(±)-Hypernumqulins A-H: Eight pairs of unexpected [2+2] cycloaddition sesquiterpenoid alkaloid with 6/6/6/4/10 ring system from Hypericum monogynum L.

(±)-Hypernumqulins A-H (1-8), eight pairs of enantiomeric quinoline alkaloids fused with an isopentenyl and a germacrane-type sesquiterpenoid, featuring an unprecedented skeleton with 6/6/6/4/10 ring system, were isolated from Hypericum monogynum L. under the guidance of molecular networking strategy. Their structures including absolute configuration were elucidated by NMR spectroscopy analysis, X-ray crystallography and quantum chemical calculation. The proposed [2+2] cycloaddition may play a key biogenic step in building the unexpected skeleton. Most of the isolates exhibited cytotoxicity with IC50 values ranging from 2.82 ± 0.03 to 45.25 ± 1.26 µM against MCF-7, A549 or SGC7901 cells. Furthermore, compounds (±)-1 and (-)-1 could induce apoptosis by upregulating the protein expression level of Bax and downregulating of Bcl-2 in MCF-7 cells. These findings provided the first example of germacrane sesquiterpene quinoline alkaloids, and supported the possibilities for the development of new anti-tumor agents.

Ptehosides A-I: Nine undescribed iridoids with in vitro cytotoxicity from the whole plant of Pterocephalus hookeri (C.B. Clarke) Höeck.

Nine previously undescribed iridoids, ptehosides A-I (1-9), together with 12 known ones (10-21), were isolated from Pterocephalus hookeri (C.B. Clarke) Höeck. Their structures were elucidated using various spectroscopic methods including HR-ESI-MS, NMR, UV, IR and CD, etc. The cytotoxic activities of all isolates were evaluated using MTT method in three human cancer cell lines (Caco2, Huh-7, and SW982). As result, compound 9 exhibited substantial inhibitory activity on Caco2, Huh-7, and SW982 cells with IC50 values of 1.17 ± 0.05, 1.15 ± 0.05 and 1.14 ± 0.04 µM, respectively. A preliminary mechanism study showed that 9 arrested the cell cycle of SW982 cells in the G0/G1 phase and induced apoptosis by upregulating Bax expression and downregulating Bcl-2 expression.

Discovery of a selective TRF2 inhibitor FKB04 induced telomere shortening and senescence in liver cancer cells.

Telomere repeat binding factor 2 (TRF2), a critical element of the shelterin complex, plays a vital role in the maintenance of genome integrity. TRF2 overexpression is found in a wide range of malignant cancers, whereas its down-regulation could cause cell death. Despite its potential role, the selectively small-molecule inhibitors of TRF2 and its therapeutic effects on liver cancer remain largely unknown. Our clinical data combined with bioinformatic analysis demonstrated that TRF2 is overexpressed in liver cancer and that high expression is associated with poor prognosis. Flavokavain B derivative FKB04 potently inhibited TRF2 expression in liver cancer cells while having limited effects on the other five shelterin subunits. Moreover, FKB04 treatment induced telomere shortening and increased the amounts of telomere-free ends, leading to the destruction of T-loop structure. Consequently, FKB04 promoted liver cancer cell senescence without modulating apoptosis levels. In corroboration with these findings, FKB04 inhibited tumor cell growth by promoting telomeric TRF2 deficiency-induced telomere shortening in a mouse xenograft tumor model, with no obvious side effects. These results demonstrate that TRF2 is a potential therapeutic target for liver cancer and suggest that FKB04 may be a selective small-molecule inhibitor of TRF2, showing promise in the treatment of liver cancer.