Abstracts
1999 Digestive Disease Week

# 3487 ESOPHAGOGASTRIC ADENOCARCINOMA IN AN E1A/E1B TRANSGENIC MODEL INVOLVES P53 DISRUPTION
Mark D Duncan, Johns Hopkins Bayview Med Ctr, Baltimore, MD; Tarik Tihan, David M Donovan, Quy H Phung, The Johns Hopkins Univ Sch of Medicine, Baltimore, MD; John W Harmon, Johns Hopkins BAyview Med Ctr, Baltimore, MD; Patricia J Gearhart, Kimberly LK Duncan, The Johns Hopkins Univ Sch of Medicine, Baltimore, MD

Purpose: To study tumorigenesis in a murine transgenic model introducing E1A/E1B under the control of the mouse mammary tumor virus-long terminal repeat (MMTV-LTR) promoter in which adenocarcinoma occurs at the squamocolumnar junction in the foregut, predominantly in males, and at no other site. The MMTV-LTR promoter when used without E1A/E1B does not produce forestomach tumors. The known oncogenic properties of the E1A and E1B genes may elucidate pathways of carcinogenesis in the human disease. The human adenovirus 12 E1B gene product interferes with p53-mediated apoptosis, inhibiting tumor suppression at the G1/S checkpoint. Mutations of p53 are frequent in human esophageal adenocarcinoma. Methods: A purified, linear 6.7 kb fragment of plasmid DNA containing MMTV-LTR/E1A/E1B was transferred by pronuclear microinjection into single cell embryos which were implanted in pseudopregnant females. Transgenic offspring were identified by dot blot hybridization of tail DNA to 32P-labeled E1A/E1B probe and PCR amplification with E1A primer pairs. Animals were observed for morbidity and weighed. Non-transgenic litter mates served as controls. Animals were sacrificed if weight loss reached 20%. The foregut was examined histologically. Immunohistochemistry was performed with monoclonal anti-p53 antibodies. Results: Eleven of 45 animals were transgenic (24% efficiency) with an estimated 5 to 57 copies of the gene per genome. A steep decline in weight of transgenic animals corresponded to observed listlessness. Profound weight loss (>20%) led to sacrifice or death of 1/5 females (at 12 weeks) and 4/6 males (at 16-17 weeks). Grossly visible tumors (2-10 mm) were noted in the forestomach of the female and 2/3 examined males at the margin between the shiny proximal stomach and the thicker rugae of the distal stomach. Histologic sections confirmed adenocarcinoma arising in each case at the squamocolumnar junction with gladular formation, pleomorphism, and frequent mitotic figures. At necropsy, no other tissue evidenced tumors. Immunostaining was positive for p53 indicating accumulation of mutated or altered p53 protein (Table). Conclusions: E1A/E1B transgenic animals developed macroscopic and microscopic adenocarcinoma at the squamocolumnar junction which corresponds to adenocarcinoma at the human espohagogastric junction. A male predominance was suggested, akin to human disease. Disruption of p53 was present in the transgenic model as in the human cancer. This reproducible transgenic model of human esophageal adenocarcinoma at the esophagogastric junction allows identification and characterization of precursor genetic and histologic changes at this hot-spot for carcinogenesis.
and poorly differentiated tumors

Transgenics	Weight loss	Age (wk)	Pathology	p53
male (n=6)	4	16 weeks	adenocarcinoma	+
		16 weeks	adenocarcinoma	+
		17 weeks	adenocarcinoma	+
		17 weeks	†(unavailable)
female (n=5)	1	12 weeks	adenocarcinoma, stromal	+

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