Thymidylate Synthase and Methylenetetrahydrofolate Reductase Gene Polymorphisms and Toxicity to Capecitabine in Advanced Colorectal Cancer Patients Rohini Sharma, Janelle M. Hoskins, Laurent P. Rivory, Manuela Zucknick, Rosyln London, Christopher Liddle, and StephenJ. Clarke Abstract Purpose: To evaluate the effect of thymidylate synthase (TYMS) and methylenetetrahydrofolate reductase (MTHFR) genotypes on toxicity in patients treated with capecitabine for advanced colorectal cancer and to determine the effect of these polymorphisms on the pretreatment levels of serum folate and plasma homocysteine. Experimental Design: Fifty-four patients with a diagnosis of metastatic colorectal cancer were treated with fixed-dose capecitabine. Germ line DNA from patients was genotyped for TYMS TSER,TSER*3G>C, and 3¶ -untranslated 6 bp insertion/deletion (3¶ untranslated region insertion/ deletion), and MTHFR c.677C>Tand c.1298A>C using PCRs and RFLP. Toxicity was graded by National Cancer Institute Common Toxicity Criteria version 2.0. Response was assessed by Response Evaluation Criteria in Solid Tumors. Results: MTHFR c.677C>Tand c.1298A>C genotypes and diplotypes predicted for grade 2/3 toxicities, whereas the TYMS genotypes had no influence. MTHFR c.677 genotype tended to predict overall survival (P = 0.08). MTHFR c.677 influenced pretreatment homocysteine (P < 0.05) and serum folate levels (P < 0.05). Multivariate analysis suggests that MTHFR c.1298 is an independent predictor of toxicity. Conclusions: This study suggests that common genetic variation in MTHFR but not TYMS may be useful for predicting toxicity from capecitabine in patients with advanced colorectal cancer. In addition, MTHFR single nucleotide polymorphisms predicted serum folate and plasma homocysteine levels, and, combined, these factors may be important predictors of capecitabine- induced toxicity. Despite recent advances in the treatment of metastatic colorectal cancer, 5-fluorouracil (5-FU) remains the mainstay of therapy (1). Capecitabine is a rationally designed oral fluoropyrimidine that is being increasingly used both in the adjuvant and metastatic setting. Capecitabine preferentially delivers 5-FU to the tumor via a three-step enzymatic conversion, the final step being catalyzed by thymidine phos- phorylase, which has a higher activity within tumor compared with healthy tissue (2). Little is known about predictors of toxicity, response, and survival in patients with colorectal cancer treated with capecitabine. It is widely recognized that apart from confound- ing environmental and physiologic factors, inherited variability in drug-metabolizing enzymes, drug transporters, and drug targets plays an important role in the variability of treatment outcomes, when drugs are prescribed uniformly to all patients. Drug-related toxicity relates almost exclusively to nontumor tissue and, therefore, inherited polymorphisms can play a central role in determining toxicity. Pharmacogenetic screening may identify those patients that are likely to respond and those that are likely to have severe toxicity due to cytotoxic chemotherapy. As toxicity remains the major limitation to adequate dosing, the ability to predict toxicity before the administration of chemotherapy, and to provide individualized treatment, would likely result in improved outcomes. Thymidylate synthase (TS) is a key enzyme in nucleotide biosynthesis, and is the main intracellular target of the active metabolite of 5-FU, fluorodeoxyuridylate, which forms a ternary complex with TS and 5,10-methylenetetrahydrofolate (5,10-MTHF). This complex prevents methylation of dUMP to Cancer Therapy: Clinical Authors’Affiliation: Department of Molecular Pharmacology, Sydney Cancer Centre, University of Sydney and Storr Liver Unit,Westmead Millennium Institute, Sydney, New SouthWales, Australia Received 2/19/07; revised 7/11/07; accepted10/9/07. Grant support: Cancer Institute of New South Wales research scholarship (R. Sharma). The costs of publication of this article were defrayed in part by the payment of page charges.This article must therefore be hereby marked advertisement in accordance with18 U.S.C. Section1734 solely to indicate this fact. Note: Current address for J.M. Hoskins: University of North Carolina Institute for Pharmacogenomics and Individualized Therapy, University of North Carolina, Chapel Hill, North Carolina. Current address for L.P. Rivory: Johnson & Johnson Research Pty. Ltd., AustralianTechnology Park, Level 4, 1Central Avenue, Eveleigh, NSW 1430, Australia. Current address for M. Zucknick: Imperial College, Department of Epidemiology and Public Health, London, United Kingdom. Preliminary results were presented in poster form at the Annual Meeting of the American Society of Clinical Oncology, 2004. Requests for reprints: Stephen Clarke, Department of Medicine, Concord Hospital and University of Sydney, Concord, NSW 2139, Australia. Phone: 61-2- 97676587; Fax: 61-2-97677603; E-mail: sclarke@med.usyd.edu.au. F 2008 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-07-0425 www.aacrjournals.org ClinCancerRes2008;14(3)February1,2008 817 Downloaded from http://aacrjournals.org/clincancerres/article-pdf/14/3/817/1979268/817.pdf by guest on 24 June 2022