Estrogen Receptor β of Host Promotes the Progression of Lung Cancer Brain Metastasis of an Orthotopic Mouse Model

Estrogen receptors (ERα and ERβ) in the brain play critical roles in maintaining brain tissue homeostasis and in tissue repair after injury. Growth of cancer metastasis in the brain is a constant damaging process. The role of ERs of the host in the progression of cancer brain metastasis is unknown. To determine the role of ERβ of host in the progression of lung cancer brain metastasis, we used an isogenic murine lung cancer cell line, Lewis lung carcinoma cells (3LL), to produce orthotopic lung cancer brain metastases in wild type and ERβ knockout (ERβ) mice. In the wild type mice, we found that ERα and ERβ appeared in the tumor associated reactive astrocytes at 24 hr after injection of tumor cells, and ERβ remained thereafter while ERα disappeared after 1 week. The metastasis bearing ERβ mice survived significantly longer than the wild type mice. To further test the role of ERβ of reactive astrocytes in the survival of cancer cells, we knocked down ERβ in cultured actrocytes using shRNA and performed 3D co-culture with 3LL cells in the presence/absence of chemotherapeutic agents, oxaliplatin and 5-fluorouracil. We found that loss of ERβ in astrocytes significantly reduced the survivability of 3LL cells co-cultured with astrocytes. It is concluded that ERβ of host, especially ERβ in reactive astrocytes, promotes the progression of lung cancer brain metastasis and ERβ might be a potential therapeutic target for lung cancer brain metastasis.