Background: Advancements in experimental therapeutics for esophageal cancers have been hampered by the lack of a reliable preclinical model that recapitulates the biology of human cancer, including in vivo growth in an animal model.
Methods: Bilious reflux was induced by esophago-jejunostomy in Sprague-Dawley rats. Nine of 12 (75%) Sprague-Dawley rats developed squamous or adenosquamous cancers, and three cell lines were created by in vitro propagation of freshly resected tumors, JA and JB lines from one cancer, and the AMY cell line from another. We subsequently tested the ability of these cell lines to propagate long-term in vitro and form xenografts in vivo, both hallmarks of transformed cells. In addition, we determined the effects of small molecule inhibitors of two important oncogenic pathways-the epidermal growth factor receptor (EGFR) and Hedgehog (Hh) signaling pathways, in vitro, as a "proof of principle" of using these unique cell lines for developing targeted therapies for esophageal cancer. Mechanism-based growth inhibition was assessed by down-regulation of activated downstream targets of EGFR in the case of Iressa, and by Hh luciferase reporter activity with cyclopamine.
Results: JA, JB, and AMY cell lines were able to grow continuously in vitro and consistently form xenografts in vivo in athymic mice, both subcutaneously, as well as in the "orthotopic" location at the gastroesophageal serosal junction (n = 2 mice per line, six of six engrafted). By histology, the tumors grow in vivo as well-differentiated keratinizing squamous cell carcinomas. JB cells had the highest expression of EGFR protein and also the most profound response to Iressa (gefitinib), an EGFR inhibitor (IC50 < 1 microm). Growth inhibition by Iressa was mirrored functionally by down-regulation of activated targets of the EGFR pathway, phospho-ERK1/2 and phospho-MEK levels. AMY cells expressed approximately 900-fold elevation of the Hh ligand, Indian Hh (Ihh), compared with normal esophageal epithelium, whereas expression of another Hh ligand, Sonic Hh (Shh), was not detected. On treatment with the specific Hh small molecule inhibitor cyclopamine, AMY cells demonstrated growth inhibition, which was accompanied by significant down-regulation of endogenous Hh luciferase reporter activity at 24 h and increased apoptosis in treated cells.
Conclusions: We have established a model of esophageal carcinogenesis, capable of long-term in vitro and in vivo passage, and demonstrated therapeutic potential of targeting the EGFR and Hh pathways in the cell lines created from the rodent cancers. These unique cell lines should provide a platform for rapid preclinical validation of novel therapeutics for esophageal cancers.