The novel EpCAM-targeting monoclonal antibody 317I linked to saporin is highly cytotoxic after photochemical internalization in breast, pancreas and colon cancer cell lines
Kaja Lund*, Monica Bostad, Ellen Skarpen, Michael Braunagel, Stefan Krauss, Alex Duncan, Anders Høgset, Pål K. Selbo*View affiliations
The epithelial cell adhesion molecule (EpCAM) is expressed by a wide range of human carcinomas, making it an attractive diagnostic and therapeutic target in oncology. Its recent identification on cancer stem cells has raised further interest in its use for tumor targeting and therapy. Here, we present the characterization and therapeutic potential of a novel, fully human EpCAM-targeting mAb, 317I. Strong reaction of 317I was observed in all lung, colon, and breast human tumor biopsies evaluated. By flow cytometry and confocal fluorescence microscopy, we demonstrate that 317I specifically targets EpCAM-positive cell lines. We also show evidence for mAb-sequestration in endo-/lysosomes, suggesting internalization of 317I by receptor-mediated endocytosis. The ribosomal-inactivating toxin saporin was linked to 317I, creating the per se non-toxic immunotoxin 317I-saporin, a promising candidate for the drug delivery technology photochemical internalization (PCI). PCI is based on a light-controlled destruction of endolysosomal membranes and subsequent cytosolic release of the sequestered payload upon light exposure. EpCAM-positive human cancer cell lines MCF7 (breast), BxPC-3 (pancreas), WiDr (colon), and the EpCAM-negative COLO320DM (colon), were treated with 317I-saporin in combination with the clinically relevant photosensitizer TPCS2a (Amphinex), followed by exposure to light. No cytotoxicity was observed after treatment with 317I-saporin without light exposure. However, cell viability, proliferation and colony-forming capacity was strongly reduced in a light-dependent manner after PCI of 317I. Our results show that 317I is an excellent candidate for diagnosis of EpCAM-positive tumors and for development of clinically relevant antibody-drug conjugates, using PCI for the treatment of localized tumors.