Preliminary studies of a novel oral fluoropyrimidine carbamate: capecitabine

Capecitabine in the management of colorectal cancer

Significant progress has been made in the chemotherapy of colorectal cancer. The author discusses new available options and the development of a new oral fluoropyrimidine, capecitabine (Xeloda). The rational development of this targeted drug with its selective activation in tumor tissue is highlighted. The clinical development of capecitabine and its present and future role in the management of colorectal cancer are reviewed.

Multicenter, Phase II study of capecitabine in taxane-pretreated metastatic breast carcinoma patients

BACKGROUND

Capecitabine is an oral, tumor-targeted fluoropyrimidine carbamate with high activity in metastatic breast carcinoma and in paclitaxel-pretreated metastatic breast carcinoma.

METHODS

The current multicenter, Phase II trial assessed the efficacy and safety of intermittent oral capecitabine, 1255 mg/m(2) twice daily (2 weeks of treatment followed by a 1-week rest period), in patients with metastatic breast carcinoma in whom prior taxane therapy had failed. All patients had failed treatment or had disease that was refractory to two or three previous chemotherapy regimens, one of which contained a taxane. Nearly all patients (96%) also had received prior anthracycline chemotherapy. Seventy-five patients were recruited at 5 centers, 74 of whom received treatment.

RESULTS

The overall response rate was 26%, with response rates of 27% and 20%, respectively, in the subgroups of patients previously pretreated with paclitaxel (n = 47) or docetaxel (n = 27). The median survival was 12.2 months, the median duration of response was 8.3 months, and the median time to disease progression was 3.2 months. The most common treatment-related adverse events (all grades) were hand-foot syndrome (62%), diarrhea (58%), nausea (55%), emesis (37%), and stomatitis (34%). However, the majority were mild to moderate in intensity and only three patients experienced Grade 4 (according to the National Cancer Institute of Canada Common Toxicity criteria) adverse events. The only Grade 3 treatment-related adverse events reported in > or = 10% of the patients were hand-foot syndrome (22%), diarrhea (16%), and stomatitis (12%). Myelosuppression and alopecia were rare, and there were no reported treatment-related deaths.

CONCLUSIONS

The results of the current study demonstrate that capecitabine is an effective and well tolerated treatment in patients with taxane-refractory or taxane-failing metastatic breast carcinoma. In addition, it is a convenient, orally administered drug, which makes it an attractive agent for use in outpatient treatment.

Recent advances in the use of radiosensitizing nucleosides

Chemotherapeutic drugs that perturb nucleotide metabolism have the potential to produce substantial sensitization of tumor cells to radiation treatment. The clinical effectiveness of fluoropyrimidines as radiosensitizers has been proven in multiple randomized trials. The development of oral fluoropyrimidine formulations may allow protracted exposure without the need for indwelling intravenous lines and infusion pumps. These agents may also provide more selective radiosensitization and are likely to be widely incorporated into chemoradiotherapy regimens for patients with gastrointestinal malignancies. Gemcitabine has been well studied in the laboratory, with respect to mechanisms of radiosensitization and strategies that may increase the therapeutic index. Clinical trials based on these studies are now defining the role of this radiosensitizing nucleoside. Issues regarding the use oral fluoropyrimidines and gemcitabine need to be viewed in the context of both local and distant disease control, given the potential systemic activity of these agents.

Impact of thymidine phosphorylase surexpression on fluoropyrimidine activity and on tumour angiogenesis

Tumoral thymidine phosphorylase (TP) appears to play a dual role by being involved in neoangiogenesis and by activating 5FU prodrugs at the tumoral target site. The aim of the study was to investigate more thoroughly these potential physiological and pharmacological roles of TP. A rat carcinoma cell line (PROb) was transfected with TP/PD-ECGF in order to study the effect of the overexpression of this enzyme (1) on the sensitivity of cells to 5'DFUR and 5FU in vitro and (2) on tumour growth in vivo by using a syngenic tumour model in the BDIX rat (hepatic tumours, sub-cutaneous tumours). Cytotoxic effects of 5'DFUR, and to a lesser extent those of 5FU, were enhanced in TP clones as compared to control cells: there was a highly significant correlation between TP activity and in vitro sensitivity to 5'DFUR (r2= 0.91, P = 0.0002, n = 8) and, to a lesser extent, to 5FU (r2= 0.49, P = 0.053, n = 8). The impact of TP transfection on tumour growth was relatively modest and concerned only the initial stages of tumour expansion. Staining of TP tumours for endothelial (factor VIII) cells was always higher than controls. The staining ratio (TP/controls) tended to be reduced as tumours increased in size. The stability of TP expression was checked both in vitro (TP activity measurement) and in vivo (RT-PCR determinations) and there was no loss of TP expression over time which could be advanced to explain the progressive weakening of the impact of TP overexpression on both tumour growth and neoangiogenesis.

Oral fluoropyrimidine treatment of colorectal cancer

5-Fluorouracil (5-FU) has been utilized as part of standard chemotherapy for treatment of early-stage and metastatic colorectal cancer for more than 4 decades. The oral fluoropyrimidines have been studied extensively as an alternative to intravenous 5-FU. The goal of such an approach is to simplify drug administration and to improve the toxicity profile while maintaining efficacy that is at least equivalent to intravenous therapy. The goal of this article is to review the features of the main oral 5-FU prodrugs, which include capecitabine, uracil and tegafur (UFT)/leucovorin, S-1, and BOF-A2 and to describe their potential efficacy in treating colorectal cancer.

A physiologically based pharmacokinetic analysis of capecitabine, a triple prodrug of 5-FU, in humans: the mechanism for tumor-selective accumulation of 5-FU

PURPOSE

To identify the factors governing the dose-limiting toxicity in the gastrointestine (GI) and the antitumor activity after oral administration of capecitabine, a triple prodrug of 5-FU, in humans.

METHOD

The enzyme kinetic parameters for each of the four enzymes involved in the activation of capecitabine to 5-FU and its elimination were measured experimentally in vitro to construct a physiologically based pharmacokinetic model. Sensitivity analysis for each parameter was performed to identify the parameters affecting tissue 5-FU concentrations.

RESULTS

The sensitivity analysis demonstrated that (i) the dihydropyrimidine dehydrogenase (DPD) activity in the liver largely determines the 5-FU AUC in the systemic circulation, (ii) the exposure of tumor tissue to 5-FU depends mainly on the activity of both thymidine phosphorylase (dThdPase) and DPD in the tumor tissues, as well as the blood flow rate in tumor tissues with saturation of DPD activity resulting in 5-FU accumulation, and (iii) the metabolic enzyme activity in the GI and the DPD activity in liver are the major determinants influencing exposure to 5-FU in the GI. The therapeutic index of capecitabine was found to be at least 17 times greater than that of other 5-FU-related anticancer agents, including doxifluridine, the prodrug of 5-FU, and 5-FU over their respective clinical dose ranges.

CONCLUSIONS

It was revealed that the most important factors that determine the selective production of 5-FU in tumor tissue after capecitabine administration are tumor-specific activation by dThdPase, the nonlinear elimination of 5-FU by DPD in tumor tissue, and the blood flow rate in tumors.

The oral fluorinated pyrimidines

The fluorinated pyrimidines have played a major role in the treatment of many common tumors since 5-fluorouracil (5FU) was first introduced. Studies of the cellular and clinical pharmacology of 5FU have led to an improved understanding of the mechanisms of action of this agent. This knowledge has allowed the optimal and rational development of fluoropyrimidine therapy, with significant therapeutic advances in recent years. Efforts to improve the therapeutic index of 5FU have included alteration of schedule, and the addition of biochemical modulators such as folinic acid. Although protracted continuous infusion of 5FU has led to better response rates and decreased toxicity, the administration of 5FU by protracted infusion is not only costly, but also inconvenient to the patient. Furthermore it is often associated with infectious and thrombotic complications related to the required indwelling intravenous catheter. Protracted oral administration is a rational route for administering 5FU, being preferred by the patient and the pharmaco-economist. The unpredictable and low oral bioavailability of 5FU initially discouraged this form of treatment. This problem has now been overcome by the new generation of oral fluoropyrimidines. Two main strategies have been pursued: 1) The administration of an inactive prodrug of 5FU, which is absorbed intact, and subsequently converted to 5FU. Capecitabine is converted to 5FU by a 3 step enzymatic process. 2) The administration of 5FU with an inhibitor of dihydropyrimidine dehydrogenase (DPD) to minimise the erratic absorption and variable clearance of 5FU: the preparations UFT, S1, and ethinyluracil/5FU contain an oral fluoropyrimidine co-administered orally with inhibitors of this enzyme. The development and characteristics of these agents are discussed.

Novel chemotherapy agents for colorectal cancer: oral fluoropyrimidines, oxaliplatin, and raltitrexed

Agents now under investigation for treatment of advanced colorectal cancer (CRC) include the oral fluoropyrimidines, oxaliplatin, and raltitrexed. Research efforts directed at finding agents that conveniently and effectively deliver 5-fluorouracil (5-FU) in a protracted fashion have led to the development of several oral fluoropyrimidines. These agents, which include capecitabine; tegafur and uracil plus leucovorin (UFT/LV); eniluracil plus oral 5-FU; and S-1, are convenient and less toxic than intravenous bolus 5-FU. Oxaliplatin has a uniquely different mechanism of action compared with that of 5-FU and has demonstrated activity not only in the first-line treatment setting but also in patients whose disease has progressed during or following 5-FU treatment. In the first-line setting, when oxaliplatin is combined with 5-FU plus LV, response rates and time to disease progression are remarkably improved compared with 5-FU/LV alone. Raltitrexed, a unique thymidylate synthase inhibitor, has undergone extensive phase III evaluation in CRC. The advent of these novel agents has led to development of combined chemotherapy regimens now being introduced into the adjuvant setting.

Phase I and pharmacologic study of i.v. hydroxyurea infusion given with i.p. 5-fluoro-2'-deoxyuridine and leucovorin

Preclinical data suggests that the action of fluoropyrimidines may be enhanced by the addition of hydroxyurea. We developed a phase I trial to determine the maximum tolerated dose and pharmacokinetics of i.v. hydroxyurea (HU) in combination with i.p. 5-fluoro-2'-deoxyuridine (FUdR) and leucovorin (LV). Eligible patients had metastatic carcinoma confined mostly to the peritoneal cavity, and adequate hepatic, renal and bone marrow function. Patients were treated with a fixed dose of FUdR (3 g) and LV (640 mg) administered on days 1--3. HU was administered as a 72-h infusion starting simultaneously with i.p. therapy on day 1. The following dose levels were studied: 2.0, 2.5, 3.0 and 3.6 g/m(2)/day. Pharmacokinetics were studied in blood and peritoneal fluid. Twenty-eight patients were accrued. Steady-state plasma and peritoneal fluid HU levels increased with increasing dose, and steady state was achieved within 12 h of continuous dosing. The steady-state HU plasma:peritoneal fluid concentration ratio ranged from 1.06 x 10(3) to 1.25 x 10(3) and the plasma HU clearance ranged from 4.63 to 5.81 l/h/m(2). Peritoneal fluid AUC = 137,639 +/- 43,914 microg/ml x min, t(1/2) = 100.9 +/- 56.4 min and Cl = 25.29 +/- 10.88 ml/min. Neutropenia represented the dose-limiting toxicity. We conclude that i.p. FUdR and LV in combination with i.v. HU is well tolerated. The addition of systemic HU increased the incidence of myelosuppression.

Oral fluoropyrimidines among the new drugs for patients with metastatic breast cancer

Although drugs such as the taxoids and vinorelbine have increased the options available for anthracycline-resistant metastatic breast cancer, new therapeutic options are needed, particularly for taxoid-refractory tumours. Increasing emphasis is being placed on the development of oral agents, which many patients prefer provided efficacy is not compromised, particularly if the oral agents are less toxic than current intravenous agents. Capecitabine, a new, oral fluoropyrimidine, mimics continuous infusion 5-FU and is activated preferentially at the tumour site. Phase II studies of capecitabine have demonstrated encouraging response rates in patients with few further treatment options (20% response with an additional 43% achieving stable disease in paclitaxel-refractory patients; 36% response with a further 23% achieving stable disease in anthracycline-refractory patients). In addition, a randomized, phase II trial demonstrated a response rate of 30% (95% Cl: 19-43%) with capecitabine as first-line treatment for metastatic breast cancer, compared with 16% (95% Cl: 5-33%) in patients receiving low-dose CMF. These trials also showed that capecitabine has a favourable safety profile typical of infused fluoropyrimidines. Both alopecia and myelosuppression were rare. Capecitabine may therefore provide an effective, well-tolerated and convenient alternative to intravenous cytotoxic agents, not only in taxoid-resistant patients, but also in anthracycline-resistant metastatic breast cancer or as first-line therapy. Furthermore, the low incidence of myelosuppression makes capecitabine an attractive agent for incorporation into combination regimens with agents such as epirubicin/doxorubicin, the taxoids and vinorelbine.

A phase I and pharmacologic study of capecitabine and paclitaxel in breast cancer patients

BACKGROUND

Based on preclinical studies demonstrating that treatment with paclitaxel upregulates intratumoral thymidine phosphorylase (dTHdPase), which catalyzes the final step in the conversion of the oral fluoropyrimidine capecitabine to 5-fluorouracil (5-FU), as well as the overlapping spectra of activity for these agents, particularly in metastatic breast cancer, this phase I study evaluated the feasibility of administering capecitabine on an intermittent schedule in combination with paclitaxel in previously-treated patients with locally advanced or metastatic breast cancer. The study also sought to recommend doses for subsequent disease-specific studies, identify clinically significant pharmacokinetic interactions, and detect preliminary antitumor activity.

PATIENTS AND METHODS

Nineteen previously treated women with metastatic breast cancer whose prior treatment included neither paclitaxel or capecitabine received one hundred one courses of capecitabine and paclitaxel. Paclitaxel was administered as a three-hour intravenous (i.v.) infusion at a fixed dose of 175 mg/m2 and capecitabine was administered as 2 divided daily doses for 14 days followed by a seven-day rest period every 3 weeks. The dose of capecitabine was increased from a starting dose of 1650 mg/m2/d. The plasma sampling scheme in the first course permitted characterization of the pharmacokinetics of each agent given alone and concurrently to detect major pharmacokinetic interactions.

RESULTS

Palmar plantar erythrodysesthesia (hand foot syndrome) and neutropenia were the principal dose-limiting toxicities (DLT). Other toxicities included diarrhea and transient hyperbilirubinemia. Three of eight new patients treated with capecitabine 2000 mg/m2/d and paclitaxel 175 mg/m2 experienced DLT in the first course, whereas none of eleven new patients treated with capecitabine 1650 mg/m2/d and paclitaxel 175 mg/m2 developed DLT. Pharmacokinetic studies indicated that capecitabine did not grossly affect the pharmacokinetics of paclitaxel, and there were no major effects of paclitaxel on the pharmacokinetics of capecitabine and capecitabine metabolites. However, AUC values for the major 5-FU catabolite, fluorobeta-alanine (FBAL), were significantly lower in the presence of paclitaxel. Two complete and seven partial responses (56% response rate) were observed in sixteen patients with measurable disease; four of six patients whose disease was previously treated with high-dose chemotherapy and hematopoietic stem-cell support had major responses. Seven of nineteen patients had stable disease as their best response.

CONCLUSIONS

Recommended combination doses of capecitabine on an intermittent schedule and paclitaxel are capecitabine 1650 mg/m2/d orally for 14 days and paclitaxel 175 mg/m2 i.v. every 3 weeks. The favorable preclinical interactions between capecitabine and paclitaxel, as well as the acceptable toxicity profile and antitumor activity in patients with metastatic breast cancer, support further clinical evaluations to determine an optimal role for the combination of capecitabine and paclitaxel in breast cancer and other relevant malignancies.

Integrating the oral fluoropyrimidines into the management of advanced colorectal cancer

In colorectal cancer, leucovorin-modulated 5-fluorouracil (5-FU) has been the mainstay of both adjuvant treatment and treatment of metastatic disease for many years. In advanced disease, response rates of 10-43% are reported; efforts to improve efficacy through schedule modification, including prolonged infusions, have led to limited success. New agents with improved efficacy, tolerability and ease of administration are required. Among the newer drugs, irinotecan and oxaliplatin are becoming established as first- and second-line treatment for advanced disease. Their novel mechanisms of action have proven to be of value in 5-FU-resistant patients. In tandem with these developments, thymidylate synthase inhibition has remained an important objective and oral fluoropyrimidines such as capecitabine and UFT (uracil plus tegafur)/leucovorin have been developed with this goal in mind. Two large, phase III studies of capecitabine in metastatic disease demonstrated objective response rates of 26.6 and 24.8%. UFT/leucovorin has also been evaluated in phase III trials, with an 11.7% response rate reported. Both agents are being evaluated in combination with oxaliplatin and irinotecan, and ultimately oral fluoropyrimidines as monotherapy or combination therapy may replace intravenous (i.v.) 5-FU as first-line treatment for metastatic colorectal cancer.

The role of capecitabine, an oral, enzymatically activated fluoropyrimidine, in the treatment of metastatic breast cancer

Capecitabine is an oral fluoropyrimidine that mimics continuous infusion 5-fluorouracil and generates 5-fluorouracil preferentially at the tumor site. It is activated via a three-step enzymatic pathway, the final step of which requires thymidine phosphorylase, an enzyme that is significantly more active in tumor than normal tissue. As an oral agent, capecitabine is more convenient for patients and medical personnel, and avoids the complications associated with venous access. This paper reviews the development and clinical experience of capecitabine in breast cancer treatment. Clinical trials have established the efficacy and tolerability of capecitabine in anthracycline- and taxane-pretreated metastatic breast cancer, showing that capecitabine is an effective therapy for patients who have exhausted all established treatment options. Moreover, randomized, phase II studies have demonstrated that capecitabine is effective in anthracycline-pretreated patients and as first-line therapy for metastatic breast cancer. In addition to its confirmed efficacy, the favorable safety profile of capecitabine, particularly the low myelosuppression rate, makes it an attractive agent for incorporation into combination regimens. Therefore numerous trials have assessed the feasibility of capecitabine-containing regimens, and have shown promising results. Capecitabine is an important new treatment option for breast cancer patients, and ongoing clinical trials should further define its role in a range of settings.

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.

5-fluorouracil/leucovorin versus capecitabine in patients with stage III colon cancer

Capecitabine is an orally administered fluoropyrimidine carbamate that is preferentially converted to 5-fluorouracil in tumors relative to normal tissue. Three different dosing regimens were investigated in phase I studies: continuous monotherapy, intermittent monotherapy, and intermittent therapy supplemented with leucovorin. These studies defined the maximum tolerated dose for each regimen. Dose-limiting toxicities were diarrhea, hand-foot syndrome, and leukopenia. Each phase I study recommended a dose; these were directly compared in a phase II study. This phase II study showed that the intermittent regimen of capecitabine monotherapy was the most favorable on the basis of tumor response rates, time to progression, dose intensity, and toxicities. The intermittent regimen of capecitabine has been compared with the Mayo Clinic regimen of 5-fluorouracil/leucovorin in two large, phase III studies of patients with advanced colorectal cancer. The combined data from the two studies showed that capecitabine was superior to 5-fluorouracil/leucovorin in terms of tumor response rate (22% v 13%; P < .0001) and similar in terms of time to disease progression and overall survival. Capecitabine is now being compared with the Mayo Clinic regimen as an adjuvant treatment for patients with Dukes' C colon cancer.

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.

New horizons in treating metastatic disease

The management of metastatic breast cancer is changing as a consequence of extraordinary discoveries in cancer research and the development of more advanced diagnostic technologies. Although traditional chemotherapeutics such as anthracyclines and taxanes still represent the mainstay of treatment for this disease, new drugs are demonstrating significant clinical activity and sometimes a better toxicity profile. Furthermore, the successful introduction into clinical practice of biological agents, in particular the monoclonal antibody trastuzumab, offers a key to the future of managing metastatic breast cancer. A therapeutic approach based on modifications of a specific molecular target (e.g., gene therapy, vaccines, and antiangiogenesis) alone or combined with the traditional chemotherapeutic drugs is expected to be used more commonly and will, we hope, bring significant improvement in the clinical response and quality of care of our patients.

Capecitabine in breast cancer: current status

Anthracyclines, together with taxanes, are at present the most active agents in metastatic breast cancer, while single-agent, bolus 5-fluorouracil (5-FU) is not very active in this setting. In view of encouraging results and tolerable toxicity of continuous infusion of 5-FU in gastrointestinal cancer, innovative oral 5-FU agents such as capecitabine have been developed. Capecitabine is a prodrug that is converted into the active compound 5-FU preferentially at the tumor site. An intermittent dosing schedule of capecitabine twice daily at a dose of 2510 mg/m2/day on days 1-14 in a 3-week cycle appeared to be feasible and resulted in a high dose intensity. A large phase II study investigating capecitabine in 135 advanced breast cancer patients, pretreated with anthracyclines and taxanes, observed three complete and 24 partial responses (response rate, 20%), with a mean duration of 8.0 months. Preliminary results of a study comparing capecitabine with paclitaxel in 42 breast cancer patients failing anthracyclines indicate that the efficacy of capecitabine is comparable to that of paclitaxel, with response rates of 36% and 21%, respectively. Another study reported a response rate of 25% for capecitabine as first-line therapy for advanced breast cancer in women aged > or = 55 years, which tended to be better than combination chemotherapy with cyclophosphamide/methotrexate/5-FU. In all studies, capecitabine side effects were mainly mild, and treatment-related grade 3/4 toxicity consisted of diarrhea (8%-11%), nausea (4%-11%), hand-foot syndrome (10%-18%), neutropenia (3%-20%), and bilirubin elevation (6%). Capecitabine is clearly an active agent for the treatment of breast cancer. It is currently registered in various countries for use in third-line treatment of metastatic disease. Its further role will have to be defined from data of randomized phase III studies.

Capecitabine

Drug development has undergone rapid shifts in methodology and the use of rationally derived agents which either target specific tissues or molecules such as receptors or enzymatic sites. Capecitabine is a rationally derived prodrug of 5-fluorouracil which is based upon the known high concentration of the enzyme thymidine phosphorylase in many human tumors. The first prodrug designed to exploit this biochemical finding was 5-DFUR which allowed cytotoxic 5-fluorouracil to be preferentially concentrated in tumors. Unfortunately, in man this agent was associated with significant gastrointestinal toxicity. Further manipulation of this molecular resulted in capecitabine which is a relatively inert prodrug, undergoes three enzymatic steps, and offers the potential of less gastrointestinal toxicity. Phase I trials have examined several schedules with the divided oral daily x 14 schedule every 3 weeks as the preferred phase II and phase III dosing method. This agent demonstrates significant antitumor effect in diseases known to be responsive to fluoropyrimidines. Further study is needed to determine whether capecitabine has a broader spectrum of action thus affecting other tumor types than 5-fluorouracil. Major dose limiting toxicities have been hand foot syndrome, nausea/vomiting, and diarrhea.

Capecitabine in the treatment of metastatic renal cell carcinoma

To evaluate the therapeutic effects and systemic toxicities of a capecitabine-based home therapy regimen in patients with metastatic renal cell carcinoma, 30 patients were enrolled in a phase II clinical trial. Treatment consisted of oral capecitabine combined with subcutaneous recombinant human interferon-alpha 2a, recombinant human interleukin-2 and oral 13-cis-retinoic acid. There were two (7%) complete responses (CRs) and eight (27%) partial remissions (PRs), for an overall objective response rate of 34% (95% CI 17-53%). Except one, all responses are ongoing, with a median duration of 9+ and 8+ months for CRs and PRs, respectively. Additionally, 12 patients (40%) reached stable disease. Eight patients (27%) showed continued disease progression despite treatment. Therapy was well tolerated and was given in the outpatient setting. Capecitabine-related World Health Organization (WHO) grade 2 and 3 toxicities were observed in five and two patients respectively, and were limited to fatigue, nausea/vomiting, diarrhoea, stomatitis, dermatitis and hand-and-foot syndrome. The substitution of capecitabine for 5-FU in the pre-existing biochemotherapy regimen did not result in a reduced therapeutic efficacy and showed significant anti-tumour activity in patients with advanced renal cell carcinoma.

Systemic chemotherapy of liver tumors

Primary and secondary liver tumors have a reputation for being resistant to chemotherapy and, in the absence of surgical resection, rapidly fatal. Until recently, such a reputation was well justified: response rates above 20% were not seen, and complete responses were distinctly rare. Over the past 5 years, the mood of those in the field has become rather more optimistic and a pattern of effective therapy is emerging. This involves combination therapy in patients with unresectable disease to increase the operative rates, and postoperative adjuvant therapy to decrease the high relapse rate which is so characteristic of both primary and secondary liver tumors. In the case of hepatocellular carcinoma, the combination therapy involves cytotoxic drugs and interferon. With secondary colorectal cancer (CRC), the combination of 5-fluorouracil (FU) and leucovorin, together with one of the new cytotoxic agents such as oxaliplatin or irenotecan, is producing much higher response rates and prolonged survival, and permitting a higher resection rate. Postoperative treatment is also showing promise in decreasing the relapse rate. With CRC metastatic to the liver, this involves hepatic artery infusion (HAI), systemic 5-FU, and leucovorin. Adjuvant systemic therapy of HCC has not yet been widely tested, but success with locoregional lipiodol iodine131 is proof of principle. The coming decade should see a significant improvement in the outlook of patients with malignant liver tumors as multimodality treatment becomes more widely investigated and practiced.

Capecitabine, a new oral fluoropyrimidine for the treatment of colorectal cancer

Capecitabine (Xeloda)(R) was developed as a tumour-selective fluoropyrimidine carbamate to achieve higher intratumoural 5-FU level and lower toxicity than 5-FU. Capecitabine passes unchanged through the gastrointestinal tract and is metabolised in the liver to 5'-deoxy-5-fluorocytidine (5'-DFCR). Here it is converted to doxifluridine (5'-DFUR) and finally, 5'-DFUR is metabolised by thymidine phosphorilase to 5-FU at the tumour site. Preclinical studies have demonstrated capecitabine's activity in both 5-FU-sensitive and 5-FU-resistant tumours. In a randomised phase II trial in advanced colorectal cancer the recommended dose and schedule of Capecitabine is 2.510 mg/m(2)/day (total dose divided into two equal morning and evening doses) given in an intermittent schedule (2 weeks on/1 week off). Phase III trials in patients with advanced colorectal cancer show a better response rate than the Mayo Clinic schedule, with no differences in terms of DR, PFS. Diarrhoea and hand-foot syndrome were the principal grade 3/4 toxicities noted, occurring in 10% and 16% of patients, respectively. The selectivity of this drug opens an important prospective in the treatment of colorectal cancer in advanced and adjuvant setting.

The oral route for the administration of cytotoxic drugs: strategies to increase the efficiency and consistency of drug delivery

There is an increasing interest to administer cytotoxic drugs to patients by the oral route. Quality of life issues, treatment advantages and pharmaco-economics are major arguments in favor of oral therapy. However, low or moderate bioavailability in combination with considerable interpatient variability are frequently observed which may reduce the feasibility of the oral route for this class of drugs with a generally narrow therapeutic window. Until recently, investigators focused on absorption enhancers which slightly damage the intestinal surface such as salicylates, methylxanthines and surfactants to improve the oral bioavailability of drugs. To date, a shift can be seen towards more subtle mechanisms to enhance the absorption. This review article focuses on two important mechanisms that determine the oral bioavailability of cytotoxic drugs. These include the presence of drug transporters in the intestinal epithelium pumping drugs into the intestinal lumen, such as MDR1 type P-glycoproteins, and first-pass elimination by cytochrome P450 isoenzymes (e.g. 3A4 and 3A5) or other enzymes in the intestines and/or liver. Currently preclinical and clinical studies are being performed to explore the feasibility of blocking these transporters/enzymes in order to achieve higher and less variable systemic drug levels after oral dosing. This review gives an update of the results of these studies. It is concluded however, that further research to unravel the processes involved in oral drug uptake is warranted to make the oral route a more efficient and consistent way of drug administration.

Phase I clinical and pharmacokinetic study of oral S-1 in patients with advanced solid tumors

PURPOSE

To investigate the side effects, determine the maximum-tolerated dose (MTD), and study the pharmacokinetics of S-1, an oral fluoropyrimidine-based antineoplastic agent consisting of the fluorouracil (5-FU) prodrug tegafur combined with two modulators, 5-chloro-2,4-dihydroxypyridine and potassium oxonate.

PATIENTS AND METHODS

Patients with advanced solid tumors received S-1 bid for 28 days, followed by 1 week of rest. 5-FU pharmacokinetics were investigated after a single initial dose of S-1 during the first 24 hours and weekly thereafter.

RESULTS

Twenty-eight patients received S-1 at the four consecutive dose levels of 25, 45, 35, and 40 mg/m(2). The MTD was initially found at 45 mg/m(2), with diarrhea as the dose-limiting toxicity (DLT). Diarrhea was also the DLT at the dose of 40 mg/m(2), which was the MTD for patients exposed to extensive prior chemotherapy. Other toxicities were generally mild. Two patients had a reduction of more than 50% in tumor dimension. Plasma pharmacokinetics of 5-FU were linear; at the highest S-1 dose level, 5-FU plasma peak concentrations reached 1 to 2 micromol/L, and the half-life of 5-FU was 3 to 4 hours. A statistically significant relationship was observed between the severity of diarrhea and pharmacokinetic parameters of 5-FU.

CONCLUSION

The recommended dose of S-1 in chemotherapy-naive or minimally chemotherapy-exposed patients is 40 mg/m(2) bid on 28 consecutive days, every 5 weeks. In heavily pretreated patients, the recommended dose is 35 mg/m(2) bid. Phase II trials are warranted in tumors known to be responsive to 5-FU treatment.

Five-day infusion fluorouracil plus vinorelbine in women with breast cancer previously treated with anthracyclines and paclitaxel

The continuous infusion of fluorouracil presents a superior pharmacological profile than its bolus administration, while vinorelbine is a new drug associated with good clinical activity in pretreated metastatic breast cancer. We investigated the combination of this two antitumor drugs with the aim to determine a tolerant and active second-line therapy in metastatic pretreated patients.

PATIENTS AND METHODS

Fifty six patients pretreated with chemotherapy received a median of six cycles [2-11] of fluorouracil, 700 mg/m2 for 5 day-continuous i.v. infusion and vinorelbine, 20 mg/m2 on days 1 and 6, every three weeks. The inclusion and evaluation criteria required measurable disease by conventional clinical and/or instrumental means.

FINDINGS

Iatrogenic toxicity in 340 administered cycles was mild: stomatitis = 11% (Grade 3 = 5%), constipation and abdominal pain = 12%, G2 neutropenia = 4%, G1 thrombocytopenia = 0.5%. In nine cases moderate infections occurred and six women experienced catheter related complications. Complete and partial remissions were observed in 12% and 36% of evaluable patients, respectively. In particular major tumor regression was documented in 28% of anthracyclines or taxol unresponsive cases.

CONCLUSIONS

This drug combination is active in metastatic pretreated breast cancer patients and devoid of serious iatrogenic toxicity. Although it deserves future optimization, for instance with the inclusion of oral fluoropirimidines, it represents a good choice for second-line or non cross-resistant regimens.

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.

A phase I and pharmacokinetic study of the combination of capecitabine and docetaxel in patients with advanced solid tumours

Capecitabine and docetaxel are both active against a variety of solid tumours, while their toxicity profiles only partly overlap. This phase I study was performed to determine the maximum tolerated dose (MTD) and side-effects of the combination, and to establish whether there is any pharmacokinetic interaction between the two compounds. Thirty-three patients were treated with capecitabine administered orally twice daily on days 1-14, and docetaxel given as a 1 h intravenous infusion on day 1. Treatment was repeated every 3 weeks. The dose of capecitabine ranged from 825 to 1250 mg m(-2) twice a day and of docetaxel from 75 to 100 mg m(-2). The dose-limiting toxicity (DLT) was asthenia grade 2-3 at a dose of 1000 mg m(-2) bid of capecitabine combined with docetaxel 100 mg m(-2). Neutropenia grade 3-4 was common (68% of courses), but complicated by fever in only 2.4% of courses. Other non-haematological toxicities were mild to moderate. There was no pharmacokinetic interaction between the two drugs. Tumour responses included two complete responses and three partial responses. Capecitabine 825 mg m(-2) twice a day plus docetaxel 100 mg m(-2) was tolerable, as was capecitabine 1250 mg m(-2) twice a day plus docetaxel 75 mg m(-2).

Vascular endothelial growth factor, platelet-derived endothelial cell growth factor and angiogenesis in non-small-cell lung cancer

High microvessel density, an indirect measure of angiogenesis, has been shown to correlate with increased tumour size, lymph node involvement and poor prognosis in non-small-cell lung cancer (NSCLC). Tumour cell vascular endothelial growth factor (VEGF) and platelet-derived endothelial cell growth factor (PD-ECGF) expression correlate with angiogenesis and a poor outcome in this disease. In a retrospective study VEGF and PD-ECGF expression and microvessel density were evaluated immunohistochemically in surgically resected specimens (T1-3, N0-2) from 223 patients with operable NSCLC using the VG1, P-GF.44C and JC70 monoclonal antibodies respectively. High VEGF immunoreactivity was seen in 104 (46.6%) and PD-ECGF in 72 (32.3%) cases and both were associated with high vascular grade tumours (P= 0.009 and P= 0.05 respectively). Linear regression analysis revealed a weak positive correlation between VEGF and PD-ECGF expression in cancer cells (r= 0.21; P = 0.002). Co-expression of VEGF and PD-ECGF was not associated with a higher microvessel density than VEGF or PD-ECGF only expressing tumours. Furthermore a proportion of high vascular grade tumours expressed neither growth factor. Univariate analysis revealed tumour size, nodal status, microvessel density and VEGF and PD-ECGF expression as significant prognostic factors. Tumour size (P < 0.02) and microvessel density (P < 0.04) remained significant on multivariate analysis. In conclusion, VEGF and PD-ECGF are important angiogenic growth factors and have prognostic significance in NSCLC. Furthermore the study underlines the prognostic significance of microvessel density in operable NSCLC.

Capecitabine, an oral fluoropyrimidine carbamate with substantial activity in advanced colorectal cancer: results of a randomized phase II study

PURPOSE

To evaluate in patients with advanced colorectal cancer (CRC) three treatment regimens of oral capecitabine in order to select the most appropriate regimen for testing in phase III.

PATIENTS AND METHODS

Three capecitabine schedules were evaluated in a randomized phase II design: arm A, 1,331 mg/m(2)/d bid continuously; arm B, 2,510 mg/m(2)/d bid intermittently (2 weeks on/1 week off); and arm C, 1,657 mg/m(2)/d plus oral leucovorin 60 mg/d bid intermittently (2 weeks on/1 week off).

RESULTS

One hundred nine patients were randomized; 39 patients were assessable for efficacy in arm A, 34 in arm B, and 35 in arm C. Patient characteristics were balanced in the arms. Confirmed tumor responses (partial response [PR] + complete response [CR]) were reported for eight patients with two CRs (21%; 95% confidence interval [CI], 9% to 36%) in arm A, eight patients with one CR (24%; 95% CI, 11% to 41%) in arm B, and eight patients with two CRs (23%; 95% CI, 10% to 40%) in arm C. Median times to progression (TTP) in arms A, B, and C were 127, 230, and 165 days, respectively. Overall, more toxicity was seen with capecitabine plus leucovorin, particularly diarrhea and hand-foot syndrome. There was no grade 3 or 4 marrow toxicity.

CONCLUSION

Capecitabine offers a new, effective treatment option as an oral single agent in advanced CRC. Promising overall response rates were reported for all three regimens. The addition of leucovorin to the intermittent regimen had no marked effect on tumor response or median TTP. The intermittent single-agent capecitabine schedule is proposed for phase III evaluation, based on considerations of toxicity, dose-intensity, response rate, and TTP.

Novel oral chemotherapy agents

The development of anticancer drugs has conventionally focused on intravenous rather than oral regimens. Recently, interest in oral administration of chemotherapy has been stimulated by the discovery of oral fluoropyrimidines, which appear to possess at least an equivalent efficacy and the potential to reduce toxicity compared with intravenous therapies. Using rational drug design, several oral fluoropyrimidines have been developed, including capecitabine, UFT (tegafur and uracil), eniluracil plus oral 5-fluorouracil (5-FU), and S-1. In addition to the oral fluoropyrimidines, other novel agents available for potential oral administration include irinotecan and temozolomide.

Novel agents for colorectal cancer

The compound 5-fluorouracil (5-FU) has been investigated for over four decades; research has focussed on examining various schedules and biochemical modulators in an attempt to improve its therapeutic activity in advanced colorectal cancer. Combination chemotherapy regimens have not been developed because of the lack of other active agents. Recently, several novel agents are under clinical development for advanced colorectal cancer, including irinotecan, oxaliplatin, oral fluoropyrimidines, raltitrexed, monoclonal antibody 17-1A and tumour vaccines. Both irinotecan and oxaliplatin have uniquely different mechanisms of action compared to 5-FU, and have demonstrated activity in patients whose disease has progressed with 5-FU treatment. Recent randomised trials comparing 5-FU plus leucovorin (5-FU/LV) to combinations of either irinotecan or oxaliplatin plus 5-FU/LV have demonstrated that the addition of these novel agents to 5-FU improve response rates (RRs) and time to progression (TTP). The role and acceptance of these combinations need to be defined, but are rapidly being introduced into the adjuvant therapy of colorectal cancer. Oral fluoropyrimidines (UFT plus leucovorin, capecitabine, eniluracil plus oral 5-FU, and S-1) provide the convenience of oral delivery with a marked reduction in febrile neutropenia and mucositis. To gain clinical acceptance, oral fluoropyrimidines must provide not only convenience and toxicity reduction, but also maintenance of survival advantages associated with optimal use of iv. 5-FU/LV regimens. These novel agents discussed herein provide treatment options which may allow for more individualised treatment strategies.

Oral fluoropyrimidines: a closer look at their toxicities

Patient preferences, quality of life issues, and economic considerations are driving the development of orally administered chemotherapy. Oral fluorinated pyrimidines, which have been used in Japan, are attracting increasing interest as a means to provide convenient, less toxic treatment without compromising efficacy. The oral fluoropyrimidines provide prolonged 5-fluorouracil (5-FU) exposure at lower peak concentrations than those observed with bolus intravenous administration. Moreover, depending on the dose schedule, the pharmacokinetics of the oral fluoropyrimidines may mimic the pharmacokinetics of continuous-infusion 5-FU. This review focuses on the toxicity profiles of five emerging oral fluoropyrimidine antineoplastic drugs: combined uracil and tegafur (UFT), capecitabine, eniluracil, S-1, and emitefur (BOF-A2). Different patterns of toxicities emerge from an analysis of the clinical trials of these agents relative to 5-FU administered as an intermittent intravenous bolus or as continuous infusion. The results of ongoing phase III trials comparing the oral fluoropyrimidines with conventional regimens of 5-FU plus leucovorin and 5-FU by continuous intravenous infusion are necessary before their therapeutic role in the management of colorectal carcinoma can be defined.

Induction of thymidine phosphorylase expression and enhancement of efficacy of capecitabine or 5'-deoxy-5-fluorouridine by cyclophosphamide in mammary tumor models

Thymidine phosphorylase (dThdPase) is an essential enzyme for the activation of the oral cytostatic drugs capecitabine (N(4)-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine, Xeloda(trade mark)) and its intermediate metabolite doxifluridine [5'-deoxy-5-fluorouridine (5'-dFUrd, Furtulon((R)))] to 5-fluorouracil (5-FUra) in tumors. In a previous study, we found that several cytostatics were able to up-regulate tumor levels of dThdPase in a human colon cancer xenograft model. In the present study, we confirmed that the administration of cytostatics used for breast cancer treatment, such as taxanes and cyclophosphamide (CPA), up-regulated the tumor level of dThdPase in mammary tumor models as well. Because the dThdPase up-regulation was observed even when CPA was given orally, we investigated further the usefulness of combination therapy with the 2 oral drugs, 5'-dFUrd/capecitabine and CPA in mammary tumor models. Daily oral administration of CPA up-regulated human dThdPase levels in the tumor tissue of mice bearing a human mammary tumor xenograft, MX-1, whereas in the small intestine and liver, it did not affect levels of pyrimidine nucleoside phosphorylases (PyNPase) including dThdPase and uridine phosphorylase. The preferential up-regulation of PyNPase activity in the tumor by CPA administration was also confirmed in mice bearing a syngeneic murine mammary adenocarcinoma, A755. In both models, combination therapy of 5'-dFUrd/capecitabine with CPA showed synergistic antitumor activity, without significant potentiation of toxicity. In contrast, treatment with CPA and either 5-FUra or UFT (a mixture of tegafur and uracil) in combination showed only additive activity. Our results suggest that CPA and capecitabine/5'-dFUrd, both available for oral administration, would be good partners, and that clinical trials with this drug combination against breast cancer are warranted.

Developments in fluoropyrimidine therapy for gastrointestinal cancer

The combination of 5-fluorouracil and leucovorin is the standard treatment in metastatic colorectal cancer and in Dukes' C colon cancer. There is, however, no agreement on the method for administration in metastatic colorectal cancer. Several new studies published in 1998 suggest that infusional 5-fluorouracil gives a higher response rate and better toxicity profile compared with a standard bolus 5-fluorouracil/leucovorin regimen. The median survival rate, however, is not different. Several new active drugs are being developed for advanced colorectal cancer. It has not yet been shown that these drugs as single agents are superior to an optimal 5-fluorouracil regimen. Combination trials of 5-fluorouracil/leucovorin with oxaliplatin, CPT-11 and raltitrexed are ongoing, and it can be expected that several of these combinations will be more active than 5-fluorouracil/leucovorin. The challenge for the future will be to show the most active combination and the best sequence of these combinations. The development of the orally administered fluoropyrimidines was rapid in 1998. Randomized studies comparing UFT, capecitabine, and eniluracil plus 5-fluorouracil with 5-fluorouracil/leucovorin are ongoing.

Novel chemotherapeutic agents for gastrointestinal cancers

Although 5-fluorouracil has been the most commonly prescribed chemotherapy agent in the treatment of patients with gastrointestinal malignancies, new agents discussed herein provide options for the treatment of patients with colorectal, gastric, and pancreas cancer. Irinotecan was recently approved for the treatment of patients with colorectal cancer refractory to 5-fluorouracil. It has also been evaluated in chemotherapy-naïve patients both alone and in combination with 5-fluorouracil plus leucovorin or with oxaliplatin. Evaluated primarily in patients with colorectal cancer, oxaliplatin, a novel platinum compound, is an active agent. In combination with 5-fluorouracil and leucovorin, oxaliplatin provides a higher response rate than 5-fluorouracil and leucovorin alone. Furthermore, when oxaliplatin was added to the same 5-fluorouracil-based regimen in which patients had disease progression, clinical activity was observed. Other agents discussed herein are raltitrexed and the oral fluorinated pyrimidines, including uracil:tegafur plus leucovorin, capecitabine, eniluracil plus oral 5-fluorouracil, and S-1. Gemcitabine has been demonstrated to be more effective than 5-fluorouracil in the alleviation of disease-specific symptoms in patients with advanced pancreatic cancer. Gemcitabine also confers a modest survival advantage. Combinations of these novel compounds are evaluated in gastrointestinal malignancies in the advanced disease setting and in adjuvant therapy programs.

Phase I and pharmacokinetic study of the oral fluoropyrimidine capecitabine in combination with paclitaxel in patients with advanced solid malignancies

PURPOSE

To evaluate the feasibility of administering the oral fluoropyrimidine capecitabine in combination with paclitaxel, to characterize the principal toxicities of the combination, to recommend doses for subsequent disease-directed studies, and to determine whether significant pharmacokinetic interactions occur between these agents when combined.

PATIENTS AND METHODS

Sixty-six courses of capecitabine and paclitaxel were administered to 17 patients in a two-stage dose-escalation study. Paclitaxel was administered as a 3-hour intravenous (IV) infusion every 3 weeks, and capecitabine was administered continuously as two divided daily doses. During stage I, capecitabine was escalated to a target dose of 1,657 mg/m(2)/d, whereas the paclitaxel dose was fixed at 135 mg/m(2). In stage II, paclitaxel was increased to a target dose of 175 mg/m(2), and the capecitabine dose was the maximum established in stage I. Pharmacokinetics were characterized for each drug when given alone and concurrently.

RESULTS

Myelosuppression, predominately neutropenia, was the principal dose-limiting toxicity (DLT). Other toxicities included hand-foot syndrome, diarrhea, hyperbilirubinemia, skin rash, myalgia, and arthralgia. Two patients treated with capecitabine 1,657 mg/m(2)/d and paclitaxel 175 mg/m(2) developed DLTs, whereas none of six patients treated with capecitabine 1,331 mg/m(2)/d and paclitaxel 175 mg/m(2) developed DLTs during course 1. Pharmacokinetic studies indicated that capecitabine and paclitaxel did not affect the pharmacokinetic behavior of each other. No major antitumor responses were noted.

CONCLUSION

Recommended combination doses of continuous capecitabine and paclitaxel are capecitabine 1,331 mg/m(2)/d and paclitaxel 175 mg/m(2)/d IV every 3 weeks. Favorable preclinical mechanistic interactions between capecitabine and paclitaxel, as well as an acceptable toxicity profile without clinically relevant pharmacokinetic interactions, support the performance of disease-directed evaluations of this combination.

The role of chemotherapy for metastatic breast cancer

Metastatic breast cancer remains a devastating and largely incurable disease. Currently available therapies offer meaningful palliation for many and modest prolongation of survival for some patients. Single-agent hormonal therapy remains the treatment of choice for patients with ER-positive disease, with sequential use of further hormonal agents or cytotoxic chemotherapy at the time of disease progression. Chemotherapy is appropriate as initial therapy for patients with receptor-negative or rapidly progressive visceral disease. Although combination regimens may increase response rates, the lack of survival benefit does not justify the increased toxicity of aggressive combination regimens in most patients. Maintenance chemotherapy deserves consideration in selected well-informed patients, especially those with few therapy-related side effects. High-dose regimens confer substantial toxicity with no clear therapeutic advantage and cannot be recommended outside of ongoing trials. New chemotherapy agents offer the hope of effective salvage therapy with acceptable toxicity to a larger number of patients. Perhaps most promising, the development of targeted, biologically based therapies such as rhuMAbHER2 offers encouragement for the future.

Multicenter phase II study of capecitabine in paclitaxel-refractory metastatic breast cancer

PURPOSE

Capecitabine is a novel, oral, selectively tumor-activated fluoropyrimidine carbamate. This large multicenter phase II trial tested the efficacy and safety of twice-daily oral capecitabine at 2,510 mg/m2/d given for 2 weeks followed by a 1-week rest period and repeated in 3-week cycles, in patients with paclitaxel-refractory metastatic breast cancer.

PATIENTS AND METHODS

Patients were to have received at least two but not more than three prior chemotherapeutic regimens, one of which had to have contained paclitaxel given for metastatic disease. One hundred sixty-three patients were entered onto the study at 25 centers, and 162 patients received capecitabine. One hundred thirty-five patients had bidimensionally measurable disease, and 27 patients had assessable disease.

RESULTS

The overall response rate was 20% (95% confidence interval, 14% to 28%). All responding patients were resistant to or had failed paclitaxel, and all had received an anthracycline. Three complete responses were seen, with complete response durations of 106, 109, and 194+ days. Median duration of response was 8.1 months, median survival time was 12.8 months, and the median time to disease progression was 93 days. The most common treatment-related adverse events were hand-foot syndrome, diarrhea, nausea, vomiting, and fatigue. Diarrhea (14%) and hand-foot syndrome (10%) were the only treatment-related adverse events that occurred with grade 3 or 4 intensity in more than 10% of patients.

CONCLUSION

Capecitabine is an active drug in the treatment of paclitaxel-refractory metastatic breast cancer. It has a favorable toxicity profile with the added advantage of being an oral drug administered at home.

Nucleoside transporters of mammalian cells

In this review, we have summarized recent advances in our understanding of the biology of nucleoside transport arising from new insights provided by the isolation and functional expression of cDNAs encoding the major nucleoside transporters of mammalian cells. Nucleoside transporters are required for permeation of nucleosides across biological membranes and are present in the plasma membranes of most cell types. There is growing evidence that functional nucleoside transporters are required for translocation of nucleosides between intracellular compartments and thus are also present in organellar membranes. Functional studies during the 1980s established that nucleoside transport in mammalian cells occurs by two mechanistically distinct processes, facilitated diffusion and Na(+)-nucleoside cotransport. The determination of the primary amino acid sequences of the equilibrative and concentrative transporters of human and rat cells has provided a structural basis for the functional differences among the different transporter subtypes. Although nucleoside transporter proteins were first purified from human erythrocytes a decade ago, the low abundance of nucleoside transporter proteins in membranes of mammalian cells has hindered analysis of relationships between transporter structure and function. The molecular cloning of cDNAs encoding nucleoside transporters and the development of heterologous expression systems for production of recombinant nucleoside transporters, when combined with recombinant DNA technologies, provide powerful tools for characterization of functional domains within transporter proteins that are involved in nucleoside recognition and translocation. As relationships between molecular structure and function are determined, it should be possible to develop new approaches for optimizing the transportability of nucleoside drugs into diseased tissues, for development of new transport inhibitors, including reagents that are targeted to the concentrative transporters, and, eventually, for manipulation of transporter function through an understanding of the regulation of transport activity.

Oral fluoropyrimidines in the treatment of colorectal cancer

5-Fluorouracil (5-FU) has been the mainstay of systemic therapy for colorectal cancer since its initial development 40 years ago. Efforts to improve the therapeutic index of 5-FU have included alteration of schedule and addition of biochemical modulators. An understanding of 5-FU mechanisms of action has resulted in major therapeutic advances in the past 10 years; however, a plateau has been reached in the efficacy of 5-FU, mandating a paradigm shift for those involved in colorectal cancer drug development. One direction vigorously pursued is the development of orally administered fluoropyrimidines that maintain or improve upon the effectiveness of intravenous 5-FU. In this paper the preclinical and clinical development of oral fluoropyrimidines and their modulators is reviewed, including UFT, capecitabine, ethynyluracil and S-1.