Recommendations and best practices for calibration curves in quantitative LC-MS bioanalysis

Development and validation of an LC-MS/MS method for simultaneous quantification of eight drugs in plasma and brain: Application in a pharmacokinetic study in mice

A selective and sensitive liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed and validated for simultaneous quantitation of a cassette of 8 drugs, including docetaxel, erlotinib, loperamide, riluzole, vemurafenib, verapamil, elacridar and tariquidar. Stable isotopically labeled compounds were available for use as internal standards for all compounds, except for tariquidar for which we used elacridar-d4. Sample pre-treatment involved liquid-liquid extraction using tert-butyl-methyl ether as this resulted in good recovery and low ion suppression. Chromatographic separation was achieved using a Zorbax Extend C18 analytical column and a linear gradient from 20 % to 95 % methanol in 0.1 % (v/v) formic acid in water. MS/MS detection using multiple reaction monitoring was done in positive ionization mode. We validated this assay for human and mouse plasma and mouse brain homogenates. The calibration curves were linear over a range 1-200 nM for each drug in the mix, except for tariquidar probably due to the lack of a stable isotope labeled analog. The intra-day and inter-day accuracies were within the 85-115 % range for all compounds at low, medium and high concentrations in the three different matrices. Similarly, the precision for all compounds at three different concentration levels ranged below 15 %, with the exception of tariquidar in mouse plasma and brain homogenate and riluzole in brain homogenate. Pilot studies have confirmed that the method is suitable for the analysis of mouse plasma samples and brain homogenates following cassette dosing of this mixture in mice.

Quantification of Remimazolam Besylate (CNS7056B) and Its Metabolite (CNS7054X) by LC-MS/MS in Human Plasma Using Midazolam-d4 Maleate as Internal Standard

A new assay was developed to measure the concentration of remimazolam besylate (CNS7056B) and its major carboxylic acid metabolite (CNS7054X) in human plasma. For this new assay method, midazolam-d4 maleate was used as an internal standard. After setting up a previously described assay method, using CNS7056-d4 and CNS7054-d4 as internal standards, analytical results of both methods were compared. For the new analytical method, ultra-high-performance liquid chromatography (UHPLC) with tandem mass spectrometry was applied. A purification method, using solid phase extraction, was developed and validated. The chromatographic separation of the analytes was achieved with a mobile phase gradient using a Water Acquity™ UHPLC-System. The Kinetex™ biphenyl 50 × 2.1 mm UHPLC column was used with a particle diameter of 1.7 μm (Phenomenex, Germany). A measuring range of 0.6-2,000 ng/mL for CNS7056B and of 6-20,000 ng/mL for CNS7054X could be achieved with this new assay. The lower limit of quantification was 0.6 ng/mL for CNS7056B and 6 ng/mL for CNS7054X. The assay was validated according to US Food and Drug Administration guidelines. The new method showed an accuracy of 96.9-110.4% and a precision of 2.1-6.7% for both analytes.

Probing Liquid Chromatography-Tandem Mass Spectrometry Response Dynamics and Nonlinear Effects for Response Level Defined Calibration Strategies with Simple Methods To Expand Linear Dynamic Ranges

The response characteristics of liquid chromatography-tandem mass spectrometry (LC-MS/MS) serve as the basis for selecting calibration methods in quantitative analysis. LC-MS/MS inherently exhibits nonlinear detection behavior, primarily attributed to the disproportionate growth observed between peak area and peak height at elevated response levels, potentially leading to signal saturation. This disproportionate peak growth results in reduced unit response (UR), which quantifies the instrument's detection sensitivity. LC-MS/MS typically operates within a narrow near-linear response range (NLRR) due to approximately proportional peak growth, yet the NLRR width varies across different analytes or platforms. Although the inclusion of stable isotope-labeled (SIL) internal standards (IS) in LC-MS/MS analysis can mitigate certain instrument response variations, it does not eliminate the fundamental cause of nonlinearity. Moreover, the concentration range accommodated by the NLRR can significantly fluctuate at different sensitivity levels. LC-MS/MS also encounters various other nonlinear effects, including ion suppression during ionization, signal cross-contribution between the analyte/IS, and matrix effects (ME). Consequently, quadratic regression emerges as a more adaptable approach to LC-MS/MS nonlinear response dynamics, offering a broader calibration range. The application of linear regression, on the other hand, requires strict conditions. Although the signal saturation zone typically remains inaccessible to calibration methods, reducing responses by employing less-optimal selected reaction monitoring (SRM) transitions and/or lower detection gain can facilitate fitting a wide concentration range into the NLRR, thereby enabling accurate linear regression calibration. This report delves into examining the LC-MS/MS response profile, its dynamics, and major nonlinear effects through instrument response mapping to elucidate their influence on the selection of calibration methods.

Non-regulated LC-MS/MS bioanalysis in support of early drug development - a Novartis perspective

Scientifically qualified LC-MS/MS methods are essential for the determination of small molecule drug candidates and/or their metabolite(s) in support of various non-regulated safety assessment and in vivo absorption, distribution, metabolism and excretion studies in preclinical development. This article outlines an effective method development workflow to fit for this purpose. The workflow features a 'universal' protein precipitation solvent for efficient sample extraction, a mobile phase additive for managing chromatographic resolution and addressing carryover and an internal standard cocktail to select the best analogue internal standard to track the analyte of interest in LC-MS/MS. In addition, good practices are recommended to prevent bioanalytical pitfalls due to instability, non-specific binding and dosing vehicle-induced matrix effect. Proper handling of non-liquid matrix is also discussed.

Calibration Practices in Clinical Mass Spectrometry: Review and Recommendations

Background

Calibration is a critical component for the reliability, accuracy, and precision of mass spectrometry measurements. Optimal practice in the construction, evaluation, and implementation of a new calibration curve is often underappreciated. This systematic review examined how calibration practices are applied to liquid chromatography-tandem mass spectrometry measurement procedures.

Methods

The electronic database PubMed was searched from the date of database inception to April 1, 2022. The search terms used were "calibration," "mass spectrometry," and "regression." Twenty-one articles were identified and included in this review, following evaluation of the titles, abstracts, full text, and reference lists of the search results.

Results

The use of matrix-matched calibrators and stable isotope-labeled internal standards helps to mitigate the impact of matrix effects. A higher number of calibration standards or replicate measurements improves the mapping of the detector response and hence the accuracy and precision of the regression model. Constructing a calibration curve with each analytical batch recharacterizes the instrument detector but does not reduce the actual variability. The analytical response and measurand concentrations should be considered when constructing a calibration curve, along with subsequent use of quality controls to confirm assay performance. It is important to assess the linearity of the calibration curve by using actual experimental data and appropriate statistics. The heteroscedasticity of the calibration data should be investigated, and appropriate weighting should be applied during regression modeling.

Conclusions

This review provides an outline and guidance for optimal calibration practices in clinical mass spectrometry laboratories.

A stable isotope dilution method for a highly accurate analysis of karrikins

BACKGROUND

Karrikins (KARs) are recently described group of plant growth regulators with stimulatory effects on seed germination, seedling growth and crop productivity. So far, an analytical method for the simultaneous targeted profiling of KARs in plant tissues has not been reported.

RESULTS

We present a sensitive method for the determination of two highly biologically active karrikins (KAR₁ and KAR₂) in minute amounts of plant material (< 20 mg fresh weight). The developed protocol combines the optimized extraction and efficient single-step sample purification with ultra-high performance liquid chromatography-tandem mass spectrometry. Newly synthesized deuterium labelled KAR₁ was employed as an internal standard for the validation of KAR quantification using a stable isotope dilution method. The application of the matrix-matched calibration series in combination with the internal standard method yields a high level of accuracy and precision in triplicate, on average bias 3.3% and 2.9% RSD, respectively. The applicability of this analytical approach was confirmed by the successful analysis of karrikins in Arabidopsis seedlings grown on media supplemented with different concentrations of KAR₁ and KAR₂ (0.1, 1.0 and 10.0 µmol/l).

CONCLUSIONS

Our results demonstrate the usage of methodology for routine analyses and for monitoring KARs in complex biological matrices. The proposed method will lead to better understanding of the roles of KARs in plant growth and development.

The Impact of Immunofunctional Phenotyping on the Malfunction of the Cancer Immunity Cycle in Breast Cancer

Simple Summary

The cancer-immunity cycle (CIC) is a series of self-sustaining stepwise events to fight cancer growth by the immune system. We hypothesized that immunofunctional phenotyping that represent the malfunction of the CIC is clinically relevant in breast cancer (BC) utilizing total of 2979 BC cases; 1075 from TCGA cohort, 1904 from METABRIC cohort were analyzed. The immunofunctional phenotype was classified as follows: hot T-cell infiltrated, high immune cytolytic activity (CYT), cold T-cell infiltrated, high frequency of CD8+ T cells and low CYT, and non-inflamed, low frequency of CD8+ T cells and low CYT. We demonstrated that immunofunctional phenotyping not only indicated the degree of anti-cancer immune dysfunction, but also served as a prognostic biomarker and HTI was inversely related to estrogen response.

Abstract

The cancer-immunity cycle (CIC) is a series of self-sustaining stepwise events to fight cancer growth by the immune system. We hypothesized that immunofunctional phenotyping that represent the malfunction of the CIC is clinically relevant in breast cancer (BC). Total of 2979 BC cases; 1075 from TCGA cohort, 1904 from METABRIC cohort were analyzed. The immunofunctional phenotype was classified as follows: hot T-cell infiltrated (HTI), high immune cytolytic activity (CYT), Cold T-cell infiltrated (CTI), high frequency of CD8+ T cells and low CYT, and non-inflamed, low frequency of CD8+ T cells and low CYT. The analysis of tumor immune microenvironment in the immunofunctional phenotype revealed that not only immunostimulatory factors, but also immunosuppressive factors were significantly elevated and immunosuppressive cells were significantly decreased in HTI. Patients in HTI were significantly associated with better survival in whole cohort and patients in CTI were significantly associated with worse survival in triple negative. Furthers, HTI was inversely related to estrogen responsive signaling. We demonstrated that immunofunctional phenotype not only indicated the degree of anti-cancer immune dysfunction, but also served as a prognostic biomarker and HTI was inversely related to estrogen response.

Simultaneous quantification of candesartan and irbesartan in rabbit eye tissues by liquid chromatography-tandem mass spectrometry

Diabetic retinopathy is a major cause of vision loss in adults. Novel eye-drop formulations of candesartan and irbesartan are being developed for its cure or treatment. To support a preclinical trial in rabbits, it was critical to develop and validate a new LC-MS/MS method for simultaneous quantification of candesartan and irbesartan in rabbit eye tissues (cornea, aqueous humor, vitreous body and retina/choroid). Eye tissue samples were first homogenized in H₂ O-diluted rabbit plasma. The candesartan and irbesartan in the supernatants together with their respective internal standards (candesartan-d₄ and irbesartan-d₄ ) were extracted by solid-phase extraction. The extracted samples were injected onto a C₁₈ column for gradient separation. The MS detection was in the positive electrospray ionization mode using the multiple reaction monitoring transitions of m/z 441 → 263, 445 → 267, 429 → 207, and 433 → 211 for candesartan, candesartan-d₄ , irbesartan and irbesartan-d₄ , respectively. For the validated concentration ranges (2-2000 and 5-5000 ng/g for candesartan and irbesartan, respectively), the within-run and between-run accuracies (% bias) were within the range of -8.0-10.0. The percentage CV ranged from 0.6 to 7.3. There was no significant matrix interference nor matrix effect from different eye tissues and different rabbits. The validated method was successfully used in the Good Laboratory Practice (GLP) study of rabbits.

Late recurrence of breast cancer is associated with pro-cancerous immune microenvironment in the primary tumor

The fact that 20–40% of all breast cancer (BC) patients develop recurrence when 5 year survival is 90% strongly suggests that late recurrence, i.e. more than 5 years after diagnosis, is the remaining challenge to decrease the absolute number of BC deaths. Better understanding late recurrence is an essential first step to address this issue. We hypothesized that primary tumors with a distinctive tumor immune microenvironment will develop late recurrence. Accordingly, we evaluated the relationship between the timing of cancer recurrence, clinical factors, gene expression profiles, and immune status utilizing two published large cohorts. 308 primary BCs in TCGA were analyzed and categorized as: recurrence ≤2 years (Early, n = 49), between 2–5 years (Mid, n = 54), recurrence >5 years (Late, n = 20), and no recurrence >5 years (Survivors, n = 185). 1,727 primary BCs in METABRIC were analyzed and categorized similarly: Early, n = 170; distant (D), n = 19; local (L), Mid, n = 213; D, n = 21; L, Late, n = 199; D, n = 57, L, and Survivors, n = 1048. Utilizing pre-ranked GSEA, we showed that primary tumors with Survivors were associated with anti-cancer signaling such as INF-α/-γ response and TNF-α signaling, compared with all recurrence groups in pre-ranked GSEA. Furtherrmore, we found that host defense immunity (leukocyte fraction, lymphocyte infiltration, and macrophage fractions) was decreased in primary tumors with Late recurrence compared with Survivors. Utilizing the CIBERSORT algorithm, we showed anti-cancer lymphocytes, memory CD4+ T cells and γδT cells, were significantly lower, and pro-cancerous regulatory T cells were significantly higher in Late tumors compared with Survivors. In agreement, cytolytic activity score that assesses immune cell cytolytic activity was significantly lower in Late compared with Survivors. We demonstrated that not only host defense immunity, but also pro-cancerous immune cells and immune cell cytolytic activity in primary BC was associated with late recurrence.

Late recurrence of breast cancer is associated with pro-cancerous immune microenvironment in the primary tumor

The fact that 20-40% of all breast cancer (BC) patients develop recurrence when 5 year survival is 90% strongly suggests that late recurrence, i.e. more than 5 years after diagnosis, is the remaining challenge to decrease the absolute number of BC deaths. Better understanding late recurrence is an essential first step to address this issue. We hypothesized that primary tumors with a distinctive tumor immune microenvironment will develop late recurrence. Accordingly, we evaluated the relationship between the timing of cancer recurrence, clinical factors, gene expression profiles, and immune status utilizing two published large cohorts. 308 primary BCs in TCGA were analyzed and categorized as: recurrence ≤2 years (Early, n = 49), between 2-5 years (Mid, n = 54), recurrence >5 years (Late, n = 20), and no recurrence >5 years (Survivors, n = 185). 1,727 primary BCs in METABRIC were analyzed and categorized similarly: Early, n = 170; distant (D), n = 19; local (L), Mid, n = 213; D, n = 21; L, Late, n = 199; D, n = 57, L, and Survivors, n = 1048. Utilizing pre-ranked GSEA, we showed that primary tumors with Survivors were associated with anti-cancer signaling such as INF-α/-γ response and TNF-α signaling, compared with all recurrence groups in pre-ranked GSEA. Furtherrmore, we found that host defense immunity (leukocyte fraction, lymphocyte infiltration, and macrophage fractions) was decreased in primary tumors with Late recurrence compared with Survivors. Utilizing the CIBERSORT algorithm, we showed anti-cancer lymphocytes, memory CD4+ T cells and γδT cells, were significantly lower, and pro-cancerous regulatory T cells were significantly higher in Late tumors compared with Survivors. In agreement, cytolytic activity score that assesses immune cell cytolytic activity was significantly lower in Late compared with Survivors. We demonstrated that not only host defense immunity, but also pro-cancerous immune cells and immune cell cytolytic activity in primary BC was associated with late recurrence.