ProBDNF is a Novel Mediator of the Interaction Between MDA-MB- 231 Breast Cancer Cells and Brain Microvascular Endothelial Cells

Aim: The current work aims to assess the role of proBDNF/BDNF in the interaction between brain microvascular endothelial cells and the MDA-MB-231 breast cancer cell line that has been consistently reported to cause brain metastasis. Background: Breast cancer brain metastasis (BM) is a significant health problem with limited therapeutic options. The development of BM is a multistep process that requires constant interaction with brain vasculature and the development of tumor blood supply. The benefits of anti-angiogenic modalities, based on antagonizing vascular endothelial growth factor in breast cancer metastasis, did not prove to be effective. Brain-derived neurotrophic factor (BDNF) is a neurotrophin with a reported angiogenic effect. There is a lack of data regarding the involvement of BDNF in metastatic breast cancer interaction with brain microvascular endothelial cells (HBEC-5i). Methods: Using an adaptive transfer design, the cross-talk between HBEC-5i and MDAMB- 231 cell was investigated. HBEC-5i were treated with MDA-MB-231-conditioned media, and the involvement of BDNF/proBDNF in the interaction was assessed using both release and inhibitor-based assays in migration and in vitro tube formation assay. Results: MDA-MB-231 and HBEC-5i released total BDNF (250 vs. 80 pg/ml, respectively). MDA-MB-231 conditioned media inhibited the migration of HBEC-5i by more than 80% (p<0.05) and tube formation by 75% (p<0.05). Neutralizing mature BDNF did not alter the MDA-MB-231 induced anti-angiogenic effect, which was completely blunted by antagonizing proBDNF. MDA-MB-231 released proBDNF (131.5 pg/ml), and more than 60% of total BDNF released was in the pro-form. Conclusion: proBDNF is a novel mediator of breast cancer-induced anti-angiogenic effect in brain endothelial cells.