Abstract P1-05-18: Determining the molecular mechanism of the breast cancer-induced brain metastasis and a role of a novel pan-TGF-β inhibitor as a potential therapy for brain metastasis in a mouse xenograft model
Authors: De Mukhopadhyay K , Elkahloun AG , Hinck AP , Yoon K , Cornell JE , Shu L , Yang J , Sun L 
Published: August 2014

Breast cancer (BCa) is the most common malignant disease in women in the U.S. Nearly 20% of patients with advanced BCa are eventually diagnosed with brain lesions, which is a devastating complication in patients with BCa over-expressing EGF receptor family members including Her2 positive and triple negative breast cancer. It is the most feared complication of BCa in part because are not capable of significantly treating the BCa-induced brain metastases due to the inability of the available treatment regimens to effectively penetrate the blood brain barrier (BBB) and also due to our limited knowledge on cellular and molecular mechanisms that drive the homing to and growth in the brain of BCa cells. Therefore, there is a need of efficient model system that can significantly contribute towards our understanding of different factors from both host and tumor leading to brain metastasis. We have recently isolated a novel BCa cell line B6TC that was generated through fusion between human BCa, MDA-MB-231 and ZR-75-1 cells in mouse bone marrow. This B6TC cell line showed higher propensity to metastasize to brain than its parental cells when inoculated through intracardiac injection in female athymic nude mice. In order to generate a highly brain metastatic breast cancer model for mechanistic research, we subjected the B6TC cells through four rounds of selection for cells that were capable of trans-endothelial cell invasion to obtain cells that could invade through BBB. This in vitro selected cell line was further subjected through three rounds of in vivo selection for cells that were capable of metastasizing to the brain and the cells after third round selection was named N3LR, which has the highest potential to cause brain metastasis. In searching for genes and pathways that may contribute to the increased brain metastasis of N3-LR cell with microarray analysis, we found that the transforming growth factor-beta (TGFβ) signaling pathway is upregulated in N3-LR cell in comparison with B6TC cell, in addition to the EGF and prostaglandin signaling pathways that have been reported to be associated with brain metastatic breast cancer cells. Functional comparison also showed that N3-LR cell was more migratory than B6TC cell and more responsive to TGFβ-induced phosphorylation of Smad3 as well as migration, suggesting that TGFβ signaling may contribute to the increased brain metastatic potential. We next investigated whether metastatic tumor growth in the brain microenvironment can be inhibited by systemic administration of a potent pan-TGFβ inhibitor, BGERII- a recombinant fusion protein containing the endoglin domain of betaglycan (BGE) and the extracellular domain of RII. The animals were inoculated intracardically with N3LR, the most potent subline of highly metastatic B6TC cells, and were then treated with vehicle or BGERII systemically via i.p. injection right after the inoculation. After three weeks, the BGERII treated group showed lower brain metastasis incidence and tumor burden as detected by whole mouse bioluminescence and GFP imaging. Further analyses to understand the underlying molecular and regulatory mechanism of brain metastasis and its intervention in our mouse model is underway for the discovery of novel molecularly targeted drugs to prevent and eradicate BCa metastasis initiation, progression and recurrence.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-18.