本研究主要探討磯松素(plumbagin)的抗乳癌活性和相關分子機轉。結果發現磯松
素會造成細胞週期停滯(cell cycle arrest)以及細胞自噬(autophagy)。磯松素促使細
胞週期停滯於G2/M 期主要透過增加p21 表現、Chk2 活化以及降低cyclin B1、
cyclin A、cdc2 和cdc25C 的表現。除此，磯松素還會透過增加p21 和Cdc2 的結
合，以及增加Chk2 的活化促使Cdc2 和Cdc25C 的磷酸化而抑制Cdc2 的功能。
在細胞死亡誘導方面，磯松素主要會誘導細胞進行細胞自噬，而非細胞凋亡。磯
松素可藉由抑制AKT 的活化以及相關下游分子，包括mammalian target of
rapamycin (mTOR)、forkhead transcription factors (FKHR)和glycogen synthase
kinase-3beta (GSK)，有效的阻斷PI3K (phosphatidylinositol 3-kinase)/AKT 訊息傳
遞。再者，mTOR 的數個下游分子，包括p70 ribosomal protein S6 kinase (p70S6
kinase)和4E-BP1 的磷酸化也都一併受到抑制。當細胞過度表現AKT 時會抑制
磯松素所造成的細胞自噬作用。相對的，當AKT 表現受到抑制時會明顯增加磯
松素所造成的細胞自噬作用，因此證明磯松素透過AKT 的抑制作用促使啟動細
胞自噬。除此，磯松素在裸鼠(nude mice)的研究也證實了其在in vivo 的條件下
仍然具有抑制乳癌細胞增生、啟動細胞自噬以及抑制AKT 活化的能力。綜合以
上結果，本研究證實磯松素可藉由抑制PI3K/AKT/mTOR 路徑促使細胞停滯以及
啟動細胞自噬。 This study is the first to investigate the anticancer effect of plumbagin in human
breast cancer cells. Plumbagin exhibited cell proliferation inhibition by inducing cells
to undergo G2/M arrest and autophagic cell death. Blockade of the cell cycle was
associated with increased p21/WAF1 expression and Chk2 activation, and reduced
amounts of cyclinB1, cyclinA, Cdc2 and Cdc25C. Plumbagin also reduced Cdc2
function by increasing the association of p21/WAF1/Cdc2 complex and the levels of
inactivated phospho-Cdc2 and phospho-Cdc25C by Chk2 activation. Plumbagin
triggered autophagic cell death, but not, predominantly, apoptosis. Pretreatment of
cells with autophagy inhibitor bafilomycin suppressed plumbagin-mediated cell death.
We also found that plumbagin inhibited survival signaling through the PI3K
(phosphatidylinositol 3-kinase)/AKT signaling pathway by blocking the activation of
AKT and downstream targets, including the mammalian target of rapamycin (mTOR),
forkhead transcription factors (FKHR) and glycogen synthase kinase-3beta (GSK).
Phosphorylation of both of mTOR’s downstream targets, p70 ribosomal protein S6
kinase (p70S6 kinase) and 4E-BP1, was also diminished. Overexpression of AKT by
AKT cDNA transfection decreased plumbagin-mediated autophagic cell death,
whereas reduction of AKT expression by siRNA potentiated plumbagin’s effect,
supporting inhibition of AKT beneficial to autophagy. Furthermore, suppression of
AKT by plumbagin enhanced the activation of Chk2, resulting in increased inactive
phosphorylation of Cdc25C and Cdc2. Further investigation revealed that plumbagin’s
inhibition of cell growth was also evident in a nude mice model. Taken together, these
results imply a critical role for AKT inhibition in plumbagin-induced G2/M arrest and
autophagy of human breast cancer cells.
