Elimination study of the chemotherapy drug tamoxifen by different advanced oxidation processes: Transformation products and toxicity assessment

Tamoxifen is a chemotherapy drug considered as recalcitrant contaminant (with low biodegradability in conventional activated sludge wastewater treatment), bioaccumulative, ubiquitous, and potentially hazardous for the environment. This work studies the removal of Tamoxifen from water by advanced oxidation processes, paying special attention to the formation of transformation products (TPs) and to the evolution of toxicity (using the Microtox^® bioassay) during the oxidation processes. Five types of treatments were evaluated combining different technologies based on ozone, hydrogen peroxide and UV radiation: i) O₃, ii) O₃/UV, iii) O₃/H₂O₂ (peroxone), iv) UV and v) UV/H₂O₂. Complete removal of tamoxifen was achieved after 30 min for all the treatments carried out with O₃ while a residual concentration (about 10% of initial one) was observed in the treatments based on UV and UV/H₂O₂ after 4 h of reaction. Eight TPs were tentatively identified and one (non-ionizable molecule) was suspected to be present by using ultra high performance liquid chromatography coupled to high resolution mass spectrometry. An increase of toxicity was observed during all the oxidation processes. In the case of ozone-based treatments that increase was attributed to the presence of some of the TPs identified, whereas in the case of UV-based treatments there was no clear correlation between toxicity and the identified TPs.

High-speed liquid chromatography/tandem mass spectrometry using a monolithic column for high-throughput bioanalysis

With the ever-increasing workload from a variety of in vitro and in vivo screening procedures, new analytical methodologies to perform bioanalysis in an accurate and high-throughput manner are in great demand. In this work, monolithic columns were used instead of conventional particulate HPLC columns to perform chromatographic separations. Because the pressure drop on a monolithic column was considerably lower than that on a particulate column, a high flow rate (6 mL/min) was used for a 4.6 x 50 mm monolithic column with a total backpressure of about 61 bar measured using acetonitrile/water (50:50). The capability of using a regular column length at high flow rates, combined with the extremely small dependency of separation efficiency on linear flow velocity, allowed for the generation of sufficient chromatographic resolving power in a significantly reduced runtime. As demonstrated in this work, a plasma extract of a mixture of tempazepam, tamoxifen, fenfluramine, and alprozolam were baseline separated within a total analysis time of one minute. An average peak width at half maximum of approximately one second was noted using a generic broad gradient. It was also found that the separation efficiency and signal/noise (S/N) ratios for this separation remained almost constant at flow rates of 1, 3, and 6 mL/min, respectively. The ruggedness of the separation was evaluated by injecting 600 plasma extracts containing the replicates of a standard curve of the above mixture during an overnight run. The chromatographic retention time, separation quality, peak response and sensitivity were highly reproducible throughout the run. This high-speed liquid chromatography/tandem mass spectrometry (LC/MS/MS) system has been used routinely in the authors' laboratory to support drug discovery programs.

Mutagenic potential of alpha-(N2-deoxyguanosinyl)tamoxifen lesions, the major DNA adducts detected in endometrial tissues of patients treated with tamoxifen

Breast cancer patients treated with the antiestrogen tamoxifen (TAM) show an increased risk of developing endometrial cancer. We have recently detected TAM-DNA adducts in endometrium obtained from patients treated with TAM and identified them as trans- and cis-forms of alpha-(N2-deoxyguanosinyl)tamoxifen (dG-N2-TAM). To explore the mutagenic properties of these TAM-DNA adducts, we prepared site-specifically modified oligodeoxynucleotides containing a single isomer of dG-N2-TAM by reacting a 15-mer oligodeoxynucleotide containing a single dG (5'-TCCTCCTCGCCTCTC) with tamoxifen alpha-sulfate. These modified oligodeoxynucleotides were inserted into a single-stranded shuttle vector to investigate mutagenic specificities of the adducts in simian kidney (COS-7) cells. An epimer of dG-N2-trans-TAM showed targeted mutations ranging from 0.7 to 1.5%. The other dG-N2-trans-TAM adduct showed 9.6% G-->T transversions, accompanied by 2.8% G-->A transitions. Both dG-N2-cis-TAM adducts showed similar mutation spectra, where G-->T transversions (11-12%) predominated, along with a small number of G-->A transitions and G-->C transversions. Thus, dG-N2-TAMs are mutagenic lesions in mammalian cells. The tamoxifen-DNA adducts detected in patient endometrium may cause mutations and initiate endometrial cancer.

Optimised separation of E- and Z- isomers of tamoxifen, and its principal metabolites using reversed-phase high performance liquid chromatography

A reversed phase isocratic high-performance liquid chromatographic method is reported in which a formal structured procedure, the solvent selectivity triangle, was applied to predict the mobile phase composition giving baseline resolution of the clinically important triphenylethylene antioestrogenic agent (Z)-tamoxifen, its principal (Z)-metabolites, and also the clinically relevant (E)-geometric isomers of tamoxifen and 4-hydroxytamoxifen. The technique of solvent selectivity triangle was used to select the optimal organic modifier parameter for use with a Hichrom ODS 1 column, to achieve baseline separation of six triphenylethylene solutes. The detection system utilised post-column ultraviolet irradiation to convert solutes into their respective photocyclisation products, followed by fluorescence detection (lambda[ex] = 254 nm, lambda[em] = 360 nm), and the low detection limit for tamoxifen in serum of 0.1 microM. The optimal mobile phase composition was determined to be methanol-acetonitrile-water-trichloroacetic acid (50:31:18.9:0.1, v/v, pH 2.9). A single stage liquid-liquid extraction method for determination of triphenylethylene drugs in serum was developed. Reproducible recoveries for the (Z)-geometric isomers of tamoxifen (84 +/- 3%) and its principal metabolites including Metabolite Y (94 +/- 3%), N-desmethyltamoxifen (94 +/- 3%) and 4-hydroxytamoxifen (92 +/- 3%) were achieved, though more variable results were obtained for their corresponding (E)-geometric isomers (71 +/- 7% and 70 +/- 10%, respectively).

Column-switching techniques in the biomedical analysis of stereoisomeric drugs: why, how and when

The application of stereoselective chromatographic techniques to bioanalytical problems has become a routine procedure. However, this approach is not always straightforward; particularly when the separation involves chromatographic chiral stationary phases. Matrix interferences and more importantly, overlapping metabolite peaks often make direct analysis impractical. One strategy to overcome these problems is to combine two or more columns with different selectivities to produce a multi-dimensional chromatographic system. This review addresses the use of coupled column chromatography in HPLC systems including different coupling methods and the application of the resulting arrangements to bioanalytical analyses.

Identification of tamoxifen-DNA adducts formed by alpha-sulfate tamoxifen and alpha-acetoxytamoxifen

alpha-Sulfate trans-tamoxifen and alpha-sulfate cis-tamoxifen were synthesized as proposed active metabolites of tamoxifen that react with DNA. alpha-Acetoxytamoxifen was prepared as a model-activated form to produce a reactive carbocation. Calf thymus DNA was reacted with alpha-hydroxytamoxifen or the activated forms of tamoxifen, and tamoxifen-DNA adducts were analyzed by a 32P-postlabeling method. The reactivity of alpha-sulfate trans-tamoxifen to DNA was much higher than that of alpha-hydroxytamoxifen. The formation of tamoxifen-DNA adducts induced by alpha-acetoxytamoxifen and alpha-sulfate cis-tamoxifen was 1100- and 1600-fold, respectively, higher than that of alpha-hydroxytamoxifen. Both alpha-sulfate tamoxifens and alpha-acetoxytamoxifen were highly reactive to 2'-deoxyguanosine. Four reaction products of dG-tamoxifen were isolated by HPLC and characterized by mass- and proton magnetic resonance spectroscopy. Fractions 1 and 2 that eluted first were identified as the epimers of trans form of dG-N2-tamoxifen. Fractions 3 and 4 were identified as the epimers of cis form of dG-N2-tamoxifen. When DNA was reacted with alpha-acetoxytamoxifen in vitro, three isomers of dG-N2-tamoxifen were detected: fraction 2 was the major adduct while fractions 1 and 3 were minor adducts.

Fundamental studies in reversed-phase liquid-solid extraction of basic drugs; I: Ionic interactions

Seven basic solutes with known and controlled pKa (7.93-9.5) and log P (0.23-6.63) values have been used as test probes to study the mechanism involved in liquid-solid extraction with C2 and C18 bonded silica phases. A limited comparison has also been made with underivatized silica and CN phases. In addition to the reversed-phase mechanism, cation-exchange was shown to play a very significant role in the retention process. Various cations both organic and inorganic were assessed for their elution strength, and the ordering was similar to that for classical ion-exchange chromatography. Control of selectivity in the elution process can be achieved by varying the concentration of cation or methanol in the eluent. The C2 cartridge in combination with an aqueous ammonium acetate-methanol eluent proved to be the most versatile in that all compounds, irrespective of pKa or log P could be recovered in high yield. The optimal eluent in terms of selectivity with respect to related compounds could be predicted from the solute log P. Blocking of silanols by pre-conditioning the cartridges with cations prior to sample applications was also studied. The order of cation strengths although somewhat variable was similar to that established at the elution stage. To achieve quantitative elution with methanol or aqueous methanol solutions however, high concentrations of inorganic cations, equivalent to 1 ml of a 1 M solution were required to pre-condition a 100 mg cartridge.

Biodistribution of a novel antiestrogen (Analog II) in the mouse and rat

The biodistribution of a novel antiestrogen Analog II was determined in the mouse and rat. The tritiated product, [3H]-Analog II was prepared by New England Nuclear and was purified by preparative chromatography using silica gel and petroleum ether/methylene chloride (80:20). The fat tissue had the highest uptake due to the hydrophobic nature of Analog II. The second highest uptake was in the mouse uterine tissue which was greater than that observed in the rat. The differences in biodistribution between the mouse and rat may partially explain the differences in biological activity of Analog II previously observed in these two animal species.

Difference in extractability of estradiol- and tamoxifen-receptor complex in the nuclei from MCF-7 cells with Nonidet P-40

The extraction of [3H]estradiol- and [3H]tamoxifen-receptor complex in the nuclei from MCF-7 cells with the nonionic detergent Nonidet P-40 has been studied. We found that there is a striking difference in the extractability of estradiol- and tamoxifen-receptor complex from nuclei with 0.5% Nonidet P-40. The nuclear bound estradiol-receptor complex is scarcely extractable with Nonidet P-40. In contrast, almost all of the nuclear bound tamoxifen-receptor complex is extractable. The nuclear [3H]tamoxifen-receptor complex extracted in the presence of Nonidet P-40 sediments in two peaks at 7 S and 5 S. The latter sedimentation rate is the same with that of the nuclear [3H]tamoxifen-receptor complex extracted with 0.4 M KCl. The nuclear [3H]estradiol-receptor complex extracted with 0.4 M KCl sediments at 4 S. The results suggest that interaction of tamoxifen-receptor complex with chromatin is different from that of estradiol-receptor complex.

Determination of tamoxifen and metabolites in human serum by high-performance liquid chromatography with post-column fluorescence activation

Sensitive and reproducible analyses were developed for assaying tamoxifen, monohydroxytamoxifen, N-desmethyltamoxifen, metabolite E [trans-1(4-hydroxyphenyl)1,2-diphenylbut-1-ene] and a new metabolite, metabolite Y [trans-1(4-hydroxyethoxyphenyl)-1,2-diphenylbut-1-ene] in human serum using high-performance liquid chromatography (HPLC). Three different systems were developed for specific purposes. All chromatography was performed using serum extracts made with hexane-butanol. Detection was by fluorimetry of phenanthrene derivatives formed by on-stream UV irradiation with a newly described device for post-column irradiation of the HPLC stream. This device may be of use in other HPLC systems requiring post-column photochemical reactions.