Iodoacetamide is a known cysteine protease inhibitor and reacts readily with the free thiol of cysteine residues required for the hydrolyzing proteases such as cancer procoagulant [18, selleck kinase inhibitor 30]. The amount of CP-AP that is generated in the serum of cancer patients is inversely proportional to the concentration of iodoacetamide added (Additional file 2: Figure S2). This demonstrates that the cleavage of CP-RP and the accumulation of CP-AP

is a specific reaction that is related to cysteinprotease activity. Most interestingly, the proteolytic activity of serum specimens towards CP-RP is conserved for up to 24 h indicating a good preanalytical stability making it useful for diagnostic application (Figure 4). One major challenge of functional protease profiling is the appropriate selection of exogenous reporter peptides, which are exclusively cleaved by tumor-associated proteases. However, serum is a difficult matrix with high intrinsic proteolytic activity caused by different endoproteases e.g. from the coagulation cascade and the complement system [14, 31, 32] as well as a multitude of exoproteases [33]. Furthermore, the proteolytic profile in blood specimens is not only altered in malignant disease but also under non-malignant conditions e.g. inflammation [16]. In order GF120918 mw to be useful for diagnostics, such proteolytic patterns must be distinguishable

from e.g. the inflammatory responses in unrelated non-malignant conditions. As these patterns overlap to a great extent, the classification of tumour patients on the basis of proteolytic

activity is a demanding task. Our study addresses this important question by demonstrating the diagnostic accuracy Methocarbamol of functional protease profiling with exogenous reporter peptides in a proof-of-concept SC79 chemical structure experiment including patients with inflammatory conditions during non-malignant diseases into the control cohort. Most importantly, there were no statistically significant differences of CP-AP concentrations between the healthy controls and inflammatory controls, while CP-AP concentrations were significantly higher in serum specimens from tumor patients (see Figure 5A). This indicates that changes of the proteolytic profile related to inflammation do not affect the specific processing of the reporter peptide CP-RP. However, we emphasize that this small proof-of-principle profiling experiment has serious shortcomings concerning the limited number of analyzed specimens and the selection of late-stage tumor patients with highly elevated CEA concentrations (see Table 2). Further studies will have to integrate also early tumor stages and in addition should evaluate the impact of therapeutic interventions to clarify the potential benefit of functional protease profiling. Finally, it is likely that tumor heterogeneity during progression of malignant disease may result in different protease patterns [34].