Reverse-phase liquid chromatography of 5-fluorouracil nucleosides and nucleotides in the presence of quaternary ammonium ions

Liquid chromatographic study of the stability of 5-halogeno-2'-deoxyuridines

The stability of a series of 5-halogeno-2'-deoxyuridines was investigated using liquid chromatography as the analytical technique. Characteristics and profiles of the acidic, neutral and alkaline degradation are described, together with Arrhenius relationships and activation parameters for weakly acidic media.

Highly sensitive method for the determination of 5-fluorouracil in biological samples in the presence of 2'-deoxy-5-fluorouridine by gas chromatography-mass spectrometry

A highly sensitive and convenient gas chromatographic-mass spectrometric (GC-MS) method is described for the determination of 5-fluorouracil in the presence of 2'-deoxy-5-fluorouridine (which breaks down into 5-fluorouracil during ordinary GC derivatization) in biological samples such as plasma and urine. After extraction with ethyl acetate, 5-fluorouracil and 5-chlorouracil, the latter being used as an internal standard, were converted into their tert.-butyldimethylsilyl derivatives by allowing the mixture to stand for 30 min at room temperature and were assayed by electron-impact ionization GC-MS. Under these conditions, 2'-deoxy-5-fluorouridine did not decompose or interfere with the determination of 5-fluorouracil. The assay method, including the extraction and tert.-butyldimethylsilyl derivatization of 5-fluorouracil, showed good linearity in the range 0-100 ng/ml for 5-fluorouracil in plasma (detection limit 0.5 ng/ml) and urine (detection limit 1 ng/ml). The usefulness of this method was demonstrated by determining plasma concentrations of 5-fluorouracil in rats treated intravenously with 5-fluorouracil and 2'-deoxy-5-fluorouridine.

Biochemical pharmacology and analysis of fluoropyrimidines alone and in combination with modulators

After more than three decades since their introduction, fluoropyrimidines, especially FUra, are still a mainstay in the treatment of various solid malignancies. The antitumor effects of fluoropyrimidines are dependent upon metabolic activation. FdUMP, FUTP and FdUTP were identified as the key cytotoxic metabolites that interfere with the proper function of thymidylate synthase and nucleic acids. The relevance of these metabolites is cell-type specific. Recently, fluorouridine diphospho sugars have been detected, but the precise function of this class of metabolites is currently unknown. In mammalian systems fluoropyrimidines and their natural counterparts share the same metabolic pathways since the substrate properties in enzyme-catalyzed reactions are frequently comparable. Ongoing studies indicate that the metabolism and action of fluoropyrimidines exhibit circadian rhythms, which appear to be due to variations in the activity of metabolizing enzymes. Essential for the expanding knowledge of the pathways and effects of fluoropyrimidines has been the constant improvement of analytical methods. These include ligand binding techniques, numerous dedicated HPLC systems and 19F-NMR. Because the overall response rates achieved with fluoropyrimidines are modest, strategies based on biochemical modulation have been devised to enhance their therapeutic index. Biochemical modulators include a wide range of various compounds with different modes of action. In recently completed clinical trials, combinations of FUra with leucovorin, a precursor for 5,10-methylene tetrahydrofolate, or with levamisole, an anthelminthic with immunomodulatory activity, appeared to be superior to FUra alone. At the preclinical level combinations of fluoropyrimidines with, e.g. interferons or L-histidinol were demonstrated to be interesting candidates for further testing. The future therapeutic utility of fluoropyrimidines will depend on both the improvement of combination regimens currently used in the treatment of cancer patients and the judicious clinical implementation of promising experimental modulation strategies. Moreover, novel fluoropyrimidines with superior pharmacological properties may become important as part of or instead of modulation approaches.

Photochemistry of uridine on high intensity laser UV irradiation

The method of high performance liquid chromatography was applied to investigate the products of single-quantum and two-quantum photo-reactions which occur when an aqueous solution of uridine is irradiated with high intensity nanosecond and picosecond laser UV pulses. A comparison of the experimental results obtained with theoretical models enables a number of photophysical parameters of the highly excited electronic states of the uridine molecule to be determined.

Intestinal 5-fluorouracil absorption: use of Ussing chambers to assess transport and metabolism

We have employed an in vitro system to study transport and metabolism of organic molecules by gastrointestinal tissues. Such a system would aid in the evaluation of the potential for oral delivery of organic molecules. Transport and metabolism of 5-fluorouracil (5-FU) were studied using rabbit intestinal preparations. Unidirectional fluxes and metabolism were measured in vitro in Ussing chambers under short-circuit conditions. Results from these studies reveal that in ileum, proximal, and distal colon, steady-state fluxes of 5-FU (10 microM added to both bathing solutions) are established after 30 min and remain constant for at least 110 min. Transport of 5-FU under "sink" conditions with 10 microM 5-FU present in the mucosal or serosal bathing solution alone demonstrated similar rates of transport as under "nonsink" conditions. The concentration dependence of 5-FU fluxes indicates that the mucosal (m)-to-serosal (s) flux is composed of both a saturable and a linear component over the range of 1-100 microM in the ileum, whereas the s-to-m flux in the ileum and both fluxes in the colon are linear functions of concentration. Over the concentration range employed and the time course of these studies, 5-FU had no effect on the electrical properties of the ileum or colon. In the ileum, the m-to-s but not the s-to-m flux of 5-FU was reduced by (1) serosal ouabain (0.1 mM); (2) reduction of the bathing solution Na concentration; and (3) addition of uracil, thymine, thymidine, uridine, 2-deoxyuridine, or uridine-5'-monophosphate.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug level monitoring: cytostatics

The present review on the quantification of cytostatic drugs has mainly been focussed on chromatographic techniques. Special attention has been paid to the precautions that have to be taken into account to ensure the selectivity and accuracy of the various methods. The various cytostatics that have been dealt with are: alkylating agents, antimetabolites, vinca alkaloids, antibiotics, cis-diamminedichloroplatinum, podophyllotoxine derivatives, and nitrosoureas.

Determination of adenine nucleotides and inosine in human myocard by ion-pair reversed-phase high-performance liquid chromatography

An isocratic high-performance liquid chromatographic system for the quantitation of AMP, ADP and ATP is presented. The separations were achieved at room temperature by reversed-phase chromatography (Supelcosil LC-18). The standard solvent was 220 mM potassium phosphate, pH 6.9, 1% (v/v) methanol and 0.3 mM tetrabutylammonium hydrogen sulphate. A selective retention of the adenine nucleotides as a group relative to the mono-, di- and triphosphates of guanosine, uridine and cytidine was observed under these experimental conditions. The adopted procedure was applied to the separation of adenine nucleotides in biological extracts, i.e., human myocard. The adenine nucleotides in an extract of myocard were quantitated in less than 20 min. Only 5-10 mg (wet weight) of myocard were needed in order to determine the energy charge of a myocardial sample. Also inosine was easily quantitated in this liquid chromatographic system.

Reversed-phase ion-pair high-performance liquid chromatographic assay of 5-fluorouracil, 5'-deoxy-5-fluorouridine, their nucleosides, mono-, di-, and triphosphate nucleotides with a mixture of quaternary ammonium ions

Several quaternary ammonium ions were evaluated in the development of a reversed-phase ion-pair high-performance liquid chromatographic assay for the separation of the known nucleosides and nucleotides of 5-fluorouracil (FU) and its analogue, 5'-deoxy-5-fluorouridine (5'-dFUR). The capacity factors of FU, 5'-dRUR, and their eight anabolites including 5-5-fluorouridjine and its mono-, di-, triphosphate and diphosphoglucose, 5-fluorodeoxyuridine and its mono;- and diphosphate nucleotides, were dependent on the chain length and concentration of the counter ions, pH, type of buffer, as well as the type of bonded stationary phase. Separation of FU, 5'-dFUR, their nucleosides and monophosphate nucleotides was readily achieved using tetrabutylammonium ion alone as the counter ion. However, under these conditions, the di- and triphosphate nucleotides were eluted from the column only after lengthy gradient elution and with poor reproducibility. Optimal conditions for a simultaneous separation of the ten fore-mentioned compounds were achieved using a two-step elution with a mixture of tetraethylammonium (C8) and tetrabutylammonium (C16) ions. The first eluent consisted of C8 and C16 ions in a mixture of acetate--phosphate buffer and methanol, the second eluent contained an additional 30 mM phosphate. FU, 5'-dFUR, their nucleosides and monophosphates and diphosphoglucose were separated by isocratic elution from a microBondapak C18 reversed-phase column using the first eluent; and the di- and triphosphate nucleotides were subsequently eluted, isocratically with the second eluent. This assay does not require gradient elution and can be completed within 50 min with good reproducibility.

Comparison of the reversed-phase high-performance liquid chromatographic separations of fluoropyrimides, pyrimidines, and purines

The reversed-phase, high-performance liquid chromatographic separation of fluoropyrimidines, pyrimidines, and purines was investigated under isocratic conditions at ambient temperature. The performance of nine analytical, commercially available columns with five mobile phases is compared, and capacity and resolution factors are reported. The variables determining resolution are discussed, and the systems accomplishing the desired separation of fluoropyrimidine and pyrimidine bases and nucleosides are described. The best chromatographic results are achieved by using Spherisorb ODS-2 as stationary phase and 0.05 M monobasic ammonium phosphate (pH 3.5) as mobile phase.

Dynamic cation-exchange systems for rapid separations of nucleobases and nucleosides by high-performance liquid chromatography

The retention behaviour of nucleobases and nucleosides in dynamic cation-exchange systems, consisting of a hydrophobic support as the stationary phase and water-ethanol mixtures containing small amounts of sodium dodecylsulphate as anionic detergent as the mobile phase was investigated. The retention of nucleobases and nucleosides can be influenced over a wide range by variation of the pH and the concentration of the ethanol, anionic detergent and counter ion in the eluent. With respect to separation speed and selectivity, these dynamic cation-exchange systems are in many instances superior to conventional ion-exchange and reversed-phase systems. It is shown that, by optimizing the different retention parameters, the separation of fourteen nucleobases and nucleosides, simultaneously and under isocratic conditions, can be achieved in ca. 6 min. The performance of the phase system is demonstrated by the analysis of a calf thymus DNA hydrolysate.