Dua Hammash,1,2 Mona Mahfood,3 Ghalia Khoder,4 Munazza Ahmed,1,2 Abdelaziz Tlili,3 Rifat Hamoudi,2,5,6 Rania Harati1,2 1Department of Pharmacy Practice and Pharmacotherapeutics, College of Pharmacy, University of Sharjah, Sharjah, United Arab Emirates; 2Sharjah Institute for Medical Research, University of Sharjah, Sharjah, United Arab Emirates; 3Department of Applied Biology, College of Sciences, University of Sharjah, Sharjah, United Arab Emirates; 4Department of Pharmaceutics and Pharmaceutical Technologies, College of Pharmacy, University of Sharjah, Sharjah, United Arab Emirates; 5Clinical Sciences Department, College of Medicine, University of Sharjah, Sharjah, United Arab Emirates; 6Division of Surgery and Interventional Science, University College London, London, UKCorrespondence: Rania Harati, Department of Pharmacy Practice and Pharmacotherapeutics, College of Pharmacy, University of Sharjah, Sharjah, United Arab Emirates, Tel +971 6 505 7438, Fax +971 6 558 5812, Email rharati@sharjah.ac.aeBackground: Most breast cancer-related deaths result from metastasis. Understanding the molecular basis of metastasis is needed for the development of effective targeted and preventive strategies. Matrix metalloproteinase-1 (MMP1) plays an important role in brain metastasis (BM) of triple-negative breast cancer (TNBC) by promoting extravasation of cancer cells across the brain endothelium (BE). MMP1 expression is controlled by endogenous microRNAs. Preliminary bioinformatics analysis has revealed that miR-623, known to target the 3ʹUTR of MMP1, is significantly downregulated in brain metastatic tumors compared to primary BC tumors. However, the involvement of miR-623 in MMP1 upregulation in breast cancer brain metastatic cells (BCBMC) remains unexplored. Here, we investigated the role of miR-623 in MMP1 regulation and its impact on the extravasation of TNBC cells through the BE in vitro.Materials and Methods: A loss-and-gain of function method was employed to address the effect of miR-623 modulation on MMP1 expression. MMP1 regulation by miR-623 was investigated by real-time PCR, western blot, luciferase and transwell migration assays using an in vitro human BE model.Results: Our results confirmed that brain metastatic TNBC cells express lower levels of miR-623 compared with cells having low propensity to spread toward the brain. miR-623 binds to the 3â²-untranslated region of MMP1 transcript and downregulates its expression. Restoring miR-623 expression significantly decreased MMP1 expression, preserved the endothelial barrier integrity, and attenuated transmigration of BCBMC through the BE.Conclusion: Our study elucidates, for the first time, the crucial role of miR-623 as MMP1 direct regulator in BCBMC and sheds light on miR-623 as a novel therapeutic target that can be exploited to predict and prevent brain metastasis in TNBC. Importantly, the presents study helps in unraveling a brain metastasis-specific microRNA signature in TNBC that can be used as a guide to personalized metastasis prediction and preventive approach with better therapeutic outcome.Keywords: brain metastasis, triple-negative breast cancer, brain endothelium, brain endothelial junctions, matrix metalloproteinase-1, microRNA-623, personalized preventive therapy, targeted prevention, metastasis prediction, precision medicine, primary and secondary care