Paraoxonase-2 is upregulated in triple negative breast cancer and contributes to tumor progression and chemoresistance

Triple negative breast cancer (TNBC) displays a high aggressive behavior, tendency to relapse and early metastasize, leading to poor prognosis. The lack of estrogen receptors, and human epidermal growth factor receptor 2, prevents the use of endocrine or molecular targeted therapy, being therapeutical options for TNBC managements mostly limited to surgery, radiotherapy and mainly chemotherapy. While an important number of TNBCs initially responds to chemotherapy, they are prone to develop chemoresistance over the time. Thus, there is an urgent need to identify novel molecular targets to improve the outcome of chemotherapy in TNBC. In this work we focused on the enzyme paraoxonase-2 (PON2) which has been reported to be overexpressed in several tumors contributing to cancer aggressiveness and chemoresistance. Through a case-control study, we analyzed PON2 immunohistochemical expression in breast cancer molecular subtypes Luminal A, Luminal B, Luminal B HER2+, HER2 + and TNBC. Subsequently, we evaluated the in vitro effect of PON2 downregulation on cell proliferation and response to chemotherapeutics. Our results showed that the PON2 expression levels were significantly upregulated in the infiltrating tumors related to the subtypes Luminal A, HER2+ and TNBC compared to the healthy tissue. Furthermore, PON2 downregulation led to a decrease in cell proliferation of breast cancer cells, and significantly enhanced the cytotoxicity of chemotherapeutics on the TNBC cells. Although further analyses are necessary to deeply understand the mechanisms by which the enzyme could participate to breast cancer tumorigenesis, our results seem to demonstrate that PON2 could represent a promising molecular target for TNBC treatment.