Cancer cells hijack autophagy pathway to evade anti-cancer therapeutics. Many molecular signaling pathways associated with drug-resistance converge on autophagy induction. Honokiol (HNK), a natural phenolic compound purified from Magnolia grandiflora, has recently been shown to impede breast tumorigenesis and, in the present study, we investigated whether breast cancer cells evoke autophagy to modulate therapeutic efficacy and functional networks of HNK. Indeed, breast cancer cells exhibit increased autophagosomes-accumulation, MAP1LC3B-II/LC3B-II-conversion, expression of ATG proteins as well as elevated fusion of autophagosomes and lysosomes upon HNK treatment. Breast cancer cells treated with HNK demonstrate significant growth inhibition and apoptotic induction, and these biological processes are blunted by macroautophagy/autophagy. Consequently, inhibiting autophagosome formation, abrogating autophagosome-lysosome fusion or genetic-knockout of BECN1 and ATG7 effectively increase HNK-mediated apoptotic induction and growth inhibition. Next, we explored the functional impact of tumor suppressor STK11 in autophagy induction in HNK-treated cells. STK11-silencing abrogates LC3B-II-conversion, and blocks autophagosome/lysosome fusion and lysosomal activity as illustrated by LC3B-Rab7 co-staining and DQ-BSA assay. Our results exemplify the cytoprotective nature of autophagy invoked in HNK-treated breast cancer cells and put forth the notion that a combined strategy of autophagy inhibition with HNK would be more effective. Indeed, HNK and chloroquine (CQ) show synergistic inhibition of breast cancer cells and HNK-CQ combination treatment effectively inhibits breast tumorigenesis and metastatic progression. Tumor-dissociated cells from HNK-CQ treated tumors exhibit abrogated invasion and migration potential. Together, these results implicate that breast cancer cells undergo cytoprotective autophagy to circumvent HNK and a combined treatment with HNK and CQ can be a promising therapeutic strategy for breast cancer.

癌细胞劫持自噬途径以逃避抗癌治疗。许多与耐药性相关的分子信号传导途径都集中在自噬诱导上。和厚朴酚 (HNK) 是一种从广玉兰中纯化出来的天然酚类化合物，最近被证明可以阻碍乳腺肿瘤的发生，在本研究中，我们研究了乳腺癌细胞是否会引起自噬来调节 HNK 的治疗功效和功能网络。事实上，在 HNK 治疗后，乳腺癌细胞表现出自噬体积累、MAP1LC3B-II/LC3B-II 转换、ATG 蛋白表达增加以及自噬体和溶酶体融合增强。用 HNK 处理的乳腺癌细胞表现出显着的生长抑制和细胞凋亡诱导，并且这些生物过程被巨自噬/自噬削弱。因此，抑制自噬体形成、消除自噬体-溶酶体融合或BECN1和ATG7基因敲除可有效增加 HNK 介导的细胞凋亡诱导和生长抑制。接下来，我们探讨了肿瘤抑制因子 STK11 对 HNK 处理细胞自噬诱导的功能影响。STK11 沉默消除了 LC3B-II 转换，并阻断自噬体/溶酶体融合和溶酶体活性，如 LC3B-Rab7 共染色和 DQ-BSA 测定所示。我们的结果例证了 HNK 处理的乳腺癌细胞中引发的自噬的细胞保护性质，并提出了自噬抑制与 HNK 联合策略将更有效的概念。事实上，HNK 和氯喹 (CQ) 对乳腺癌细胞具有协同抑制作用，HNK-CQ 联合治疗可有效抑制乳腺肿瘤的发生和转移进展。来自 HNK-CQ 处理的肿瘤的肿瘤分离细胞表现出消除的侵袭和迁移潜力。总之，这些结果表明乳腺癌细胞通过细胞保护性自噬来规避 HNK，并且 HNK 和 CQ 的联合治疗可能是一种有前途的乳腺癌治疗策略。