Abstract LB-277: Microenvironment-induced changes in miRNA levels promote brain metastasis, drug resistance andKRAexpression.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Brain metastases remain a serious obstacle that negatively impacts cancer patient survival. Nearly 180,000 patients in the U.S. are diagnosed annually with metastatic brain lesions, more than ten times the incidence of primary brain tumors such as glioblastoma. Brain metastases remain a challenging complication despite advances in surgical, chemo-radiation and targeted therapies. Most deaths due to cancer result from the progressive growth of metastatic, drug-resistant lesions. Moreover, the incidence of brain metastases is rising as a result of superior imaging modalities, earlier cancer detection and more effective treatment of systemic disease. To investigate the role of the brain microenvironment in metastasis, lung and breast tumor cells were co-cultured with astrocytes, the most abundant normal cell type in the metastatic brain tumor niche. Astrocyte co-culture led to increased tumor cell viability, proliferation and chemoresistance. After co-culture with astreocytes, tumor cells were then removed and total RNA was isolated. A panel of individual microRNAs (miRNAs) were identified that were reduced in tumor cells after co-culture. The rationale for developing miRNA therapeutic replacements is based upon the premise that aberrantly expressed miRNAs play a key role in controlling tumorigenesis, drug resistance and metastasis. Correcting these miRNA deficiencies through antagonisitc or replacement of miRNA function may provide a therapeutic benefit. Microarray-based profiling revealed that astrocyte co-culture reduced miRNAs-768-3p, 886-5p and 200c in the lung tumor cells. Vector-based forced expression of sequence complementary to miRNA768-3p or transfection of inhibitory miRNA-768-3p oligonucleotide inhibitors into tumor cells led to increased cell growth. Also, inhibition of miRNA-768-3p increased KRas expression, and a specific binding site was identified in the KRas 3′UTR was validated using a luciferase construct. Moreover, shRNA-mediated KRas knockdown reduced growth-promotion by the miRNA-768-3p inhibitor. MiRNA-768-3p levels were lower in tissue samples obtained from patients diagnosed with brain metastases relative to normal human adult brain tissue. In addition, the level of miRNA-768-3p was lower in tissue from patients diagnosed with brain metastases compared to the primary tumors in matched paired samples obtained from the same patient. The results demonstrate that the brain microenvironment modulates numerous miRNA, sush as miRNA-768-3p, in metastatic lesions to enhance KRas -mediated tumor growth and drug resistance and ultimately to promote brain metastasis. The therapeutic application of miRNA may allow for the rapid and coordinated manipulation of proteins that regualte multiple key intracellular pathways that promote tumorigenesis and metastasis. Citation Format: James J. Driscoll, Arasakumar Subramani, Samer Alsidawi, Sajjeev Jagannathan, Kazutaka Sumita, Atsuo Sasaki, Ronald E. Warnick, Sean Lawler. Microenvironment-induced changes in miRNA levels promote brain metastasis, drug resistance and KRA expression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-277. doi:10.1158/1538-7445.AM2013-LB-277