doi:10.1016/j.ijrobp.2006.05.067 BIOLOGY CONTRIBUTION ORAZIPONE, A LOCALLY ACTING IMMUNOMODULATOR, AMELIORATES INTESTINAL RADIATION INJURY: A PRECLINICAL STUDY IN A NOVEL RAT MODEL MARJAN BOERMA,PH.D.,* JUNRU WANG, M.D., PH.D.,* KONRAD K. RICHTER, M.D., PH.D.,* AND MARTIN HAUER-JENSEN, M.D., PH.D.* † Departments of *Surgery, and † Pathology, University of Arkansas for Medical Sciences and Central Arkansas Veterans Healthcare System, Little Rock, AR Purpose: Intestinal radiation injury (radiation enteropathy) is relevant to cancer treatment, as well as to radiation accidents and radiation terrorism scenarios. This study assessed the protective efficacy of orazipone, a locally-acting small molecule immunomodulator. Methods and Materials: Male rats were orchiectomized, a 4-cm segment of small bowel was sutured to the inside of the scrotum, a proximal anteperistaltic ileostomy was created for intraluminal drug administration, and intestinal continuity was re-established by end-to-side anastomosis. After three weeks postoperative recovery, the intestine in the “scrotal hernia” was exposed locally to single-dose or fractionated X-radiation. Orazipone (30 mg/kg/day) or vehicle was administered daily through the ileostomy, either during and after irradiation, or only after irradiation. Structural, cellular, and molecular aspects of intestinal radiation toxicity were assessed two weeks after irradiation. Results: Orazipone significantly ameliorated histologic injury and transforming growth factor- immunoreac- tivity levels, both after single-dose and fractionated irradiation. Intestinal wall thickness was significantly reduced after single-dose and nonsignificantly after fractionated irradiation. Mucosal surface area and numbers of mast cells were partially restored by orazipone after single-dose irradiation. Conclusions: This work (1) demonstrates the utility of the ileostomy rat model for intraluminal administration of response modifiers in single-dose and fractionated radiation studies; (2) shows that mucosal immunomodu- lation during and/or after irradiation ameliorates intestinal toxicity; and (3) highlights important differences between single-dose and fractionated radiation regimens. © 2006 Elsevier Inc. Radiation injuries, Disaster planning, Intestines, Immunomodulation. INTRODUCTION Radiation therapy is used in 70% of cancer patients and is a critical factor in 25% of cancer cures. Advances in treatment planning and radiation delivery techniques have improved the ability to concentrate the radiation beam to the target volume. However, radiation therapy remains dose limited by the tolerance of surrounding normal tissues. Increased focus on the avoidance of treatment-related side effects in cancer patients, as well as the recently emergent need for medical countermeasures against radiologic accidents or terrorism, have resulted in a resurgence of interest in the development of interventions that may help reduce radia- tion-induced normal tissue toxicity. The intestine is a major dose-limiting organ during ab- dominal, pelvic, and retroperitoneal radiation therapy (1–3). It was previously believed that the severity of intestinal radiation toxicity is determined exclusively by the extent of radiation-induced intestinal crypt cell death. It is now rec- ognized that radiation-induced changes in cellular function, as well as secondary alterations, notably inflammatory changes, contribute substantially to the pathophysiologic manifestations of intestinal radiation toxicity. These consid- erations apply particularly to clinical (fractionated) radia- tion therapy regimens, because successive fractions of ra- diation inflict injury in cells and tissue compartments that exhibit progressive inflammatory changes (4). Conse- quently, modifiers of inflammatory responses or immune function have attracted significant attention as potential radiation response modifiers. Orazipone (3-[[4-(methylsulfonyl)phenyl]methylene]-2,4- Reprint requests to: Martin Hauer-Jensen, M.D., Ph.D., Univer- sity of Arkansas for Medical Sciences, 4301 West Markham, Slot 725, Little Rock, AR 72205. Tel: (501) 686-7912; Fax: (501) 421-0022; E-mail: mhjensen@life.uams.edu Supported by National Institutes of Health Grant No. CA71382, and Orion Pharma Research. M.B. and J.W. contributed equally to this work. Acknowledgments—We thank Jennifer D. James of the Arkansas Cancer Research Center Experimental Pathology Core Laboratory for excellent assistance in tissue processing and staining. Received March 24, 2006, and in revised form April 27, 2006. Accepted for publication May 2, 2006. Int. J. Radiation Oncology Biol. Phys., Vol. 66, No. 2, pp. 552–559, 2006 Copyright © 2006 Elsevier Inc. Printed in the USA. All rights reserved 0360-3016/06/$–see front matter 552