Species-dependent extracranial manifestations of a brain seeking breast cancer cell line

Metastatic brain tumors are a severe problem in the treatment of patients with breast carcinoma. We developed a rat model for brain metastasis that allows follow-up by MRI. Injection of cancer cells labeled with iron oxide particles, allows tracking from the single-cell stage until the appearance of full-blown metastases.

MDA-MB-231br/eGFP human breast cancer cells were labeled with micron-sized particles of iron oxide (MPIO; 1μm). 13 female immunodeficient rats were intracardially injected with 100.000 labeled cells at the age of 5 weeks (1). MRI was performed on a 7T system (PharmaScan) at day 1, and then weekly until 10 weeks post-injection. T2*W images were acquired one day post-injection to show the initial distribution of MPIO-labeled cells in the brain. T2W sequences were acquired to visualize the brain metastases. A static whole-body 18F-FDG PET-CT (bèta-CUBE, MOLECUBES NV, 10 MBq, 30 minutes acquisition) was performed to determine metastasis development outside the brain. For detection of bone metastases full body spiral high-resolution CT acquisitions were performed (X-CUBE, MOLECUBES NV, 7 minutes acquisition).

At week 3 to 4 the first signs of brain metastasis development were visible as hyperintensities on T2W images in all animals. The metastases visible on T2W images could be correlated to their corresponding hypointensities on T2*W images. Whole-body PET imaging suggested hot spots in the lungs of 2 animals. Cellular alterations in the lung were confirmed with haematoxylin and eosin staining. Bone metastases were detected in 11 out of 13 animals with CT evaluation.

Our aim was to develop a rat model for brain metastasis. However, early formation of metastases outside the brain was observed in the lungs and bone, as evidenced by PET and CT, respectively. This indicates that this model is currently not suited for investigating brain metastasis and associated treatment strategies. Therefore, the brain metastatic propensity of the cell line will be optimized by in vivo passaging.