Differential reactions of microglia to brain metastasis of lung cancer.
The brain is a common metastatic site for various types of cancers, especially lung cancer. Patients with brain metastases have a poor prognosis in spite of radiotherapy and/or chemotherapy. It is postulated that immune cells in the brain may play a major role in cancer metastasis, dormancy, and relapse. Although microglia may serve as a major component in the brain immune system, the interaction between metastatic cancer cells and microglia is still largely unknown and remains to be elucidated. In this study, we have investigated microglial reactions in brain tissues with metastatic lung cancer cells and evaluated the cytotoxic effects of lipopolysaccharide (LPS)-activated microglia on metastatic lung cancer cells in vitro. In the vicinity of metastatic lung cancer mass in the brain, microglia showed signs of significant activation. There was an obvious increase in the number of microglia labeled with ionized calcium binding adaptor molecule 1 (Iba-1) antibody, a specific marker of microglia. The microglia were observed to form a clear boundary between the tumor mass and normal brain tissue. In the region where the tumor mass was situated, only a few microglia expressed inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha), indicating differential activation in those microglia. The supernatant from LPS-activated microglia induced apoptosis of metastatic lung cancer cells in vitro in a dose- and time-dependent manner. However, at lower concentrations of activated microglial supernatant, trophic effects on cancer cells were observed, some lung cancer cells being insensitive to microglial cytotoxicity. Together with the observation that TNF-alpha alone induced proliferation of the tumor cells, the findings provide possible clues to the mechanism involved in metastasis of lung cancer cells to the brain.
He
Bei Ping
BP
Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Wang
Jian Jun
JJ
Zhang
Xian
X
Wu
Yan
Y
Wang
Miao
M
Bay
Boon-Huat
BH
Chang
Alex Yuang-Chi
AY
D000818:Animals; D017302:Annexins / Q000378:metabolism; D001932:Brain Neoplasms / Q000473:pathology / Q000556:secondary*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007150:Immunohistochemistry; D008070:Lipopolysaccharides / Q000494:pharmacology; D008175:Lung Neoplasms / Q000473:pathology*; D051379:Mice; D017628:Microglia / Q000187:drug effects / Q000473:pathology*; D009569:Nitric Oxide / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D011419:Propidium / Q000378:metabolism; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects
D017302:Annexins; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D011419:Propidium; D052247:Nitric Oxide Synthase Type II