Vascular endothelial growth factor expression promotes the growth of breast cancer brain metastases in nude mice

Patients with breast cancer brain metastases cannot be cured and have a poor prognosis, with a median survival time of six months after diagnosis, despite developments in diagnostic and therapeutic modalities. In large part the progress in understanding the biology of breast cancer brain metastasis has been limited by the lack of suitable cell lines and experimental models. The objective of this study was to develop a reliable experimental model to study the pathogenesis of breast cancer brain metastases, using intra-internal carotid artery injection of breast cancer cells into nude mice. Brain metastasis-selected variant cells were recovered after three cycles of injection into the internal carotid artery of nude mice and harvest of brain metastases, resulting in variants termed MDA-231 BR1, -BR2 and -BR3. The metastasis-selected cells had increased potential for experimental brain metastasis and mice injected with these cells had significantly shorter mean survival than mice injected with the original cell line. Brain metastatic lesions of the selected variants contained significantly more CD31-positive blood vessels than metastases of the non-selected cell line. The variants selected from brain metastases released significantly more VEGF-A and IL-8 into culture supernatants than the original cell line, and more VEGF-A RNA when cultured in normoxic conditions. Mice injected with MDA-231 BR3 into the carotid artery were treated with the VEGF-receptor tyrosine kinase inhibitor PTK787/Z 222584. Oral administration of the inhibitor resulted in a significant decrease in brain tumor burden, reduced CD31-positive vessels in the brain lesions and incidence of PCNA positive tumor cells, and increased apoptosis in the tumor, as measured by TUNEL labeling. We conclude that elevated VEGF expression contributes to the ability of breast cancer cells to form brain metastases. Targeting endothelial cells with a VEGF-receptor specific tyrosine kinase inhibitor reduced angiogenesis and restricted the growth of the brain metastases.