Abstract 991: Brain metastasis depends on tumor cell initiated coagulation
Authors: Gay Laurie J. , Day John , LeBoeuf Sarah , Ritland Melissa , Ruggeri Zaverio , Ruf Wolfram , Felding Brunhilde H. 
Published: May 2015

Abstract
Background: The incidence of brain metastasis exceeds that of primary brain tumors tenfold and is most frequently associated with lung cancer, breast cancer and melanoma. Despite a prognosis of only 6-9 months for patients with brain metastases, mechanisms of tumor cell brain colonization from the blood stream are unknown. Understanding this step could enable effective therapeutic strategies to prevent the development of incurable metastatic brain disease.
We found that blood borne metastatic cancer cells reside within the cerebral microvasculature for several days and associate with platelets while crossing the blood brain barrier. Intravascular tumor cell survival and extravasation during this time may critically limit the success of brain metastasis. Activation of coagulation, platelets and fibrin formation contribute to tumor progression, cancer-associated thrombosis and metastatic spread to peripheral organs. However the function of coagulation in the seeding of brain metastases is unknown.
Aims: We evaluated whether tumor cell-expressed tissue factor, a key activator of coagulation, promotes tumor cell seeding of brain metastases by initiating critical tumor cell-vascular interactions.
Methods: We developed models of experimental brain metastasis to study how intravascular tumor cells cooperate with the coagulation system during early stages of brain colonization to survive and cross the blood brain barrier. Human breast cancer cells, injected into the left cardiac ventricle of immune deficient mice, are tracked during the initial phase of brain metastasis and progressive metastatic brain disease by detailed and quantitative histological analyses. We address how coagulation contributes to brain metastasis by targeting human tissue factor with specific inhibitory antibodies. We use ex-vivo bioluminescence imaging and immunohistochemical analyses at later stages of brain metastasis to determine the extent to which an early, transient treatment will result in long-term inhibition of brain metastatic disease.
Results: We demonstrate that inhibition of tissue factor expressed by tumor cells reduces brain colonization. Targeting of tissue factor inhibits development of breast cancer brain metastasis and extends animal survival. We find that tissue factor properties which initiate coagulation or promote cytoprotective signaling pathways differentially contribute to brain metastasis development. Blockade of tissue factor-initiated coagulation inhibits intravascular tumor cell survival and prevents brain metastases in vivo. Our findings indicate that the inhibition of coagulation can prevent the seeding of breast cancer cells into the brain.
Conclusions: Our studies provide mechanistic insights into the process of tumor cell brain colonization and identify targets for development of therapeutics to prevent cancer metastasis to the brain and enhance patient survival.
Citation Format: Laurie J. Gay, John Day, Sarah LeBoeuf, Melissa Ritland, Zaverio Ruggeri, Wolfram Ruf, Brunhilde H. Felding. Brain metastasis depends on tumor cell initiated coagulation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 991. doi:10.1158/1538-7445.AM2014-991