Background: Emerging evidence has suggested that the capability to sustain tumor formation, growth, and chemotherapy resistance in ovarian as well as other human malignancies exclusively resides in a small proportion of tumor cells termed cancer stem cells. During the characterization of CD44(+) ovarian cancer stem cells, we found a high expression of the genes encoding for claudin-4. Because this tight junction protein is the natural high-affinity receptor for Clostridium perfringens enterotoxin (CPE), we have extensively investigated the sensitivity of ovarian cancer stem cells to CPE treatment in vitro and in vivo.
Methods: Real-time polymerase chain reaction and flow cytometry were used to evaluate claudin-3/-4 expression in ovarian cancer stem cells. Small interfering RNA knockdown experiments and MTS assays were used to evaluate CPE-induced cytotoxicity against ovarian cancer stem cell lines in vitro. C.B-17/SCID mice harboring ovarian cancer stem cell xenografts were used to evaluate CPE therapeutic activity in vivo.
Results: CD44(+) ovarian cancer stem cells expressed claudin-4 gene at significantly higher levels than matched autologous CD44(-) ovarian cancer cells, and regardless of their higher resistance to chemotherapeutic agents died within 1 hour after exposure to 1.0 μg/mL of CPE in vitro. Conversely, small-interfering RNA-mediated knockdown of claudin-3/-4 expression in CD44(+) cancer stem cells significantly protected cancer stem cells from CPE-induced cytotoxicity. Importantly, multiple intraperitoneal administrations of sublethal doses of CPE in mice harboring xenografts of chemotherapy-resistant CD44(+) ovarian cancer stem cells had a significant inhibitory effect on tumor progression leading to the cure and/or long-term survival of all treated animals (ie, 100% reduction in tumor burden in 50% of treated mice; P < .0001).
Conclusions: CPE may represent an unconventional, potentially highly effective strategy to eradicate chemotherapy-resistant cancer stem cells.
Copyright © 2011 American Cancer Society.