Mammary glands reconstituted with Neu/ErbB2 transformed HC11 cells provide a novel orthotopic tumor model for testing anti-cancer agents.

The ErbB2 receptor tyrosine kinase (RTK) has been intensely pursued as a cancer therapy target due to its association with breast cancer. In this study we used the HC11 mammary epithelial cell line to develop an orthotopic, ErbB2-driven tumor model for testing efficacy of anti-cancer compounds. HC11 cells were infected with a retrovirus encoding oncogenic NeuT, the rat homolog of ErbB2. Drug-selected populations were introduced into mammary fat pads of Balb/c syngeneic mice cleared of host tissue. The majority of glands injected with HC11-NeuT cells developed mammary tumors which appeared after a 3-4 week latency period and grew rapidly. HC11 cells infected with the control retrovirus showed no tumor growth after injection. Tumor-bearing mice were used to compare the in vivo efficacy of two anti-cancer agents: PKI166, a kinase inhibitor selective for EGF receptor and ErbB2, and Taxol, a microtubule assembly blocker. PKI166 inhibited NeuT-induced mammary tumor growth in a dose-dependent manner and at a dose below the maximum tolerated dose (MTD) was significantly more inhibitory than Taxol at its MTD (57% vs. 25% tumor regression). Importantly, there was a dose-dependent decrease in the phosphotyrosine content of NeuT isolated from PKI166-treated, tumor-bearing mice, providing a mechanistic link between kinase inhibition and its anti-tumor activity. Thus, implantation of genetically manipulated HC11 cells into mammary glands appears to be an excellent model for studying effects of anti-cancer agents in an orthotopic site.