Discovery of Novel Orally Bioavailable Polθ Inhibitors with Arylalkyne Scaffolds for Targeting HR-Deficient Cancers

Polθ, a key enzyme mediating microhomology-mediated end joining (MMEJ), is overexpressed in multiple human cancers and represents a promising therapeutic target, particularly in tumors with homologous recombination (HR) deficiency. Herein, we report the discovery and optimization of a novel series of Polθ polymerase (Polθ-pol) inhibitors featuring an arylalkyne scaffold, which extends into a peripheral channel within the polymerase domain to enhance target engagement. Among the synthesized compounds, compound <b>20</b> exhibited potent inhibitory activity against Polθ-pol at a nanomolar level (IC₅₀ = 1.3 nM), along with antiproliferative activity against the HR-deficient cancer cell lines, such as MDA-MB-436, Capan-1, and DLD-1 (BRCA2^-/-). Moreover, compound <b>20</b> demonstrated favorable pharmacokinetic properties, with oral bioavailability values of 103.36% in mice and 63.71% in rats, respectively. In an MDA-MB-436 xenograft model, compound <b>20</b> significantly suppressed tumor growth without evident toxicity. These findings underscore the arylalkyne scaffold as a highly promising strategy for the development of orally active Polθ-targeted therapeutics.