GASTROENTEROLOGY Cytosine deaminase-producing human mesenchymal stem cells mediate an antitumor effect in a mouse xenograft model Mi-Hyeon You, 1 * Wang-Joon Kim, 1† Wooyoung Shim, 1† Sang-Rim Lee, ‡ Gwang Lee, †,§ Sangdun Choi, † Dae-Yong Kim,* Yong Man Kim, ¶ Hyunsoo Kim ¶ and Sang-Uk Han †,‡ *Department of Veterinary Pathology, Seoul National University, Seoul, † Department of Molecular Science and Technology, ‡ Department of Surgery, § Institute for Medical Science, Ajou University, Suwon, and ¶ FCB-Pharmicell, Sungnam, Korea Abstract Background and Aim: Stem cell transplantation offers potential gene therapy for brain tumors. However, this approach has received little attention as a treatment for gastrointes- tinal tumors. In the present study, we explored the possibility of human bone marrow- derived mesenchymal stem cells (hMSC) producing cytosine deaminase (CD), followed by systemic 5-fluorocytosine (5-FC) administration, showing an antitumor effect on a mouse gastric cancer xenograft. Methods: We first explored the ability of hMSC, coated with fluorescent dye, to migrate to human gastric cancer MKN45 cells in vitro and in vivo. We then used hMSC in which a gene expressed the prodrug-activating enzyme CD, which can convert the prodrug 5-FC into the cytotoxic agent 5-fluorouracil (5-FU), and further investigated the potential of these cells to deliver the CD gene and to reduce tumor growth in nude mice. The migratory capacity of hMSC was confirmed by an in vitro migration assay, as well as in an in vivo model of nude mice bearing subcutaneous tumors of MKN45 cells when hMSC were injected. Results: The migration ability of hMSC towards MKN45 cells was confirmed by migra- tion assay. Effective conversion of 5-FC to 5-FU by hMSC transfected with the CD gene (CD-hMSC) showed therapeutic anticancer potential in a MKN45 cell co-culture system, as confirmed by thin layer chromatography. Nude mice bearing MKN45 tumors were intravenously injected with CD-hMSC, followed by systemic 5-FC treatment (500 mg/kg/ day) for 7 days. Tumor volumes and weights of mice injected with CD-hMSC decreased significantly after treatment with 5-FC. However, the 5-FC-treated group without CD-hMSC injection showed neither a decrease in tumor volume nor bodyweight loss. Conclusion: The CD-hMSC system showed anticancer therapeutic potential, and mini- mized the side-effects of 5-FU. Key words cytosine deaminase, gastric cancer, gene therapy, mesenchymal stem cell, suicide effect. Accepted for publication 4 March 2009. Correspondence Sang-Uk Han, Department of Surgery, Ajou University School of Medicine, San 5, Wonchon-dong, Yeongtong-gu, Suwon 443-721, Korea. Email: hansu@ajou.ac.kr 1 These authors contributed equally to this work. Introduction Cancer remains a major cause of death worldwide. 1,2 Annually, about 1.18 million, 598 000, and 700 000 deaths are attributable to lung, liver, and stomach cancer, respectively. When cancer progresses to more advanced stages, prognosis is poor and both tumor recurrence and metastasis are to be expected. 5-fluororacil (5-FU) has been the chemotherapeutic choice for the majority of solid tumors, including gastric and colon cancers. However, the serious side-effects of this drug and the high doses required for effectiveness have limited the use of 5-FU as a chemotherapeutic agent. Therefore, therapeutic 5-FU strategies affording fewer side-effects are strongly in demand and, recently, so called ‘molecular chemotherapy’ has been proposed as one of several potential alternatives. 3–5 Molecular chemotherapy is based on the concept of target- specific therapeutic suicide gene delivery using a cell-based system. As mesenchymal stem cells (MSC) have the property of tracking tumor cells, molecular chemotherapy using MSC as the vehicle can mediate antitumor effects in tumor lesions. 6,7 Because MSC are acquired from a patient’s body and can easily be expanded in culture, they are suitable for the approach described. Furthermore, MSC are easily transfected with plasmids and trans- duced using adenoviral, retroviral and lentiviral vectors. 3,4 Several types of suicidal genes have been studied and used for therapeutic purposes. One of the most widely used genes is doi:10.1111/j.1440-1746.2009.05862.x 1393 Journal of Gastroenterology and Hepatology 24 (2009) 1393–1400 © 2009 The Authors Journal compilation © 2009 Journal of Gastroenterology and Hepatology Foundation and Blackwell Publishing Asia Pty Ltd