Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.5.4.1 (cytosine deaminase)
747 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Incorporation of labelled 14C-pyrimidines and 5-fluoropyrimidines (5-FC and 5-FU) in four different phenotypes of wild strains of Candida isolated from man showed comparable results to those obtained by the minimal inhibition concentration (MIC) test. Kinetics studies demonstrated significant rates of incorporation after 24 hours of culture in each case. It was also possible to infer the biochemical mechanisms of resistance to 5-FC, namely a defect in UMP pyrophosphorylase, cytosine deaminase and 5-FU permease in the ease of the following phenotypes: 5-FCR 5-FUR, 5-FCR 5-FUS and 5-FCS 5-FUR (R = resistant; S = sensitive). In this study, the permeation process was approached by a consumption assay which determined the rate of labelled substrates into the medium before and after 24 hours of culture. Thus, it was found that the consumption levels of the phenotype 5-FCS 5-FUS were very high, while those of the phenotype 5-FCR 5-FUR were minimal. The 5-FCS 5-FU5 phenotype had no detectable consumption of 5-FU. With regard to the 5-FC5 5-FUS phenotype, it seems that the non-incorporation of 5-FC into the RNAs after the consumption by the yeasts has a feed back effect on the permeation process.
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PMID:Sensitivity and resistance of pathogenic yeasts to 5-fluoropyrimidines. II.--Mechanisms of resistance to 5-fluorocytosine (5-FC) and 5-fluorouracil (5-FU) (author's transl). 121 21

Flucytosine (5-FC)-resistant strains were isolated from the haploid opportunistic pathogen Candida glabrata by UV-induced mutation and fluoropyrimidine selection. These strains were characterized biochemically, and the metabolism of fluorinated pyrimidines was studied by 19F nuclear magnetic resonance spectroscopy. No evidence was obtained from these studies for degradative metabolism of the fluorinated derivatives. In the parental susceptible strain of C. glabrata, 5-fluorouracil but not 5-FC was detected within the cells. 5-Fluorouracil was also present in the culture supernatant after incubation of the cells with 5-FC. The distribution of fluorinated derivatives within the 5-FC-resistant strains was consistent with their genotype. Two strains of C. glabrata which had only a partial loss of cytosine deaminase and UMP pyrophosphorylase activity had high levels of resistance to 5-FC. Both C. glabrata and Candida albicans were susceptible to 5-fluorouridine. This compound but not the anticancer drug 5-fluoro-2-deoxyuridine was shown to be transported into susceptible cells by a specific uridine permease.
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PMID:19F nuclear magnetic resonance study of fluoropyrimidine metabolism in strains of Candida glabrata with specific defects in pyrimidine metabolism. 229 66

5-Fluorocytosine (5-FC) lacks antineoplastic activity in human subjects because of the absence of cytosine deaminase (CDase) in mammalian cells. Intratumoral conversion of 5-FC into 5-fluorouracil (5-FUra) by locally implanted capsules containing CDase followed by systemic administration of 5-FC can be expected to induce antineoplastic activity at a local site with minimal systemic toxicity. In vitro and in vivo experiments were performed to evaluate this hypothesis. Spectrophotometric analysis confirmed the deamination of 5-FC to 5-FUra by CDase extracted from cultivated Escherichia coli. In vitro studies showed that 5-FC combined with CDase induced significant growth-inhibitory effects on the cultured glioma cells. An active CDase capsule, made of cellulose tubing, was newly designed for local implantation. 5-FC concentrations in the s.c. tumors of the rats given these CDase capsules, followed by 5-FC administration, showed a sufficient amount of delivery of 5-FC to the tumor tissue. 5-FUra appearing in the tumor reached the level of 8.0 micrograms/g at 2 h and stayed at more than 1.0 microgram/g at between 1 and 6 h. Significant reduction of the tumor growth and cytotoxic changes were observed. The passive cutaneous anaphylaxis reaction demonstrated no allergic reaction to the host due to the capsule. These results suggest that this chemotherapeutic method is effective for human brain tumors.
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PMID:Antineoplastic effects in rats of 5-fluorocytosine in combination with cytosine deaminase capsules. 397 37

We report that in vitro 5-fluorocytosine sensitizes B16(F10) melanoma cells to radiation damage when they are transfected with cytosine deaminase gene (CD). The greatest enhancement of radiation cytotoxicity was observed when B16(F10)/CD cells were incubated in medium with 500 microM 5-fluorocytosine for 3 hours, with incubation starting 1 hour after irradiation. 5-Fluorocytosine did not change radiosensitivity of parental, nontransfected cells. The isoeffective dose for CD-transfected cells treated with 5-fluorocytosine was reduced by 20% at a 2-Gy level of effect for nontransfected cells. We believe that the observed outcome is related to 5-fluorouracil generated by CD and subsequent 5-fluorouracil anabolites. Our results support the development of in vivo models for tumor radiosensitization using the CD gene/5-fluorocytosine system.
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PMID:Selective augmentation of radiation effects by 5-fluorocytosine on murine B16(F10) melanoma cells transfected with cytosine deaminase gene. 925 13

Gene therapy combined with radiation therapy to enhance selectively radiation cytotoxicity in malignant cells represents a new approach for cancer treatment. We investigated the efficacy of adenoviral (Ad5)-directed cytosine deaminase/5-fluorocytosine (CD/5-FC) enzyme/prodrug gene therapy to enhance selectively the tumoricidal action of ionizing radiation in human cancer xenografts derived from a human squamous carcinoma cell line (SQ-20B). Tumor xenografts grown in hindlimbs of nude mice were transfected with an adenoviral vector (Ad.CMV.CD) containing the cytosine deaminase (CD) gene under the control of a cytomegalovirus (CMV) promoter. Mice were injected i.p. with 800 mg/kg of 5-FC for 12 days, and tumors were treated with fractionated radiation at a dose of 5 Gy/day to a total dose of 50 Gy. In larger tumors with a mean volume of 1069 mm3, marked tumor regression to 11% of the original tumor volume was observed at day 21 (P = 0.01). The volumetric regression of smaller tumors with a mean volume of 199 mm3, which received the same combined treatment protocol, was significant at day 12 (P = 0.014). However, unlike large tumors, regression of the smaller tumors continued until day 36 (P = 0.01), with 43% cured at day 26. No cures or significant volumetric reduction in size was observed in tumors treated with radiation alone; Ad.CMV.CD with or without radiation; or with Ad.CMV.CD and 5-FC. These results suggest that the CD/5-FC gene therapy approach is an effective radiosensitizing strategy and may lead to substantial improvement in local tumor control that would translate into improved cure rates and better survival.
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PMID:Virally directed cytosine deaminase/5-fluorocytosine gene therapy enhances radiation response in human cancer xenografts. 933 Oct 76

Suicide genes such as cytosine deaminase (CD) and herpes simplex virus thymidine kinase (TK) encode products that convert nontoxic substances (prodrugs) into toxic metabolites. Suicide gene transfer is currently being used in cancer therapy or can be used as a safety modality. To analyze the reliability of suicide genes as a safety modality for a vaccination study with viable cytokine/B7 gene-modified tumor cells, the individual and combined efficacy of the two suicide genes was compared for in vitro and in vivo cell killing of a murine mammary adenocarcinoma cell line (TS/A). To adapt the system to an in vivo gene delivery situation, bulk cultures cotransfected with the CD and TK gene were used instead of selected clones. In vitro, both CD and TK conferred sensitivity to the respective prodrug but the combined cytotoxic effects of both gene products were always superior. For in vivo analysis BALB/c mice were injected subcutaneously with CD- and TK-modified TS/A cells, treated with prodrugs, and tumor size was evaluated for a period of 100 days. In the in vivo situation the combination of both enzyme/prodrug systems was again most effective. The highest single concentration of 5-FC (500 mg/kg) or GCV (100 mg/kg) was not able to fully protect the animals from developing tumors, whereas a combination of 5-FC (250 mg/kg) and GCV (50 mg/kg) resulted in complete tumor eradication. In nude mice treated in the same way, most CD/TK tumors could not be eliminated. Furthermore, BALB/c mice cured of TS/A-CD/TK tumors developed a systemic tumor immunity against challenge with parental TS/A cells. These findings indicate that reliable tumor elimination by the suicide genes depends on T cells. The cooperative effect of both suicide genes was confirmed in vitro with the human renal cell carcinoma line RCC26. We conclude that TK and CD together, but neither gene alone, act as a safety mechanism for the elimination of tumor cells in a reliable fashion and suggest that a rapid and quantitative antigen release by effective TK- and CD-mediated tumor destruction is necessary for T cell immunity to develop.
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PMID:Double suicide gene (cytosine deaminase and herpes simplex virus thymidine kinase) but not single gene transfer allows reliable elimination of tumor cells in vivo. 958 8

B cell lymphomas in immunocompromised patients frequently contain the Epstein-Barr virus (EBV) genome (MacMahon et al, 1991), suggesting that gene therapy strategies that target EBV-positive cells for destruction might be useful for the therapy of such tumors. We have previously shown that stable expression of the cytosine deaminase (CD) gene in EBV-positive lymphoblastoid cell lines induces cell killing in the presence of the prodrug 5-fluorocytosine, with a substantial bystander killing effect (Rogers et al., 1996). To promote specific killing of EBV-positive tumor cells, we have constructed two different EBV-based vectors containing the cytosine deaminase gene. The first vector (OriP-CD), which contains the intact EBV oriP enhancer/replication element, replicates as an episome specifically in EBV-positive cells and likewise enhances transcription in an EBV-specific manner. The OriP-CD vector cannot be packaged or spread from cell to cell. The second vector (OriLyt-CD) contains the EBV lytic origin of replication (oriLyt), the EBV packaging sequences (located in the viral termini), the oriP enhancer element (but not the complete replication origin), and the EBV BZLF1 gene (which induces expression of the EBV proteins required for replication of oriLyt). The OriLyt-CD vector is replicated through the oriLyt origin specifically in EBV-positive cells and packaged as an EBV pseudovirion. The packaged oriLyt-CD virion can subsequently infect cells containing the EBV receptor, CD21, and initiate another round of replication in EBV-positive cells. Here we demonstrate that each of these two different EBV-based gene therapy strategies induces specific killing of EBV-positive B cells in vitro (in the presence of 5-FC). The advantages and disadvantages of each strategy are discussed.
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PMID:Gene therapy strategies for treating Epstein-Barr virus-associated lymphomas: comparison of two different Epstein-Barr virus-based vectors. 962 50

Two obstacles limiting the efficacy of nearly all cancer gene therapy trials are low gene transduction efficiencies and the lack of tumor specificity. Recently, a replication-competent, E1B-attenuated adenovirus (ONYX-015) was developed that could overcome these limitations, because it was capable of efficiently and selectively destroying tumor cells lacking functional p53. In an attempt to improve both the efficacy and safety of this approach, we constructed a similar adenovirus (FGR) containing a cytosine deaminase (CD)/herpes simplex virus type-1 thymidine kinase (HSV-1 TK) fusion gene, thereby allowing for the utilization of double-suicide gene therapy, which has previously been demonstrated to produce significant antitumor effects and potentiate the therapeutic effects of radiation. The FGR virus exhibited the same tumor cell specificity and replication kinetics as the ONYX-015 virus in vitro. Importantly, both the CD/5-FC and HSV-1 TK/GCV suicide gene systems markedly enhanced the tumor cell-specific cytopathic effect of the virus, and, as expected, sensitized tumor cells to radiation. By contrast, neither the FGR virus nor either suicide gene system showed significant toxicity to normal human cells. Both suicide gene systems could be used to suppress viral replication effectively, thereby providing a means to control viral spread. The results support the thesis that the three-pronged approach of viral therapy, suicide gene therapy, and radiotherapy may represent a powerful and safe means of selectively destroying tumor cells in vivo.
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PMID:A novel three-pronged approach to kill cancer cells selectively: concomitant viral, double suicide gene, and radiotherapy. 965 Jun 10

A negative selection system for glioma gene therapy was established in vitro. C 6 rat glioma cells were infected with recombined retrovirus which contain Escherichia coli cytosine deaminase (EC-CD) gene. The enzyme CD can transform the non-toxic prodrug 5-Fluorocytosine (5-FC) to the highly cellular toxic compound 5-Fluorouracil (5-FU). The growth inhibition studies proved that CD-positive cells were highly sensitive to 5-FC, the IC50 about 3 mumol/L, compared with an IC50 of approximately 6000 mumol/L in parental C 6 cells. Both CD-positive and negative cells were sensitive to 5-FU at very low concentration (IC50 < 1 mumol/L). Mixed cellular assay showed CD-positive cells had "bystander effect" on CD-negative cells when exposed to 5-FC. Our results demonstrate that EC-CD gene should be an efficient suicide gene for the treatment of glioma.
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PMID:[Experimental treatment of brain tumor cells using CD suicide gene]. 977 83

Recent evidence has suggested that tumor cells having a wild-type p53 status are more sensitive to chemotherapeutic agents and radiation than cells that lack functional p53. The heightened sensitivity of wild-type p53 cells is thought to be attributable to their propensity to undergo p53-mediated apoptosis after insult. Given that suicide gene therapy is essentially tumor-targeted chemotherapy, we examined the hypothesis that coexpression of wild-type p53 could enhance the efficacy of adenovirus-mediated suicide gene therapy. Human Hep3B and SK-OV-3 cells, which are null for p53, were infected with a pair of replication-deficient adenoviruses that expressed a cytosine deaminase/herpes simplex virus thymidine kinase (CD/HSV-1 TK) fusion gene without (fusion gene nonreplicative adenovirus, FGNR) or with (FGNRp53) the wild-type human p53 gene. The sensitivity of cells to the CD/5-fluorocytosine (CD/5-FC) and HSV-1 TK/ ganciclovir (GCV) enzyme/prodrug systems was determined in vitro and in vivo. Coexpression of p53 did not enhance the cytotoxicity of either the CD/5-FC or HSV-1 TK/GCV system in vitro. The failure to observe an effect of p53 could not be explained on the basis of insufficient or transient p53 expression, because FGNRp53-infected cells growth arrested in G1, induced Bax, and underwent apoptosis at an increased rate after prodrug treatment, particularly when the adenovirus E1A protein was present. Intratumoral injection of FGNRp53 concomitant with single or double pro-drug therapy resulted in a tumor growth delay that was equal to or less than that observed with the FGNR virus. Our results indicate that coexpression of p53 may not necessarily improve the efficacy of adenovirus-mediated CD/ 5-FC and HSV-1 TK/GCV suicide gene therapies in vivo.
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PMID:Efficacy of adenovirus-mediated CD/5-FC and HSV-1 thymidine kinase/ganciclovir suicide gene therapies concomitant with p53 gene therapy. 1063 64


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