Discovery of a small-molecule inhibitor that traps Polθ on DNA and synergizes with PARP inhibitors

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Therapeutics

Background:

• DNA Polymerase θ (Polθ) is a key protein in the DNA damage response (DDR).
• Polθ is synthetically lethal with homologous recombination (HR) factors, making it a target for BRCA1/2 mutant cancers.
• Targeting Polθ offers a promising strategy for selective cancer therapy.

Purpose of the Study:

• To discover and characterize a novel class of allosteric Polθ inhibitors (Polθi).
• To elucidate the mechanism of action of Polθi.
• To evaluate the therapeutic potential of Polθi in combination with PARP inhibitors (PARPi).

Main Methods:

• Biochemical assays to determine IC50 values and enzyme kinetics.
• X-ray crystallography to visualize inhibitor-enzyme interactions.
• Cell-based assays to assess selective killing of HR-deficient cells and synergy with PARPi.

Main Results:

• Identified a Polθi class with high affinity (4-6 nM IC50) for Polθ.
• Polθi selectively inhibits Polθ polymerase (Polθ-pol) in its closed conformation on B-form DNA/DNA.
• Inhibitor binding traps Polθ on DNA, revealing a unique DNA polymerase:DNA trapping mechanism.

Conclusions:

• Polθi represents a novel therapeutic strategy for HR-deficient cancers.
• The DNA trapping mechanism induces synthetic lethality in HR-deficient cells.
• Polθi potentiates the efficacy of PARPi, offering a synergistic treatment approach.