Characterization of Binding
Epitopes of CA125 Monoclonal
Antibodies
- Publication date
- Publisher
Abstract
The
most used cancer serum biomarker is the CA125 immunoassay for
ovarian cancer that detects the mucin glycoprotein MUC16. Several
monoclonal antibodies (mAbs) including OC125 and M11 are used in CA125
assays. However, despite considerable efforts, our knowledge of the
molecular characteristics of the recognized epitopes and the role
played by glycosylation has remained elusive. Here a comprehensive
set of recombinant MUC16 tandem repeats (TRs) expressed in glycoengineered
mammalian cells and <i>E. coli</i>, together with overlapping
peptides, was used to probe antigen-binding epitopes. We present a
complete analysis of N- and O-glycosylation sites of a MUC16 TR expressed
in CHO cells and demonstrate that neither N- nor O-glycosylation appear
to substantially influence binding of OC125 and M11 mAbs. A series
of successive N- and C-terminal truncations of a MUC16 TR construct
expressed in <i>E. coli</i> narrowed down the epitopes for
OC125 and M11 to a segment containing parts of two consecutive SEA
domains with a linker. Thus, a complete SEA domain is not required.
These findings suggest that binding epitopes of mAbs OC125 and M11
are dependent on conformation but not on glycosylation. The availability
of recombinant TR constructs with and without aberrant glycosylation
now opens the way for vaccine studies