Discovery of Novel Heterotetracyclic DNA-Dependent Protein Kinase (DNA-PK) Inhibitors with Improved Oral Bioavailability and Potent Cancer Immunotherapy-Potentiating Activity

A novel series of heterotetracyclic DNA-PK inhibitors was rationally designed, synthesized, and biologically evaluated. Most compounds showed potent DNA-PK inhibition (IC₅₀: 10.2-88.9 nM), with lead D11 (IC₅₀ = 10.2 nM) inducing γH2A.X upregulation and robust antiproliferative activity across six cancer cell lines. Remarkably, D11 exhibited excellent pharmacokinetics in SD rats (oral bioavailability: 42.6%; half-life: 50 h) and outperformed the clinical candidate AZD-7648 in LoVo xenografts (TGI = 72.9% vs 54.6% at 50 mg/kg, p.o.). It also synergized with anti-PD-L1 mAb to enhance CD8⁺ T-cell infiltration. Overall, D11 is a promising heterotetracyclic DNA-PK inhibitor with superior in vivo efficacy, favorable pharmacokinetics, and immunomodulatory potential, supporting further development.