Abstract 153: High neuropilin-1 expression on monocytes is positively associated with trastuzumab-mediated antibody-dependent cellular cytotoxicity of the HER2-overexpressing breast cancer cell line

Abstract

Abstract Purpose Neuropilin-1 (Nrp1) was initially characterized as a guide for migrating cells and axons in developing nervous systems and is essential for the precise formation of neurons and vasculature. However, it was recently reported to also play an important role in the immune system. This study aimed to investigate the role of Nrp1 on monocytes in trastuzumab-mediated antibody-dependent cellular cytotoxicity (ADCC) targeting the HER2-positive human breast cancer cell line SKBR3. In addition, we evaluated the gene expression profile of monocytes expressing high and low levels of Nrp1. Methods Peripheral blood mononuclear cells from healthy volunteers were prepared using BD Vacutainer CPT Cell Preparation Tubes. The cells were stained with fluorescein isothiocyanate-conjugated anti-CD14 and allophycocyanin-conjugated anti-Nrp1 antibodies, and Nrp1high and Nrp1low monocyte subsets were sorted using FACSAria. These cells were used as effector cells in a conventional ADCC assay with SKBR3 as target cells and trastuzumab as the antibody. Target cell cytotoxicity was measured using the LDH cytotoxic test kit. The effector cell to target cell ratios of 20:1 and 10:1 were used. Gene expression analysis was performed by Affymetrix GeneChip microarrays. All study protocols were approved by the Ethics Committee for Clinical Research, Kyoto University Hospital, Kyoto, Japan (authorization number G424). Results The LDH cytotoxic test revealed significantly higher target cancer cell cytotoxicity in sorted Nrp1high monocytes than in Nrp1low monocytes (75% vs. 45%, p<0.01). Trastuzumab-mediated ADCC was significantly suppressed by Nrp1 neutralization antibodies in a dose-dependent manner (Control arm 14.3%, Treatment arm 6%; p<0.01). Gene expression analysis revealed that 308 genes were up-regulated in the Nrp1high population, including monocyte-specific chemokine receptor and hematopoietic transcriptional factor. Conclusion These results suggest that determination of Nrp1 expression can be used to classify monocytes as populations with and without cellular cytotoxic activity. Analysis of Nrp1 expression levels in monocytes can therefore be used to identify HER2-positive breast cancer patients for whom trastuzumab therapy will be less effective. Citation Format: Kosuke Kawaguchi, Eiji Suzuki, Masao Kawashima, Masakazu Toi. High neuropilin-1 expression on monocytes is positively associated with trastuzumab-mediated antibody-dependent cellular cytotoxicity of the HER2-overexpressing breast cancer cell line. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 153. doi:10.1158/1538-7445.AM2014-153