If You Cannot Win Them, Join Them: Understanding New Ways to Target STAT3 by Small Molecules

Area of Science:

• Biochemistry
• Molecular Biology
• Computational Biology

Background:

• Signal transducer activator of transcription 3 (STAT3) is a key oncogenic transcription factor implicated in cancer initiation, progression, metastasis, and immune evasion.
• Constitutive STAT3 activation, often due to mutations, contributes to malignant phenotypes in cancers like glioblastoma and triple-negative breast cancer.
• Challenges in STAT3 structural studies and drug discovery are linked to difficulties in protein expression, purification, and obtaining ligand-bound crystal structures.

Purpose of the Study:

• To investigate the impact of reported STAT3 mutations on protein structure, dynamics, DNA-binding, and dimerization using molecular modeling and simulations.
• To link STAT3 structure, dynamics, energetics, and biological function at an atomistic level.
• To elucidate the mechanism of STAT3 inhibition by mutations and identify novel drug targets.

Main Methods:

• Atomistic molecular dynamics simulations.
• Umbrella-sampling simulations of wild-type and four mutated human STAT3 dimers.
• Molecular modeling to assess STAT3 dimer druggability and analyze mutation effects.
• Mapping of binding sites and characterization of ligand-binding modes.

Main Results:

• Mutations significantly modulate STAT3 activity by altering protein structure, dynamics, DNA-binding, and dimerization.
• The D570K inhibitory mutation enhances STAT3-DNA interactions, impeding DNA release and inhibiting transcription factor function.
• The clinical candidate napabucasin/BBI-608 binds to STAT3, mimicking the inhibitory effect of the D570K mutation.
• A novel small-molecule binding site on STAT3 was discovered.

Conclusions:

• Molecular simulations provide insights into STAT3 activation/inhibition mechanisms and the molecular basis of STAT3 inhibition by BBI-608.
• The findings enhance understanding of how STAT3 mutations affect its function.
• The identified novel binding site offers potential for designing new STAT3 inhibitors and developing therapeutic strategies for aggressive cancers.