Cell-Type-Dependent Responses to Oleuropein in MDA-MB-231 Breast Cancer Cells and HUVECs.

Breast cancer progression is associated with dysregulation of cell survival, apoptosis, and cell-cycle control. Oleuropein (OL), a major secoiridoid constituent of olive-derived products, has attracted interest because of its diverse biological activities and potential relevance to cancer research. This study evaluated the cellular and molecular responses to OL in MDA-MB-231 triple-negative breast cancer cells and non-malignant human umbilical vein endothelial cells (HUVECs). Cell viability was assessed following exposure to 10-250 µg/mL OL for 24, 48, and 72 h. OL produced an exposure-time-dependent reduction in MDA-MB-231 cell viability, with estimated IC₅₀ values of >250 µg/mL at 24 h, 117.5 µg/mL at 48 h, and 26.42 µg/mL at 72 h. Based on the overall viability profiles of the two cell models, 100 µg/mL OL was selected for subsequent functional and molecular analyses. At this concentration, MDA-MB-231 viability progressively decreased with prolonged exposure, whereas HUVEC MTT-derived viability values were maintained. OL treatment reduced clonogenic capacity and wound closure in MDA-MB-231 cells, while increased clonogenic capacity and wound closure were observed in HUVECs. qRT-PCR analysis showed increased BAX and CDKN1B and reduced BCL2 expression in MDA-MB-231 cells, whereas HUVECs exhibited reduced BAX and increased BCL2 and CDKN1B expression. Western blot analysis revealed time-dependent changes in BAX, BCL-2, and p27 protein abundance, with partial directional correspondence to the transcriptional findings, particularly at later exposure times. Collectively, these findings indicate that OL elicits distinct cell type-dependent responses in malignant breast cancer and non-malignant endothelial cells. The coordinated viability, clonogenic, wound closure, and molecular expression profiles observed in MDA-MB-231 cells support further investigation of OL in breast cancer models, while the distinct HUVEC response highlights the need to clarify its endothelial and angiogenesis-related effects.