1237 Bioanalysis (2015) 7(10), 1237–1251 ISSN 1757-6180 Research Article part of 10.4155/BIO.15.56 © 2015 Future Science Ltd Background: In preclinical studies, monoclonal antibodies (mAbs) are traditionally assayed by ligand-binding-assays. Recently, quantitative liquid chromatography mass spectrometry (MS)-based assays have emerged which circumvent a number of challenges. These assays may also be multiplex, making them potentially compatible with pharmacokinetic assays for combined antibody therapies. Materials & Methods: We combined a quantitative MS-based approach with the protein standard for absolute quantification (PSAQ™) strategy to simultaneously quantify three mAb variants presenting minor sequence differences. Stable isotopically labeled mAbs were produced and used as quantification standards. Titration curves were performed to assess the analytical performances of the method. LC-MS/MS and ELISA data were cross-compared. Results: The approach presented provides similar accuracy and precision than ELISA, while being multiplex and faster to develop. It has applications at all stages of the pharmaceutical development. Background Monoclonal antibodies (mAbs) and related derivatives have become a major class of therapeutic compounds used to treat can- cers, infectious diseases, allergies, inflam- mation, and autoimmune diseases due to their high specificity and efficacy. There are currently more than 50 approved mAb- based products available on the market [1] . Since the first approval of a therapeutic mAb drug in the late nineties [2] , over 400 thera- peutic monoclonal antibodies (mAbs) have been tested in clinical trials. As a result, the clinical development of this type of bio- therapeutics is increasingly competitive. Newly developed therapeutic mAbs should have optimized physicochemical and phar- maceutical properties, such as high affinity and avidity for the target, controlled biodis- tribution, known effector functions and an optimized half-life [3,4] . Indeed, suboptimal pharmacokinetic (PK) properties are among the reasons that a compound may fail to reach the market. To avoid discovering these properties late in the selection process, multiple structural and sequence variants of mAb candidates are selected and tested in early preclinical studies. One of the chal- lenges for pharmaceutical companies lies in identifying the candidates with the best pharmaceutical and clinically relevant fea- tures as early as possible. These candidates will have a greater probability of success (OptimAbs project, which was launched on 26 November 2010, aimed at transforming therapeutic ‘research leads’ into drug can- didates by including ‘developability’ crite- ria beforehand). Meanwhile, R&D strate- gies have to be developed to limit costs, to save time and to reduce the risks related to developing lead candidates. As part of this, one approach consists in co-injecting several variant compounds and comparing their PK properties in a rodent-based tri- age study, with the objective to limit the number of later monkey triaging studies. To do this, robust and rapid bioanalyti- cal methods are being developed to select candidates that demonstrate suitable clini- cal potential based on PK properties. Cur- rently, ligand-binding-assays (LBAs), such as ELISA, remain the most common and Absolute and multiplex quantification of antibodies in serum using PSAQ™ standards and LC-MS/MS Dorothee Lebert* ,1 , Guillaume Picard 1 , Charlotte Beau-Larvor 2 , Lysiane Troncy 2 , Christine Lacheny 2 , Bernadette Maynadier 3 , Walter Low 4 , Nicolas Mouz 1 , Virginie Brun 5,6,7 , Christine Klinguer-Hamour 2 , Michel Jaquinod 5,6,7 & Alain Beck 2 1 PROMISE Advanced Proteomics, Grenoble, F-38040, France 2 Centre d’Immunologie Pierre Fabre (CIPF), 5 Av. Napoléon III, BP 60497, 74164 Saint-Julien-en- Genevois, France 3 Centre d’Etudes Pré-Cliniques Pierre Fabre, Campans, France 4 PX-Therapeutics, Grenoble, F-38040, France 5 Université Grenoble Alpes, iRTSV-BGE, F-38000 Grenoble, France 6 CEA, iRTSV-BGE, F-38000 Grenoble, France 7 INSERM, BGE, F-38000 Grenoble, France *Author for correspondence: Tel.: +33 438 023 650 dorothee.lebert@ promise-proteomics.com For reprint orders, please contact reprints@future-science.com