Bacterial toxins are known to be effective for
cancer therapy.
Clostridium perfringens enterotoxin (CPE) is produced by the bacterial Clostridium type A strain. The transmembrane
proteins claudin-3 and -4, often overexpressed in numerous human epithelial
tumors (for example, colon, breast, pancreas, prostate and ovarian), are the targeted receptors for CPE. CPE binding to them triggers formation of membrane pore complexes leading to rapid cell death. In this study, we aimed at selective
tumor cell killing by CPE gene transfer. We generated expression vectors bearing the bacterial wild-type CPE
cDNA (wtCPE) or translation-optimized CPE (optCPE)
cDNA for in vitro and in vivo gene therapy of claudin-3- and -4-overexpressing
tumors. The CPE expression analysis at
messenger RNA and
protein level revealed more efficient expression of optCPE compared with wtCPE. Expression of optCPE showed rapid cytotoxic activity, hightened by CPE release as bystander effect. Cytotoxicity of up to 100% was observed 72 h after gene transfer and is restricted to claudin-3-and -4-expressing
tumor lines. MCF-7 and HCT116 cells with high
claudin-4 expression showed dramatic sensitivity toward CPE toxicity. The
claudin-negative
melanoma line SKMel-5, however, was insensitive toward CPE gene transfer. The non-viral intratumoral in vivo gene transfer of optCPE led to reduced
tumor growth in MCF-7 and HCT116
tumor-bearing mice compared with the vector-transfected control groups. This novel approach demonstrates that CPE gene transfer can be employed for a targeted suicide gene therapy of claudin-3- and -4-overexpressing
tumors, leading to the rapid and efficient
tumor cell killing in vitro and in vivo.