In Vivo and Mechanistic Studies on Antitumor Lead 7‑Methoxy-4-(2-methylquinazolin-4-yl)-3,4-dihydroquinoxalin-2(1H)‑one and Its Modification as a Novel Class of Tubulin-Binding Tumor-Vascular Disrupting Agents

7-Methoxy-4-(2-methylquinazolin-4-yl)-3,4-dihydroquinoxalin-2­(1H)-one (2), a promising anticancer lead previously identified by us, inhibited tumor growth by 62% in mice at 1.0 mg/kg without obvious signs of toxicity. Moreover, compound 2 exhibited extremely high antiproliferative activity in the NIH-NCI 60 human tumor cell line panel, with low to sub-nanomolar GI₅₀ values (10^–10 M level). It also showed a suitable balance between aqueous solubility and lipophilicity, as well as moderate metabolic stability in vivo. Mechanistic studies using Mayer’s hematoxylin and eosin and immunohistochemistry protocols on xenograft tumor tissues showed that 2 inhibited tumor cell proliferation, induced apoptosis, and disrupted tumor vasculature. Moreover, evaluation of new synthetic analogues (6a–6t) of 2 indicated that appropriate 2-substitution on the quinazoline ring could enhance antitumor activity and improve druglike properties. Compound 2 and its analogues with a 4-(2-methylquinazolin-4-yl)-3,4-dihydroquinoxalin-2­(1H)-one scaffold thus represent a novel class of tubulin-binding tumor-vascular disrupting agents (tumor-VDAs) that target established blood vessels in tumors.