspase-dependent apoptosis in targeted cells (M. S. Iordanov, O. P. Ryabinina, J. Wong, T. H. Dinh, D. L. Newton, S. M. Rybak, and B. E. Magun. Cancer Res. 60, 1983-1994, 2000). The proapoptotic action of onconase depends on its RNase activity, but the molecular mechanisms leading to RNA damage-induced caspase activation are completely unknown. In this study, we have investigated whether onconase activates two signal-transduction pathways commonly stimulated by conventional chemo- and radiotherapy, namely the stress-activated protein kinase (SAPK) cascade and the pathway leading to the activation of nuclear factor-kappa B (NF-kappaB). We found that, in all cell types tested, onconase is a potent activator of SAPK1 (JNK1 and JNK2) and SAPK2 (p38 MAP kinase), but that it is incapable of activating NF-kappaB. Inhibition of p38 MAP kinase activity with a pharmacological inhibitor, SB203580, demonstrated that p38 MAP kinase is not required for onconase cytotoxicity. Using explanted fibroblasts from mice that contain targeted disruption of both jnk1 and jnk2 alleles, we found that JNKs are important mediators of onconase-induced cytotoxicity. Surprisingly, following the immortalization of these same cells with human papilloma virus (HPV16) gene products E6 and E7, additional proapoptotic pathways (exclusive of JNK) were provoked by onconase. Our results demonstrate that onconase may activate proapoptotic pathways in tumor cells that are not able to be accessed in normal cells. These results present the possibility that the cytotoxic activity of onconase in normal cells may be reduced by blocking the activity of JNKs.
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PMID:Differential requirement for the stress-activated protein kinase/c-Jun NH(2)-terminal kinase in RNAdamage-induced apoptosis in primary and in immortalized fibroblasts. 1117 Aug 43

Onconase (ONC) is a ribonuclease isolated from amphibian oocytes that is cytostatic and cytotoxic to numerous tumor lines. ONC shows in vivo anti-tumor activity in mouse tumor models and is currently in Phase III clinical trials. Previous studies indicated that ONC induces apoptosis of the target cells most likely along the mitochondrial pathway involving caspase-9 as the initiator caspase. We have recently developed an approach to detect the activation of serine (Ser) proteases during apoptosis. The method is based on affinity labeling of Ser protease active centers with fluorochrome-tagged inhibitors. The aim of the present study was to reveal whether Ser proteases are activated during apoptosis induced by ONC. Human leukemic HL-60 cells were treated with ONC for up to 72 h and then exposed to 5(6)-carboxyfluoresceinyl-L-phenylalanylchloromethyl ketone (FFCK) or 5(6)-carboxyfluoresceinyl-L-leucylchloromethyl ketone (FLCK), the fluorescing green reagents reactive with active centers of the chymotrypsin-like enzymes that cleave proteins at the Phe (FFCK) or Leu (FLCK) site. Activation of caspases was assayed in the same cells using sulforhodamine-labeled (fluorescing red) pan-caspases inhibitor (SR-VAD-FMK). Administration of 1.67 microM ONC into cultures of HL-60 cells led to the appearance of cells that bound SR-VAD-FMK as well as FFCK and FLCK. Most labeled cells had features characteristic of apoptosis. We interpret the binding of these ligands, which was irreversible and withstood cell fixation, as revealing activation of caspases and chymotrypsin-like Ser proteases. Because the induction of binding of each of the three ligands occurred at approximately the same time, the data suggest that during apoptosis caspases and Ser proteases may transactivate each other. The intercellular and subcellular pattern of binding SR-VAD-FMK vs FFCK or vs FLCK was different indicating a variability in abundance and localization of these enzymes within individual apoptotic cells. The FFCK- and FLCK-reactive proteins were of similar molecular mass, approximately 59 and approximately 57 kDa, respectively.
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PMID:Activation of caspases and serine proteases during apoptosis induced by onconase (Ranpirnase). 1212 58

Onconase (Onc) is an amphibian ribonuclease of the pancreatic RNase family that is cytostatic and cytotoxic to several tumor lines. It also shows anti-tumor activity in mouse tumor models and is currently in phase III clinical trials. In animal tests and clinical trials Onc shows lesser toxicity and fewer side effects compared to most chemotherapeutic drugs. Intriguingly, repeated infusions of this protein do not cause apparent immunological reactions in patients. The aim of the present study was to investigate sensitivity to Onc of human lymphocytes during their mitogenic stimulation in response to the polyvalent mitogen phytohemagglutinin (PHA), and in mixed allogeneic lymphocyte cultures. Unexpectedly, we observed that frequency of cells undergoing activation-induced apoptosis was markedly increased in all cultures containing Onc. Apoptosis was measured by flow cytometry using markers that detect activation of caspases, the in situ presence of DNA strand breaks, and loss of fragmented DNA ('sub-G1' cell subpopulation). The enhancement of frequency of activation-induced apoptosis (up to 244%) was observed at 4.2-83 nM Onc concentration, which is at least an order magnitude lower than its minimal concentration reported to affect proliferation or induce apoptosis of leukemic and solid tumor cell lines. The cell cycle progression of lymphocytes that responded to PHA mitogenically was not affected at 8.3 or 83 nM Onc concentration. Because activation-induced apoptosis is the key mechanism regulating several in vivo immunological functions including induction of tolerance, the observed effects of Onc may explain the apparent lack of immune reactions to this protein in treated patients. The propensity of Onc to potentiate the activation-induced apoptosis suggests that this drug may have clinical utility as immunomodulating agent, e.g., to suppress transplant rejection or treat autoimmune diseases.
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PMID:Enhancement of activation-induced apoptosis of lymphocytes by the cytotoxic ribonuclease onconase (Ranpirnase). 1242 74

Onconase (rONC), otherwise known as ranpirnase or P-30 protein, which was initially purified from extracts of Rana pipiens oocytes and early embryos, exhibits anticancer activity both in vitro and in vivo and is in phase III clinical trials for tumor therapy. We have determined the solution NMR structure of a recombinant onconase with Met(-1), Gln1, and Leu23 residues (M-1, Q1, M23L)rONC. The 20 best solution structures had a backbone root mean square deviation of 0.41 +/- 0.09 A with respect to the average structure. The energy-minimized average NMR structure had a backbone root mean square deviation of 0.72 A from the x-ray crystallographic structure of native onconase; however, the orientation of the N-terminal residue in the two structures was very different. Comparison of the 15N HSQC spectrum of (M-1, Q1, M23L)rONC with that of a mutant E1S-rONC, which is identical to the nONC except with the N-terminal pyroglutamyl residue replaced by Ser, showed that N-terminal and residue 23 mutations induced structural changes in regions beyond the mutation sites. Model-free analysis of the backbone amide 15N-T1, 15N-T2, and 15N-1H NOE relaxation data for (M-1, Q1, M23L)rONC and E1S-rONC revealed that the E1S-rONC molecule showed very little flexibility, whereas (M-1, Q1, M23L)rONC exhibited substantial flexibility, which may account for the previously observed reduced stability and increased protease susceptibility. The alpha1 helix and beta-sheets of (M-1, Q1, M23L)rONC displayed bending motions. These data provided strong evidence for the presence of an N-terminal hydrogen bond network in E1S-rONC, but not in (M-1, Q1, M23L)rONC.
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PMID:Effect of N-terminal and Met23 mutations on the structure and dynamics of onconase. 1464 26

Onconase (ONC) and bovine seminal ribonuclease (BS-RNase) are homologs of bovine pancreatic ribonuclease (RNase A). Unlike RNase A, ONC and BS-RNase can evade the cytosolic ribonuclease inhibitor protein and are potent cytotoxins. Here, the endogenous cytotoxic activities of ONC and BS-RNase are compared in a wide variety of assays. Injections of ONC into one or both testes of mice and rats evokes a stronger aspermatogenic activity than does the injection of BS-RNase. Epididymides exposed to ONC lose mass and all sperm. Testicular tissue is gradually colonized by immunite and fibrocytic cells. Yet, Leydig cells are always present and functional in the ligamented parts of testicles injected with ONC or BS-RNase. ONC is likewise more toxic to mouse embryos than is BS-RNase, both in vitro and in vivo. The antiproliferative effect of ONC on human tumor cell line ML-2 and lymphocytes in a mixed lymphocyte culture is also more pronounced than is that of BS-RNase. The number of granulocyte-macrophage colony-forming units is repressed almost completely by ONC, whereas a five-fold higher dose of BS-RNase does not cause substantial inhibition. In mice, ONC is less immunogenic than BS-RNase but more immunogenic than RNase A. Together, these data indicate that ONC is a pluripotent cytotoxin, and serves as the benchmark with which to gauge the cytotoxicity of other ribonucleases.
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PMID:Comprehensive comparison of the cytotoxic activities of onconase and bovine seminal ribonuclease. 1501 6

Onconase, a ribonuclease purified from Rana pipiens oocytes, has cytotoxic activity against several tumor cell lines in vitro. With the characteristic of containing four pairs of disulfide bonds internal and N terminal sequence attributing mostly to its biological functions, it is difficult to obtain the active Onconase from Escherichia coli expression system with normal strategy. Here, we fused the cDNA coding for Onconase in frame with the pelB signal sequence in pET22b(+) expression vector. Onconase can be effectively expressed in inclusion body without additional residues at N terminal under the proper inducing condition. After refolding and purifying process, we can get the recombined Onconase which has a similar ribonuclease activity as the one isolated from oocytes. The recombined Onconase has a pronounced effect on proliferation of Hut-78 cells (IC50=0.5 micromol/L).
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PMID:[Effective expression of ribonuclease-onconase in Escherichia coli and assaying its cytotoxic potential]. 1532 25


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