Simple and rapid LC-MS/MS method for the absolute determination of cetuximab in human serum using an immobilized trypsin

A robust and validated LC-MS/MS method for the quantification of ramucirumab in rat and human serum using direct enzymatic digestion without immunoassay

A new liquid chromatography tandem mass spectrometry (LC-MS/MS) method was established to quantify the anti-gastric cancer fully human monoclonal antibody (ramucirumab) in rat and human serum. The surrogate peptide (GPSVLPLAPSSK) for ramucirumab was generated by trypsin hydrolysis and quantified using the isotopically labeled peptide GPSVLPLAPSSK[13C6, 15N2]ST containing two more amino acids at the carboxyl end as an internal standard to correct for variations introduced during the enzymatic hydrolysis process and any mass spectrometry changes. Additionally, the oxidation and deamidation of unstable peptides (VVSVLTVLHQDWLNGK and NSLYLQMNSLR) were detected. The quantitative range of the proposed method was 1-1000 μg/mL, and complete methodological validation was performed. The precision, accuracy, matrix effect, sensitivity, stability, selectivity, carryover, and interference of the measurements met the required standards. The validated LC-MS/MS method was applied to pharmacokinetic studies in rats administered ramucirumab at 15 mg/kg intravenously. Overall, a robust, efficient, and cost-effective LC-MS/MS method was successfully developed for quantifying ramucirumab in rat and human serum.

Rapid and simple quantification of belimumab in human plasma using ultra-high performance liquid chromatography with tandem mass spectrometry

OBJECTIVE

Belimumab is a monoclonal antibody against the B-lymphocyte stimulating factor and is approved for the treatment of patients with systemic lupus erythematosus (SLE) not responding adequately to existing therapies. In this study, we established and validated an assay for quantifying belimumab in human plasma.

METHODS

From the peptides generated by trypsin digestion of belimumab, in silico analysis was used to search for unique peptides to determine the surrogate peptides. Samples were trypsin digested, pretreated with solid phase extraction, and analyzed by ultra-high performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS) to quantify the surrogate peptide in the samples. The assay was validated according to the Food and Drug Administration (FDA) bioanalytical method validation guidance. We used the established assay to quantify plasma belimumab concentrations in two SLE patients treated with belimumab.

RESULTS

Among the unique peptides identified by the in silico analysis, the peptide with the best peak shape when measured by UHPLC-MS/MS was selected as the surrogate peptide. The validation results of this assay met the acceptable criteria recommended by the FDA guidance. The lower limit of quantification (LLOQ) for belimumab was 2 µg/mL. Recovery rates and matrix effects when corrected for internal standards were 91.5-114.3 % and 96.9-108.4 %, respectively. Plasma concentrations of belimumab were measured in 12 samples from two belimumab-treated SLE patients. All concentrations were within the calibration range.

CONCLUSIONS

We have established and validated a method for measuring plasma belimumab concentrations using UHPLC/MS-MS. By measuring plasma belimumab concentrations in more patients, this method is expected to contribute to appropriate use of belimumab.

Recent developments in mass-spectrometry-based targeted proteomics of clinical cancer biomarkers

Routine measurement of cancer biomarkers is performed for early detection, risk classification, and treatment monitoring, among other applications, and has substantially contributed to better clinical outcomes for patients. However, there remains an unmet need for clinically validated assays of cancer protein biomarkers. Protein tumor markers are of particular interest since proteins carry out the majority of biological processes and thus dynamically reflect changes in cancer pathophysiology. Mass spectrometry-based targeted proteomics is a powerful tool for absolute peptide and protein quantification in biological matrices with numerous advantages that make it attractive for clinical applications in oncology. The use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) based methodologies has allowed laboratories to overcome challenges associated with immunoassays that are more widely used for tumor marker measurements. Yet, clinical implementation of targeted proteomics methodologies has so far been limited to a few cancer markers. This is due to numerous challenges associated with paucity of robust validation studies of new biomarkers and the labor-intensive and operationally complex nature of LC-MS/MS workflows. The purpose of this review is to provide an overview of targeted proteomics applications in cancer, workflows used in targeted proteomics, and requirements for clinical validation and implementation of targeted proteomics assays. We will also discuss advantages and challenges of targeted MS-based proteomics assays for clinical cancer biomarker analysis and highlight some recent developments that will positively contribute to the implementation of this technique into clinical laboratories.

Liquid chromatography - tandem mass spectrometry method for determination of natalizumab in serum and cerebrospinal fluid of patients with multiple sclerosis

Natalizumab is a humanized recombinant monoclonal IgG4 antibody used in the treatment of multiple sclerosis. Commonly used methods for natalizumab and anti-natalizumab antibodies quantification are enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay, respectively. Measurement of therapeutic monoclonal antibodies can be challenging due to the resemblance to human plasma immunoglobulins. Recent developments in mass spectrometry enables to analyze vast variety of large protein molecules. The aim of this study was to develop a LC-MS/MS method for determining natalizumab in human serum and cerebrospinal fluid (CSF) and apply it to clinical settings. For successful quantification, it was necessary to find specific sequences of peptides in natalizumab. This immunoglobulin was treated with dithiothreitol and iodoacetamide, cleaved with trypsin into short specific peptides and determined on a UPLC-MS/MS system. An Acquity UPLC BEH C18 column at 55 °C and gradient elution was used for analysis. Intra- and interassay accuracies and precisions were tested at four concentration levels. Precision was determined by coefficients of variation and was in the range of 0.8-10.2 %, with accuracy in the range of 89.8-106.4 %. The concentration of natalizumab in patient samples ranged from 1.8 to 193.3 μg/mL. The method was validated according to the European Medicines Agency (EMA) guideline, met all acceptance criteria for accuracy and precision, and is suitable for clinical applications. In comparison to immunoassay, which can be elevated by cross-reaction with endogenous immunoglobulins, the results of developed LC-MS/MS method are more accurate and specific.

LC-MS/MS method for the quantitation of serum tocilizumab in rheumatoid arthritis patients using rapid tryptic digestion without IgG purification

The quantitation of serum tocilizumab using liquid chromatography tandem-mass spectrometry (LC-MS/MS) method has not been widely applied in clinical settings because of its time-consuming and costly sample pretreatments. The present study aimed to develop a validated LC-MS/MS method for detecting serum tocilizumab by utilizing immobilized trypsin without an immunoglobulin G purification step and evaluate its applicability in the treatment of rheumatoid arthritis (RA) patients administered intravenously or subcutaneously with tocilizumab. The tocilizumab-derived signature peptide was deciphered using a nano-LC system coupled to a hybrid quadrupole-orbitrap mass spectrometer. The serum tocilizumab was rapidly digested by immobilized trypsin for 30 min. The chromatographic peak of the signature peptide and that of the internal standard were separated from the serum digests for a total run time of 15 min. The calibration curve of serum tocilizumab concentration was linear with a range of 2-200 μg/mL. The intra- and inter-day accuracy and relative standard deviation (RSD) were 90.7%-109.4% and <10%, respectively. The serum tocilizumab concentrations in the RA patients receiving intravenous and subcutaneous injections were 5.8-28.9 and 2.4-63.5 μg/mL, respectively. The serum tocilizumab concentrations using the current method positively correlated with those using the enzyme-linked immunosorbent assay, although a systematic error was observed between these methods. In conclusion, a validated LC-MS/MS method with minimal sample pretreatments for monitoring serum tocilizumab concentrations in RA patients was developed.

A rapid and universal liquid chromatograph-mass spectrometry-based platform, refmAb-Q nSMOL, for monitoring monoclonal antibody therapeutics

Accurate multiplexed quantitation of unique signature peptides derived from monoclonal antibody therapeutics with a universal reference antibody refmAb-Q using Fab-selective proteolysis nSMOL coupled with LC-MS/MS.

The Role of Akt in Acquired Cetuximab Resistant Head and Neck Squamous Cell Carcinoma: An In Vitro Study on a Novel Combination Strategy

The epidermal growth factor receptor (EGFR) is a therapeutic target in head and neck squamous cell carcinoma (HNSCC). Resistance to EGFR-targeted therapies, such as cetuximab, poses a challenging problem. This study aims to characterize acquired cetuximab resistance mechanisms in HNSCC cell lines by protein phosphorylation profiling. Through this, promising combination treatments can be identified to possibly overcome acquired cetuximab resistance in HNSCC. Protein phosphorylation profiling showed increased phosphorylation of Akt1/2/3 after cetuximab treatment in acquired cetuximab resistant cells compared to cetuximab sensitive cells, which was confirmed by western blotting. Based on this protein phosphorylation profile, a novel combination treatment with cetuximab and the Akt1/2/3 inhibitor MK2206 was designed. Synergy between cetuximab and MK2206 was observed in two cetuximab sensitive HNSCC cell lines and one acquired cetuximab resistant variant in simultaneous treatment schedules. In conclusion, this study demonstrates that increased Akt1/2/3 phosphorylation seems to be characteristic for acquired cetuximab resistance in HNSCC cell lines. Our results also show an additive to synergistic interaction between cetuximab and MK2206 in simultaneous treatment schedules. These data support the hypothesis that the combination of cetuximab with PI3K/Akt pathway inhibition might be a promising novel therapeutic strategy to overcome acquired cetuximab resistance in HNSCC patients.

Structure-Indicated LC-MS/MS Bioanalysis of Therapeutic Antibodies

Monoclonal antibodies bind to Protein A/G resin with 100 nm-diameter pores, which orients the Fab toward the reaction solution. Then, they can be proteolyzed using trypsin immobilized on the surface of 200 nm-diameter nanoparticles. The difference between the two particle diameters allows Fab-selective proteolysis by limiting trypsin access to the antibody substrate. The specific signature peptide of monoclonal antibody is collected, which comprises the complementarity-determining regions (CDRs). Excess trypsin protease and peptide fragments from common sequences in Fc that inhibit the analysis can then be separated and removed. The resulting peptide samples are separated through high performance liquid chromatography on a 20 nm-diameter pore-size reversed-phase C18 column. These are then sequentially ionized with an electrospray interface and subjected to mass spectrometry (MS). In MS, peptide ions are trapped and fragment ions are generated by the collision-induced dissociation with argon gas. These are detected with multiple reaction monitoring measurements to perform a highly sensitive and accurate quantitative analysis.By focusing on various physicochemical features at each analytical scene, such as characteristic structure and orientation of antibody, control of trypsin reaction field, carry-over on HPLC column, ionization suppression effect from endogenous proteins, and detection of amino acid sequence specificity of antibody, we optimized the overall conditions from the sample processing up to MS detection and developed analytical validation and clinical application of many therapeutic antibodies using our Fab-selective proteolysis technology that is based on the structure-indicated approach.

Cross-Validation of a Multiplex LC-MS/MS Method for Assaying mAbs Plasma Levels in Patients with Cancer: A GPCO-UNICANCER Study

BACKGROUND

Different liquid chromatography tandem mass spectrometry (LC-MS/MS) methods have been published for quantification of monoclonal antibodies (mAbs) in plasma but thus far none allowed the simultaneous quantification of several mAbs, including immune checkpoint inhibitors. We developed and validated an original multiplex LC-MS/MS method using a ready-to-use kit to simultaneously assay 7 mAbs (i.e., bevacizumab, cetuximab, ipilimumab, nivolumab, pembrolizumab, rituximab and trastuzumab) in plasma. This method was next cross-validated with respective reference methods (ELISA or LC-MS/MS).

METHODS

The mAbXmise kit was used for mAb extraction and full-length stable-isotope-labeled antibodies as internal standards. The LC-MS/MS method was fully validated following current EMA guidelines. Each cross validation between reference methods and ours included 16-28 plasma samples from cancer patients.

RESULTS

The method was linear from 2 to 100 µg/mL for all mAbs. Inter- and intra-assay precision was <14.6% and accuracy was 90.1-111.1%. The mean absolute bias of measured concentrations between multiplex and reference methods was 10.6% (range 3.0-19.9%).

CONCLUSIONS

We developed and cross-validated a simple, accurate and precise method that allows the assay of up to 7 mAbs. Furthermore, the present method is the first to offer a simultaneous quantification of three immune checkpoint inhibitors likely to be associated in patients.

Correlations between serum cetuximab and EGFR-related markers, and skin disorders in head and neck cancer patients

PURPOSE

Cetuximab inhibits epidermal growth factor receptor (EGFR) signaling in cancer and skin cells, thereby inducing anti-cancer effects and skin disorders. The present study aimed to evaluate the relationships between serum cetuximab and EGFR-related markers, and adverse effects in head and neck cancer patients.

METHODS

Thirty-four head and neck cancer patients receiving weekly intravenous cetuximab were enrolled. Serum cetuximab levels were determined just before dosing. Blood samples for determination of serum EGFR-related markers including soluble epidermal growth factor receptor (sEGFR) and interleukin-6 (IL-6) were obtained. The severities of skin disorders, their medications, and hypomagnesemia treatment were also assessed.

RESULTS

Serum levels of cetuximab and sEGFR were negatively and positively correlated with that of IL-6, respectively. The serum cetuximab level was twofold higher in the patients with a grade 2-3 skin rash than with a grade 0-1 rash. The serum cetuximab cutoff value related to severe skin rash was 71 μg/mL (sensitivity, 59%; and specificity, 94%). The use of a strong topical corticosteroid for skin rash was also associated with a higher serum cetuximab level. Serum levels of sEGFR and IL-6 had no correlations with the skin disorder severities or their medications. Hypomagnesemia treatment using intravenous magnesium sulfate was not related to serum cetuximab and EGFR-related markers.

CONCLUSIONS

Head and neck cancer patients with a higher serum IL-6 level tended to have a lower serum cetuximab level. Serum cetuximab had positive correlations to skin rash severity and its medication in the study population.

Bottom-up sample preparation for the LC-MS/MS quantification of anti-cancer monoclonal antibodies in bio matrices

Therapeutic monoclonal antibodies (mAbs) are rapidly taking over the treatment of many malignancies, and an astonishing number of mAbs is in development. This causes a high demand for quantification of mAbs in biomatrices both for measuring therapeutic mAb concentrations and to support pharmacokinetics and pharmacodynamics studies. Conventionally, ligand-binding assays are used for these purposes, but LC-MS is gaining popularity. Although intact (top-down) and subunit (middle-down) mAb quantification is reported, signature peptide (bottom-up) quantification is currently most advantageous. This review provides an overview of the reported bottom-up mAb quantification methods in biomatrices as well as general recommendations regarding signature peptide and internal standard selection, reagent use and optimization of digestion in bottom-up quantification methods.

Pathway-Specific Genome Editing of PI3K/mTOR Tumor Suppressor Genes Reveals that PTEN Loss Contributes to Cetuximab Resistance in Head and Neck Cancer

Cetuximab, an mAb targeting EGFR, is a standard of care for the treatment for locally advanced or metastatic head and neck squamous cell carcinoma (HNSCC). However, despite overexpression of EGFR in more than 90% of HNSCC lesions, most patients with HNSCC fail to respond to cetuximab treatment. In addition, there are no available biomarkers to predict sensitivity or resistance to cetuximab in the clinic. Here, we sought to advance precision medicine approaches for HNSCC by identifying PI3K/mTOR signaling network-specific cetuximab resistance mechanisms. We first analyzed the frequency of genomic alterations in genes involved in the PI3K/mTOR signaling circuitry in the HNSCC TCGA dataset. Experimentally, we took advantage of CRISPR/Cas9 genome editing approaches to systematically explore the contribution of genomic alterations in each tumor suppressor gene (TSG) controlling the PI3K-mTOR pathway to cetuximab resistance in HNSCC cases that do not exhibit PIK3CA mutations. Remarkably, we found that many HNSCC cases exhibit pathway-specific gene copy number loss of multiple TSGs that normally restrain PI3K/mTOR signaling. Among them, we found that both engineered and endogenous PTEN gene deletions can mediate resistance to cetuximab. Our findings suggest that PTEN gene copy number loss, which is highly prevalent in HNSCC, may result in sustained PI3K/mTOR signaling independent of EGFR, thereby representing a promising mechanistic biomarker predictive of cetuximab resistance in this cancer type. Further prospective studies are needed to investigate the impact of PTEN loss on cetuximab efficacy in the clinic.

Quantification of T Cell Binding Polyclonal Rabbit Anti-thymocyte Globulin in Human Plasma with Liquid Chromatography Tandem-Mass Spectrometry

The addition of rabbit anti-human thymocyte globulin (ATG) to the conditioning regimen prior to allogeneic hematopoietic cell transplantation has significantly reduced the risk of graft-versus-host disease (GvHD) and graft failure. However, ATG has a small therapeutic window. Overexposure of ATG post-HCT hampers T cell immune reconstitution and has been associated with increased relapse rates and viral reactivations, whereas underexposure has been associated with an increased incidence of GvHD, both of which lead to increased mortality. Therapeutic drug monitoring of T cell binding ATG plasma levels provides a means to optimize dosing for patients at high risk for graft failure to ensure timely T cell immune reconstitution and subsequently increase survival chances. This manuscript describes the first liquid chromatography tandem-mass spectrometry (LC-MS/MS) method to quantify the pharmacologically active fraction of polyclonal ATG in plasma. This was achieved through immunoaffinity purification of active ATG from plasma with Jurkat T cells. After the binding and washing, samples were eluted, denatured, and trypsin-digested. Signature peptides originating from the IgG constant chain were measured with LC-MS/MS. Critical method parameters were optimized, and the method was successfully validated following European Medicines Agency (EMA) guidelines. The method covered the therapeutic range of ATG and was validated at a lower limit of quantification (LLOQ) of 1 AU/mL with an overall CV and bias of 11.8% and - 2.5%, respectively. In conclusion, we developed a LC-MS/MS-based method to quantify active polyclonal rabbit ATG in human plasma. We suggest that this novel assay can be used to monitor and optimize dosing of ATG in clinical practice.

Palbociclib and cetuximab in platinum-resistant and in cetuximab-resistant human papillomavirus-unrelated head and neck cancer: a multicentre, multigroup, phase 2 trial

BACKGROUND

Most head and neck squamous-cell carcinomas (HNSCCs) are driven by p16^INK4A inactivation and cyclin D1 overexpression that results in hyperactivation of cyclin-dependent kinase 4 and 6 (CDK4/6), rather than by the human papillomavirus (HPV). Deregulated cyclin D1 expression also causes resistance to EGFR inhibitors. We previously reported that palbociclib (a selective CDK4/6 inhibitor) given with cetuximab (an EGFR inhibitor) was safe. The aim of this study was to establish the proportion of patients achieving an objective response with palbociclib and cetuximab in recurrent or metastatic HNSCC.

METHODS

We did a multicentre, multigroup, phase 2 trial to evaluate the activity of palbociclib and cetuximab in platinum-resistant (group 1) and cetuximab-resistant (group 2) HPV-unrelated HNSCC. The study was done across eight university sites in the USA. Eligibility required measurable disease (according to Response Evaluation Criteria in Solid Tumors, version 1·1 [RECIST 1·1]), Eastern Cooperative Oncology Group (ECOG) performance status of 0-2, age of 18 years or older, and disease progression on platinum but cetuximab-naive (group 1) or disease progression on cetuximab (group 2). All patients received palbociclib orally (125 mg/day, on days 1-21) and intravenous cetuximab (400 mg/m² on cycle one, day 1, then 250 mg/m² once per week) in 28-day cycles. The primary endpoint was objective response (complete responses and partial responses per RECIST 1·1). Analyses were done per protocol. This trial was registered with ClinicalTrials.gov, NCT02101034, and is ongoing, but both groups are closed to accrual.

FINDINGS

Between Oct 19, 2015, and Nov 7, 2018, 62 patients were enrolled onto the trial: 30 patients were enrolled in group 1 and 32 in group 2. Median follow-up was 5·4 months (IQR 4·4-12·1) for group 1 and 5·5 months (4·3-8·3) for group 2. In group 1, of 28 evaluable patients, an objective response was achieved by 11 (39%; 95% CI 22-59). In group 2, of 27 evaluable patients, an objective response was achieved by five (19%; 6-38) in group 2. The most common grade 3-4 palbociclib-related adverse event was neutropenia (in 21 [34%] of 62 patients). No treatment-related deaths occurred.

INTERPRETATION

In patients with platinum-resistant or cetuximab-resistant HPV-unrelated HNSCC, palbociclib and cetuximab results in promising activity outcomes. Further studies of CDK4/6 inhibitors are warranted in HPV-unrelated HNSCC.

FUNDING

Pfizer.

Determination of Cetuximab in Plasma by Liquid Chromatography-High-Resolution Mass Spectrometry Orbitrap With a Stable Labeled 13C,15N-Cetuximab Internal Standard

BACKGROUND

Cetuximab (CTX) is a chimeric IgG1 Kappa monoclonal antibody used to treat head and neck cancer and colorectal cancer. Previous clinical studies indicated that the pharmacokinetics of CTX influences patient survival. Thus, individualizing CTX treatment by measuring trough levels of the drug in plasma could have a major impact on clinical efficacy.

METHODS

To measure these levels, a full-length stable isotope-labeled CTX standard was used in a generic, rapid, and high-throughput sample preparation protocol based on IgG capture followed by trypsin digestion, on-line solid-phase extraction cleanup, and liquid chromatography-high resolution mass spectrometry (LC-HRMS).

RESULTS

The optimized method displayed good analytical performance and was linear over a range from 5 to 150 mcg/mL. The within-run and between-run imprecision of the assay were equal to or less than 10%, for 6 replicates at 3 different concentrations and for runs performed on 5 separate days. The plasma CTX concentrations in 19 patients were also determined.

CONCLUSIONS

The results showed that quantification of mAb in clinical samples does not strictly require a tandem mass spectrometry system, and LC-HRMS is also relevant in this context. This first study implementing a quantitative LC-HRMS assay with a specific stable isotope-labeled mAb internal standard paves the way for more robust clinical monitoring of anticancer mAbs.

Six-step workflow for the quantification of therapeutic monoclonal antibodies in biological matrices with liquid chromatography mass spectrometry - A tutorial

The promising pipeline of therapeutic monoclonal antibodies (mAbs) demands robust bioanalytical methods with swift development times for pharmacokinetic studies. Over the past decades ligand binding assays were the methods of choice for absolute quantification. However, the production of the required anti-idiotypic antibodies and ligands limits high-throughput method development for sensitive, accurate, and reproducible quantification of therapeutic mAbs. In recent years, high-resolution liquid chromatography tandem mass-spectrometry (LC-MS) systems have enabled absolute quantification of therapeutic mAbs with short method development times. These systems have additional benefits, such as a large linear dynamic range, a high specificity and the option of multiplexing. Here, we briefly discuss the current strategies for the quantification of therapeutic mAbs in biological matrices using LC-MS analysis based on top-down and middle-down quantitative proteomics. Then, we present the widely used bottom-up method in a six-step workflow, which can be used as guidance for quantitative LC-MS/MS method development of mAbs. Finally, strengths and weaknesses of the bottom-up method, which currently provides the most benefits, are discussed in detail.

Simple LC-MS/MS Methods Using Core-Shell Octadecylsilyl Microparticulate for the Quantitation of Total and Free Daptomycin in Human Plasma

BACKGROUND

Daptomycin, a cyclic lipopeptide antibiotic, displays high plasma protein binding. This study developed the simple method of liquid chromatographic separation using a core-shell octadecylsilyl microparticulate coupled to tandem mass spectrometry for the quantitation of total and free daptomycin in human plasma.

METHODS

Free daptomycin in plasma was obtained by centrifugal ultrafiltration. Deproteinized plasma specimens were directly separated using a core-shell octadecylsilyl microparticulate with isocratic elution. The mass spectrometer was run in positive-ion electrospray ionization mode. This method was applied to the quantitation of plasma samples in patients treated with intravenous daptomycin.

RESULTS

Daptomycin and diazepam as an internal standard were eluted with a total run time of 10 minutes. The calibration curves of total and free daptomycin in human plasma were linear over the concentration ranges of 1-100 and 0.1-10 mcg/mL, respectively. The lower limits of quantitation of the total and free daptomycin in human plasma were 1.0 and 0.1 mcg/mL, respectively. Their extraction recovery rates in nonfiltrated and ultrafiltrated plasma samples were 106.1% and 98.2%, respectively. Total and free daptomycin did not exhibit any matrix effects in human plasma. The intraday and interday accuracies and imprecisions of total daptomycin were 88.7%-106.0% and 98.7%-105.9%, and within 4.1% and 10.4%, whereas those of free daptomycin were 86.8%-101.6% and 103.0%-107.8%, and within 14.6% and 14.6%, respectively. The plasma concentration ranges of total and free daptomycin in 15 infected patients were 3.01-34.1 and 0.39-3.64 mcg/mL, respectively. The plasma protein binding rate of daptomycin ranged from 80.8% to 94.9%.

CONCLUSIONS

The present simple method with an acceptable analytical performance can be helpful for monitoring the pharmacokinetics of daptomycin in infected patients observed in clinical settings.

Overcoming Intrinsic and Acquired Cetuximab Resistance in RAS Wild-Type Colorectal Cancer: An In Vitro Study on the Expression of HER Receptors and the Potential of Afatinib

The epidermal growth factor receptor (EGFR) is an important therapeutic target in colorectal cancer (CRC). After the initial promising results of EGFR-targeted therapies such as cetuximab, therapeutic resistance poses a challenging problem and limits the success of effective anti-EGFR cancer therapies in the clinic. In order to overcome resistance to these EGFR-targeted therapies, new treatment options are necessary. The objective of this study was to investigate the expression of human epidermal growth factor (HER) receptors and the efficacy of afatinib, a second-generation irreversible EGFR-tyrosine kinase inhibitor, in RAS wild-type CRC cell lines with different cetuximab sensitivities. CRC cell lines with different sensitivities to cetuximab showed rather low EGFR expression but high HER2 and HER3 expression. These results were in line with the The Cancer Genome Atlas (TCGA) data from CRC patients, where higher mRNA levels of HER2 and HER3 were also detected compared to EGFR. Therefore, the targets of afatinib were indeed expressed on the CRC cell lines used in this study and in CRC patients. Furthermore, cetuximab resistance had no significant influence on the expression levels of HER receptors in CRC cell lines (p ≥ 0.652). This study also demonstrated that afatinib was able to induce a concentration-dependent cytotoxic effect in RAS wild-type CRC cell lines with different cetuximab sensitivities. Neither cetuximab resistance (p = 0.233) nor hypoxia (p = 0.157) significantly influenced afatinib’s cytotoxic effect. In conclusion, our preclinical data support the hypothesis that treatment with afatinib might be a promising novel therapeutic strategy for CRC patients experiencing intrinsic and acquired cetuximab resistance.

LC-MS/MS method for denosumab quantitation in human serum with rapid protein digestion using immobilized trypsin

BACKGROUND

Proteomics-based LC-MS/MS methods using trypsin solution have some problems including ion suppression and long protein digestion times. Few practical methods to quantify denosumab in human serum have been published.

METHODOLOGY

Immunoglobulins in serum were extracted using immobilized protein G. Denatured, reduced and alkylated serum samples were digested with immobilized trypsin for 14 min. A denosumab-unique peptide was identified using a Fourier transform mass spectrometer as a signature peptide. The signature peptide was quantitated with a hybrid triple-quadrupole/linear ion-trap mass spectrometer.

CONCLUSION

A rapid and practical proteomics-based LC-MS/MS method using immobilized trypsin for denosumab quantitation in human serum was developed. The present method has an acceptable analytical performance and can be helpful for the determination of serum denosumab in clinical settings.

Quantification of total dinutuximab concentrations in neuroblastoma patients with liquid chromatography tandem mass spectrometry

Neuroblastoma is one of the most commonly found solid tumors in children. The monoclonal antibody dinutuximab (DNX) targets the sialic acid-containing glycosphingolipid GD2 expressed on almost all neuroblastoma tumor cells and induces cell lysis. However, the expression of GD2 is not limited to tumor cells only, but is also present on central nerve tissue and peripheral nerve cells explaining dinutuximab toxicity. The most common adverse reactions are pain and discomfort, which may lead to discontinuation of the treatment. Furthermore, there is little to no data available on exposure and effect relationships of dinutuximab. We, therefore, developed an easy method in order to quantify dinutuximab levels in human plasma. Ammonium sulfate (AS) was used to precipitate all immunoglobulins (IgGs) in human plasma. After centrifugation, supernatant containing albumin was decanted and the precipitated IgG fraction was re-dissolved in a buffer containing 0.5% sodium dodecyl sulfate (SDS). Samples were then reduced, alkylated, and digested with trypsin. Finally, a signature peptide in complementarity determining region 1 of DNX heavy chain was quantified on LC-MS/MS using a stable isotopically labeled peptide as internal standard. AS purification efficiently removed 97.5% of the albumin fraction in the supernatant layer. The validation performed on DNX showed that within-run and between-run coefficients of variation (CV) for lower limit of quantification (LLOQ) were 5.5 and 1.4%, respectively. The overall CVs for quality control (QC) low, QC med, and QC high levels were < 5%. Linearity in the range 1-32 mg/L was excellent (r2 > 0.999). Selectivity, stability, and matrix effect were in concordance with EMA guidelines. In conclusion, a method to quantify DNX in human plasma was successfully developed. In addition, the high and robust process efficiency enabled the utilization of a stable isotopically labeled (SIL) peptide instead of SIL DNX, which was commercially unavailable. Graphical abstract.