Background: Gastric cancer (GC) is a common malignant tumor with limited treatment options. The natural flavonoid nobiletin (NOB) is a beneficial antioxidant that possesses anticancer activity. However, the mechanisms by which NOB inhibits GC progression remain unclear.

Methods: A CCK-8 assay was performed to determine cytotoxicity. Cell cycle and apoptosis analyses were performed by flow cytometry. RNA-seq was performed to detect differential gene expression after NOB treatment. RT‒qPCR, Western blotting and immunofluorescence staining were used to examine the underlying mechanisms of NOB in GC. Xenograft tumor models were constructed to verify the effect of NOB and its specific biological mechanism in GC.

Results: NOB inhibited cell proliferation, caused cell cycle arrest and induced apoptosis in GC cells. KEGG classification identified that the inhibitory effect of NOB on GC cells mainly involved the lipid metabolism pathway. We further showed that NOB reduced de novo fatty acid (FA) synthesis, as evidenced by the decreased levels of neutral lipids and the expression levels of ACLY, ACACA and FASN, and ACLY abrogated the effect of NOB on lipid deposits in GC cells. In addition, we also found that NOB triggered endoplasmic reticulum (ER) stress by activating the IRE-1α/GRP78/CHOP axis, but overexpression of ACLY reversed ER stress. Mechanistically, inhibiting ACLY expression with NOB significantly reduced neutral lipid accumulation, thereby inducing apoptosis by activating IRE-1α-mediated ER stress and inhibiting GC cell progression. Finally, in vivo results also demonstrated that NOB inhibited tumor growth by decreasing de novo FA synthesis.

Conclusion: NOB could inhibit the expression of ACLY to activate IRE-1α-induced ER stress, which ultimately led to GC cell apoptosis. Our results provide novel insight into the use of de novo FA synthesis for GC treatment and are the first to reveal that NOB inhibits GC progression by ACLY-dependent ER stress.

背景：胃癌 (GC) 是一种常见的恶性肿瘤，治疗选择有限。天然类黄酮川陈皮素 (NOB) 是一种有益的抗氧化剂，具有抗癌活性。然而，NOB 抑制 GC 进展的机制仍不清楚。

方法：进行 CCK-8 测定以确定细胞毒性。通过流式细胞术进行细胞周期和细胞凋亡分析。进行 RNA-seq 以检测 NOB 处理后的差异基因表达。RT-qPCR、蛋白质印迹和免疫荧光染色用于检查 GC 中 NOB 的潜在机制。构建异种移植肿瘤模型，验证NOB在GC中的作用及其具体生物学机制。

结果：NOB 抑制细胞增殖，导致细胞周期停滞并诱导 GC 细胞凋亡。KEGG分类鉴定NOB对GC细胞的抑制作用主要涉及脂质代谢途径。我们进一步表明 NOB从头减少脂肪酸 (FA) 合成，如中性脂质水平降低和 ACLY、ACACA 和 FASN 的表达水平所证明，ACLY 消除了 NOB 对 GC 细胞脂质沉积的影响。此外，我们还发现 NOB 通过激活 IRE-1α/GRP78/CHOP 轴触发内质网 (ER) 应激，但 ACLY 的过表达逆转了 ER 应激。从机制上讲，用 NOB 抑制 ACLY 表达可显着减少中性脂质积累，从而通过激活 IRE-1α 介导的 ER 应激和抑制 GC 细胞进展来诱导细胞凋亡。最后，体内结果还表明 NOB 通过减少从头合成 FA 来抑制肿瘤生长。

结论：NOB可抑制ACLY的表达，激活IRE-1α诱导的内质网应激，最终导致GC细胞凋亡。我们的结果提供了对从头FA 合成用于 GC 治疗的新见解，并且是第一个揭示 NOB 通过 ACLY 依赖性 ER 应激抑制 GC 进展的研究结果。