Diterpene pyrones (DTPs) are a group of well-known, mainly fungal, natural products, first isolated in 1966. As the name indicates, they are composed of two main structural features: a diterpenyl moiety and a pyrone ring. Various names have been given to this class of metabolites; however, biogenetic evidence indicates that they originate through the same metabolic pathway. Based on their biosynthesis, which leads to differences in their structural architecture, the DTPs can be classified into three main types. In addition to their intriguing chemistry, these compounds demonstrate a wide range of biological activities rendering them a desirable target for total synthesis. To date, sixty-seven DTPs have been isolated from various fungal species, with one example originating from the plant kingdom. This review aims at unifying the classification of these compounds, in addition to presenting a detailed description of their isolation, bioactivities, biosynthesis, and total synthesis.
The plant Andrographis paniculata found throughout Southeast Asia contains Andrographolide 1, a diterpenoid lactone, which has antitumour activities against in vitro and in vivo breast cancer models. In the present study, we report on the synthesis of andrographolide derivatives, 3,19-isopropylideneandrographolide (2), 14-acetyl-3,19-isopropylideneandrographolide (3) and 14-acetylandrographolide (4), and their in vitro antitumour activities against a 2-cell line panel consisting of MCF-7 (breast cancer cell line) and HCT-116 (colon cancer cell line). Compounds 2 and 4 were also screened at the US National Cancer Institute (NCI) for their activities against a panel of 60 human cancer cell lines derived from nine cancer types. Compound 2 was found to be selective towards leukaemia and colon cancer cells, and compound 4 was selective towards leukaemia, ovarian and renal cancer cells at all the dose-response parameters. Compounds 2 and 4 showed non-specific phase of the cell cycle arrest in MCF-7 cells treated at different intervals with different concentrations. NCI's COMPARE and SOM mechanistic analyses indicated that the anticancer activities of these new class of compounds were not similar to that of standard anticancer agents, suggesting novel mechanism(s) of action.
BACKGROUND AND PURPOSE: Andrographolide, the major phytoconstituent of Andrographis paniculata, was previously shown by us to have activity against breast cancer. This led to synthesis of new andrographolide analogues to find compounds with better activity than the parent compound. Selected benzylidene derivatives were investigated for their mechanisms of action by studying their effects on the cell cycle progression and cell death.
EXPERIMENTAL APPROACH: Microculture tetrazolium, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and sulphorhodamine B (SRB) assays were utilized in assessing the in vitro growth inhibition and cytotoxicity of compounds. Flow cytometry was used to analyse the cell cycle distribution of control and treated cells. CDK1 and CDK4 levels were determined by western blotting. Apoptotic cell death was assessed by fluorescence microscopy and flow cytometry.
KEY RESULTS: Compounds, in nanomolar to micromolar concentrations, exhibited growth inhibition and cytotoxicity in MCF-7 (breast) and HCT-116 (colon) cancer cells. In the NCI screen, 3,19-(2-bromobenzylidene) andrographolide (SRJ09) and 3,19-(3-chloro-4-fluorobenzylidene) andrographolide (SRJ23) showed greater cytotoxic potency and selectivity than andrographolide. SRJ09 and SRJ23 induced G(1) arrest and apoptosis in MCF-7 and HCT-116 cells, respectively. SRJ09 downregulated CDK4 but not CDK1 level in MCF-7 cells. Apoptosis induced by SRJ09 and SRJ23 in HCT-116 cells was confirmed by annexin V-FITC/PI flow cytometry analysis.
CONCLUSION AND IMPLICATIONS: The new benzylidene derivatives of andrographolide are potential anticancer agents. SRJ09 emerged as the lead compound in this study, exhibiting anticancer activity by downregulating CDK4 to promote a G(1) phase cell cycle arrest, coupled with induction of apoptosis.
Andrographolide (AGP) is the main bioactive constituent isolated from the traditional medicinal, Andrographis paniculata which contributes towards its various biological activities, including anticancer property. In this study, a series of new AGP derivatives were semi-synthesised and screened against the NCI in vitro 60 cell lines. From the screening results, we had identified SRS07 as the most potent AGP derivative, against breast and colon cancer cell lines. Subsequently, SRS07 was tested for its capability to induce cell cycle arrest and apoptosis in MCF-7 and HCT116 cancer cells. SRS07 effectively induced G1 cell cycle arrest in both cell lines and ultimately apoptosis by inducing DNA fragmentation in HCT116 cells. The apoptotic cell death induced by SRS07 was confirmed via FITC Annexin-V double staining. Western blot analysis of SRS07-treated HCT116 cells revealed that the compound induced apoptosis be activating caspase 8 which in turn cleaved Bid to t-Bid to initiate cell death cascade. Prediction of the possible mode of action of SRS07 by utilising NCI COMPARE analysis failed to reveal a distinct mechanism category. Hence, it is speculated that SRS07 possesses novel mechanism of action. In conclusion, SRS07 demonstrated superior in vitro anticancer profiles and emerged as a potential lead anticancer candidate.