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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Onconase (Ranpirnase), a novel ribonuclease isolated from Rana pipiens oocytes, was reported to suppress cancer cell growth in vitro, reduce tumor size in animals, and augment cytotoxicity of several chemotherapeutic agents. Since onconase is currently in phase III clinical trials tested in treatment of mesothelioma, much emphasis has been placed on the mechanism of its anti-tumor activity. Previous studies have shown that onconase-responsive cells become arrested at the G1/S checkpoint of the cell cycle and also undergo apoptosis. A proposed mechanism for these effects is that the enzymatic activity of onconase targets cellular RNAs, in particular tRNA, with an accompanying inhibition of protein synthesis. In the present study, we have investigated the time- and dose-dependent effects of onconase on growth of Jurkat SN acute T-lymphocytic leukemia cells. Significant suppression of cell proliferation became evident after 72 and 96 h of treatment, and was most pronounced at the highest concentration (10 microg/ml; 8.3x10(-7) M) of onconase. This reduction of cell proliferation, however, was not accompanied by measurable changes in distribution of cells at different phases of the cell cycle, but was paralleled by the induction of apoptosis, as assayed by flow cytometry, and with a modest decrease in the expression of a cell cycle regulatory retinoblastoma protein (Rb). Further biochemical analysis revealed that growth suppression was closely coordinated with a down-regulation in the steady state and subcellular distribution of NF-kappaB, a transcription factor known to be functionally associated with cell survival. The reduction in expression of NF-kappaB by onconase appeared to coincide or even precede growth suppression, suggesting a causal relationship. To further test the hypothesis that cellular localization and expression of NF-kappaB may be critical to cellular response to onconase, we also studied the growth effects of onconase in Jurkat-BalphaM cells, which, unlike the parent SN T cells, contain a stably transfected dominant-negative IkappaB gene. Growth suppression by onconase in BalphaM cells was more pronounced and occurred earlier compared to SN cells, although still did not affect changes in cell cycle phase distribution. Contrary to expectation, however, diminution in NF-kappaB expression by onconase was even more pronounced in BalphaM cells, suggesting that this transcription factor, while presumably prevented from dissociation from its inhibitory protein IkappaB in these cells, is even more efficiently targeted for degradation by onconase. These results implicate NF-kappaB and its turnover as important determinants in the anti-proliferative/apoptotic effects of onconase in acute T-lymphocytic leukemia cells.
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PMID:Treatment of Jurkat acute T-lymphocytic leukemia cells by onconase (Ranpirnase) is accompanied by an altered nucleocytoplasmic distribution and reduced expression of transcription factor NF-kappaB. 1554 13

Malignant mesothelioma is an aggressive cancer with no known cure, which has become a therapeutic challenge. Onconase is one of few chemotherapeutic agents that have been studied in patients with malignant mesothelioma that has the advantage of low toxicity and limited side effects. Here, we evaluate the effect of Onconase on killing of malignant mesothelioma cells and how the phosphatidylinositol 3-kinase/AKT (PI3-K/AKT) survival pathway influences this effect. Our results show that Onconase induces apoptosis in malignant mesothelioma cell lines and that this effect is tumor cell specific. Malignant mesothelioma cell lines with the highest AKT activation, which correlated with the presence of the SV40 large and small T antigen (SV40+), were the most resistant to the drug. Finally, a cooperative effect was observed between small molecule inhibitors of PI3-K and Onconase in the killing of malignant mesothelioma cells. Our results suggest that kinase screening of individual malignant mesotheliomas for endogenous levels of activated PI3-K/AKT may be predictive of the efficacy of Onconase and possibly other chemotherapeutic agents.
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PMID:Human mesothelioma cells exhibit tumor cell-specific differences in phosphatidylinositol 3-kinase/AKT activity that predict the efficacy of Onconase. 1589 48

Bovine seminal ribonuclease (BS-RNase) is a homologue of bovine pancreatic ribonuclease (RNase A). Unlike RNase A, BS-RNase has notable toxicity for human tumor cells. Wild-type BS-RNase is a homodimer linked by two intermolecular disulfide bonds. This quaternary structure endows BS-RNase with resistance to inhibition by the cytosolic ribonuclease inhibitor protein (RI), which binds tightly to RNase A and monomeric BS-RNase. Here, we report on the creation and analysis of monomeric variants of BS-RNase that evade RI but retain full enzymatic activity. The cytotoxic activity of these monomeric variants exceeds that of the wild-type dimer by up to 30-fold, indicating that the dimeric structure of BS-RNase is not required for cytotoxicity. Dimers of these monomeric variants are more cytotoxic than wild-type BS-RNase, suggesting that the cytotoxicity of the wild-type enzyme is limited by RI inhibition following dissociation of the dimer in the reducing environment of the cytosol. Finally, the cytotoxic activity of these dimers is less than that of the constituent monomers, indicating that their quaternary structure is a liability. These data provide new insight into structure-function relationships of BS-RNase. Moreover, BS-RNase monomers described herein are more toxic to human tumor cells than is any known variant or homologue of RNase A including Onconase, an amphibian homologue in phase III clinical trials for the treatment of unresectable malignant mesothelioma.
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PMID:Cytotoxicity of bovine seminal ribonuclease: monomer versus dimer. 1631 79

By reason of their cytotoxicity, ribonucleases (RNases) are potential anti-tumor drugs. Particularly members from the RNase A and RNase T1 superfamilies have shown promising results. Among these enzymes, Onconase, an RNase from the Northern Leopard frog, is furthest along in clinical trials. A general model for the mechanism of the cytotoxic action of RNases includes the interaction of the enzyme with the cellular membrane, internalization, translocation to the cytosol, and degradation of ribonucleic acid. The interplay of these processes as well as the role of the thermodynamic and proteolytic stability, the catalytic activity, and the capability of the RNase to evade the intracellular RNase inhibitor has not yet been fully elucidated. This paper discusses the various approaches to exploit RNases as cytotoxic agents.
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PMID:Natural and engineered ribonucleases as potential cancer therapeutics. 1690 46

Onconase (ONC), (ranpirnase) a cytotoxic ribonuclease isolated from amphibian oocytes and early embryos targeting tumor cells in vitro and in vivo, is currently in a confirmatory Phase IIIb clinical trial for unresectable malignant mesothelioma where it demonstrates antitumor activity with relatively minor overall toxicity to patients. Since hyperthermia has been shown to be synergistic with certain antitumor modalities, the aim of the present study was to explore whether the cytotoxic effects of ONC can be enhanced under conditions of mild hyperthermia. Treatment of human lymphoblastoid TK6 cells with 2 or 5 microg/ml of ONC at 40 degrees C for 24 or 48 h led to 64-200% enhancement in incidence of apoptosis assessed by frequency of cells showing the presence of activated (cleaved) caspase-3 or activated serine proteases, compared to treatment at 37.5 degrees C. The incidence of apoptosis at 40 degrees C in the absence of ONC was unchanged compared to 37.5 degrees C, for up to 48 h. Although at 41 degrees C in absence of ONC the incidence of apoptosis was elevated compared to 37 degrees C the cytotoxicity of ONC was further enhanced and the overall pro-apoptotic effect was above the level of additive effects of ONC plus that of 41 degrees C-hyperthermia. While the mechanism of the observed enhancement of ONC cytotoxicity is currently under investigation, the findings suggest that a combination of ONC and mild hyperthermia should be explored to increase effectiveness of ONC in cancer treatment.
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PMID:Mild hyperthermia predisposes tumor cells to undergo apoptosis upon treatment with onconase. 1733 22

Onconase (ONC) is a cytotoxic ribonuclease of the pancreatic ribonuclease A superfamily isolated from oocytes or early embryos of the Northern leopard frog (Rana pipiens). It shows anticancer activity and currently is in Phase IIIb clinical trial for unresectable malignant mesothelioma. We generated several variants of ONC possessing mutations in selected structural regions of the molecule that have altered ribonucleolytic activity and/or conformational stability. The relationship between the stability and ribonucleolytic activity of these variants and their cytostatic and cytotoxic properties was investigated on several tumor cell lines. Similar to ONC, all variants were inducing reproductive cell death detected by reduced clonogenicity. The surviving cells proliferated at reduced rates as reflected by diminished size of colonies and prolongation of G(0/1) phase of the cell cycle. Some cells were undergoing apoptosis. The cytotoxic and cytostatic effects of ONC and its variants were predominantly determined by their catalytic activity rather than by conformational stability.
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PMID:The interdependence between catalytic activity, conformational stability, and cytotoxicity of onconase. 1763 63

Onconase (ONC), an antitumor ribonuclease from oocytes of a frog Rana pipiens, capable of inducing apoptosis in many cell lines is synergistic with several other anticancer drugs. Since cytotoxic effects of numerous drugs are modulated by reactive oxygen intermediates (ROI), we have studied effects of ONC on the intracellular level of oxidants in several normal cell types as well as tumor cell lines. It is demonstrated for the first time that ONC substantially decreases the content of ROI in all cell lines studied. This effect depends on the ribonucleolytic activity of the enzyme and is due to both, decreased rate of ROI generation and accelerated rate of their degradation. Onconase decreases the mitochondrial transmembrane potential and consequently, generation of ATP. Simultaneously the enzyme decreases the expression of an antiapoptotic protein Bcl-2, and upregulates the proapoptotic Bax protein. These finding are consistent with the enzyme propensity to induce apoptosis. The observed antioxidant activity of ONC may be an important element of its cytotoxicity towards cancer cells. The enzyme seems to exert its biological activities by interfering with the redox system of cellular regulation.
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PMID:Onconase, an anti-tumor ribonuclease suppresses intracellular oxidative stress. 1767 95

The cytotoxic RNase, Onconase (ONC), isolated from amphibian oocytes, was used to study its effect on the radiation response in A549 human NSCLC in vitro and in vivo. In cell culture studies, we found that ONC increased the radiation response by ONC-induced inhibition of O2 consumption (QO2). The occurrence of apoptosis was increased by ONC and was dependent on dosages and time exposure (measured by a Tunnel in situ cell death detection assay). Moreover, ONC inhibited sublethal damage repair (SLDR), confirmed by a split dose experiment. In animal studies, ONC significantly increased the radiation-induced tumor growth delay of A549 tumors in vivo. Using a non-invasive DCE-MRI technology, ONC-induced changes of perfusion were observed in A549 tumors. We concluded that the ONC-induced enhancement in tumor oxygenation was mainly due to the reduction in QO2 rather than an increase in tumor blood flow. This investigation suggests important potential clinical uses of ONC for the treatment of NSCLC cancer patients.
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PMID:Possible mechanisms of improved radiation response by cytotoxic RNase, Onconase, on A549 human lung cancer xenografts of nude mice. 1772 47

Onconase (Onc), is a novel amphibian cytotoxic ribonuclease with antitumor activity, and is currently in a confirmatory phase III clinical trial for the treatment of malignant mesothelioma. It was recently reported that Rana pipiens oocytes contain still another ribonuclease, named Amphinase (Amph). Amph shows 38-40% amino acid sequence identity with onconase, presents as four variants varying between themselves from 87-99% in amino acid sequence identity and has a molecular mass approximately 13,000. In the present study we describe the effects of Amph on growth of several tumor cell lines. All four variants demonstrated cytostatic and cytotoxic activity against human promyelocytic HL-60-, Jurkat T-cell- and U-937 monocytic leukemia cells. The pattern of Amph activity to certain extent resembled that of Onc. Thus, cell proliferation was suppressed at 0.5-10.0 mug/ml (40-80 nM) Amph concentration with distinct accumulation of cells in G(1) phase of the cell cycle. In addition, the cells were undergoing apoptosis, which manifested by DNA fragmentation (presence of "sub-G1" cells, TUNEL-positivity), caspases and serine proteases activation as well as activation of transglutaminase. The cytostatic and cytotoxic effects of Amph required its ribonuclease activity: the enzymatically inactive Amph-2 having histidine at the active site alkylated was ineffective. The effectiveness and cell cycle specificity was generally similar for all four Amph variants and at the equimolar concentrations was somewhat more pronounced than that of Onc. The observed cytostatic and cytotoxic activity of Amph against tumor cell lines suggests that similar to Onc this cytotoxic ribonuclease may have antitumor activity and find an application in clinical oncology.
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PMID:Cytostatic and cytotoxic properties of Amphinase: a novel cytotoxic ribonuclease from Rana pipiens oocytes. 1807 26

Onconase (Onc), a ribonuclease from oocytes or early embryos of Northern Leopard frog (Rana pipiens), is cytostatic and cytotoxic to a variety of tumor lines in vitro, inhibits growth of tumors in animal in vivo models and is currently in Phase IIIb clinical trials for malignant mesothelioma where it displays antitumor activity with minor overall toxicity to the patient. One of the characteristic features of Onc is a synergism with a variety of other antitumor modalities. Cepharanthine (Cep), a biscoclaurine alkaloid from Stephania cepharantha Hayata, is widely used in Japan to treat variety of ailments. It also shows low toxicity to patients. The aim of the present study was to assess the interaction of these two drugs on different tumor cell lines. When human promyelocytic leukemia HL-60, histiomonocytic lymphoma U937, multiple myeloma RPMI-8228, prostate carcinoma DU 145 and prostate adenocarcinoma LNCaP cells were exposed to relatively low concentrations of Onc or Cep their growth rates were somewhat suppressed but the cells were still able to proliferate. Cell growth, however, was totally abolished in each of these cell lines when treated with Onc and Cep combined. The frequency of apoptosis was also many-fold higher in cultures treated with a combination of Onc and Cep than in respective cultures treated with Onc or Cep alone. The mechanism of the observed synergism is unclear but it may be associated with the Onc activity in targeting microRNAs and/or NFkappaB and Cep activity also targeting NFkappaB. The data suggest that the combination of these two drugs, that individually express a low toxic profile, may have strong antitumor potential.
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PMID:Remarkable enhancement of cytotoxicity of onconase and cepharanthine when used in combination on various tumor cell lines. 1844 30


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