Degradation of the cytostatic 5-Fluorouracil in water by Fenton and photo-assisted oxidation processes

Cytostatics are part of the forefront research topics due to their high prescription, high toxicity, and the lack of effective solutions to stop their entrance and spread in the environment. Among them, 5-Fluorouracil (5-Fu) has received particular attention because is one of the most prescribed active substances in chemotherapy worldwide. The degradation of 5-Fu by advanced oxidation processes (AOPs) is a poorly addressed topic, and this work brings valuable inputs concerning this matter. Herein, the efficacy of Fenton's process in the degradation of 5-Fu is explored for the first time; the study of the main variables and its successful application to the treatment of real wastewaters is demonstrated. Moreover, hydrogen peroxide-based and photo-assisted techniques (direct photolysis, photodegradation with H₂O₂ and photo-Fenton) are also investigated for purposes of comparison. Under the best operation conditions obtained (T = 30 °C, [Fe²⁺]₀ = 0.5 mM; [H₂O₂]₀ = 240 mM and pH = 3 for [5-Fu]₀ = 0.38 mM), 5-Fu was completely eliminated after 2 h of Fenton's reaction and about 50 % of mineralization was reached after 8 h. The best performance was obtained by the photo-Fenton process, with 5-Fu mineralization level as high as 67 %, using an iron dose within the legal limits required for direct water discharge. Toxicity (towards Vibrio fischeri) of the effluents that resulted from the application of the above-mentioned AOPs was also evaluated; it was found that the degradation products generated from the photo-assisted processes are less toxic than the parent compound, putting into evidence the relevance of such technologies for degradation of cytostatics like 5-Fu.

Degradation of cyclophosphamide and 5-fluorouracil by UV and simulated sunlight treatments: Assessment of the enhancement of the biodegradability and toxicity

The presence of pharmaceuticals in the environment has triggered concern among the general population and received considerable attention from the scientific community in recent years. However, only a few publications have focused on anticancer drugs, a class of pharmaceuticals that can exhibit cytotoxic, genotoxic, mutagenic, carcinogenic and teratogenic effects. The present study investigated the photodegradation, biodegradation, bacterial toxicity, mutagenicity and genotoxicity of cyclophosphamide (CP) and 5-fluorouracil (5-FU). The photodegradation experiments were performed at a neutral to slight pH range (7-7.8) using two different lamps (medium-pressure mercury lamp and a xenon lamp). The primary elimination of the parent compounds was monitored by means of liquid chromatography tandem mass spectrometry (LC-IT-MS/MS). NPOC (non-purgeable organic carbon) analyses were carried out in order to assess mineralization rates. The Closed Bottle Test (CBT) was used to assess ready biodegradability. A new method using Vibrio fischeri was adopted to evaluate toxicity. CP was not degraded by any lamp, whereas 5-FU was completely eliminated by irradiation with the mercury lamp but only partially by the Xe lamp. No mineralization was observed for the experiments performed with the Xe lamp, and a NPOC removal of only 18% was registered for 5-FU after 256 min using the UV lamp. Not one of the parent compounds was readily biodegradable in the CBT. Photo transformation products (PTPs) resulting from photolysis were neither better biodegradable nor less toxic than the parent compound 5-FU. In contrast, the results of the tests carried out with the UV lamp indicated that more biodegradable and non-toxic PTPs of 5-FU were generated. Three PTPs were formed during the photodegradation experiments and were identified. The results of the in silico QSAR predictions showed positive mutagenic and genotoxic alerts for 5-FU, whereas only one of the formed PTPs presented positive alerts for the genotoxicity endpoint.

[Distribution of 5-fluorouracil between lymphocytes and blood plasma]

In blood plasma of 8 healthy volunteers with resuspended lymphocytes incubated with 5-fluorouracil (5-FU) the drug distribution between cells and liquid was assessed by means of HPLC. Rapid accumulation of 5-FU in lymphocytes was proved (the drug concentration on the 3-rd minute is 2.5-fold higher than in plasma) as well as the absence of temporal changes of 5-FU content both in lymphocytes and blood plasma during 30 minutes of experiment.

5-fluorouracil as a phosensitiser

5-FU exhibits a high fluorescence after irradiation with UV-vis light. An enhancement of the cytostatic activity of 5-FU under UV-vis irradiation was observed on an in vivo experimental model.

The effect of gamma-irradiation on drug release from bioerodible microparticles: a quantitative treatment

The two major objectives of this study were: (i) to monitor the effect of different gamma-irradiation doses (4-33 kGy) on the release kinetics from 5-fluorouracil (5-FU)-loaded poly(D,L-lactide-co-glycolide) (PLGA)-based microparticles, and (ii) to analyze the obtained experimental data with a new mathematical model giving insight into the occurring mass transport phenomena. Drug release was found to depend significantly on the applied gamma-irradiation dose. Interestingly, the obtained release profiles were all biphasic: a rapid initial drug release phase ("burst") was followed by a slower, approximately constant drug release phase. Surprisingly, only the initial rapid drug release was accelerated by gamma-irradiation; the subsequent zero-order phase was almost unaffected. Importantly, the new mathematical model which is based on Fick's second law of diffusion and which considers polymer degradation was applicable to all the investigated systems. In addition, the gamma-irradiation dose could be quantitatively related to the resulting drug release rate. In conclusion, diffusion seems to be the dominating release rate controlling mechanism in all cases, with a significant contribution of the polymer degradation process.

Stereoelectronic effect on one-electron reductive release of 5-fluorouracil from 5-fluoro-1-(2-oxocycloalkyl)uracils as a new class of radiation-activated antitumor prodrugs

A series of 5-fluoro-1-(2'-oxocycloalkyl)uracils (3-11) that are potentially novel radiation-activated prodrugs for the radiotherapy of hypoxic tumor cells have been synthesized to evaluate a relationship between the molecular structure and the reactivity of one-electron reductive release of antitumor 5-fluorouracil (1) in anoxic aqueous solution. All the compounds 3-11 bearing the 2'-oxo group were one-electron reduced by hydrated electrons (eaq-) and thereby underwent C(1')-N(1) bond dissociation to release 5-fluorouracil 1 in 47-96% yields upon radiolysis of anoxic aqueous solution, while control compounds (12, 13) without the 2'-oxo substituent had no reactivity toward such a reductive C(1')-N(1) bond dissociation. The decomposition of 2-oxo compounds in the radiolytic one-electron reduction was more enhanced, as the one-electron reduction potential measured by cyclic voltammetry in N,N-dimethylformamide became more positive. The efficiency of 5-fluorouracil release was strongly dependent on the structural flexibility of 2-oxo compounds. X-ray crystallographic studies of representative compounds revealed that the C(1')-N(1) bond possesses normal geometry and bond length in the ground state. MO calculations by the AM1 method demonstrated that the LUMO is primarily localized at the pi* orbital of C(5)-C(6) double bond of the 5-fluorouracil moiety, and that the LUMO + 1 is delocalized between the pi* orbital of 2'-oxo substituent and the sigma* orbital of adjacent C(1')-N(1) bond. The one-electron reductive release of 5-fluorouracil 1 in anoxic aqueous solution was presumed to occur from the LUMO + 1 of radical anion intermediates possessing a partial mixing of the antibonding C(2')=O pi* and C(1')-N(1) sigma* MO's, that may be facilitated by a dynamic conformational change to achieve higher degree of (pi* + sigma*) MO mixing.

Stacking-controlled phototransformations of the 5-fluorouracil residues in dinucleotide model compounds

5-Fluorouracil residues can form cyclobutane-type photodimers in a direct excitation stacking-controlled process. The stacking also has an important effect on the photohydration of uracil and 5-fluorouracil in our model compounds 5RUra(CH2)35FUra, where R = H, CH3, C2H5, C3H7, F or Cl.

External control of drug release. IV. Controlled release of 5-fluorouracil from a hydrophilic polymer matrix by microwave irradiation

A polymeric system capable of delivering 5-fluorouracil (5-FU) at increased rates on demand by external microwave irradiation was developed. Sustained-release systems were made by incorporating 5-FU into an ethylene-vinyl alcohol copolymer. When exposed to release medium, the delivery systems released the drug slowly and continuously. Upon exposure to microwave irradiation, the drug was released at a much higher rate. Release rates returned to base line levels when the microwave irradiation was discontinued. This study demonstrated that release rates of 5-FU from a polymer matrix can be increased at desired times by external microwave irradiation.

Solid-state radiation chemistry of DNA and its constituents

The molecular structure as well as the mechanisms of formation and decay of free radicals produced in DNA and its constituents by ionizing radiation is reviewed. Starting with the description of the spectral parameters for cations and anions in natural nucleic acid bases, emphasis is given to the comparable species formed in the group of the 5-halogen substituted uracil derivatives. The consequences of the attachment of a ribose or ribosephosphate group to the bases is discussed in terms of the distribution of primary radicals which, again, is shown to be different from those of the subunits in DNA itself. The quantitative aspects of radical formation are discussed in terms of G values and their dependence on the temperature of irradiation. Finally, a schematic presentation of the major modes of radical reactions is given occurring upon warming of the primary species in the DNA subunits and in DNA itself.

5-fluorouracil uptake by irradiation perturbed tumor

An in vitro system was used to study the uptake of 5-fluorouracil by LSA ascites tumor cells. Changes in drug uptake with cell age and following a 1,000-rad radiation perturbation of the cell population were studied. DNA synthesis and drug uptake were highest during early rapid tumor growth and decreased with tumor age and stationary phase. Radiation perturbation by 1,000 rad caused a second peak of cellular DNA synthetic activity and drug uptake. These results indicate that irradiation stimulated regrowth activity of tumor in vivo after the 1,000-rad exposure. In vivo survival time changes of stationary phase tumor after in vivo irradiation correlated with the vitro assay data. This indicates that combined treatment modalities depends in part on the regrowth of tumor after tumor cell killing.

Effect of microwave radiation on redissolving precipitated matter in fluorouracil injection

The effect on the stability of fluorouracil injection of using microwave radiation to redissolve precipitated matter was studied. Fifteen ampuls each of Fluorouracil Injection, USP, containing precipitate were heated to 60 degrees C in a microwave oven and water bath, respectively. The contents of each heated ampul and of 15 control ampuls (unheated, no precipitate) were assayed by high-performance liquid chromatography, and the pH value of each sample was measured. Each test group fell within USP concentration requirements and showed no significant decrease in potency. Among the microwave-heated ampuls, a mean drop of 0.03 pH units was significant (p less than 0.05) but did not affect drug stability or solubility, since all samples remained within the USP pH range of 8.6-9.0. Precipitated matter in fluorouracil injection can be redissolved by heating with microwave radiation without significantly affecting the drug's stability.

Controlled release of multi-component cytotoxic agents from radiation polymerized composites

Multi-component cytotoxic (anticancer) agents such as mitomycin C (MMC), adryamycin (ADM) and 1-(2-tetrahydrofuryl-5-fluorouracil) (FT-207), were entrapped in a single common composite by radiation-induced polymerization of glass-forming monomers in the presence of polymers. The release profiles of each cytotoxic agent were controlled by the contents and compositions of three cytotoxic agents in the matrix. The release rates of each cytotoxic agent were retarded by addition of an adsorbent and accelerated by addition of a pore-making agent. The release fom the common matrix of a cytotoxic agent and its promoter which have markedly different molecular weights [e.g. MMC and urokinase (UK)] was also investigated. A double entrapping method was successfully used for controlled release in such cases. In conclusion it was found that the release profiles of multi-components in a single matrix could be controlled by using these techniques.

Radiation damage in solid 5-halouracils: free radicals in single crystals of 5-fluorouracil

X-irradiation at 300 K of single crystals of 5-fluorouracil results in the formation of two different radical species observable by e.s.r. and ENDOR-spectroscopy. One is an alpha-fluoro radical RCF(CH2)R' formed by saturation of the 5,6-double bond of the pyrimidine ring. The principal values of its alpha-fluorine interaction are 170, -9 and -18 G; the isotropic part of the methylene beta-proton couplings are 46.3 and 28 G, respectively; the g-tensor has principal values of 2.0029, 2.0066, and 2.0052. The other radical species is formed by enolization of the C4-carbonyl function. The resulting spin-density distribution gives rise to three observable interactions, an alpha-proton (-5.2, -14.9, -11.2 G) at C6, an OH-proton from the C4--OH group (-1.7, -5.0, -4.1 G) and a residual alpha-fluorine interaction (0,0,11.2G). Irradiation at 77 K yields an e.s.r.-pattern which is tentatively assigned to the molecular anion radical. These findings are related to the radiation chemistry of solid 5-halouracils.

E.s.r. studies of halogenated pyrimidines in gamma-irradiated alkaline glasses

The reactions of mobile electrons (em-) and oxygen radical anions (O--) with halogenated bases and nucleosides have been studies in gamma-irradiated alkaline glasses by e.s.r. and specific halogen-ion electrode techniques. It is shown that electrons react with halogenated uracil bases (XUr where X = Cl, Br. I but not F) by dissociative electron attachment to form uracil-5-yl radicals (U-) and halogen anions. The relative rates of reaction of em- with XUr decrease in the sequence BrUr greater than ClUr greater than FUr greater than IUr. Thermal annealing studies carried out on U- in H2O and D2O matrices support the hypothesis that U- in H2O hydrates across the 5-6 double bond in the temperature region 135 degrees-155 degrees K, and deuterates to a much smaller extent in D2O at temperatures above 155 degrees K. Studies on bromouridine and bromodeoxyurinde suggest that em- reacts with the base moieties to form U- type radicals which abstract H- from the sugar moieties of adjacent nucleosides.

Thermoluminescent properties of crystalline halogen substituted uracils

The thermoluminescent properties of crystalline uracil (U), and its halogen-substituted derivatives, 5 bromo-uracil (5BrU), 5 fluorouracil (5FU) and 5 iodo-uracil (5IU), have been investigated. The X-ray-induced thermoluminescent output increases in the order U less than 5 FU less than 5BrU less than 5IU. However, a reversed relationship is found for the U.V.-stimulated thermoluminescence. The thermoluminescence-emission spectra suggest that the same de-excitation process operates in all the halogen-substituted uracils, but the glow curves show that the charge-trapping characteristics are different for each material.