Polymorphisms in the thymidylate synthase gene predict response to 5-fluorouracil therapy in colorectal cancer

Increased Mean Corpuscular Volume of Erythrocytes during Capecitabine Treatment: A Simple Surrogate Marker for Clinical Response

Aims and Background

Capecitabine, as all fluoropyrimidines, interferes with vitamin metabolism and may thus have an impact on hematopoiesis. It is metabolized to its active form 5-fluoruracil by the enzyme thymidine phosphorylase, which exists in higher concentrations in tumor tissue and liver than in normal tissues. In the study, we investigated the changes in mean corpuscular volume (MCV) of red blood cells and the possible correlation of these changes with the clinical outcome of capecitabine treatment in women with metastatic breast cancer.

Methods and Study Design

Data from 75 metastatic breast cancer patients were analyzed retrospectively. Capecitabine was used at a dose of 2500 mg/m2 daily for 14 days of every 3-week period. Mean corpuscular volume of red blood cells and other parameters of complete blood count were recorded at the beginning of the treatment, in the ninth week, and periodically thereafter.

Results

Mean age was 51.5 ± 10.8 and 61.3% of the patients were premenopausal. Capecitabine was administered as the median 3rd line (min-max: 1–9) treatment and a median of 6 cycles (min-max: 1–24) for metastatic breast cancer. Median ΔMCV level (post-treatment values at ninth week - baseline) was 8. ΔMCV was ≥8 in 37 patients and <8 in 38 patients. The 35 of the 37 patients with ΔMCV level ≥8 and 25 of the 38 patients with ΔMCV level <8 had clinical benefit (complete response + partial response + stable disease) from capecitabine treatment (P = 0.02). However, the difference between progression-free survival of the patients with ΔMCV levels higher than 8 and those with ΔMCV levels lower than 8 according to Kaplan-Meier survival analysis was not statistically significant (6.7 and 4.3 months, respectively, P = 0.26). Additionally, median ΔMCV level was 9.1 (min-max: −2.4 to 24.9) among patients who had clinical benefit and 5.90 (min-max: −0.8 to 12.3) among nonresponders (P = 0.016).

Conclusions

Capecitabine increases the mean corpuscular volume levels of red blood cells by a yet unidentified mechanism. Early increment of mean corpuscular volume levels is higher than 8, i.e. by the 9th week, might predict clinical benefit from the treatment.

Lack of prognostic value of mean corpuscular volume with capecitabine therapy in metastatic breast cancer

BACKGROUND

Capecitabine is an oral fluoropyrimidine derivative which is frequently used alone or in combination regimens for the treatment of metastatic breast cancer. Although overall and progression free survivals have increased in recent years with the use of new generation drugs, predictive factors that would further improve the outcomes are needed. Previous studies have demonstrated the relation between post-treatment increase in mean corpuscular volume (MCV) and predicting therapy response as well as survival. The present study investigated the clinical impact of MCV elevation in metastatic breast cancer patients treated with capecitabine.

MATERIALS AND METHODS

The data of a total of 82 patients from three centers followed between June 2005 and June 2013 were retrospectively analyzed. The demographic data and hormone receptor status of the patients, as well as initial examination before and after treatment and data concerning progression were recorded. MCV ≥ 100 fl was considered as macrocytosis. Capecitabine was given at a dose of 2500 mg/m2 daily for 14 days every three weeks. Pre-treatment and post-treatment MCV and other parameters of complete blood count were recorded. Post-treatment initial evaluation was performed after 2 cycles of therapy.

RESULTS

The median age of the patients was 46.5 years (range 26-72 years) and 54% were premenopausal. Performance status was ECOG 0 and 1 in 81 (99%) patients. The median number of cycles for capecitabine therapy was 5 (min-max: 2-18). The median ΔMCV level (post-treatment values at sixth week - baseline) was 6.4. Whilst ΔMCV was ≥ 6.4 in 42 patients, it was <6.4 in 40 patients. Clinical benefit (complete response+partial response+stable disease) was observed in 37 (88%) of 42 patients with a median ΔMCV ≥ 6.4 and in 30 (75%) of 40 patients with ΔMCV <6.4 with no statistically significant difference (p=0.158). No significant difference was determined between the group with ΔMCV ≥ 6.4 and the group with ΔMCV <6.4 in terms of progression-free survival (11 vs 12 months) (p=0.55) and overall survival (20 months vs. 24 months) (p=0.11).

CONCLUSIONS

The identification of new predictive markers in metastatic breast cancer is very important. In some recent studies, increase in MCV has been suggested as a marker in tumor response. In the present study, however, no significant difference was determined between tumor response and increase in MCV. Further studies including higher numbers of patients are needed to determine whether increase in MCV is a predictive marker or not.

UGT1A1 predicts outcome in colorectal cancer treated with irinotecan and fluorouracil

AIM: To evaluate effects of UDP-glucuronosyltransferase1A1 (UGT1A1) and thymidylate synthetase (TS) gene polymorphisms on irinotecan in metastatic colorectal cancer (mCRC).

METHODS: Two irinotecan- and fluorouracil-based regimens, FOLFIRI and IFL, were selected as second-line therapy for 138 Chinese mCRC patients. Genomic DNA was extracted from peripheral blood samples before treatment. UGT1A1 and TS gene polymorphisms were determined by direct sequencing and restriction fragment length polymorphism, respectively. Gene polymorphisms of UGT1A1*28, UGT1A1*6 and promoter enhancer region of TS were analyzed. The relationship between genetic polymorphisms and clinical outcome, that is, response, toxicity and survival were assessed. Pharmacokinetic analyses were performed in a subgroup patients based on different UGT1A1 genotypes. Plasma concentration of irinotecan and its active metabolite SN-38 and inactive metabolite SN-38G were determined by high performance liquid chromatography. Differences in irinotecan and its metabolites between UGT1A1 gene variants were compared.

RESULTS: One hundred and eight patients received the FOLFIRI regimen, 29 the IFL regimen, and one irinotecan monotherapy. One hundred and thirty patients were eligible for toxicity and 111 for efficacy evaluation. One hundred and thirty-six patients were tested for UGT1A1*28 and *6 genotypes and 125 for promoter enhancer region of TS. Patients showed a higher frequency of wild-type UGT1A1*28 (TA6/6) compared with a Caucasian population (69.9% vs 45.2%). No significant difference was found between response rates and UGT1A1 genotype, although wild-type showed lower response rates compared with other variants (17.9% vs 24.2% for UGT1A1*28, 15.7% vs 26.8% for UGT1A1*6). When TS was considered, the subgroup with homozygous UGT1A1*28 (TA7/7) and non-3RG genotypes showed the highest response rate (33.3%), while wild-type UGT1A1*28 (TA6/6) with non-3RG only had a 13.6% response rate, but no significant difference was found. Logistic regression showed treatment duration was closely linked to clinical response. In toxicity comparison, UGT1A1*28 TA6/6 was associated with lower incidence of grade 2-4 diarrhea (27.8% vs 100%), and significantly reduced the risk of grade 4 neutropenia compared with TA7/7 (7.8% vs 37.5%). Wild-type UGT1A1*6 (G/G) tended to have a lower incidence of grade 3/4 diarrhea vs homozygous mutant (A/A) genotype (13.0% vs 40.0%). Taking UGT1A1 and TS genotypes together, lower incidence of grade 2-4 diarrhea was found in patients with non-3RG TS genotypes, when TA6/6 was compared with TA7/7 (35.3% vs 100.0%). No significant association with time to progression (TTP) and overall survival (OS) was observed with either UGT1A1 or TS gene polymorphisms, although slightly longer TTP and OS were found with UGT1A1*28 (TA6/6). Irinotecan PK was investigated in 34 patients, which showed high area under concentration curve (AUC) of irinotecan and SN-38, but low AUC ratio (SN-38G / SN-38) in those patients with UGT1A1*28 TA7/7.

CONCLUSION: A distinct distribution pattern of UGT1A1 genotypes in Chinese patients might contribute to relatively low toxicity associated with irinotecan and 5-fluorouracil in mCRC patients.

[Antimetabolites]

Antimetabolites are cytotoxic agents, which have been developed for more than 50  years. Which cancer patient did not receive or will not receive 5-fluorouracil or methotrexate during the evolution his or her disease? Antimetabolites are defined as interfering with the synthesis of the DNA constituents; they are structural analogues, either of purine and pyrimidine bases (or the corresponding nucleosides), or of folate cofactors, which are involved at several steps of purine and pyrimidine biosynthesis. Their first mechanism of action is, therefore, to induce depletion in nucleotides inducing in turn an inhibition of DNA replication. However, some of them are able to get inserted fraudulently into nucleic acids, inducing structural abnormalities leading to cell death by other mechanisms, including DNA breaks. We present in this paper, for the three classes of antimetabolites, both ancient and recent molecules as well as molecules still in clinical trials, without exhaustivity.

Molecular analysis of the polymorphisms of thymidylate synthase on cell-free circulating DNA in blood of patients with advanced colorectal carcinoma

As a key enzyme in folate metabolism, the thymidylate synthase (TS) is important for the synthesis of nucleotides. Its polymorphisms may affect the TS gene expression and the susceptibility for Fluoropyrimidine (FU)-based chemotherapies. In this study, we assessed the relationship between the TS genotypes and clinical outcome to 5-FU-based chemotherapy, and examined whether cell-free circulating DNA is applicable for these molecular analyses. We combined the variable number tandem repeat (VNTR) and single nucleotide (SNP) polymorphisms of the TS promoter and the deletion variants (1494del6) in the 3'UTR with the occurrence of loss of heterozygosity (LOH) at the microsatellite markers D18S59, D18S1140, and D18S976 mapped up- and downstream to the TS locus. Cell-free blood DNA, tumor tissues, and leukocytes of 51 patients with advanced colorectal cancer were used. Genotyping revealed linkage disequilibrium between TS promoter and 3'UTR (p = 0.03) in blood and leukocytes. Inverse associations of the response to therapy with the number of polymorphisms (p = 0.05) and the 494del6 polymorphism (p < 0.02) were detected on serum DNA. The quantification of serum DNA showed significant correlations with the 1494del6 variant (p = 0.006) in tumor tissues and the combined polymorphisms in leukocytes (p < 0.04). In contrast to the low LOH frequency in blood, LOH spanned more than one marker in the primary tumor of the majority of the patients suggesting the loss of the entire TS locus. Our data provide insight into the molecular diversity of the regulation of the TS gene expression. This is the first study that compares multi-variant TS genotypes in different clinical specimens.

Predictive diagnostics in colorectal cancer: impact of genetic polymorphisms on individual outcomes and treatment with fluoropyrimidine-based chemotherapy

The 5-fluorouracil (5-FU)-based chemotherapy is a standard treatment for patients with colorectal cancer. However, a relevant number of patients suffer from severe toxic side effects, such as haemotoxicity, while lacking clinical response to adjuvant therapy. The inter-individual variations of drug toxicity and efficacy of the pyrimidine antagonist observed in clinical practice are mainly determined by genetic polymorphisms. The screening of genotypes, such as thymidylate synthase, dihydropyrimidine dehydrogenase, methylene tetrahydrofolate reductase, orotate phosphoribosyltransferase or glutathione S-transferase, could help identifying those patients with colorectal carcinoma who can actually benefit from a 5-FU-based therapy. The current chapter elucidates the roles of the polymorphisms in the enzymes involved in the 5-FU metabolic pathway as prognostic and predictive markers. It reports on the relationship between various genotypes in patients with colorectal carcinoma and their responsiveness to a 5-FU-based chemotherapy, and concludes with an outlook on possible future directions in treatment of colorectal cancer.