Infiltration of Neutrophils Is Required for Acquisition of Metastatic Phenotype of Benign Murine Fibrosarcoma Cells

Abstract

QR-32 tumor cells, a clone derived from a murine fibrosarcoma, are poorly tumorigenic and nonmetastatic when injected into syngeneic C57BL/6 mice. However, they are converted to highly malignant ones once they have grown in vivo after being co-implanted in a subcutaneous site with a foreign body, a gelatin sponge. Early phase of inflammation induced by the gelatin sponge participates in the conversion and histological analysis shows predominant infiltration of neutrophils. The objective of this study was to determine whether the depletion of the infiltrating neutrophils has any effect on the tumor progression. Intraperitoneal administration of a monoclonal anti-granulocyte antibody, RB6-8C5 (RB6), depleted neutrophils from both the peripheral blood circulation and the local inflamed site in mice with co-implantation of QR-32 tumor cells and gelatin sponge. The RB6 administration did not inhibit either tumor development or growth of QR-32 tumor cells. In contrast, tumor cell lines established from RB6-administered mice showed a significant decrease in metastatic incidence as compared with the tumor cell lines obtained from the mice with administration of control rat IgG or saline. Metastatic ability was significantly suppressed when RB6 had been administered in the early phase (from day -2 to day 6 after implantation); however, the administration in the middle (from day 6 to day 14) or late (from day 14 to day 22) phase did not affect the metastatic ability. We confirmed the phenomena by using integrin beta(2) knockout mice that had impaired neutrophil infiltration into inflamed sites. In the knockout mice, neutrophils hardly infiltrated into the gelatin sponge and the tumors showed dramatically suppressed metastatic phenotype as compared with those in wild-type mice or nude mice. Immunohistochemical analysis demonstrated that expressions of 8-hydroxy-2'-deoxyguanosine and nitrotyrosine were parallel to those in the presence of neutrophils. These results suggested that inflammation, especially when neutrophils infiltrate into tumor tissue, is primarily important for benign tumor cells to acquire metastatic phenotype.

The Multifaceted Roles Neutrophils Play in the Tumor Microenvironment

“…Under certain circumstances, administration of neutrophilneutralizing antibodies reduced the number and size of tumors [261,264,265]. The tumorigenic effect of MMP-9, predominantly provided by neutrophils and mast cells, was also reported in a mouse model of skin cancer where MMP-9 knockout mice showed decreased incidence of invasive tumors [266].…”

“…TANs were shown to support tumor growth by producing angiogenic factors and matrix-degrading enzymes [8,57,64,252,264,277]. Neutrophils were also shown to promote the acquisition of a metastatic phenotype [265] and to suppress antitumor immune responses [278]. Neutrophil-derived CXCL2 enhances angiogenesis as well as neutrophil accumulation, ultimately inducing carcinogenesis [247].…”

Transient inflammatory response induced by apoptotic cells is an important mediator of melanoma cell engraftment and growth

“…33 The role of neutrophils in carcinogenesis initiation and promotion remains unclear. Although present in small numbers in most tumors, some experiments show that they act as immunosurveillance cells against most tumors, 34,35 while in others they may oppose 36 or favor malignant growth and progression. 36 -38 These different outcomes are probably the result of interplay between the cytokine/chemokine profile and the degree of activation of intratumor PMNs.…”

Neutrophils in cancer: neutral no more

“…Enhanced retention of human melanoma cells in lungs can be seen as early as 24 hours after co-injection with neutrophils into nude mice 143 . In experimental lung or liver metastasis models where cancer cell lines are injected into the circulation or spleen, respectively, systemic depletion of neutrophils (via anti-Gr1 antibodies) reduces the formation of metastases 144,145 . Intravital imaging has shown that cancer cells colocalize with endothelial cell-associated neutrophils in a CD11b-dependent manner 144 , suggesting that neutrophils guide cancer cells into tissues and/or retain them there rather than supporting the outgrowth of secondary tumors.…”