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Expression of Epidermal Growth Factor Receptor by an Experimental Murine Tumor of Acute Myeloid Leukemia Origin

esthesia with ketamine (n = 18). All inserted discs contained exclusively C-1498 AML cells. The mice received food (Purina) and water ad lib. The experiments were carried out according to the regulations of the Committee of Animal Handling of the Hebrew University, Hadassah Medical School, Jerusalem, Israel. Two to three weeks after AML cell implantation, tumors of approximately 1 cm in diameter developed ( fig. 1 a). The mice were sacrificed before signs of suffering appeared due to generalized leukemia. The tumors were excised and processed for histology and immunohistochemistry. Frozen sections were mounted on slides and immunostained with the appropriate primary antibodies as described below, followed by immunostaining with fluorescent secondary antibodies. The specimens were examined with a confocal microscope. The AML cells from culture were similarly immunostained and examined by confocal microscopy. The tumor was examined by light microscopy and consisted mainly of leukemic cells and a few stromal cells ( fig. 1 b). In previous studies using the same experimental model, the leukemia had spread by the time of sacrifice as indicated by approximately 20% leukemic cells of normal bone marrow cells per long bone [16, 17] . As mentioned above, the disc-implanted mice were nonleukemic, thus these marrow leukemic cells had originated from the tumor. Epidermal growth factor receptor (EGFR) and its ligand were first isolated and purified from normal and tumor human and mouse cells during the early 1980s [1– 8] . It was later recognized that mutated or overexpressed EGFR is a potent oncogene that occurs in many solid human tumors. It was the first receptor to be targeted by monoclonal antibodies and EGFR tyrosine kinase inhibitors in epithelial tumors [9–15] . Although it is generally expressed by tumors of epithelial origin, we now report expression of EGFR by a murine tumor that was induced by subcutaneous implantation of cells of mesenchymal origin – acute myeloid leukemia (AML). In this report, we investigated the mesenchymal-epithelial transition (MET) process of murine AML cells upon transfer to mice. To this end, murine AML C-1498 cells of C57Bl/6 origin (National Cancer Institute, Frederick, Md., USA) were incubated in Dulbecco’s modified Eagle’s medium with 15% fetal calf serum. C-1498 is an AML cell line which is carefully handled in the laboratory to prevent cell contamination. A total of 0.5 × 10 6 AML cells were placed in small molded discs (0.8 cm in diameter) of 1% agar solution. Agar stabilizes the cells, preventing their spread at onset and disintegrating later. Each disc was inserted subcutaneously into the upper back region of nonleukemic, female, C57Bl/6, specific pathogen-free mice aged 8–10 weeks, under general anReceived: April 24, 2013 Accepted after revision: July 22, 2013 Published online: November 12, 2013