Chemotherapy failure is often caused by drug resistance, for which no effective treatment strategy has been established. Many studies have been undertaken with the aim of overcoming drug resistance using natural products. Arctigenin (ATG), a natural product, has been investigated for its anti-cancer effects in HER2-overexpressing, ER-positive, and triple-negative breast cancer cells. We investigated the efficacy of ATG against self-established doxorubicin (DOX)-resistant breast cancer cells (MCF-DR and MDA-DR cells) derived from MCF-7 and MDA-MB-231 cells, respectively. ATG was found to increase DOX intracellular levels by downregulating multidrug Resistance 1 (MDR1) mRNA expression in DOX-resistant cells. In addition, combined treatment with DOX and ATG (DOX/ATG) reduced the viability of and colony formation by DOX-resistant cells. DOX/ATG also significantly induced G2/M cell cycle arrest by suppressing the Cyclin D1/CDK4/RB pathways and suppressed the expressions of MDR1 and Cyclin D1 by inhibiting the Mitogen-activated protein kinase (MAPK)/Activating protein-1 (AP-1) signaling pathways. Furthermore, DOX/ATG induced DNA damage and attenuated the expressions of RAD51 and Ku80. However, PARP1 (Poly [ADP-ribose] polymerase1) cleavage and AIF (Apoptosis-inducing factor) induced apoptosis did not occur despite DNA damage-induced cell death. Rather, flow cytometry showed that DOX/ATG caused necrosis. In summary, DOX/ATG increased intracellular DOX levels by inhibiting MDR1 and inducing G2/M arrest by inhibiting the Cyclin D1/CDK4/RB pathways and causing necrosis by damaging DNA. Our results suggest that ATG might be used as an adjuvant to enhance the efficacy of DOX in DOX-resistant breast cancer.

中文翻译：

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阿霉素和牛蒡甙元联合治疗通过促进阿霉素耐药乳腺癌细胞对阿霉素的摄取，诱导细胞周期停滞相关的细胞死亡

化疗失败往往是由耐药性引起的，目前尚未建立有效的治疗策略。为了使用天然产品克服耐药性，已经进行了许多研究。牛蒡甙元 (ATG) 是一种天然产物，已在 HER2 过表达、ER 阳性和三阴性乳腺癌细胞中研究其抗癌作用。我们研究了 ATG 对分别源自 MCF-7 和 MDA-MB-231 细胞的自建耐药阿霉素 (DOX) 乳腺癌细胞（MCF-DR 和 MDA-DR 细胞）的功效。研究发现 ATG 通过下调 DOX 耐药细胞中的多药耐药 1 (MDR1) mRNA 表达来增加细胞内 DOX 水平。此外，DOX 和 ATG (DOX/ATG) 联合治疗降低了 DOX 抗性细胞的活力和集落形成。DOX/ATG 还通过抑制 Cyclin D1/CDK4/RB 通路显着诱导 G2/M 细胞周期停滞，并通过抑制丝裂原激活蛋白激酶 (MAPK)/激活蛋白-1 (AP- 1）信号通路。此外，DOX/ATG 诱导 DNA 损伤并减弱 RAD51 和 Ku80 的表达。然而，尽管DNA损伤诱导细胞死亡，但PARP1（聚[ADP-核糖]聚合酶1）裂解和AIF（凋亡诱导因子）诱导的细胞凋亡并未发生。相反，流式细胞术显示 DOX/ATG 导致坏死。总之，DOX/ATG 通过抑制 MDR1 增加细胞内 DOX 水平，并通过抑制 Cyclin D1/CDK4/RB 途径诱导 G2/M 停滞，并通过破坏 DNA 引起坏死。我们的结果表明，ATG 可以用作佐剂，以增强 DOX 对 DOX 耐药乳腺癌的疗效。