γ‐Irradiated cancer cells promote tumor growth by activation of Toll‐like receptor 1‐mediated inducible nitric oxide synthase in macrophages

• Published in: Journal of leukocyte biology Vol. 97; no. 4; pp. 711 - 721
• Main Authors: Ryu, Yun‐Kyoung, Lee, Mi‐Hee, Lee, Jiyoung, Lee, Jae‐Wook, Jang, Su‐Jin, Kang, Joo‐Hyun, Moon, Eun‐Yi
• Format: Journal Article
• Language: English
• Published: United States 01-04-2015
• Subjects: 3T3 Cells; Adenocarcinoma - immunology; Adenocarcinoma - pathology; Adenocarcinoma - radiotherapy; Animals; Bone Marrow Cells - metabolism; Cell Line, Tumor; Cercopithecus aethiops; Coculture Techniques; Colonic Neoplasms - immunology; Colonic Neoplasms - pathology; Colonic Neoplasms - radiotherapy; COS Cells; Disease Progression; Enzyme Induction; Gamma Rays; iNOS; Macrophages - classification; Macrophages - metabolism; Macrophages, Peritoneal - metabolism; Melanoma, Experimental - immunology; Melanoma, Experimental - pathology; Melanoma, Experimental - radiotherapy; Mice; Mice, Inbred BALB C; Neoplasm Proteins - biosynthesis; Neoplasm Proteins - genetics; Neoplasm Proteins - physiology; Nitric Oxide - biosynthesis; Nitric Oxide - physiology; Nitric Oxide Synthase Type II - biosynthesis; Nitric Oxide Synthase Type II - physiology; omega-N-Methylarginine - pharmacology; postradiotherapeutic effect; radiotherapy; Recurrence; TLR1; Toll-Like Receptor 1 - biosynthesis; Toll-Like Receptor 1 - genetics; Toll-Like Receptor 1 - physiology; Tumor Microenvironment - radiation effects; TLR1; postradiotherapeutic effect; radiotherapy; NO; iNOS
• ISSN: 0741-5400; 1938-3673
• DOI: 10.1189/jlb.3A0114-055R

Post‐radiotherapeutic tumor re‐growth may be caused by interaction of irradiated cancer cells with macrophages, which induce TLR1‐mediated iNOS expression and NO production.
RT is commonly used to treat malignant tumors. However, tumor regrowth is a major limitation to RT as an antitumor treatment. In the present study, we investigated the tumor‐promoting effects of high‐dose (or ablative) RT treatments on tumor‐bearing mice. We focused on the role of macrophages that interact with IR‐CCs in the TME, which cause tumor regrowth. We observed that CT26(H‐2d) tumor growth was enhanced by i.v. injection of IR‐CT26 cells compared with NR control CT26 cells. The levels of iNOS gene expression and NO production from RAW264.7 macrophages (H‐2d) in response to the interaction with IR‐CT26 cells were higher than with NR‐CT26 cells. When CT26 tumor‐bearing mice were treated i.v. with L‐NMMA, a NOS inhibitor, the reduction in in vivo tumor growth was higher in the IR‐CT26‐injected group compared with the NR‐CT26‐injected control group. In vivo CT26 tumor growth was decreased after transplanting PEM extracted from L‐NMMA‐treated, tumor‐bearing mice. Although iNOS activity was reduced by inhibiting TLR1 expression with TLR1‐siRNA, it was enhanced by TLR1 overexpression. Transcriptional activation and protein expression levels of iNOS were also decreased in the presence of TLR1‐siRNA but increased as a result of TLR1 overexpression. These results demonstrate that postradiotherapeutic tumor regrowth may be caused by interaction of IR‐CCs with macrophages that induce TLR1‐mediated iNOS expression and NO production. Our data suggest that iNOS in macrophages could be a useful target to regulate postradiotherapeutic responses in hosts and subsequently limit tumor regrowth.