Fenbendazole (Sigma, St Louis, MO) is an antihelmintic drug used to treat rodent pinworm infections. It is also known to inhibit cancer cell growth and has a chemical structure similar to that of hypoxia-selective nitroheterocyclic cytotoxins and radiosensitizers. Its cytotoxic activity is enhanced by oxygen deprivation and can be used to inhibit the growth of lymphoma tumors in SCID mice. The effect of fenbendazole on the radiation sensitivity of EMT6 cells in vitro was examined using a colony formation assay and showed a dose-response curve with a steep decrease in cell numbers at low drug concentrations followed by a plateau.
Neither diet alone nor fenbendazole in the diet caused significant inhibition of tumor growth. When the diet was supplemented with both fenbendazole and vitamins, however, tumor growth was significantly reduced. This synergy was not observed in other tumor models. No local invasion into the surrounding tissues nor lymph node metastases were seen on necropsy for any of the fenbendazole-treated groups of animals. Moreover, fenbendazole treatment did not alter the number of spontaneous lung metastases that were seen in control mice.
It was speculated that the lack of a greater reduction in tumor growth in the fenbendazole-plus-vitamin group could have been due to the fact that the vitamin concentrates in the prepared diets were close to their expiration date at the time of this experiment and therefore contained lower concentrations than during the initial observation. Nonetheless, the results are consistent with the hypothesis that this class of compounds can enhance the radiation sensitivity of certain cancer cells and deserve further study. sanare lab fenbendazole