Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com Original Paper Pathobiology 2011;78:181–192 DOI: 10.1159/000325538 Hypoxia Induces Tumor Aggressiveness and the Expansion of CD133-Positive Cells in a Hypoxia-Inducible Factor-1  -Dependent Manner in Pancreatic Cancer Cells Okito Hashimoto   a Kazuya Shimizu   c Shuho Semba   a Sachie Chiba   b Yonson Ku   b Hiroshi Yokozaki   a Yuichi Hori   b   a  Division of Pathology, Department of Pathology, and b  Division of Hepato-Billiary-Pancreatic Surgery, Department of Surgery, Kobe University Graduate School of Medicine, and c  Department of Internal Medicine, Kobe Medical Center, Kobe, Japan of CD133+ pancreatic cancer cells. The behavior of HIF- 1  ODD-transfected cells under normoxia was compatible with that of the parent cells under hypoxia. Furthermore, a xenograft model of HIF-1  ODD cells showed aggressive- ness, including metastasis and highly tumorigenic ability. Conclusion: Hypoxia induces tumor aggressiveness associ- ated with the expansion of CD133+ pancreatic cancer cells in a predominantly HIF-1 -dependent manner. Copyright © 2011 S. Karger AG, Basel Introduction The presence of intratumoral hypoxia is a negative prognostic indicator for many patients as it has been as- sociated with an increased degree of local failure follow- ing radiotherapy, chemotherapy and increased distant metastasis. Hypoxia can drive the metastatic phenotype secondary to both genetic instability and the clonal se- lection of aggressive tumor cell phenotypes [1]. How- ever, the direct link between hypoxia, genetic instability and an aggressive phenotype remains to be elucidated [2–4]. Key Words CD133  Hypoxia  Pancreatic cancer  Cancer stem cell  Hypoxia-inducible factor-1   CXC chemokine receptor 4 Abstract Background: Intratumoral hypoxia is known to lead to in- creased aggressiveness and distant metastasis. However, the interplay underlying these actions is still unknown. Objec- tive: We explored whether cancer cells might acquire a stem-like phenotype under hypoxia, consequently leading to an aggressive phenotype, including invasiveness and me- tastasis. Methods: Under normoxia (20% O 2 ) or hypoxia (1% O 2 ), the expression of CD133 (cancer stem cell marker), CXC chemokine receptor 4 (CXCR4) and hypoxia-inducible factor- 1  (HIF-1 ) was examined by RT-PCR and immunostaining using human pancreatic cancer cell lines. We also examined if hypoxia facilitates the invasiveness of CD133+ cancer cells. Furthermore, we transfected dominant active HIF-1  (HIF- 1  ODD) by the retroviral gene transfer and examined the effects both in vitro and in vivo. Results: Compared with normoxia, hypoxia elevated the expression of CD133, CXCR4 and HIF-1 . Moreover, hypoxia facilitated the invasiveness Received: January 14, 2011 Accepted after revision: February 15, 2011 Yuichi Hori, MD, PhD Division of Hepato-Biliary-Pancreatic Surgery, Department of Surgery Kobe University Graduate School of Medicine 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017 (Japan) Tel. +81 78 382 6302, E-Mail horiy  @  med.kobe-u.ac.jp © 2011 S. Karger AG, Basel 1015–2008/11/0784–0181$38.00/0 Accessible online at: www.karger.com/pat