Tumor invasion and metastasis is accompanied by significant activations of specific proteolysis enzymes. Tumor area is known to have increased infiltration of immunoglobulins G (“IgG”), so IgG may undergo proteolysis in this area. Serine proteases usually cleave peptide bonds between positively charged amino acids lysine and arginine. Since the intact PLG molecules as well as its fragments have lysine binding sites, they can bind to damaged IgG or fragments thereof with free C-terminal lysine that can appear in a circulation after proteolysis in the malignant tumor area. In the present invention we demonstrated the increased binding of damaged IgG or fragments thereof with free C-terminal lysine to fragments of PLG in samples from patients with breast cancer, ovarian cancer, lung cancer, colorectal cancer, prostate cancer vs. samples from healthy donors, and thus we proposed a novel diagnostic method.

The invention provides novel peptide binders for streptavidin (SA), Taq polymerase and several human proteins: Prostate Specific Antigen (PSA), thrombin, Tumor Necrosis Factor Alpha (TNF), and Urokinase-type Plasminogen Activator (uPA).

Tumor invasion and metastasis is accompanied by significant activations of specific proteolysis enzymes. Tumor area is known to have increased infiltration of immunoglobulins G (IgG), so IgG may undergo proteolysis in this area. Serine proteases usually cleave peptide bonds between positively charged amino acids lysine and arginine. Since the intact PLG molecules as well as its fragments have lysine binding sites, they can bind to damaged IgG or fragments thereof with free C-terminal lysine that can appear in a circulation after proteolysis in the malignant tumor area. In the present invention we demonstrated the increased binding of damaged IgG or fragments thereof with free C-terminal lysine to fragments of PLG in samples from patients with breast cancer, ovarian cancer, lung cancer, colorectal cancer, prostate cancer vs. samples from healthy donors, and thus we proposed a novel diagnostic method.

The present invention relates to the fields of medicine and immunology. In particular, this invention relates to immunological diagnostic methods that use the whole-length molecule of plasminogen or its peptide fragments as universal detectors of proteolysis products having a C-terminal lysine. The method of this immunological diagnostic is to identify the human diseases associated with increased activity of proteolytic enzymes. The inventions also relate to a diagnostic test system comprised of a detectorthe full-length molecule and its presented peptide fragments. The technical result is comprised of achieving the required degree of dissociation of the antigen-antibody complex in a sample from the subject, as well as changing the conformation of proteins using an incubation buffer containing organic solvents in the disclosed ratios, that can significantly increase the sensitivity of the method for determining the concentration of proteolytic fragments with a C-terminal lysine binding with plasminogen or fragments thereof.