This Article Full Text Full Text (PDF) All Versions of this Article: 0008-5472.CAN-08-3610v1 69/3/984    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Brody, J. R. Articles by Kern, S. E. Search for Related Content PubMed PubMed Citation Articles by Brody, J. R. Articles by Kern, S. E.

Limits to Thymidylate Synthase and TP53 Genes as Predictive Determinants for Fluoropyrimidine Sensitivity and Further Evidence for RNA-Based Toxicity as a Major Influence

Departments of ¹ Surgery and ² Pathology, Jefferson Pancreas, Biliary, and Related Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania; and ³ Department of Oncology, Johns Hopkins University, Baltimore, Maryland

Requests for reprints: Scott E. Kern, Department of Oncology, Johns Hopkins University, CRB 451, 1600 Orleans Street, Baltimore, MD 21231. Phone: 410-614-3314; Fax: 410-614-9705; E-mail: sk{at}jhmi.edu.

Key Words: Thymidylate synthase expression • 5-fluorouracil • sensitivity • chemotherapeutic resistance • p53

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. [Cancer Res 2009;69(3):984–91]