ent-Kaurane Diterpenoids from Chinese Liverworts and Their Antitumor Activities through Michael Addition As Detected in Situ by a Fluorescence Probe

Abstract

It is generally accepted that the origin of the cytotoxicity of ent-kaurane diterpenoids is due to the formation of reactive oxygen species (ROS) and that the α,β-unsaturated carbonyl is a pivotal moiety. Herein we demonstrate the isolation of 32 new and 12 known ent-kaurane diterpenoids from two Chinese liverworts. These compounds and three semisynthesized derivatives were screened against human cancer cell lines. The results revealed that their anticancer activities are caused by ROS formation through Michael modification of the protein thiols and depletion of glutathione unselectively. We also found that N-acetylcysteine reverses the cytotoxicity of these diterpenoids by forming Michael adducts, not through a well-recognized ROS scavenging pathway as previously reported. In situ intracellular thiol detection helped us visualize the intracellular distribution of the diterpenoids and determine the potency of their cytotoxicity. An alkaline analogue was found to be more selective because of the altered subcellular distribution.

Cytotoxic, apoptotic, and sensitization properties of ent‐kaurane‐type diterpenoids from Croton tonkinensis Gagnep on human liver cancer HepG2 and Hep3b cell lines

“…Enhanced ROS production has been associated to the synergistic effects between doxorubicin and withaferin A in ovarian cancer or selenocysteine in HCC . Interestingly, as discussed above, ent ‐kaurane diterpenoid‐induced formation of ROS also mediates cytotoxicity and apoptosis . The fact that ROS generation is also one of the mechanisms of action involved in doxorubicin antitumor activity may be a possible explanation of the observed additive effects between compound 5 and doxorubicin.…”

“…The fact that no significant difference was observed in the cytotoxic effect against HepG2 and Hep3b despite the distinct pharmacological properties of the two cell lines [11], suggested a cell line-independent mechanism of action of the compounds. Indeed, it is accepted that the cytotoxicity of ent-kaurane diterpenoids results from the formation of reactive oxygen species (ROS) through Michael reaction with regulatory thiol-containing enzymes or coenzymes [15][16][17], likely to be shared by the two HepG2 and Hep3b cell lines and others. Cytotoxicity of compound 1 on HepG2 and Hep3b cell lines was in the same range as that measured on the SK-HEP1 cell line for the identical ent-kaurane diterpenoid named CrT1 [9].…”

Jungermannenone A and B induce ROS- and cell cycle-dependent apoptosis in prostate cancer cells in vitro

“…The screening assay of 44 naturally occurring diterpenoids previously led us to the identification of JA and JB as chemicals that potentially inhibit cancer cell proliferation [21] . Here, we extended our observations to determine the inhibitory effects of JA and JB on a panel of cancer cell lines and the human non-neoplastic prostate epithelial cell line RWPE-1.…”

“…Given that over-expression is a common feature in various human tumors [17,18] , the downregulation of c-Myc, resulting in a G 0 /G 1 arrest and reduction in the growth rate, also contributes to the inhibitory effect of antitumor drugs [19,20] . Most recently, we have reported that two new ent-kaurane diterpenoids, Jungermannenone A (JA) and Jungermannenone B (JB), from the Chinese liverwort Jungermannia fauriana [21] , show potential anti-proliferation activity with a low IC 50 against a panel of cancer cell lines. The present study was designed to uncover the cellular/molecular basis by which JA and JB exert their antitumor effects, in addition to their ability to modify protein thiols through the Michael reaction and the depletion of glutathione, mainly in PCa cells.…”

ent-Eudesmane-Type Sesquiterpenoids from the Chinese Liverwort Chiloscyphus polyanthus var. rivularis

“…3) were similar to those of 4, except that the correlations of H 3 -14/H-1α, H-5/H-1β, and H-1β/H-2 inferred the methoxy group was α-oriented, and its structure was defined as (2R,5S,6R,7S,10R)-6,7-dihydroxy-2-methoxy-eudesma-3Z-ene (7). Six known analogues, namely, eudesm-4(15)-ene-6α,7β-diol (8), eudesm-3-ene-7β-ol (9), eudesm-3-ene-6α,7β-diol (10), eudesm-3-ene-6β,7β-diol (11), eudesm-3-ene-6β-acetoxy-7β-ol (12), and 7β-hydroxy-3-oxo-eudesma-4-ene (13), were isolated and identified to be ent-eudesmane derivatives by comparing their observed and reported ESIMS, NMR, and optical rotation data [15,16]. Compounds 1-13 were evaluated for cytotoxic activity against the A549, K562, and MCF7cancer cell lines and normal human vascular (HY926) cells using the MTT method [19], with doxo- Table 3).…”