Polθ-IN-4 is an orally active prodrug of a DNA polymerase θ (Polθ) inhibitor with Kms of 3.7, 3.7 and 5.2 μM in human, mouse and rat recombinant alkaline phosphatases. Polθ-IN-4 that inhibits Polθ activity by targeting its ATP-dependent helicase domain. Polθ-IN-4 demonstrates significant anti-tumor activity in multiple animal experiments. Polθ-IN-4 can be used for the studies of breast cancer and ovarian cancer[1].