Benzimidazoles belong to a new class of bioreductive agents with cytotoxic activity towards solid
tumor cells, especially in their first stage of growth, which is characterized by low
oxygen concentration. Bioreductive agents represent a class of
prodrugs that target hypoxic
tumor cells. Their bioactivity depends on the reactivity of their functional chemical groups. Their efficacy requires metabolic reduction and subsequent generation of toxic
prodrugs. Chemoresistance of
tumor cells is a major problem for successful antitumor
therapy for many types of
tumors, especially for
breast cancer. The present study was performed to assess the effect of the antiproliferation activity of the tested
benzimidazoles by way of NF-κB expression inhibition. The activity of the tested compounds on T47D and MCF7 cells was examined by WST, western blot, NF-κB transactivation assay, and apoptotic cell population analysis. Compound 3 was highly cytotoxically active against T47D cells, especially in hypoxic conditions. Its IC50 of 0.31 ± 0.06 nM, although weaker than
tirapazamine, was significantly higher than the other tested compounds (2.4-3.0 fold). The increased
bax protein expression upon exposure to the tested compounds indicated intercellular apoptotic pathway activity, with
tumor cell death by way of apoptosis. Increased
bax protein synthesis and apoptotic cell dominance upon treatment, especially with N-
oxide derivatives (92% apoptotic cells among T47D cell populations during treatment with compound 3), were correlated with each other. Additionally, both increased
bax protein and decreased NF-κB
protein expression supported antiproliferative activity via NF-κB-
DNA binding inhibition associated with the tested compounds. Compound 3 appeared to be the strongest inhibitor of NF-κB expression in hypoxic conditions (the potency against NF-κB expression was about 75% of that of
tirapazamine). The present studies involving this class of heterocyclic small molecules proved their potential usefulness in anticancer
therapy as compounds be able to limit
tumor cell proliferation and reverse drug resistance by NF-κB repression.