Regulating the ARNT/TACC3 Axis: Multiple Approaches to Manipulating Protein/Protein Interactions with Small Molecules

For several well-documented reasons, it has been challenging
to develop artificial small molecule inhibitors of protein/protein
complexes. Such reagents are of particular interest for transcription
factor complexes given links between their misregulation and disease.
Here we report parallel approaches to identify regulators of a hypoxia
signaling transcription factor complex, involving the ARNT subunit
of the HIF (Hypoxia Inducible Factor) activator and the TACC3 (Transforming
Acidic Coiled Coil Containing Protein 3) coactivator. In one route,
we used in vitro NMR and biochemical screening to
identify small molecules that selectively bind within the ARNT PAS
(Per-ARNT-Sim) domain that recruits TACC3, identifying KG-548 as an
ARNT/TACC3 disruptor. A parallel, cell-based screening approach previously
implicated the small molecule KHS101 as an inhibitor of TACC3 signaling.
Here, we show that KHS101 works indirectly on HIF complex formation
by destabilizing both TACC3 and the HIF component HIF-1α. Overall,
our data identify small molecule regulators for this important complex
and highlight the utility of pursuing parallel strategies to develop
protein/protein inhibitors.