EZH2 mediates lidamycin-induced cellular senescence through regulating p21 expression in human colon cancer cells.

Lidamycin (LDM) is a novel member of the enediyne antibiotics identified in China with potent antitumor activity. However, it remains unclear whether LDM has potential molecular targets that may affect its antitumor activity. Enhancer of zeste homolog 2 (EZH2) functions as a histone lysine methyltransferase and mediates trimethylation on histone 3 lysine 27 (H3K27me3). High EZH2 level is found to be positively correlated with the aggressiveness, metastasis and poor prognosis of cancer. Here, we aim to study the role of EZH2 in LDM-induced senescence, as well as in the cytotoxicity of LDM in human colon cancer cells. LDM is found to be relatively more potent in inhibiting the colon cancer cells harboring high EZH2 level and induces irreversible cellular senescence at IC50 dose range, as evidenced by senescence-associated ß-galactosidase staining, cell cycle arrest and molecular changes of senescence regulators including p21 in HCT116 and SW620 cells. More importantly, LDM is found to markedly inhibit EZH2 expression at both protein and mRNA levels upon the induction of p21 and cellular senescence. LDM also selectively inhibits EZH2 expression as compared with other histone lysine methyltransferases. Knockdown of p21 with siRNAs abolishes LDM-induced senescence, whereas EZH2 knockdown markedly increases p21 expression and causes senescent phenotype. Enrichment of both EZH2 and H3K27me3 levels in the p21 promoter region is reduced by LDM. Moreover, EZH2 overexpression reduces cellular senescence, p21 expression and DNA damage response upon LDM exposure. LDM also demonstrates potent antitumor efficacy in xenografted animal models. Collectively, our work provides first demonstration that EZH2 may mediate, at least partially, the senescence-inducing effects of LDM by regulating p21 expression and DNA damage effect. Thus, EZH2 may serve as a potential target and biomarker to indicate the clinical efficacy of the potent enediyne antitumor drug.

Design, synthesis and biological evaluation of novel benzimidazole-2-substituted phenyl or pyridine propyl ketene derivatives as antitumour agents.

A series of novel benzimidazole-2-subsituted phenyl or pyridine propyl ketene derivatives were designed and synthesized. The biological activities of these derivatives were then evaluated as potential antitumour agents. These compounds were assayed for growth-inhibitory activity against HCT116, MCF-7 and HepG2 cell lines in vitro. The IC50 values of compounds A1 and A7 against the cancer cells were 0.06-3.64 µM and 0.04-9.80 µM, respectively. Their antiproliferative activities were significantly better than that of 5-Fluorouracil (IC50: 56.96-174.50 µM) and were close to that of Paclitaxel (IC50: 0.026-1.53 µM). The activity of these derivatives was over 100 times more effective than other reported structures of chalcone analogues (licochalcone A). A preliminary mechanistic study suggested that these compounds inhibit p53-MDM2 binding. Compounds A1, A7 and A9 effectively inhibited tumour growth in BALB/c mice with colon carcinoma HCT116 cells. The group administered 200 mg/kg of compound A7 showed a 74.6% tumour growth inhibition with no signs of toxicity at high doses that was similar to the inhibition achieved with the 12.5 mg/kg irinotecan positive control (70.2%). Therefore, this class of benzimidazole-2-subsituted phenyl or pyridine propyl ketene derivatives represents a promising lead structure for the development of possible p53-MDM2 inhibitors as new antitumour agents.