The University of Texas at Dallas Richardson, Texas, United States
Neutrophils, the most abundant immune cells in humans, can be recruited from circulation into the tumor tissue by cancer cells and promote tumor progression in many solid tumors such as pancreatic cancer. Studies in mice have shown that blockade of neutrophil recruitment to tumor via inhibition of chemokine receptor CXCR2 is a promising neutrophil-targeting immunotherapy for pancreatic cancer. However, both the mechanisms by which neutrophils play a tumor-promoting role in humans and the mechanisms by which CXCR2 inhibition might have a therapeutic effect in human cancer are not completely understood. Specifically, it is unclear whether CXCR2 inhibition could reduce neutrophil recruitment to human tumor tissue. It is unclear whether neutrophils could promote tumor progression through direct contact with cancer cells in addition to release of pro-tumor soluble factors. It is also unclear whether CXCR2 inhibition could attenuate neutrophil-promoted tumor progression via blocking release of soluble factors by neutrophils or blocking direct contact between neutrophils and cancer cells. These knowledge gaps exist partially due to the lack of suitable tools to tease out and measure specific immune cell-cancer cell interactions in the highly complex tumor microenvironment of the human body. In this study, we engineered a human cell-based, reductionist microphysiological system to monitor in real-time and measure interactions between neutrophils and 3D hydrogel-embedded pancreatic tumor spheroids with single-cell resolution, temporal dynamics, and spatial control. We utilized the system to evaluate the effects of CXCR2 antagonist AZD-5069 on neutrophil-tumor spheroid interactions both when neutrophils were physically separated from tumor spheroids and when neutrophils were allowed to engage in direct contact with tumor spheroids. We found that CXCR2 inhibition reduces neutrophil migration toward tumor spheroids in terms of forward migration index, velocity, directionality, and displacement. We also found that neutrophils promote invasion of tumor spheroids into the surrounding hydrogel via both release of soluble factors and direct contact but promote proliferation of tumor spheroids via direct contact only. More interestingly, CXCR2 inhibition attenuates invasion and proliferation of tumor spheroids only when they are allowed to engage in direct contact with neutrophils. Furthermore, CXCR2 inhibition significantly reduces the frequency and duration of direct contact between neutrophils and tumor spheroids. These results shed new light on the tumor-promoting mechanisms of human neutrophils and the tumor-suppressive mechanisms of CXCR2 inhibition in pancreatic cancer and may aid in the design and optimization of novel immunotherapeutic strategies based on neutrophils.
