Anti-Inflammatory 8-Shogaol Mediates Apoptosis by Inducing Oxidative Stress and Sensitizes Radioresistance in Gastric Cancer

Radiotherapy is a powerful tumor therapeutic strategy for gastric cancer patients. However, radioresistance is a major obstacle to kill cancer cells. Ginger (<i>Zingiber officinale</i> Roscoe) exerts a potential function in various cancers and is a noble combined therapy to overcome radioresistance in gastric cancer radiotherapy. In this study, we suggested that 8-shogaol, a monomethoxybenzene compound extracted from <i>Zingiber officinale</i> Roscoe, has an anti-cancer and anti-inflammatory activity. In lipopolysaccharide (LPS)-induced inflammatory murine models in vivo and in vitro, 8-shogaol suppressed LPS-mediated cytokine production, including COX-2, TNFα, IL-6, and IL-1β. In xenograft mouse models of AGS gastric cancer cell lines, 8-shogaol reduced tumor volume. In gastric cancer cell lines AGS and NCI-N87, 8-shogaol reduced cell viability and increased caspase-3 activity and cytotoxicity LDH. However, combined with Z-VAD-FMK, 8-shogaol blocked caspase-dependent apoptotic cell death. 8-Shogaol induced intracellular reactive oxygen species (ROS) production, intracellular calcium (Ca²⁺) release, and endoplasmic reticulum (ER) stress response via the PERK-CHOP signaling pathway. Thapsigargin (TG), an ER stressor, mediated synergistic apoptosis and cell death in 8-shogaol-treated AGS and NCI-N87 cell lines. Nevertheless, loss of PERK or CHOP function suppressed ER-stress-induced apoptosis and cell death in 8-shogaol-treated AGS and NCI-N87 cell lines. 8-Shogaol-induced NADPH oxidase 4 (NOX4) activation is related to ROS generation. However, NOX4 knockdown and ROS inhibitors DPI or NAC blocked ER-stress-induced apoptosis by suppressing the inhibition of cell viability and the enhance of caspase-3 activity, intracellular ROS activity, and cytotoxicity LDH in 8-shogaol-treated AGS and NCI-N87 cell lines. Radioresistant gastric cancer models (AGSR and NCI-N87R) were developed and combined with 8-shogaol and radiation (2 Gy) to overcome radioresistance via the upregulation of N-cadherin and vimentin and the downregulation of E-cadherin. Therefore, these results indicated that 8-shogaol is a novel combined therapeutic strategy in gastric cancer radiotherapy.