Design, synthesis and biological evaluation of benzimidazole-rhodanine conjugates as potent topoisomerase II inhibitors

Abstract

In this study, a series of benzimidazole-rhodanine conjugates were designed, synthesized and investigated for their topoisomerase II (Topo II) inhibitory and cytotoxic activities. The results from Topo II-mediated pBR322 DNA relaxation and cleavage assays showed that the synthesized compounds might act as Topo II catalytic inhibitors. Certain compounds displayed potent Topo II inhibition at 10 μM. The cytotoxic activities of these compounds against HeLa, A549, Raji, PC-3, MDA-MB-201, and HL-60 cancer cell lines were evaluated. The results indicated that these compounds exhibited strong antiproliferative activity. A good relationship was observed between the Topo II inhibitory potency and the cytotoxicity of these compounds. The structure-activity relationship revealed that the electronic effects, the phenyl group, and the rhodanine moiety were particularly important for the Topo II inhibitory potency and cytotoxicity.

Fig. 1. Design of novel agents as potential Topo II-targeting anticancer agents.

Scheme 1. Synthesis route of the target compounds. Reagents and conditions: (a) glycolic acid, 4 N HCl, 100 °C, 6 h; (b) DMF, appropriate benzyl bromide, bromoethane or 2-bromo-1-phenylethanone, K₂CO₃, rt, 24 h; (c) DCM, Dess–Martin reagent, 4 °C, 1 h; (d) rhodanine moiety, NaOAc, acetic acid, 110 °C, 4 h.

Fig. 2. Chemical structure of the target compounds.

Fig. 3. Agarose gel assay for Topo II inhibition by the synthesized compounds. (A–D) Lane D, pBR322 DNA; lane T, pBR322 DNA + Topo II; lane E, pBR322 DNA + Topo II + etoposide (100 μM); other lanes, pBR322 DNA + Topo II + the synthesized compounds.

Fig. 4. Topo I inhibitory activity of the synthesized compounds. (A) and (B) Lane D: pBR322 DNA; lane T: pBR322 DNA + Topo I; lane C: pBR322 DNA + Topo I + camptothecin (100 μM); other lanes: pBR322 DNA + Topo I + the synthesized compounds (50 μM).

Fig. 5. (A) Effects of compounds 8g and 8j on Topo II-mediated DNA cleavage complex formation. Lanes 1 and 2: control group of supercoiled pBR322 DNA without or with Topo II; lanes 3–5, effects of etoposide (100 μM) and tested compounds (50 μM) on Topo II with DNA; lanes 6 and 7, pretreatment of the tested compounds (50 μM) antagonizes the etoposide (100 μM)-enhanced DNA cleavage. The positions of supercoiled DNA (S), relaxed DNA (R), linear DNA (L), and nicked DNA (N) are indicated. (B) The unwinding capacity of 8g and 8j. Lane D, pBR322 DNA; lane T, pBR322 DNA + Topo I; other lanes, pBR322 DNA + Topo I + 8g, 8j, or EB at different concentrations.

Fig. 6. Schematic representation of the proposed binding modes of 8g and 8j with the catalytic site of the ATPase domain of Topo II (PDB code:; 1ZXM) (A, compound 8g; B, compound 8j).