title: Development and characterization of a human colon adenocarcinoma xenograft deficient in thymidine salvage.
abstract: In order to determine the contribution of thymidine (dThd) salvage to intrinsic resistance to antimetabolites (5-fluoropyrimidines, antifolates) in the human colon adenocarcinoma xenograft, H X GC3, a subline deficient in thymidine kinase has been developed. A cell line (GC3/M) was established in continuous culture that demonstrated a karyotype identical to that of the stem line of H X GC3 (46,X, - Y + 12). After inoculation of GC3/M cells into immune-deprived CBA/CaJ mice, the H X GC3/M xenografts retained histological, histochemical, and growth characteristics of the H X GC3 xenograft. To develop a line deficient in dThd salvage, GC3/M cells were selected with BrdUrd (100 micrograms/ml). Three clones characterized were unable to proliferate in HAT medium, and were deficient (less than 10% control) in the cytosolic form of thymidine kinase. Activities of dThd phosphorylase and dTMP synthase were unchanged from parental GC3/M cells. Of the three clones inoculated into mice, GC3/M TK- 100 C3 was tumorigenic, the xenografts demonstrating histological and growth characteristics similar to H X GC3. The in vivo activity of the cytosolic form of dThd kinase was 3.5% of that in H X GC3 xenografts. Incorporation in vivo of [methyl-3H]dThd into acid insoluble material was 14% of that in H X GC3 tumors. Autoradiographs prepared from these tumors demonstrated that incorporation of radiolabel into nuclei occurred only in stromal cells derived from the host. It is anticipated that H X GC3/M TK- 100 C3 will be a line valuable for determining the role of dThd salvage in intrinsic resistance to 5-fluoropyrimidines or antifolates in human colon adenocarcinomas growing as xenografts and also the relevance of dTMp synthase as a target for antimetabolites in this histiotype.
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D002272:Carcinoembryonic Antigen / Q000032:analysis; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D005472:Fluorouracil / Q000627:therapeutic use; D006801:Humans; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D051379:Mice; D009077:Mucins / Q000378:metabolism; D009368:Neoplasm Transplantation; D013936:Thymidine / Q000378:metabolism*; D013937:Thymidine Kinase / Q000172:deficiency; D014183:Transplantation, Heterologous
chemical_list: D002272:Carcinoembryonic Antigen; D007527:Isoenzymes; D009077:Mucins; D007770:L-Lactate Dehydrogenase; D013937:Thymidine Kinase; D005472:Fluorouracil; D013936:Thymidine