Rational design of chromeno[8,7-d]oxazoles as CDK16-directed inhibitors with improved solubility and antitumor...

Acquired resistance to established molecularly targeted therapies remains a major challenge in non-small cell lung cancer (NSCLC). In this study, a series of chromeno[8,7-d]oxazole derivatives was designed from the CDK9-preferring hit HS-36 through structure-guided modification of the C-8 side chain and N-1 substituent. Among these derivatives, AT-11 showed the strongest inhibition of CDK16/Cyclin Y (CDK16/CycY), with an IC₅₀ value of 125.2 nM. Single-concentration measurements performed under the same kinase assay conditions were consistent with a relative shift in the CDK16/CDK9 inhibitory profile compared with HS-36. AT-11 showed a solubility of 617 μg/mL in PBS (pH 7.4). In H460 cells, AT-11 inhibited proliferation and colony formation, was associated with S-phase accumulation and increased apoptosis, and reduced cell migration. Across an expanded panel of tumor and comparator cell lines, AT-11 displayed differential antiproliferative activity, with low-micromolar GI₅₀ values in H460, A549, and MV-4-11 cells. Western blot analysis in H460 cells showed reduced relative p53 Ser315 phosphorylation and increased total p53 levels following AT-11 treatment. Intravenous administration of AT-11 at 20 mg/kg produced 48.2% tumor growth inhibition in an H460 xenograft model without marked body-weight loss or apparent histopathological abnormalities under the tested conditions. These findings identify AT-11 as an early-stage chromeno[8,7-d]oxazole lead and extend the structure-activity basis for CDK16-directed inhibitor development.