Phase I trial of low-dose, prolonged continuous infusion fluorouracil plus interferon-alfa: evidence for enhanced fluorouracil toxicity without pharmacokinetic perturbation

Circadian variation in plasma 5-fluorouracil concentrations during a 24 hour constant-rate infusion

Background

Varying the rate of continuous intravenous infusions of 5-fluorouracil (5FU) chemotherapy over a 24-hour period has been reported to improve patient outcomes. It has been hypothesized that circadian variation in drug disposition is a contributing factor. We analyzed 5-FU concentrations during a 24-hour continuous 5-FU infusion.

Methods

Sixty-four subjects with advanced malignancies including pancreatic, hepatocellular, colorectal as well as other epithelial malignancies and either abnormal hepatic or renal function were treated on a phase I and pharmacokinetic study of weekly 24-hour intravenous infusions of 5-FU and leucovorin. No other concomitant anticancer therapy was administered. Blood samples were collected every three hours from 61 subjects for measurement of plasma 5-FU during the first two weekly infusions.

Results

After adjusting for differences in dose, elapsed time from start of infusion and infusion number (2 versus 1), mean 5-FU concentration was highest at 6 am and lowest at 3 pm, with an overall change in the mean from 3 pm to 6 am of +20 percent (95% CI = 12–28%). However, this variation in mean concentration associated with time of day was comparable in magnitude to the between-patient differences, within-patient differences between infusions, and the residual variation within infusion (coefficient of variation = 21%).

Conclusions

Our data show systematic variation by time of day in plasma concentrations of 5-FU administered at a constant rate over 24 hours, but it is small compared to the total variation in plasma concentration contributed by other sources. Circadian variation in men was more pronounced than in women.

Potential of interferon-alpha in solid tumours: part 2

The second part of this review examines the use of recombinant interferon-alpha (rIFNalpha) in the following solid tumours: superficial bladder cancer, Kaposi's sarcoma, head and neck cancer, gastrointestinal cancers, lung cancer, mesothelioma and ovarian, breast and cervical malignancies. In superficial bladder cancer, intravesical rIFNalpha has a promising role as second-line therapy in patients resistant or intolerant to intravesical bacille Calmette-Guérin (BCG). In HIV-associated Kaposi's sarcoma, rIFNalpha is active as monotherapy and in combination with antiretroviral agents, especially in patients with CD4 counts >200/mm(3), no prior opportunistic infections and nonvisceral disease. rIFNalpha has shown encouraging results when used in combination with retinoids in the chemoprevention of head and neck squamous cell cancers. It is effective in the chemoprevention of hepatocellular cancer in hepatitis C-seropositive patients. In neuroendocrine tumours, including carcinoid tumour, low-dosage (</=3 MU) or intermediate-dosage (5 to 10 MU) rIFNalpha is indicated as second-line treatment, either with octreotide or alone in patients resistant to somatostatin analogues. Intracavitary IFNalpha may be useful in malignant pleural effusions from mesothelioma. Similarly, intraperitoneal IFNalpha may have a role in the treatment of minimal residual disease in ovarian cancer. In breast cancer, the only possible role for IFNalpha appears to be intralesional administration for resistant disease. IFNalpha may have a role as a radiosensitising agent for the treatment of cervical cancer; however, this requires confirmation in randomised trials. On the basis of current evidence, the routine use of rIFNalpha is not recommended in the therapy of head and neck squamous cell cancers, upper gastrointestinal tract, colorectal and lung cancers, or mesothelioma. Pegylated IFNalpha (peginterferon-alpha) is an exciting development that offers theoretical advantages of increased efficacy, reduced toxicity and improved compliance. Further data from randomised studies in solid tumours are needed where rIFNalpha has activity, such as neuroendocrine tumours, minimal residual disease in ovarian cancer, and cervical cancer. A better understanding of the biological mechanisms that determine response to rIFNalpha is needed. Studies of IFNalpha-stimulated gene expression, which are now feasible, should help to identify molecular predictors of response and allow us to target therapy more selectively to patients with solid tumours responsive to IFNalpha.

Potential of interferon-alpha in solid tumours: part 1

Interferon-alpha (IFNalpha) is a pleiotropic cytokine with direct and indirect antitumour effects. These include prolongation of the cell cycle time of malignant cells, inhibition of biosynthetic enzymes and apoptosis, interaction with other cytokines, and immunomodulatory and antiangiogenic effects. The first clinical trials in solid tumours used crude preparations of natural IFNalpha and demonstrated that tumour regressions in solid tumours and haematological malignancies were possible. Since the advent of genetic engineering technology, recombinant (r) IFNalpha has been widely evaluated in solid tumours. This review discusses the use and potential of rIFNalpha in solid tumours; the first part focuses on malignant melanoma and metastatic renal cell carcinoma (RCC). In the adjuvant treatment of malignant melanoma, rIFNalpha has been tested in randomised trials in more than 6000 patients. High-dosage IFNalpha (> or =10MU) prolongs disease-free survival (DFS) but not overall survival (OS). Low-dosage IFNalpha (< or =3MU) has not been shown to prolong DFS or OS, and current data do not support its use outside clinical trials. The latest United Kingdom Co-ordinating Committee on Cancer Research meta-analysis of ten randomised trials that used adjuvant rIFNalpha has shown that there is a benefit in DFS but not OS. No conclusions can be reached for intermediate-dosage IFNalpha (5 to 10MU) until the mature results of the European Organization for Research and Treatment of Cancer (EORTC) study 18952 are available. In RCC, current evidence does not support the use of adjuvant IFNalpha. In metastatic malignant melanoma and RCC, reported response rates to rIFNalpha are approximately 15%. In a minority of responding patients, however, these responses can be long-standing. In metastatic malignant melanoma, IFNalpha combined with other cytotoxic agents with or without interleukin-2 has achieved high response rates but has not improved survival. In metastatic RCC, intermediate dosages of rIFNalpha should be used and therapy should probably be prolonged (>12 months); response depends on prognostic factors such as good performance status, whereas survival is affected by factors such as low tumour burden. Nephrectomy should therefore be considered in patients with good performance status prior to IFNalpha immunotherapy in advanced RCC, even in patients with metastatic disease. The toxicity of high-dosage IFNalpha and the lack of definite benefit on OS with high- or low-dosage IFNalpha do not support its use outside clinical trials. Data from the ongoing US Intergroup studies, the ongoing EORTC 18991 study (long-term therapy with pegylated IFNalpha) and mature data from EORTC 18952 (intermediate-dosage IFNalpha) will help establish the role of IFNalpha as adjuvant therapy in malignant melanoma.

A phase I trial of weekly gemcitabine and subcutaneous interferon alpha in patients with refractory renal cell carcinoma

INTRODUCTION

Recombinant human interferon-a2b (rHuIFN-alpha2b) and Interleukin-2 have limited effectiveness in the treatment of metastatic renal cell carcinoma (MRCC). Gemcitabine (Gemzar) is also reported to have activity against MRCC, and recent in vitro, in nude mice xenografts, and human data suggests increased activity of gemcitabine (Gemzar) when combined with IFN-alpha2b.

PURPOSE

A phase I clinical trial utilizing gemcitabine (Gemzar and rHuIFN-alpha2b was conducted in patients with metastatic renal cell carcinoma.

METHODS

Treatment consisted of: gemcitabine (Gemzar) 600 mg/m2 I.V. weekly and rHuIFN-alpha2b 1.0 MU/m2 (dose level A) or 3.0MU/m2 S.C. (dose level B) three times a week for 6 weeks with a 2 weeks rest period.

RESULTS

Thirteen patients were entered into the trial and were evaluated. Dose limiting toxicity was predominantly hematologic, and was seen at dose level B. This included grade 3 anemia (1 patient), neutropenia (1 patient), and nausea (1 patient) and grade 4 neutropenia (1 patient). The maximal tolerated dose was gemcitabine (Gemzar) 600 mg/m2 I.V. weekly and rHuIFN-alpha2b 1.0 MU/m2 three times a week.

CONCLUSION

This combination of gemcitabine (Gemzar) and rHuIFN-alpha2b has significant hematologic toxicity despite low doses of each agent. Further investigation of this combination using this schedule is not recommended.

Continuous venous infusion 5-fluorouracil and interferon-alpha in pancreatic carcinoma

Chemotherapy treatment for advanced pancreatic cancer is universally disappointing. Evidence suggested the possibility of improved activity of 5-fluorouracil (5-FU) in this disease when administered by continuous infusion in combination with interferon-alpha. Thirteen patients who had histologically documented stage III and IV adenocarcinoma of the pancreas were treated with 5-FU, 250 mg/m2/day by continuous infusion, in combination with interferon-alpha, 3 million units subcutaneously 3 times per week. Treatment was adjusted for toxicity and was continued until disease progression, unacceptable toxicity, or 8 weeks after a complete response. Responses were documented on two separate occasions that were separated by 4 weeks. Eleven men and two women were treated an average of 48 days. There was one responder, for a response rate of 7.7% (95% confidence interval, 0.1%-36%). The duration of response was 90 days. The median survival of the entire group was 8.3 months. Toxicity was significant, with more than 50% of patients requiring treatment breaks and dosage reductions. The most common toxicities were mucositis, hand-foot syndrome, diarrhea, and nausea. There were no treatment-related deaths. Treatment of advanced adenocarcinoma of the pancreas with continuous-infusion 5-FU and interferon-alpha is associated with significant toxicity without significant evidence of response.

Phase II trial of prolonged continuous infusion of 5-fluorouracil and interferon-alpha in patients with advanced pancreatic cancer. Eastern Cooperative Oncology Group Protocol 3292

Evidence suggests that interferon-alpha (IFN-alpha) augments the antineoplastic activity of 5-fluorouracil (5-FU) in human adenocarcinoma cell lines in vitro and may enhance the efficacy of 5-FU in patients with advanced colorectal carcinoma. In addition, 5-FU may be more effective when given as a prolonged, continuous i.v. infusion (PCI). The Eastern Cooperative Oncology Group performed a Phase II trial of PCI 5-FU plus IFN-alpha in patients with advanced pancreatic carcinoma. Twenty-six patients with advanced, surgically incurable adenocarcinoma of the pancreas received PCI 5-FU (250 mg/m2 daily for 28 days) in combination with IFN-alpha (5 x 10(6) IU/m2 s.c. thrice weekly). Treatment cycles were repeated 14 days or longer after completion of the previous cycle. Treatment was interrupted prior to day 28 if intolerable toxicity developed, and the dose of 5-FU was reduced in subsequent cycles. Partial response occurred in two of 24 evaluable patients (8%; 95% confidence interval, 0-19%). The majority of the study group (88%) had liver metastases. Patients whose serum lactate dehydrogenase (LDH) was more than twofold elevated developed 5-FU-related toxicity significantly sooner than patients with smaller elevations in serum LDH (9 vs. 22 days; p = 0.003). A similar trend was observed for patients with a more than twofold elevation in serum glutamic-oxaloacetic transaminase (SGOT; 9 vs. 15 days; p = 0.07). In conclusion, PCI 5-FU plus IFN-alpha has minimal activity in patients with advanced pancreatic carcinoma, and elevated serum LDH and/or SGOT may be useful for predicting greater toxicity from 5-FU-based therapy in patients with liver metastases.

Treatment of stage D2 hormone refractory carcinoma of the prostate with 5-fluorouracil and Roferon-A: a Southwest Oncology Group study

Based upon prior data suggesting that alpha-interferon possesses chemomodulatory activity, the Southwest Oncology Group conducted a study in which patients with hormone refractory, metastatic (stage D2) adenocarcinoma of the prostate were treated with 5-fluorouracil (5-FU) and Roferon-A. All patients had bidimensionally measurable disease. Treatment consisted of 5-FU 750 mg/m2/day by continuous i.v. infusion for 5 days with Roferon-A 9 million units subcutaneously ono days 1, 3 and 5. Roferon-A was continued three times weekly throughout treatment. Following a one week hiatus from 5-FU (week 2), 5-FU was continued at a dose of 750 mg/m2 i.v. bolus weekly. Nineteen patients were evaluable for toxicity. The most common toxicities were gastrointestinal and mucosal, hematologic and a flu-like syndrome. There were no deaths related to treatment. Among the 14 patients evaluable for response, the response rate was 0% (95% confidence interval, 0-18%). Thirteen of the 19 evaluable patients have died with a median survival of 9 months. The combination of 5-FU and Roferon-A does not have sufficient activity against advanced, hormone refractory prostate cancer to warrant further investigation.

Measurement of plasma 5-fluorouracil by high-performance liquid chromatography with comparison of results to tissue drug levels observed using in vivo 19F magnetic resonance spectroscopy in patients on a protracted venous infusion with or without interferon-alpha

PURPOSE

To measure plasma 5-fluorouracil (5-FU) levels using high-performance liquid chromatography (HPLC) and compare the findings to the tissue metabolism of 5-FU evaluated using 19F magnetic resonance spectroscopy (MRS), during a protracted venous infusion (PVI) with or without interferon-alpha.

METHODS

Patients receiving PVI 5-FU (300 mg/m2/day) with or without interferon-alpha (5 x 10(6) units 3 times per week), had 2 weekly plasma 5-FU levels evaluated using reverse-phase ion-pairing HPLC. These samples were drawn just prior to the patient undergoing MRS using a 1.5T Siemens Magnetom whole body magnetic resonance system with a 16 cm surface coil placed over normal liver or metastatic tumour. Semi-quantitated MRS values were compared with the plasma 5-FU levels using linear regression analysis. Data were available from patients given interferon-alpha with PVI 5-FU from day 1 or at the point of 5-FU refractory disease.

RESULTS

A total of 30 patients were studied. Plasma 5-FU concentrations while on a protracted venous infusion varied from <25 ng/ml (0.192 mu M) to 25,000 ng/ml (192 mu M). A high plasma 5-FU concentration was associated with an increase in patient toxicity. Patients given interferon-alpha with 5-FU had higher median plasma 5-FU levels higher than patients on 5-FU alone (6138 vs. 218 ng/ml; p = 0.03). There was no correlation between the plasma 5-FU concentration and tumour response. A comparison of the plasma 5-FU data to the MRS studies in normal liver revealed a positive correlation between plasma 5-FU and liver catabolite signal (r = 0.68; p = 0.016) but a negative correlation with the log plasma 5-FU concentration and 5-FU liver signal (r = -0.63; p = 0.022). The patients experiencing toxicity, in addition to having a higher plasma 5-FU concentration did not exhibit a liver 5-FU signal, while the reverse was true for those having no toxicity.

CONCLUSIONS

Plasma 5-FU levels may show greater interpatient variation when given as a protracted venous infusion. Levels of 5-FU correlated with treatment toxicity but not with anti-tumour activity. The addition of interferon-alpha to 5-FU increases plasma 5-FU levels. MRS findings suggest patients with low plasma 5-FU levels have higher 5-FU levels in normal liver tissue than in those with higher plasma levels.

The role of interferon-alpha as a modulator of fluorouracil and leucovorin

Several preclinical studies have demonstrated that interferon-alpha (IFN-alpha) may enhance the cytotoxicity of fluoropyrimidines in a greater-than-additive manner in a variety of human cancer cell lines. The underlying mechanism(s) have varied in different cancer cell lines, and include increased fluorouracil anabolism to fluorodeoxyuridine monophosphate, further inhibition of thymidylate synthase, stimulation of thymidine and uridine phosphorylase activities, greater DNA damage, and enhanced natural killer cell-mediated lysis of tumour targets. These preclinical studies stimulated clinical evaluation of IFN-alpha in combination with 5-fluorouracil (5-FU) with and without leucovorin (LV), and the initial clinical results appeared promising. We summarise preclinical research concerning the interaction of 5-FU and IFN-alpha. The rationale for combining 5-FU with IFN-alpha and LV is discussed, and we describe our clinical experience with the combination of 5-FU, LV and IFN-alpha-2a. The insights and unresolved questions concerning the clinical application of this combination are also discussed.

Treatment of advanced colorectal cancer with 5-fluorouracil and interferon-alpha: an overview of clinical trials

5-Fluorouracil (5-FU) is the most active single agent for treatment of advanced colorectal cancer, although objective responses occur in only 20% of patients, and there seems to be no impact on overall survival. Experimental findings suggesting that interferon-alpha (IFN-alpha) enhances 5-FU cytotoxicity have stimulated an increasing number of clinical trials to evaluate the therapeutic potential of this combination. This article summarises the possible mechanisms of interaction of 5-FU and IFN-alpha, and provides an overview of the current status of this approach in advanced colorectal cancer. A computerised (Medline) and manual search were performed to identify all trials using 5-FU and IFN-alpha for the treatment of advanced colorectal cancer published in the English literature between 1960 and 1994. Information abstracted included treatment regimen, number of patients, pretreatment status, complete and partial remissions, remission duration, overall survival, and toxicity. A total of 417 patients were enrolled in 16 trials using different regimens of 5-FU and IFN-alpha, and double modulation of 5-FU with leucovorin (LV) and IFN-alpha was investigated in nine trials involving 332 patients. The mean overall response rate in these phase II trials was only 31% (range 3-76) and 35% (range 0-54), respectively. Early results of six prospectively randomised studies of 5-FU or 5-FU/LV +/- IFN-alpha also did not suggest a significant enhancement of the antitumour effectiveness with the addition of IFN-alpha. There is increasing evidence, however, that administration of IFN-alpha along with 5-FU enhances toxicity. Because of their modest therapeutic index, currently employed regimens of 5-FU +/- LV plus IFN-alpha cannot be recommended for routine use at the present time. The combination of 5-FU plus LV represents an equally effective and less expensive alternative. Nevertheless, there is still hope that further attempts to elucidate the complex mechanisms of this potentially synergistic drug combination will allow the rational design of regimens with a superior therapeutic index.

Interferon-alpha does not improve the antineoplastic efficacy of high-dose infusional 5-fluorouracil plus folinic acid in advanced colorectal cancer. First results of a randomized multicenter study by the Association of Medical Oncology of the German Cancer Society (AIO)

BACKGROUND

High-dose 5-FU given weekly as a 24-h infusion in combination with folinic acid (FA) has been associated with low toxicity and a high response rate. Interferon-alpha (IFN) either alone or in combination with FA has also improved treatment results by modulating 5-FU activity. We therefore initiated a randomized multicenter trial comparing the ability of FA or IFN to modulate infusional 5-FU. The statistical design using a sequential analysis allows us to report on the comparison of 5-FU/FA vs. 5-FU/FA/IFN while randomization of patients into 5-FU/FA vs. 5 FU/IFN continues.

METHODS

Chemotherapy-naive patients with advanced progressive colorectal cancer and measurable metastatic lesions were randomized to receive 5-FU 2600 mg/m2 i.v. as a 24-h infusion, combined with either FA 500 mg/m2 as a 2-h infusion (A), or IFN 3 x 10(6) U s.c. 3 x/week (B), or the combination of FA plus IFN as in arms A and B (C). Treatment arms were repeated weekly for 6 weeks followed by a 2-week rest period. These 8-week cycles were administered until tumor progression. Because of the occurrence of 2 toxic deaths among the first 17 patients treated in arm C, 5-FU was reduced to 2000 mg/m2 for all patients in arm C. Sequential analysis according to Whitehead for objective response was planned with alpha = 0.05/3 and a power of 80% (beta = 0.2) to detect a difference of > or = 25% (delta = 0.25) or equivalence of response rates. For pairwise comparison of treatment arms a minimum of 30 patients per arm and a maximum of 90 patients per arm were expected in case of equivalence or difference.

RESULTS

An interim analysis was performed after the first 93 of 149 randomized patients were evaluable for response and toxicity (A 31 pts, B 33 pts, C 29 pts). Despite the 5-FU dose reduction in arm C, 28% of patients experienced grade 3/4 toxicity (CTC) including diarrhea, mucositis and handfoot syndrome compared to 16% in arm A and 12% in arm B (not significant). No treatment related toxic death occurred in arms A or B, but 3 patients (10%) in arm C died of diarrhea and septicemia. Among patients treated with 5-FU/FA objective tumor response occurred in 12/31 patients (39%) (21%-56%, 95% confidence interval) (3 CR, 9 PR), no change in 13/31 (42%) and PD in 6/31 (19%) patients. Eleven of 29 patients (38%) (20%-56%, 95% confidence interval) receiving 5-FU/FA/IFN achieved complete (3 patients) or partial (8 patients) remissions, 10/29 patients (34%) had stable disease and 8/29 patients (28%) tumor progression. According to the sequential analysis the rates of objective responses observed in patients treated with 5-FU/FA or 5-FU/FA/IFN were equivalent.

CONCLUSION

This interim analysis allows the conclusion that infusional 5-FU plus FA/IFN is no more active than infusional 5-FU plus FA alone. However, 5-FU/FA/IFN despite 5-FU dose reduction was associated with unacceptably high toxicity, including 10% deaths. Therefore, further investigation of this regimen is not justified. The study is continued with the comparison of 5-FU/FA vs. 5-FU/IFN.

Pharmacokinetic interaction of 5-fluorouracil and interferon alpha-2b with or without folinic acid

The purpose of this study was to evaluate a potential pharmacokinetic (PK) interaction between fluorouracil (5-FU) and the biomodulating agent interferon alpha (IFN-alpha) in patients with metastatic colorectal carcinoma. 5-FU was applied as an intravenous bolus injection of 750 mg m-2 weekly and IFN-alpha 2b (IFN) 5 MU was injected 3 times weekly (TIW) subcutaneously. In the first study, 13 patients were treated by this schedule, 5-FU plasma levels were determined by HPLC on day (d) one as baseline before starting IFN; the analysis was repeated at the second or third cycle of 5-FU administration 1 hour after the last IFN injection respectively. In the second study, 10 patients additionally received folinic acid (FA) 200 mg m-2 as a short time infusion immediately before 5-FU, and a third analysis of FU kinetics was performed in order to compare the influence of a double modulation of IFN and FA to IFN alone. Combination of 5-FU and IFN resulted in a significant increase of the AUC of 5-FU (80%) and the fictive initial concentration (C0, 65%) obviously caused by a reduction of 5-FU clearance by 50%. However, when FA was added to this schedule, no significant changes of FU kinetics compared to 5-FU alone could be documented. Finally, in two pilot patients 5-FU 750 mg was given as a continuous infusion (CI) over 5 days and IFN 5 x 10(6) u was added daily from d2 to d5.(ABSTRACT TRUNCATED AT 250 WORDS)

A clinical and pharmacological study of 5-fluorouracil, leucovorin and interferon alfa in advanced colorectal cancer

Modulation of 5-fluorouracil (FUra) using leucovorin (LV) is a standard treatment approach in patients with metastatic colorectal cancer. Modulation of FUra with interferon alfa has also shown some promise. Laboratory data have demonstrated increased cytotoxicity when FUra is combined with both LV and interferon. The current study examined the effects of double modulation of FUra using LV and interferon. Patients with measurable advanced colorectal cancer received bolus FUra 375 mg/m2 plus LV 20 mg/m2 daily for 5 days, repeated every 28 days. Recombinant human interferon alfa-2a, 3 million IU/m2 subcutaneously, was given daily on the days of chemotherapy then three times weekly. There was one complete response and nine partial responses (10/41) seen for an overall response rate of 24% (95% CI 12.0-40.0%). Overall, 70% of patients experienced one or more episodes of nonhematologic toxicity of grade 3 or more. Weight loss was common, with a mean decrease of 2.9 kg over the first two months (P < 0.0001). Improvements in tumor-related symptoms were balanced by increased fatigue and a deterioration in body weight and performance status. There was no evidence of progressive changes in FUra metabolism from interferon usage.

Lack of effect of interferon alpha 2a upon fluorouracil pharmacokinetics

The disposition of 5-fluorouracil (FUra) was studied in 19 colorectal cancer patients during treatment with FUra and high-dose leucovorin (LV) with or without interferon alpha 2a (IFN-alpha). All received LV 200 mg m-2 over 2 h, then FUra 400 mg m-2 over 5 min then FUra 400 mg m-2 over 22 h, repeated on day 2, on a 14 day cycle. Nine patients also received IFN-alpha 6 MU every 48 h, starting at least 2 weeks before the study. Series of 14 blood samples were assayed for FUra by reversed-phase high-performance liquid chromatography (HPLC). Minimum Akaike information criterion estimation was used to determine the simplest effective pharmacokinetic model. This consisted of a single compartment with first-order (linear) and Michaelis-Menten (non-linear) components to drug elimination. This model gave r2 > 0.98 in 19/20 data sets. With the Michaelis constant (KM) set at 15 microM, values were derived for the volume of distribution (Vd), the maximum rate of non-linear elimination (Vmax) and the first-order elimination rate constant (K1.e). Mean (+/- s.d.) values in control (no IFN-alpha) patients were: Vd 10.4 (+/- 1.9) l m-2, Vmax 182 (+/- 59) mumol l-1 h-1 and k1.e 4.35 (+/- 0.58) h-1. No significant differences were detected in patients receiving IFN-alpha, in whom the equivalent mean values were Vd 10.0 (+/- 0.9) l m-2, Vmax 141 (+/- 27) mumol l-1 h-1 and k1.e 3.96 (+/- 0.5) h-1. Mean trapezoidal AUC0-22 h was similar in the two groups (control patients 116 microM h, IFN-alpha patients 125 microM h). No significant correlations with renal or hepatic function were detected. These results, while not inconsistent with previous reports of a reduced rate of FUra elimination at higher IFN-alpha doses, suggest that any clinical effect of this moderate dose of IFN-alpha on FUra toxicity or activity is due to modulation at target cells, not to pharmacokinetic interaction.

Inhibition of dihydropyrimidine dehydrogenase by alpha-interferon: experimental data on human tumor cell lines

Interferons (IFNs) are very promising fluorouracil (FU) biochemical modulators. The pharmacological origin sustaining the FU-IFN synergistic interaction is not clearly understood. It was recently shown that alpha-IFN was associated with a dose-dependent decrease in FU clearance in treated patients. Dihydropyrimidine dehydrogenase (DPD) is the key regulating enzyme for FU catabolism. The effects on DPD exerted by both the IFN dose and the duration of exposure were evaluated in a panel of five human cancer cell lines. All cell lines investigated exhibited quantifiable DPD activity with inter-cell-line variability (0.118-0.318 nmol min-1 mg protein-1). A prolonged exposure to IFN (up to 5 days) was necessary to obtain a significant inhibition of DPD activity. A concentration-dependent significant decrease in DPD activity, reaching 50% of the initial activity determined for the highest IFN concentration (10(5) IU/ml), was demonstrated in all cell lines tested (5-day IFN exposure). For three cell lines, IFN potentiated the FU-induced growth inhibition in a concentration-dependent manner. Considering all cell lines and all IFN concentrations, it appears that globally, the greater the inhibition of DPD activity, the greater the FU potentiation (Spearman rank correlation on all cell lines, P = 0.011).