Abstracts
2000 Digestive Disease Week

# 2458 Tumor Suppressor Gene Therapy and COX 2 Inhibition Additively Reduces Intestinal Neoplasia.
J. I. Lew, L. Vargish, R. K. Kim, Y. Guo, F. Michelassi, R. B. Arenas, Chicago, IL

The Adenomatous Polyposis Coli (APC) gene is implicated early in the tumorigenesis of colon cancer. Multiple Intestinal Neoplasia (Min) mice possess a mutation of the APC gene and develop neoplastic intestinal polyps with elevated cyclooxygenase-2 (COX-2) levels similar to Familial Adenomatous Polyposis (FAP) in humans. Liposomal delivery of human APC gene may prevent or reduce intestinal neoplasia. Furthermore, the relationship of intestinal cancer cells to increased COX-2 levels provides a rationale for the early use of selective COX-2 inhibitors such as Vioxx to prevent polyp formation. This study was performed to determine whether liposomal tumor suppressor APC gene therapy and further selective COX-2 inhibition with Vioxx may have an additive effect in the reduction of intestinal neoplasia in the Min mouse. METHODS: Three-week old C57BL/6J-Min/+ mice, heterozygous for the Apc gene mutation were weaned onto a high fat (30%) diet with or without Vioxx. The animals were randomized to a control group (n=6), an APC only group (n=4), a Vioxx only group (n=4) and an APC/Vioxx group (n=4). For the APC treatment groups, plasmid (20mg) containing the human APC gene driven by a viral cytomegalovirus promoter (pCMV-APC) was mixed with lipofectin (200ml) and administered transorally biweekly. Vioxx was administered orally to the mice at 200 ppm in the high fat diet. For the control group, mice were treated with a similar plasmid construct lacking APC (pCMV-neo) in an identical fashion. After two months, mice were sacrificed and polyp counts were obtained. Confirmation of gene expression was determined by Western blot analysis using a polyclonal anti-APC antibody. RESULTS: Examination of the intestines demonstrated a significant reduction in the overall number of intestinal polyps in all treatment groups, especially in the distal small bowel where polyp formation was greatest. There was an 84% reduction in the total number of intestinal polyps after combined APC and Vioxx treatment (APC/Vioxx treated, 10.5±3.4 vs. control, 64.3±28.4, p£0.05). Furthermore, there was a 53% and 55% reduction in total number of polyps after APC only and Vioxx only treatment respectively (APC treated, 30.5±5.8 vs. control, p£0.05; Vioxx treated, 28.8±15.7 vs. control, p£0.05). Among the treatment groups, there was a significant difference between the combined APC/Vioxx group compared to the APC only and Vioxx only group respectively. Western blot analysis showed higher levels of normal APC protein formation in repetitively treated mice. CONCLUSION: APC gene mutations and increased COX-2 levels play a critical role in the tumorigenesis of colon cancer. APC gene replacement and COX-2 inhibition have an additive effect in the prevention of polyp formation as shown in the Min mouse, and thereby may prove therapeutic and contribute to new strategies in the treatment of colon cancer.