X‑ray Crystallography-Guided Design, Antitumor Efficacy, and QSAR Analysis of Metabolically Stable Cyclopenta-Pyrimidinyl Dihydroquinoxalinone as a Potent Tubulin Polymerization Inhibitor

Small molecules that interact with
the colchicine binding site
in tubulin have demonstrated therapeutic efficacy in treating cancers.
We report the design, syntheses, and antitumor efficacies of new analogues
of pyridopyrimidine and hydroquinoxalinone compounds with improved
drug-like characteristics. Eight analogues, 5j, 5k, 5l, 5m, 5n, 5r, 5t, and 5u, showed significant
improvement in metabolic stability and demonstrated strong antiproliferative
potency in a panel of human cancer cell lines, including melanoma,
lung cancer, and breast cancer. We report crystal structures of tubulin
in complex with five representative compounds, 5j, 5k, 5l, 5m, and 5t,
providing direct confirmation for their binding to the colchicine
site in tubulin. A quantitative structure–activity relationship
analysis of the synthesized analogues showed strong ability to predict
potency. In vivo, 5m (4 mg/kg) and 5t (5 mg/kg) significantly inhibited tumor growth as well
as melanoma spontaneous metastasis into the lung and liver against
a highly paclitaxel-resistant A375/TxR xenograft model.