鐵依賴性細胞死亡（ferroptosis）為一種新型態的細胞死亡方式，透過鐵代謝失調造成脂質過氧化物堆積所導致。本研究結果指出臨床生存率低的乳癌患者具較高的HMOX-1（鐵釋出）以及較低的FTH1（鐵儲存）與SLC40A1（鐵排出）表現，此現象有助於利用ferroptosis作為治療策略。相較於Luminal A亞型的MCF-7細胞，三陰性乳癌MDA-MB-231細胞對臨床用藥有較高的抗藥性，但對ferroptosis敏感度較佳。MDA-MB-231相較於MCF-7，在鐵代謝相關蛋白、脂質合成能力與間質細胞標誌表現量較高，抗氧化能力卻較薄弱。本研究透過轉錄體導引治療策略發現南非醉茄的酯類成分Withaferin A（WA）具有作為新型態ferroptosis誘導物的潛力。實驗證實RSL3與WA在MDA-MB-231所引起的細胞死亡可被脂質過氧化物清除劑（ferrostatin-1，Fer-1）與鐵螯合劑（deferoxamine）恢復。WA造成之MDA-MB-231脂質過氧化物大量累積可被Fer-1所降低，但MCF-7無此現象。機制研究發現WA引起兩種參與ferroptosis的路徑，可透過降低GPX4、xCT與Nrf2活化典型路徑，同時藉由自噬體包裹FTH1後降解與減少FPN表現以活化非典型路徑。綜合以上結果，WA為新型態ferroptosis誘導物，且對於Luminal A與TNBC兩種亞型之間有選擇性誘導TNBC產生ferroptosis的能力，可做為解決TNBC臨床預後不佳的治療策略之一。

Ferroptosis is a new type of regulated cell death driven by lipid peroxidation from dysregulated iron metabolism. Our results showed that breast cancer patients with higher HMOX1 (iron release) and lower FTH1 (iron storage) and SLC40A1 (iron export) expressions have shorter survival, indicating susceptibility of advanced breast cancer to ferroptosis. Compared to luminal A MCF-7 cells, triple-negative breast cancer (TNBC) MDA-MB-231 cells were resistant to anticancer drugs but sensitive to ferroptosis inducer (RSL3). This was paralleled by higher iron metabolism, fatty acid synthesis and mesenchymal marker as well as lower antioxidation genes expressions in MDA-MB-231 than MCF-7. Importantly, transcriptome-guided therapeutic strategies identified natural ester Withaferin A (WA) as a novel ferroptosis inducer. Indeed, RSL3- and WA-triggered cell death was more pronounced in MDA-MB-231, which was attenuated by lipid ROS scavenger (ferrostatin-1) and iron chelator (deferoxamine) separately. WA-elevated lipid ROS in MDA-MB-231 but not MCF-7 was reversed by ferrostatin-1. Mechanistically, WA activated both canonical ferroptosis characterized by reduced GPX4, xCT and Nrf2 and non-canonical ferroptosis depicted by NCOA4-mediated ferritinophagy and diminished ferroportin. Collectively, our data demonstrated WA as a potential ferroptosis inducer, revealed a discrepancy between TNBC and luminal A in ferroptosis and proposed a strategy to overcome poor prognosis of TNBC via WA-triggered ferroptosis.

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