Gemcitabine-generated ROS promotes neutrophil chemotactic activity through CXCL8 production via PKCδ/ERK pathway in a murine 4T1 breast cancer model

Abstract

Abstract Chemotherapy-induced neutropenia (CIN) is a common side effect that necessitate dose reductions during treatment of cancer patients. Preventing CIN is critical in chemotherapy because a rapid decline of neutrophil counts increase susceptibility to infection of cancer patients. In spite of its importance, the mechanism of CIN still remains unclear. This study is aimed to investigate the mechanism of CIN in an aspect of neutrophil activation by chemotaxis in gemcitabine-treated breast tumor model. We hypothesized that gemcitabine-generated ROS promotes CXCL8 or MIP-2 production by upregulating ERK pathway in PKCδ-activated intratumoral macrophages and thus neutrophil recruitment to the chemokine gradient. In 4T1 breast tumor mouse model, we found that the basal level of PKCδ activity was higher than in normal mice. The number of blood and peritoneal leukocytes was analyzed at 24h after intraperitoneal administration of gemcitabine. The neutrophil counts decreased in the blood but increased in the peritoneal cavity. In addition, intratumoral neutrophils were elevated in the gemcitabine-treated group. The mRNA levels of neutrophil attracting chemokines/receptors were increased in the peritoneal and tumoral cells. ROS inhibitors N-Acetyl-L-cysteine and Apocynin blocked gemcitabine-induced neutrophil migration, mRNA expression of the chemokines and receptors and PKCδ/ERK phosphorylation. CXCR1/2 inhibitor reparixin decreased neutrophil recruitment to the peritoneal cavity and the tumor tissue. Together, our results suggest that gemcitabine treatment promotes neutrophil chemotactic activity by increasing ROS/PKCδ/ERK/CXCL8 pathway. These findings will provide new insights for developing a therapeutic for CIN.