Objective: The aim of this study was to explore the possibility of creating a toxin, C-CPE-ETA', by fusing C-terminal high affinity binding domain of CPE (C-CPE) with a truncated form of Pseudomonas aeruginosa exotoxin A (ETA') and to examine whether C-CPE-ETA' could specifically target CLDN-3, 4 molecule and the targeted toxin was cytotoxic against CLDN-3,4-overexpressing ovarian cancer.
Methods: CLDN-3 and CLDN-4 expressions were analyzed at the mRNA level in three ovarian cancer cell lines and epithelial ovarian cancer tissues from 20 patients. After transforming an expression plasmid of C-CPE-ETA' into E. coli BL21 (DE3) plysS strain, the recombinant protein was purified using His-Bind resin chromatography column and analyzed by Western blot and Coomassie blue staining. The specific binding, proapoptotic and cytolytic activities were evaluated by flow cytometry, fluorescence microscopy with the JC-1 probe and MTT assay in CLDN-3,4-overexpressing ovarian cancer cells.
Results: Quantitive RT-PCR results showed there existed high levels of CLDN-3 and CLDN-4 in ovarian cancer cells, CAOV3, OVCAR3 and SKOV3. Moreover, high expressions of CLDN-3 and CLDN-4 were observed in 90.0% (18/20) and 60.0% (12/20) of ovarian cancer tissues, with an expression level 10-fold higher than that in the normal ovarian tissue. A 58 000 recombinant protein C-CPE-ETA' was demonstrated by Western blot and Coomassie blue staining. Purified and recombinant C-CPE-ETA' was bound with high affinity to CLDN-3,4-overexpressing ovarian cancer cells, CAOV3, OVCAR3 and SKOV3 cells. C-CPE-ETA' was strongly proapoptotic and cytotoxic towards the CLDN-3,4-overexpressing ovarian cancer cells. The concentration of IC(50) was 7.364 ng/ml for CAOV3 cells, 8.110 ng/ml for OVCAR3 cells and 22.340 ng/ml for SKOV3 cells, respectively. However, control CLDN-3,4-deficient cell line HUVEC was not susceptible to the recombinant C-CPE-ETA' at a concentration up to 10 µg/ml.
Conclusions: The C-CPE-ETA' protein exhibits remarkably specific cytotoxicity for CLDN-3,4-overexpressing ovarian cancer cells. Its therapeutic potential warrants further development for ovarian cancer molecular targeted therapy.