A novel mutant allele of the CYP2A6 gene (CYP2A6*11 ) found in a cancer patient who showed poor metabolic phenotype towards tegafur

Efficacy and safety of SOXIRI versus mFOLFIRINOX in advanced pancreatic cancer

Background

Modified fluorouracil/leucovorin/irinotecan/oxaliplatin (FOLFIRINOX) regimen (mFOLFIRINOX), comprised of fluorouracil, leucovorin, irinotecan and oxaliplatin, is the first-line standard chemotherapy in patients with advanced pancreatic cancer. The S-1/oxaliplatin/irinotecan (SOXIRI) regimen has also been studied recently under similar conditions. This study compared its efficacy and safety.

Methods

All cases of locally advanced or metastatic pancreatic cancer treated with the SOXIRI or mFOLFIRINOX regimen in Sun Yat-sen University Cancer Centre from July 2012 to June 2021 were reviewed retrospectively. The data of patients who satisfied the inclusion criteria were compared between two cohorts, including overall survival (OS), progression-free survival (PFS), objective response rate, disease control rate and safety.

Results

A total of 198 patients were enrolled in the study, including 102 patients treated with SOXIRI and 96 patients treated with mFOLFIRINOX. There was no significant difference in OS [12.1 months versus 11.2 months, hazard ratio (HR) = 1.04, p = 0.81] or PFS (6.5 months versus 6.8 months, HR = 0.99, p = 0.96) between patients treated with SOXIRI and mFOLFIRINOX. In the subgroup analysis, patients with slightly elevated baseline total bilirubin (TBIL) or underweight patients before chemotherapy were more likely to have a longer OS or PFS from SOXIRI than from mFOLFIRINOX. In addition, the carbohydrate antigen (CA)19-9 decline was a good predictor for the efficacy and prognosis of both chemotherapy regimens. All grade adverse events were parallel in all kinds of toxicities except that anaemia was more common in the SOXIRI group than in the mFOLFIRINOX group (41.4% versus 24%, p = 0.03). The occurrence of any grade 3 to 4 toxicity was similar in the two groups.

Conclusions

For locally advanced or metastatic pancreatic cancer patients, the SOXIRI regimen had similar efficacy and controllable safety compared with the mFOLFIRINOX regimen.

Potential of cytochrome P450, a family of xenobiotic metabolizing enzymes, in cancer therapy

SIGNIFICANCE

Targeted cancer therapy with minimal off-target consequences has shown promise for some cancer types. Although cytochrome P450 (CYP) consists of 18 families, CYP1-4 families play key role in metabolizing xenobiotics and cancer drugs. This eventually affects the process of carcinogenesis, treatment outcome, and cancer drug resistance. Differential overexpression of CYPs in transformed cells, together with phenotypic alterations in tumors, presents a potential for therapeutic intervention.

RECENT ADVANCES

Recent advances in molecular tools and information technology have helped utilize CYPs as cancer targets. The precise expression in various tumors, X-ray crystal structures, improved understanding of the structure-activity relationship, and new approaches in the development of prodrugs have supported the ongoing efforts to develop CYPs-based drugs with a better therapeutic index.

CRITICAL ISSUES

Narrow therapeutic index, off-target effects, drug resistance, and tumor heterogeneity limit the benefits of CYP-based conventional cancer therapies. In this review, we address the CYP1-4 families as druggable targets in cancer. An emphasis is given to the CYP expression, function, and the possible mechanisms that drive expression and activity in normal and transformed tissues. The strategies that inhibit or activate CYPs for therapeutic benefits are also discussed.

FUTURE DIRECTIONS

Efforts are needed to develop more selective tools that will help comprehend molecular and metabolic alterations in tumor tissues with biological end-points in relation to CYPs. This will eventually translate to developing more specific CYP inhibitors/inducers.

Deciphering Structural Alterations Associated with Activity Reductions of Genetic Polymorphisms in Cytochrome P450 2A6 Using Molecular Dynamics Simulations

Cytochrome P450 (CYP) 2A6 is a monooxygenase involved in the metabolism of various endogenous and exogenous chemicals, such as nicotine and therapeutic drugs. The genetic polymorphisms in CYP2A6 are a cause of individual variation in smoking behavior and drug toxicities. The enzymatic activities of the allelic variants of CYP2A6 were analyzed in previous studies. However, the three-dimensional structures of the mutants were not investigated, and the mechanisms underlying activity reduction remain unknown. In this study, to investigate the structural changes involved in the reduction in enzymatic activities, we performed molecular dynamics simulations for ten allelic mutants of CYP2A6. For the calculated wild type structure, no significant structural changes were observed in comparison with the experimental structure. On the other hand, the mutations affected the interaction with heme, substrates, and the redox partner. In CYP2A6.44, a structural change in the substrate access channel was also observed. Those structural effects could explain the alteration of enzymatic activity caused by the mutations. The results of simulations provide useful information regarding the relationship between genotype and phenotype.

Drug resistance: from bacteria to cancer

The phenomenon of drug resistance has been a hindrance to therapeutic medicine since the late 1940s. There is a plethora of factors and mechanisms contributing to progression of drug resistance. From prokaryotes to complex cancers, drug resistance is a prevailing issue in clinical medicine. Although there are numerous factors causing and influencing the phenomenon of drug resistance, cellular transporters contribute to a noticeable majority. Efflux transporters form a huge family of proteins and are found in a vast number of species spanning from prokaryotes to complex organisms such as humans. During the last couple of decades, various approaches in analyses of biochemistry and pharmacology of transporters have led us to understand much more about drug resistance. In this review, we have discussed the structure, function, potential causes, and mechanisms of multidrug resistance in bacteria as well as cancers.

Independent and Interactive Effect of CYPs and GSTs Genetic Variants and Tobacco Smoking on the Risk of Non-Small Cell Lung Carcinoma

BACKGROUND

CYP and GST gene families detoxify tobacco carcinogens and have been linked to the risk of non-small cell lung carcinoma (NSCLC).

AIM

Independent and combined effects of CYP and GST genetic variations and smoking on the risk of non-small cell lung carcinoma (NSCLC) and its sub-histological types.

METHODS

We modelled an epistatic interaction via the effects of particular genotypes in two genes as OR (odds ratio), OR1, and OR2, a combination of both genotypes were characterized as OR_combine. In contrast, the two ORs' epistatic interaction for the individual genotypes has been represented as OR_interaction = OR_combine/(OR1 × OR2).

RESULTS

The variant genotypes of CYP2A6 (OR:4.2, p <0.001), GSTT1 (OR:3.9, p <0.001), and GSTM1 (OR: 4.5, p <0.001) were showed a significant risk with NSCLC. GSTM1 (del.)/CYP2A6 (variant) genotype was associated with a higher risk of NSCLC (OR:12.5, p <0.001). GSTM1 (del.)/CYP2A6 (Ser/Pro+Pro/Pro) and GSTM1 (del.)/CYP2A13 (CT+TT) interacted redundantly (OR_intraction = 0.66 and 0.64). A co-suppressive interaction was observed between GSTT1 (del.)/CYP2A6 (Ser/Pro+Pro/Pro) (OR_intraction = 0.41). Simultaneously, both GSTT1/GSTM1 del. genotype was associated with a significantly higher risk to NSCLC. In contrast, GSTT1 del./GSTM1 del. genotype interaction displayed a co-suppressive effect (OR_intraction = 0.15). CYP1A1(TC+CC)/CYP2A13(CT+TT)mutually interacted synergistically (OR_intraction = 1.27).CYP1A1 (TC+CC)/GSTP1 (Val/Val+Ile/Val) genotype demonstrated an additive (OR_intraction = 1) effect. GSTP1(Val/Val+Ile/Val) interacts with GSTT1 (del.) genotype exerted a suppressive effect (OR_intraction = 0.69). CYP2A6 in smokers increased risk by 4.2 (p = 0.001) to 5.6 fold (p <0.001), while GSTM1 and GSTT1 were independent of smoking.

CONCLUSION

Epistatic interactions revealed that CYPs/GSTs might follow a web of the interactions to modify the risk of NSCLC.

Molecular Bases of Mechanisms Accounting for Drug Resistance in Gastric Adenocarcinoma

Gastric adenocarcinoma (GAC) is the most common histological type of gastric cancer, the fifth according to the frequency and the third among the deadliest cancers. GAC high mortality is due to a combination of factors, such as silent evolution, late clinical presentation, underlying genetic heterogeneity, and effective mechanisms of chemoresistance (MOCs) that make the available antitumor drugs scarcely useful. MOCs include reduced drug uptake (MOC-1a), enhanced drug efflux (MOC-1b), low proportion of active agents in tumor cells due to impaired pro-drug activation or active drug inactivation (MOC-2), changes in molecular targets sensitive to anticancer drugs (MOC-3), enhanced ability of cancer cells to repair drug-induced DNA damage (MOC-4), decreased function of pro-apoptotic factors versus up-regulation of anti-apoptotic genes (MOC-5), changes in tumor cell microenvironment altering the response to anticancer agents (MOC-6), and phenotypic transformations, including epithelial-mesenchymal transition (EMT) and the appearance of stemness characteristics (MOC-7). This review summarizes updated information regarding the molecular bases accounting for these mechanisms and their impact on the lack of clinical response to the pharmacological treatment currently used in GAC. This knowledge is required to identify novel biomarkers to predict treatment failure and druggable targets, and to develop sensitizing strategies to overcome drug refractoriness in GAC.

Phase I study of DFP-11207, a novel oral fluoropyrimidine with reasonable AUC and low Cmax and improved tolerability, in patients with solid tumors

5-fluorouracil (5-FU) and 5-FU derivatives, such as capecitabine, UFT, and S-1, are the mainstay of chemotherapy treatment for gastrointestinal cancers, and other solid tumors. Compared with other cytotoxic chemotherapies, these drugs generally have a favorable safety profile, but hematologic and gastrointestinal toxicities remain common. DFP-11207 is a novel oral cytotoxic agent that combines a 5-FU pro-drug with a reversible DPD inhibitor and a potent inhibitor of OPRT, resulting in enhanced pharmacological activity of 5-FU with decreased gastrointestinal and myelosuppressive toxicities. In this Phase I study (NCT02171221), DFP-11207 was administered orally daily, in doses escalating from 40 mg/m²/day to 400 mg/m²/day in patients with esophageal, colorectal, gastric, pancreatic or gallbladder cancer (n = 23). It was determined that DFP-11207 at the dose of 330 mg/m²/day administered every 12 hours was well-tolerated with mild myelosuppressive and gastrointestinal toxicities. The pharmacokinetic analysis determined that the 5-FU levels were in the therapeutic range at this dose. In addition, fasted or fed states had no influence on the 5-FU levels (patients serving as their own controls). Among 21 efficacy evaluable patients, 7 patients had stable disease (33.3%), of which two had prolonged stable disease of >6 months duration. DFP-11207 can be explored as monotherapy or easily substitute 5-FU, capecitabine, or S-1 in combination regimens.

The Multifarious Link between Cytochrome P450s and Cancer

Cancer is a leading cause of death worldwide. Cytochrome P450s (P450s) play an important role in the metabolism of endogenous as well as exogenous substances, especially drugs. Moreover, many P450s can serve as targets for disease therapy. Increasing reports of epidemiological, diagnostic, and clinical research indicate that P450s are enzymes that play a major part in the formation of cancer, prevention, and metastasis. The purposes of this review are to shed light on the current state of knowledge about the cancer molecular mechanism involving P450s and to summarize the link between the cancer effects and the participation of P450s.

Phase II Study of the Triple Combination Chemotherapy of SOXIRI (S-1/Oxaliplatin/Irinotecan) in Patients with Unresectable Pancreatic Ductal Adenocarcinoma

LESSONS LEARNED

The triple combination chemotherapy of SOXIRI (S-1/oxaliplatin/irinotecan) in patients with unresectable pancreatic ductal adenocarcinoma was an effective treatment that appeared to be better tolerated than the widely used FOLFIRINOX regimen.SOXIRI regimen may provide an alternative approach for advanced pancreatic cancer.

BACKGROUND

In our previous phase I study, we determined the recommended dose of a biweekly S-1, oxaliplatin, and irinotecan (SOXIRI) regimen in patients with unresectable pancreatic ductal adenocarcinoma (PDAC). This phase II study was conducted to assess the safety and clinical efficacy in patients with unresectable PDAC.

METHODS

Patients with previously untreated metastatic and locally advanced PDAC were enrolled. The primary endpoint was response rate (RR). Secondary endpoints were adverse events (AEs), progression-free survival (PFS), and overall survival (OS). Patients received 80 mg/m² of S-1 twice a day for 2 weeks in alternate-day administration, 150 mg/m² of irinotecan on day 1, and 85 mg/m² of oxaliplatin on day 1 of a 2-week cycle.

RESULTS

Thirty-five enrolled patients received a median of six (range: 2-15) treatment cycles. The RR was 22.8% (95% confidence interval [CI]: 10.4-40.1); median OS, 17.7 months (95% CI: 9.8-22.0); and median PFS, 7.4 months (95% CI: 4.2-8.4). Furthermore, the median OS in patients with distant metastasis was 10.1 months, whereas that in patients with locally advanced PDAC was 22.6 months. Major grade 3 or 4 toxicity included neutropenia (54%), anemia (17%), febrile neutropenia (11%), anorexia (9%), diarrhea (9%), and nausea (9%). There were no treatment-related deaths.

CONCLUSION

SOXIRI is considered a promising and well-tolerated regimen in patients with unresectable PDAC.

[Metastatic stomach cancer: Clinical trials in Asia and in Occident]

Although cytotoxic chemotherapy is the main therapeutic option to treat gastric cancer in the metastatic setting, molecular targeted agents have recently been introduced in an effort to improve survival outcomes which in average do not exceed 1 year. Trastuzumab and ramucirumab, antibodies directed against HER2 and VEGFR2, respectively, may provide clinical benefit for some patients. Results of clinical studies show that Asian patients have increased survival compared to Caucasian patients. Differences between populations, and in particular the presence of polymorphisms capable of influencing the availability of fluorouracil, have been suggested as possible explanations. Other factors including histology, surgical procedures, administration of neoadjuvant chemotherapy in Western countries and screening programs in Asia have also been suggested. However, none of these elements can fully explain this phenomenon. The aim of this article is to present the main protocols used in clinical practice, the perspectives of metastatic gastric cancer treatment and the particularities observed in Asian and Caucasian patients.

CYP2A6 Polymorphisms Associate with Outcomes of S-1 Plus Oxaliplatin Chemotherapy in Chinese Gastric Cancer Patients

Gastric carcinoma is a heterogeneous malignant disease involving genetic factors. To identify predictive markers for gastric cancer treatment in Chinese patients, we evaluated the association between polymorphisms of the gene encoding cytochrome P450 2A6 (CYP2A6) and outcomes of S-1 plus oxaliplatin (SOX) chemotherapy treatment. Clinical data on 60 consecutive gastric cancer patients receiving SOX regimen were collected prospectively. We sequenced all exons of CYP2A6 and a total of 22 different polymorphisms were detected in the present study. Comprehensive analyses of these genetic polymorphisms were performed to determine their association with both safety and efficacy of SOX regimen. Our results showed that polymorphisms of CYP2A6 were associated with the safety and efficacy of SOX treatment. Among them, missense mutations CYP2A6 rs60823196 and rs138978736 could be possible risk factors (P < 0.05) for severe diarrhea induced by SOX, whereas CYP2A6 rs138978736 could be a conceivable predictor for overall survival of patients treated with SOX adjuvant chemotherapy. Further large-scale randomized prospective studies are warranted to confirm these findings.

Distribution of polymorphic variants of CYP2A6 and their involvement in nicotine addiction

Tobacco consumption has become a major public health issue, which has motivated studies to identify and understand the biological processes involved in the smoking behavior for prevention and smoking cessation treatments. CYP2A6 has been identified as the main gene that codifies the enzyme that metabolizes nicotine. Many alleles have been identified after the discovery of CYP2A6, suggesting a wide interethnic variability and a diverse smoking behavior of the allele carrying individuals. The main purpose of this review is to update and highlight the effects of the CYP2A6 gene variability related to tobacco consumption reported from diverse human populations. The review further aims to consider CYP2A6 in future studies as a possible genetic marker for the prevention and treatment of nicotine addiction. Therefore, we analyzed several population studies and their importance at addressing and characterizing a population using specific parameters. Our efforts may contribute to a personalized system for detecting, preventing and treating populations at a higher risk of smoking to avoid diseases related to tobacco consumption.

Functional Characterization of 34 CYP2A6 Allelic Variants by Assessment of Nicotine C-Oxidation and Coumarin 7-Hydroxylation Activities

CYP2A6, a member of the cytochrome P450 (P450) family, is one of the enzymes responsible for the metabolism of therapeutic drugs and such tobacco components as nicotine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, and N-nitrosodiethylamine. Genetic polymorphisms in CYP2A6 are associated with individual variation in smoking behavior, drug toxicities, and the risk of developing several cancers. In this study, we conducted an in vitro analysis of 34 allelic variants of CYP2A6 using nicotine and coumarin as representative CYP2A6 substrates. These variant CYP2A6 proteins were heterologously expressed in 293FT cells, and their enzymatic activities were assessed on the basis of nicotine C-oxidation and coumarin 7-hydroxylation activities. Among the 34 CYP2A6 variants, CYP2A6.2, CYP2A6.5, CYP2A6.6, CYP2A6.10, CYP2A6.26, CYP2A6.36, and CYP2A6.37 exhibited no enzymatic activity, whereas 14 other variants exhibited markedly reduced activity toward both nicotine and coumarin. These comprehensive in vitro findings may provide useful insight into individual differences in smoking behavior, drug efficacy, and cancer susceptibility.

Pharmacogenetics of the Cytochrome P450 Enzyme System: Review of Current Knowledge and Clinical Significance

Genetic variation in drug metabolizing enzymes is an important contributor to interindividual variation in drug disposition and response and is associated with significant clinical consequences. Many commonly used drugs are dependent on the cytochrome P450 monooxygenase enzymes (CYP450) for their metabolism and elimination. At present, more than 57 active human CYP450 genes are known, and the majority of these genes are polymorphic. Despite the large number of CYP450 genes, only the CYP1, CYP2, and CYP3 families of enzymes have a major role in drug metabolism. Approximately 10 CYP450s are responsible for the metabolism of a large number of pharmacologic agents in human beings. The polymorphic forms of the CYP450s are responsible for the development of a significant number of adverse drug reactions and may also contribute to drug response. Genetic polymorphisms have now been identified in the genes encoding all the main CYP450s that contribute to drug and other xenobiotic metabolism, and there are marked interethnic differences in the distribution and frequency of variant alleles. A review of the progress in the pharmacogenetics of P450s that are important for drug metabolism is presented with particular emphasis on the clinical relevance of this research.

Can S-1 replace fluorouracil for advanced gastric cancer? A PRISMA-compliant systematic review and meta-analysis

It remains to be seen whether S-1 can be a replacement for infusional fluorouracil (5-FU) for advanced gastric cancer (AGC). The aim of this study was to compare the efficacy and safety of S-1 with 5-FU in AGC.PubMed and Cochrane Library were searched. Randomized controlled trials and meta-analyses comparing S-1 with 5-FU for AGC were eligible. Meta-analysis was performed using RevMan 5.2.Seven trials involving 2443 patients were included. Compared with 5-FU, S-1 showed no significant prolongation of overall survival (OS) (hazard ratio [HR] = 0.91, 95% confidence interval [CI] [0.83-1.01], P = 0.07) and progression-free survival (HR = 0.89, 95% CI [0.70-1.13], P = 0.35), but longer time to treatment failure (HR = 0.74, 95% CI [0.56-0.97], P = 0.03). The objective response rates were comparable (risk ratio [RR] = 1.36, 95% CI [0.95, 1.96], P = 0.10). Regarding treatment-related deaths and hematological toxicities, there was significant heterogeneity between Asian and non-Asian trials, and subgroup analysis was applied. In Asian patients, there was a significant increase in hematological toxicities such as leukopenia (grade 1-4: RR = 1.22, 95% CI [1.08, 1.37], P = 0.001; grade 3-4: RR = 2.21, 95% CI [1.52, 3.21], P < 0.0001), neutropenia (grade 1-4: RR = 1.29, 95% CI [1.11, 1.48], P = 0.0005; grade 3-4: RR = 1.87, 95% CI [1.11, 3.17], P = 0.02), and thrombocytopenia (grade 1-4: RR = 1.71, 95% CI [1.22, 2.41], P = 0.002) in S-1-containing regimens compared with 5-FU-containing regimens, but without significant difference in treatment-related mortality rate (risk difference [RD] = 0.00, 95% CI [-0.01, 0.01], P = 0.68). In non-Asian patients, S-1-containing regimens were, however, associated with significantly fewer treatment-related deaths (RD = -0.02, 95% CI [-0.05, -0.00], P = 0.04), as well as less all grade 1-4 and grade 3-4 hematological toxicities except anemia. There was no significant heterogeneity in nonhematologic toxicities between Asian and non-Asian trials. Lower incidence of grade 1-4 nausea, diarrhea, mucositis, grade 3-4 mucositis, increased creatinine, and decreased calculated creatinine clearance was observed in S-1-containing regimens.S-1 could not improve OS, but increase some hematological toxicities in Asian patients. Therefore, special attention on hematological toxicities should be paid to Asian patients because S-1 is administered on an outpatient basis.

Fluoropyrimidine-Based Chemotherapy as First-Line Treatment for Advanced Gastric Cancer: a Bayesian Network Meta-Analysis

Fluoropyrimidine-based regimens are the most common treatments in advanced gastric cancer. We used a Bayesian network meta-analysis to identify the optimal fluoropyrimidine-based chemotherapy by comparing their relative efficacy and safety. We systematically searched databases and extracted data from randomized controlled trials, which compared fluoropyrimidine-based regimens as first-line treatment in AGC. The main outcomes were overall survival (OS), progression-free survival (PFS), overall response rate (ORR), and grade 3 or 4 adverse events (AEs). A total of 12 RCTs of 4026 patients were included in our network meta-analysis. Pooled analysis showed S-1 and capecitabine had a significant OS benefit over 5-Fu, with hazard ratios of 0.90 (95%CI = 0.81-0.99) and 0.88 (95%CI = 0.80-0.96), respectively. The result also exhibited a trend that S-1 and capecitabine prolonged PFS in contrast to 5-Fu, with hazard ratios of 0.84 (95%CI = 0.66-1.02) and 0.84 (95%CI = 0.65-1.03), respectively. Additionally, all the three fluoropyrimidine-based regimens were similar in terms of ORR and grade 3 or 4 AEs. Compared with regimens based on 5-Fu, regimens based on S-1 or capecitabine demonstrated a significant OS improvement without compromise of AEs as first-line treatment in AGC in Asian population. S-1 and capecitabine can be interchangeable according their different emphasis on AEs.

Phase I/II trial of chemoradiotherapy with concurrent S-1 and cisplatin for clinical stage II/III esophageal carcinoma (JCOG 0604)

We carried out a phase I/II trial of chemoradiotherapy concurrent with S-1 and cisplatin to determine the maximum tolerated dose and recommended dose and to evaluate the efficacy and safety of this treatment in patients with esophageal carcinoma. Thoracic esophageal cancer patients with clinical stage II/III disease, excluding T4, were eligible. Chemotherapy consisted of S-1 at a dose of 60–80 mg/m²/day on days 1–14, and cisplatin at 75 mg/m² on day 1, repeated twice every 4 weeks. Single daily radiation of 50.4 Gy was given in 28 fractions concurrently starting on day 1. Patients achieving an objective response after chemoradiotherapy underwent two additional cycles of chemotherapy. Patient accrual was terminated early due to slow enrolment after 44 patients were accrued. In the phase I part, two of six patients experienced dose-limiting toxicities at each level of S-1 (S-1 60 or 80 mg/m²/day). Considering treatment compliance, the recommended dose was determined to be S-1 60 mg/m²/day. The complete response rate, the primary endpoint of phase II, was 59.5% (22/37; 90% confidence interval, 44.6–73.1%; weighted threshold, 57.2%; P = 0.46 by the exact binomial test) on central review. In the phase II part, 3-year progression-free survival was 48.4%, with a 3-year overall survival of 61.9%. Grade 3 or 4 toxicity in phase II included leukopenia (57.9%), neutropenia (50%), hyponatremia (28.9%), anorexia (21.1%), anemia (18.4%), thrombocytopenia (18.4%), and febrile neutropenia (2.6%). No treatment-related deaths were observed. Although this combination showed acceptable toxicity and favorable 3-year survival, the study did not meet its primary endpoint. This trial was registered at the UMIN Clinical Trials Registry as UMIN000000710.

Phase II trial of chemoradiotherapy with S-1 plus cisplatin for unresectable locally advanced head and neck cancer (JCOG0706)

We conducted a phase II study to evaluate the efficacy and safety of chemoradiotherapy concurrent with S-1 plus cisplatin in patients with unresectable locally advanced squamous cell carcinoma of the head and neck. Chemotherapy consisted of S-1 twice daily on days 1–14 at 60 mg/m²/day and cisplatin at 20 mg/m²/day on days 8–11, repeated twice at a 5-week interval. Single daily radiation of 70 Gy in 35 fractions was given concurrently starting on day 1. For patients achieving an objective response after chemoradiotherapy, two additional cycles of chemotherapy were administered. Of the 45 enrolled patients, the percentage of clinical complete remission, the primary endpoint, was 64.4% (8 complete response, 21 good partial response) on central review. After a median follow-up of 3.52 years, 3-year local progression-free survival was 62.2%, with 3-year progression-free survival of 60.0%, 3-year overall survival of 64.4%, and 3-year time to treatment failure of 48.9%. Grade 3 or 4 toxicity included pharyngeal mucositis (46.7%), oral mucositis (44.4%), dysphagia (46.7%), anorexia (42.2%), radiation dermatitis (26.7%), neutropenia (26.7%), and febrile neutropenia (4.4%). No treatment-related deaths were observed. This combination showed promising efficacy with acceptable toxicities.

Cytochrome P450 in Cancer Susceptibility and Treatment

Cytochrome 450 (CYP450) designates a group of enzymes abundant in smooth endoplasmic reticulum of hepatocytes and epithelial cells of small intestines. The main function of CYP450 is oxidative catalysis of various endogenous and exogenous substances. CYP450 are implicated in phase I metabolism of 80% of drugs currently in use, including anticancer drugs. They are also involved in synthesis of various hormones and influence hormone-related cancers. CYP450 genes are highly polymorphic and their variants play an important role in cancer risk and treatment. Association studies and meta-analyses have been performed to decipher the role of CYP450 polymorphisms in cancer susceptibility. Cancer treatment involves multimodal therapies and evaluation of CYP450 polymorphisms is necessary for pharmacogenetic assessment of anticancer therapy outcomes. In addition, CYP450 inhibitors are being evaluated for improved pharmacokinetics and oral formulation of several anticancer drugs.

Efficacy of S-1 in colorectal cancer

INTRODUCTION

S-1 is an oral fluoropyrimidine that consists of tegafur, 5-chloro-2, 4-dihydroxypyridine and potassium oxonate. It has been developed as a prodrug of 5-fluorouracil with the goal of improving therapeutic efficacy and tolerability.

AREAS COVERED

This review aims to provide an evidence-based update of clinical trials that have investigated the clinical efficacy, adverse-event profile, dosage and administration of S-1, given alone or in combination with conventional chemotherapeutics and new target-oriented drugs, in the management of colorectal cancer (CRC). Additionally, differences in the tolerability and pharmacokinetics of S-1 between Caucasians and Asians have been described. Finally, the therapeutic efficacy of S-1 regarding metastatic CRC or postoperative CRC has been discussed. Available data have stimulated further research, including Phase III trials for the treatment of advanced CRC.

EXPERT OPINION

Treatment using S-1 combined with oxaliplatin (± bevacizumab) and irinotecan has achieved promising results in terms of feasibility, safety and effectiveness. Furthermore, S-1 is an acceptable treatment as adjuvant chemotherapy for colon cancer.

Novel CYP2A6 variants identified in African Americans are associated with slow nicotine metabolism in vitro and in vivo

OBJECTIVE

Nicotine, the main addictive ingredient in tobacco, is metabolically inactivated to cotinine primarily by the hepatic enzyme CYP2A6. Considerable genetic variation in the CYP2A6 gene results in large variation in the rates of nicotine metabolism, which in turn alters smoking behaviours (e.g. amount of cigarettes smoked, risk for dependence and success in smoking cessation). The aim of this study was to identify and characterize novel variants in CYP2A6.

MATERIALS AND METHODS

The CYP2A6 gene from African American phenotypically slow nicotine metabolizers was sequenced and seven novel variants were identified [CYP2A6*39 (V68M), CYP2A6*40 (I149M), CYP2A6*41 (R265Q), CYP2A6*42 (I268T), CYP2A6*43 (T303I), CYP2A6*44 (E390K), CYP2A6*44 (L462P)]. Variants were introduced into a bi-cistronic cDNA expression construct containing CYP2A6 and P450 oxidoreductase and assessed for protein expression, enzymatic activity and stability as evaluated using western blotting and nicotine metabolism. Genotyping assays were developed and allelic frequencies were assessed in 534 African Americans.

RESULTS

The variants showed significantly lower protein expression (P<0.001) when compared with the wild-type as well as reduced metabolism of nicotine to cotinine when controlling for cDNA expression using P450 oxidoreductase (P<0.001). The variants also showed reduced stability at 37°C. Allelic frequencies ranged from 0.1 to 0.6% with a collective genotype frequency of 3.2%; the impact in vitro correlated significantly with in-vivo activity (R(2)=0.40-0.48, P<0.05). Together, those with a novel variant had significantly lower nicotine metabolism in vivo than those without genetic variants (P<0.01).

CONCLUSION

Here, we identified a number of novel variants with reduced/loss of CYP2A6 activity, increasing our understanding of CYP2A6 genetic variability.

Effect of CYP2A6 genetic polymorphism on the metabolic conversion of tegafur to 5-fluorouracil and its enantioselectivity

Tegafur (FT), a prodrug of 5-fluorouracil, is a chiral molecule, a racemate of R- and S-isomers, and CYP2A6 plays an important role in the enantioselective metabolism of FT in human liver microsomes (R-FT >> S-FT). This study examined the enantioselective metabolism of FT by microsomes prepared from Sf9 cells expressing wild-type CYP2A6 and its variants (CYP2A6*7, *8, *10, and *11) that are highly prevalent in the Asian population. We also investigated the metabolism of coumarin and nicotine, both CYP2A6 probe drugs, in these variants. Enzyme kinetic analyses showed that CYP2A6.7 (I471T) and CYP2A6.10 (I471T and R485L) had markedly lower Vmax values for both enantiomers than wild-type enzyme (CYP2A6.1) and other variant enzymes, whereas Km values were higher in most of the variant enzymes for both enantiomers than CYP2A6.1. The ratios of Vmax and Km values for R-FT to corresponding values for S-FT (R/S ratio) were similar among enzymes, indicating little difference in enantioselectivity among the wild-type and variant enzymes. Similarly, both CYP2A6.7 and CYP2A6.10 had markedly lower Vmax values for coumarin 7-hydroxylase and nicotine C-oxidase activities than CYP2A6.1 and other variant enzymes, whereas Km values were higher in most of the variant enzymes for both activities than CYP2A6.1. In conclusion, the amino acid substitutions in CYP2A6 variants generally resulted in lower affinity for substrates, while Vmax values were selectively reduced in CYP2A6.7 and CYP2A6.10. Consistent R/S ratios among CYP2A6.1 and variant enzymes indicated that the amino acid substitutions had little effect on enantioselectivity in the metabolism of FT.

The role of reduced intracellular concentrations of active drugs in the lack of response to anticancer chemotherapy

A major difficulty in the treatment of cancers is the poor response of many tumors to pharmacological regimens. This situation can be accounted for by the existence of a variety of complex mechanisms of chemoresistance (MOCs), leading to reduced intracellular concentrations of active agents, changes in the molecular targets of the drugs, enhanced repair of drug-induced modifications in macromolecules, stimulation of anti-apoptotic mechanisms, and inhibition of pro-apoptotic mechanisms. The present review focuses on alterations in the expression and appearance of the genetic variants that affect the genes involved in reducing the amount of active agents inside tumor cells. These alterations can occur through two mechanisms: either by lowering uptake or enhancing efflux (so-called MOC-1a and MOC-1b, respectively), or by decreasing the activation of prodrugs or enhancing inactivation of active agents through their biotransformation (MOC-2). The development of chemosensitizers that are useful in implementing the pharmacological manipulation of these processes constitutes a challenge to modern pharmacology. Nevertheless, the important physiological roles of the most relevant genes involved in MOC-1a, MOC-1b, and MOC-2 make it difficult to prevent the side effects of chemosensitizers. A more attainable goal in this area of pharmacological enquiry is the identification of proteomic profiles that will permit oncologists to accurately predict a lack of response to a given regimen, which would be useful for adapting treatment to the personal situation of each patient.

Clinical development of S-1 for non-small cell lung cancer: a Japanese perspective

For more than a decade, S-1 has been investigated aggressively against non-small cell lung cancer (NSCLC) in Japan. Recently, two randomized phase III trials of S-1 combined with cisplatin (CDDP) or carboplatin (CBDCA) compared with the standard platinum doublet chemotherapy were reported. S-1 and CDDP was noninferior to CDDP and DTX in terms of overall survival (OS) (median survival time [MST] 16.1 versus 17.1 months, respectively; hazard ratio [HR] 1.013; 96.4% confidence interval [CI] 0.837-1.227). Noninferiority of S-1 and CBDCA compared with CBDCA and paclitaxel was also confirmed for OS (MST 15.2 versus 13.3 months, respectively; HR 0.928; 99.2% CI 0.671-1.283). The noninferiority design employed an upper CI limit of HR<1.322 in the former trial and HR<1.33 in the latter. S-1 combined with CDDP or CBDCA was thought to be one of the standard platinum doublet regimens in the first-line setting for patients with advanced NSCLC in Japan. Some additional interesting phase I and II studies have been published in Japan. They include studies of S-1 as first-line chemotherapy when combined with nonplatinum agents; as second-line chemotherapy; within chemoradiotherapy for locally advanced disease; and in the postoperative adjuvant setting. This review will also describe the use of S-1 for the treatment of NSCLC in these settings.

Advances in molecular modeling of human cytochrome P450 polymorphism

Cytochrome P450 (CYP) is a supergene family of metabolizing enzymes involved in the phase I metabolism of drugs and endogenous compounds. CYP oxidation often leads to inactive drug metabolites or to highly toxic or carcinogenic metabolites involved in adverse drug reactions (ADR). During the last decade, the impact of CYP polymorphism in various drug responses and ADR has been demonstrated. Of the drugs involved in ADR, 56% are metabolized by polymorphic phase I metabolizing enzymes, 86% among them being CYP. Here, we review the major CYP polymorphic forms, their impact for drug response and current advances in molecular modeling of CYP polymorphism. We focus on recent studies exploring CYP polymorphism performed by the use of sequence-based and/or protein-structure-based computational approaches. The importance of understanding the molecular mechanisms related to CYP polymorphism and drug response at the atomic level is outlined.

A retrospective comparison of S-1 plus cisplatin and capecitabine plus cisplatin for patients with advanced or recurrent gastric cancer

BACKGROUND

Based on the results of the SPIRITS trial, combination chemotherapy of S-1 plus cisplatin (SP) is now considered the standard treatment for patients with advanced gastric cancer (AGC) in Japan. On the other hand, several non-Japanese studies have shown the efficacy of capecitabine plus cisplatin (XP), which has been used as the reference arm in recent global studies of AGC.

METHODS

We retrospectively compared the efficacy and safety of SP and XP in first-line treatment for patients with AGC.

RESULTS

From August 2006 to November 2008, 26 AGC patients received XP in the context of 2 global trials (AVAGAST and ToGA), and 50 patients received SP during the same period. The objective response rate was 43.2 % in the SP group and 50 % in the XP group, with no significant difference (p = 0.62). There were also no significant differences in progression-free survival (median 5.8 vs. 5.2 months; p = 0.91) and overall survival (median 13.8 vs. 13.5 months; p = 0.97) between the SP and XP groups. The frequencies of hematological toxicities of grade 3 or more and non-hematological toxicities were not significantly different between the 2 groups. Although grade 1 or 2 hand-foot syndrome was more common in the XP group, no patients experienced grade 3 or more.

CONCLUSIONS

Although the retrospective nature of this study and the small number of patients is a major limitation, SP and XP were associated with similar efficacy and safety in patients with AGC.

Polymorphic metabolism by functional alterations of human cytochrome P450 enzymes

The study of cytochrome P450 pharmacogenomics is of particular interest because of its promise in the development of rational means to optimize drug therapy with respect to patient's genotype to ensure maximum efficacy with minimal adverse effects. Drug metabolizing P450 enzymes are polymorphic and are the main phase I enzymes responsible for the metabolism of clinical drugs. Therefore, polymorphisms in the P450s have the most impact on the fate of clinical drugs in phase I metabolism since almost 80% of drugs in use today are metabolized by these enzymes. Predictive genotyping for P450 enzymes for a more effective therapy will be routine for specific drugs in the future. In this review, we discuss the current knowledge of polymorphic metabolism by functional alterations in nonsynonymous SNPs of P450 1A2, 2A6, 2C8, 2C9, 2C19, 2D6, and 3A4 enzymes.

Mechanism-based inhibition of cytochrome P450 (CYP)2A6 by chalepensin in recombinant systems, in human liver microsomes and in mice in vivo

BACKGROUND AND PURPOSE

Chalepensin is a pharmacologically active furanocoumarin compound found in rue, a medicinal herb. Here we have investigated the inhibitory effects of chalepensin on cytochrome P450 (CYP) 2A6 in vitro and in vivo.

EXPERIMENTAL APPROACH

Mechanism-based inhibition was studied in vitro using human liver microsomes and bacterial membranes expressing genetic variants of human CYP2A6. Effects in vivo were studied in C57BL/6J mice. CYP2A6 activity was assayed as coumarin 7-hydroxylation (CH) using HPLC and fluorescence measurements. Metabolism of chalepensin was assessed with liquid chromatography/mass spectrometry (LC/MS).

KEY RESULTS

CYP2A6.1, without pre-incubation with NADPH, was competitively inhibited by chalepensin. After pre-incubation with NADPH, inhibition by chalepensin was increased (IC(50) value decreased by 98%). This time-dependent inactivation (k(inact) 0.044 min(-1) ; K(I) 2.64 µM) caused the loss of spectrally detectable P450 content and was diminished by known inhibitors of CYP2A6, pilocarpine or tranylcypromine, and by glutathione conjugation. LC/MS analysis of chalepensin metabolites suggested an unstable epoxide intermediate was formed, identified as the corresponding dihydrodiol, which was then conjugated with glutathione. Compared with the wild-type CYP2A6.1, the isoforms CYP2A6.7 and CYP2A6.10 were less inhibited. In mouse liver microsomes, pre-incubation enhanced inhibition of CH activity. Oral administration of chalepensin to mice reduced hepatic CH activity ex vivo.

CONCLUSIONS AND IMPLICATIONS

Chalepensin was a substrate and a mechanism-based inhibitor of human CYP2A6. Formation of an epoxide could be a key step in this inactivation. 'Poor metabolizers' carrying CYP2A6*7 or *10 may be less susceptible to inhibition by chalepensin. Given in vivo, chalepensin decreased CYP2A activity in mice.

A comprehensive review of S-1 in the treatment of advanced gastric adenocarcinoma

Gastric cancer is the fourth most common malignancy worldwide with Japan, Korea, Taiwan, China, Mongolia and many countries in South America and eastern Europe, as well as parts of the Middle East, contributing to the majority of cases. In the USA, it was estimated that approximately 10,620 deaths would be caused by gastric cancer in 2010. Gastric cancer is often diagnosed in its advanced stages. Current first-line treatment for advanced gastric cancer (AGC) using triplet combination chemotherapy containing a platinum-based compound, a fluoropyrimidine with an anthracycline (frequently added in Europe) or a taxane (more often used in the USA and elsewhere) has resulted in higher response rates and modest improvement in overall survival compared with doublet combinations. However, triplet combinations can be associated with increased toxicity compared with the doublets and patient selection becomes important. A desirable research strategy is to improve outcomes of patients with AGC by identifying treatments that are effective, convenient and safe. The interest in oral agents compared with intravenous agents is mounting. One oral fluoropyrimidine, S-1, is novel as it combines tegafur, 5-chloro-2,4-dihydroxypyridine and potassium oxonate. S-1 is approved in Japan, China, Taiwan, Korea and Singapore for the treatment of patients with gastric cancer, and more recently has been approved in 27 European countries to treat AGC. Initial clinical trials in the USA and Europe observed diarrhea as the dose-limiting toxicity; however, initial Japanese studies reported myelosuppression as the dose-limiting toxicity. The differing dose tolerance in these two populations is likely due to polymorphisms in the CYP2A6 gene. Based on our review of Phase II and III studies, we conclude that S-1 is a convenient oral fluoropyrimidine that provides safety advantage over intravenous fluorouracil without compromising efficacy against AGC.

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.

Population pharmacokinetic analysis of letrozole in Japanese postmenopausal women

PURPOSE

Letrozole is an orally active aromatase inhibitor for the treatment of breast cancer. The objectives of this study were to examine the pharmacokinetic profile of letrozole in Japanese subjects and to identify factors that influence variability in the pharmacokinetics of letrozole using population pharmacokinetic (PPK) analysis.

METHODS

Twenty-five healthy postmenopausal Japanese women were enrolled in the study and received 2.5 mg letrozole once daily for 14 or 28 days. A PPK model was developed using NONMEM software. Age, body weight (WT), AST, ALT, total bilirubin, serum creatinine (CRE), and genotype of CYP2A6 were studied as covariates. Estrone, estrone sulfate, and estradiol in plasma were measured as pharmacodynamic markers.

RESULTS

CYP2A6 genotype, CRE, and AST were significant covariates for apparent systemic clearance (CL/F), and WT was a significant covariate for apparent distribution volume (Vd/F). Population mean estimates of CL/F and Vd/F in subjects without CYP2A6 mutation were 1.03 × (CRE/0.70)(-1.27) × (AST/17.5)(-0.793) L/h and 94.2 × (WT/51.1)(1.12) L respectively. CL/F in subjects possessing 1 and 2 CYP2A6 mutation alleles were 84.3% and 44.8% of the value in the subjects without mutation respectively. Estrogen levels fell to below detection limits in most subjects after letrozole administration. Three mild and transient adverse events (upper respiratory tract inflammation, arthralgia, and vomiting) were reported in the study.

CONCLUSIONS

CYP2A6 genotype largely influences CL/F of letrozole. Genetic polymorphism of CYP2A6 and body weight will be causes of ethnic difference in PK. However, dose adjustment is not necessary, because of the wide therapeutic range.

Phase I trial of chemoradiotherapy with the combination of S-1 plus cisplatin for patients with unresectable locally advanced squamous cell carcinoma of the head and neck

The aim of the present study was to determine the maximum tolerated dose (MTD) of S-1 in combination with chemoradiotherapy (CRT) in patients with unresectable locally advanced squamous cell carcinoma of the head and neck, and evaluate the difference in pharmacokinetics of S-1 when administered as a suspension via a feeding tube or orally as a capsule. Chemotherapy consisted of administration of S-1 twice daily on days 1-14 at escalating doses of 40, 60 and 80 mg/m(2) per day, and cisplatin at 20 mg/m(2) per day on days 8-11, repeated twice at a 5-week interval. Single daily radiation of 70 Gy in 35 fractions was given concurrently starting on day 1. Two additional cycles of chemotherapy were planned after the completion of CRT. Before starting CRT, each patient received S-1 via two different administration methods. Twenty-two patients were enrolled. The MTD was reached with S-1 at 80 mg/m(2) per day, with two of six patients experiencing febrile neutropenia lasting more than 4 days. All four patients whose creatinine clearance was decreased to <60 mL/min after the first cycle of chemotherapy developed febrile neutropenia lasting more than 4 days. Pharmacokinetic analysis revealed that the 5-fluorouracil area under the curve did not significantly differ by the administration route. S-1 at 60 mg/m(2) per day for 14 days was well tolerated with concurrent CRT. Administration of S-1 as a suspension or by whole capsule can be considered therapeutically interchangeable. Although these data are preliminary, activity was highly promising, and this approach warrants further investigation.

Associations of various gene polymorphisms with toxicity in colorectal cancer patients receiving oral uracil and tegafur plus leucovorin: a prospective study

BACKGROUND

To assess the predictive value of polymorphism in nine genes, primarily thymidylate synthase (TS) and orotate phosphoribosyltransferase (OPRT), which relates to 5-fluorouracil (5-FU) metabolism, for toxicity in patients treated with oral uracil/tegafur (UFT) plus leucovorin (LV).

PATIENTS AND METHODS

We treated 99 patients with stage II or III colorectal carcinoma with oral UFT + LV. Germline DNA from patients was genotyped for 5-FU and folate metabolism-relating genes. CYP2A6, tegafur-activating enzyme, and uridine diphosphate-glucuronosyltransferase 1A1 genetic variation were also assessed. Toxicity was graded by the National Cancer Institute Common Toxicity Criteria, version 2.0.

RESULTS

The multivariate logistic regression revealed that OPRT 638G>C polymorphism was associated with grade 3 diarrhea [odds ratio (OR) 19.84 for patients with the C/C homozygous type compared with patients with wild type, P = 0.014] and polymorphisms of UGT1A1 were associated with hyperbilirubinemia (OR 38.76 for homozygotes and double heterozygotes of *6 or *28 compared with wild type, P = 0.0008). No relationships were observed between TS polymorphisms and any toxicity.

CONCLUSIONS

OPRT polymorphism predicts toxicity, especially grade 3 or greater diarrhea to oral UFT + LV adjuvant chemotherapy, whereas TS does not, in our study cohort. UGT1A1 polymorphism seems to be a risk factor for hyperbilirubinemia due to UFT+LV.

Multicenter phase III comparison of cisplatin/S-1 with cisplatin/infusional fluorouracil in advanced gastric or gastroesophageal adenocarcinoma study: the FLAGS trial

PURPOSE

Patients with advanced gastric or gastroesophageal adenocarcinoma need more efficacious and safer treatments than established today. S-1, a contemporary oral fluoropyrimidine, can provide that advantage.

PATIENTS AND METHODS

This study was conducted in 24 countries and 146 centers. One thousand fifty-three patients were stratified (center, number of metastatic sites, prior adjuvant therapy, and measurable cancer) and randomly assigned. Patients received either S-1 at 50 mg/m(2) divided in two daily doses for 21 days and cisplatin at 75 mg/m(2) intravenously on day 1, repeated every 28 days (527 patients) or infusional fluorouracil at 1,000 mg/m(2)/24 hours for 120 hours and cisplatin at 100 mg/m(2) intravenously on day 1, repeated every 28 days (526 patients). The primary end point was superiority in overall survival (OS) from cisplatin/S-1 compared with cisplatin/infusional fluorouracil in patients with advanced, untreated gastric, or gastroesophageal adenocarcinoma. The secondary end points were response rate, progression-free survival, time to treatment failure, and safety.

RESULTS

The median OS was 8.6 months in the cisplatin/S-1 arm and 7.9 months in the cisplatin/infusional fluorouracil arm (HR, 0.92; 95% CI, 0.80 to 1.05; P = .20). Significant safety advantages were observed in the cisplatin/S-1 arm compared with the cisplatin/infusional fluorouracil arm for the rates of grade 3/4 neutropenia (32.3% v 63.6%), complicated neutropenia (5.0% v 14.4%), stomatitis (1.3% v 13.6%), hypokalemia (3.6% v 10.8%), and treatment-related deaths (2.5% v 4.9%; P < .05).

CONCLUSION

Cisplatin/S-1 did not prolong OS of patients with advanced gastric or gastroesophageal adenocarcinoma compared with cisplatin/infusional fluorouracil, but it did result in a significantly improved safety profile.

Pharmacogenomics in chemotherapy for GI tract cancer

The study of pharmacogenomics (PGx) has recently been intensively applied to gastrointestinal tract cancer. It has become clear that there are genetic differences in the activities of enzymes that influence the kinetics of chemotherapeutic agents. Moreover, genetic differences related to cellular sensitivity to anti-cancer agents have also been elucidated. In GI-tract cancer chemotherapy, 5-FU, gemcitabine, taxanes (docetaxel and paclitaxel), platinum (cisplatin and oxaliplatin) and irinotecan are often used, and molecular targeting therapy has also been developed. The respective PGx markers to such agents have been reported. Of the candidate PGx markers, K-ras mutation and UGT1A1 polymorphisms have sufficient evidence to justify routine clinical assessment for the selection of anti-cancer regimens. Progress in this field would facilitate the further development of PGx-guided individualized therapy, which could be expected to increase therapeutic efficacy and decrease the risk of adverse events.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Multicenter, phase II study of gemcitabine and S-1 combination chemotherapy in patients with advanced biliary tract cancer

PURPOSE

To evaluate the efficacy and safety of gemcitabine and S-1 combination chemotherapy in patients with advanced biliary tract cancer.

METHODS

Patients with a measurable lesion and no previous history of chemotherapy or radiotherapy were enrolled. Gemcitabine was administered intravenously at a dose of 1,000 mg/m(2) over 30 min on day 1 and 15, repeated every 4 weeks. S-1 was administered orally at a dose of 40 mg/m(2) b.i.d. on days 1-14. Tumor response was assessed every two cycles using Response Evaluation Criteria in Solid Tumors criteria.

RESULTS

As much as 35 patients were enrolled between December 2006 and July 2008; 14 patients (40%) with gallbladder cancer and 14 (40%) with intrahepatic cholangiocarcinoma were included and 7 patients (20%) had received previous surgical resection. The overall response rate was 34.3% and the overall disease control rate was 82.9%. The median overall survival time was 11.6 months (95% CI, 7.3-15.6 months), and the median time to progression was 5.9 months (95% CI, 4.0-7.7 months). The grade 3/4 toxicities were leucopenia (23%), neutropenia (34%), anemia (20%), thrombocytopenia (6%) and anorexia (3%).

CONCLUSIONS

Gemcitabine and S-1 combination chemotherapy has promising efficacy and good tolerability in patients with advanced biliary tract cancer.