Phosphorothioate oligonucleotides block the VDAC channel

Area of Science:

• Mitochondrial biophysics
• Molecular interactions
• Drug discovery

Background:

• Proapoptotic phosphorothioate oligonucleotides, such as G3139, induce apoptosis independently of Bcl-2.
• These oligonucleotides may interact with the voltage-dependent anion channel (VDAC), reducing metabolite flow across the mitochondrial outer membrane.

Purpose of the Study:

• To analyze the molecular-level interactions between phosphorothioate oligonucleotides and VDAC.
• To elucidate the mechanism of VDAC pore blockage by G3139.

Main Methods:

• Electrophysiological recordings of VDAC conductance in the presence of G3139.
• Analysis of VDAC blockage kinetics, voltage-dependence, and concentration-dependence.
• Comparison with a phosphodiester congener and a shorter oligonucleotide (polydeoxythymidine).

Main Results:

• G3139 induces flickering and blockage of VDAC conductance, occurring in the open VDAC conformation.
• Blockage is voltage-dependent (effective valence of -3) and concentration-dependent.
• Kinetics suggest a two-state binding model: an unstable bound state causing flickering and a long-lived blocked state.
• Polydeoxythymidine alters VDAC ion selectivity, indicating proximity to the ion stream.
• The phosphodiester congener is ineffective, highlighting the role of sulfur atoms.

Conclusions:

• Phosphorothioate oligonucleotides, particularly G3139, bind to VDAC, inducing a blockage.
• The interaction involves sulfur atoms and is consistent with a binding-induced blockage mechanism.
• These findings provide molecular insights into the interaction of oligonucleotides with VDAC and their proapoptotic effects.