Association of CYP2A6 polymorphisms with S-1 plus docetaxel therapy outcomes in metastatic gastric cancer

Impact of CYP2A6 Gene Polymorphism on the Efficacy and Safety of S-1 Therapy in Patients with Gastric Cancer: A Systematic Review and Meta-Analysis

INTRODUCTION

The relationship of CYP2A6 polymorphisms with S-1 therapy outcomes in gastric cancer is unclear. This review aimed to assess the association between CYP2A6 gene polymorphisms (CYP2A6*4, *7, *9, *10) and S-1 therapy outcomes in gastric cancer, aiming to identify predictive markers for S-1 efficacy and adverse reactions.

METHODS

We searched seven databases, using random or fixed-effect models to calculate hazard ratio (HR) and 95% confidence interval (CI) based on study heterogeneity.

RESULTS

A total of 1,143 articles were retrieved from multiple online databases as of March 28, 2023. After screening, seven articles containing seven investigations were included in the meta-analysis. Our results revealed a significant association between the CYP2A6 polymorphism site and the overall survival (OS) of variant/variant group (V/V) patients compared to wild-type/wild-type (W/W) or wild-type/variant (W/V) patients (HR = 2.73, 95% CI: 1.45-5.14, p = 0.002). S-1 was more beneficial for W/W or W/V patients than V/V patients in terms of progression-free survival (PFS) (HR = 3.15, 95% CI: 1.47-6.75, p = 0.003). There was no association between CYP2A6 polymorphism and hematological adverse reactions (OR = 0.52, 95% CI: 0.23-1.15, p = 0.104).

CONCLUSION

CYP2A6 polymorphisms correlate with S-1 efficacy (OS and PFS) in gastric cancer, suggesting their potential as predictive markers. However, the generalizability of findings is limited by the small number of studies from Eastern countries and variations in chemotherapy regimens and detection methods. Further, large-scale studies are needed to confirm these associations.

Pharmacogenomic-guided dosing of fluoropyrimidines beyond DPYD: time for a polygenic algorithm?

Fluoropyrimidines are chemotherapeutic agents widely used for the treatment of various solid tumors. Commonly prescribed FPs include 5-fluorouracil (5-FU) and its oral prodrugs capecitabine (CAP) and tegafur. Bioconversion of 5-FU prodrugs to 5-FU and subsequent metabolic activation of 5-FU are required for the formation of fluorodeoxyuridine triphosphate (FdUTP) and fluorouridine triphosphate, the active nucleotides through which 5-FU exerts its antimetabolite actions. A significant proportion of FP-treated patients develop severe or life-threatening, even fatal, toxicity. It is well known that FP-induced toxicity is governed by genetic factors, with dihydropyrimidine dehydrogenase (DPYD), the rate limiting enzyme in 5-FU catabolism, being currently the cornerstone of FP pharmacogenomics. DPYD-based dosing guidelines exist to guide FP chemotherapy suggesting significant dose reductions in DPYD defective patients. Accumulated evidence shows that additional variations in other genes implicated in FP pharmacokinetics and pharmacodynamics increase risk for FP toxicity, therefore taking into account more gene variations in FP dosing guidelines holds promise to improve FP pharmacotherapy. In this review we describe the current knowledge on pharmacogenomics of FP-related genes, beyond DPYD, focusing on FP toxicity risk and genetic effects on FP dose reductions. We propose that in the future, FP dosing guidelines may be expanded to include a broader ethnicity-based genetic panel as well as gene*gene and gender*gene interactions towards safer FP prescription.

Influence of SLCO1B1 in gastric cancer patients treated with EOF chemotherapy

Cytochrome-P450 enzymes, ATP-binding cassette transporters, and solute carriers mediate drug metabolism as metabolic enzymes and membrane transporters, respectively. The present study investigated whether single nucleotide polymorphisms (SNPs) in genes encoding these proteins were predictive or prognostic factors in patients with metastatic gastric cancer (MGC) undergoing chemotherapy. A retrospective study of 108 MGC patients who received epirubicin, oxaliplatin, and 5-fluorouracil (EOF) as first-line treatment was performed. A total of 13 SNPs were genotyped, including SLCO1B1 (rs4149056), SLC2A9 (rs16890979, rs6449213, rs734553), ABCG2 (rs2231142), CYP2C9 (rs1057910, rs1799853), CYP2C19 (rs72552267, rs28399504, rs56337013, rs41291556) and CYP1A2 (rs12720461, rs56107638). The associations between these genotypes and disease-control rate (DCR), progression-free survival (PFS) and overall survival (OS) were analyzed. Patients with SLCO1B1 rs4149056 TT genotype had a significantly shorter OS compared with those with a C allele (CC + CT; 312 vs. 565 days, P=0.039). Multivariate analysis revealed that the rs4149056 TT homozygous genotype was an independent prognostic factor for shorter OS (hazard ratio: 2.565, 95% confidence interval: 1.215–5.415, P=0.014). However, no significant associations between SLCO1B1 rs4149056 and PFS were observed, between the other 12 SNPs and PFS or OS, or between any of the 13 SNPs and DCR. In conclusion, SLCO1B1 rs4149056 TT may be an independent predictor of survival in patients with MCG treated with EOF chemotherapy.

Cytochrome P450 in Pharmacogenetics: An Update

Interindividual variability in drug disposition is a major cause of lack of efficacy and adverse effects of drug therapies. The majority of hepatically cleared drugs are metabolized by cytochrome P450 (CYP) enzymes, mainly in families CYP1, CYP2, and CYP3. Genes encoding these enzymes are highly variable with allele distribution showing considerable differences between populations. Genetic variability of especially CYP2C9, CYP2C19, CYP2D6, and CYP3A5 is known to have clear clinical impact on drugs that are metabolized by these enzymes. CYP1A2, CYP2A6, CYP2B6, CYP2C8, and CYP3A4 all show variability that affects pharmacokinetics of drugs as well, but so far the evidence regarding their clinical implications is not as conclusive. In this review, we provide an up-to-date summary of the pharmacogenetics of the major human drug-metabolizing CYP enzymes, focusing on clinically significant examples.

Variation in CYP2A6 Activity and Personalized Medicine

The cytochrome P450 2A6 (CYP2A6) enzyme metabolizes several clinically relevant substrates, including nicotine-the primary psychoactive component in cigarette smoke. The gene that encodes the CYP2A6 enzyme is highly polymorphic, resulting in extensive interindividual variation in CYP2A6 enzyme activity and the rate of metabolism of nicotine and other CYP2A6 substrates including cotinine, tegafur, letrozole, efavirenz, valproic acid, pilocarpine, artemisinin, artesunate, SM-12502, caffeine, and tyrosol. CYP2A6 expression and activity are also impacted by non-genetic factors, including induction or inhibition by pharmacological, endogenous, and dietary substances, as well as age-related changes, or interactions with other hepatic enzymes, co-enzymes, and co-factors. As variation in CYP2A6 activity is associated with smoking behavior, smoking cessation, tobacco-related lung cancer risk, and with altered metabolism and resulting clinical responses for several therapeutics, CYP2A6 expression and enzyme activity is an important clinical consideration. This review will discuss sources of variation in CYP2A6 enzyme activity, with a focus on the impact of CYP2A6 genetic variation on metabolism of the CYP2A6 substrates.

A phase II study of preoperative chemoradiation with tegafur-uracil plus leucovorin for locally advanced rectal cancer with pharmacogenetic analysis

BACKGROUND

This study aimed to evaluate the efficacy of a high dose of oral tegafur-uracil (400 mg/m²) plus leucovorin with preoperative chemoradiation of locally advanced rectal cancer and to explore the impact of polymorphisms of cytochrome P 2A6 (CYP2A6), uridine monophosphate synthetase (UMPS), and ATP-binding cassette B1 (ABCB1) on clinical outcome.

METHODS

Patients with cT3 or cT4 rectal cancer were enrolled and were given tegafur-uracil 400 mg/m²/day and leucovorin 90 mg/m²/day for 7 days a week during preoperative chemoradiation (50.4 Gy/28 fractions) in this phase II trial. Primary endpoint was pathologic complete response rate, and the secondary endpoint was to explore the association between clinical outcomes and genetic polymorphisms CYP2A6 (*4, *7, *9 and *10), UMPS G638C, and three ABCB1 genotypes (C1236T, C3435T, and G2677T).

RESULTS

Ninety-one patients were given study treatment, and 90 underwent surgery. Pathologic complete response was noted in 10 patients (11.1%). There was no grade 4 or 5 toxicity; 20 (22.0%) experienced grade 3 toxicities, including diarrhea (10, 11.0%), abdominal pain (2, 2.2%), and anemia (2, 2.2%). Relapse-free survival and overall survival at 5 years were 88.6% and 94.2%, respectively. Patients with the UMPS 638 CC genotype experienced significantly more frequent grade 2 or 3 diarrhea (p for trend = 0.018).

CONCLUSIONS

Preoperative chemoradiation with tegafur-uracil 400 mg/m²/day with leucovorin was feasible, but did not meet the expected pathologic complete response rate. The UMPS 638 CC genotype might be a candidate biomarker predicting toxicity in patients receiving tegafur-uracil/leucovorin-based preoperative chemoradiation for locally advanced rectal cancer.

TRIAL REGISTRATION

ISRCTN11812525 , registered on 25 July 2016. Retrospectively registered.

Associations between CYP2A6 polymorphisms and outcomes of adjuvant S-1 chemotherapy in patients with curatively resected gastric cancer

BACKGROUND

Oral fluoropyrimidine S-1 contains tegafur, which is metabolized to 5-fluorouracil by cytochrome P450 2A6 (CYP2A6). We here examined associations between CYP2A6 polymorphisms and treatment outcomes of adjuvant S-1 in gastric cancer patients.

METHODS

Patients received adjuvant S-1 (40 mg/m² twice daily, days 1-28, every 6 weeks for eight cycles) after curative surgery for pathological stage II-III gastric cancer. We analyzed the wild-type allele (W) (CYP2A6*1) and four variant alleles (V) (CYP2A6*4, *7, *9, *10) that abolish or reduce this enzyme activity.

RESULTS

Patients (n = 200) were enrolled between November 2007 and July 2013 with the following clinical characteristics: median age, 57 years (range, 32-83 years); 128 men, 72 women. With a median follow-up of 46.4 months, the 3-year relapse-free survival (RFS) and overall survival (OS) rates were 83.1 % (95 % CI, 77.7-88.5 %) and 94.8 % (95 % CI, 91.6-98.0 %), respectively. Genotype distributions were as follows: W/W (n = 49, 24.5 %), W/V (n = 94, 47.0 %), and V/V (n = 57, 28.5 %). Overall toxicity did not differ according to genotype for any grade (p = 0.612) or grade ≥3 (p = 0.143). However, RFS differed significantly according to CYP2A6 genotype. The 3-year RFS rates were 95.9 % for W/W, 83.1 % for W/V, and 72.5 % for V/V (p = 0.032). Carriers of W/V and V/V genotypes had a poorer RFS with a hazard ratio of 3.41 (95 % CI, 1.01-11.52; p = 0.049) and 4.03 (95 % CI, 1.16-13.93; p = 0.028), respectively, compared with the W/W genotype.

CONCLUSIONS

CYP2A6 polymorphisms are not associated with toxicity of S-1 chemotherapy, but correlate with the efficacy of S-1 in the adjuvant setting for gastric cancer.

Phase II trial of S-1 plus leucovorin in patients with advanced gastric cancer and clinical prediction by S-1 pharmacogenetic pathway

Background

The first one-arm phase II trial aimed to evaluate and predict efficacy and safety of S-1 plus oral leucovorin (S-1/LV) as first-line chemotherapy for patients with advanced gastric cancer (AGC), using S-1 pharmacogenetic pathway approach.

Patients and methods

A total of 39 patients orally took S-1 at conventional dose and LV simultaneously at a dose of 25 mg twice daily for a week, within a 2-week cycle. The primary endpoint was overall response rate (ORR), while the secondary endpoints were progression-free survival (PFS), time to failure (TTF), overall survival (OS), disease control rate (DCR), and adverse events (AEs). Peripheral blood was sampled prospectively for baseline expression of dihydropyrimidine dehydrogenase (DPD), orotate phosphoribosyltransferase (OPRT), thymidine phosphorylase (TP), and thymidylate synthase (TS), CYP2A6 gene polymorphisms, and 5-FU pharmacokinetics.

Results

The ORR and DCR were 41.0 and 76.9%. The median PFS, TTF, and OS were 4.13, 3.70, and 11.40 months. Grade 3–4 AEs occurred in only 13 patients, and grade 4 AEs occurred in only 1 of them. High OPRT/TS and peritoneal metastasis (vs. liver metastasis) independently predicted responding. High OPRT/DPD independently predicted grade 3–4 AEs. High AUC_0–24h of 5-FU and metastatic/recurrent sites ≤2 (vs. >3) independently predicted prolonged PFS. Low baseline plasmic DPD independently predicted prolonged OS.

Conclusions

Two-week, oral S-1/LV regimen demonstrated promising efficacy and safety as first-line chemotherapy for AGC.

ClinicalTrials.gov identifier

NCT02090153

Electronic supplementary material

The online version of this article (doi:10.1007/s00280-016-3209-1) contains supplementary material, which is available to authorized users.

A phase II study of perioperative S-1 combined with weekly docetaxel in patients with locally advanced gastric carcinoma: clinical outcomes and clinicopathological and pharmacogenetic predictors for survival

BACKGROUND

We conducted a phase II study to evaluate the efficacy and safety of perioperative S-1 plus docetaxel in locally advanced gastric cancer (LAGC) and to investigate the association between CYP2A6 genotype and outcome.

METHODS

Patients with LAGC [clinical stage III-IV (M0) by the Japanese staging system] received three cycles of pre- and postoperative chemotherapy (S-1 40 mg/m(2) twice daily on days 1-14; intravenous docetaxel 35 mg/m(2) on days 1 and 8, every 3 weeks) followed by gastrectomy with D2 dissection. We also performed a pharmacokinetic and CYP2A6 genotyping study (*1, *4, *7, *9, *10) for S-1.

RESULTS

From October 2006 to June 2008, 44 patients entered the study. 43 eligible patients completed preoperative chemotherapy and 40 completed postoperative chemotherapy. The most common G3/4 toxicities during pre- and postoperative chemotherapy were neutropenia, stomatitis, and abdominal pain. The clinical response rate by RECIST was 74.4 % (95 % CI, 61.4-87.4 %), and the R0 resection rate was 97.7 %. Clinical downstaging in T or N occurred in 41.9 % of patients. The 3-year progression-free survival (PFS) rate was 62.8 % and 5-year overall survival (OS) rate was 69.6 %. PFS and OS differed significantly according to clinical response, clinical downstaging, and CYP2A6 genotype. Patients with CYP2A6 variant/variant genotypes had a higher tegafur C max and worse survival than those with wild/wild or wild/variant genotypes.

CONCLUSION

Perioperative S-1 plus docetaxel is active with a manageable toxicity in patients with LAGC receiving D2 surgery. Clinical tumor response, clinical downstaging, and CYP2A6 genotype may predict efficacy.

Single tube genotyping of CYP2A6 gene deletion based on copy number determination by quantitative real-time PCR

The CYP2A6*4 allele, characterized as the whole deletion of this gene, is closely associated with nicotine dependence, cancer susceptibility, and drug responsiveness. It has long been a significant challenge for pharmacogenetics scientists to develop a reliable method to detect this molecular variant due to its high homology with its homologous genes CYP2A6 and CYP2A3 in the clinical setting. Here, we introduce a quantitative real-time PCR assay that specifically amplifies CYP2A6 by designing a specific set of primers and the probe, which effectively prevent the amplification of the CYP2A7 and CYP2A13 alleles. CYP2A6 gene copy numbers were normalized to albumin (ALB) which was co-amplified simultaneously in a single-tube duplex reaction and at a setting as the internal reference gene. The established assay was validated with a selection of previously genotyped DNA samples, which harbored none, one or two CYP2A6 gene copies. The results were in complete concordance with previously published data and no overlap between the three groups was observed. Further analysis of a cohort of 120 samples revealed high specificity and sensitivity of this assay as demonstrated by the agreement of determined gene copy numbers in all of the cases. In conclusion, this novel assay allows reliable and sensitive detection of the CYP2A6 gene deletion, which will be useful for pharmacogenetics studies and routine clinical settings.

p16 Methylation is associated with chemosensitivity to fluorouracil in patients with advanced gastric cancer

No effective biomarkers have been confirmed to predict chemosensitivity for patients with gastric cancer. The purpose of this study was to investigate whether DNA methylation is associated with chemosensitivity in patients with gastric cancer. Tumors and matched non-tumor biopsy tissues collected from 134 advanced gastric cancer (AGC) patients prior to fluorouracil-based chemotherapy were retrospectively analyzed. The methylation status of p16, E-cadherin (CDH1), MGMT (O-6-methylguanine-DNA methyltransferase), and human mutL homolog 1 (hMLH1) was evaluated using a Methylight assay, and the association between p16 methylation and the sensitivity of 5-fluorouracil in cell lines was determined by in vitro assay. The methylation of p16 (17.9 vs. 0 %, P = 0.002), CDH1 (20.9 vs. 2.2 %, P < 0.001), MGMT (17.9 vs. 0 %, P = 0.052), and hMLH1 (14.9 vs. 2.2 %, P = 0.024) was more common in gastric cancer tissues (n = 134) than in non-tumor tissues (n = 46). For all patients, a reverse correlation was only found between p16 methylation and clinical response (P = 0.017), which suggested that p16 methylation might be associated with chemosensitivity of fluorouracil in gastric cancer patients. Results from in vitro experiments demonstrated that p16 methylation was closely correlated with the sensitivity of 5-fluorouracil in gastric cancer cells. The present results indicated that the methylation of p16, CDH1, MGMT, and hMLH1 was both frequent and specific in gastric cancer tissues. p16 Methylation might be used to predict chemosensitivity of fluorouracil for patients with AGC when validated in large samples in the future.

Effectiveness and safety profile of S-1-based chemotherapy compared with capecitabine-based chemotherapy for advanced gastric and colorectal cancer: A meta-analysis

The aim of the present analysis was to compare the efficacy and safety profile of S-1-based chemotherapy (SBCT) versus capecitabine-based chemotherapy (CBCT) for advanced gastric cancer (AGC) and advanced colorectal cancer (ACRC). A meta-analysis was performed, which included eligible randomized controlled trials (RCTs) that were identified using RevMan 5.1.0 software. A total of 1,064 patients from 11 RCTs, comprising of 527 patients in the SBCT group and 537 patients in the CBCT group, were included in the analysis. For AGC, the meta-analysis of overall survival (OS) [hazard ratio (HR), 0.98; 95% confidence interval (CI), 0.85–1.12], time to progression (HR, 0.95; 95% CI, 0.80–1.12) and overall response rate (ORR) [odds ratio (OR), 1.06; 95% CI, 0.72–1.55] of patients in the SBCT group indicated no statistical significance when compared with those in the CBCT group. Furthermore, for ACRC, a pooled analysis demonstrated no significant difference between the SBCT and CBCT groups (OS: HR, 0.82; 95% CI, 0.61–1.10; progression-free survival: HR, 0.79; 95% CI=0.60–1.04; ORR: OR, 1.27; 95% CI, 0.91–1.78). The statistically significant differences identified in the overall meta-analysis indicated a low incidence of grade 3–4 hand-foot-syndrome (OR, 0.15; 95% CI, 0.06–0.36) in the SBCT group; however no statistically significant difference was observed in the incidence of grade 3–4 anemia, thrombocytopenia, leucopenia, neutropenia, diarrhea, stomatitis or nausea/vomiting. The SBCT treatment exhibited similar efficacy and an approximately equivalent safety profile compared with the CBCT treatment and was an alternative to CBCT for patients with AGC or ACRC; however, further investigation is required to provide confirmation.

Gastric cancer pharmacogenetics: progress or old tripe?

Gastric cancer remains the second most frequent cause of cancer-related mortality. While surgery is traditionally the initial treatment for early-stage disease, the addition of chemotherapy has been shown to significantly increase overall survival and progression-free survival in advanced and metastatic stages of disease. However, despite the incorporation of newer chemotherapies and regimens into gastric cancer clinical trials, the response rate and median overall survival for treated patients has not significantly improved throughout the years; therefore, newer therapeutic approaches to improve upon the medication selection process are warranted. Treatment and dose selection based on patient factors, such as genetic variation, may provide a more rational and potentially more powerful means of personalizing chemotherapy. This review provides an update on the current status of pharmacogenetic studies regarding germline DNA mutations that may alter response to chemotherapeutic agents used to treat gastric cancer, including perspectives on clinical translation and future work.

Dose-finding study on adjuvant chemotherapy with S-1 plus oxaliplatin for gastric cancer

Gastric cancer (GC) is the fourth most common type of cancer, accounting for an estimated one million new cases annually worldwide. Locally advanced GC often recurs, even following curative surgical resection. Therefore, there is a need for an effective adjuvant chemotherapy regimen. The aim of this trial was to investigate the maximum tolerated dose (MTD) of S-1 when administered in combination with oxaliplatin in postoperative GC patients. Oxaliplatin was administered at a fixed dose of 130 mg/m² on day 1. S-1 was administered from day 1 to 14 of a 3-week cycle and escalated by 10 mg/m²/day from 60 to 80 mg/m²/day. A total of 15 patients were enrolled in this study. No dose-limiting toxicities (DLTs) occurred at level 1 (S-1, 60 mg/m²; n=3). One case of DLT (grade 3 vomiting) occurred at level 2 (S-1, 70 mg/m²; n= 6), whereas 2 cases of grade 3 vomiting were observed at level 3 (S-1, 80 mg/m²; n=6). Based on these results, the MTD of S-1 was initially determined to be 70 mg/m². Furthermore, we observed that cytochrome P450 2A6 (CYP2A6) 41349640C>G was associated with severe neutropenia (C/C vs. C/G vs. G/G = 0 vs. 33.33 vs. 100%; P=0.03297, Fisher's exact test) during the entire course of the treatment.

S-1 plus irinotecan and oxaliplatin for the first-line treatment of patients with metastatic colorectal cancer: a prospective phase II study and pharmacogenetic analysis

BACKGROUND

S-1 is an oral fluoropyrimidine that mimics infusional 5-fluorouracil. The aim of this phase II trial was to explore the clinical efficacy of the triplet regimen TIROX, which consists of S-1, irinotecan and oxaliplatin.

METHODS

Forty-two chemo-naive patients with metastatic colorectal cancer (mCRC) were planned to be enrolled and be treated with irinotecan 150 mg m(-2) followed by oxaliplatin 85 mg m(-2) on day 1 and S-1 80 mg m(-2) per day from day 1 to 14 every 3 weeks. Polymorphisms in the UGT1A1, UGT1A6, UGT1A7 and CYP2A6 genes were analysed.

RESULTS

Between July 2007 and February 2008, 43 patients were enrolled. An objective response was noted in 29 patients (67.4%, 95% confidence interval: 53.4-81.4), of which 2 achieved durable complete responses. The median progression-free survival was 10.0 months and the median overall survival was 19.2 months. Significant grade 3 or 4 adverse events were neutropenia (45.2%), febrile neutropenia (9.5%), diarrhoea (7.1%) and vomiting (9.5%). Increased gastrointestinal toxicities were associated with the presence of UGT1A6*2 or UGT1A7*3 and an improved tumour response was noted in those without variant alleles of CYP2A6 or UGT1A1*60.

CONCLUSION

The combination of S-1, irinotecan and oxaliplatin showed favourable efficacy and tolerability in untreated patients with mCRC.

Phase I clinical and pharmacokinetic/pharmacogenetic study of a triplet regimen of S-1/irinotecan/oxaliplatin in patients with metastatic colorectal or gastric cancer

PURPOSE

We conducted a phase I study of S-1 combined with irinotecan and oxaliplatin (TIROX) to determine the maximum-tolerated dose (MTD) and recommended dose (RD) and to assess its safety, pharmacokinetics, pharmacogenetics, and preliminary efficacy in patients with metastatic colorectal cancer (MCRC) or metastatic gastric cancer (MGC).

METHODS

Patients received escalating doses of S-1 (30-40 mg/m² b.i.d.) orally on days 1-14, an escalating dose of intravenous irinotecan (120-150 mg/m²) on day 1, and a fixed dose of intravenous oxaliplatin (85 mg/m²) on day 1 every 3 weeks.

RESULTS

Twenty-three patients (10 MCRC, 13 MGC; 13 chemonaive, 10 previously treated for metastatic disease) were treated across six dose levels. Because only one patient experienced a dose-limiting toxicity of grade 3 anorexia at the highest dose level (S-1 40 mg/m² b.i.d., irinotecan 150 mg/m², and oxaliplatin 85 mg/m²) (n = 8), the MTD was not obtained, and this level was established as the RD. With a median of 10 cycles per patient, the most common grade 3 or 4 adverse events included neutropenia (43 %), diarrhea (13 %), and nausea (13 %). In 22 efficacy-evaluable patients, the objective tumor response rate was 59.1 % (75 % for both MCRC and MGC in the first-line setting) and the disease control rate was 100 %. The exploratory pharmacokinetic/pharmacogenetic study showed that CYP2A6 variants (*4, *7, *9) are associated with a lower metabolic ratio of S-1 (exposure ratio of 5-fluorouracil to tegafur).

CONCLUSIONS

The new triplet TIROX regimen has shown promising antitumor activity and a favorable toxicity profile in patients with MCRC and MGC.

Ethanol-mediated regulation of cytochrome P450 2A6 expression in monocytes: role of oxidative stress-mediated PKC/MEK/Nrf2 pathway

Cytochrome P450 2A6 (CYP2A6) is known to metabolize nicotine, the major constituent of tobacco, leading to the production of toxic metabolites and induction of oxidative stress that result in liver damage and lung cancer. Recently, we have shown that CYP2A6 is induced by ethanol and metabolizes nicotine into cotinine and other metabolites leading to generation of reactive oxygen species (ROS) in U937 monocytes. However, the mechanism by which CYP2A6 is induced by ethanol is unknown. In this study, we have examined the role of the PKC/Nrf2 pathway (protein kinase C-mediated phosphorylation and translocation of nuclear erythroid 2-related factor 2 to the nucleus) in ethanol-mediated CYP2A6 induction. Our results showed that 100 mM ethanol significantly induced CYP2A6 mRNA and protein (~150%) and increased ROS formation, and induction of gene expression and ROS were both completely blocked by treatment with either a CYP2E1 inhibitor (diallyl sulfide) or an antioxidant (vitamin C). The results suggest the role of oxidative stress in the regulation of CYP2A6 expression. Subsequently, we investigated the role of Nrf2 pathway in oxidative stress-mediated regulation of CYP2A6 expression in U937 monocytes. Our results showed that butylated hydroxyanisole, a stabilizer of nuclear Nrf2, increased CYP2A6 levels >200%. Staurosporine, an inhibitor of PKC, completely abolished ethanol-induced CYP2A6 expression. Furthermore, our results showed that a specific inhibitor of mitogen-activated protein kinase kinase (MEK) (U0126) completely abolished ethanol-mediated CYP2A6 induction and Nrf2 translocation. Overall, these results suggest that CYP2E1-mediated oxidative stress produced as a result of ethanol metabolism translocates Nrf2 into the nucleus through PKC/MEK pathway, resulting in the induction of CYP2A6 in monocytes. An increased level of CYP2A6 in monocytes is expected to further increase oxidative stress in smokers through CYP2A6-mediated nicotine metabolism. Thus, this study has clinical relevance because of the high incidence of alcohol use among smokers, especially in HIV-infected individuals.

Association analysis of CYP2A6 genotypes and haplotypes with 5-fluorouracil formation from tegafur in human liver microsomes

AIM

Tegafur is primarily converted to 5-fluorouracil (5-FU) by CYP2A6 in the human liver to exert its antitumor effect. Our objective was to comprehensively investigate the effects of CYP2A6 genetic polymorphisms on tegafur bioactivation activity.

MATERIALS & METHODS

Using a set of over 45 Chinese livers, the association between CYP2A6 genetic variations and 5-FU formation rates from tegafur, as well as CYP2A6 mRNA and protein levels, was determined.

RESULTS

A total of 20 polymorphic variants and 20 haplotypes of CYP2A6 were identified. From genotype/haplotype-phenotype association tests, we demonstrated that CYP2A6*4 was the main allele responsible for the decreased 5-FU formation from tegafur and CYP2A6 expression in this population. By contrast, haplotype 14 (a novel CYP2A6*1B allele) was associated with increased microsomal 5-FU formation activity and CYP2A6 expression, and this may be attributed to the combined effects of three single variants (g.22C>T, g.1620T>C and a gene conversion in the 3´-UTR) included in this haplotype.

CONCLUSION

We concluded that CYP2A6*4 and the novel CYP2A6*1B variant were the major genetic determinants of interindividual variability in 5-FU formation from tegafur in Chinese livers. Original submitted 2 November 2010; Revision submitted 3 December 2010.

Phase II study of S-1 combined with oxaliplatin as therapy for patients with metastatic biliary tract cancer: influence of the CYP2A6 polymorphism on pharmacokinetics and clinical activity

Background:

Advanced biliary cancer is often treated with fluoropyrimidine-based chemotherapy. In this study, we evaluated the efficacy and tolerability of a combination of S-1, an oral fluoropyrimidine prodrug, and oxaliplatin in patients with metastatic biliary cancer.

Methods:

Patients with histologically confirmed metastatic biliary cancer and no history of radiotherapy or chemotherapy were enrolled. Oxaliplatin was administered intravenously (130 mg m⁻²), followed by 14-day administration of oral S-1 (40 mg m⁻² twice daily) with a subsequent 7-day rest period every 21 days. Pharmacokinetic analysis of S-1 was performed at cycle 1. Patients were genotyped for CYP2A6 polymorphisms (^*1, ^*4, ^*7, ^*9 or ^*10), and pharmacokinetic and clinical parameters compared according to the CYP2A6 genotype.

Results:

In total, 49 patients were evaluated, who received a median of four cycles. The overall response rate was 24.5%. Median progression-free and overall survival was 3.7 and 8.7 months, respectively. The most common haematological grade 3 out of 4 toxicity was neutropenia (14%), while non-hematological grade 3 out of 4 toxicities included anorexia (14%), nausea (12%), asthenia (10%), vomiting (10%), and diarrhoea (4%). Biotransformation of S-1 (AUC_0−24 h of 5-fluorouracil/AUC_0−24 h of tegafur) was 1.85-fold higher for the *1/*1 group than for the other groups (90% confidence interval 1.37–2.49). Diarrhoea (P=0.0740), neutropenia (P=0.396), and clinical efficacy (response rate, P=0.583; PFS, P=0.916) were not significantly associated with CYP2A6 genotype, despite differences in 5-FU exposure.

Conclusion:

The combination of S-1 and oxaliplatin appears to be active and well tolerated in patients with metastatic biliary cancer, and thus is feasible as a therapeutic modality. CYP2A6 genotypes are associated with differences in the biotransformation of S-1. However, the impact of the CYP2A6 polymorphism on variations in clinical efficacy or toxicity requires further evaluation.

CYP2A6 and ERCC1 polymorphisms correlate with efficacy of S-1 plus cisplatin in metastatic gastric cancer patients

Background:

We evaluated the association between polymorphisms of cytochrome P450 2A6 (CYP2A6)/excision repair cross-complementation group 1 (ERCC1)/X-ray repair cross-complementing group 1(XRCC1) and treatment outcomes of metastatic gastric cancer (MGC) patients treated with S-1/cisplatin.

Methods:

Among MGC patients (n=108), who received S-1 (40 mg m⁻² b.i.d., days 1–14) and cisplatin (60 mg m⁻², day 1) every 3 weeks, we analysed the wild-type allele (W) and variants (V) of CYP2A6 (*4, *7, *9, *10), and the polymorphisms of ERCC1 (rs11615, rs3212986) and XRCC1 (rs25487).

Results:

Patients having fewer CYP2A6 variants had better response rates (W/W vs W/V other than *1/*4 vs V/V or *1/*4=66.7 vs 58.3 vs 32.3% P=0.008), time to progression (TTP) (7.2 vs 6.1 vs 3.5 months, P=0.021), and overall survival (23.2 vs 15.4 vs 12.0 months, P=0.004). ERCC1 19442C>A (rs3212986) was also associated with response rate (C/C, 46.7% vs C/A, 55.3% vs A/A, 87.5%) (P=0.048) and TTP (4.4 vs 7.6 vs 7.9 months) (P=0.012). Patients carrying both risk genotypes of CYP2A6 (V/V or 1/*4) and ERCC1 19442C>A (C/C) vs those carrying none showed an adjusted odds ratio of 0.113 (P=0.004) for response, and adjusted hazard ratios of 3.748 (P=0.0001) for TTP and 2.961 (P=0.006) for death.

Conclusion:

Polymorphisms of CYP2A6 and ERCC1 19442C>A correlated with the efficacy of S-1/cisplatin.