title: Limits to thymidylate synthase and TP53 genes as predictive determinants for fluoropyrimidine sensitivity and further evidence for RNA-based toxicity as a major influence.
abstract: The major determinants of 5-flurouracil (5-FU) response would seem, based on accumulated literature, to be thymidylate synthase (TYMS, TS) expression levels, TS gene modifications, and TP53 status. We tested 5-FU sensitivity in yeast and human cancer cell models in which TS or TP53 alleles and expression were varied. Polymorphic TS tandem repeat status, TS expression levels reported, TS intragenic mutations, and TP53 status in outbred and experimental cancer cell lines did not predict 5-FU sensitivity or resistance. Novel observations included a dose-resistant persistence of unbound TS protein in many cancers and, upon 5-FU treatment of the colon cancer cell line, HCT116, evidence of allelic switching favoring transcripts of the mutant TS allele. The reported alleles having an intragenic mutation could not be causally associated with major degrees of 5-FU sensitivity. In yeast, TS protein was altered upon treatment with FdUMP, but 5-FU toxicity seemed to be largely RNA-based, being rescued by uridine rather than by thymidine. Cancer cell lines were also rescued from 5-FU toxicity with uridine rather than thymidine. Additionally, a TS (CDC21) knockout yeast strain, obviating any potential role for TS protein as a target, was hypersensitive to 5-FU. When denatured proteins from cancer cells treated with radiolabeled 5-FU were labeled, species with alternative molecular weights other than TS were visualized, providing further evidence for alternative 5-FU protein targets. These data emphasize that TS and TP53 status do not consistently explain the variance in responses of fluoropyrimidine-treated cancer cells, in part due to RNA-based toxicity.
authors.affiliation: Department of Surgery and Pathology, Jefferson Pancreas, Biliary, and Related Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Brody
authors.forename: Tomas
authors.initials: T
authors.lastname: Hucl
authors.forename: Christina L
authors.initials: CL
authors.lastname: Costantino
authors.forename: James R
authors.initials: JR
authors.lastname: Eshleman
authors.forename: Eike
authors.initials: E
authors.lastname: Gallmeier
authors.forename: Heng
authors.initials: H
authors.lastname: Zhu
authors.forename: Michiel S
authors.initials: MS
authors.lastname: van der Heijden
authors.forename: Jordan M
authors.initials: JM
authors.lastname: Winter
authors.forename: Agnieszka K
authors.initials: AK
authors.lastname: Wikiewicz
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Yeo
authors.forename: Scott E
authors.initials: SE
authors.lastname: Kern
mesh_terms: D000483:Alleles; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D001483:Base Sequence; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics; D005472:Fluorouracil / Q000494:pharmacology*; D016158:Genes, p53; D045325:HCT116 Cells; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012334:RNA, Neoplasm / Q000187:drug effects* / Q000235:genetics; D013936:Thymidine / Q000494:pharmacology; D013940:Thymidylate Synthase / Q000096:biosynthesis* / Q000172:deficiency / Q000235:genetics; D014529:Uridine / Q000494:pharmacology; D015003:Yeasts / Q000187:drug effects / Q000201:enzymology / Q000235:genetics
chemical_list: D000964:Antimetabolites, Antineoplastic; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D013940:Thymidylate Synthase; D005472:Fluorouracil; D013936:Thymidine; D014529:Uridine