e13626 Background: Cancer stem cells (CSCs) are established firmly to play a key role in tumor formation, maintenance, and resistance to the conventional therapies. This resistance is reported to depend on quiescence of CSCs, and controlling cell cycle of CSCs is indispensable to eliminate CSCs. We constructed a telomerase-specific oncolytic adenovirus (OBP-301 [Telomelysin]), in which the hTERT promoter drives expression of E1 genes. OBP-301 causes selective replication and lysis of a variety of human cancer cells. A phase I study has been completed in the US to confirm the safety and pharmacokinetics of OBP-301 in patients with advanced solid tumors. Since telomerase activity is one of the stem-cell properties, OBP-301 may be capable of targeting human CSCs. Here, we examined the molecular mechanism of OBP-301-mediated cytotoxicity on CD133+ CSCs isolated from human gastric cancer cells. Methods: Radioresistant MKN45 and MKN7 human gastric cancer cells were obtained by sequential irradiation, and sorted for CD133+ and CD133− cells by flow cytometry. The CD133+ cells were confirmed for the characteristics of CSCs. We compared antitumor effects of chemotherapeutic agents, ionizing radiation, and OBP-301 on CD133+ and CD133-cells by XTT analysis. Western blotting was performed to determine the protein expression essential for the maintenance of stemness. Results: Although the fraction of CD133+ cells was 1-2% in untreated cells, radiation increased the CD133+ population to 18-20%. The CD133+ cells only have asymmetric division ability, sphere formation ability, and tumorigenicity. The cell viability assay demonstrated that CD133+ cells were less sensitive to the chemotherapeutic agents and ionizing radiation compared to CD133- cells, whereas OBP-301 could efficiently kill both CD133+ and CD133- cells. As CD133+ cells showed a higher telomerase activity, OBP-301 could replicate more efficiently in CD133+ cells. OBP-301 mediated cell cycle progression on quiescent CD133+ cells, while protein expression associated with the growth and stemness was reduced. Conclusions: Our data indicate that telomerase-specific OBP-301 might be a promising anticancer treatment against human gastric CSCs. No significant financial relationships to disclose.
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