Human epididymis protein 4 (HE4) is

Human epididymis protein 4 (HE4) is a glycoprotein secreted by the epithelial ovarian cancer (EOC) cells, which is considered as a novel and specific biomarker for the diagnosis and prognosis of epithelial ovarian cancer. Previous studies showed that the overexpression of HE4 was correlated with tumorigenesis and chemoresistance of EOC. However, less has been reported regarding the direct effect of secretory HE4 protein as an autocrine factor in EOC cells. Here we investigate the molecular mechanism of the secretory HE4 on the growth of EOC cells by applying nanobody with targeting interaction on free HE4. Three anti-HE4 nanobodies were selected from an immune library by phage display. HE4 secreted by serum-free cultured OVCAR3 cells increased largely and effectively neutralized by anti-HE4 nanobodies resulting in the inhibition of cell viability. Treatment with anti-HE4 nanobody 1G8 decreased the expression of Bcl-2 and increased the level of BAX, cleaved PARP and p53, resulting in apoptosis of OVCAR3 cells. Moreover, 1G8 significantly improved the cisplatin response in OVCAR3 cells. Our data suggested that secretory HE4 played a novel pro-survival autocrine role and can be targeted by the anti-HE4 nanobody to improve therapeutic effects of cisplatin-based chemotherapy.