Recent advances in trace analysis of pharmaceutical genotoxic impurities

Preparation and optimization of dummy molecularly imprinted polymer-based solid-phase extraction system for selective enrichment of p-toluene sulfonate esters genotoxic impurities

Sulfonate esters, one class of genotoxic impurities (GTIs), have gained significant attention in recent years due to their potential to cause genetic mutations and cancer. In the current study, we employed the dummy template molecular imprinting technology with a dummy template molecule replacing the target molecule to establish a pretreatment method for samples containing p-toluene sulfonate esters. Through computer simulation and ultraviolet-visible spectroscopy analysis, the optimal functional monomer acrylamide and polymerization solvent chloroform were selected. Subsequently, a dummy template molecularly imprinted polymer (DMIP) was prepared by the precipitation polymerization method, and the polymer was characterized in morphology, particle size, and composition. The results of the adsorption and enrichment study demonstrated that the DMIP has high adsorption capability (Q = 7.88 mg/g) and favorable imprinting effects (IF = 1.37); Further, it could simultaneously adsorb three p-toluene sulfonate esters. The optimal adsorption conditions were obtained by conditional optimization of solid-phase extraction (SPE). A pH 7 solution was selected as the loading condition, the methanol/1 % phosphoric acid solution (20:80, v/v) was selected as the washing solution, and acetonitrile containing 10 % acetic acid in 6 mL was selected as the elution solvent. Finally, we determined methyl p-toluene sulfonate alkyl esters, ethyl p-toluene sulfonate alkyl esters, and isopropyl p-toluene sulfonate alkyl esters in tosufloxacin toluene sulfonate and capecitabine at the 10 ppm level (relative to 1 mg/mL active pharmaceutical ingredient (API) samples) by using DMIP-based SPE coupled with HPLC. This approach facilitated the selective enrichment of p-toluene sulfonate esters GTIs from complex API samples.

Deep eutectic solvents as green and sustainable diluents in headspace gas chromatography for the determination of trace level genotoxic impurities in pharmaceuticals

Genotoxic impurities (GTIs) are potential carcinogens that need to be controlled down to ppm or lower concentration levels in pharmaceuticals under strict regulations. The static headspace gas chromatography (HS-GC) coupled with electron capture detection (ECD) is an effective approach to monitor halogenated and nitroaromatic genotoxins. Deep eutectic solvents (DESs) possess tunable physico-chemical properties and low vapor pressure for HS-GC methods. In this study, zwitterionic and non-ionic DESs have been used for the first time to develop and validate a sensitive analytical method for the analysis of 24 genotoxins at sub-ppm concentrations. Compared to non-ionic diluents, zwitterionic DESs produced exceptional analytical performance and the betaine : 7 (1,4- butane diol) DES outperformed the betaine : 5 (1,4-butane diol) DES. Limits of detection (LOD) down to the 5-ppb concentration level were achieved in DESs. Wide linear ranges spanning over 5 orders of magnitude (0.005-100 µg g-1) were obtained for most analytes with exceptional sensitivities and high precision. The method accuracy and precision were validated using 3 commercially available drug substances and excellent recoveries were obtained. This study broadens the applicability of HS-GC in the determination of less volatile GTIs by establishing DESs as viable diluent substitutes for organic solvents in routine pharmaceutical analysis.

Determination of genotoxic impurities of aromatic aldehydes in pharmaceutical preparations by high performance liquid chromatography after derivatization with N-Cyclohexyl-4-hydrazino-1,8-naphthalenediimide

The detection of aromatic aldehydes, considered potential genotoxic impurities, holds significant importance during drug development and production. Current analytical methods necessitate complex pre-treatment processes and exhibit insufficient specificity and sensitivity. This study presents the utilization of naphthalenediimide as a pre-column derivatisation reagent to detect aromatic aldehyde impurities in pharmaceuticals via high-performance liquid chromatography (HPLC). We screened a series of derivatisation reagents through density functional theory (DFT) and investigated the phenomenon of photoinduced electron transfer (PET) for both the derivatisation reagents and the resulting products. Optimal experimental conditions for derivatisation were achieved at 40 °C for 60 min. This approach has been successfully applied to detect residual aromatic aldehyde genotoxic impurities in various pharmaceutical preparations, including 4-Nitrobenzaldehyde, 2-Nitrobenzaldehyde, 1,4-Benzodioxane-6-aldehyde, and 5-Hydroxymethylfurfural. The pre-column derivatisation method significantly enhanced detection sensitivity and reduced the limit of detection (LOD), which ranged from 0.002 to 0.008 μg/ml for the analytes, with relative standard deviations < 3 %. The correlation coefficient (R2) >0.998 demonstrated high quality. In chloramphenicol eye drops, the concentration of 4-Nitrobenzaldehyde was measured to be 8.6 µg/mL below the specified concentration, with recoveries ranging from 90.0 % to 119.2 %. In comparison to existing methods, our work simplifies the pretreatment process, enhances the sensitivity and specificity of the analysis, and offers comprehensive insights into impurity detection in pharmaceutical preparations.

Development of a Triphenylmethyl Alkylation Pre-Column Derivatization Method for HPLC Quantitative Analysis of Chemically Unstable Halogenated Compounds

The primary limitations of the quantitative analysis of thermally labile halogenated compounds by traditional gas chromatography (GC) are the inadequacy of identifying the insufficiently volatile impurity (often with a high boiling point) and the difficulty in obtaining a standard substance with a reliable standardized assay. Taking the 4-(Chloromethyl)-5-methyl-1,3-dioxol-2-one (DMDO-Cl, 1) as an example, we reported a triphenylmethanamino-derivatization method to overcome the challenges of the assay determination of such species. During the quantification of 1, the presence of GC-undetectable polymeric impurity 10 poses a critical challenge in assessing the material quality. Moreover, the standard substance of 1 is not available on the market due to its inherent instability during storage and handling, further complicating the quantitative analysis. In this work, a precolumn HPLC-UV derivatization method based on triphenylmethanamino-alkylation was developed to quantitatively analyze 1. The resulting derivative 2 exhibits excellent crystallinity and superior physical and chemical stability and possesses effective chromophores for UV detection. The conversion from analyte 1 to derivative 2 demonstrates desirable reactivity and purity, facilitating quantitative analysis using the external standard method. The chemical derivatization-chromatographic detection method was optimized and validated, demonstrating its high specificity, good linearity, precision, accuracy, and stability. This method offers a valuable alternative to the general quantitative NMR (qNMR) detection technique, which exhibits reduced specificity in the presence of increased levels of impurities in compound 1.

In silico toxicity assessment and trace level quantification of two genotoxic impurities in silodosin using capillary gas chromatography

A capillary gas chromatographic method using flame ionization detection was developed and validated for the trace quantification of 2-bromoethanol (2-BE) and 2-bromoethylmethanesulfonate (2-BEM) in silodosin, used in the treatment of benign prostatic hyperplasia. Chromatographic separation was performed in spilt mode using nitrogen as carrier gas on a column containing crosslinked polyethylene glycol (30 m × 0.32 mm, 0.25 µm) stationary phase modified with nitroterephthalic acid. A simple matrix precipitation strategy was implemented to eliminate the sample overload and the matrix interference problems. The developed method was linear and accurate in the concentration range of 24–3000 ppm for 2-BE and 24–300 ppm for 2-BEM with r2 ˃ 0.999 and percent recoveries greater than 90% for both the analytes. The developed method was precise for both the analytes with RSD(%) of not more than 4.5%. In silico genotoxicity and carcinogenicity potential of 2-BEM were assessed using ICH M7 principles. The developed method can be applied in the quality control laboratories of pharmaceutical industries for trace level quantification of 2-BE and 2-BEM in silodosin.

Determination of Three Alkyl Camphorsulfonates as Potential Genotoxic Impurities Using GC-FID and GC-MS by Analytical QbD

Camphorsulfonic acid salts are commonly used in the manufacturing production of active pharmaceutical ingredients (APIs) and have the potential to form alkyl camphorsulfonates, which can be considered as potential genotoxic impurities (PGIs). Alkyl camphorsulfonates should be controlled using the Threshold of Toxicological Concern (TTC) when detected in APIs due to their genotoxicity. An in silico study utilizing the ICH M7 guideline was performed in order to classify the alkyl camphorsulfonates that can be produced from the reaction of camphorsulfonic acid salts with methanol, ethanol, and isopropyl alcohol, which are commonly used solvents in API manufacturing processes. Two sensitive, reproducible, and accurate analytical methods using GC-FID and GC-MS were developed using the analytical Quality By Design (QbD) approaches for the quantitation of three alkyl camphorsulfonates in APIs satisfying the control limit of PGIs according to the TTC. The detection limits of the GC-FID method were found to be between 1.5 to 1.9 ppm, and the detection limits of the GC-MS method were found to be between 0.055 to 0.102 ppm. The method was validated in terms of accuracy, linearity, precision, detection limit, quantitation limit, specificity and robustness.

Analytical Method Development for 19 Alkyl Halides as Potential Genotoxic Impurities by Analytical Quality by Design

Major issues in the pharmaceutical industry involve efficient risk management and control strategies of potential genotoxic impurities (PGIs). As a result, the development of an appropriate method to control these impurities is required. An optimally sensitive and simultaneous analytical method using gas chromatography with a mass spectrometry detector (GC–MS) was developed for 19 alkyl halides determined to be PGIs. These 19 alkyl halides were selected from 144 alkyl halides through an in silico study utilizing quantitative structure–activity relationship (Q-SAR) approaches via expert knowledge rule-based software and statistical-based software. The analytical quality by design (QbD) approach was adopted for the development of a sensitive and robust analytical method for PGIs. A limited number of literature studies have reviewed the analytical QbD approach in the PGI method development using GC–MS as the analytical instrument. A GC equipped with a single quadrupole mass spectrometry detector (MSD) and VF-624 ms capillary column was used. The developed method was validated in terms of specificity, the limit of detection, quantitation, linearity, accuracy, and precision, according to the ICH Q2 guideline.

Exposure to Low UV-B Dose Induces DNA Double-Strand Breaks Mediated Onset of Endoreduplication in Vigna radiata (L.) R. Wilczek Seedlings

Multiple lines of evidence indicate that solar UV-B light acts as an important environmental signal in plants, regulating various cellular and metabolic activities, gene expression, growth and development. Here, we show that low levels of UV-B (4.0 kJ m-2) significantly influence plant response during early seedling development in the tropical legume crop Vigna radiata (L.) R. Wilczek. Exposure to low doses of UV-B showed relatively less growth inhibition yet remarkably enhanced lateral root formation in seedlings. Both low and high (8.0 kJ m-2) doses of UV-B treatment induced DNA double-strand breaks and activated the SOG1-related ATM-ATR-mediated DNA damage response pathway. These effects led to G2-M-phase arrest with a compromised expression of the key cell cycle regulators, including CDKB1;1, CDKB2;1 and CYCB1;1, respectively. However, along with these effects, imbibitional exposure of seeds to a low UV-B dose resulted in enhanced accumulation of FZR1/CCS52A, E2Fa and WEE1 kinase and prominent induction of endoreduplication in 7-day-old seedlings. Low dose of UV-B mediated phenotypical responses, while the onset of endoreduplication appeared to be regulated at least in part via UV-B induced reactive oxygen species accumulation. Transcriptome analyses further revealed a network of co-regulated genes associated with DNA repair, cell cycle regulation and oxidative stress response pathways that are activated upon exposure to low doses of UV-B.

Recent progress of microfluidic technology for pharmaceutical analysis

In recent years, the progress of microfluidic technology has provided new tools for pharmaceutical analysis and the proposal of pharm-lab-on-a-chip is appealing for its great potential to integrate pharmaceutical test and pharmacological test in a single chip system. Here, we summarize and highlight recent advances of chip-based principles, techniques and devices for pharmaceutical test and pharmacological/toxicological test focusing on the separation and analysis of drug molecules on a chip and the construction of pharmacological models on a chip as well as their demonstrative applications in quality control, drug screening and precision medicine. The trend and challenge of microfluidic technology for pharmaceutical analysis are also discussed and prospected. We hope this review would update the insight and development of pharm-lab-on-a-chip.

Liquid Chromatography-Mass Spectrometric Methods for Trace Quantification of Potential Genotoxic Impurities in Ivacaftor and Lumacaftor

OBJECTIVE

The objective of the current study was to develop and validate the sensitive LC-MS methods for trace analysis of genotoxic impurities in Ivacaftor and Lumacaftor. The first method is for the trace analysis of 2,4-di-tert-butyl-5-nitrophenol in ivacaftor and the second method is for the trace analysis of 1-(2,2-difluoro-1,3-benzodioxol-5yl)-cyclopropane carboxylic acid and 3-carboxyphenyl boronic acid in lumacaftor.

MATERIALS AND METHODS

High pure analytical grade solvents and reagents were used for this study. The chromatographic separation was performed on Luna C18 (250 × 4.6 mm, 5.0 µm) at a column temperature of 25 °C using eluent consisting of acetonitrile and 0.1% v/v formic acid in water in a gradient elution mode. The eluent was run at a flow of 1.0 mL/min and injection volume of 20 µL.

RESULTS

The linearity, precision and accuracy of the developed methods was validated over the concentration range of 0.35 - 15.0 ppm for 2,4-di-tert-butyl-5-nitrophenol, 0.30 - 15.0 ppm for 1-(2,2-difluoro-1,3-benzodioxol-5yl)-cyclopropane carboxylic acid and 0.23 - 15.0 ppm for 3-carboxyphenyl boronic acid. In both methods, interference was not observed at the retention time of analyte peaks. All the analytes were found to be stable in solution for a period of 48 h.

CONCLUSION

The proposed methods are reliable, sensitive, precise, accurate, and robust for the trace level quantification of genotoxic impurities in Ivacaftor and Lumacaftor. These methods can be successfully implemented in the quality control lab for routine analysis.

Liquid chromatography-tandem mass spectrometric method for trace quantification of ethyl methanesulfonate: a genotoxic impurity in dapoxetine hydrochloride

Background

Dapoxetine hydrochloride is a selective serotonin reuptake inhibitor drug for treating premature ejaculation. This study was designed to develop and validate a sensitive and selective LC–MS/MS method for trace analysis of genotoxic impurity ethyl methanesulfonate in Dapoxetine hydrochloride.

Results

Chromatographic separation was achieved on the Shodex RSpak DS-413 column, 150 × 4.6 mm, 3.0 µm using eluent containing a equal volumes of acetonitrile and 0.1% v/v formic acid in water was used in the isocratic elution mode at a pump flow of 1.0 mL/min. No interference was observed at the retention time of ethyl methanesulfonate, indicating that the developed method is specific and selective for trace level quantification.The developed method was found to be linear in the concentration range of 1–50 ppm with coefficient of regression of 0.9997. Detection limit and quantification limit were determined to be 0.6 ppm and 1.0 ppm respectively. Acceptable RSD values (< 10.0%) and recovery results (> 90%) obtained from the accuracy and precison experiments indicate that the developed method is precise and accurate in the concentration range of 1–50 ppm. Ethyl methanesulfonate solutions were stable for two days when stored at room and refrigerated temperatures.

Conclusion

The developed method has the ability to quantify ethyl methanesulfonate in dapoxetine hydrochloride. Thus, the anticipated method has high probability to adopt in the quality testing laboratories of pharmaceutical industry.

Development and Validation of a UPLC-MS/MS Method for Ultra-Trace Level Determination of Acyl Chloride Potential Genotoxic Impurity in Mezlocillin

3-Chlorocarbonyl-1-methanesulfonyl-2-imidazolidinone (CMI) is a critical intermediate used in the synthesis of mezlocillin drug substance and also a potential genotoxic impurity with acyl chloride moiety. The content of CMI in mezlocillin should be <0.16 ppm to avoid the carcinogenicity and mutagenicity threats to patients. Therefore, a workable determination of CMI was critically crucial for ensuring the safety of mezlocillin drug products. However, the conventional HPLC method is insufficient for detection limits at ppm or lower levels. Besides, the high activity of acyl chloride also raises a challenge to the direct measurement of CMI. Thus, we explored a simple esterification approach, which converts CMI into methyl 3-(methylonyl)-2-oxoimidazolidine-1-carboxylate completely by optimizing the reaction temperature and time. Furthermore, the selected reaction monitoring model of triple quadrupole mass spectrometer optimized by the Box-Behnken design significantly enhanced the sensitivity of ultra-trace level determination. The limit of detection and limit of quantification of the method were reached 0.014 and 0.02 ppm, respectively, in the following validation study. A sensitive and specific ultra-performance liquid chromatography tandem mass spectrometry method for ultra-trace level determination of acyl chloride potential genotoxic impurity in mezlocillin drug substance has been successfully established in this study, which will provide a practical quality control tool of mezlocillin.

Critical Analysis of Drug Product Recalls due to Nitrosamine Impurities

A product recall is the outcome of a careful pharmacovigilance; and it is an integral part of drug regulation. Among various reasons for product recall, the detection of unacceptable levels of carcinogenic impurities is one of the most serious concerns. The genotoxic and carcinogenic potential of N-nitrosamines raises a serious safety concern, and in September 2020, the FDA issued guidance for the pharmaceutical industry regarding the control of nitrosamines in drug products. The FDA database shows that >1400 product lots have been recalled from the market due to the presence of carcinogenic N-nitrosamine impurities at levels beyond the acceptable intake limit of 26.5 ng/day. The drugs that were present in recalled products include valsartan, irbesartan, losartan, metformin, ranitidine, and nizatidine. This perspective provides a critical account of these product recalls with an emphasis on the source and mechanism for the formation of N-nitrosamines in these products.

Stability Indicating Methods for Determination of Third Generation Antiepileptic Drugs and Their Related Substances

The third generation of antiepileptic drugs that have been approved by international regulatory agencies between 2007 and 2018 include rufinamide, stiripentol, eslicarbazepine acetate, lacosamide, perampanel, brivaracetam and everolimus. As part of demonstrating their safety profile, stability indicating methods are developed to monitor these drugs and their impurities. In this context, this review describe some characteristics, impurities and the stability indicating methods used for the determination of these drugs and the presence of their related substances. Through a search in official compendia and scientific articles, fifty-six analytical methodologies were identified up to October 2020. The methodologies were developed using techniques of HPLC, UPLC, HPTLC, GC and UV/Vis spectrophotometry. A majority of the methods (∼70%) employed HPLC-UV. A number of these antiepileptic drugs were found to have had a small number of studies related to their stability and for the detection of impurities. The presentation of the current level of research on third generation antiepileptic drugs highlights the need for new stability and safety studies that are necessary to develop new pharmaceutical products containing these drugs.

Machine learning guided prediction of liquid chromatography-mass spectrometry ionization efficiency for genotoxic impurities in pharmaceutical products

The limitation and control of genotoxic impurities (GTIs) has continued to receive attention from pharmaceutical companies and authorities for several decades. Because GTIs have the ability to damage deoxyribonucleic acid (DNA) and the potential to cause cancer, low-level quantitation is required to protect patients. A quick and easy method of determining the liquid chromatography-mass spectrometry (LC/MS) conditions for high-sensitivity analysis of GTIs may prospectively accelerate pharmaceutical development. In this study, a quantitative structure-property relationship (QSPR) model was developed for predicting the ionization efficiency of compounds using liquid-chromatography-mass spectrometry (LC/MS) parameters and molecular descriptors. Before implementing the QSPR prediction model, linear regression analysis was performed to model the relationship between the ionization efficiency and the LC/MS parameters for each compound. Comparison of the predicted peak areas with the experimentally observed peak areas showed good agreement based on the coefficient of determination (R² > 0.96). The machine learning-based QSPR approach begins with computation of the molecular descriptors expressing the physicochemical properties of a compound, followed by a genetic algorithm-based feature selection. Linear and nonlinear regression were performed, and support vector machine (SVM) was selected as the best machine learning algorithm for the prediction. The SVM algorithm was developed and optimized using 1031 experimental data points for nine compounds, including well-known GTIs. Validation of the model by comparison of the predicted and observed relative ionization efficiencies (RIE) showed a high coefficient of determination (R² = 0.96) and low root mean squared error value (RMSE = 0.118). Finally, this established prediction model was applied to hydrophilic interaction liquid chromatography coupled with MS for a new compound in new mobile phase compositions and new MS parameter settings. The RMSE of the predicted versus observed RIE was 0.203. This prediction accuracy was sufficient to determine the starting point of the LC/MS method development. The methodology demonstrated in this study can be used to determine the LC/MS conditions for high sensitivity analysis of GTIs.

UHPLC-fluorescence method for the determination of trace levels of hydrazine in allopurinol and its formulations: Validation using total-error concept

The present approach poses an interesting way to quantify residues of the genotoxic impurity hydrazine in allopurinol and its pharmaceutical formulations using ultra high performance liquid chromatography coupled to fluorescence detection. Hydrazine was pre-column derivatized through a unique chemistry with o-phthalaldehyde under acidic conditions. Using highly acidic mobile phase the derivative exhibits a strong fluorescence intensity. Derivatization and chromatographic parameters were thoroughly investigated. The validation of the developed method has been carried out in the range of 10 to 200% of the target concentration limit of the analyte using the accuracy profiles as a graphical decision-making tool. The β-expectation tolerance intervals did not exceed the acceptance criteria of ±20% which means that 95% of future results will be included in the defined bias limits. The variation of the relative bias ranged between -6.0 and 0.5% and the RSD values for repeatability and intermediate precision were lower than 6.9% in all cases. The limit of detection (LOD) and the lower limit of quantification (LLOQ) were satisfactory and found to be 0.3 ng mL^-1 (corresponding to 0.03 μg g^-1 in solid sample). Experimental designs were constructed to study the robustness of the instrumental method and the derivatization procedure. The developed method has been successfully applied for the analysis of hydrazine in allopurinol API batches and tablets indicating that this methodology could be adopted from QC laboratories.

Development and Validation of LC-MS/MS for Analyzing Potential Genotoxic Impurities in Pantoprazole Starting Materials

Pantoprazole sodium (PPZS) is a selective proton pump inhibitor used in the prevention and treatment of gastric acid-related diseases. Six potentially genotoxic impurities (PGIs) are involved in 5-difluoromethoxy-2-mercapto-1H-benzimidazole (DMBZ), which is the starting material of PPZS. To date, no suitable method has yet been developed for PGI separation and quantification at the threshold of toxicological concern levels. In this study, a sensitive and reliable liquid chromatography-tandem mass spectrometry method was developed and validated for the quantitative analysis of six PGIs in DMBZ according to the guidelines of the International Council for Harmonization (ICH). The calibration curves showed good linearity within the studied range, and the correlation coefficient of fitting exceeded 0.998 for each impurity. The sensitivity of the proposed method was in the range of 0.6-10.0 ng/mL. Good recoveries were observed in the range of 94.32%-107.43% with RSD values below 6.5%. Quantitative analysis of impurities in substance batches of DMBZ showed the high efficiency of the developed method at a low level. Hence, the proposed method is practical and useful in the detection and qualification of PGIs in DMBZ and may be applied to ensure the safe use of PPZS in clinical treatment.

A new HPLC-UV derivatization approach for the determination of potential genotoxic benzyl halides in drug substances

Benzyl halides, widely used as alkylation reagents in drug synthesis, are potential genotoxic impurities (PGTIs) required to be controlled at trace levels. However, the existing analytical methods for benzyl halides often suffer from matrix interferences or low derivatization efficiency of benzyl chlorides. In this paper, a simple derivatization HPLC-UV method was developed for the analysis of these residual trace benzyl halides in drug substances. 1-(4-Nitrophenyl) piperazine (4-NPP) was selected as a new derivatization reagent because it shifted well the benzyl halides derivatives away to the near visible range (392 nm), which could minimize the matrix interferences from the drug substances and related impurities. Meanwhile, potassium iodide (KI) was used to convert the mixed benzyl halides into benzyl iodides before derivatization. The derivatization parameters were also optimized using the design of experiments (DoE) for achieving the best reaction efficiency. The results showed that the new approach had high specificity and sensitivity, and the LOQs were 7–9 μg g⁻¹ relative to 5 mg mL⁻¹ antipyrine and 17.5–22.5 μg g⁻¹ relative to 2 mg mL⁻¹ oroxylin A. The method is a valuable alternative for the determination of residual benzyl halides in the drug substances.

Benzyl halides, widely used as alkylation reagents in drug synthesis, are potential genotoxic impurities (PGTIs) required to be controlled at trace levels.

Simultaneous quantitation of 14 DNA alkylation adducts in human liver and kidney cells by UHPLC-MS/MS: Application to profiling DNA adducts of genotoxic reagents

A rapid, sensitive and wide coverage ultra-high-performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS) method has been developed and validated for the simultaneous quantitation of 14 alkylation DNA adducts in cell genomic DNA, RNA and cell contents isolated from the in vitro cultured human kidney cell line 293 T and the human liver cell line L02 exposed to 3 genotoxic reagents: N-methyl-N-nitrosourea (MNU), methyl methanesulfonate (MMS) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). After exposure, DNA was isolated and directly hydrolysed under acid conditions or digested by enzymes to obtain the hydrolysates containing DNA alkylation adducts followed by optimization of the pretreatment method and chromatographic separation conditions. Quantification was performed on a Waters ACQUITY UPLC BEH Amide column (1.7 μm, 2.1 × 150 mm) using an electrospray ionization (ESI) source in positive mode by selective reaction monitoring (SRM) at the precursor to product ion transitions of 14 analytes. The method showed selectivity, good linearity (r＞0.9950), accuracy (82.1%-115%), and intra-day (RSD%＜14%) and inter-day (RSD%＜15%) precision for 14 analytes. The recoveries of two pretreatment methods were all more than 50.5%, and no relative matrix effects were observed. Additionally, the samples were stable after short-term storage at 20 ℃ for 2 h, at 4 ℃ for 48 h or one cycle of freeze-thaw at -80 ℃. The established UHPLC-MS/MS method was used to evaluate the changes in alkylation DNA adducts and epigenetic modification-related methylcytosine after exposure to genotoxic reagents. For the first time, the results demonstrated that 3 genotoxic reagents induced different total amounts of adducts in the following sequence: MMS ＞ NNK ＞ MNU, and showed significant differences in the ratios of 7MeG to 1MeA and 1MeG to 1MeA in the 293 T cell model. Meanwhile, 293 T and L02 cells revealed significantly different DNA adduct formation characteristics in the contents of 1MeG and 1MeA. The DNA adduct formation relationships between DNA, RNA, and cell contents were probed to predict cancer risk and potential genotoxic exposure. This approach could be used to investigate the DNA adducts, their formation and the relationship to the mutagenicity or carcinogenicity of genotoxic reagents in future studies.

How changes in interfacial pH lead to new voltammetric features: the case of the electrochemical oxidation of hydrazine

The electrochemical oxidation of hydrazine was investigated in strongly and weakly pH buffered solutions to reveal the role of buffer capacity in proton–electron transfer redox reactions.

Determination of genotoxic epoxide at trace level in drug substance by direct injection GC/MS

A novel direct injection gas chromatography method coupled with selective ion monitoring mass spectrometry (GC/SIM-MS) was developed for quantitation of trace levels of high boiling point (HBP) epoxide genotoxic impurity (GTI) in drug substance. The injector temperature was optimized with the aims to minimize matrix effects and enhance SIM signal response. The final injector temperature 160°C was selected after balancing between these two factors. The column screening was conducted as well and MN OPTIMA delta-3 silica capillary column was selected since it showed good peak symmetry without column bleeding. The good linearity was established for the concentration in the range from 0.0045μg/mL to 0.5μg/mL with a R²=0.9999. The limit of detection (LOD) and the limit of quantitation (LOQ) were 0.0014μg/mL and 0.0045μg/mL, respectively. The recovery which ranged from 95.0% to 112.5% could meet the ICH acceptance criteria. The validation results demonstrated the good linearity, precision and accuracy of the method which can be further adopted as an adequate quality control tool for quantitation of epoxide impurity at trace levels in drug substance and drug product.

Determination of five potential genotoxic impurities in dalfampridine using liquid chromatography

A sensitive and selective HPLC method was developed for identification and quantification of five Potential genotoxic impurities (PGIs) viz. Impurity-I, Impurity-II, Impurity-III, Impurity-IV and Impurity-V in Dalfampridine (Drug substance). The method utilizes Zorbax silica column (250mm×4.6mm, 5.0μm) with UV detector in HILIC (Hydrophilic Interaction Liquid Chromatography) mode for quantitation of five PGIs. It has been validated as per International Council for Harmonisation (ICH) guidelines and is able to quantitate all PGIs at 75ppm with respect to 20mg/mL of sample concentration. It is linear in the range of 22.5-112.5ppm for all PGIs, which matches the range of LOQ-150% of estimated permitted level (75ppm). Its accuracy was established in the range from 88.14 to 107.65% for these PGIs. The correlation coefficient of each impurity was >0.999. It is a good quality control tool for quantitation of PGIs in Dalfampridine at low level.

Sample Preparation for Bioanalytical and Pharmaceutical Analysis

Biological and pharmaceutical samples represent formidable challenges in sample preparation that hold important consequences for bioanalysis and genotoxic impurity quantification. This Feature will emphasize significant advances toward the development of rapid, sensitive, and selective sample preparation methods.

Analysis of 4-bromo-3-fluorobenzaldehyde and separation of its regioisomers by one-dimensional and two-dimensional gas chromatography

A starting material, 4-bromo-3-fluorobenzaldehyde, was used for active drug substance (API) AMG 369 production. The presence of the regioisomer impurities in the starting material 4-bromo-3-fluorobenzaldehyde presented significant challenges for the API synthetic route development due to the physical-chemical similarities of the impurities. These impurities significantly impact on the purity of the starting-material and final drug substance. Control of these impurities is important due to the potential genotoxicity of these impurities (p-GTI). Analytical development was carried out to develop GC methods with high resolving power and high sensitivity to quantify the regioisomers presented in starting material and therefore to control the purity of the starting material and the final drug substance. In the study, complete resolution of the ten regioisomers by 1D-GC and heart-cutting two-dimensional GC (2D-GC) was achieved. A sensitive GC/micro electron capture detection (μ-ECD) method with high resolving power and sensitivity to fully resolve all the ten regioisomers of 4-bromo-3-fluorobenzaldehyde was obtained by using a CHIRALDEX GC column (1D- GC). To facilitate the systematic GC method development, heart-cutting two-dimensional gas chromatography (2D-GC) using a Deans switch was exploited for the separation of the ten regioisomers. The resulting heart-cutting 2D-GC method successfully separated all the ten regioisomers with better sensitivity and resolution. Regioisomer impurities in the starting material were identified and quantified by these GC methods. The sensitivity for the methods is in the range of 0.004ng to 0.02ng for the regioisomers. Linearity for the methods is: R(2)=0.999 to 1.000. The methods were suitable for control of the regioisomer impurities, p-GTIs, in the starting material and final drug substance.

Identification and genotoxicity evaluation of two carbamate impurities in rasagiline

During the synthesis of a second-generation monoamine oxidase-B inhibitor rasagiline, two unknown impurities (impurity A and impurity B) were detected and isolated by preparative liquid chromatography.