50P - P-Rex1 expression in breast cancer patients

Abstract

BackgroundWorldwide, Breast cancer (BC) is the leading cause of cancer-related mortality in women. In Argentina, breast cancer is the second leading cause of death in women, with an incidence of 18.47%. Given the importance of breast cancer for public health, and the diversity of patients’ response to current therapies, the identification of new therapeutic targets is crucial. Rac1 is a Rho GTPase widely involved in motility, mitogenesis, transformation, and metastasis. P-Rex1 is a Rac1 activator essential for the migration of breast cancer cells. It has been reported that P-Rex1 is overexpressed in breast cancer of the luminal type and that its silencing inhibits the migration of cancer cells. In order to validate P-Rex1 as a therapeutic target and/or prognostic biomarker, we aimed to analyze its presence in samples of Argentinean patients from the Marie Curie Hospital of Buenos Aires City, and determine its relationship with clinical and histopathological parameters. MethodsThe levels of P-Rex1 were determined both in biopsy material and in tumor tissue (and its corresponding healthy adjacent tissue) from primary surgery of patients not undergoing neoadjuvant therapy. The levels of messenger RNA (mRNA) were analyzed by quantitative PCR and protein by western blot (WB) and immunohistochemistry. ResultsWhen the mRNA levels of the biopsies classified according to the molecular subtype were compared, elevated P-Rex1 levels were observed not only in those samples classified as ER+/PR+ breast cancer but also in 50% of the samples of triple negative breast cancer (TNBC). These data were validated by an in-silico analysis made from public access databases (Metabric and the GEO repository of NCBI). P-Rex overexpression in TNBC patients has not been previously reported. The aberrant expression of P-Rex1 was detected in all stages of the disease, and a negative correlation between the expression of P-REX1 and the proliferation marker Ki-67 was determined. P-Rex1 levels were significantly higher in tumors compared to normal breast samples, in agreement with previous reports. ConclusionsThese results confirm the potential of P-Rex1 as a therapeutic target not only for the treatment of luminal tumors but also for a certain population of TNBC patients. Legal entity responsible for the studyEva Wertheimer. FundingInstituto Nacional del Cáncer-Ministerio de Salud-Argentina (INC, Asistencia Financiera IV, 2018). DisclosureAll authors have declared no conflicts of interest.