Endostatin and prolactin combination trigger PRLR induction and channelize CD1d signaling in TNBC

Triple-negative breast cancer (TNBC) is a very aggressive breast cancer subtype and therapeutically challenging because of the absence of hormone receptors (ER, PR and HER2). TCGA datasets revealed that prolactin receptor (PRLR) was downregulated in TNBC, associated with poor overall survival. PRLR induction has been shown to reduce tumor proliferation in TNBC. However, no pharmacologically active molecule has been reported that can induce PRLR. In addition, natural killer T (NKT) cells, potent antitumorigenic immune cells activated via CD1d lipid antigen interactions, are diminished in TNBC tumors. Prior studies have demonstrated that CD1d expression is crucial for the progression of breast tumors and regulates antitumor immune responses mediated by NKT cell activation. In this study, we found that treating endostatin (2.5 μM), an anti-angiogenic protein, in combination with prolactin (2.5 nM) significantly reduced the proliferation and colony-forming potential of TNBC cells. The treatment combination was found to induce PRLR and CD1d expression (CD1d A and B isoforms) in the TNBC cell line MDA-MB-468. Further, we observed that the combination reduced epithelial-mesenchymal transition (EMT) markers and oxidative phosphorylation marker COXIV. Human NKT cells were isolated from PBMCs and co-cultured with treated TNBC cells. NKT activation was quantified by IFN-gamma secretion using ELISA. Additional analyses using TNBC tissue slides are undergoing to determine PRLR and CD1d co-expression patterns. Our findings identify endostatin-mediated restoration of the PRLR as a novel strategy to restrict TNBC cell growth while simultaneously enhancing CD1d-dependent NKT cell activation, representing a promising therapeutic option for TNBC.