Protoapigenone, a natural derivative of apigenin, induces mitogen-activated protein kinase-dependent apoptosis in human breast cancer cells associated with induction of oxidative stress and inhibition of glutathione S-transferase π

Abstract

Protoapigenone, a natural derivative of the flavonoid apigenin, has been shown to exhibit potent antitumor activity in vitro and in vivo; the precise mechanism of action, however, is not fully elucidated. In this study, we investigated and compared the mechanisms by which protoapigenone and apigenin caused cell death in the human breast cancer MDA-MB-231 cells. Flow cytometry analysis revealed that protoapigenone induced apoptosis with 10-fold greater potency than apigenin. Cancer cells treated with protoapigenone resulted in persistent activation of mitogen-activated protein kinase (MAPK) ERK, JNK, and p38, hyperphosphorylation of Bcl-2 and Bcl-xL, and loss of mitochondrial membrane potential (MMP). The MAPK inhibitors effectively prevented the loss of MMP and apoptosis induced by protoapigenone. Treatment of cells with protoapigenone led to increased levels of reactive oxygen species (ROS) and decreased levels of intracellular glutathione. The thiol-antioxidant N-acetylcysteine abolished protoapigenone-induced MAPK activation, mitochondrial dysfunction, and apoptosis. These results suggest that the induction of oxidative stress preceding the activation of MAPK is required to initiate the mitochondria-mediated apoptosis induced by protoapigenone. Additionally, protoapigenone-induced JNK activation was linked to thiol modification of glutathione S-transferase π (GSTpi), which impeded GSTpi inhibition of JNK. In contrast to protoapigenone, apigenin-induced apoptosis was neither dependent on ROS nor on MAPK. Structure-activity relationship studies suggested that the thiol reacting effect of protoapigenone might be associated with an α, β-unsaturated ketone moiety in the structure of ring B.

Inhibition of ATR-Dependent Signaling by Protoapigenone and Its Derivative Sensitizes Cancer Cells to Interstrand Cross-link–Generating Agents In Vitro and In Vivo

“…However, phosphorylation of the p53 Ser 15 residue did not contribute to this WYC02-induced p53 protein accumulation, suggesting that WYC02 does not directly damage DNA because DNA damage normally stimulates ATM/ATR-dependent p53 Ser 15 phosphorylation. Our result is similar to previous reports that p38 MAPK is activated by WYC02 (19,21,22), as its downstream target MAPKAPK2 was found to be phosphorylated starting as early as 2 hours after WYC02 exposure (Fig. 1C).…”

“…1A) were shown to induce oxidative stress, consequently activating the p38 and c-jun-NH 2 -kinase (JNK) 1/2 mitogen-activated protein kinase (MAPK) pathways following cell-cycle arrest and apoptosis in several cancer cell types. These compounds were also found to reduce the size of tumor xenografts in nude mice without exerting toxic effects on the recipient (18)(19)(20)(21)(22). Recently, WYCs were found to induce chromosomal breakage through oxidative stress (18,20), implicating a role for WYCs in interfering with DNA metabolism.…”

RY10-4, a novel anti-tumor compound, exhibited its anti-angiogenesis activity by down-regulation of the HIF-1α and inhibition phosphorylation of AKT and mTOR

“…RY10-3 that has a similar structure to RY10-4 showed little cytotoxicity in the MTT assay against HUVECs and breast cancer cells. A similar conclusion was concluded between protoapigenone and apigenin [25]. This gave us the opinion that the 1-hydroxycyclohexa-2,5-dien was the essential pharmacophore in the series of compounds.…”

Lower antioxidative capacity of multidrug-resistant cancer cells confers collateral sensitivity to protoflavone derivatives

“…As such, these compounds can severely interfere with the redox homeostasis of cancer cells on multiple levels, leading to an oxidative stress-mediated apoptosis [9]. Based on protoapigenone (PA; compound 1), a natural protoflavone derived from apigenin, a set of prospective leads is under development including the synthetic β-naphthoflavone derivative WYC0209 (compound 2) [10].…”