Characterization of 10 new monoclonal antibodies against prostate‐specific antigen by analysis of affinity, specificity and function in sandwich assays

While prostate‐specific antigen (PSA) is already an invaluable marker for prostate cancer, there is continuing demand for new anti‐PSA antibodies with specific characteristics, e.g., high sensitivity and specificity and equimolar binding to free PSA (f‐PSA) and the PSA‐α‐1‐antichymotrypsin complex (PSA‐ACT), as well as the ability to distinguish between these 2 immunoreactive forms of PSA. We have therefore generated and characterized 10 anti‐PSA monoclonal antibodies (MAbs). Apparent dissociation constants (Kd) of MAbs were determined by direct ELISA yielding Kd‐0.2‐164.0 nM. Western blots suggested that 3 of the MAbs (60‐1A2, 60‐8A2 and 17‐1A2) bind to linear epitopes. Sandwich assays identified 5 major antigenic regions as binding targets of the MAbs. Three combinations of MAbs recognize f‐PSA and PSA‐ACT in equimolar fashion with high sensitivity. Two of the MAb combinations are specific for f‐PSA. Physical analysis of the new antibodies has allowed us to assign the MAbs to binding classes (based on their sandwiching capabilities) and to determine accurate apparent dissociation constants. Int. J. Cancer 71: 1019‐1028, 1997. © 1997 Wiley‐Liss Inc.