Design, Synthesis, and Anti-tumor Activity of Novel 2-Aryl Benzimidazole Compounds

Combretastatin A-4 (CA-4) is a natural product isolated from the bark of the South African bush willow tree Combretum caffrum, which exerts tubulin inhibition, but its clinical application is limited due to poor stability and water solubility. 2-aryl benzimidazoles are excellent pharmacological skeletons with many activities, especially in tumor inhibition, and better pharmacokinetic properties. Several scaffold CA-4 analogs have been synthesized to date possessing antitumor activities.

The benzimidazole was applied as the core moiety to replace the B ring and unstable linkage of CA-4, and the 5-aryl acetenyl group was introduced to improve the antitumor activity. MCF-7, A549, Caco-2, Siha, and Eca-109 tumor cell lines were used to study inhibition by these agents in vitro.

The benzimidazole structure was constructed from the oxidation of o-nitroaniline and aldehyde and the following schemes, and the structural characterization was carried out. The antitumor effects were evaluated in vitro through MTT assay, cell cycle arrest, and apoptosis assay. Molecular docking with tubulin (Protein ID: 1SA0) was analyzed for the structure-activity relationship.

Among these derivatives, 4a-4h series (with 6-methoxy group) compounds inhibited the tumor cell lines much stronger than the CA-4 and cisplatin, especially compound 4f showed prominently inhibitory activity in Siha cell with IC₅₀ value as 0.61 μmol/L. The further assay showed that the cell cycle was arrested at the G₀/G₁ phase as well verified in apoptosis assay. Molecular docking indicated that 4f had stronger affinity energy and hydrogen bond than CA-4.

The compound 4f has the potency to be used as an anti-tubulin agent and the 2-trimethoxyphenyl benzimidazole skeleton deserves further study as an antitumor structure.