An epigenetic bifunctional that toggles between transactivation and repression.

Area of Science:

• Chemical Biology
• Molecular Biology
• Epigenetics

Background:

• Precise control of cellular processes relies on targeted gene expression modulation.
• Bifunctional small molecules offer a strategy for precise control of gene expression.
• FKBP(F36V) binders can be conjugated to epigenetic machinery binders to create bifunctionals.

Purpose of the Study:

• To screen for bifunctional molecules capable of inducing gene expression.
• To investigate the mechanisms of action of potent bifunctional transactivators.
• To determine if induced proximity dictates a fixed functional outcome.

Main Methods:

• Conjugation of FKBP(F36V) binder AP1867 to epigenetic binders.
• Testing bifunctionals in an FKBP(F36V)-tagged transcription factor reporter system.
• Evaluation of aTAG-2 in FKBP(F36V)-tagged oncogenic fusion protein models, including Ewing sarcoma.

Main Results:

• Bifunctional-induced transactivation is common with BET, p300/CBP, CDK9, and BRD9 ligands.
• aTAG-2 demonstrated potent transactivation with single-digit nanomolar activity.
• aTAG-2 unexpectedly induced rapid collapse of oncogenic fusion protein transcriptional programs via multiple mechanisms, including protein degradation and chromatin remodeling.

Conclusions:

• Bifunctional molecules targeting p300/CBP can switch between potent transactivation and repression based on cellular context.
• Induced proximity does not guarantee a fixed functional outcome.
• aTAG-2 exhibits context-dependent dual activity, offering potential therapeutic strategies for cancers driven by fusion proteins.