Abstract 1533: The roles of novel tumor-associated macrophages (TAMs) in invasion and metastasis of pancreatic cancer.
Authors: Sonshin Takao , Ding Qiang , Nagai Taku , Kurahara Hiroshi , Yoshimitsu Makoto , Miyazaki Yumi , Imakiire Ryoko , Ueno Shoko , Tokushige Hiromi , Matsubara Shyuichiro , Obara Toru , Matsuyama Takami 
Published: August 2014

Background: Pancreatic cancer (PC) is a lethal disease due to its systemic metastasis. In the recent years, compelling evidence has emerged that the complex crosstalk between stromal cells and cancer cells in the tumor microenvironment may regulate tumor growth, invasion and metastasis. The tumor microenvironment of PC consists mainly of a dense, desmoplastic stroma rich in collagen fibers, extracellular matrix proteins, fibroblasts, and infiltrating inflammatory cells. M2 macrophages, so-called tumor-associated macrophages (TAMs), infiltrate and interact with cancer cells. However, the interaction between PC and TAMs are not fully understood underlying mechanism. Our evidence suggests that the expression of FRβ is limited to activated macrophages in human malignancy, such as PC. Recently, we are trying to investigate the role of FRβ+ TAMs in PC. The aim of this study is to investigate how PC cells cooperate with FRβ+ TAM infiltration in the invasive front.

Methods: Tumor samples were obtained from 76 patients with PC. None of these patients had received any preoperative chemotherapy or radiotherapy. Both FRβ+ and tumor-infiltrating (CD68+) macrophages were examined in each tumor specimen by immunohistochemical and immunofluorescence staining using a newly developed anti-human FRβ monoclonal antibody and CD68 antibody.

Results: 1) FRβ+ macrophages showed a heterogeneous distribution with foci of high density in PC. In contrast, they were rarely observed in noncancerous pancreatic tissues. Compared with CD68+ macrophages, a larger population of FRβ+ macrophages existed in the invasive front.

Although the numbers of CD68+ and FRβ+ macrophages were both higher in the invasive front compared to the central portion of pancreatic tumors, the proportion of FRβ+ macrophages to CD68+ macrophages in the invasive front (71.8%) was significantly higher than that in the central portion (44.6%). 2) We evaluated the expression of VEGF in tumor-infiltrating macrophages by double immunofluorescence staining. The majority of FRβ+ macrophages showed distinct VEGF expression. By contrast, lower numbers of CD68+ macrophages showed VEGF expression. The mean proportion of FRβ+ macrophages with VEGF expression (70.1%) was significantly higher than that of CD68+ macrophages with VEGF expression (40.5%). 3) A high number of FRβ+ macrophages showed a positive association with high MVD, high incidence of hematogenous metastasis and a poor prognosis in PC patients.

Conclusions: Our findings revealed for the first time that FRβ+ macrophages are a novel subset of TAMs in PC and may play an important role in the tumor microenvironment in association with systemic metastasis through the interaction with tumor cells and vessels. Therefore, FRβ+ macrophages may be promising a targeted therapy for PC.

Citation Format: Takao Sonshin, Qiang Ding, Taku Nagai, Hiroshi Kurahara, Makoto Yoshimitsu, Yumi Miyazaki, Ryoko Imakiire, Shoko Ueno, Hiromi Tokushige, Shyuichiro Matsubara, Toru Obara, Takami Matsuyama. The roles of novel tumor-associated macrophages (TAMs) in invasion and metastasis of pancreatic cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1533. doi:10.1158/1538-7445.AM2013-1533