5-fluorouracil Toxicity Research Articles

The study of innate drug resistance of human hepatocellular carcinoma Bel7402 cell line

The innate drug resistance of human hepatocellular carcinoma (HCC) Bel7402 cell line was studied in vitro. MTT assay showed that Bel7402 cells were innately resistant to doxorubicin (Dox), and even more resistant to vincristine (VCR). This resistance could be effectively reversed by verapamil (Ver), one of the classical multidrug resistance (MDR) modulating agents. However, the differences in 5-fluorouracil (5-FU) toxicity between these two cell lines is much less and the resistance of Bel7402 cells could only be slightly reversed by Ver, which may be experimental noise. Immunocytochemical staining using anti-p-glycoprotein monoclonal antibody JSB-1 indicated that the expression of the P-glycoprotein (P-gp) in the innate Bel7402 cells was elevated compared with the sensitive KB cells. The accumulation of Dox in innate resistant Bel7402 cells was 50.7% lower than that in sensitive KB cells by using spectrofluometric analyses, and the accumulation of Dox increased 1.6 fold in Bel7402 cells in the presence of Ver. The susceptibility of Dox-induced apoptosis was also increased in the presence of Ver by using flow cytometric assay and DNA fragmentation quantitative assay as well as by Hoechst 33258 staining. It appears that the innate Bel7402 cells might be useful in screening new antitumour drugs or new chemosensitisers which could overcome the innate or acquired resistant mechanism, and the toxicity and reversal effects with 5-FU are different from those known to be P-gp substrates such as VCR, Dox, and taxol.

Chemically-induced apoptosis: p21 and p53 as determinants of enterotoxin activity

The relationship between toxin-induced apoptosis and longer-term (>72 h) intestinal toxicity was investigated in vivo using p53 wild type (+/+) and `knockout' (−/−) mice. The enterotoxic antimetabolite 5-fluorouracil (5-FU) induced acute p53-dependent apoptosis in the crypts of both small intestine and midcolon. Although the amount of apoptosis was the same order of magnitude at its peak (24 h) at both 40 and 400 mg/kg 5-FU, only 400 mg/kg 5-FU brought about changes in the integrity of the gut after 96 h. These were characterised by the loss of epithelial cells from crypts and villi. Only after 400 mg/kg 5-FU were mitotic index and DNA synthesis significantly suppressed in both small intestinal and midcolonic crypts. This correlated with a prolonged, p53-dependent expression of p21waf-1/cip1. In p53 null (−/−) mice significant reductions in 5-FU-induced apoptosis and relief from the inhibition of cell cycle progression permitted retention of crypt integrity after 5-FU. Thus, quantitative measures of acute apoptosis in vivo did not accurately predict subsequent pathological changes in the gut. Rather, p53-dependent inhibition of cell cycle progression together with cell loss by apoptosis caused a loss of crypt integrity. Importantly, the tissue toxicity of 5-fluorouracil was genetically determined at a locus (p53) separate from that directly associated with toxin action. The selectivity of toxin action is therefore also determined by events `downstream' of those associated with the direct mode of action of the toxin.

Risk factors associated with mucositis in cancer patients receiving 5-fluorouracil.

Oral mucositis is a dose-limiting toxicity of 5-fluorouracil (5-FU). This prospective cohort study investigated factors associated with mucositis in patients receiving 5-FU for cancer of the digestive tract. Sixty-three patients (mean age 65 years) completed self-administered questionnaires and had interviews, oral examinations and unstimulated whole salivary flow measurements at baseline and follow-up appointments. The duration of follow-up was 2 months. Predictor variables included sociodemographic data, body surface area, diabetes, smoking, alcohol consumption, salivary flow, oral hygiene, presence of prostheses, performance status, regimen of cytotoxic drugs, hematological data, and herpes simplex virus antibody titer. Forty-six per cent of patients developed at least one episode of oral mucositis during cytotoxic treatment. Pearson's chi-square analysis showed that mucositis was significantly associated with xerostomia at baseline, xerostomia during chemotherapy, and lower baseline neutrophil counts (P < or = 0.05). Multiple logistic regression analysis indicated that xerostomia at baseline (odds ratio, OR = 10.0), or baseline neutrophil level under 4000 cells/mm3 (OR = 3.9) were significant predictors of mucositis. Taking into account the effect of neutrophil level at baseline, xerostomia during chemotherapy (OR = 4.5) was also a significant predictor of mucositis. The results showed that xerostomia and lower baseline neutrophil levels are significantly associated with oral mucositis. These variables should be taken into consideration in the design of intervention studies to reduce the frequency and severity of mucositis. More research is required to investigate the role of saliva and neutrophils in the pathogenesis of chemotherapy-induced mucositis.

Possible prediction of adverse reactions to fluorouracil by the measurement of urinary dihydrothymine and thymine.

Dihydropyrimidine dehydrogenase (DPD) deficiency with a defect of the pyrimidine catabolic pathway has recently become the focus of considerable attention, due to the severe 5-fluorouracil (5-FU) toxicities occurring in DPD deficiency patients. Studies also suggest that 5-FU toxicities could occur in another pyrimidine metabolic disorder, dihydropyrimidinuria (DHPuria). This study shows that urinary dihydrothymine (DHT) and thymine (THY) are useful indexes for detection of DPD deficiency and DHPuria. We measured urinary DHT and THY in 276 Japanese adults to establish reference ranges. When males and females were compared, both DHT and THY levels were found to be significantly higher in females. The reference ranges (mean +/- SD with logarithmic values) for males were found to be 1.56-5.70 micromol/g of creatinine for DHT and 0.40-1.47 micromol/g of creatinine for THY. The reference ranges for females were found to be 1.89-8.33 micromol/g of creatinine for DHT and 0.58-2.30 micromol/g of creatinine for THY. In addition to this study we analyzed a DPD deficiency case and a DHPuria case. In the DPD deficiency case, the THY concentrations of all urine samples were out of the reference range. However, uracil levels in most of the samples were within the normal range. The DHPuria case excreted large amounts of DHT and dihydrouracil, both out of the normal range.

Dihydropyrimidinase Deficiency: Structural Organization, Chromosomal Localization, and Mutation Analysis of the Human Dihydropyrimidinase Gene

Dihydropyrimidinase (DHP) deficiency (MIM 222748) is characterized by dihydropyrimidinuria and is associated with a variable clinical phenotype. This disease might be associated with a risk of 5-fluorouracil toxicity, although no cases have been reported. We present here both the molecular characterization of the human DHP gene and, for the first time, the mutations causing DHP deficiency. The human DHP gene spans >80 kb and consists of 10 exons. It has been assigned to 8q22, by FISH. We performed mutation analysis of genomic DNA in one symptomatic and five asymptomatic individuals presenting with dihydropyrimidinuria. We identified one frameshift mutation and five missense mutations. Two related Japanese adult subjects were homozygous for the Q334R substitution, whereas two other, unrelated Japanese infant subjects were heterozygous for the same mutation, but this mutation is not common in the Japanese population. A Caucasian pediatric patient exhibiting epileptic attacks, dysmorphic features, and severe developmental delay was homozygous for W360R. Using a eukaryotic expression system, we showed that all mutations reduced enzyme activity significantly, indicating that these are crucial DHP deficiency-causing mutations. There was no significant difference, in residual activity, between mutations observed in the symptomatic and those observed in the asymptomatic individuals.

Characterization of the Human Dihydropyrimidine Dehydrogenase Gene

Dihydropyrimidine dehydrogenase (DPD) catabolizes endogenous pyrimidines and pyrimidine-based antimetabolite drugs. A deficiency in human DPD is associated with congenital thymine-uraciluria in pediatric patients and severe 5-fluorouracil toxicity in cancer patients. The dihydropyrimidine dehydrogenase gene (DPYD) was isolated, and its physical map and exon–intron organization were determined by analysis of P1, PAC, BAC, and YAC clones. TheDPYDgene was found to contain 23 exons ranging in size from 69 bp (exon 15) to 961 bp (exon 23). A physical map derived from a YAC clone indicated thatDPYDis at least 950 kb in length with 3 kb of coding sequence and an average intron size of about 43 kb.The previously reported 5′ donor splice site mutation present in pediatric thymine-uraciluria and cancer patients can now be assigned to exon 14. All 23 exons were sequenced from a series of human DNA samples, and three point mutations were identified in three racial groups as G1601A (exon 13, Ser534Asn), A1627G (exon 13, Ile543Val), and G2194A (exon 18, Val732Ile). These studies, which have established that theDPYDgene is unusually large, lay a framework for uncovering new mutations that are responsible for thymine-uraciluria and toxicity to fluoropyrimidine drugs.

Population and family studies of dihydropyrimidinuria: prevalence, inheritance mode, and risk of fluorouracil toxicity.

To evaluate the prevalence of dihydropyrimidinuria (DHPuria), we analyzed urine samples from 21,200 healthy Japanese infants, and found two cases of DHPuria without clinical symptoms. Based on this result, we estimated the prevalence to be approximately 1/10,000 births in Japan. In addition, we analyzed pyrimidine catabolism on a previously reported family with an adult DHPuria case. We newly identified the sister of the propositus as the second case of DHPuria in this family, because she excreted large amounts of dihydrouracil and dihydrothymine. The parents and the child of the propositus showed slight increases of dihydrouracil and dihydrothymine. This is the first family with 2 cases of DHPuria, indicating that DHPuria is an inherited condition. To determine the inheritance of DHPuria in this family and to examine the risk of 5-fluorouracil (5-FU) toxicity, a uracil loading test was performed on the parents. Urinary dihydrouracil concentrations in the parents after the loading were several times higher than those in normal control persons, the finding being consistent with DHPuria heterozygotes. This, along with data on the propositus, his sister, and his child, indicates that DHPuria is an autosomal recessive condition. In addition, DHPuria homozygotes may have a high risk of 5-FU toxicity, while the risk is relatively low in heterozygotes.

Interferon- α enhances CD95L-induced apoptosis of human malignant glioma cells

CD95 ligand (CD95L)-induced apoptosis is a novel immunotherapeutic approach to malignant glioma. Here, we report that interferon- α (IFN- α) sensitizes LN-229 and T98G human malignant glioma cells to CD95L-induced apoptosis. In contrast to the effects of IFN- γ and TNF- α which sensitize glioma cells to CD95 antibody-induced apoptosis in part by enhancing CD95 expression, IFN- α has no effect on CD95 expression at the cell surface of LN-229 and T98G cells. To confirm that changes in CD95 expression are not required for the effects of IFN- α, we show that IFN- α enhances CD95L-induced apoptosis even in CD95-transfected LN-308 glioma cells. These LN-308 cells have little endogenous CD95 expression but express high levels of CD95 from a stably integrated CD95 expression plasmid. The sensitizing effects of IFN- α appear to be independent of cell cycle effects of IFN- α and are unaffected by ectopic expression of the bcl-2 proto-oncogene. IFN- α enhances CD95L-induced activation of caspase-3, a critical mediator of CD95L-induced cell death. IFN- α also increases the cytotoxic effects of BCNU, teniposide and cytarabine in both cell lines, and of vincristine in LN-229 cells. Doxorubicin and 5-fluorouracil toxicity are unaffected by IFN- α. IFN- α may be a useful adjunct to novel strategies of immunochemotherapy for malignant gliomas that target CD95-mediated apoptosis.

Effects of levofolinate calcium on subacute intravenous toxicity of 5-fluorouracil in rats.

To clarify whether levofolinate calcium (1-LV) enhances 5-fluorouracil (5-FU) toxicity, a 4-week toxicity study of 5-FU (10 mg/kg/day) in combination with 1-LV (6, 20 or 60 mg/kg/day) was conducted in rats. In the 5-FU alone group, a decrease in body weight gain, food consumption, RBC parameter and WBC counts were detected. Histopathologically, lymphoid depletion of lymphatic organs, hematopoiesis enhancement of the spleen and myelosuppression were observed. In the group for which 5-FU was combined with 1-LV, the RBC counts decreased, extramedullary hematopoiesis increased and the suppression of lymphatic organs was enhanced. Changes in the lymphatic organs were observed at 20 mg/kg/day of 1-LV and above. In monitoring of blood drug concentrations of 1-LV, 5-methyl tetrahydrofolic acid, a metabolite of 1-LV, and 5-FU after the 1st and 14th dosings, there was no apparent difference between 5-FU alone and 5-FU combined with 1-LV in Cmax and AUC0-infinity. The potentiation induced by 1-LV in the toxicity of 5-FU appeared to be mainly immuno-suppression and myelosuppression, which were related to the anti-tumor activity of 5-FU. Plasma concentrations of 5-FU and 1-LV in this study overwhelmed the concentrations that enhancement of thymidylate synthetase (TS) inhibition due to 5-FU was observed by addition of 1-LV in vitro. Therefore toxic potentiation of 5-FU due to simultaneous 1-LV dosing is presumed to be concerned with an increased ternary complex (FdUMP-TS-5,10-methylenetetrahydrofolate) formation and a greater extent of TS inhibition.

Clonogenic Inactivation of Colon Cancer-derived Cells Treated with 5-Fluorouracil and Indomethacin in Hybrid Spheroids

The clonogenic hybrid spheroid assay has been used to determine the toxicity of 5-fluorouracil (5-FU), alone or in combination with indomethacin, in LoVo cells (a human colon adenocarcinoma line). The principal finding was that 5-FU toxicity, determined as loss of colony-forming ability, increased as a function of dose (concentration x duration of exposure), and that indomethacin causes a generalized alleviation of 5-FU toxicity, but only if given concurrently with 5-FU. The implications of these findings in the control of cancer cells by 5-FU are discussed.

Phase II Trial of 5-Fluorouracil and High-Dose Leucovorin in Recurrent Adenocarcinoma of the Cervix: A Gynecologic Oncology Group Study

Objective.The objective of the study was to determine the response rate and associated toxicity of 5-fluorouracil and high-dose leucovorin in patients with recurrent adenocarcinoma of the cervix. Methods.Between December 1993 and October 1995, 53 patients with recurrent adenocarcinoma of the cervix were entered into a Phase II trial utilizing 200 mg/m 2of intravenous (iv) leucovorin with 370 mg/m 2of iv 5-fluorouracil daily for 5 days every 4 weeks for two courses, then every 5 weeks until disease progression. Eligibility criteria were a Gynecologic Oncology Group (GOG) performance status of 0–2, adequate bone marrow reserve, adequate liver function with bilirubin ≤ 1.5× normal and SGOT and alkaline phosphatase ≤ 3× normal, serum creatinine ≤ 2 mg%, and signed informed consent. Standard GOG toxicity and response criteria were employed. Results.Six patients were ineligible because of wrong cell type ( N= 3), insufficient pathology materials ( N= 2), or a second primary ( N= 1); therefore 45 were evaluable for toxicity. Two patients did not have adequate response assessment; thus, 43 were evaluable for response. The median age was 50 (range, 28–79). Prior chemotherapy had been administered to 16 patients and radiotherapy to 40 patients. The median number of courses delivered was three (range, 1–22). The site of evaluable disease was pelvic in 25 patients and extra–pelvic in 18. Grade 3 neutropenia was seen in 17.8% (8/45) patients and 35.5% (16/45) developed grade 4 neutropenia. Grade 3 or 4 thrombocytopenia was seen in 1 patient each (2.1%). Grade 3 gastrointestinal toxicity with nausea, vomiting, diarrhea, dehydration, or stomatitis was of grade 3 severity in 11.1% (5/45) and grade 4 in 6.7% (3/45). There were four partial responses and two complete responses for an overall response rate of 14%. The duration of the complete responses was 17.3 and 8.8+ months. None of the patients with responses had previously received chemotherapy. Conclusion.The schedule of 5-fluorouracil and leucovorin exhibits moderate activity in patients with previously treated adenocarcinoma of the cervix and should be considered for a trial in chemotherapy-naive patients.

Concomitant 5-FU, hydroxyurea and cisplatin with external beam radiation therapy for locally advanced pancreatic cancer

The aim of the study was to determine the efficacy and toxicity of alternate week concurrent 5-fluorouracil, hydroxyurea, and cisplatin with radiotherapy for locally advanced pancreatic adenocarcinoma. Patients received 5-fluorouracil, hydroxyurea and cisplatin with radiotherapy on an alternate week basis. Chemoradiotherapy was given day 1-5, and no therapy given day 6-14 for each 14 day cycle. Chemotherapy doses were as follows: hydroxyurea 1 mg every 12 h starting day 0, 5-fluorouracil 800 mg/m(2)/day for 5 days starting day 1, and cisplatin 20 mg/m(2) daily for 5 days every other cycle. A radiation dose of 6000 cGy was prescribed. Acute toxicities were monitored and therapy modified for hematologic toxicity. Nine patients enrolled, however eight were evaluable; one patient expired prior to therapy. The median radiation dose delivered was 5540 cGy. Sixty-three percent required a chemotherapy dose reduction. Fifty percent achieved local control by radiographic imaging after completion of therapy. Median survival was 12 months. Acute toxicity included: 38% grade 2-3 nausea, 37% grade 2-3 vomiting, 63% grade 2-3 mucositis, 63% grade 2-3 neutropenia, and 88% grade 3-4 thrombocytopenia. Other sequelae included hand-foot syndrome, deep venous thrombosis, hearing loss, seizures, and anorexia. Patients achieved the same median survival as compared to other reported studies of radiation therapy with single agent 5-fluorouracil. We do not recommend this protocol due to the significant toxicity. Future studies to incorporate conformal radiation therapy with more active, less toxic chemotherapeutic agents should be investigated.

Platelet-derived endothelial cell growth factor thymidine phosphorylase in tumour growth and response to therapy.

Angiogenesis plays an important role in the growth and metastasis of solid tumours. Platelet-derived endothelial cell growth factor (PD-ECGF) is known to be chemotactic for endothelial cells in vitro and angiogenic in vivo. It is also known as gliostatin, a factor promoting neuronal survival, and thymidine phosphorylase (dThdPase), which catalyses the reversible phosphorylation of thymidine to thymine and 2-deoxyribose-1-phosphate. This enzymatic activity is critical for angiogenic activity. PD-ECGF protein is highly expressed in tumours compared with most normal tissues and has been correlated with tumour growth, invasion and metastasis in clinical studies. In addition, dThdPase activity (by inference PD-ECGF) has been found to be a major determinant of the toxicity of 5-fluorouracil and its prodrugs, which are extensively studied clinically as anti-cancer agents. This review attempts to summarize recent gains in understanding the nature, location and action of PD-ECGF and its specific relevance to tumour biology.

Semi-automated radioassay for determination of dihydropyrimidine dehydrogenase (DPD) activity screening cancer patients for DPD deficiency, a condition associated with 5-fluorouracil toxicity

Dihydropyrimidine dehydrogenase (DPD) catalyzes the reduction of the naturally occurring pyrimidines, uracil and thymine, and the fluoropyrimidine anticancer drug, 5-fluorouracil (FUra) to 5,6-dihydropyrimidines. Previous studies have demonstrated that cancer patients who are DPD deficient exhibit severe toxicity (including death) following treatment with FUra. To date, the direct measurement of DPD enzyme activity has been the only reliable method to identify DPD deficient cancer patients. We now report a semi-automated radioassay for measuring DPD activity in human peripheral lymphocytes. Following incubation of lymphocyte cytosol (at a fixed protein concentration of 200 μg) with [6- 14C]FUra at timepoints ranging from 0 to 30 min, samples are ethanol precipitated, filtered and analyzed by HPLC. Determination of radioactivity is accomplished using an in-line flow scintillation analyzer with automatic quantitation of peaks. This method provides the first specific assay for DPD enzyme activity which is rapid, reproducible and sensitive enough to be used in the routine screening of cancer patients for DPD deficiency prior to treatment with FUra.

Fluorouracil and High-dose Leucovorin with Radiotherapy as Adjuvant Therapy for Rectal Cancer: Results of a Phase II Study

The purpose of this phase II study was to evaluate the efficacy and toxicity of fluorouracil and high-dose leucovorin (5-FU/LV) with pelvic irradiation as adjuvant therapy for patients with macroscopical resected rectal or recto-sigmoid cancer. Following surgery for stages II-III primary (52) or recurrent rectal cancer (4), 56 patients received 8 cycles of 5-FU/LV and pelvic irradiation. 5-FU doses were 200 mgr/m2 for cycles 2–3 and 300 mgr/m2 for cycles 1 and 4–8. LV doses remained fixed at 200 mgr/m2. Pelvic radiation was started in the third week, between the first and second cycle. The total dose was 50.4 Gy. No severe complications had been recorded. The incidence of grade 3 diarrhea was 19%. Three patients presented leukopenia grade 3 (5%). In 44 patients (78%) the planned treatment could be administered. The median follow-up was 40 months (range 22–66). Seven patients had a local relapse (13%) and 6 developed distant metastasis (10%). The 3-year disease-free survival was 72% and the overall survival was 76%. These preliminary results show that combined post-operative 5-FU/LV and pelvic radiotherapy are well tolerated and present a reasonable local control and survival rates. This adjuvant treatment should be evaluated in randomized trials.

Tiazofurin enhances the anabolism and toxicity of 5-fluorouracil.

Tiazofurin, a clinically active anticancer agent, is undergoing additional clinical testing in combination with other agents. We found that tiazofurin is an effective biochemical modulator of 5-fluorouracil anabolism. Pretreatment of cultured L1210 cells with tiazofurin at concentrations of 1-100 microM results in an increase in the rate of conversion of 5-fluorouracil to phosphorylated metabolites. Concentrations of tiazofurin effective in increasing 5-fluorouracil anabolism cause a corresponding increase in the 5-phosphoribosyl-1-pyrophosphate pool. Studies in mice show that tiazofurin increases the lethal toxicity of 5-fluorouracil and increases the antitumor effectiveness of low doses of 5-fluorouracil: however, the combination is not more effective than an optimal dose of 5-fluorouracil given alone. These results indicate that caution should be exercised in the concurrent use of tiazofurin with other drugs, particularly 5-fluorouracil, that require 5-phosphoribosyl-1-pyrophosphate for activation or that are affected by a decrease in pyrimidine nucleotide synthesis.

Neoadjuvant Chemotherapy with Continuous Infusion of Cisplatin and Fluorouracil in Stage II-IV, M0 Squamous Cell Carcinoma of the Head and Neck

The aim of the study was to assess the activity and the toxicity of cisplatin (DDP) and fluorouracil (FU) administered by continuous infusion as neoadjuvant chemotherapy for patients with stage II-IV, M0 squamous cell carcinoma of the head and neck. Thirty previously untreated patients were submitted to chemotherapy with DDP (20 mg/m2) and FU (1000 mg/m2), both in continuous infusion for 5 days, repeated every 21 days, for a maximum of 5 cycles. Following completion of chemotherapy, the patients underwent radiotherapy; in some patients surgery was performed immediately after chemotherapy. All patients were monitored for response, time to failure, survival, treatment-related events and toxicity. All patients were evaluated for response; after chemotherapy the complete response rate was 27% and the partial response rate 33%. Twenty-four patients underwent radiotherapy: the overall response rate was 83% (complete response 79%). After a median follow-up of 34 months, the median survival time was 22 months with a median time to failure of 15 months. Acute vascular accidents were the main and unexpected adverse events, with 2 deaths for pulmonary embolism and 1 for stroke. The response rate to the regimen does not seem to be better than that obtained with the standard combination of cisplatin bolus and fluorouracil continuous infusion. The disadvantage of the regimen is that it causes more discomfort for the patient in that it requires hospitalization. For this reason, we believe that there are no elements for recommending the schedule as neoadjuvant treatment of patients with squamous cell carcinoma of the head and neck or as an experimental arm in a randomized trial.

Randomized trial assessing the addition of interferon alpha-2a to fluorouracil and leucovorin in advanced colorectal cancer. Colorectal Cancer Working Party of the United Kingdom Medical Research Council.

To determine the effects of interferon alpha-2a (IFN alpha) on the efficacy and toxicity of fluorouracil (FUra) and leucovorin (LV) in patients with advanced colorectal cancer. Two hundred sixty chemotherapy-naive patients were randomized to FUra/LV alone or FUra/LV plus IFN alpha. All patients received: LV 200 mg/m2 intravenous (IV) infusion over 2 hours, then FUra 400 mg/m2 i.v. bolus plus 400 mg/m2 i.v. infusion over 22 hours, all repeated on day 2. Treatment was every 2 weeks for up to 12 cycles. Patients randomized to IFN alpha received 6 x 10(6) IU subcutaneously every 48 hours throughout. Objective response (OR) and toxicity were assessed conventionally; in addition, palliative benefit and adverse effects were assessed using quality-of-life (QoL) questionnaires. There were no differences in OR rate, progression-free survival, or overall survival. OR rates in assessable patients were as follows: FUra/LV alone (n = 104), complete or partial response (OR) = 27%, no change (NC) = 34%; FUra/LV/IFN alpha (n = 101), OR = 28%, NC = 30%. Median survival was 10 months in both arms. Dose-limiting FUra toxicities were not significantly increased by co-administration of IFN alpha, and the delivered FUra dose-intensity was not significantly reduced. However, QoL was adversely affected: patients on IFN alpha were less likely to report improvement in pretreatment physical and psychologic symptoms, and more likely to report new or worsening symptoms. IFN alpha, at a dose that impaired QoL, did not improve the efficacy of FUra/LV. The power of this trial is sufficient to exclude with 95% confidence a benefit of 15% in OR or 10 weeks in median survival. Accordingly, we cannot recommend the use of IFN alpha as a clinical modulator of FUra/LV in the treatment of advanced colorectal cancer.

Molecular basis of the human dihydropyrimidine dehydrogenase deficiency and 5-fluorouracil toxicity.

Dihydropyrimidine dehydrogenase (DPD) deficiency constitutes an inborn error in pyrimidine metabolism associated with thymine-uraciluria in pediatric patients and an increased risk of toxicity in cancer patients receiving 5-fluorouracil (5-FU) treatment. The molecular basis for DPD deficiency in a British family having a cancer patient that exhibited grade IV toxicity 10 d after 5-FU treatment was analyzed. A 165-bp deletion spanning a complete exon of the DPYD gene was found in some members of the pedigree having low DPD catalytic activity. Direct sequencing of lymphocyte DNA from these subjects revealed the presence of a G to A point mutation at the 5'-splicing site consensus sequence (GT to AT) that leads to skipping of the entire exon preceding the mutation during pre-RNA transcription and processing. A PCR-based diagnostic method was developed to determine that the mutation is found in Caucasian and Asian populations. This mutation was also detected in a Dutch patient with thymine-uraciluria and completely lacking DPD activity. A genotyping test for the G to A splicing point mutation could be useful in predicting cancer patients prone to toxicity upon administration of potentially toxic 5-FU and for genetic screening of heterozygous carriers and homozygous deficient subjects.

Permeability of 5-fluorouracil and prodrugs in Caco-2 cell monolayers

The toxicity and permeability of 5-fluorouracil (5FU) and 13 5FU prodrugs was investigated in Caco-2 monolayers grown on permeable supports. Only one of the prodrugs (VII) was toxic to the cell monolayers at 1 × 10 −4 M, as assessed by an increased permeability of the cell monolayers to the hydrophilic probe 14C-mannitol. The monolayer integrity was restored after a 4-fold reduction in the concentration of this prodrug. The permeabilities of 5FU and prodrugs increased roughly with the apparent partition coefficients ( P octanol-buffer) ( r = 0.74). Attempts to correlate the permeabilities with other single physicochemical parameters such as hydrogen-bonding capacity and solubility resulted in poorer correlations. A slightly better relationship was obtained when the permeability was correlated with the two physicochemical parameters ( P octanol-buffer) and aqueous solubility by multiple linear regression analysis ( r = 0.81). The ranking of the permeabilities of four of the compounds previously studied in rabbit colon and rectum was comparable in the cell monolayers and in the intestinal segments. These results indicate that Caco-2 monolayers can be used to predict drug absorption, not only of conventional drugs but also of small prodrugs such as those used here.