An EGP-2/Ep-CAM-expressing transgenic rat model to evaluate antibody-mediated immunotherapy

Abstract

The human pancarcinoma-associated epithelial glycoprotein-2 (EGP-2), also known as 17-1A or Ep-CAM, is a 38-kDa transmembrane antigen, commonly used for targeted immunotherapy of carcinomas. Although strongly expressed by most carcinomas, EGP-2 is also expressed in most simple epithelia. To evaluate treatment-associated effects and side-effects on tumor and normal tissue respectively, we generated an EGP-2-expressing transgenic Wistar rat. To express the cDNA of the EGP-2 in an epithelium-specific manner, the 5' and 3' distal flanking regions of the human keratin 18 (K18) gene were used. EGP-2 protein expression was observed in the liver and pancreas, whereas EGP-2 mRNA could also be detected in lung, intestine, stomach and kidney tissues. In this rat, EGP-2-positive tumors can be induced by injecting a rat-derived carcinoma cell line transfected with the GA733-2 cDNA encoding EGP-2. Transgenic rats were used to study specific in vivo localization of an i.v. anti-EGP-2 monoclonal antibody, MOC31, applied i.v. Immunohistochemical analyses showed the specific localization of MOC31 in s.c. induced EGP-2-positive tumors, as well as in the liver. In contrast, in EGP-2-transgenic rats, MOC31 did not bind to EGP-2-negative tumors, the pancreas, or other normal tissues in vivo. In conclusion, an EGP-2-transgenic rat model has been generated that serves as a model to evaluate the efficacy and safety of a variety of anti-EGP-2-based immunotherapeutic modalities.

MOC‐31/Ep‐CAM immunoreactivity in Merkel cells and Merkel cell carcinomas

“…The antibody MOC‐31 has been employed experimentally for scintigraphy of small‐cell lung carcinomas 26 and for therapy with immunotoxins or anthracycline immunoconjugates in different carcinoma types 27–31 . A transgenic rat model has been created to evaluate the efficacy and safety of a variety of MOC‐31‐based immunotherapeutic modalities 32 . MOC‐31 has also been used for immunomagnetic detection of micrometastatic cells in bone marrow of colorectal cancer patients, 33 as well as of circulating tumour cells in the peripheral blood and bone marrow of patients with ovarian carcinoma 34 .…”

A3—a novel colon and pancreatic cancer reactive antibody from a primate phage library selected using intact tumour cells

“…With the objective to induce tumour responses even in more advanced stage patients, the introduction of potent effector molecules in conjunction with this antibody will challenge the "normal tissue resistance" seen in the treatment with the naked 17-1A MAb (Mack et al, 1997). Preclinically, this could be studied in model systems using toxin-conjugated antibodies specific to the murine version of this antigen or animals transgenic for human colon cancer-associated antigens (Clarke et al, 1998;McLaughlin et al, 1999;Basak et al, 1998). Previously, antibody immunotoxins have been successfully used to cure mice in models with metastatically growing tumours (Liu et al, 1996;Rosendahl et al, 1999;Trail et al, 1993) expressing xeno (human) tumour antigens not expressed in mouse tissues.…”

Challenges of general safety evaluations of biologics compared to small molecule pharmaceuticals in animal models

“…Prior to use for nonclinical testing, the model was fully characterized to show that the murine CD4 was replaced with human CD4 and that the human protein mediated its physiologic functions for cellular and humoral immunity [63][64][65]. Use of the humanized knock-in transgenic animal models may not be appropriate if the expression pattern or physiologic role differs from humans as was shown for the epithelial glycoprotein 2 (EPCAM) transgenic Wistar rat model which was deemed inappropriate for use in the nonclinical safety evaluation of anti-EPCAM immunotherapeutics because the transgenic rat had a different EPCAM tissue expression pattern compared to humans [66]. Transgenic models have also been used to evaluate the carcinogenicity of some small molecule drug candidates; however, as discussed in a recent review [67], use of the transgenic rodent carcinogenicity models also remains controversial and should be considered on a case-by-case basis.…”