Electrospray ionization mass spectrometry and tandem mass spectrometry of clodronate and related bisphosphonate and phosphonate compounds

Long-term detection of clodronate in equine plasma by liquid chromatography-tandem mass spectrometry

Clodronate is a non-nitrogen-containing bisphosphonate drug approved in equine veterinary medicine. Clodronate is prohibited for use in competition horses; therefore, to set up an appropriate control, detection times and screening limits are required. The quantitative method in plasma consisted of addition of chloromethylene diphosphonic acid as internal standard. Automated sample preparation comprised a solid phase extraction with weak anion exchange properties on microplate. After methylation of the residue with trimethyl orthoacetate, analysis was conducted by high-performance liquid chromatography-tandem mass spectrometry. Using a weighting factor of 1/(concentration)² , good linearity was observed in the range of 1 to 500 ng/ml, with low limits of detection and quantification of 0.5 and 1 ng/ml, respectively. Precision and accuracy determined at four concentrations were satisfactory, with an error percentage less than 15%. Absence of carry-over and good stability of clodronic acid in plasma after a long-term storage at -20°C were verified. The method was successfully applied to the quantification of clodronic acid in plasma samples from horses administered with a single intramuscular administration of Osphos® at a mean dose of 1.43 ± 0.07 mg/kg. The observed detection time will be verified in a clinical population study conducted in diseased horses.

Rapid and sensitive determination of four bisphosphonates in rat plasma after MTBSTFA derivatization using liquid chromatography-mass spectrometry

Bisphosphonates (BPs) have broad medical applications against osteoporosis, bone metastasis and Paget's disease. The BP-related jaw osteonecrosis limits their use extensively and has a causal relationship with the process of drug disposition, such as deposition on bone and slow elimination rate. Thus it is imperative to accurately determine BP levels in either clinical or pharmacological/toxicological studies. The ability of trimethylsilyl diazomethane (TMSD) to alkylate the hydroxyls in phosphoric groups is an advantage in terms of decreasing polarity and enhancing mass response of BPs. There are, however, practical limitations to the cumbersome sample preparation procedure, the prolonged reaction time, the by-products and the obstacle to ionization. To overcome these disadvantages, a simplified and rapid precolumn derivatization method with N-(tert-Butyldimethylsilyl)-N-methyl-trifluoroacetamide (MTBSTFA) to quantify etidronate, clodronate, alendronate and zoledronate BPs in rat plasma was established in this work. The derivatization reaction was conducted within 2 min at room temperature, and the unitary di-tert-butyldimethylsilyl (di-tBDMS) derivative was obtained for each BP. Derivatives were separated on a XTerra® MS C₈ column (2.1 × 50 mm, 3.5 μm) with the mobile phase of 5 mM ammonium acetate buffer (pH 8.5) and acetonitrile, then detected using electrospray ionization tandem mass spectrometry in negative mode. An easy extraction process instead of the time-consuming solid-phase extraction (SPE) was employed for plasma treatment. The proposed method showed good linearity for BPs over the range of 2-500 ng/mL in 20 μL plasma and high sensitivity owing to the larger molecular ions, higher ionization capacity and more stable fragments of di-tBDMS derivatives. The intra- and inter-batch precision were <13.1 %, and the accuracy ranged within ±10 %. The extraction recovery varied from 75.4 to 88.0 %. The optimized method was successfully applied to characterize the pharmacokinetic profile of zoledronate in rats. Moreover, it is a promising approach for the determination of other phosphoric acid-containing metabolites.

Preparation, Characterization, and Radiolabeling of [68Ga]Ga-NODAGA-Pamidronic Acid: A Potential PET Bone Imaging Agent

Early diagnosis of bone metastases is crucial to prevent skeletal-related events, and for that, the non-invasive techniques to diagnose bone metastases that make use of image-guided radiopharmaceuticals are being employed as an alternative to traditional biopsies. Hence, in the present work, we tested the efficacy of a gallium-68 (⁶⁸Ga)-based compound as a radiopharmaceutical agent towards the bone imaging in positron emitting tomography (PET). For that, we prepared, thoroughly characterized, and radiolabeled [⁶⁸Ga]Ga-NODAGA-pamidronic acid radiopharmaceutical, a ⁶⁸Ga precursor for PET bone cancer imaging applications. The preparation of NODAGA-pamidronic acid was performed via the N-Hydroxysuccinimide (NHS) ester strategy and was characterized using liquid chromatography-mass spectrometry (LC-MS) and tandem mass spectrometry (MSⁿ). The unreacted NODAGA chelator was separated using the ion-suppression reverse phase-high performance liquid chromatography (RP-HPLC) method, and the freeze-dried NODAGA-pamidronic acid was radiolabeled with ⁶⁸Ga. The radiolabeling condition was found to be most optimum at a pH ranging from 4 to 4.5 and a temperature of above 60 °C. From previous work, we found that the pamidronic acid itself has a good bone binding affinity. Moreover, from the analysis of the results, the ionic structure of radiolabeled [⁶⁸Ga]Ga-NODAGA-pamidronic acid has the ability to improve the blood clearance and may exert good renal excretion, enhance the bone-to-background ratio, and consequently the final image quality. This was reflected by both the in vitro bone binding assay and in vivo animal biodistribution presented in this research.

Study of bisphosphonates by matrix-assisted laser desorption/ionization mass spectrometry--influence of alkali atoms on fragmentation patterns

1-hydroxymethylene-1,1-bisphosphonic acids (or bisphosphonates) are compounds that have interesting pharmacological applications. However, few mass spectrometric investigations have been carried out to determine their fragmentation patterns. Herein, we evaluated different matrices for the study by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) of the formation and fragmentation of the protonated, the cationized (MNa+ and MK+) and the deprotonated bisphosphonates. Some in-source fragmentations were observed both in positive and in negative ion modes. The fragmentation patterns obtained in post-source decay mode are also discussed. In contrast to previous electrospray ionization/multi-stage mass spectrometry (ESI-MSn) studies, some new fragmentation pathways were deduced and the effects of alkali ions on the fragmentation patterns were shown. The results summarized here completed the data previously recorded by ESI-MSn and could be used for the characterization of bisphosphonates as alkali complexes in biological mixtures.

Electrospray tandem mass spectrometry of alendronate analogues: fingerprints for characterization of new potential prodrugs

1-hydroxymethylene-1,1-bisphosphonic acids (HMBPs) are important drugs for the treatment of a variety of bone diseases. Since these compounds have no chromophore, their detection is challenging and mass spectrometry (MS) appears to be an appropriate sensitive tool. Our work deals with the analysis by electrospray ionization tandem mass spectrometry (ESI-MSn) of the well-known nitrogen-containing HMBP alendronate and of three analogues, considered as potential prodrugs. These four molecules share a common structure with different protecting groups on the phosphonic acid and on the amine functions. We describe the dissociation mechanisms of nitrogen-containing HMBPs in positive ion mode and we compare, in negative ion mode, our results with literature data. In both modes, the dissociations are essentially losses of ROH, and of phosphorus-containing species (HPO2, ROP(OH)2 and ROPO(OH)2), where R=H, C6H5, or CH3OC6H5. These fingerprints will be of great value for differentiating alendronate from its potential prodrugs in complex biological mixtures.

Fragmentation patterns of new esterified and unesterified aromatic 1-hydroxymethylene-1, 1-bisphosphonic acids by ESI-MSn

1-Hydroxymethylene-1,1-bisphosphonic acids (HMBPs) are compounds that have interesting pharmacological applications. Unfortunately few studies exist on their analyses by mass spectrometry (MS). In this work, we have analyzed new aromatic HMBPs and their prodrugs with electrospray tandem mass spectrometry (ESI-MS(n)). We describe, for the first time, a complete study of fragmentation patterns, in both positive and negative-ion modes. In positive mode, the cation dissociations are mainly elimination of water and phosphorus fragments. In negative mode, losses of ROH (R==H, C(6)H(5), CH(3)OC(6)H(5)) and HPO(2) were observed. The results have revealed specific structural fingerprints for the screening of these compounds in complex biological mixtures.

Characterization of industrial alkylpolyphosphonates by infusion electrospray ionization-ion trap mass spectrometry with identification of the impurities by tandem capillary zone electrophoresis

Technical grade diethylene-triaminepentakis(methylenephosphonic acid) (I), dihexamethylene-triaminepentakis(methylenephosphonic acid) (II), ethylene-diaminetetrakis(methylenephosphonic acid) (III), hexamethylene-diaminetetrakis(methylenephosphonic acid) (IV), amino-tris(methylenephosphonic acid) (V), hydroxyethyl-aminobis(methylenephosphonic acid) (VI), 1-hydroxyethylidene-1,1-diphosphonic acid (VII), and 2-phosphonobutane-1,2,4-tricarboxylic acid (VIII) were characterized by ion trap mass spectrometry with electrospray ionization (ESI-ITMS). Using the negative ion mode and acid and alkaline media, peak series corresponding to the nominal compounds and to impurities with a lower number of phosphonate groups were distinguished in I-V. Each series was constituted by [M - nH + (n - 1)Na](-) peaks and peaks produced from them by losses of water, H(3)PO(3)(or water plus HPO(2)), and combined losses. For each [M - nH + (n - 1)Na](-) peak, the number of losses coincided with the number of phosphonate groups not bound to sodium ions minus one (the group bearing the charge). Owing to the hydroxyethyl group, the spectrum of VI was dominated by the formation of intermolecular esters, with both losses and gains of water according to [nM - H +/- mH(2)O](-). A series of [M - nH + (n - 1)Na](-) peaks were observed for VII and VIII, showing in the latter case that the carboxylate groups may also form adducts with sodium ions. Losses of water and H(3)PO(3)were observed in VII, whereas losses of water, CO(2), and HPO(3) were seen in VIII. The reaction pathways leading to the production of the observed ions are described. The nominal compounds and the impurities were also separated and identified by capillary electrophoresis with ESI-ITMS detection.

Preparation of porous n-type silicon sample plates for desorption/ionization on silicon mass spectrometry (DIOS-MS)

This study focuses on porous silicon (pSi) fabrication methods and properties for desorption ionization on silicon mass spectrometry (DIOS-MS). PSi was prepared using electrochemical etching of n-type silicon in HF-ethanol solution. Porous areas were defined by a double-sided illumination arrangement: front-side porous areas were masked by a stencil mask, eliminating the need for standard photolithography, and backside illumination was used for the backside ohmic contact. Backside illumination improved the uniformity of the porosified areas. Porosification conditions, surface derivatizations and storage conditions were explored to optimize pSi area, pore size and pore depth. Chemical derivatization of the pSi surfaces improved the DIOS-MS performance providing better ionization efficiency and signal stability with lower laser energy. Droplet spreading and drying patterns on pSi were also examined. Pore sizes of 50-200 nm were found to be optimal for droplet evaporation and pore filling with the sample liquid, as measured by DIOS efficiency. With DIOS, significantly better detection sensitivity was obtained (e.g. 150 fmol for midazolam) than with desorption ionization from a standard MALDI steel plate without matrix addition (30 pmol for midazolam). Also the noise that disturbs the detection of low-molecular weight compounds at m/z < 500 with MALDI could be clearly reduced with DIOS. Low background MS spectra and good detection sensitivity at the 100-150 fmol level for pharmaceutical compounds were achieved with DIOS-MS.