Hedgehog antagonists cyclopamine and dihydroveratramine can be mistaken for each other in Veratrum album

A toxic plant, Veratrum album (ssp. viriscens), was found to have an inhibitory effect on Hedgehog (Hh), a developmental signaling pathway that has been shown to be active during development, in adult stem cells and in numerous human tumors. Based on earlier studies it was believed that the known Hh inhibitor cyclopamine was present in V. album (ssp. viriscens). Here we show that instead of cyclopamine, dihydroveratramine (DHV) was found in V. album (ssp. viriscens). These compounds are easily mistaken for each other, as both substances share the same molecular weight, and the same main MS/MS fragments. DHV was found to be a less potent Hh inhibitor compared to cyclopamine. This is the first reported occurrence of DVH in nature.     

Identification and characterization of a photolytic degradation product of telmisartan using LC–MS/TOF,LC–MS,LC–NMR and on-line H/D exchange mass studies

Telmisartan, an anti-hypertensive drug, was subjected to stress studies under ICH prescribed conditions of hydrolysis (acidic, neutral and basic), photolysis, oxidation and thermal stress. The drug showed labiality under only photo-acidic condition by forming a single degradation product. HPLC separation of the drug and the degradation product was achieved on C-8 column using gradient method. To characterize the product, a complete mass fragmentation pathway of the drug was initially established. Subsequently, the degradation product peak was subjected to LC–MS/TOF and on-line H/D exchange mass studies. Based on these studies, a tentative structure was assigned to the product as 3-((1,7′-dimethyl-2′-propyl-1H,3′H-2,5′-bibenzo[d]imidazol-3′-yl)methyl)-6H-benzo[c]chromen-6-one, which was verified through ¹H LC–NMR experiments.     

Identification and characterization of degradation products of irbesartan using LC–MS/TOF,MS, on-line H/D exchange and LC–NMR

Irbesartan was subjected to hydrolytic, oxidative, photolytic and thermal stress, according to ICH guideline Q1A (R2). The drug showed degradation only in acidic, basic and photoacidic conditions, while it was stable to other stress conditions. A total of three degradation products were formed, which were separated on a C-8 column employing a gradient HPLC method. Initially, a complete mass fragmentation pathway of the drug was established with the help of MS/TOF, MSⁿ and H/D exchange studies. Subsequently, the degradation products were subjected to LC–MS/TOF and on-line H/D exchange mass studies to obtain their accurate mass, fragment pattern and number of labile hydrogens. The MS results helped to assign tentative structures to degradation products, which were verified through ¹H and 2D COSY LC–NMR experiments. The products were identified as (2′-(1H-tetrazol-5-yl)biphenyl-4-yl)methanamine, 1-(1-((2′-(1H-tetrazol-5-yl)biphenyl-4-yl)methylamino)pentylideneamino)cyclopentane carboxylic acid and 2-butyl-3-(tetrazolo[1,5-f]phenanthridin-6-ylmethyl)-1,3-diazaspiro[4.4]non-1-en-4-one. The structures were justified by mechanisms of their formation.     

Detection,identification and quantification of a new de-fluorinated impurity in casopitant mesylate drug substance during late phase development: An analytical challenge involving a multidisciplinary approach

During late phase development of the selective NK1 receptor antagonist casopitant mesylate, a de-fluorinated impurity was discovered and quantified by an orthogonal analytical approach, using NMR and LC–MS. A dedicated ¹⁹F NMR method was initially developed for first line identification and semi-quantification of the impurity. Subsequently, a more accurate quantification was achieved by means of a selective normal-phase LC–MS method, which was fully validated. The results obtained on the development batches of the drug substance were used by the project team to set up a suitable control strategy and ultimately to ensure patient safety and the progression of the project.     

The multikinase inhibitor axitinib is a potent inhibitor of human CYP1A2

The tyrosine kinase inhibitors (TKIs) and multikinase inhibitors (MKIs) are oncology drugs of increasing importance that have improved the treatment of multiple tumors types. In some patients these agents produce adverse effects, including pharmacokinetic drug–drug interactions, due to cytochrome P450 (CYP) inhibition. Information on the propensity of the drugs to elicit such effects often only becomes evident as the drugs enter clinical use. The present study assessed 18 kinase inhibitors (1 and 50 μM) for the inhibition of major drug metabolizing CYPs 1A2, 2C9, 2D6 and 3A4 in human liver microsomes. Most TKIs and MKIs inhibited CYP reactions at the higher concentration but axitinib also potently inhibited CYP1A2-dependent 7-ethoxyresorufin O-deethylation activity at the lower concentration. Kinetic analyses of CYP1A2 inhibition by axitinib were undertaken in microsomes and found a K_i of 0.11 ± 0.01 μM, which was 7.5-fold lower than the K_m for 7-ethoxyresorufin oxidation (0.83 ± 0.06 μM); the inhibition mechanism was linear-mixed. From computational modeling two potential binding modes for axitinib were identified in the active site of CYP1A2: one in which the oxidizable axitinib thioether sulfur atom is within ∼4.45 Å of the CYP1A2 heme, and is likely to favor biotransformation of the drug, and a second in which the pyridine moiety is in proximity to the heme, which may contribute to inhibition. The applicability of these findings to potential pharmacokinetic interactions in patients during axitinib treatment should now be assessed.     

Identification,isolation and characterization of process-related impurities in Rizatriptan benzoate

Three process-related impurities were observed in routine monitoring of the samples by HPLC. These impurities were identified by LC–MS. One of the impurities, Imp-3 [rizatriptan-2,5-dimer] was reported in literature. Other two impurities were isolated by preparative HPLC and characterized by NMR, Mass and IR. Pure impurities obtained by isolation were co-injected with Rizatriptan benzoate sample to confirm the retention times in HPLC. Structure elucidation of these impurities by spectral data has been discussed in detail. These impurities were identified as 4-(5-((1H-1,2,4-triazol-1-yl)methyl)-3-(2-(dimethylamino)ethyl)-1H-indol-1-yl)-4-(5-((1H-1,2,4-triazol-1-yl)methyl)-3-(2-(dimethylamino)ethyl)-1H-indol-2-yl)-N,N-dimethylbutan-1-amine [rizatriptan-1,2-dimer] and [4,4-bis-(5-((1H-1,2,4-triazol-1-yl)methyl)-3-(2-(dimethylamino)-ethyl)-1H-indol-2-yl)-N,N-dimethylbutan-1-amine [rizatriptan-2,2-dimer].     

Simultaneous determination of irbesartan and hydrochlorothiazide in human plasma using HPLC coupled with tandem mass spectrometry: Application to bioequivalence studies

A sensitive, specific and selective liquid chromatography/tandem mass spectrometric method has been developed and validated for the simultaneous determination of irbesartan and hydrochlorothiazide in human plasma. Plasma samples were prepared using protein precipitation with acetonitrile, the two analytes and the internal standard losartan were separated on a reverse phase C₁₈ column (50 mm × 4 mm, 3 μm) using water with 2.5% formic acid, methanol and acetonitrile (40:45:15, v/v/v (%)) as a mobile phase (flow rate of 0.70 mL/min). Irbesartan and hydrochlorothiazide were ionized using ESI source in negative ion mode, prior to detection by multiple reaction monitoring (MRM) mode while monitoring at the following transitions: m/z 296 → 269 and m/z 296 → 205 for hydrochlorothiazide, 427 → 175 for irbesartan. Linearity was demonstrated over the concentration range 0.06–6.00 μg/mL for irbesartan and 1.00–112.00 ng/mL for hydrochlorothiazide. The developed and validated method was successfully applied to a bioequivalence study of irbesartan (300 mg) with hydrochlorothiazide (12.5 mg) tablet in healthy volunteers (N = 36).     

A multi-technique approach using LC–NMR,LC–MS,semi-preparative HPLC,HR–NMR and HR–MS for the isolation and characterization of low-level unknown impurities in GW876008, a novel corticotropin-release factor 1 antagonist

A multi-technique approach was applied in order to fully characterize four low-level unknown impurities of GW876008, a novel CRF₁ receptor antagonist. Liquid chromatography (LC)–NMR spectroscopy was used in combination with LC–MS to obtain detailed information regarding the structure of the two major impurities present in batches of GW876008 and observed in the first synthetic scale-up for preclinical use. Two additional impurities were unexpectedly found at greater levels in a large scale synthesis for clinical use and their structure was elucidated by means of high resolution (HR)–MS and HR–NMR, after a small scale preparative HPLC purification step. This structural information was useful in terms of shedding light on the typical impurity profile of this new chemical entity with the aim to support the early development package for Phase I clinical studies.     

Rapid structure elucidation of drug degradation products using mechanism-based stress studies in conjunction with LC–MS and NMR spectroscopy: identification of a photodegradation product of betamethasone dipropionate

Betamethasone dipropionate is an active pharmaceutical ingredient (API) that is used in various dosage forms of finished products for the treatment of inflammatory disorders. An unknown degradant was observed during a solution stability study of betamethasone dipropionate. An approach that combines LC–MSⁿ, mechanism-based stress studies, semi-preparative HPLC purification and structure elucidation by NMR spectroscopy was used to identify the unknown species. The key step of this approach is the design of relevant stress studies based on the plausible degradation mechanism that is revealed by the informative LC–MSⁿ analysis. The appropriately designed mechanism-based stress studies not only verify the degradation mechanism but also produce enough quantities of the unknown species for further structure elucidation/confirmation by NMR spectroscopy. With this strategy, the unknown degradant was rapidly identified as lumibetametasone dipropionate, a photodegradation product of betamethasone dipropionate.     

LC/MS characterization of impurities and degradation products of a potent antitumor peptidic dimer,CU201

Compound CU201 [SUIM-(d-Arg-Arg-Pro-Hyp-Gly-Igl-Ser-d-Igl-Oic-Arg)₂, where SUIM = suberimidyl; Hyp = trans-4-hydroxyproline; Igl = α-(2-indanyl)-glycine; Oic = octahydroindole-2-carboxylic acid], is a dimeric analog of the potent bradykinin antagonist peptide B9430. It blocks the G_αq,11 signal of the heterotrimeric G proteins, stimulates c-Jun kinases, and induces apoptosis in lung cancer cells with neuroendocrine features. CU201 shows potent inhibition for small-cell lung cancer cells in vitro (ED₅₀ = 0.15 μM), as well as for small-cell lung cancer SHP-77 tumor growth in vivo. An HPLC method was developed, as part of a study supported by the National Cancer Institute's (NCI's) Rapid Access to Interventional Development (RAID) program, to assess the purity and stability of CU201. Impurities and degradation products were characterized by LC/MS. The identity of a major impurity, with 1 mass unit different from CU201, was confirmed by high resolution LC/MS and the investigation of model compounds. Susceptible linkages in the peptide chains were revealed by the degradation study.     

Liquid chromatography/tandem mass spectrometry for the determination of changrolin in rat plasma: Application to a bioavailability study

A sensitive and specific LC–CMS/MS method was developed for the quantification of changrolin, an anti-arrhythmic drug, in rat plasma using tiapride as internal standard. Liquid–liquid extraction was employed for sample preparation and analyzed using a multiple reaction monitoring mode with electrospray positive ionization source. The calibration curve for changrolin was linear over the range 5–1600 ng/mL with coefficients of correlation >0.99. The intra- and inter-batch precision was less than 8.6%, and accuracy ranged from 94.6% to 104.5%. This validated LC–MS/MS method was successfully applied to a bioavailability study of oral and intravenous administration of changrolin with 20 mg/kg dosage in SD rats.     

Evaluation of oligosaccharide methods for carbohydrate analysis in a fully human monoclonal antibody and comparison of the results to the monosaccharide composition determination by a novel calculation

Carbohydrates can change a drug's properties including solubility, affinity towards antigen, pharmacokinetics and pharmacodynamics. Due to this importance, carbohydrate composition is utilized as a parameter to evaluate a drug candidate's quality. In this study, the compositional monosaccharides of a drug candidate are measured by HPAEC-PAD, while the oligosaccharides are studied by HPAEC-PAD, CE-LIF and LC–MS. The advantages and limitations of these various approaches for oligosaccharide analysis are reviewed in this work. While the methods used for oligosaccharide analysis are well established we have devised a new and novel calculation for determining monosaccharide content using the relative percentages of the N-glycans. This calculation was used to evaluate the accuracy of the oligosaccharide determination methods by comparison of the N-glycan data to the experimental monosaccharide data. The results obtained from this novel calculation demonstrate that the relative abundance of carbohydrates as determined from these various approaches are consistent.     

Characterization of degradation products of amorphous and polymorphic forms of clopidogrel bisulphate under solid state stress conditions

The present study deals with the stress degradation studies on amorphous and polymorphic forms of clopidogrel bisulphate. The objective was to characterize the degradation products and postulate mechanism of decomposition of the drug under solid state stress conditions. For that, amorphous form, polymorph I and polymorph II of the drug were exposed to 40 °C/75% relative humidity (RH), with and without stressors for 3 months. The samples were analyzed by HPLC, and the relative extent of degradation as well as nature of decomposition was compared among three solid forms. In total, eight degradation products were observed under various stress conditions. The structures of all of them were elucidated using LC–MS/TOF and LC–MSⁿ studies. While one matched the known hydrolytic decomposition product of the drug in solution, seven others were new. The postulated degradation pathway and mechanism of decomposition are discussed.     

Structure elucidation of thioketone analogues of sildenafil detected as adulterants in herbal aphrodisiacs

Two analogues of sildenafil were detected in herbal dietary supplements marketed as aphrodisiacs. Both compounds were identified as thioketone analogues of sildenafil in which the carbonyl group in the pyrimidine ring of sildenafil was substituted with a thiocarbonyl group. The first compound was identified as thiosildenafil, a compound that has recently been reported as an adulterant in health supplements. The structure of the second compound was established using LC–MS, UV spectroscopy, ESI-MSⁿ, NMR and a hydrolytic process. A detailed study of the hydrolysis products of sildenafil, thiosildenafil, and the second unknown compound proved that the second compound, named thiomethisosildenafil, had a structure analogous to sildenafil in which the N-methylpiperazine moiety had been replaced with 2,6-dimethylpiperazine and the oxygen atom of the carbonyl group in the heterocyclic ring had been replaced with a sulfur atom. Under the hydrolytic reaction conditions employed in this study, thioketones hydrolyze to ketones (e.g., thiosildenafil → sildenafil), making this a valuable technique for the structure elucidation of thiosildenafil analogues. Ten herbal dietary supplements, each as a capsule dosage form, were found to contain 8–151 mg of thiomethisosildenafil per capsule, and one herbal dietary supplement was found to contain 35 mg of thiosildenafil per capsule.     

Profiling and quantification of isoflavone-C-glycosides impurities in puerarin injection by liquid chromatography coupled to ESI-ion trap mass spectrometry

An HPLC/DAD/MSⁿ method was established for the qualitative and quantitative analysis of the impurities in puerarin injection (PI), a widely used drug in China. The analytical HPLC was performed on an Agela RP-C18 column using 0.1% aqueous formic acid (v:v) and methanol as mobile phase. A total of nine impurities were detected and eight of them were identified as isoflavone-C-glycosides basing on their UV spectra and MSⁿ spectra and comparing with the literature data. An HPLC method for the assay of two common impurities in the commercial PI samples, i.e., neopuerarin A and neopuerarin B, was then established. The validation of the method, including sensitivity, linearity, precision, accuracy, was carried out. The calibration curves showed good linearity of R² > 0.9999 and LOQ (S/N = 10) were less than 3.73 ng. The precision was evaluated by intra- and inter-day assays and R.S.D. values were less than 0.94%. The average recovery rates were 97.0% and 99.5%, respectively, with R.S.D. less than 1.38%. The contents of neopuerarin A and neopuerarin B in various commercial brands of PI samples varied over the range of 0.30–1.16% and 0.42–1.66%, respectively. This is the first report on the impurities in PI.     

Structural characterization of sulfoaildenafil,an analog of sildenafil

Phosphodiesterase type 5 (PDE-5) inhibitors represent a class of drugs used primarily in the treatment of erectile dysfunction. Currently, three PDE-5 inhibitors have been approved by the U.S. Food and Drug Administration (FDA) for use in the United States: sildenafil citrate, tadalafil, and vardenafil hydrochloride trihydrate. A bulk material, labeled as an ingredient for a dietary supplement, was analyzed for the presence of PDE-5 inhibitors. The compound that was detected displayed structural similarities to sildenafil, and was characterized further using LC–MSⁿ, FTICRMS, X-ray crystallography and NMR. The compound was given the name sulfoaildenafil. When compared to sildenafil, sulfoaildenafil contains a sulfur atom substitution for the oxygen atom in the pyrazolopyrimidine portion of the molecule, and a 3,5-dimethyl substitution on the piperazine ring, rather than the 4-methyl moiety. The X-ray crystallographic data indicate that the material in this sample is comprised of two polymorphs, which may affect the chemical and/or biological properties of any product formulated with this compound.     

A proteomic approach to investigate AuNPs effects in Balb/3T3 cells

Although gold nanoparticles (AuNPs) are currently used in several industrial products and biomedical applications, information about their biological effects is very limited. Thus, it is becoming crucial to assess their safety and adequately investigate the complexity of cell–nanoparticles interactions. In this work, the Balb/3T3 mouse fibroblast cell line was selected as an in vitro model to study the effects of AuNPs. Alteration of cellular processes and biochemical pathways caused by AuNPs exposure was investigated by analysing the differentially expressed proteome. Of interest was the difference observed in the protein pattern expression of cells exposed to AuNPs. It was found that 88 and 83 proteins were de-regulated after exposure to 5 and 15 nm AuNPs, respectively. Analysis of the proteome revealed that AuNPs triggers several pathways related to cellular growth and proliferation, cell morphology, cell cycle regulation, cellular function and maintenance, oxidative stress, and inflammatory response. Moreover, SPR analysis showed an increase of ECM proteins biosynthesis in cells exposed to AuNPs. We observed by TEM analysis that NPs are internalized and confined mainly in autophagosomes. Endoplasmic reticulum stressed and modification at mitochondrial level occurred. This study aims to improve existing knowledge necessary for a correct assessment of the balance between AuNPs potential adverse and beneficial effects and might have important implications for biomedical applications (e.g. nanomedicine).     

Maternal glucocorticoid elevation and associated blood metabonome changes might be involved in metabolic programming of intrauterine growth retardation in rats exposed to caffeine prenatally

Our previous studies demonstrated that prenatal caffeine exposure causes intrauterine growth retardation (IUGR), fetuses are over-exposed to high levels of maternal glucocorticoids (GC), and intrauterine metabolic programming and associated metabonome alteration that may be GC-mediated. However, whether maternal metabonomes would be altered and relevant metabolite variations might mediate the development of IUGR remained unknown. In the present studies, we examined the dose- and time-effects of caffeine on maternal metabonome, and tried to clarify the potential roles of maternal GCs and metabonome changes in the metabolic programming of caffeine-induced IUGR. Pregnant rats were treated with caffeine (0, 20, 60 or 180 mg/kg · d) from gestational days (GD) 11 to 20, or 180 mg/kg · d caffeine from GD9. Metabonomes of maternal plasma on GD20 in the dose–effect study and on GD11, 14 and 17 in the time–course study were analyzed by ¹H nuclear magnetic resonance spectroscopy, respectively. Caffeine administration reduced maternal weight gains and elevated both maternal and fetal corticosterone (CORT) levels. A negative correlation between maternal/fetal CORT levels and fetal bodyweight was observed. The maternal metabonome alterations included attenuated metabolism of carbohydrates, enhanced lipolysis and protein breakdown, and amino acid accumulation, suggesting GC-associated metabolic effects. GC-associated metabolite variations (α/β-glucoses, high density lipoprotein-cholesterol, β-hydroxybutyrate) were observed early following caffeine administration. In conclusion, prenatal caffeine exposure induced maternal GC elevation and metabonome alteration, and maternal GC and relevant discriminatory metabolites might be involved in the metabolic programming of caffeine-induced IUGR.     

Benzylidenemalononitrile compounds as activators of cell resistance to oxidative stress and modulators of multiple signaling pathways. A structure-activity relationship study

Benzylidenemalononitrile (BMN) tyrphostins are well known as potent tyrosine kinase inhibitors. Moreover, in recent years it has been recognized that members of the tyrphostin family possess additional biological activities independent of their ability to inhibit protein tyrosine kinases. In this study, we examined the relationship between the structure of 49 BMNs and related compounds, and their capacity to induce heme oxygenase 1 (HO-1) gene expression in U937 human monocytic cells, to activate upstream signaling pathways and to protect cells against menadione-induced oxidative stress. It was found that the electron-withdrawing (NO₂, CN, halogen) groups in BMN molecules and double meta-MeO substituents increased the HO-1 gene induction, while the electron-donating groups in ortho/para position (OH, MeO and N-morpholino) significantly decreased it. The magnitude of activation of c-Jun, Nrf2, p38 MAPK, and p70S6K correlated with specific substitution patterns in the BMN structure. BMN-dependent maximal up-regulation of HO-1 required parallel increase in Nrf2 and phospho-c-Jun cellular levels. Liquid chromatography mass spectrometry (LC–MS) analysis revealed that BMNs can generate conjugates with one or two glutathione equivalent(s). This study supports the hypothesis that BMNs induce the expression of protective genes by alkylating sensitive cysteine residues of regulatory factors.