OS7.1 Identification and characterization of brain metastasis initiating cells

AbstractBrain metastases (BM) are an increasing challenge. Insight in the pathology of the brain metastatic cascade, and in particular in the characteristics of the BM initiating cells can help to identify new treatment targets. PHK26 membrane dye was used in stably GFP expressing human breast cancer to differentiate slow from fast cycling cells by membrane signal intensity changes using multiphoton laser scanning microscopy, both in vitro and in vivo. The heterogeneous population of fast and slow cycling cells as well as resting cells was injected intracardially and followed with in vivo repetitive multiphoton laser microcopy via a chronic intracranial window. Here, slow cycling cells, representing only 16% of the entire cell population, were the only ones that mastered all steps of the brain metastatic cascade (0% marcometastasis formation after intravascular arrest of fast cycling cells vs. 6.15% marcometastasis formation after intravascular arrest of slow cycling cells; p<0.001), namely intravascular arrest, extravasation, perivascular survival, and marcometastasis outgrowth. These slow cycling cells showed a high overlap with established markers for tumor stem-like cells, like Oct4/Sox2, Notch and WNT, and also (but less) with low 26S proteasome activity. Illumina gene expression profiling of slow versus fast cycling JIMT1 breast cancer cells revealed up-regulation of N-Myc down regulated gene (NDGR1). Knock down of NDRG1 resulted in complete inhibition of BM formation by preventing successful colonization of the perivascular niche. In conclusion, slow cycling cells resemble the population of BM initiating cells. Increased NDRG1 expression is a characteristic of slow cycling cells, and is a pivotal molecular precondition for successful BM formation that might serve as a potential target for BM prevention or treatment.