Copy-number analysis of topoisomerase and thymidylate synthase genes in frozen and FFPE DNAs of colorectal cancers

Jinsheng Yu, Ryan Miller, Wanghai Zhang, Mala Sharma, Vicky Holtschlag, Mark A. Watson, Howard L. McLeod

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

Background: Archived formalin-fixed, paraffin-embedded specimens represent an important resource for pharmacogenomic analysis in retrospective clinical studies but the quality of results from formalin-fixed, paraffin-embedded samples is of concern due to the fact of the degradation of DNAs and RNAs from formalin-fixed, paraffin-embedded tissues. Methods: In the present study, we used DNA from fresh frozen as well as formalin-fixed, paraffin-embedded tumor to detect copy-number changes in colorectal cancer, and our data shows that formalin-fixed, paraffin-embedded DNAs were able to deliver reliable copy-number data, and that quantitative PCR had the ability to detect copy-number changes from deletion to amplification, with high concordance of copy-number calls among formalin-fixed, paraffin-embedded and frozen DNAs. Results: The amplification of topoisomerase I and deletion of thymidylate synthase were found in 23% (12/52) and 27% (14/52) of colorectal cancers, but EGF receptor amplification was not common (5/52, <10%). Among 52 colorectal cancers, 31 tumors were both topoisomerase I and thymidylate synthase diploid, which may have a worse outcome for tumor chemotherapy; and there were five tumors with favorable genomics (topoisomerase I amplification and thymidylate synthase deletion). Furthermore, topoisomerase I-amplified tumors had a two-times higher RNA level and a nearly twofold higher protein expression level than did the diploid tumors (p < 0.001 and 0.01, respectively), but there were no correlations between copy-number status and RNA or protein level for thymidylate synthase. Conclusions: Our study suggests a potential pharmacogenomic influence of topoisomerase I copy-number alteration on its RNA/protein expressions, which could be reflected on tumor response to chemotherapy in human colorectal cancer.

Original languageEnglish
Pages (from-to)1459-1466
Number of pages8
JournalPharmacogenomics
Volume9
Issue number10
DOIs
StatePublished - 2008

Keywords

  • Colorectal cancer
  • DNA copy-number
  • Formalin-fixed paraffin-embedded tissue
  • Quantitative PCR
  • Thymidylate synthase
  • Topoisomerase I

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