Dissecting the molecular determinants of clinical PARP1 inhibitor selectivity for tankyrase1

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• Poly(ADP-ribosyl) polymerase 1 (PARP1) is a key target in breast cancer therapy due to its role in DNA repair and synthetic lethality with BRCA1/2.
• PARP inhibitors' efficacy stems from enzymatic inhibition and trapping PARP1 on DNA, with talazoparib being highly effective at trapping.
• Talazoparib is also suspected to inhibit PARP5a/b (tankyrase1/2, TNKS1/2), regulators of the Wnt/β-catenin pathway.

Purpose of the Study:

• To investigate talazoparib's interaction with TNKS1 at clinically relevant concentrations.
• To quantify the binding affinities of talazoparib and other PARP inhibitors (olaparib, niraparib, veliparib) for PARP1 and TNKS1.
• To elucidate the molecular mechanisms underlying the differential selectivity of these inhibitors.

Main Methods:

• Competition experiments in cell lysate to assess talazoparib-TNKS1 binding.
• Surface Plasmon Resonance (SPR) to measure dissociation constants (Kd) for inhibitor-protein interactions.
• Crystallography and Hydrogen-Deuterium Exchange Mass Spectroscopy (HDX-MS) to analyze molecular interactions and protein dynamics.

Main Results:

• Talazoparib demonstrated potential binding and engagement with TNKS1 at clinical concentrations.
• Talazoparib exhibited strong affinity for PARP1 and a uniquely strong affinity for TNKS1.
• SPR data quantified differential binding affinities, highlighting talazoparib's dual specificity.
• Structural and dynamic analyses revealed molecular basis for selectivity differences.

Conclusions:

• Talazoparib possesses a dual inhibitory profile against PARP1 and TNKS1.
• Differences in binding sites, ligand properties, protein dynamics, and energetics explain inhibitor selectivity.
• Findings provide insights for designing novel therapeutics targeting Wnt/β-catenin pathway-driven cancers, such as colorectal cancer.