Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.21 (thymidine kinase)
 7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Maloney murine leukemia virus-based, replication-defective retroviral vectors containing the neomycin resistance gene (neo) were developed to transfer the Escherichia coli ada gene coding for O6-alkylguanine-DNA alkyltransferase, into mammalian cells. To optimize gene transfer and expression, the following promoters were linked to ada: the Maloney murine leukemia virus promoter within the long-terminal repeat, the Rous sarcoma virus promoter, the thymidine kinase promoter, or the human phosphoglycerate kinase promoter. Sequences were transfected into the helper virus-free retroviral packaging psi-2 cell line. Recombinant retroviruses were tested in CCL-1 cells, which, like most murine tissues, have low levels of alkyltransferase and are sensitive to 1,3-bis(2-chloroethyl)nitrosourea (BCNU), and in NIH-3T3 cells, which are BCNU resistant and have high levels of alkyltransferase. Lines infected with each of the four retroviruses were selected for neo expression and found to have intact proviral integration and ada gene expression. Alkyltransferase activity was greatest with retrovirus containing the Rous sarcoma virus-ada gene; infected NIH-3T3 cells had up to 2300 units of alkyltransferase/mg of protein compared with 151 units/mg of protein in control cells, and infected CCL-1 cells had up to 1231 units/mg of protein compared with 33 units/mg of protein in control cells. CCL-1 cells expressing ada were more resistant to BCNU cytotoxicity than were controls. However, NIH-3T3 cells expressing ada were only slightly more resistant to BCNU than controls, possibly because most of the ada protein was cytoplasmic rather than nuclear as suggested by immunohistochemical stain. These studies establish a series of retroviruses containing the bacterial ada gene, which efficiently infect mammalian cells. ada expression increases nitrosourea resistance in cells with low mammalian alkyltransferase activity.
 ...
PMID:Increase in nitrosourea resistance in mammalian cells by retrovirally mediated gene transfer of bacterial O6-alkylguanine-DNA alkyltransferase. 267 54

5-fluorouracil (5-FU), an inhibitor of thymidylate synthase (EC 2.1.1.45), is clinically used in the treatment of several solid tumors, including colorectal, head and neck, gastric, and pancreatic cancer. The drug effectively inhibits deoxynucleoside triphosphate de novo synthesis. However, this inhibition can be circumvented by increased thymidine kinase (EC 2.7.1.21) activity. In the present study we examined the effects of 5-FU combined with azidothymidine (AZT), a competitive inhibitor of thymidine kinase in human colon tumor cells in vitro, including three 5-FU resistant cell lines. The cells were simultaneously incubated with various concentrations of 5-FU (0.015 to 150 microM) and AZT (20 to 300 microM) for 6 days. 5-FU alone yielded an IC50 of 18 microM in the parental CCL 227 cell line and IC50s of 470 and 1100 microM in the 5-FU resistant cell lines as determined by a MTT chemosensitivity assay. Addition of 100 microM AZT alone, a drug concentration that can be achieved in patients, had no effect on the growth of the cell lines examined. However, when added simultaneously with 5-FU, the IC50s of 5-FU synergistically decreased to 10 microM in the sensitive and to 360 or 760 microM in the resistant cell lines, respectively. Our results demonstrate that the combination of 5-FU with AZT synergistically inhibited the growth of 5-FU resistant cells, suggesting the use of 5-FU in combination with AZT for the treatment of 5-FU sensitive as well as resistant human colon tumors.
 ...
PMID:Modulation of 5-fluorouracil resistance in human colon tumor cell lines by azidothymidine. 888 11