A common and widely used antihelminthic drug, fenbendazole, has been claimed by some to have anti-cancer effects. Although a number of peer-reviewed studies using cancer cells in petri dishes and mice have shown some promising results, there is no evidence that fenbendazole cures cancer in humans. In addition, many of these reports are based on anecdotal stories from people who say they have been cured by taking fenbendazole. However, these cases are often not properly investigated and may be misleading.
A benzimidazole antibiotic, fenbendazole is used to treat parasites in animals and is well-tolerated in humans at the recommended dosage. It has been shown to have anti-inflammatory and immunosuppressive properties, and has also been reported to have cytostatic (antiproliferative) activities in various tumors.
In this article, we discuss the findings of several recent experiments examining fenbendazole’s effect on cancer cell growth and radiation resistance. In addition, we explain why these results do not support the claim that fenbendazole is an effective treatment for cancer.
The first experiment examined whether fenbendazole could suppress the growth of EMT6 colorectal cancer cells in vitro. In this experiment, fenbendazole was added to EMT6 cells at concentrations close to the cellular IC50 value for fenbendazole (0.5 mM for SNU-C5 and 5 mM for SNU-C5/5-FUR). This treatment significantly inhibited the proliferation of the EMT6 cells.
This finding was subsequently confirmed in a series of experiments examining the effect of fenbendazole on the sensitivity of EMT6 cells to radiation and the chemotherapy agent docetaxel. In these experiments, cultures were grown in glass culture bottles that were made hypoxic by sealing them with rubber gaskets and inserting needles for the influx and efflux of oxygen, before treating the cultures with graded doses of docetaxel and/or 10 mM fenbendazole for 2 h. The relative surviving fractions were calculated by comparing the clonogenicity of the untreated control cultures to those of the cultures treated with docetaxel and fenbendazole.
In the next set of experiments, the growth of EMT6 tumors was monitored in the presence or absence of three daily injections of fenbendazole given i.p. The growth of the untreated tumors was not affected by fenbendazole, and this result was confirmed in a second experiment in which the same three fenbendazole treatments were given one day before, two hours before, and one day after irradiation of the EMT6 tumors. In both experiments, when the tumors reached a volume of 1000 mm3, the mice were euthanized and the tumors were removed and evaluated. The Table below shows that the growth of irradiated tumors was not altered by fenbendazole treatment, and that this effect was augmented by docetaxel.
The growth of unirradiated EMT6 tumors was not altered by fenbendazole and, in fact, was enhanced by the combined action of irradiation and fenbendazole. This result is consistent with our earlier experiment, in which irradiation of the EMT6 xenografts was significantly improved by the combination of fenbendazole and the taxane paclitaxel. This observation is also in accord with data from a recent meeting presentation, which showed that high concentrations of fenbendazole significantly inhibited the growth of paclitaxel-resistant ovarian carcinoma cells.fenbendazole for cancer
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