AR5 - Inhibition of Neutrophil Extracellular Traps (NETs) with Chloroquine Reduces Peritoneal Metastatic Tumor Burden

Introduction: Neutrophil extracellular traps (NETs), a process through which activated neutrophils release their intracellular contents including DNA, histones, and granules into the circulation, has been implicated in the formation of peritoneal metastatic disease. Therefore, NETs may represent a novel target in the treatment and prevention of peritoneal carcinomatosis. We evaluated chloroquine (CQ), a known NET inhibitor, as a potential therapeutic agent to combat peritoneal disease.

Methods: Intra-peritoneal injections of 5x105 murine colon cancer cells (MC38) were performed in 8 week old C57/Bl6 mice. Mice were randomized (n=10 per group) to receiving either CQ (0.5 mg/mL in drinking water) or normal water for 2 weeks, and then sacrificed and assessed for peritoneal tumor burden. Blood was obtained via cardiac puncture. Murine pancreatic cancer cells (Pan02) were also evaluated utilizing the same methods. Plasma cell-free DNA (cf-DNA) concentration (ng/mL), a measure of NET formation, was measured with Quan-iT PicoGreen. Data are reported as the mean ± SEM.

Results: MC38 peritoneal tumor burden was markedly reduced with CQ treatment (7.8±2.6 vs 2.4±1.7, p<0.05). Peritoneal tumor burden was similarly reduced in CQ treated, Pan02 injected mice (11.5±4.8 vs 6.5±3.6, p<0.05). Plasma cf-DNA was diminished in CQ treated mice (565.1 ± 37.6 vs 383 ± 0.9, p < 0.05), consistent with NET inhibition.

Discussion: Chloroquine reduces peritoneal metastases with a concomitant reduction in circulating cell-free DNA, a marker of NET formation. These findings provide evidence for the role of NETs in metastatic disease and highlight a novel therapeutic strategy to reduce peritoneal disease formation.