The MUC1 oncoprotein as a functional target: immunotoxin binding to alpha/beta junction mediates cell killing.
MUC1, a heavily glycosylated mucin, has generated considerable interest as a target for tumor killing because of its overexpression in malignancies. Full-length MUC1 (MUC1/TM) is proteolytically cleaved after synthesis generating alpha and beta subunits, which specifically bind in a noncovalent interaction. Although the beta chain remains on the cell surface, the alpha chain binds in an on-and-off interaction. Most anti-MUC1 antibodies (Abs) described to date recognize epitopes within the highly immunogenic alpha-chain tandem repeat. Because the alpha-chain is shed, such Abs are sequestered and fail to reach MUC1-expressing cells. Immunizing with cDNA encoding MUC1/TM and the spliced MUC1/X isoform from which the tandem repeat has been deleted yielded antibodies to the MUC1 alpha/beta junction. Pseudomonas toxin PE38 linked to polyclonal anti-MUC1 alpha/beta junction Abs both bound and killed MUC1-positive malignant cells. Monoclonal DMC209 binds the MUC1 alpha/beta junction in both MUC1/X and MUC1/TM. When injected into SCID mice xenotransplanted with human breast cancer MDA-MB-231, monoclonal DMC209 showed significant in vivo tumor-suppressive activity. The MUC1/X alpha/beta junction presents a biologically-significant target in MUC1-expressing malignancies because (i) antibodies directed against cell-bound alpha/beta junction epitopes reach the intended cellular target, (ii) antibodies to junction epitope are internalized into cells, (iii) anti alpha/beta junction antibodies can effectively kill high MUC1-expressing cancer cells as antibody-toxin conjugates and (iv) antibodies targeting the MUC1 cell-bound alpha/beta junction results in tumor suppression in vivo. Our results indicate that cell-bound MUC1 alpha/beta junction, unlike shed alpha chain, represents a highly effective moiety for targeting and killing MUC1-expressing malignancies.
Rubinstein
Daniel B
DB
National Cancer Institute, National Institutes of Health, Bethesda, MD, USA. danielhw@post.tau.ac.il
Karmely
Maya
M
Pichinuk
Edward
E
Ziv
Ravit
R
Benhar
Itai
I
Feng
Ningping
N
Smorodinsky
Nechama I
NI
Wreschner
Daniel H
DH
D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D000939:Epitopes / Q000737:chemistry; D005260:Female; D006801:Humans; D006825:Hybridomas / Q000378:metabolism; D007167:Immunotherapy / Q000379:methods*; D000922:Immunotoxins / Q000737:chemistry*; D051379:Mice; D016513:Mice, SCID; D018396:Mucin-1 / Q000378:metabolism / Q000502:physiology*; D009368:Neoplasm Transplantation; D011487:Protein Conformation; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary
D000911:Antibodies, Monoclonal; D000939:Epitopes; D000922:Immunotoxins; C060192:MUC1 protein, human; D018396:Mucin-1; D020033:Protein Isoforms