Determination of the complex between urokinase and its type-I inhibitor inplasma from healthy donors and breast cancer patients

Background: The complex between urokinase (uPA) and its type-1 inhibitor (P AI-1) is formed exclusively from the active forms of these components; thus , the complex concentration in a biological sample may reflect the ongoing degree of plasminogen activation. Our aim was to establish an ELISA for spe cific quantification of the uPA:PAI-1 complex in plasma of healthy donors a nd breast cancer patients. Methods: A kinetic sandwich format immunoassay was developed, validated, an d applied to plasma from 19 advanced-stage breast cancer patients, 39 age-m atched healthy women, and 31 men. Results: The assay detection limit was <2 ng/L, and the detection of comple x in plasma was validated using immunoabsorption, competition and recovery tests. Eighteen cancer patients had a measurable complex concentration (med ian, 68 ng/L; range, <16 to 8700 ng/L), whereas for healthy females and mal es the median signal values were below the detection limit (median, <16 ng/ L; range, <16 to 200 ng/L; P <0.0001). For patient plasma, a comparison wit h total uPA and PAI-1 showed that the complex represented a variable, minor fraction of the uPA and PAI-1 concentrations of each sample. Conclusion: The reported ELISA enables detection of the uPA:PAI-1 complex i n blood and, therefore, the evaluation of the complex as a prognostic marke r in cancer. (C) 1999 American Association for Clinical Chemistry.