ABSTRACT
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.
Subject(s)
Cell Survival/drug effects , Coumarins/chemistry , Phenazines/chemistry , Pyrazines/pharmacology , Steroids/chemistry , Cell Line, Tumor , Cell Proliferation/drug effects , Cells, Cultured , Drug Delivery Systems , Endoplasmic Reticulum Chaperone BiP , Heat-Shock Proteins/metabolism , Humans , Molecular Probes , Molecular Structure , Protein Binding/drug effects , Pyrazines/chemistryABSTRACT
The cephalostatin and ritterazine natural products comprise a potent family of bis-steroidal pyrazines that display potent single-digit nanomolar inhibition of tumor cell growth. An active fluorescent ritterazine-cephalostatin hybrid probe was developed using detailed SAR data derived through total synthetic efforts. A combination of time course and confocal imaging studies indicate that this natural product family is rapidly taken up in tumor cells and localizes subcellularly within ER and surrounding the nuclear-ER interface.
Subject(s)
Fluorescent Dyes/chemical synthesis , Phenazines/chemical synthesis , Spiro Compounds/chemical synthesis , Steroids/chemical synthesis , Fluorescent Dyes/metabolism , HCT116 Cells , Humans , Molecular Structure , Phenazines/metabolism , Spiro Compounds/metabolism , Steroids/metabolism , Structure-Activity RelationshipABSTRACT
We describe the first effective H/D exchange reaction with acidic substrates in CDCl(3) at room temperature. The particularly mild reaction conditions involved (solvent, base, and temperature) allow the chemoselective deuteration of ketones over esters. An NMR study was conducted with the aim of rationalizing the results obtained in the presence of TBD as catalyst.
