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PubMed1997

Neoadjuvant chemotherapy with cisplatin and 5-fluorouracil in advanced squamous cell carcinoma of the head and neck: a randomized phase III study.

BACKGROUND AND PURPOSE: In 1986 a prospective, randomized, multi-centre trial for evaluation of neoadjuvant chemotherapy with cisplatin and 5-fluorouracil in the treatment of advanced squamous cell carcinoma of the head and neck was initiated. As survival in this group of patients is poor the purpose was to find a possible survival benefit of the chemotherapy in addition to radiotherapy compared to radiotherapy only. METHODS: Four-hundred sixty-one patients from Denmark, Norway and Sweden with tumors in oral cavity, oropharynx, hypopharynx and larynx were randomized to receive either standard treatment (radiotherapy or radiotherapy followed by surgery) or neoadjuvant chemotherapy followed by standard treatment. Chemotherapy included three courses of cisplatin 100 mg/m2 i.v. infusion on day 1 followed by 5-fluorouracil 1000 mg/m2 per day continuous i.v. infusion for 120 hours. Radiotherapy 64-70 Gy in 2 Gy per fraction, 5 times/week, was given to patients in both treatment arms. RESULTS: Response rate was 71% for patients randomized to chemotherapy-radiotherapy and 66% for patients randomized to standard treatment (not statistically significant). Residual tumors were excised if possible. After surgery 62% of the patients randomized to chemotherapy-radiotherapy and 60% of the patients in the standard treatment group were clinically tumor free. CONCLUSIONS: No statistically significant benefit in survival was observed for patients treated with neoadjuvant chemotherapy followed by radiotherapy. Nor was there any impact of chemotherapy on the number of patients achieving loco-regional tumor control after primary treatment.

Adult↗
PubMed2003

Microsphere design for the colonic delivery of 5-fluorouracil.

The treatment of colon cancer has been aimed by approaches of oral drug administration. 5-Fluorouracil is the standard treatment still nowadays and would be a candidate to be delivered orally to the colon. A pH-sensitive polymer Eudragit P-4135F was used to prepare microspheres by a simple oil/water emulsification process. Process parameters were analyzed in order to optimize the drug loading and release profiles. In further attempts mixtures with Eudragit RS100 were prepared to prolong drug release. Scanning electron microscopy and confocal laser scanning microscopy permitted a structural analysis. The solvent extraction was preferable over solvent evaporation with a view to the encapsulation rate (extraction: 37%; evaporation: 19%) due to the hydrophilic character of the drug while release pattern were nearly unchanged. Eudragit P-4135F, pure or in mixture, was found to retain drug release at pH 6.8 lower than 35% within 6 h. At pH 7.4, nearly immediate release (within 30 min) was observed for pure P-4135F, while mixtures enabled to prolong the release slightly. Analysis of the morphology led to an inhomogeneous polymer distribution of P-4135F and RS100 throughout the particle core. A capsule-like structure was concluded which allowed only slight changes of the release kinetics by the addition of RS100. However, the formulation proved its applicability in-vitro as a promising device for pH-dependent colon delivery of 5-fluorouracil.

Acrylic Resins↗
PubMed1998

In vitro drug release from self-catalyzed poly(ortho ester): case study of 5-fluorouracil.

Self-catalyzed poly(ortho esters) are a new variation of linear poly(ortho esters) prepared by the addition of diols to the diketene acetal 3,9-diethylidene-2,4,8,10-tetraoxaspiro[5,5]undecane where dimer segments of lactic acid or glycolic acid are built into the polymer backbone. By varying the concentration of these segments, polymer erosion rate can be controlled. The present investigation describes the in vitro drug release characteristics from these new polymers. Because poly(ortho esters) have potential applications for the delivery of antifibroblastic agents for example after glaucoma-filtering surgery, the in vitro release studies were evaluated using 5-fluorouracil as the active compound. It was shown that a mole ratio of 90/10 or 80/20 diol/diol-lactate incorporated into the polymer lead to a release of 5-fluorouracil by an erosion process. Smaller amounts of diol-lactate lead to a concomitant drug release by diffusion and erosion. It was also shown that the release rate depends on the alkyl chain length of the diol in the polymer backbone but it does not depend on the drug loading.

Catalysis↗
PubMed1982

Treatment of multiple keratoacanthomas with intralesional fluorouracil.

A keratoacanthoma is a benign epithelial growth most often found in sun-exposed skin of the elderly. Two main groups of multiple keratoacanthomas have been described: the Ferguson-Smith type and the Grzybowski type. A patient with multiple keratoacanthomas of the Ferguson Smith type is described and the treatment with intralesional 5-fluorouracil is explained. Intralesional therapy with 5-fluorouracil is a safe treatment and may be the treatment of choice for multiple keratoacanthomas and solitary lesions which are difficult to remove surgically.

Fluorouracil↗
PubMed1988

Scrotal dermatitis caused by 5-fluorouracil (Efudex).

Four patients are described who experienced an acute episode of eczematous dermatitis of the scrotum where 5-fluorouracil (Efudex) cream had inadvertently been applied in the course of treating warts and keratoses. The reaction was not allergic in origin but resulted from the unique absorptive capabilities of scrotal skin, which permitted entrance and local toxic effects of 5-fluorouracil.

Adolescent↗
PubMed2002

[Angina related to 5-Fluorouracil].

Treatment with 5-fluorouracil is common in oncological patients. Side effects on bone marrow, skin, and mucous membranes have been reported. Cardiotoxicity, which is less predictable, can be life-threatening. Manifestations include angina, arrhythmias, infarction, heart failure and cardiogenic shock. The toxic mechanisms that might be involved have been much discussed but have not yet been clearly established. Current evidence supports the possibility of a metabolic effect in common with the cascade secondary to ischemia due to coronary disease. Based on a case report, we discuss the usual clinical presentation, treatment and prognosis. Finally we make recommendations for managing patients being treated with 5-fluorouracil.

Adenocarcinoma↗
PubMed2001

Dual role of vitamin C on lipid profile and combined application of cyclophosphamide, methotrexate and 5-fluorouracil treatment in fibrosarcoma-bearing rats.

Combined application of cyclophosphamide, methotrexate, 5-fluorouracil (CMF) has been followed in the treatment of breast cancer. The combined effect of CMF and vitamin C on plasma lipid and lipoprotein is important, since vitamin C encumbers the lipid abnormalities instigated by CMF. Hence, the study was launched to appraise the salubrious role of vitamin C in CMF administered fibrosarcoma-bearing rats. Fibrosarcoma cell line-induced rats were treated with CMF (cyclophosphamide 10 mg/kg b.w., methotrexate 1 mg/kg b.w., 5-fluorouracil 10 mg/kg b.w. and vitamin C 200 mg/kg b.w.) individually and in combination for 120 days. The concentration of plasma lipids and lipoprotein was determined in control and experimental rats. The untreated as well as CMF administered fibrosarcoma-bearing rats divulged significantly in increased levels of plasma total cholesterol, triglycerides, phospholipids, very low density lipoprotein (VLDL) and low density lipoprotein (LDL) cholesterol, as compared with their respective control animals. Whereas ester and high density lipoprotein (HDL) cholesterol levels exhibited a marked decrease in these animals. However, these lipid abnormalities were found to be moderated by co-administration of vitamin C. These results suggested that some clinical entanglement of CMF was refrained by co-administration of vitamin C in tumor stress condition.

Animals↗
PubMed1998

Dose rate effectiveness and potentially lethal damage repair in normal and double-strand break repair deficient murine cells by gamma-rays and 5-fluorouracil.

SCID (severe combined immunodeficiency) fibroblasts established from C.B 17-scid/scid embryos showed higher sensitivity to high (1.105 Gy/min) and low (0.00069 Gy/min) dose rate gamma-rays and also to 5-fluorouracil, a cancer sedative producing double-strand breaks, than wildtype cells from C.B17- +/+ embryos. Furthermore, SCID cells were deficient in repairing DNA damage induced by high dose rate gamma-rays even after dose fractionation and after 24 h recovery periods, while wildtype cells showed an apparent repair ability on DNA damage after these gamma-ray exposures. This is the first report to prove that SCID cells lack the repair of gamma-ray-induced potentially lethal damage and also of 5-fluorouracil-induced double-strand breaks. However, SCID cells showed a significantly higher survival rate by low dose rate exposure than by high dose rate exposure as in the case of wildtype cells, indicating that SCID cells have a deficiency in DNA repair for high dose rate gamma-rays, but not for low dose rate exposure. This suggests an important finding that the dose rate effect (diminution of cell killing by low dose rate exposure) is caused not only by the repair of double-strand breaks induced by gamma-rays but in most parts by less yields of double-strand breaks due to dispersed or low intensity ionization in the cell.

Animals↗
PubMed2001

RTOG 96-10: reirradiation with concurrent hydroxyurea and 5-fluorouracil in patients with squamous cell cancer of the head and neck.

PURPOSE: Patients with recurrent squamous cell cancer of the head and neck (SCH&N) are generally treated with systemic chemotherapy. Improvement in survival has not occurred, despite an increased objective response rate. This study was undertaken to explore the feasibility and toxicity, and estimate the therapeutic impact of, reirradiation (RRT) with concurrent hydroxyurea and 5-fluorouracil. METHODS AND MATERIALS: The eligibility requirements included SCH&N presenting as a second primary or recurrence > or =6 months after definitive RT to > or =45 Gy, with > or =75% of the tumor volume within the previous field. The cumulative spinal cord dose was limited to 50 Gy, and measurable disease was required. Four weekly cycles were given, each separated by 1 week of rest. A cycle consisted of 5 days, Monday through Friday, of 1.5-Gy twice-daily repeated RT, with the fractions separated by > or =6 h, with 1.5 g of hydroxyurea given 2 h and 300 mg/m2 of a 5-fluorouracil IV bolus given 30 min before each second daily fraction. RESULTS: Eighty-six patients were entered; 81 patients were assessable. The median prior radiation dose was 61.2 Gy. The 4 planned cycles were delivered in 79% of patients. Grade 3 mucositis occurred in 14% of patients, and Grade 4 in 5%. Grade 3 acute pharyngeal toxicity was seen in 17%. Grade 3 neutropenia occurred in 9%, Grade 4 in 10%, and Grade 5 in 7%. Six patients died of treatment-related toxicity. Two died of hemorrhage from the tumor site without thrombocytopenia. With a median follow-up of 16.3 months for living patients, the estimated median overall survival was 8.2 months and the estimated 1-year survival rate 41.7%. Patients treated >3 years after the previous RT had a 1-year survival rate of 48% compared with 35% for patients treated within 3 years (p = 0.017). The 1-year survival rate for patients with a second primary was 54% compared with 38% for patients with recurrence (p = 0.083). CONCLUSION: Repeated RT with concurrent chemotherapy as given in this study is a feasible approach for selected, previously irradiated patients with SCH&N and may produce increased median and 1-year survival rates compared with systemic chemotherapy trials reported in the literature. A randomized study should be conducted to compare these two different approaches.

Adult↗
PubMed2004

Toxic cure: Hyperfractionated radiotherapy with concurrent cisplatin and fluorouracil for Stage III and IVA head-and-neck cancer in the community.

PURPOSE: To evaluate efficacy and toxicity of the Duke University chemoirradiation regimen for locally advanced head-and-neck cancer in a regional community cancer center. METHODS AND MATERIALS: Between June 1998 and June 2002, 50 patients with Stage III or IVA squamous cell carcinoma of the head and neck were treated definitively with concurrent combined modality therapy (CMT). Patients received accelerated, hyperfractionated radiotherapy (AFRT), 1.2-1.25 Gy b.i.d., to a median prescribed dose of 70 Gy. Chemotherapy consisted of cisplatin 12 mg and fluorouracil 600 mg/m(2) daily for 5 consecutive days during Weeks 1 and 6, followed by two cycles after AFRT. Patients with N2-N3 neck disease (n = 21; 42%) were considered for neck dissection depending on their response to AFRT and chemotherapy. Twenty-nine patients with Stage III and IVA disease treated between 1991 and 1997 with definitive RT alone served as historical controls. RESULTS: Forty-nine patients (98%) in the CMT group completed the prescribed AFRT and 38 (76%) completed four cycles of chemotherapy. Three of 8 patients who underwent neck dissection had a pathologically complete response. The median follow-up for all patients was 23 months. The actuarial progression-free survival rate at 2 years was 75% for the CMT group vs. 40% (p <0.01) for the RT group. The overall survival rate was 80% and 43% (p <0.01), respectively, for the CMT and RT groups. Acute Radiation Therapy Oncology Group Grade 3 toxicities for the CMT group were mucosal (n = 50; 100%), skin (n = 9; 18%), and hematologic (n = 3; 6%). Late Grade 3-4 toxicities consisted of pharyngeal stricture (n = 7; 14%), laryngeal chondritis (n = 3; 6%), osteoradionecrosis (n = 2; 4%), and peripheral neuropathy (n = 1; 2%). CONCLUSION: This aggressive regimen of AFRT with concurrent cisplatin and fluorouracil with or without neck dissection is feasible in the community setting for patients with Stage III and IVA head-and-neck cancer. Early results indicated excellent survival, albeit with universal acute mucosal, and considerable, although acceptable, late toxicity.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1999

Preoperative chemoradiation with cisplatin and 5-fluorouracil for extraperitoneal T3 rectal cancer: acute toxicity, tumor response, sphincter preservation.

PURPOSE: To evaluate the impact of preoperative external radiation therapy intensified by systemic chemotherapy including bolus cisplatin (c-DDP) and 4-day infusional 5-fluorouracil (PLAFUR-4) on tumor response and sphincter preservation in patients with extraperitoneal T3 rectal cancer with acceptable toxicity, and to compare the results to our previous experience with bolus mitomycin c (MMC) and 4-day infusion 5-FU (FUMIR). METHODS AND MATERIALS: Between October 1995 and March 1998, 40 consecutive patients with resectable extraperitoneal adenocarcinoma of the rectum were treated with preoperative chemoradiation: slow infusion i.v. c-DDP, 60 mg/m2, day 1 and 29 plus 24-h continuous infusion i.v. 5-fluorouracil (5-FU) 1000 mg/m2, days 1-4 and 29-32, and concurrent external beam radiotherapy (45 Gy whole pelvis followed by 5.4 Gy boost). All but 3 patients had T3 disease. Surgery was performed 6-8 weeks after the end of chemoradiation. RESULTS: No patient had Grade 4 acute toxicity. Grade 3 hematological toxicity was observed only in 2 (5%) patients. No patient had major gastrointestinal, skin, or urological acute toxicity. All patients had radical surgery. There was no perioperative mortality; perioperative morbidity rate was 12%. Overall, 23% (9 of 40) of patients had a complete pathological response and 10% (4 of 40) of patients had rare isolated residual cancer cells (Tmic). Comparing the stage at the diagnostic workup with the pathological stage, tumor downstaging was observed in 27 (68%) patients; nodal status downstaging was detected in 24 (60%) patients. Thirty-four (85%) patients had a sphincter-saving surgical procedure. In 4 of 10 (40%) patients who were definitive candidates for an abdominoperineal resection (APR), the sphincter was preserved, as it was in 13 of 13 (100%) probable candidates. Lengthening of the distance between the anorectal ring and the lower pole of the tumor > or =20 mm was observed in 9 (23%) patients. None of the patients had soilage after the sphincter-saving procedure. In our previous experience with FUMIR the complete pathological response was 9%, the sphincter-saving surgical procedure was performed in 66% cases, and the Grade 3+ toxicity was observed in 13% of patients. CONCLUSIONS: The addition of c-DDP to 5-FU (PLAFUR-4) in a neoadjuvant radiochemotherapy schedule improved the pathological response rate in comparison with our previous experience. Toxicity was low indeed, thus we commenced another study adding one more day of 5-FU infusion (PLAFUR-5) to further improve our results.

Adult↗
PubMed1981

Quantitative determination of 1-hexylcarbamoyl-5-fluorouracil and its metabolites in man.

A high-performance liquid chromatographic (HPLC) method for the quantitative determination of 1-hexylcarbamoyl-5-fluorouracil (HCFU) and its metabolites using mu Bondapak C18 and mu Porasil has been developed. Two mobile phases containing PIC-B7 (consisting of acetic acid and 1-heptanesulphonic acid) were used for the separation, and good separations were obtained. With methanol-water (56:44) as the mobile phase, the separation of HCFU and its three metabolites was achieved within 4 min. With methanol-water (32:68) a new metabolite, 1-omega-carboxymethylcarbamoyl-5-fluorouracil, was revealed in human plasma. The recovery of each substance was 80% or greater and the sensitivity was at the nanograms per millilitre level. The coefficient of variation was less than 3.6% for each component.

Chromatography, High Pressure Liquid↗
PubMed1988

Determination of 5-fluorouracil in plasma and whole blood by ion-pair high-performance liquid chromatography.

5-Fluorouracil in blood or plasma was determined by extraction and column liquid chromatography. Acetonitrile was added to blood or plasma and the mixture was stirred and centrifuged. Zinc sulfate addition was followed by stirring and centrifuging. The acetonitrile was salted out with ammonium sulfate, and an aliquot was evaporated with nitrogen. The residue was dissolved in mobile phase and chromatographed. The stationary phase was a styrene-divinylbenzene copolymer, and the mobile phase was 10 mM tetrabutylammonium hydroxide-methanol (74:26). 5-Fluorouracil was detected by UV absorption at 266 nm. Time of the assay was less than 30 min. The detection limit was 10 ng/ml and the relative standard deviation was 4 to 10% depending on the concentration.

Chromatography, High Pressure Liquid↗
PubMed1985

Highly sensitive determination of 5-fluorouracil in human plasma by capillary gas chromatography and negative ion chemical ionization mass spectrometry.

A sensitive method using gas chromatography and electron-capture negative ion mass spectrometry for the determination of 5-fluorouracil in plasma is described. 5-Chlorouracil was used as internal standard. Sample clean-up consisted of extraction of the 5-halogenated uracil derivatives with 2-propanol--diethyl ether (22:78, v/v) at pH 6, followed by a back-extraction into aqueous buffer at pH 10.5. Pentafluorobenzyl derivatives of 5-fluoro- and 5-chlorouracil were prepared by extractive alkylation with pentafluorobenzyl bromide with dichloromethane as solvent and tetrabutylammonium as counter-ion. The limit of sensitivity employing this technique was 50 fg on-column. Quantitation in human plasma was possible down to 3 X 10(-9) M (0.39 ng/ml). Mass fragmentographic analysis of 5-fluorouracil in plasma of patients after a bolus injection of 500 mg/m2 is presented. Plasma concentrations could be determined for at least 8 h after administration.

Alkylation↗
PubMed2000

Combined versus sequential phacotrabeculectomy with intraoperative 5-fluorouracil.

PURPOSE: To determine and compare the intraocular pressure (IOP) lowering effects of single-incision combined phacoemulsification and trabeculectomy with phacoemulsification done after previous trabeculectomy, both with an intraoperative dose of 5-fluorouracil (5-FU). SETTING: Hospital Del Salvador Ophthalmology Service, Clínica Oftalmológica Pasteur, Santiago, Chile. METHODS: The effects on IOP after phacoemulsification in eyes with previous trabeculectomy using intraoperative 5-fluorouracil (5-FU) (Group 1, n = 18) were compared with those in a matched group of eyes having combined phacoemulsification and trabeculectomy, also with intraoperative 5-FU (Group 2, n = 22). The mean postoperative IOPs and survival curves for IOP values less than 20 mm Hg and 15 mm Hg or less were determined in both groups. Data were retrospectively collected. Comparisons were made with the paired Student t test, and survival curves were compared using log-rank analysis. RESULTS: Mean postoperative IOP without medications was 12.6 mm Hg in Group 1 and 12.2 mm Hg in Group 2 (P = .64). Group 2 had a significant postoperative decrease in IOP (P = .0575); Group 1 did not have a significant increase or decrease. There was no significant difference in the survival curves between groups using arbitrarily defined failure criteria: (1) IOP greater than 15 mm Hg or (2) IOP equal to or greater than 20 mm Hg, both without medication (log-rank analysis, P = .333 and P = 1.00, respectively). CONCLUSION: Combined cataract and glaucoma surgery with intraoperative 5-FU was associated with good long-term IOP control similar to that after phacoemulsification with intraoperative 5-FU in eyes with previous trabeculectomy.

Aged↗
PubMed1998

Dose-response effect of adjuvant cyclophosphamide, methotrexate, 5-fluorouracil (CMF) in node-positive breast cancer. International Breast Cancer Study Group.

There is evidence in the literature of a relationship between dose and response to adjuvant chemotherapy for breast cancer, although published results are conflicting. We therefore retrospectively analysed the role of dose response in patients included in four adjuvant trials of the International Breast Cancer Study Group (IBCSG, formerly the Ludwig Breast Cancer Study Group (trials I, II, III and V), all using 'classical' cyclophosphamide, methotrexate, and 5-fluorouracil (CMF). A total of 1385 node-positive patients were treated with oral cyclophosphamide, and intravenous methotrexate plus 5-fluorouracil (CMF) for at least six 4 week courses. 1350 of these were included in 6 month landmark treatment outcome analyses. A total of 1029 patients were premenopausal, 321 were postmenopausal; 800 had one to three and 550 more than three involved axillary nodes at surgery. The median follow-up ranged from 12 years for trial V to 15 years for trials I-III. Patients were grouped according to three prospectively defined dose levels based on the percentage of the protocol prescribed dose that was actually administered (level I > or = 85%, level II 65-84%, level III < 65%). Patients who received dose level II had a higher disease-free (P = 0.07) and overall survival (P = 0.03) than those who received a higher (level I) or lower (level III) percentage. The 10 year overall survival was 60% for dose level II, 56% for dose level I, 51% for dose level III. The results were generally consistent within trial, menopausal status, and oestrogen receptor status groups. The results within nodal groups showed a large difference among the dose levels for the group with one to three positive nodes (P = 0.02), but no difference for the group with four or more positive nodes. Our results indicate that the dose-response effect remains a crucial factor in adjuvant chemotherapy of breast cancer. Reductions larger than 35% in the dose administered of oral CMF adversely influenced the outcome of breast cancer patients and should be avoided. The better outcome of the intermediate dose group indicates the need to investigate other aspects involved in the cytotoxicity of adjuvant CMF chemotherapy.

Adult↗
PubMed1999

Doxorubicin versus methotrexate both combined with cyclophosphamide, 5-fluorouracil and tamoxifen in postmenopausal patients with advanced breast cancer--a randomised study with more than 10 years follow-up from the Danish Breast Cancer Cooperative Group. Danish Breast Cancer Cooperative Group (DBCG).

To evaluate the substitution of methotrexate with doxorubicin (Dox) in CMF-(cyclophosphamide, methotrexate, 5-fluorouracil) containing regimen for advanced breast cancer, 415 postmenopausal patients below the age of 66 years, naïve to chemotherapy, were accrued from 1980 to 1984 and followed-up until 1995. They received tamoxifen 30 mg daily orally and by randomisation either 400 mg/m2, cyclophosphamide, 25 mg/m2 doxorubicin and 500 mg/m2 5-fluorouracil (CAF) or 40 mg/m2 methotrexate instead of Dox (CMF) intravenously (i.v.) days 1 + 8 repeated every 4 weeks. Dox was substituted by methotrexate at a cumulative dose of 550 mg/m2. Among 341 eligible patients the response rate and median time to progression was significantly in favour of CAF: 53% CAF versus 36% CMF (P = 0.002) and 11.8 months CAF versus 6.5 months CMF (P = 0.001). Median duration of response was 19.5 CAF versus 18.0 CMF months, and survival 20.8 CAF versus 17.4 CMF months (non-significant). The two regimens were equimyelotoxic. There were no treatment-related fatalities but 1 patient with congestive heart failure on CAF was reported. Nausea/vomiting, stomatitis and infections were modest in both groups, whilst alopecia was more common with CAF. Regression analysis showed that long recurrence free interval, good performance status, and no visceral involvement was significantly related to long-term survival, whilst the treatment regimen was not. It is concluded that in chemotherapy-naïve patients with advanced breast cancer Dox-containing regimens are superior and remain the first choice of chemotherapy, especially in patients with visceral metastases, until newer drugs and combinations have been proven to be superior.

Adult↗
PubMed1992

Solution structure of the EcoRI DNA octamer containing 5-fluorouracil via restrained molecular dynamics using distance and torsion angle constraints extracted from NMR spectral simulations.

The self-complementary DNA octamer [d(GGAATUFCC)]2, containing the EcoRI recognition sequence with one of the thymines replaced by 5-fluorouracil (UF), was synthesized. Proton homonuclear two-dimensional nuclear Overhauser effect (2D NOE) and double-quantum-filtered correlation (2QF-COSY) spectra, as well as one-dimensional spectra at different temperatures, were recorded for the octamer. Consequently, all proton resonances were assigned. The thermally induced transition from the duplex to single strands has been followed, demonstrating the stability of the duplex containing 5-fluorouracil. Simulations of the 2QF-COSY cross-peaks by means of the programs SPHINX and LINSHA were compared with experimental data, establishing scalar coupling constants for the sugar ring protons and hence sugar pucker parameters. The deoxyribose rings exhibit a dynamic equilibrium of N- and S-type conformers with 75-95% populations of the latter. Two programs used for complete relaxation matrix analysis 2D NOE spectra, CORMA and MARDIGRAS, were modified to account for the influence of the fluorines on dipolar interactions in the proton system. Quantitative assessment of the 2D NOE cross-peak intensities for different mixing times, in conjunction with the program MARDIGRAS, gave a set of interproton distances for each mixing time. The largest and smallest values of each of the interproton distances were chosen as the upper and lower bounds for each distance constraint. The distance bounds define the size of a flat-well potential function term, incorporated into the AMBER force field, which was employed for restrained molecular dynamics calculations. Torsion angle constraints in the form of a flat-well potential were also constructed from the analysis of the sugar pucker data. Several restrained molecular dynamics runs of 35 ps were performed, utilizing 284 experimental distance and torsion angle constraints and two different starting structures, energy-minimized A- and B-DNA. Convergence to similar structures with a root-mean-square deviation of 1.2 A was achieved for the central hexamer of the octamer, starting from A- and B-DNA. The average structure from six different molecular dynamics runs was subjected to final restrained energy minimization. The resulting final structure was in good agreement with the structures derived from different molecular dynamics runs and showed a substantial improvement of the 2D NOE sixth-root residual index in comparison with classical and energy-minimized B-DNA. A detailed analysis of the conformation of the final structure and comparison with structures of similar sequences, obtained by different methods, were performed.

Deoxyribonuclease EcoRI↗