5-Fluorouracil, measurement

The hydrate formed by photolysis of this substance is one of the few such products (the others are uracil hydrate, 5-fluorouracil hydrate, and uridine hydrate) that have actually been isolated and compared with authentic material of known structure.7 It is nearly the only product formed in the photolysis, is definitely stable at room temperature and neutral pH, and the thermal reversal to dimethyluracil is nearly quantitative. These properties, as Moore observed, make the reaction ideal for mechanistic investigation. Burr and Park have investigated the reaction mechanism by measuring the photolysis rate of dimethyluracil in mixtures of water with several nonaqueous, nonreactive solvents as a function of water concentration.64 The photolysis rate for 10" iM DMU was found to be the same in water-saturated cyclohexane (about 5 x 10-3M in water) as in dry cyclohexane. The photolysis rate in dry, highly purified dioxane was quite insensitive to water, and it was observed that hydrate formation (measured by thin-layer chromatography and by thermal absorbance reversal) became appreciable only at water concentrations above 40%. 

Cell viability studies of HT29 colon cancer cells treated with the CO-releasing compound [Mn(CO)3(tpm)]PF6, 33 R = H, revealed a significant photoinduced cytotoxicity comparable to that of established agent 5-fluorouracil [205]. Subsequently, [Mn(CO)3(tpm)]PF6, 33, was modified by replacing R with peptides to permit cellular recognition [206]. 34, R = H, Me, releases nearly 2 mol of CO to myoglobin on photolysis while 35, E = lone pair, O, S, releases approximately 1 mol of CO. The n-octanol/water partition coefficients were also measured [207]. 

In a pilot study in six patients receiving intravenous flucytosine, hematotoxicity was monitored by measuring platelet and leukocyte counts flucytosine and 5-fluorouracil serum concentrations were measured using HPLC (19). The concentrations of 5-fluorouracil in the 34 available serum samples were below the limit of quantification (0.05 pg/ml), but flucytosine was detectable in all samples and the 5-fluorouracil metabolite, a-fluoro-P-alanine (FBAL), was detected at low concentrations in several samples. One patient developed thrombocytopenia (50 X 10 /1) during therapy, and one developed leukopenia (2.6 X 10 /1). The fact that 5-fluorouracil was not detected... 

The efficacy of levamisole has been studied in several studies of patients with colorectal carcinoma (13-15). In a phase III trial 5-fluorouracil alone, 5-fluorouracil with levamisole, and 5-fluorouracil with hepatic irradiation have been compared in patients with residual, non-measurable, intra-abdominal metastases after resection of colorectal carcinoma (13). The adverse effects were as expected, and there were no differences between any of the treatments. The main adverse effects were hematological and gastrointestinal. However, analysis of life-threatening adverse effects showed some slight differences there were fewer than expected in the 5-fluorouracil alone group, and more than expected in the 5-fluorouracil plus hepatic irradiation group. There was no treatment advantage for any of the combinations over 5-fluorouracil alone. 

Use of in vivo 19F MR spectroscopy to directly measure the pharmocokinetics of 5-FU in liver tumors and metastases enabled identification of drug mechanism of action and investigation of tumor pathophysiology. Similar studies were undertaken to evaluate the ability of a range of medications to modulate the in vivo effectiveness of fluorouracil and its prodrugs [3-5, 7-10], These studies have served as a model for other in vivo drug MR... 

AK usually presents as a small (2 to 6 mm), erythematous papule that feels flat, rough, or scaly when palpated (Fig. 94-12, Plate 12). It tends to be found in chronically sun-exposed areas, such as the top of the hands, head, neck, and forearms. Typically, patients with AKs are elderly and have fair skin, light-colored eyes, freckles, and a history of significant sun exposure and tend to sunburn easily. Because AKs are likely caused by ultraviolet radiation, sun-preventive measures, particularly in childhood, are of utmost importance. Most commonly, AKs are treated with liquid nitrogen, which will remove the lesion. Another frequently used therapy is topical 5-fluorouracil. Patients who are prescribed topical 5-fluorouracil should be properly counseled, as significant erythema, erosion, crusting, and even ulceration normally occur during treatment. 

The IR spectrum of reference standard fluorouracil is shown in Figure 1 (1). The spectrum of a mineral oil suspension of fluorouracil between cesium iodide discs was measured on a Perkin Elmer 621 Spectrophotometer. The assignments given in Table I to the bands in Figure 1 (1) are in good agreement with the assignments made by Brownlie (2). 

Figure 4 shows the excitation and emission spectra for reference standard fluorouracil from 250 to 600 nm (6). The spectra, measured in a methanol solution of fluorouracil (1.0 mg/ml) using a Farrand MK-1 Spectro-fluorometer, showed one excitation peak at 315 nm and one emission peak at 391 nm. 

Direct spectrophotometric analysis is carried out on fluorouracil injectable solutions. A volume of the fluorouracil injection is pipetted into a volumetric flask and diluted with pH 4.7 acetate buffer to obtain a final concentration of about 10 ugm/ral. The absorbance of this solution is measured at 266 nm along with the absorbance of a similar concentration of reference standard fluorouracil. From this data the concentration of fluorouracil in the injectable solution is calculated (20). 

With the advent of good specific ion electrodes, methods were developed to liberate the bound fluorine and directly measure the fluoride concentration. The reagent sodium-biphenyl followed by oxidation with hydrogen peroxide is used to liberate the organically bound fluorine in fluorouracil. A fluoride specific ion electrode is used, in conjunction with a high-ionic-strength-buffer solution, for direct measurement of the liberated fluoride (22). 

The determination of any free fluoride present in fluorouracil bulk samples or in fluorouracil ampuls are carried out by direct measurement using a fluoride specific ion electrode. The measurements are made in a tris(hydroxymethyl)amino-methane buffer solution (pH = 7.5). The electrode response was found to be linear throughout the working range of 0.08 to 0.2S mg F lOO ml solution (23). 

The compound Investigated. Measurements Indicated at left by an E are excluded measurements. All positive (+) and negative (-) ionic charges (for the chemical at experimental conditions) are indicated. For example, 5-fluorouracil with two negative charges and two positive charges is indicated by (+ - + -). 

Examples for good siurogate markers include an intermediate filament, which is released from apoptotic cancer cells during chemotherapy, and a collagen fragment which indicates bone decay [39-40]. Cyokeratin 18 is an efficient biomarker to measure the effect of breast cancer treatment via combination chemotherapy such as docetaxel or cyclophosphamide/epirubicin/5-fluorouracil (CEF). 

The enzymes involved in the alkaloid metabolism of P. ovoloplum become measurable during the transition from tne trophophase to the idiophase. The activity increase of cyclopeptine dehydrogenase, dehydrocyclopeptine ep-oxidase and cyclopenin m-hydioxylase is inhibited by 5-fluorouracil and cycloheximide, indicating that it depends on RNA and protein biosynthesis (7 - 9). Hence like many other secondary metabolic activities (cf, 2,... 

In some cases, however, the regulation of the in vivo activity of secondary metabolic enzymes is more complicated. In the hyphae of Penicillium cyclopium the activities of the enzymes of benzodiazepine alkaloid biosynthesis (D 8.4.2) are measurable at a relatively early stage of the mold s development, whereas alkaloid formation is expressed later (Fig. 8). The increase of the rate of biosynthesis is immediately stopped by inhibitors of gene expression, e.g., 5-fluorouracil or cycloheximide (D 3.3.7), even at developmental stages at which the in vitro measurable enzyme activities have already their maximum levels. This indicates the existence of a protein limiting the rate of alkaloid formation, which is synthesized much later than the investigated enzymes. 

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