Cytotoxic Components from Hypericum elodeoides Targeting RXRα and Inducing HeLa Cell Apoptosis through Caspase-8 Activation and PARP Cleavage

J Nat Prod. 2019 May 24;82(5):1072-1080. doi: 10.1021/acs.jnatprod.8b00680. Epub 2019 Apr 30.

Abstract

To find small-molecule regulators of RXRα, a phytochemical study of Hypericum elodeoides was conducted. Fifteen compounds, including the new 1 and 6, were isolated from the whole plant of H. elodeoides. The absolute configuration of 1 was assigned by comparison of experimental and calculated ECD data. Compounds 1 and 6 exhibited concentration-dependent inhibitory effects on RXRα transcription and selectively inhibited the proliferation of HeLa cells. Western blot analysis suggested that 1 and 6 induced apoptosis of HeLa cells with time- and dose-dependent PARP cleavage. A caspase activation assay indicated that these two compounds triggered caspase-8 activation to induce apoptosis by the extrinsic pathway. Molecular docking results suggested that 1 and 6 interacted with the Arg319 moiety of RXRα-LBD. Ligands binding to RXRα have shown promise in the discovery of anticancer drugs. A fluorescence quenching assay indicated the binding of 1 and 6 to the RXRα with the binding constant ( KD) fitted as 68.3 and 14.0 μM, respectively. A preliminary SAR study of the isolates was conducted to enhance the knowledge of the RXRα ligands. Thus, 1 and 6 might act as the small-molecule regulators of RXRα, which target RXRα and mediate HeLa cell apoptosis through the extrinsic pathways.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents, Phytogenic / chemistry
  • Antineoplastic Agents, Phytogenic / isolation & purification*
  • Antineoplastic Agents, Phytogenic / pharmacology
  • Apoptosis / drug effects*
  • Caspase 8 / metabolism*
  • Dose-Response Relationship, Drug
  • Enzyme Activation
  • HeLa Cells
  • Humans
  • Hypericum / chemistry*
  • Magnetic Resonance Spectroscopy
  • Molecular Docking Simulation
  • Poly(ADP-ribose) Polymerases / metabolism*
  • Retinoid X Receptor alpha / antagonists & inhibitors*
  • Structure-Activity Relationship

Substances

  • Antineoplastic Agents, Phytogenic
  • Retinoid X Receptor alpha
  • Poly(ADP-ribose) Polymerases
  • Caspase 8