Abstract 3167: CCL2 recruits inflammatory monocytes to facilitate perineural invasion
Authors: Bakst Richard , Xiong Huizhong , Chen Chun-Hao , Deborde Sylvie , Zhou Yi , McNamara William , Lee Sei Young , Pamer Eric , Wong Richard J. 
Published: August 2015

Abstract
Perineural invasion (PNI) by cancer cells is associated with significant patient morbidity and poor prognosis. Despite recognition of the clinical significance of PNI, the mechanisms underlying it remain poorly understood and no targeted therapies exist to date. Modern theories of PNI pathogenesis have placed significant focus on the active role of the nerve microenvironment with PNI resulting from well-orchestrated interactions between cancer and host. Inflammatory monocytes (IMs) play a critical role in mediating peripheral nerve repair and facilitating cancer metastases by differentiating into tumor-associated macrophages. Here we explore their role in PNI.
CCR2 expressed by IMs is a receptor for ligands CCL2 and CCL7, and mediates IM recruitment in infections and other cancer models. A murine model of nerve invasion in which pancreatic cancer (Panc02) is injected into the distal sciatic nerve, was utilized in mice genetically deficient in CCL2, CCL7, or CCR2. Validated functional and histopatholgic endpoints were used to quantify PNI. Fluorescence-activated cell sorting (FACS) and immunohistochemistry (IHC) were performed on specimens to assess IM and macrophage recruitment. Adoptive transfer experiments with labeled IMs were performed to elucidate the signaling pathways involved in homing to the nerve. Genetically modified green fluorescent protein (GFP)-tagged reporter mice were utilized to identify cellular sources of the relevant chemokines. IHC was performed on human tumors with PNI to assess for macrophage recruitment.
The recruitment of IMs is dependent on CCL2 synthesized within the nerve. IMs recruited to the nerve differentiate into macrophages within 24-72 hours upon arrival. Mice deficient in CCL2 or CCR2 have impaired IM recruitment and reduced macrophage differentiation in the nerve at the site of PNI, and significantly impaired invasion. Furthermore, PNI was restored in CCR2 KO mice after multiple adoptive transfers of wild type IMs with intact CCR2. By contrast, CCL7 KO mice have only a modest, non-significant decrease in PNI. In the presence of cancer, CCL2 but not CCL7, is expressed locally in the nerve, likely by Schwann cells responding to the cancer invasion. IMs recruited to the nerve serve as an alternate source of CCL2. Human tumors with PNI demonstrate CD68+ macrophages at the site of nerve invasion.
These results implicate the immune response as a key mediator of PNI and thereby further our mechanistic understanding of this ominous cancer behavior. Our data identify potential novel therapeutic targets for treating PNI.
Citation Format: Richard Bakst, Huizhong Xiong, Chun-Hao Chen, Sylvie Deborde, Yi Zhou, William McNamara, Sei Young Lee, Eric Pamer, Richard J. Wong. CCL2 recruits inflammatory monocytes to facilitate perineural invasion. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3167. doi:10.1158/1538-7445.AM2015-3167