Search

The enzyme NQO1 is a potential target for selective cancer therapy due to its overexpression in certain hypoxic tumors. A series of prodrugs possessing a variety of cytotoxic diterpenoids (oridonin and its analogues) as the leaving groups activated by NQO1 were synthesized by functionalization of 3-(hydroxymethyl)indolequinone, which is a good substrate of NQO1. The target compounds (29a-m) exhibited relatively higher antiproliferative activities against NQO1-rich human colon carcinoma cells (HT-29) and human lung carcinoma (A549) cells (IC 50  = 0.263-2.904 μM), while NQO1-defficient lung adenosquamous carcinoma cells (H596) were less sensitive to these compounds, among which, compound 29h exhibited the most potent antiproliferative activity against both A549 and HT-29 cells, with IC 50 values of 0.386 and 0.263 μM, respectively. Further HPLC and docking studies demonstrated that 29h is a good substrate of NQO1. Moreover, the investigation of anticancer mechanism showed that the representative compound 29h affected cell cycle and induced NQO1 dependent apoptosis through an oxidative stress triggered mitochondria-related pathway in A549 cells. Besides, the antitumor activity of 29h was also verified in a liver cancer xenograft mouse model. Biological evaluation of these compounds concludes that there is a strong correlation between NQO1 enzyme and induction of cancer cell death. Thus, this suggests that some of the target compounds activated by NQO1 are novel prodrug candidates potential for selective anticancer therapy., (Copyright © 2017 Elsevier Masson SAS. All rights reserved.)

The cytotoxicity of the natural ent-kaurene diterpenoid, oridonin, has been extensively studied. However, the application of oridonin for cancer therapy was hampered primarily by its moderate potency. In this study, a series of oridonin A-ring modified analogues, and their derivatives bearing various substituents on 14-OH position, were designed, synthesized, and evaluated for anticancer efficacy. Some of the derivatives were significantly more potent than oridonin against both drug-sensitive and drug-resistant cancer cells. The most potent compound, 13p, was 200-fold more efficacious than oridonin in MCF-7 cancer cells. Furthermore, 13p induced apoptosis and cell cycle arrest at the G2/M phase. A decrease in mitochondrial membrane potential and an increase in Bax/Bcl-2 ratio, accompanied by activated caspase-3 cleavage, were observed in MCF-7 cells after treatment with 13p, suggesting that the mitochondrial pathway was involved in the 13p-mediated apoptosis. Moreover, 13p significantly inhibited tumor growth in mouse xenograft models and had no observable toxic effect.

Oridonin (1) is a complex ent-kaurane diterpenoid with unique antitumor profile, which is isolated from Isodon rubescens. In order to develop novel derivatives of oridonin with improved potency, a series of nitric oxide (NO)-releasing oridonin derivatives were synthesized by coupling diazeniumdiolates with oridonin and its semisynthesized analogues. Their in vitro antiproliferative activity, nitric oxide release ability, and preliminary anticancer mechanism were further evaluated. The results displayed that all the target compounds exhibited potent antiproliferative activities, with IC50 values ranging from 1.84 to 17.01μM. Besides, it was observed that in most cases, the antiproliferative activity correlated well with levels of intracellular NO release. More interestingly, preliminary mechanism studies revealed that the most potent compound 14d induced apoptosis and arrested the cell cycle at the S phase in Bel-7402 cells, which is different from parent compound oridonin. Together, the above promising results warrant the further development of oridonin/NO hybrids as potential antitumor leads., (Copyright © 2016 Elsevier Ltd. All rights reserved.)