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 <b>D11</b> (IC₅₀ = 10.2 nM) inducing γH2A.X upregulation and robust antiproliferative activity across six cancer cell lines. Remarkably, <b>D11</b> exhibited excellent pharmacokinetics in SD rats (oral bioavailability: 42.6%; half-life: 50 h) and outperformed the clinical candidate <b>AZD-7648</b> 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, <b>D11</b> is a promising heterotetracyclic DNA-PK inhibitor with superior <i>in vivo</i> efficacy, favorable pharmacokinetics, and immunomodulatory potential, supporting further development.