title: Multi-log cytotoxicity of carbocyclic 2'-deoxyguanosine in HSV-TK-expressing human tumor cells.
abstract: Ganciclovir (GCV) is widely used as a prodrug for selective activation in tumor cells expressing herpes simplex virus thymidine kinase (HSV-TK) because of its ability to induce multi-log cytotoxicity to HSV-TK-expressing as well as nonexpressing bystander cells. We now report that another substrate for HSV-TK, D-carbocyclic 2'-deoxyguanosine (CdG), induces multi-log cytotoxicity in HSV-TK-expressing and bystander cells at concentrations <or=3 microM. We have compared the cytotoxicity and cell cycle effects of CdG to that observed with GCV in two human tumor cell lines. The results demonstrated that cytotoxicity of CdG was similar to that of GCV in both U251 glioblastoma and SW620 colon carcinoma cells that stably expressed HSV-TK. In addition, CdG induced a potent bystander effect in both cell types in co-cultures consisting of HSV-TK-expressing and nonexpressing bystander (lacZ-expressing) cells at ratios of 50:50 or 10:90. Selectivity for HSV-TK-expressing compared to lacZ-expressing cells was similar for CdG and GCV in the U251 cells, however CdG was less selective than GCV in the SW620 cell lines. Despite their ability to induce multi-log cytotoxicity at similar concentrations, CdG and GCV exhibited differential effects on cell cycle progression. Cells incubated with 1 microM CdG for 24 hr accumulated in S-phase and G(2)/M after drug washout, and the majority of cells died prior to cell division. This contrasts with the delayed effects of 1 microM GCV that were not evident until after cell division when cells attempted S-phase for the second time. Thus, CdG is a potent cytotoxic agent that merits further investigation to determine whether it will be therapeutically effective in enzyme-prodrug therapy with HSV-TK.
authors.affiliation: Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI 48109, USA. dshewach@umich.edu
authors.forename: Donna S
authors.initials: DS
authors.lastname: Shewach
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Murphy
authors.forename: Blaine W
authors.initials: BW
authors.lastname: Robinson
authors.forename: Jennifer
authors.initials: J
authors.lastname: Vuletich
authors.forename: Paul D
authors.initials: PD
authors.lastname: Boucher
authors.forename: Anna L
authors.initials: AL
authors.lastname: Blobaum
authors.forename: Laura
authors.initials: L
authors.lastname: Zerbe
authors.forename: John A
authors.initials: JA
authors.lastname: Secrist
authors.forename: William B
authors.initials: WB
authors.lastname: Parker
mesh_terms: D000998:Antiviral Agents / Q000378:metabolism / Q000494:pharmacology* / Q000627:therapeutic use; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000821:virology; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology* / Q000627:therapeutic use; D004789:Enzyme Activation / Q000187:drug effects; D015774:Ganciclovir / Q000378:metabolism / Q000494:pharmacology* / Q000627:therapeutic use; D018014:Gene Transfer Techniques; D005909:Glioblastoma / Q000188:drug therapy / Q000235:genetics / Q000821:virology; D011355:Prodrugs / Q000378:metabolism / Q000494:pharmacology* / Q000627:therapeutic use; D018139:Simplexvirus / Q000201:enzymology; D013937:Thymidine Kinase / Q000096:biosynthesis* / Q000235:genetics; D014407:Tumor Cells, Cultured; D014764:Viral Proteins / Q000096:biosynthesis*
chemical_list: D000998:Antiviral Agents; D011355:Prodrugs; D014764:Viral Proteins; C061610:2-amino-1,9-dihydro-9-(3-hydroxy-4-(hydroxymethyl)cyclopentyl)-6H-purine-6-one; D013937:Thymidine Kinase; D003849:Deoxyguanosine; D015774:Ganciclovir