Anti-free prostate-specific antigen monoclonal antibody epitopes defined by mimotopes and molecular modeling.
BACKGROUND
Prostate-specific antigen (PSA) is an important marker for the diagnosis and management of prostate cancer, and the free PSA/total PSA ratio has been shown to be efficient for distinguishing prostate cancer from benign prostatic hyperplasia. We report here the characterization of seven mouse monoclonal antibodies (mAbs) and the partial localization of two conformational epitopes identified by anti-free PSA mAbs.


METHODS
The mAbs were studied by competition and sandwich assays, and the epitope localization of the two anti-free PSA mAbs (6C8D8 and 5D3D11) was performed using phage displayed peptide libraries and molecular modeling.


RESULTS
The seven mAbs were classified into three groups according to their recognition specificities and their ability to inhibit the enzymatic activity of PSA and the formation of PSA-alpha1-antichymotrypsin (ACT) complex. Among the anti-free PSA mAb group, 6C8D8 recognized the phage displayed peptide RKLRPHWLHFHPVAV, two parts of which presented similarities with two regions distant on the PSA sequence but joined in the tridimensional structure. mAb 5D3D11 recognized the peptide DTPYPWGWLLDEGYD, which is similar to a PSA region located on the board of the groove containing the PSA enzymatic site. Both epitopes were located in the theoretical ACT binding site described previously. Moreover, these mAbs were able to inhibit the enzymatic activity of PSA.


CONCLUSIONS
These epitope localizations are in agreement with the ability of both mAbs to inhibit enzymatic activity and ACT fixation. The results presented here could bring information for the generation of clinically relevant PSA assays.
Michel
S
S
bioMérieux, Départment R&D unité Immunoessais, Chemin de lOrme, 69280 Marcy L/etoile, France.
Deléage
G
G
Charrier
J P
JP
Passagot
J
J
Battail-Poirot
N
N
Sibai
G
G
Jolivet
M
M
Jolivet-Reynaud
C
C
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000494:pharmacology; D000918:Antibody Specificity; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D018604:Epitope Mapping; D005260:Female; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017430:Prostate-Specific Antigen / Q000037:antagonists & inhibitors / Q000276:immunology* / Q000378:metabolism; D000514:alpha 1-Antichymotrypsin / Q000378:metabolism
D000911:Antibodies, Monoclonal; D000514:alpha 1-Antichymotrypsin; D017430:Prostate-Specific Antigen