Role of Cytochrome P450 Enzymes in the Maintenance of Breast Cancer Metastasized to the Bone [30D

Abstract

INTRODUCTION: Metastasis of cancer cells causes most cancer-related deaths, prompting interest in its molecular mechanisms. Cancer homeostasis depends on the tumor microenvironment. Interactions between malignant cells and surrounding stroma contribute to cancer processes, including carcinogenesis and resistance to therapy. For example, multiple myeloma and leukemia cells can be protected from systemic chemotherapy by stromal cytochrome P450 enzymes (CYPs) that are found in the bone marrow (BM). We hypothesized that stromal CYPs protect solid tumors metastases to the BM. METHODS: We used a conditioned media model to mimic tumor microenvironment, asking whether a human BM mesenchymal stroma cell line can affect growth of a breast adenocarcinoma metastatic cell line (MCF7). RESULTS: We first established that the IC50 of Doxorubicin of MCF7 cells is 50nM, a concentration which also preserved growth of stromal cells. We found that concomitant treatment of Doxorubicin and Clarithromycin (a CYP3A4 inhibitor) sensitized MCF7 cells in stromal conditioned media more than treatment with only Doxorubicin, while it had no such effect in stroma-free conditions. Preliminary results also show that the concomitant treatment of Doxorubicin and Clarithromycin rescued the sensitivity of MCF7 cell line to Doxorubicin in stromal conditioned media, while it had no rescue effect in stroma-free cultures. CONCLUSION: Our results suggest that breast carcinoma cells are relatively resistant to Doxorubicin in the presence of BM stroma and that this resistance can be overcome by Clarithromycin. Our in vitro data suggest that like its role in hematological malignancies, stroma in the BM microenvironment creates biochemical niches that protect metastases from systemic chemotherapy.