A first-in-class Polymerase Theta Inhibitor selectively targets Homologous-Recombination-Deficient Tumors

Area of Science:

• Oncology
• Molecular Biology
• Drug Discovery

Background:

• DNA polymerase theta (POLθ) is a key target in homologous recombination (HR)-deficient cancers due to synthetic lethality.
• Identifying specific inhibitors of POLθ is crucial for developing novel cancer therapies.

Purpose of the Study:

• To identify small molecules that inhibit POLθ activity.
• To evaluate the efficacy of identified inhibitors in HR-deficient cancer models.
• To explore the therapeutic potential of POLθ inhibition, particularly in cases of acquired resistance to PARP inhibitors (PARPi).

Main Methods:

• High-throughput small molecule screening to identify POLθ inhibitors.
• Biochemical assays to confirm POLθ ATPase inhibition by Novobiocin (NVB).
• In vitro and in vivo studies using various cancer models (GEMM, xenograft, PDX) to assess NVB's efficacy.
• Analysis of RAD51 foci and DNA repair mechanisms to understand NVB's mode of action.

Main Results:

• Novobiocin (NVB) was identified as a specific inhibitor of POLθ, directly binding to its ATPase domain and reducing its activity.
• NVB demonstrated selective killing of HR-deficient tumor cells in vitro and in vivo, including breast and ovarian cancers.
• Increased POLθ levels correlated with NVB sensitivity, and BRCA-deficient, PARPi-resistant cells were sensitive to NVB.
• NVB-induced cell death in resistant cells involved increased DNA-end resection and impaired RAD51 function.

Conclusions:

• Novobiocin (NVB) is a potent POLθ inhibitor with selective anti-tumor activity against HR-deficient cancers.
• NVB shows promise as a therapeutic agent for HR-deficient tumors, potentially overcoming resistance to existing treatments like PARPi.
• Combination therapy with NVB and PARPi warrants further investigation for treating HR-deficient malignancies.