5- fluorouracil action

It has long been recognized that one of the main mechanisms underlying Fluorouracil action is inhibition of thymidylate synthase by fluorodeoxyuridine monophosphate... 

Fluorinated Heterocyclic Compounds. HeterocycHc compounds containing the CF group are prepared by methods similar to those used in the fluorination of aHphatic compounds. The direct action of fluorine on uracil yields the cancer chemotherapy agent, 5-fluorouracil [51-21-8] as one special example of a selective fluorination on a commercial scale (25). 

An amount of enzyme preparation equivalent to 900 mg of wet cells was made up to 25 ml with the above potassium phosphate buffer solution. 150 mg (1.15 mmol) of 5-fluorouracil and 1.0 gram of thymidine (4.12 mmol) were dissolved in 15 ml of the above potassium phosphate buffer solution. The mixture was incubated at 37°C for 18 hours. After this time, enzyme action was stopped by the addition of four volumes of acetone and one volume of peroxide-free diethyl ether. The precipitated solids were removed by filtration, and the filtrate was evaporated under nitrogen at reduced pressure until substantially all volatile organic solvent had been removed. About 20 ml of aqueous solution, essentially free of organic solvent, remained. This solution was diluted to 100 ml with distilled water. 

Fluoro-2 -deoxyuridine has been extensively used in studies of the mechanism of action of thymidylate synthase, and 5-fluorouracil is an anticancer drug that has provided a lead to the development of others. The metabolism of 5-fluorouracil by the ascomycete fungus Nectria haematococca has been studied using F NMR (Parisot et al. 1991). a-Fluoro-P-alanine (2-fluoro-3-aminopropionate) was produced (Figure 10.27), while 5-fluorouridine-5 -mono-, di-, and triphosphate were found in acid extracts of the mycelia, and the 2 - and 3 -monophosphates were recovered from RNA. 

Capecitabine (Xeloda ) Orally active prodrug of 5-fluorouracil. Once activated, the mechanism of action is the same. Similar to continuous infusion 5-fluorouracil... 

Let s start with three examples of antitumor drugs that work by the inhibition of DNA synthesis methotrexate (MTX, Methopterin), 5-fluorouracil (Fluril), and 6-mercaptopurine (Purinethol). These are all old cancer drags, marketed under numerous trade names, including those indicated above. Although the mechanism of action of each one is different, at the end of the day they all inhibit DNA synthesis. 

Flucytosine is converted in Candida fungi to 5-fluorouracil by the action of a specific cytosine deaminase. As an antimetabolite, this compound disrupts DNA and RNA synthesis (p. 298), resulting in a fungicidal effect Given orally, flucytosine is rapidly absorbed. It is well tolerated and often combined with amphotericin B to allow dose reduction of the lattet... 

Parker WB, Cheg YC. Metabolism and mechanism of action of 5-fluorouracil. Pharmacol Ther 1990 48 381-395. 

Rich TA. Irradiation Plus 5-Fluorouracil Cellular Mechanisms of Action and Treatment Schedules. Semin Radiat Oncol 1997 7(4) 267-273. 

Fluorouracil/ Topical [5-FU] (Efudex) [Antineoplastic/ Antimetabollte] Uses Basal cell carcinoma actinic/solar k atosis Action Inhibits thymidylate S5mthetase (-1- DNA S5mth, S-phase specific) Dose 5% cream bid X 2-6 wk Caution [D, ] Irritant chemo Contra Component sensitivity Disp Cream, soln SE Rash, dry skin, photosens EMS See RuorouracU OD See RuorouracU... 

In Fig. 1 various targets of some important cytostatic agents are depicted. Their main mechanisms of action can be briefly summarized as follows. Pentostatin blocks purine nucleotides by inhibiting adenosine deaminase. 6-Mercaptopurine and 6-thioguanine inhibit purine ring biosynthesis and they inhibit nucleotide interconversions. Methotrexate by inhibiting dihydrofolate reduction blocks thymidine monophosphate and purine synthesis. 5-Fluorouracil also blocks thymidine monophosphate synthesis. Dactinomycin, daunorubicin, doxorubicin and mitoxantrone intercalate with DNA and inhibit RNA synthesis. L-asparaginase deaminates... 

Salicylates, probenecid, and sulfonamides inhibit the renal tubular secretion of methotrexate and may displace it from plasma proteins. Asparaginase inhibits protein synthesis and may protect cells from methotrexate cytotoxicity by delaying progression from Gj-phase to S-phase. Methotrexate may either enhance or inhibit the action of fluorouracil, depending on its sequence of administration. 

Another action proposed for 5-fluorouracil may involve the incorporation of the nucleotide 5-fluorouri-dine triphosphate (5-FUTP) into RNA. The cytotoxic... 

The fluorine atom can be present in position 5 in uracil derivatives, or in position 1 in that of purine, as in fludarabine, which is used in the treatment of some leukemias (Figure 6.14 cf. Chapter 8). Nucleoside derivatives of fluorouracil (e.g., capecitabine) are prodrugs that allow the oral administration of 5-FU in cancer chemotherapy. The mechanism of action of these nucleosides is detailed in Chapters 7 and 8. Nucleosides having a trifluoromethylated base have been described for example, trifluridine is active on herpesvirus (Figure 6.14). 

Fluorouracil and its derivatives are still important dmgs in the chemotherapy of numerous cancers (doxifluridine, tegafur, carmofur) (cf. Chapter 8). Studies on the mechanism of action of 5-FU had great influence on the development of other antitumor drugs that are derived from pyrimidine and purine. 5-FU is industrially prepared by fluorination of uracil with elemental fluorine (cf. Figure 2.6, Chapter 2). 

Dmgs in which fluorine atoms bring a specific biological activity to molecules that previously had no therapeutic activity. Most of the examples are enzyme inhibitors (difluoroornithine, gemcitabine, 5-fluorouracil). Synthesis of these drugs often comes from a rational approach that is based on the action mechanism. 

Mechanism of Action An antifungal that penetrates fungal cells and is converted to fluorouracil which competes with uracil interfering with fungal RNA and protein synthesis. Therapeutic Effect Damages fungal membrane. 

Flucytosine (5-FC) was discovered in 1957 during a search for novel antineoplastic agents. Though devoid of anticancer properties, it became apparent that it was a potent antifungal agent. Flucytosine is a water-soluble pyrimidine analog related to the chemotherapeutic agent fluorouracil (5-FU). Its spectrum of action is much narrower than that of amphotericin B. 

Mechanism of Action. Flucytosine is incorporated into susceptible fungi, where it undergoes enzymatic conversion to fluorouracil,7 which acts as an antimetabolite during RNA synthesis in the fungus. Fluorouracil is incorporated into RNA chains but acts as a false nucleic acid. This event ultimately impairs protein synthesis, thus disrupting the normal function of the fungus. 

Fluorouracil and fluorodeoxyuridine (floxuridine) inhibit pyrimidine nucleotide biosynthesis and interfere with the synthesis and actions of nucleic acids. To exert its effect, fluorouracil (5-FU)... 

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