Abstract
Rationale: Macrophage phagocytosis plays a role in cancer immunotherapy. The phagocytic activity of macrophages, regulated by circadian clock genes, shows time-dependent variation. Intervening in the circadian clock machinery of macrophages is a potentially novel approach to cancer immunotherapy; however, data on this approach are scarce. Microcurrent stimulation (MCS) promotes inflammation, proliferation, and remodeling, suggesting its potential to modulate macrophage function; however, its application has been limited. In this study, we investigated the impact of MCS on macrophage phagocytosis of cancer cells using mouse/human macrophage cell lines and various mouse/human cancer cell lines. Methods: Cells and mice received 300 µA, 400 Hz bidirectional pulsed MCS. Gene expression, protein expression, and phagocytosis activity were assessed in intraperitoneal macrophages collected from mice, as well as in RAW264.7, and THP-1 cells. Flow cytometry, population, phagocytosis activity, RNA-seq, and immunohistochemistry analyses were performed. Results: Noninvasive MCS prevented time-dependent reduction in macrophage phagocytosis of cancer cells by modulating the circadian clock genes. MCS also enhanced phagocytosis in mouse RAW264.7 and human THP-1 cells across various cancer types by promoting actin polymerization; similar in vivo effects were observed in mice. This enhancement occurred in abdominal macrophages of both sexes and was mediated by changes in clock gene expression. Specifically, suppressing the clock gene Per1 nullified the effects of MCS. Moreover, although macrophage phagocytosis typically declined during the dark period, MCS during the light period prevented this reduction. MCS also increased phagocytosis of peritoneally implanted cancer cells (4T1, ID8, and Hepa1-6) in mice, significantly reducing tumor engraftment and growth, and ultimately improving prognosis. Conclusions: The findings of this study suggest that targeting macrophage circadian mechanisms via MCS could enhance cancer immunity, offering new avenues for cancer immunotherapy.