title: Endoprotease profiling with double-tagged peptide substrates: a new diagnostic approach in oncology.
abstract: BACKGROUND
  The measurement of disease-related proteolytic activity in complex biological matrices like serum is of emerging interest to improve the diagnosis of malignant diseases. We developed a mass spectrometry (MS)-based functional proteomic profiling approach that tracks degradation of artificial endoprotease substrates in serum specimens.
  
  
  METHODS
  The synthetic reporter peptides that are cleaved by tumor-associated endopeptidases were systematically optimized with regard to flanking affinity tags, linkers, and stabilizing elements. Serum specimens were incubated with reporter peptides under standardized conditions and the peptides subsequently extracted with affinity chromatography before MS. In a pilot study an optimized reporter peptide with the cleavage motif WKPYDAADL was added to serum specimens from colorectal tumor patients (n = 50) and healthy controls (n = 50). This reporter peptide comprised a known cleavage site for the cysteine-endopeptidase "cancer procoagulant."
  
  
  RESULTS
  Serial affinity chromatography using biotin- and 6xHis tags was superior to the single affinity enrichment using only 6xHis tags. Furthermore, protease-resistant stop elements ensured signal accumulation after prolonged incubation. In contrast, signals from reporter peptides without stop elements vanished completely after prolonged incubation owing to their total degradation. Reporter-peptide spiking showed good reproducibility, and the difference in proteolytic activity between serum specimens from cancer patients and controls was highly significant (P < 0.001).
  
  
  CONCLUSIONS
  The introduction of a few structural key elements (affinity tags, linkers, d-amino acids) into synthetic reporter peptides increases the diagnostic sensitivity for MS-based protease profiling of serum specimens. This new approach might lead to functional MS-based protease profiling for improved disease classification.
authors.affiliation: Institute for Clinical Chemistry, Medical Faculty Mannheim of the University of Heidelberg, University Hospital Mannheim, Mannheim, Germany.
authors.forename: Teresa
authors.initials: T
authors.lastname: Peccerella
authors.forename: Nadine
authors.initials: N
authors.lastname: Lukan
authors.forename: Ralf
authors.initials: R
authors.lastname: Hofheinz
authors.forename: Dirk
authors.initials: D
authors.lastname: Schadendorf
authors.forename: Markus
authors.initials: M
authors.lastname: Kostrezewa
authors.forename: Michael
authors.initials: M
authors.lastname: Neumaier
authors.forename: Peter
authors.initials: P
authors.lastname: Findeisen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001798:Blood Proteins / Q000378:metabolism*; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000201:enzymology*; D010450:Endopeptidases / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D040901:Proteomics / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D001798:Blood Proteins; D010450:Endopeptidases