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)

Mammalian ribonucleotide reductase is rate limiting for the synthesis of DNA. The active enzyme is composed of two dissimilar components called R1 and R2, encoded by different genes. The 3' untranslated regions (3' UTRs) of R1 and R2 messages contain sequences that are important in regulating gene expression through changes in message stability. We have constructed expression plasmids containing the R1 or R2 mRNA 3' UTRs, and we show that transfection of these plasmids into highly malignant mouse 10 T1/2 cells significantly suppresses the tumorigenic properties of these cells in syngeneic mice when compared with cells transfected with the same plasmid lacking R1 or R2 3' UTR sequences or when compared with cells transfected with the same plasmid expressing a heterologous sequence as a control. Furthermore, cells expressing the R2 3' UTR exhibit significantly reduced potential to disseminate to the lungs of syngeneic animals in experimental metastasis assays. The tumor-suppressive effects of the mouse R1 and R2 3' UTRs were not confined to mouse cells, because human HeLa cells transfected with expression plasmids containing either RI or R2 3' UTRs were also significantly less tumorigenic in assays using BALB/c nu/nu mice. These studies demonstrate that the untranslated regions of ribonucleotide reductase mRNAs can function as modifiers of tumor cell development and for the more complex process of tumor dissemination. We propose that these malignancy-suppressive effects are mediated through RNA interactions with cellular components involved in growth regulation through mechanisms of posttranscriptional control of gene expression. In addition, these observations emphasize the enormous potential of untranslated RNA to act directly as modifiers of biological characteristics relevant to mechanisms of malignancy.
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PMID:Suppression of malignancy by the 3' untranslated regions of ribonucleotide reductase R1 and R2 messenger RNAs. 881 26

The present study investigated the ability of a recombinant herpes simplex virus type 1 (HSV) vector to deliver genes into disseminated brain tumor foci through intrathecal injection of the vector. The animal model was designed to simulate brain tumors with cerebrospinal fluid (CSF) metastases, which are found especially in the pediatric population. 9L gliosarcoma cells were injected both into the right frontal lobe and in through the cisterna magna of adult rats. The HSV vector, hrR3, was inoculated intrathecally 5 days later. This vector is defective in the gene for ribonucleotide reductase, and, therefore, replicates preferentially in dividing cells; it retains an intact HSV-thymidine kinase gene (HSV-tk). Two days after injection of the vector, immunohistochemical staining for HSV thymidine kinase (HSV-TK) revealed expression in frontal tumors, as well as in leptomeningeal tumor foci along the entire neuroaxis. HSV-TK-immunopositive cells were most frequent in small tumors contacting the CSF pathways. Frontal lobe tumors showed the highest density of HSV-TK-immunopositive cells around their periphery with little expression in central parts. Some paraventricular neurons temporarily showed HSV-TK-immunolabeling at this early time point. The number of HSV-TK-immunopositive tumor cells markedly decreased 5 days after injection of the HSV vector. In all animals, some toxicity was observed in the first 2-4 days after virus injection with extensive leptomeningeal inflammation. In conclusion, intrathecal application of HSV vectors can mediate widespread transfer of the therapeutic HSV-tk gene into disseminated tumors throughout the brain and CSF pathways. Although there was marked toxicity associated with intrathecal injection of this vector, this mode of gene delivery offers a promising approach for treatment of CSF-metastases in conjunction with development of less toxic vectors.
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PMID:Herpes vector-mediated delivery of marker genes to disseminated central nervous system tumors. 883 17

The R2 component of ribonucleotide reductase is rate-limiting for DNA synthesis in proliferating cells, and recently, it has been shown that aberrant expression of R2 directly alters the malignant potential of tumor cells. We show that R2 gene expression is elevated in BALB/c 3T3 cells treated with transforming growth factor (TGF)-beta 1, TGF-beta 2, or TGF-beta 3, as determined by Northern blot analysis. Gel shift assays and UV crosslinking studies demonstrated similar post-transcriptional regulation at the 3'-untranslated region (3'-UTR) of the R2 mRNA, by TGF-beta 1, TGF-beta 2, and TGF-beta 3. The three growth factors induced a common 75 kDa RNA-protein complex. A 9 nucleotide sequence, GAGUUUGAG, previously shown to be responsive to TGF-beta 1-mediated R2 message stability changes, effectively competed out the formation of the R2 3'-UTR complex. We propose that these three different members of the TGF-beta family work through a common mechanism to control an important component of cell proliferation and a potential determinant of malignant progression.
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PMID:A cis-trans interaction at the 3'-untranslated region of ribonucleotide reductase mRNA is regulated by TGF-beta 1, TGF-beta 2, and TGF-beta 3. 892 Sep 17

Brain tumors that have disseminated into cerebrospinal fluid (CSF) pathways are an unresolved therapeutic problem, especially in pediatric neurooncology. Here a gene therapy approach using the herpes simplex virus type 1 thymidine kinase (HSV-TK)/ganciclovir (GCV) paradigm was tested using an HSV vector in a rodent model of disseminated central nervous system tumors. 9L-gliosarcoma cells were implanted simultaneously into the brain and the CSF of syngeneic rats. Five days later, resulting intracerebral and leptomeningeal tumors were treated by intrathecal injection of a replication-conditional HSV vector. This vector was defective for the ribonucleotide reductase gene, but contained an intact HSV-tk gene. Systemic GCV treatment was started 2 days after vector application and continued for 14 days. Tumor-free, long-term survival (LTS) was achieved in 90% of the animals treated with this combined therapeutic approach, whereas only 30% LTS was found in animals that had received the vector alone and 10% LTS in untreated animals. This therapeutic response probably involves oncolytic, on-site replication of the vector, activation of GCV by a HSV-TK, and a strong immune response both to the vector and to 9L cells. Apparent vector-related mortality was observed in 20% of animals without subsequent GCV therapy, but no vector-related mortality was found when the animals were treated with GCV after vector application. Given the successful outcome of this experimental treatment and the apparent potential of GCV to control HSV-related toxicity, intrathecal application of HSV vectors combined with GCV treatment may be a promising approach for treatment of disseminated brain tumors.
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PMID:Long-term survival in a rodent model of disseminated brain tumors by combined intrathecal delivery of herpes vectors and ganciclovir treatment. 893 Jun 59

Ribonucleotide reductase is a highly regulated cell cycle-controlled activity that is essential for DNA synthesis and repair. A retroviral vector for the R2 component of mammalian ribonucleotide reductase, the rate-limiting protein for enzyme activity and DNA synthesis in proliferating cells, was constructed and introduced into mammalian cells. Expression of Myc epitope-tagged R2 protein in benign BALB/c 3T3 and NIH 3T3 cells leads to a greatly increased frequency of focus formation in cooperation with H-ras transformation. Four lines of H-ras-transformed mouse 10T1/2 fibroblasts showed increased growth efficiency in soft agar after infection with the recombinant R2 expression virus vector. Furthermore, cells with altered R2 expression also exhibited significantly reduced subcutaneous tumor latency and increased tumor growth rates in syngeneic mice, and showed markedly elevated metastatic potential in lung metastasis assays. The results indicate that altered R2 gene expression cooperates with ras in mechanisms of malignant progression. A major Ras pathway involves the Raf-1 protein, which is recruited to the plasma membrane for activation. We show that recombinant R2 expression leads to significant increases in membrane-associated Raf-1 protein and mitogenactivating protein kinase-2 activity suggesting a mechanism for the observed Ras/R2 synergism. In support of this finding, we observed that activated Rac-1, which operates parallel to Raf-1 and cooperates with Raf-1 in Ras activated pathways, also cooperates with R2 in cellular transformation. These studies demonstrate that the R2 protein can participate in other critical cellular functions in addition to ribonucleotide reduction, and that deregulated R2 is a novel tumor progressor determinant that cooperates in oncogene-mediated mechanisms, which control malignant potential.
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PMID:Ribonucleotide reductase R2 component is a novel malignancy determinant that cooperates with activated oncogenes to determine transformation and malignant potential. 894 56

Gemcitabine is a new deoxycytidine analog that exhibits significant cytotoxicity against a variety of cultured murine and human tumor cells. The cytotoxic action of gemcitabine appears to be due to the inhibition of DNA synthesis by inhibition of ribonucleotide reductase and by competition with dCTP for incorporation into DNA. We have previously shown that gemcitabine, but not cytosine arabinoside (ara-C), has a broad spectrum of antitumor activity against 7 different types of murine solid tumors. The activity of gemcitabine was schedule dependent. To further characterize its activity, gemcitabine was tested against 12 human carcinoma xenografts. When given on an every 3 day x 4 schedule, the following percent inhibitions (at maximally tolerated doses [MTD]; MTD/2) in tumor growth were seen: MX-1 mammary (93%; 80%), CX-1 colon (92%; 82%), HC-1 colon (96%; 92%), GC3 colon (98%; 94%), VRC5 colon (99%; 100%), LX-1 lung (76%; 61%), CALU-6 lung (75%; 38%), NCI-H460 lung (45%; 46%), HS766T pancreatic (73%; not tested), PaCa-2 pancreatic (69%; 40%), PANC-1 pancreatic (70%; 60%), and BxPC-3 pancreatic (9%; 19%). In contrast, only the LX-1 lung carcinoma xenograft was responsive to ara-C treatment, which inhibited tumor growth by a marginal 62 percent. Thus, like its activity against murine solid tumors, gemcitabine has excellent antitumor activity against a broad spectrum of human solid tumors.
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PMID:Comparison of the antitumor activity of gemcitabine and ara-C in a panel of human breast, colon, lung and pancreatic xenograft models. 895 78

Gemcitabine is a nucleoside analogue with excellent clinical activity against solid tumors. Within the cell, gemcitabine is rapidly phosphorylated to its active di- and triphosphate metabolites. Cytotoxicity with gemcitabine appears to be related to multiple effects on DNA replication, where gemcitabine triphosphate can serve as both an inhibitor and substrate for DNA synthesis. Gemcitabine diphosphate inhibits ribonucleotide reductase, producing decreases in cellular dNTP pool levels in a cell-specific manner. These two major characteristics of gemcitabine, reduction in cellular dNTP pools and incorporation into DNA, are features of other antimetabolites antitumor agents which also exhibit radiosensitizing properties. Based on these favorable metabolic characteristics and the clinical activity of gemcitabine in tumor types which are commonly treated with radiation, the ability of gemcitabine to enhance X-radiation induced cytotoxicity was evaluated. Gemcitabine has been shown to be a potent radiosensitizer in a variety of tumor cell lines, including HT-29 colorectal carcinoma, pancreatic cancer, breast, non-small cell lung and head and neck cancer cell lines. Gemcitabine was most effective as a radiosensitizer when administered at least 2 hours prior to irradiation. For most cell lines, radiosensitization was evident at non-cytotoxic concentrations. The extent of radiosensitization increased with both increasing gemcitabine concentration and duration of exposure. Radiosensitization did not require redistribution of cells into a more radiosensitive phase of the cell cycle. The major metabolic effects observed under radiosensitizing conditions were the accumulation of high levels of gemcitabine triphosphate, and a selective decrease in the cellular dATP pool. The pattern of dATP decrease paralleled the increase in radiosensitization, whereas the level of gemcitabine triphosphate was not associated with the enhanced sensitivity to radiation. Compared to other radiosensitizers, the advantage of gemcitabine is that is can induce radiosensitization at concentrations that are 1000 times lower than typical plasma levels obtained with this drug. These studies will be used as guidelines for developing clinical trials of gemcitabine with radiation.
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PMID:Gemcitabine and radiosensitization in human tumor cells. 895 80

Antitumor and radiosensitizing effects of (E)-2'-deoxy-2'-(fluromethylene) cytidine (FMdC), a novel inhibitor of ribonucleotide reductase, were evaluated on nude mice bearing s.c. xenografts and liver metastases of a human colon carcinoma. FMdC given once daily or twice weekly has a dose-dependent antitumor effect. The maximum tolerated dose in the mice was reached with 10 mg/kg applied daily over 12 days. Twice weekly administration of FMdC reduced its toxicity but lowered the antitumor effect. Treatment of preestablished liver micrometastases obtained via intrasplenic injection of tumor cells, with 5 or 10 mg/kg FMdC, significantly prolonged the survival of the mice as compared to controls (P < 0.025 and P < 0.001, respectively). Ten mg/kg resulted in longer survival than 5 mg/kg FMdC (P < 0.05). Radiotherapy alone of s.c. xenografts (10 fractions over 12 days) yielded the radiation dose required to produce local tumor control in 50% of the treated mice (TCD50) of 43.0 Gy. When combined with FMdC, TCD50 was reduced to 22.5 and 19.0 Gy at doses of 5 and 10 mg/kg given i.p. 1 h before each irradiation, respectively. The corresponding enhancement ratios were 1.91 and 2.43, respectively. FMdC produced moderate and reversible myelosuppression. When 5 mg/kg FMdC was combined with irradiation, there was no increased skin or hematological toxicity as compared to radiotherapy or FMdC alone. At the 10 mg/kg level, however, lower leukocyte counts were observed. These results show that FMdC appears to be a potent anticancer drug and radiosensitizer.
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PMID:Antitumor and radiosensitizing effects of (E)-2'-deoxy-2'-(fluoromethylene) cytidine, a novel inhibitor of ribonucleoside diphosphate reductase, on human colon carcinoma xenografts in nude mice. 930 88

Ribonucleotide reductase is a highly regulated, cell cycle-controlled activity that plays an important role in DNA synthesis and repair. Recent studies have shown that elevated expression of the rate-limiting R2 component of ribonucleotide reductase increases Raf-1 protein activation and mitogen-activated protein kinase activity and acts as a novel malignancy determinant in cooperation with activated oncogenes like H-ras. We show that hydroxyurea-resistant mouse L cells with elevated R2 gene expression and increased ribonucleotide reductase activity exhibit significantly decreased sensitivities to the chemotherapeutic compounds N-(phosphonacetyl)-L-aspartate (PALA) and methotrexate (MTX). Furthermore, BALB/c 3T3 cells containing a retroviral expression vector encoding the R2 sequence also showed decreased sensitivity to PALA and MTX when compared to cells containing the same vector but without the R2 coding region. Colonies that developed in the presence of PALA or MTX contained amplifications of the CAD or dihydrofolate reductase genes and exhibited wild-type p53 function as determined in sequence-specific p53 binding activity assays. NIH-3T3 cells containing the R2 retroviral expression vector also showed significantly decreased sensitivity to hydroxyurea and MTX but not to PALA. Furthermore, NIH-3T3 cells transfected with a vector containing the R2 sequence in antisense orientation exhibited increased sensitivity to hydroxyurea, PALA, and MTX. Similarly, mouse 10T1/2 cells that are highly transformed and drug resistant due to alterations in H-ras and a mutant oncogenic form of p53 exhibited significant increases in sensitivity to hydroxyurea, PALA, and MTX when transfected with a vector containing the R2 sequence in antisense orientation and compared to cells containing the same vector without the antisense sequence. These results indicate that altered expression of the R2 component is capable of significantly modifying drug sensitivity properties of tumor cells. We hypothesize that this occurs, at least in part, through a mechanism of increased genetic instability that is independent of direct p53 mutation or loss and involves R2 stimulation of the mitogen-activated protein kinase signal pathway.
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PMID:Ribonucleotide reductase R2 gene expression and changes in drug sensitivity and genome stability. 935 52

Our recent studies have shown that deregulated expression of R2, the rate-limiting component of ribonucleotide reductase, enhances transformation and malignant potential by cooperating with activated oncogenes. We now demonstrate that the R1 component of ribonucleotide reductase has tumor-suppressing activity. Stable expression of a biologically active ectopic R1 in ras-transformed mouse fibroblast 10T(1/2) cell lines, with or without R2 overexpression, led to significantly reduced colony-forming efficiency in soft agar. The decreased anchorage independence was accompanied by markedly suppressed malignant potential in vivo. In three ras-transformed cell lines, R1 overexpression resulted in abrogation or marked suppression of tumorigenicity. In addition, the ability to form lung metastases by cells overexpressing R1 was reduced by >85%. Metastasis suppressing activity also was observed in the highly malignant mouse 10T(1/2) derived RMP-6 cell line, which was transformed by a combination of oncogenic ras, myc, and mutant p53. Furthermore, in support of the above observations with the R1 overexpressing cells, NIH 3T3 cells cotransfected with an R1 antisense sequence and oncogenic ras showed significantly increased anchorage independence as compared with control ras-transfected cells. Finally, characteristics of reduced malignant potential also were demonstrated with R1 overexpressing human colon carcinoma cells. Taken together, these results indicate that the two components of ribonucleotide reductase both are unique malignancy determinants playing opposing roles in its regulation, that there is a novel control point important in mechanisms of malignancy, which involves a balance in the levels of R1 and R2 expression, and that alterations in this balance can significantly modify transformation, tumorigenicity, and metastatic potential.
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PMID:The R1 component of mammalian ribonucleotide reductase has malignancy-suppressing activity as demonstrated by gene transfer experiments. 937 20


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