[Dihydropyrimidine deshydrogenase (DPD): rhythm and consequences]

Dihydropyrimidine dehydrogenase mRNA expression in peripheral blood of rectal cancer patients is significantly associated with residual tumor and distant metastases following resection

BACKGROUND

DPD and TS expression have been shown to correlate with response of 5-FU based chemotherapy in colorectal cancer tissue. Little is known about mRNA expression levels of TS and DPD in peripheral blood. The goals of this study were to test the feasibility of DPD and TS detection in blood and their associations to TNM staging and complete surgical resection.

METHODS

Whole blood was drawn 1 day pre- and 10 days post-operatively from 23 patients with rectal cancer. Either adjuvant (n = 15) or neoadjuvant (n = 8) treatment was performed. Tumor cells were enriched from whole blood by density gradient centrifugation prior to extraction of total cellular RNA and subsequent direct quantitative reverse transcriptase-PCR assays.

RESULTS

DPD was detectable in 21/23 patients (91.3%) and TS in 14/23 (61.7%). Stepwise multiple linear regression models showed a significant association of DPD expression with distant metastases (P = 0.004) and residual tumor categories (P = 0.03).

CONCLUSIONS

Quantitative analysis of TS and DPD mRNA expression in peripheral blood of rectal cancer patients is technically feasible. DPD expression levels appear to be associated with residual tumor categories and might serve as a molecular marker for complete tumor resection. Larger studies seem to be warranted to scrutinize our hypothesis.

The dihydrouracil/uracil ratio in plasma, clinical and genetic analysis for screening of dihydropyrimidine dehydrogenase deficiency in colorectal cancer patients treated with 5-fluorouracil

A rapid and cost-effective reversed phase high performance liquid chromatography (HPLC) method for quantification of dihydrouracil to uracil ratio (UH2/U) in plasma has been developed and used to screen for dihydropyrimidine dehydrogenase (DPD) deficiency in nine patients treated with 5-fluorouracil (5-FU). This HPLC method is based on the use of a simultaneous UV detection at 205 and 268nm during the analysis run of the plasma extract and taking into account the particularity that UH2 shows no absorbance response at 268nm. The plasma UH2/U ratio values evaluated by the use of our HPLC assay were found to be highly correlated with the plasma 5-FU-half-life values and were significantly associated with the toxic side effects, whereas, data set provided from genetic analysis of the coding sequences of the DPD gene (DPYD) were found to be insufficient to explain all the cases of the 5-FU-related toxicity pattern. The proposed HPLC assay could be available for routine clinical use for DPD deficiency assessment in patients prior to 5-FU administration.

Regulation of genes of the circadian clock in human colon cancer: reduced period-1 and dihydropyrimidine dehydrogenase transcription correlates in high-grade tumors

Expression of dihydropyrimidine dehydrogenase (DPD) displays a regular daily oscillation in nonmalignant cells. In colorectal cancer cells, the expression of this 5-fluorouracil-metabolizing enzyme is decreased, but the reason remains unclear. In this study, we analyzed by real-time reverse transcription-PCR (RT-PCR) the expression of DPD and of members of the cellular oscillation machinery, period 1 (Per1), period 2 (Per2), and CLOCK, in primary colorectal tumors and normal colon mucosa derived from the same patients. Analysis of tumors according to differentiation grade revealed a 0.46-fold (P = 0.005) decrease for DPD mRNA and a 0.49-fold (P = 0.004) decrease for Per1 mRNA in undifferentiated (G3) tumors compared with paired normal mucosa. In this tumor cohort, the correlation between DPD and Per1 levels was r = 0.64, P < 0.01. In moderately differentiated (G2) colon carcinomas, reduction of DPD and Per1 mRNA levels did not reach significance, but a significant correlation between the respective mRNA levels was detectable (r = 0.54; P < 0.05). The decrease and correlation of DPD and Per1 mRNA levels were even more pronounced in female (G3) patients (DPD: female, 0.35-fold, P < 0.001 versus male, 0.58-fold, P < 0.05; and Per1: female, 0.47-fold, P < 0.01 versus male, 0.52-fold, P < 0.01). The highly significant correlation of DPD mRNA with Per1 mRNA expression suggests control of DPD transcription by the endogenous cellular clock, which is more pronounced in women. Our results also revealed a disturbed transcription of Per1 during tumor progression, which might be the cause for disrupted daily oscillation of DPD in undifferentiated colon carcinoma cells.

[Pro or con the phenotyping/genotyping of patients treated by 5-Fluorouracil to prevent adverse drug reactions?]

5-fluorouracil, (5-FU) is an antimetabolite used in many types of cancers. It has a narrow therapeutic index. More than 80% of administered 5-FU is detoxified in 5-fluoro-5,6-dihydrouracil (5-FUH2) by an enzyme: dihydropyrimidine dehydrogenase (DPD). Half life increased with DPD deficiency. Thus, patients presenting a partial or profound DPD deficiency have an increased risk of severe or lethal toxicity. DPD deficiency was estimated between 3 to 5% in the normal population. Different approaches have been developed: Pharmacogenetic on the DPD gene or pharmacologic measuring DPD activity. More than 30 mutations have been reported on this gene. The more common mutation is the slice-site mutation IVS14+1G>A. Analysis of the various mutations allowed to identify a population at risk with a DPD deficiency. DPD activity is determined in peripheral blood mononuclear cells. This assay offers the capability of identifying individuals who are completely deficient in DPD activity and those who are partially deficient. Assays to detect DPD deficiency are not used as a screening test to prevent 5-FU toxicity.

How may anticancer chemotherapy with fluorouracil be individualised?

Fluorouracil is used clinically against various solid tumours. Both fluorouracil toxicity and pharmacokinetics vary highly within and between individuals. The reasons why doses are not individualised routinely are difficulties in defining, predicting and achieving an optimal fluorouracil exposure or dose because of a narrow therapeutic index, nonlinear pharmacokinetics, variabilities in administration rates and metabolism, and in targets like thymidylate synthase. To individualise fluorouracil administration before the first dose, assessment of the individual dihydropyrimidine dehydrogenase (DPD) activity may be useful, because this genetically highly polymorphic enzyme controls approximately 80% of fluorouracil elimination. A complete or partial loss of DPD activity in 0.1 and 3-5% of Caucasians, respectively, leads to increased fluorouracil exposure and toxicity. Several methods to assess DPD activity in patients have been proposed (genotyping, various phenotyping methods), but each of them has limitations, as has the fluorouracil test dose approach. To adapt exposure towards fluorouracil a priori, a combination of genotyping and phenotyping may yield better prediction of toxicity than one method alone. A prerequisite for dose adaptation is the definition of fluorouracil exposure ranges with sufficient therapeutic activity, but without serious toxicity. While an increased risk of leukopenia, diarrhoea, stomatitis, and hand-foot syndrome during continuous 5-day infusions was related to fluorouracil exposures above an area under the plasma concentration-time curve (AUC) threshold of 25-30 mg.h/L, tumour response was higher when an AUC of approximately 30 mg.h/L was achieved, illustrating the extremely narrow therapeutic window of fluorouracil. Pharmacokinetic target values are less clear for other regimens, including chronomodulated regimens, which yielded a superior clinically efficacy and tolerability in several trials. However, the monitoring of fluorouracil plasma concentrations seems principally useful for individual a posteriori dose adjustment. Whether an adaptation of the fluorouracil starting dose to the results of two DPD activity tests before fluorouracil administration a priori, and the adaptation of doses to fluorouracil exposure a posteriori is a reasonable approach to better prevent toxicity and increase efficacy, remains to be evaluated in randomised clinical studies comparing these strategies to routine clinical safety monitoring.