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)

The efficacies of ganciclovir (GCV), penciclovir (PCV) and acyclovir (ACV) in inducing cell death in the herpes simplex virus thymidine kinase (HSVTK) system were compared. HSVTK-transformed baby hamster kidney cells treated with GCV, PCV or ACV were monitored for growth by viable count, and for death by TUNEL assay, propidium iodide staining, detection of phosphatidyl serine translocation and detection of DNA laddering. All compounds delayed growth or reduced viability of HSVTK-transformed cells. Drug treatment reduced levels of cyclin B1 message (which normally peaks in G2/M-phase of the cell cycle) and induced a four- to fivefold upregulation of GADD45 message. Treatment with GCV or PCV induced rapid accumulation of cells in S-phase and apoptotic death. Treatment with ACV, however, was associated with sustained S-phase arrest. GCV (and to a lesser extent PCV) increased phosphatidyl serine translocation, induced positive TUNEL results with alterations in cell morphology, caused marked propidium iodide staining and induced DNA laddering. By contrast, up to 7 days' exposure to ACV did not induce DNA laddering, with very little TUNEL staining. ACV treatment had little effect on phosphatidyl serine translocation and propidium iodide staining was markedly reduced compared with treatment with the other compounds. Thus, by all criteria, GCV was the most potent inducer of cell death. The current theories regarding apoptosis or necrosis as the preferred form of cell death in prodrug gene therapy are considered and the suitability of PCV or ACV as potential alternatives to GCV in the HSVTK system is discussed.
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PMID:Ganciclovir and penciclovir, but not acyclovir, induce apoptosis in herpes simplex virus thymidine kinase-transformed baby hamster kidney cells. 1295 26

The suicide system TK/GCV is an enzyme/prodrug therapy that involves the transfer of the cDNA for the herpes simplex virus thymidine kinase gene (TK) into tumor cells which then sensitizes the cells to the non-toxic antiviral drug ganciclovir. Although extensively characterized, the suicide system TK/GCV conceals the details of its mechanism of action. In order to shed some light on this issue, we conducted experiments designed to identify key features of sensitive cells, as compared to cells that displayed reduced sensitivity to TK/GCV. Cell lines displaying different degrees of sensitivity underwent apoptotic cell death upon treatment with TK/GCV. S-phase delay, however, was almost exclusively restricted to sensitive cells and was impaired in a model of treatment-induced resistance. In this model genes with differential expression associated to induced resistance were identified. Noteworthy, two cell cycle-related genes (CCNE1 and GADD45) were functionally validated as conditioners of cellular sensitivity to TK/GCV. The relevance of cell cycle control was further demonstrated by experiments showing the association of Chk1 activation with greater TK/GCV cytotoxicity. Combination treatment with Chk1 inhibitor UCN-01 induced, in sensitive cells, an antagonistic effect on TK/GCV cytotoxicity highlighting the relevance of Chk1's activity on TK/GCV mechanism of action. These results reveal the relevance of cell cycle control pathways in the cytotoxicity induced by the TK/GCV system identifying candidate genes as conditioners of TK/GCV sensitivity. Moreover it points out, for the first time at Chk1 activation as a key factor to mediate TK/GCV cytotoxicity.
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PMID:Cell cycle control pathways act as conditioning factors for TK/GCV sensitivity in pancreatic cancer cells. 2059 44