In our continuing search for novel small-molecule anticancer agents, we designed and synthesized a series of novel (E)-N'-(3-allyl-2-hydroxy)benzylidene-2-(4oxoquinazolin-3(4H)-yl)acetohydrazides ( 5), focusing on the modification of substitution in the quinazolin-4(3H)-one moiety. The biological evaluation showed that all 13 designed and synthesized compounds displayed significant cytotoxicity against three human cancer cell lines (SW620, colon cancer; PC-3, prostate cancer; NCI-H23, lung cancer). The most potent compound 5l displayed cytotoxicity up to 213fold more potent than 5-fluorouracil and 87-fold more potent than PAC-1, the first procaspase-activating compound. Structure-activity relationship analysis revealed that substitution of either electron-withdrawing or electron-releasing groups at positions 6 or 7 on the quinazolin-4(3H)-4-one moiety increased the cytotoxicity of the compounds, but substitution at position 6 seemed to be more favorable. In the caspase activation assay, compound 5l was found to activate the caspase activity by 291% in comparison to PAC-1, which was used as a control. Further docking simulation also revealed that this compound may be a potent allosteric inhibitor of procaspase-3 through chelation of the inhibitory zinc ion. Physicochemical and ADMET calculations for 5l provided useful information of its suitable absorption profile and some toxicological effects that need further optimization to be developed as a promising anticancer agent.

Two series of novel 4-oxoquinazoline-based N-hydroxypropenamides (9a–m and 10a–m) were designed, synthesized, and evaluated for their inhibitory and cytotoxicity activities against histone deacetylase (HDAC). The compounds showed good to potent HDAC inhibitory activity and cytotoxicity against three human cancer cell lines (SW620, colon; PC-3, prostate; NCI-H23, lung cancer). In this series, compounds with the N-hydroxypropenamide functionality impeded at position 7 on the 4-oxoquinazoline skeleton (10a–m) were generally more potent than compounds with the N-hydroxypropenamide moiety at position 6 (9a–m). Also, the N 3-benzyl-substituted derivatives (9h–m, 10h–m) exhibited stronger bioactivity than the N 3-alkyl-substituted ones (9a–e, 10a–e). Two compounds 10l and 10m were the most potent ones. Their HDAC inhibitory activity (IC50 values, 0.041–0.044 μM) and cytotoxicity (IC50 values, 0.671–1.211 μM) were approximately 2- to 3-fold more potent than suberoylanilide hydroxamic acid (SAHA). Some compounds showed up to 10-fold more potent HDAC6 inhibition compared to their inhibitory activity in total HDAC extract assay. Analysis of selected compounds 10l and 10m revealed that these compounds strongly induced both early and late apoptosis and arrested SW620 cells at the G2/M phase. Docking studies were carried out on the HDAC6 isoform for series 10a–m and revealed some important features contributing to the inhibitory activity of synthesized compounds.