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

A cell line from the Walker carcinosarcoma 256 of the rat has been established in suspension culture in medium with 5% bovine calf serum for over 350 generations, with an average population doubling time of 17 h, a plating efficiency of 56%, a colony forming efficiency of 32%, and a good capacity to form colonies in soft agar. The cells are morphologically indistinguishable from those in the solid tumor and ascites as checked by transmission and scanning electron microscopy. The karyotype is characterized by a modal number of 65 chromosomes and by the presence of a marker metacentric chromosome. The cells express thymidine kinase, gamma-glutamyl transpeptidase, and alkaline phosphatase; are agglutinable by concanavalin A; and can be synchronized by the triple thymidine block. They induce primary tumors, both subcutaneously (solid) and intraperitoneally (ascitic), in the rat; are able to metastasize upon injection by the tail vein; and invade the chorioallantoic membrane of the chick embryo. Cells in suspension can be transferred to monolayers, considerably decreasing their tumorigenicity without affecting the other parameters studied, and can be switched back to suspension culture. DNA-mediated transfection showed that DNA from these cells can transform the NIH-3T3 line. Upon growth of the monolayers in a BrdUr-containing medium, a sub-line was established that was cloned into a thymidine kinase-deficient line unable to grow in HAT medium and with properties otherwise similar to those of the parental wild type cells.
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PMID:Establishment and characterization of cell lines from the Walker carcinoma 256 able to grow in suspension culture and deficient in thymidine kinase. 646 74

Retrovirus-mediated herpes simplex virus-thymidine kinase (HSV-tk) gene therapy is a promising approach in the treatment of brain tumors. Previous in vitro and in vivo studies have demonstrated a bystander effect in which nonmodified tumor cells in proximity to HSV-tk-modified tumor cells are killed with the modified cells in the presence of ganciclovir. In the present study the authors assessed the contribution of infectious HSV-tk retrovirus made by producer cells to the bystander cytocidal effect in tissue culture using Walker 256 rat breast carcinosarcoma cells, which represent an established model for carcinomatous meningitis. The authors observed ganciclovir-dependent growth inhibition even when only one HSV-tk-positive Walker cell was mixed with 1000 HSV-tk-negative Walker cells and showed that the bystander cytocidal effect is not mediated by toxic cell lysis products. Walker cells engineered to produce HSV-tk retrovirus with titers ranging from 10(3) to 10(5) colony-forming units/ml exert no greater cytocidal effect than nonviral producer HSV-tk-positive Walker cells in vitro. Murine fibroblast-producer cells with viral titers ranging from 10(6) to 10(7) colony-forming units/ml exerted a stronger cytocidal effect than nonviral producer HSV-tk-positive murine fibroblasts. Despite the high viral titers of fibroblast producer cells, HSV-tk-modified Walker cells performed better than fibroblast producer cells in their cytotoxic effect on wild-type Walker tumor cells. Given that HSV-tk-modified tumor cells can become ganciclovir resistant, we tested gamma-irradiation as a means to overcome resistance. Lethal gamma-irradiation of the HSV-tk-positive Walker cells did not abolish their bystander effect on Walker HSV-tk-negative cells. One can infer from these results that HSV-tk-modified tumor cells, irradiated or not, may be a better alternative to murine fibroblast producer cells in the treatment of central nervous system neoplasia.
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PMID:A more potent bystander cytocidal effect elicited by tumor cells expressing the herpes simplex virus-thymidine kinase gene than by fibroblast virus-producer cells in vitro. 767 20

In vitro and animal experiments have demonstrated the potential efficacy of using the bystander effect alone in the treatment of brain tumors. A known problem in some in vitro and in vivo experiments is that a fraction of cells engineered to express the herpes simplex virus thymidine kinase (HSV-tk) gene survive ganciclovir (GCV) treatment and undergo cell division. To prevent the recurrent growth of HSV-tk+ cells in the presence of GCV we examined the potential use of lethal or sublethal irradiation of Walker 256 carcinosarcoma cells selected for expression of the HSV-tk gene (Walker-tk+). Western blot analysis of Walter-tk+ cells showed similar levels of HSV-tk protein expression at 0, 1, 3, 6 and 9 days after lethal gamma-irradiation. In vitro, there was no difference in the bystander effect exerted by non-irradiated, sublethally irradiated or lethally irradiated Walker-tk+ cells on wild-type Walker cells in the presence of GCV. In vivo experiments demonstrated long-term survival (100 days) in rats implanted intrathecally with sublethally or lethally irradiated Walker-tk+ cells with GCV treatments. Intrathecal implantation of irradiated Walker-tk+ cells either pre-mixed with Walker cells or used in in situ treatment of established Walker tumors resulted in prolonged animal survival compared to controls (p < 0.05). These experiments suggest that the bystander tumoricidal effect is preserved despite gamma-irradiation of the HSV-tk modified tumor cells and that irradiation could be an effective method to prevent long-term resistance to GCV in HSV-tk+ tumor cells.
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PMID:Preservation of the bystander cytocidal effect of irradiated herpes simplex virus thymidine kinase (HSV-tk) modified tumor cells. 894 97