Folate levels measured by LC–MS/MS in patients wit

Authors: Helena Taflin Yvonne Wettergren Elisabeth Odin Kristoffer Derwinger

Publish Date: 2014/09/20

Volume: 74, Issue: 6, Pages: 1167-1174

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Abstract

Calcium folinate leucovorin which is converted in vivo into biologically active folate enhances the potency of 5fluorouracil 5FUbased chemotherapy in colorectal cancer A common dosage of leucovorin in adjuvant and palliative settings is 60 mg/m2 The aim was to determine the levels of tetrahydrofolate THF 510methylenetetrahydrofolate methyleneTHF and 5methyltetrahydrofolate methylTHF in tumour and mucosa of colorectal cancer patients who received different dosages of leucovorin intravenously at time of surgeryEighty patients scheduled for colorectal resection with indication of colorectal cancer were randomised into four groups to receive leucovorin at 0 60 200 or 500 mg/m2 respectively Blood samples were taken 10 and 30 min after leucovorin administration Biopsy samples from tumour and mucosa were collected and snapfrozen at surgery The levels of THF methyleneTHF and methylTHF in tumour and mucosa were assessed by liquid chromatography electrospray ionisation tandem mass spectrometry LC–MS/MS and the results were related to clinical diagnosis and therapeutic regimensThe folate levels in tissue revealed extensive interindividual variability The mean methyleneTHF value for the four treatment groups were 880 1769 3024 and 3723 pmol/gww Only half of the patients who received 60 mg/m2 leucovorin had higher levels of methyleneTHF in tumour than patients who received 0 mg/m2 leucovorin Rectal cancer patients had significantly lower levels of methyleneTHF compared with colon cancer patientsThere was a large interpatient variability of tissue folate levels in colorectal cancer patients after supplementation with leucovorin at standardised dosage High leucovorin doses were needed to exceed baseline methyleneTHF values especially in rectal cancer patients The results indicate that the standardised leucovorin dose may be insufficient to attain the full antitumour effect of 5FU Further studies are needed to establish whether higher dosage yields a better treatment responseIn 2012 colorectal cancer was the second most diagnosed cancer in Europe after breast cancer Colorectal cancer was also responsible for the second highest number of cancerrelated deaths after lung cancer 1 Currently the only curative therapy for patients with colorectal cancer is surgery with radical removal of the tumour When the cancer is limited to the bowel wall surgery itself normally attains the desired oncologic outcome In cases of lymph node involvement ie stage III disease there is a high risk of tumour recurrence It has been confirmed in several studies that a 5fluorouracil 5FUbased chemotherapy regimen improves both overall and diseasefree survival for patients with stage III disease 2 3 4 Considering the numbers of patients and administered treatments it is of great importance to find methods to tailor or at least optimise the therapy However even patients with highrisk profiles such as poorly differentiated tumours without lymph node metastasis could benefit from additional treatment 5 6 In this postoperative setting the term adjuvant treatment is commonly used 5FUbased chemotherapy has also been shown to prolong overall survival in palliative settings ie for patients with confirmed distant metastasis 75Fluorouracil was developed in the 1950s by Charles Heidelberger who discovered that rat hepatomas were consuming the pyrimidine uracil more rapidly than normal rat liver tissue 8 Thus uracil was identified as a target molecule for chemotherapy 5FU is an analogue of uracil in which the hydrogen at position 5 is replaced by fluorine Using the same mechanism to enter the cell as uracil the 5FU molecule is converted into the active metabolite 5fluoro2′deoxyuridine 5′monophosphate FdUMP which forms an inhibitory ternary complex with thymidylate synthase TS and 510methylenetetrahydrofolate methyleneTHF This results in the inhibition of thymidylate synthesis and impairment of both DNA synthesis and DNA repair The greatest impact is on cells that are rapidly dividing such as tumour epithelial cellsThe response rate of colorectal tumours to 5FU monotherapy is only around 10  By adding the stable calcium salt of 5formyltetrahydrofolic acid Calciumfolinate which is converted in the liver into methyleneTHF the tumour response rate can be improved to 21  as has been shown in a metaanalysis 9 The Nordic FLV therapy which is a combination of 5FU and leucovorin REF 12 that was introduced in the 1990s is still the cornerstone of both adjuvant and palliative treatments for colorectal cancer in Nordic countries The standard dosage is 500 mg/m2 5FU plus 60 mg/m2 leucovorin in the form of calciumfolinate administered as an intravenous infusion 2 days in a row The 2day treatment is followed by a pause for 12 days The standard protocol is usually 6 months long The regimen has been duly updated with the incorporation of novel drugs such as oxaliplatin and antibodies into more effective combination therapies Although it is a well established regimen the evidence for the leucovorin dosage used is rather limited Different regimens used in clinical practice worldwide apply levels of leucovorin that range from 20 to 500 mg/m2Leucovorin has no intrinsic antitumour effect but it enhances the effect of 5FU by providing the cofactor methyleneTHF in abundance and by stabilising the ternary complex 10 However leucovorin must first be converted in two steps into methyleneTHF which is the active metabolite This requirement for metabolic activation may result in interindividual differences in uptake thereby compromising the benefit gained from the addition of leucovorin in some of the patients The leucovorin metabolism pathway has been described by Priest and colleagues 11

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