Fenbendazole is a broad-spectrum benzimidazole anthelmintic drug that has shown anticancer activity in several animal models and inhibits microtubule-associated tubulin polymerization in human cancer cells. The drug has low toxicity and tolerability in mammals, but its potential as an anticancer agent has been limited by its relatively high IC50 in normal mammalian cells. This study investigated the effect of fenbendazole in combination with hypoxia-selective nitroheterocyclic chemotherapeutic agents. We used EMT6 mammary carcinoma cells in cell culture and a mouse model of solid tumors to evaluate the cytotoxic effects of fenbendazole, oxfendazole, or mebendazole alone or in combinations with radiation and docetaxel. EMT6 cell growth was a sensitive indicator of cytotoxicity, and the addition of fenbendazole to radiation or chemotherapy regimens significantly enhanced their toxicity. The sensitivity of the cells to fenbendazole was not diminished by hypoxia or by a prior treatment with oxfendazole, mebendazole, or a cyclin-dependent chemotherapeutic agent, indicating that this drug has anticancer activity in the presence of hypoxia and that its mechanism of action is independent of the inhibition of cellular microtubules.
The benzimidazole drugs are poorly absorbed from the digestive tract after oral administration and are converted to their active metabolites, oxfendazole and mebendazole, in the liver. Because of this, the pharmacodynamics of these drugs are relatively rapid in mammals, and a recent phase 1 clinical trial showed that mebendazole is safe and tolerable in healthy volunteers at doses up to 100 mg/kg/day [1]. Oxifendazole, an activated metabolite of mebendazole, was also found to be well tolerated in patients with advanced genitourinary malignancies in a small pilot study.
Hypoxia is known to potentiate the cytotoxic activity of taxanes and other chemotherapeutic agents. However, little is known about how the activity of these agents is altered by their interaction with oxygen in vivo.
Cancer cells use glucose for energy and are therefore sensitive to the inhibition of cellular metabolism by benzimidazole compounds. To determine whether fenbendazole affects glucose uptake in cancer cells, we treated H460 and A549 human colon cancer cells with either vehicle or a 2 mM concentration of fenbendazole for 24 h. Survival of the cells was assayed by a colony formation assay. The results were compared with those of cells treated with graded doses of docetaxel for 2 h in the absence or presence of fenbendazole. The relative surviving fractions (yield-corrected SF) were superimposed on the survival curves, showing that fenbendazole and docetaxel produced additive cytotoxicity.
To investigate the effects of fenbendazole on hypoxic cell growth, cultures were made hypoxic by sealing the culture bottles with rubber gaskets, inserting needles for influx and efflux of gases, and gassing the vessels with a mixture of 95% nitrogen and 5% carbon dioxide containing 1 ppm oxygen. The cultures were then treated with fenbendazole or the vehicle, sealed and transported to an irradiator, and irradiated. Cell lysates were harvested for protein quantification and Western blot analysis, and protein expression was analyzed by chemoluminescent immunohistochemistry. The data indicated that fenbendazole reduced the viability of irradiated cancer cells in hypoxia, but did not affect normal colonic cells. fenbendazole for humans cancer