Abstract
Immunotherapy has been successful in treating many tumour types. The development of additional tumour-antigen binding monoclonal antibodies (mAbs) will help expand the range of immunotherapeutic targets. Lewis histo-blood group and related glycans are overexpressed on many carcinomas, including those of the colon, lung, breast, prostate and ovary, and can therefore be selectively targeted by mAbs. Here we examine the molecular and structural basis for recognition of extended Lea and Lex containing glycans by a chimeric mAb. Both the murine (FG88.2) IgG3 and a chimeric (ch88.2) IgG1 mAb variants showed reactivity to colorectal cancer cells leading to significantly reduced cell viability. We determined the X-ray structure of the unliganded ch88.2 fragment antigen-binding (Fab) containing two Fabs in the unit cell. A combination of molecular docking, glycan grafting and molecular dynamics simulations predicts two distinct subsites for recognition of Lea and Lex trisaccharides. While light chain residues were exclusively used for Lea binding, recognition of Lex involved both light and heavy chain residues. An extended groove is predicted to accommodate the Lea-Lex hexasaccharide with adjoining subsites for each trisaccharide. The molecular and structural details of the ch88.2 mAb presented here provide insight into its cross-reactivity for various Lea and Lex containing glycans. Furthermore, the predicted interactions with extended epitopes likely explains the selectivity of this antibody for targeting Lewis-positive tumours.
Highlights
Cancer is a leading cause of mortality worldwide, currently accounting for around 1 in 6 deaths, with the highest incidences for lung, breast and colorectal cancer
Lewis antigens are aberrantly expressed on tumours derived from tissues that are often normally negative for that specific glycan [12]
Previous work by Chua et al demonstrated the ability of FG88.2 to target colorectal cancer cells [20]
Summary
Cancer is a leading cause of mortality worldwide, currently accounting for around 1 in 6 deaths, with the highest incidences for lung, breast and colorectal cancer. Lewis glycans are fucosylated determinants known as Lea, Leb, Lex and Ley and sialylated versions, sLex and sLea. Type I glycans, known as histo-blood group antigens, include Lea and Leb, which are formed by a Galβ1-3GlcNAc core. Type I glycans, known as histo-blood group antigens, include Lea and Leb, which are formed by a Galβ1-3GlcNAc core This core glycan determinant has been referred to as the Lec antigen. While it has not been as extensively studied as other Lewis glycans, Lec is specific to Lea and Leb negative red cells and has been considered a precursor to Lea and Leb (Figure S1) [6,7,8,9,10]. Lewis antigens are known to be over-expressed on breast, lung, colorectal, prostate and ovarian cancers [13]
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