Ritterostatin GN 1N , a Cephalostatin-Ritterazine Bis-steroidal Pyrazine Hybrid, Selectively Targets GRP78

Chembiochem. 2017 Mar 16;18(6):506-510. doi: 10.1002/cbic.201600669. Epub 2017 Feb 2.


Natural products discovered by using agnostic approaches, unlike rationally designed leads or those obtained through high-throughput screening, offer the ability to reveal new biological pathways and, hence, serve as an important vehicle to unveil new avenues in drug discovery. The ritterazine-cephalostatin family of natural products displays robust and potent antitumor activities, with sub-nanomolar growth inhibition against multiple cell lines and potent activity in xenograft models. Herein, we used comparative cellular and molecular biological methods to uncover the ritterazine-cephalostatin cytotoxic mode of action (MOA) in human tumor cells. Our findings indicated that, whereas ritterostatin GN 1N , a cephalostatin-ritterazine hybrid, binds to multiple HSP70s, its cellular trafficking confines activity to the endoplasmic reticulum (ER)-based HSP70 isoform, GRP78. This targeting results in activation of the unfolding protein response (UPR) and subsequent apoptotic cell death.

Keywords: GRP78; cephalostatin; drug discovery; natural products; ritterazine.

MeSH terms

  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects*
  • Cells, Cultured
  • Coumarins / chemistry*
  • Drug Delivery Systems
  • Endoplasmic Reticulum Chaperone BiP
  • Heat-Shock Proteins / metabolism
  • Humans
  • Molecular Probes
  • Molecular Structure
  • Phenazines / chemistry*
  • Protein Binding / drug effects
  • Pyrazines / chemistry
  • Pyrazines / pharmacology*
  • Steroids / chemistry*


  • Coumarins
  • Endoplasmic Reticulum Chaperone BiP
  • HSPA5 protein, human
  • Heat-Shock Proteins
  • Molecular Probes
  • Phenazines
  • Pyrazines
  • Steroids
  • ritterostatin GN1N