Oral fluoropyrimidines: a closer look at their toxicities

Capecitabine for treating head and neck cancer

INTRODUCTION

With an increasing incidence, over half a million cases of head and neck cancer (HNC) are diagnosed annually worldwide. Various chemotherapeutic agents are utilized to achieve adequate locoregional control. Cisplatin, fluorouracil (FU), and taxanes are often used to treat HNC but these regimens have shown high toxicity and poor patient compliance. Capecitabine is an orally administered prodrug that is preferentially converted to FU in tumor cells in comparison to normal cells.

AREA COVERED

In this review, the authors evaluate the role of capecitabine in radical and palliative settings either alone or in combination with other chemotherapeutic drugs in the management of HNC. In addition, metabolic conversion, pharmacokinetics, pharmacodynamics, and toxicity profile of capecitabine are discussed.

EXPERT OPINION

Various phase II trials conducted on capecitabine in the management of recurrent HNC have shown comparable results and tolerable toxic effects especially in pre-treated fragile patients. Capecitabine, used in induction or concurrent settings in the radical management of locoregionally advanced HNC, have also shown promising results. Randomized trials are needed to validate the role of capecitabine in the management of HNC.

X-ray structure of Salmonella typhimurium uridine phosphorylase complexed with 5-fluorouracil and molecular modelling of the complex of 5-fluorouracil with uridine phosphorylase from Vibrio cholerae

Uridine phosphorylase (UPh), which is a key enzyme in the reutilization pathway of pyrimidine nucleoside metabolism, is a validated target for the treatment of infectious diseases and cancer. A detailed analysis of the interactions of UPh with the therapeutic ligand 5-fluorouracil (5-FUra) is important for the rational design of pharmacological inhibitors of these enzymes in prokaryotes and eukaryotes. Expanding on the preliminary analysis of the spatial organization of the active centre of UPh from the pathogenic bacterium Salmonella typhimurium (StUPh) in complex with 5-FUra [Lashkov et al. (2009), Acta Cryst. F65, 601-603], the X-ray structure of the StUPh-5-FUra complex was analysed at atomic resolution and an in silico model of the complex formed by the drug with UPh from Vibrio cholerae (VchUPh) was generated. These results should be considered in the design of selective inhibitors of UPhs from various species.

Thymidylate synthase and dihydropyrimidine dehydrogenase are related to histological effects of 5-fluorouracil and cisplatin neoadjuvant chemotherapy for primary gastric cancer patients

Thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), and vascular endothelial growth factor (VEGF) are associated with the effect of 5-fluorouracil (5-FU) based adjuvant chemotherapy. However, very few studies have investigated the relationship between these factors and 5-FU neoadjuvant chemotherapy for primary gastric cancer patients. In this study, we studied the correlation between these markers and the histological chemotherapeutic effect in advanced gastric cancer with neoadjuvant chemotherapy.

METHODS

Sixty-two primary advanced gastric cancer patients were recruited into the study. One cycle of continuous infusion of 5-FU (300 mg/m2/day, 14 days) plus drip infusion of cisplatin (15 mg/m2/day, Day one and Day two) was performed as neoadjuvant chemotherapy. Histological chemotherapeutic responses of the resected specimens were classified into responders and nonresponders. TS, DPD, VEGF expressions both before and after neoadjuvant chemotherapy were examined immunohistochemically.

RESULTS

There was an association between the TS-low group and the responders (p < 0.05); the DPD-low group and the responders in both biopsy and surgical specimens (p < 0.01). A combination of the low-TS and low-DPD group was further associated with responders (p < 0.01). The immunoexpressions of biopsied and surgical specimens were significantly associated with each other.

CONCLUSION

Neoadjuvant chemotherapy for primary gastric cancer with one cycle of 5-FU and cisplatin was associated with histological findings in patients with low baseline TS and DPD. This dual determination may predict for efficacy of neoadjuvant treatment with these drugs.

Simple determination of capecitabine and its metabolites by liquid chromatography with ultraviolet detection in a single injection

Capecitabine (N4-pentoxycarbonyl-5'-deoxy-5-fluorocytidine, Xeloda), a prodrug of 5-fluorouracil (5-FU), is an oral tumor-selective fluoropyrimidine carbamate approved in the treatment of colorectal and breast cancer. It has a preferential activation to 5-FU by thymidine phosphorilase (TP) in target tumor tissues through a series of three metabolic steps minimizing the exposure of normal tissues to 5-FU. It offers the potential of less gastrointestinal toxicity and advantages in terms of convenience and quality of life for the patient, in addition to cost-effectiveness as compared with intravenous 5-FU chemotherapy. We developed a high performance liquid chromatography assay for the determination of plasma capecitabine and its nucleoside metabolite concentrations and 5-FU catabolite dihydro-5-fluorouracil in a single step extraction and a single HPLC injection. The retention times of dihydro-5-fluorouracil, 5-FU, 5'-deoxy-5-fluorouridine (5'-DFUR) and capecitabine were 3.6, 4.4, 11.4 and 20.4 min, respectively and the internal standard retention times were 8.7 and 12.2 min for 5-bromouracil (5-BU) and tegafur, respectively. The limit of detection was 0.01 microg/ml for capecitabine and its nucleoside metabolites and the limit of quantification was 0.025 microg/ml. Extraction efficiency was >80% with a single solvent mixture extraction step for all analytes of interest. The assay had good precision, the within-day and between-day standard deviation of the mean (R.S.D.) being <10% in the linear range 0.025-10 microg/ml. The authors conclude that the method described here is ideally suited for the therapeutic monitoring of capecitabine and its metabolites.

Ocular surface, ocular adnexal, and lacrimal complications associated with the use of systemic 5-fluorouracil

PURPOSE

To determine the prevalence rates and associated characteristics of patients who have ocular surface, ocular adnexal, and lacrimal complications associated with the systemic use of the cancer chemotherapeutic agent 5-Fluorouracil (5-FU).

METHODS

An exposure-based cohort study was designed. Adult patients who had completed at least 3 months of systemic 5-FU therapy within the past 5 years were eligible for enrollment. Study subjects had a detailed medical history taken with emphasis on preexisting conditions known to be associated with the development of ocular surface, ocular adnexal, and lacrimal complications. An ocular examination was then performed. A complete nasolacrimal system evaluation was performed if symptoms or findings were identified. The prevalence was then determined for each ocular symptom and each ocular finding identified that was not present pretreatment. An exploratory analysis was then performed to identify patient characteristics that might influence the likelihood of developing any of the above complications.

RESULTS

Fifty-two patients were enrolled in the study. The prevalence rates of the following ocular abnormalities were calculated: ocular irritation, 5.8%; blepharitis, 3.8%; conjunctivitis, 3.8%; keratitis, 3.8%; eyelid dermatitis, 5.8%; cicatricial ectropion, 1.9%; tearing, 26.9%; punctal-canalicular stenosis, 5.8%; and blurred vision, 11.5%. Blacks had tearing at a significantly higher rate when compared with whites (P = 0.022, 2-sided Fisher exact test). Three patients had permanent complications that will require surgery for correction. Of the 7 patients who had a single abnormality, 6 had tearing and one had eyelid dermatitis. All of the 8 patients who had multiple findings had tearing as one of their abnormalities.

CONCLUSIONS

Ninety-three percent of the patients who had an ocular abnormality had tearing as one of the complications. Patients who are receiving systemic 5-FU and begin to tear should have an ocular examination, looking for ocular surface, ocular adnexal, and lacrimal complications.

Metastatic colorectal cancer: systemic treatment in the new millennium

BACKGROUND

Colorectal cancer (CRC) is common in North America. Metastatic disease is present at diagnosis in 30% of the patients, and approximately half of early-stage patients will eventually present with metastatic disease. Until recently, few chemotherapy options were available to treat metastatic CRC.

METHODS

The authors review the results of recent clinical trials and the design of ongoing trials in the management of patients with metastatic colorectal cancer.

RESULTS

Fluorouracil (5-FU) with leucovorin (LV) modulation has a marginal but positive effect on survival in those patients. The recent incorporation of irinotecan (CPT-11) and oxaliplatin for the management of advanced CRC has generated further improvement in survival. The development of oral fluoropyrimidines, mimicking continuous infusion 5-FU, is convenient. In randomized trials, capecitabine was equally effective to bolus 5-FU and LV in the management of metastatic CRC.

CONCLUSIONS

Recently completed or ongoing clinical trials to study novel targeting agents have initiated a new era of drug development. Anti-angiogenesis drugs, tyrosine kinase inhibitors, and epidermal growth factor blockers are among this new generation of agents with encouraging preliminary data. Randomized trials will determine the impact of these newer agents on survival and quality of life of patients with metastatic CRC.

The effect of dihydropyrimidine dehydrogenase deficiency on outcomes with fluorouracil

The use of fluorouracil has been complicated by unpredictable pharmacokinetics, low response rates and seemingly random toxicity. The variable pharmacology is largely due to inherited differences in expression of the metabolising enzyme dihydropyrimidine dehydrogenase (DPD). This converts fluorouracil to inactive metabolites (catabolic pathway) and ultimately dictates the amount of fluorouracil that is available to be metabolised to cytotoxic nucleotides (anabolic pathway). Absolute and partial DPD deficiency affect around 0.1 and 3% of the Caucasian population, respectively. Administration of conventional doses of fluorouracil to these individuals has resulted in profound bone marrow and gastrointestinal toxicity, especially in those with absolute DPD deficiency. Other forms of toxicity such as myocardial ischaemia have been difficult to attribute directly to DPD deficiency. Efforts to improve outcomes with fluorouracil have included monitoring of fluorouracil concentrations and modifying fluorouracil administration techniques (e.g. from bolus injections to protracted intravenous infusions). In general, these moves have met with limited therapeutic advancement. The recognition that DPD deficiency increases toxicity has lead to the suggestion that genotypic or phenotypic assessment of DPD status prior to initiating fluorouracil may help predict outcomes. The gene that encodes for DPD expression is called DPYD. Approximately 1% of Caucasians are heterozygotes for the DPYD*2A mutation which is the variant allele that is most frequently implicated in DPD deficiency. Screening for this mutation may identify around 60% of individuals with absolute DPD deficiency who are at the greatest risk of toxicity. Another approach is to determine DPD activity in peripheral blood mononuclear cells, with low activity suggesting an increased risk of toxicity. Intratumoral DPD activity may also be assessed with high activity suggesting a poorer response to fluorouracil. Recently, drugs that inhibit DPD (e.g. eniluracil) have become available. These remove much of the variability in fluorouracil pharmacokinetics and may make assessment of DPD activity redundant. Despite the considerable inroads that have been made, further study is needed before the best means of optimising fluorouracil treatment is determined.

Oxaliplatin and UFT combination chemotherapy in patients with metastatic colorectal cancer

A phase II study was performed to evaluate the clinical efficacy and toxicity of oxaliplatin combined with uracil and tegafur (UFT) in patients with advanced colorectal cancer previously treated with a fluoropyrimidine-based regimen. From January to December 1999, 34 patients were enrolled in this study. Patients received intravenous oxaliplatin 130 mg/m2 on day 1 and daily oral UFT 350 mg/m2 in 3 divided doses for 21 days and repeated every 21 days. Thirty-one of 34 patients were assessable for response and 32 patients for toxicity. Partial response was observed in four patients and stable disease in six patients. The response rate was 12.9% (95% CI, 3.6-29.8%) and median duration of response was 17 weeks. The median overall survival and progression-free survival of all patients were 26 weeks (range, 3-90+ weeks) and 9 weeks (range, 3-56 weeks), respectively. Sensory neuropathy was the most common toxicity, but there was no severe toxicity (>grade II) except for a case of grade III neutropenia. We conclude that oxaliplatin and UFT combination chemotherapy was well tolerated without significant toxicities. The results of this trial will serve as the basis for designing new clinical trials with a different dose or schedule.

Rational development of capecitabine

Capecitabine is a fluoropyrimidine carbamate that was rationally designed as an oral drug capable of mimicking continuous infusion 5-fluorouracil (5-FU) and delivering 5-FU preferentially to tumour tissue. Following extensive absorption, capecitabine is rapidly converted to 5-FU via a three-step enzymatic pathway. The final step depends on thymidine phosphorylase, an enzyme present at higher concentrations in malignant compared with normal tissue. This results in the delivery of 5-FU preferentially to the tumour site. Capecitabine has demonstrated high activity in preclinical xenograft models for a wide range of human solid tumours, including those resistant to 5-FU. Phase I studies have determined the maximum tolerated dose (MTD) of capecitabine and identified a number of dosage regimens, which were subsequently evaluated in a randomised, phase II study as first-line treatment for metastatic colorectal cancer. This established an intermittent regimen of capecitabine 1250 mg/m2 twice daily for 14 days followed by a 7-day rest period as the most appropriate regimen for further clinical development.

Capecitabine (Xeloda) improves medical resource use compared with 5-fluorouracil plus leucovorin in a phase III trial conducted in patients with advanced colorectal carcinoma

Standard therapy for advanced or metastatic colorectal cancer consists of 5-fluorouracil plus leucovorin (5-FU/LV) administered intravenously (i.v.). Capecitabine (Xeloda), an oral fluoropyrimidine carbamate which is preferentially activated by thymidine phosphorylase in tumour cells, mimics continuous 5-FU and is a recently developed alternative to i.v. 5-FU/LV. The choice of oral rather than intravenous treatment may affect medical resource use because the two regimens do not require the same intensity of medical intervention for drug administration, and have different toxicity profiles. Here we examine medical resource use in the first-line treatment of colorectal cancer patients with capecitabine compared with those receiving the Mayo Clinic regimen of 5-FU/LV. In a prospective, randomised phase III clinical trial, 602 patients with advanced or metastatic colorectal cancer recruited from 59 centres worldwide were randomised to treatment with either capecitabine or the Mayo regimen of 5-FU/LV. In addition to clinical efficacy and safety endpoints, data were collected on hospital visits required for drug administration, hospital admissions, and drugs and unscheduled consultations with physicians required for the treatment of adverse events. Capecitabine treatment in comparison to 5-FU/LV in advanced colorectal carcinoma resulted in superior response rates (26.6% versus 17.9%, P=0.013) and improved safety including less stomatitis and myelosuppression. Capecitabine patients required substantially fewer hospital visits for drug administration than 5-FU/LV patients. Medical resource use analysis showed that patients treated with capecitabine spent fewer days in hospital for the management of treatment related adverse events than did patients treated with 5-FU/LV. In addition, capecitabine reduced the requirement for expensive drugs, in particular antimicrobials fluconazole and 5-HT3-antagonists to manage adverse events. As anticipated with an oral home-based therapy patients receiving capecitabine needed more frequent unscheduled home, day care, office and telephone consultations with physicians. In the light of clinical results from the phase III trial demonstrating increased efficacy in terms of response rate, equivalent time to progression (TTP) and survival (OS), and a superior safety profile, the results from this medical resource assessment indicate that capecitabine treatment of colorectal cancer patients results in a substantial resource use saving relative to the Mayo Clinic regimen of 5-FU/LV. This benefit is derived principally from the avoidance of hospital visits for i.v. drug administration, less expensive drug therapy for the treatment of toxic side-effects, and fewer treatment-related hospitalisations required during the course of therapy for adverse drug reactions in comparison to patients treated with 5-FU/LV.

Fluorouracil and the new oral fluorinated pyrimidines

OBJECTIVE

To briefly review the biotransformation and bioavailability of fluorouracil (5-FU); discuss the effects of dihydropyrimidine dehydrogenase (DpD) on the efficacy and toxicity profiles of 5-FU; and review a new class of drugs known collectively as the oral fluorinated pyrimidines, which inhibit or circumvent DpD activity and, when administered with 5-FU, alter its pharmacokinetic and pharmacodynamic properties.

DATA SOURCES

A MEDLINE literature search was conducted (1966-March 1999) using the search terms fluoropyrimidines, fluorouracil, 5-FU, fluorinated pyrimidines, capecitabine, eniluracil, uracil-tegafur, uracil-ftorafur, UFT, S1, BMS-247616, and BOF-A2. Reference lists, bibliographies of pertinent articles, and abstracts from the American Society of Clinical Oncology and the San Antonio Breast Cancer Symposium annual meetings were also identified and reviewed. Both preclinical and clinical literature were reviewed and analyzed.

DATA SYNTHESIS

The new oral fluorinated pyrimidines appear to produce antitumor activity equivalent or superior to that of intravenously administered 5-FU by achieving higher intratumoral 5-FU concentrations or sustained 5-FU exposure. These agents are generally associated with manageable and non-life-threatening toxicities. The oral route of administration facilitates ease of administration and may reduce total healthcare costs associated with 5-FU-sensitive tumors. More studies are needed to assess the therapeutic and economic benefits of the oral fluorinated pyrimidines.

CONCLUSIONS

The bioavailability, efficacy, and toxicity of 5-FU depend on its catabolic rate-limiting enzyme, The new oral fluorinated pyrimidines inhibit or circumvent DpD activity and, when combined with 5-FU, increase 5-FU's bioavailability and cytotoxic effects and decrease its toxicities. Results of Phase I and II studies in patients with a variety of malignancies suggest positive outcomes, including greater efficacy, less drug-related toxicity, lower costs related to drug administration, and greater patient convenience.

A prospective randomized trial comparing intravenous 5-fluorouracil and oral doxifluridine as postoperative adjuvant treatment for advanced rectal cancer

BACKGROUND

Postoperative adjuvant chemoradiation treatment after curative resection for rectal cancer was needed to reduce recurrence and improve a survival rate. Intravenous 5-fluorouracil (5-FU) and leucovorin has been a mainstay of chemotherapy, but oral 5-FU derivatives have been shown a comparable antitumor activity. Intravenous 5-FU and oral doxifluridine were compared with respect to therapeutic efficacy, drug toxicity, and quality of life.

METHODS

A total of 166 patients were randomized to receive intravenous 5-FU (450 mg/m2/day) or oral doxifluridine (900 mg/m2/day) in combination with leucovorin (20 mg/m2/day) for depth of invasion, nodal status, metastasis (TNM) stage II and III patients between October 1997 and February 1999. Consecutive daily intravenous infusion for 5 days per every month for a total of 12 cycles (IV arm, n = 74) and oral doxifluridine daily for 3 weeks and 1 week rest for a total of 12 cycles (oral arm, n = 92). Drug toxicity and quality of life were observed. Quality of life was scored according to 22 daily activity items (good, > or =71; fair, < 70; poor, < 52).

RESULTS

There was no difference of sex between two groups (IV arm: male/female = 45/29, oral arm: male/female = 59/33). The mean age was 52.3 vs. 59.5, respectively. There was also no difference of TNM stage distribution and type of operation between groups (P>.05). Mean numbers of chemotherapy cycles were 6.5+/-3.7 (IV arm) vs. 7.2+/-4.3 (oral arm), respectively. The rate of recurrence was 9/74 (12.1%) in the IV arm and 6/92 (6.5 %) in the oral arm, respectively (P = .937). Local recurrence was 2/74 (stage III; 2.7%) in the IV arm and 1/92 (stage II; 1.1%) in the oral arm, respectively. Systemic recurrence was 7/74 (stage III; 9.4%) in the IV arm and 5/92 (stage III; 5.4%) in the oral arm, respectively. The most common site of systemic recurrence was the liver. Toxicity profile was as follows: leukopenia (30/74 vs. 17/92) and alopecia (21/74 vs. 13/92) were statistically more common in the IV arm. Diarrhea was more common in the oral arm. Poor quality of life score between two groups was observed at 1 month (23.9% vs. 13%) and 2 months (15.8% vs. 3.7%) after chemotherapy. Good quality of life score was observed at 1 month (19.5% vs. 49%) and 2 months (47% vs. 72%), respectively (P<.05).

CONCLUSIONS

Oral doxifluridine with leucovorin shows a comparable therapeutic efficacy to intravenous 5-FU regimen with high quality of life as postoperative adjuvant therapy. The oral regimen also can be safely given with appropriate toxicity and tolerability.

Eniluracil: an irreversible inhibitor of dihydropyrimidine dehydrogenase

One of the most widely used drugs in cancer chemotherapy is 5-fluorouracil (5-FU). 5-FU is optimally delivered via continuous iv. infusion, which is both cumbersome and expensive. Prolonged oral dosing of 5-FU could mimic continuous infusion with less inconvenience and cost. However, oral administration of 5-FU has been hampered by incomplete and erratic bioavailability due to substantial variability in the activity of dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme in 5-FU catabolism. Eniluracil (ethynyluracil, GlaxoWellcome, USA), a uracil analogue, which irreversibly inhibits DPD, increases the oral bioavailability of 5-FU to 100%, facilitating uniform absorption and predictable toxicity. Cytotoxicity is enhanced one- to five-fold in cell lines treated with eniluracil plus 5-FU compared with 5-FU alone. Though eniluracil is neither toxic nor active as a single agent in animals, it improves the antitumour efficacy and therapeutic index of 5-FU. In Phase I trials, eniluracil markedly reduced the maximum tolerated dose of oral 5-FU, increased the half-life 20-fold and decreased the clearance 22-fold. DPD is completely inactivated within 1 h of eniluracil administration. Two dosing schedules have been evaluated in combination with oral 5-FU: a 5-day schedule every 28 days and a 28-day schedule every 35 days. The dose-limiting toxicity on the first schedule is myelosuppression with diarrhoea being dose-limiting on the 28-day schedule. Phase II trials employing the 28-day schedule have been completed in cancers of the colon, breast, liver and pancreas. Phase III trials in colorectal and pancreatic carcinoma have been completed and await analysis. Eniluracil is a promising drug, which permits reliable and safe administration of oral 5-FU and has the potential to overcome 5-FU resistance mediated by overexpression of DPD.