(1/501) Adenosine deaminase activity in thymus and other human tissues.

Adenosine deaminase activity (ADA) has been estimated in human tissues. Levels in the thymus during childhood were very much higher than in any of the other 6 tissues studied. Intermediate activities were obtained from spleen and lymph nodes and also skin. Cerebral cortex, liver and kidney had relatively low levels. ADA activity in lymphocytes from peripheral blood was significantly increased after antigenic stimulation by TAB immunization. The available evidence appears to be consistent with T-lymphocyte growth and development in the thymus being dependant on ADA.  (+info)

(2/501) Superiority of yeast over bacterial cytosine deaminase for enzyme/prodrug gene therapy in colon cancer xenografts.

The enzyme/prodrug strategy using bacterial cytosine deaminase (bCD) and 5-fluorocytosine (5-FC) is currently under investigation for cancer gene therapy. A major limitation for the use of bCD is that it is inefficient in the conversion of 5-FC into 5-fluorouracil. In the present study, we show that the K(m) of yeast cytosine deaminase (yCD) for 5-FC was 22-fold lower when compared with that of bCD. HT29 human colon cancer cells transduced with yCD (HT29/yCD) were significantly more sensitive to 5-FC in vitro than HT29 cells transduced with bCD (HT29/bCD). In tumor-bearing nude mice, complete tumor regression was observed in 6 of 13 HT29/yCD tumors in response to 5-FC treatment (500 mg/kg i.p. daily, 5 days a week for 2 weeks), whereas 0 of 10 HT29/bCD tumors were cured. Our study demonstrates an improved efficacy of the CD/5-FC treatment strategy when yCD was used. This enzyme has, therefore, a high potential to increase the therapeutic outcome of the enzyme/prodrug strategy in cancer patients.  (+info)

(3/501) Adenovirus-mediated GM-CSF gene and cytosine deaminase gene transfer followed by 5-fluorocytosine administration elicit more potent antitumor response in tumor-bearing mice.

Antitumor effects of combined transfer of suicide and cytokine genes were investigated in this study. Adenovirus harboring E. coli cytosine deaminase gene (AdCD) and adenovirus harboring murine granulocyte-macrophage colony-stimulating factor gene (AdGMCSF) were used simultaneously for in vivo gene transfer in melanoma-bearing mice. Growth inhibition of established tumors and prolongation of survival period were observed more significantly in tumor-bearing mice after transfection with AdGMCSF and AdCD followed by continuous injection of prodrug 5-fluorocytosine (5FC) when compared with mice treated with control adenovirus AdlacZ/5FC, AdCD/5FC or AdGMCSF alone (P < 0.01). After combined therapy the expression of MHC-I (H-2Db) and B7-1 molecules on freshly isolated tumor cells increased greatly and more dendritic cells and CD8+ T cells infiltrated into the tumor mass. The activity of specific cytotoxic T lymphocytes was also found to be induced more significantly after the combined therapy. Further experiments showed that apoptosis of tumor cells and induction of antitumor immune response might be involved in the mechanisms of the tumor cell killing by the combined therapy. Our results demonstrated that combined transfer of the GM-CSF and CD suicide genes, being able to inhibit the growth of melanoma synergistically and induce specific antitumor immune response efficiently, thus addressing the drawbacks of suicide gene therapy or cytokine gene therapy which were proved to be not satisfactory when used alone, might be of therapeutic potential for gene therapy of cancer.  (+info)

(4/501) Effective and safe gene therapy for colorectal carcinoma using the cytosine deaminase gene directed by the carcinoembryonic antigen promoter.

We have recently isolated carcinoembryonic antigen (CEA) promoter regions consisting of 419 bp and 204 bp from CEA-producing human colorectal carcinoma (CRC). We constructed CEA419/CD and CEA204/CD retroviruses carrying the bacterial cytosine deaminase (CD) gene directed by the CEA promoter regions. pCD2 retroviruses carrying the CD gene directed by the retrovirus long terminal repeat promoter were also used. CEA419/CD or CEA204/CD retrovirus-infected CRC cells were found to be susceptible to 5-fluorocytosine (5-FC), while non-CRC cells infected with the same retroviruses were not. CD-transduced CRC xenografts in nude mice were sensitive to 5-FC treatment, resulting in arrest of tumor growth. When mice with intraperitoneally disseminated CRCs were given intraperitoneal injections of CEA419/CD retrovirus-producing cells followed by 5-FC treatment, significantly prolonged survival rates were observed compared with animals injected with pCD2 retrovirus-producing cells followed by 5-FC treatment. Importantly, bone marrow suppression was not observed in animals injected with CEA419/CD retrovirus-producing cells and 5-FC, while profound bone marrow suppression was observed in those injected with pCD2 retrovirus-producing cells and 5-FC. These results indicate that effective and safe in vivo gene therapy for advanced CRC may be feasible by transferring the CD gene controlled by the CEA promoter followed by 5-FC treatment.  (+info)

(5/501) Variability of human systemic humoral immune responses to adenovirus gene transfer vectors administered to different organs.

Administration of adenovirus (Ad) vectors to immunologically naive experimental animals almost invariably results in the induction of systemic anti-Ad neutralizing antibodies. To determine if the human systemic humoral host responses to Ad vectors follow a similar pattern, we evaluated the systemic (serum) anti-Ad serotype 5 (Ad5) neutralizing antibodies in humans after administration of first generation (E1(-) E3(-)) Ad5-based gene transfer vectors to different hosts. AdGVCFTR.10 (carrying the normal human cystic fibrosis [CF] transmembrane regulator cDNA) was sprayed (8 x 10(7) to 2 x 10(10) particle units [PU]) repetitively (every 3 months or every 2 weeks) to the airway epithelium of 15 individuals with CF. AdGVCD.10 (carrying the Escherichia coli cytosine deaminase gene) was administered (8 x 10(8) to 8 x 10(9) PU; once a week, twice) directly to liver metastasis of five individuals with colon cancer and by the intradermal route (8 x 10(7) to 8 x 10(9) PU, single administration) to six healthy individuals. AdGVVEGF121.10 (carrying the human vascular endothelial growth factor 121 cDNA) was administered (4 x 10(8) to 4 x 10(9.5) PU, single administration) directly to the myocardium of 11 individuals with ischemic heart disease. Ad vector administration to the airways of individuals with CF evoked no or minimal serum neutralizing antibodies, even with repetitive administration. In contrast, intratumor administration of an Ad vector to individuals with metastatic colon cancer resulted in a robust antibody response, with anti-Ad neutralizing antibody titers of 10(2) to >10(4). Healthy individuals responded to single intradermal Ad vector variably, from induction of no neutralizing anti-Ad antibodies to titers of 5 x 10(3). Likewise, individuals with ischemic heart disease had a variable response to single intramyocardial vector administration, ranging from minimal neutralizing antibody levels to titers of 10(4). Evaluation of the data from all trials showed no correlation between the peak serum neutralizing anti-Ad response and the dose of Ad vector administered (P > 0.1, all comparisons). In contrast, there was a striking correlation between the peak anti-Ad5 neutralizing antibody levels evoked by vector administration and the level of preexisting anti-Ad5 antibodies (P = 0.0001). Thus, unlike the case for experimental animals, administration of Ad vectors to humans does not invariably evoke a systemic anti-Ad neutralizing antibody response. In humans, the extent of the response is dictated by preexisting antibody titers and modified by route of administration but is not dose dependent. Since the extent of anti-Ad neutralizing antibodies will likely modify the efficacy of administration of Ad vectors, these observations are of fundamental importance in designing human gene therapy trials and in interpreting the efficacy of Ad vector-mediated gene transfer.  (+info)

(6/501) Systemic administration of a recombinant vaccinia virus expressing the cytosine deaminase gene and subsequent treatment with 5-fluorocytosine leads to tumor-specific gene expression and prolongation of survival in mice.

Suicide gene therapy using the cytosine deaminase (CD) gene and 5-fluorocytosine (5-FC) has shown promising results for the treatment of colon carcinoma cells in vitro. Efficient viral infection and tumor-specific gene delivery is crucial for clinically measurable treatment effects. After proving efficient gene transfer in vitro, we demonstrate here that genes can be delivered to metastatic liver tumors in vivo in a highly selective manner using systemic delivery of a thymidine kinase-deleted (TK-) recombinant vaccinia virus (Western Reserve strain). When the vector was administered systemically in C57BL/6 mice or nude/athymic mice with established disseminated MC38 liver metastases, transgene expression in tumors was usually 1,000 to 10,000-fold higher compared with other organs (n = 160; P < 0.0001). This tumor-specific gene transfer leads to significant tumor responses and subsequent survival benefits after the transfer of the CD gene to liver metastases and subsequent systemic treatment with the prodrug 5-FC (P < 0.0001). We describe reporter gene and survival experiments both in immunocompetent and athymic nude mice, establishing a gene expression pattern over time and characterizing the treatment effects of the virus delivery/prodrug system. Cure rates of up to 30% in animals with established liver metastases show that suicide gene therapy using TK- vaccinia virus as a vector may be a promising system for the clinical application of tumor-directed gene therapy.  (+info)

(7/501) Noninvasive quantitation of cytosine deaminase transgene expression in human tumor xenografts with in vivo magnetic resonance spectroscopy.

Analysis of transgene expression in vivo currently requires destructive and invasive molecular assays of tissue specimens. Noninvasive methodology for assessing the location, magnitude, and duration of transgene expression in vivo will facilitate subject-by-subject correlation of therapeutic outcomes with transgene expression and will be useful in vector development. Cytosine deaminase (CD) is a microbial gene undergoing clinical trials in gene-directed enzyme prodrug gene therapy. We hypothesized that in vivo magnetic resonance spectroscopy could be used to measure CD transgene expression in genetically modified tumors by directly observing the CD-catalyzed conversion of the 5-fluorocytosine (5-FC) prodrug to the chemotherapeutic agent 5-fluorouracil (5-FU). The feasibility of this approach is demonstrated in subcutaneous human colorectal carcinoma xenografts in nude mice by using yeast CD (yCD). A three-compartment model was used to analyze the metabolic fluxes of 5-FC and its metabolites. The rate constants for yCD-catalyzed prodrug conversion (k(1)(app)), 5-FU efflux from the observable tumor volume (k(2)(app)), and formation of cytotoxic fluorinated nucleotides from 5-FU (k(3)(app)) were 0.49 +/- 0.27 min(-1), 0.766 +/- 0.006 min(-1), and 0.0023 +/- 0.0007 min(-1), respectively. The best fits of the 5-FU concentration data assumed first-order kinetics, suggesting that yCD was not saturated in vivo in the presence of measured intratumoral 5-FC concentrations well above the in vitro K(m). These results demonstrate the feasibility of using magnetic resonance spectroscopy to noninvasively monitor therapeutic transgene expression in tumors. This capability provides an approach for measuring gene expression that will be useful in clinical gene therapy trials.  (+info)

(8/501) Simultaneous Cre catalyzed recombination of two alleles to restore neomycin sensitivity and facilitate homozygous mutations.

Cells homozygous for neo-expressing mutations can be derived by culturing heterozygotes with elevated G418. We demonstrate that this strategy is significantly less efficient if hyg is substituted for neo. Therefore, to introduce additional mutations Cre recombinase was used to remove floxed neo from both alleles of homozygotes at two different loci. The rate-determining step in Cre excision appeared independent of substrate copy number. Incorporating cytosine deaminase and Herpes simplex virus thymidine kinase allowed negative selection for both targeting and Cre excision. The resulting G418-sensitive homozygous mutants should allow mutagenesis at additional loci and avoid untoward effects of retained selection markers.  (+info)