Dynamic Structural Differences between Human and Mouse STING Lead to Differing Sensitivity to DMXAA.

Area of Science:

• Immunology
• Molecular Biology
• Computational Chemistry

Background:

• The stimulator-of-interferon-genes (STING) protein is a key regulator of innate immunity and a target for cancer immunotherapy.
• DMXAA, an antitumor agent, demonstrated efficacy in mouse models but failed in human clinical trials due to species-specific differences in STING.
• Murine STING (mSTING) is sensitive to DMXAA, while human STING (hSTING) is insensitive, posing a challenge for drug translation.

Purpose of the Study:

• To investigate the molecular differences between hSTING and mSTING that affect DMXAA binding and activity.
• To elucidate the conformational preferences of hSTING and mSTING in relation to ligand binding and activation.
• To identify strategies for designing small-molecule drugs that effectively target hSTING.

Main Methods:

• Molecular dynamics simulations were used to compare hSTING and mSTING.
• Simulations focused on the lid region of STING and its role in DMXAA interaction.
• Conformational analysis was performed to assess the propensity of STING to adopt open-inactive versus closed-active states.

Main Results:

• A single mutation (G230I) in hSTING rendered it sensitive to DMXAA by creating a steric barrier that prevents drug exit.
• Wild-type hSTING possesses a porous lid region allowing DMXAA to exit, unlike mSTING.
• hSTING favors an open-inactive conformation, even when bound to its ligand cGAMP, whereas mSTING prefers a closed-active conformation, irrespective of ligand presence.

Conclusions:

• Species-specific structural and conformational differences in STING present significant hurdles in translating mouse-active STING-targeting drugs to humans.
• Understanding these differences, particularly in the lid region and conformational dynamics, is crucial for rational drug design.
• This study provides a foundation for developing novel small-molecule therapeutics that specifically target and modulate human STING for cancer treatment.