Inhibition of neutrophil infiltration into A549 lung tumors in vitro and in vivo using a CXCR2-specific antagonist is associated with reduced tumor growth.
Neutrophils are important innate immune cells that are involved in microbial clearance at sites of infection and in wound healing. The microenvironment of tumors often resembles that of chronic inflammation and increased numbers of neutrophils have been observed in several tumors and, in some cases, these positively correlate with poor prognosis. Neutrophil recruitment into tumors appears to be dependent on chemokines that bind to CXCR1 and CXCR2 expressed by neutrophils. In our study, we used lung adenocarcinoma A549 multicellular tumor spheroids and A549 tumor xenografts along with a CXCR2-specific small molecule inhibitor (AZ10397767) to investigate the recruitment and function of human neutrophils in tumors. We found that A549 spheroids constitutively secrete high levels of CXCL chemokines and that neutrophil recruitment into A549 tumors in vitro and in vivo is largely dependent on CXCR2 activation. AZ10397767 significantly reduced the numbers of infiltrating neutrophils into both in vitro and in vivo tumor models, which was associated with slower growing tumors. Neutrophil infiltration into A549 tumor spheroids increased their size compared to noninfiltrated spheroids and neutrophil-derived factors increased the proliferation of A549 tumor cells and induced endothelial cell tubule formation in vitro. In contrast, we saw no reduction in microvascular density in AZ10397767-treated A549 tumors or in tumors grown in CXCR2(-/-) mice, suggesting that angiogenesis in these tumors is CXCR2-independent. Our data show that neutrophils can contribute to lung tumor growth and that CXCR2 antagonists may be a useful therapeutic agent in the treatment of lung carcinomas.