Epigenetic and genetic alterations of DYPD in severe toxicity to 5-fluorouracil-based chemotherapy in gastrointestinal cancer.

Abstract

e12005 Background: Deficiency of the enzyme dihydropyrimidine dehydrogenase (DPD) has been associated with the development of severe toxicity to 5-FU in gastrointestinal (GI) cancer patients. Promoter hypermethylation has been proposed as an alternative mechanism for DPD deficiency not explained by deleterious mutations. Moreover, thymidylate synthase (TYMS) activity also influences 5-FU cytotoxic effects. The primary objective of this study was to analyze the methylation status of dihydropyrimidine dehydrogenase gene (DPYD) promoter region by quantitative methylation-specific PCR in GI cancer patients who developed severe 5-FU toxicity. Secondary objectives were the analysis of large intragenic rearrangements of DPYD and the assessment of DPD and TYMS immunoexpression in tumor tissue samples. Methods: DPYD hypermethylation was evaluated through quantitative methylation-specific PCR in DNA extracted from peripheral blood (PB) samples and micro-dissected tumor tissue (MTT), using a colon cancer cell line as control. The screening for large DPYD intragenic rearrangements was performed with the MLPA method. Specific antibodies were used against DPD and TYMS to assess the immunoexpression of those enzymes in representative tissue sections. Results: DPYD promoter methylation was absent in all the PB and MTT samples from the 45 patients experiencing severe 5-FU toxicity and controls. Large DPYD intragenic rearrangements were also not detected in both groups. Severe 5-FU toxicity wasn't associated with DPD or TYMS immunoexpression either. Clinically, 5-FU toxicity was more frequent after 5-FU in bolus administration, as well as in gastric/esophageal primary site and in patients with a worse performance status score (p < 0.05). Conclusions: Promoter methylation and large intragenic rearrangements of DPYD do not contribute to the development of 5-FU severe toxicity. Additional studies are required to investigate other genetic and/or clinical factors, which might be responsible for severe forms of 5-FU toxicity in GI cancer patients. No significant financial relationships to disclose.