Briefly, blood samples were drawn by antecubital venipuncture while the individuals, who had not been fasting prior to any invasive procedure, were seated. The samples were collected in an 8.5-cc

Serum Separator Vacutainer Tube (BD Diagnostics, Plymouth, UK) and maximally within 4 h at room temperature were centrifuged at 1000 × g for 10 min. Serum samples were then distributed into sterile 500-μL barcode labeled polypropylene aliquots (TrakMate; Matrix TechCorp.) and stored at −80 °C. All serum samples were thawed on ice once and randomly placed in barcode labeled PI3K inhibitor racks in an 8-channel Hamilton STAR® pipetting robot (Hamilton) for automated aliquotting into 60-μL daughter tubes. The aliquots were stored in 96-tubes racks at −80 °C until further sample processing. Samples from the calibration and the validation set were distributed over three 96-tubes racks as following: one full 96-tube rack for both the calibration and validation set and one partially filled 96-tube rack with 63 samples from the calibration set and 18 samples from the validation set. Identical

processing steps were followed for the two sample sets. The isolation of peptides from human serum was performed using RPC18-functionalized MBs as previously described [27]. In short, RPC18-MBs were first activated by a three-step washing with a 0.1% TFA solution. Then, for each sample 5 μL of serum was added to the activated beads and incubated for 5 min at room selleck compound temperature. The beads were washed again three times with 0.1% TFA and peptides were eluted with a 1:1 mixture of water and acetonitrile. Two microliters of each

(stabilized) eluate were mixed with 10 μL of an α-cyano-4-hydroxycinnamic acid MALDI matrix solution in a 384-well PCR plate. Then, 1 μL of this mixture was spotted in quadruplicate onto a 600 μm Anchor-Chip™ MALDI-target plate (Bruker Daltonics). The so-called Palbociclib in vivo RPC18 eluates from the calibration and the validation set were spotted onto three 384-spots MALDI-target plate as following: 96 eluates from the calibration set and 96 eluates from the validation set were spotted in quadruplicate onto two distinct MALDI-target plates; the remaining eluates from the two sets were spotted in quadruplicate onto the same MALDI-target plate. This SPE- and MALDI-spotting procedure requires approximately 3 h per plate of 96 samples. MALDI-FTICR experiments were performed on a Bruker 15 tesla solariX™ FTICR mass spectrometer equipped with a novel CombiSource (Bruker Daltonics). The MALDI-FTICR system was controlled by Compass solariXcontrol software and equipped with a Bruker Smartbeam-II™ laser system that operated at a frequency of 200 Hz. The ‘medium’ predefined shot pattern was used for the irradiation.