The medication fenben, also known as Pancur or Safe-Guard, is an antiparasitic drug commonly used to treat parasites and worms (roundworms, hookworms, whipworms, and tapeworms) in dogs. In recent years, it has gained increasing popularity in the United States and elsewhere after a controversial video by veterinarian Andrew Jones went viral on Facebook and TikTok in 2019. In the videos, Jones claims that the dog dewormer cured his small-cell lung cancer, inspiring people to take fenben in an attempt to cure their own cancers as well.

Upon treatment with fenben, the number of EMT6 tumor cells in the lungs dropped significantly after just two treatments, but there was no difference in the time it took to grow each tumor from its initial volume to four times that volume after irradiation. Tumor growth was also rigorously compared between groups that received different medications and found that both fenbendazole alone or fenbendazole combined with radiation had no impact on tumor progression.

In vitro, fenbendazole reduced the clonogenicity of EMT6 cells by triggering autophagy via Beclin-1 expression. Western blot analysis of the same cells showed that fenbendazole increased LC3-I and LC3-II expression, and decreased GPX4 expression. In addition, fenbendazole triggered caspase-3-dependent apoptosis and ferroptosis in EMT6 cells.

These results show that fenbendazole triggers apoptosis in wild-type p53-dependent SNU-C5 CRC cells and 5-fluorouracil-resistant SNU-C5/5-FUR cells by activating the p53-p21 pathway and promoting mitochondrial injury. The anticancer activity of fenbendazole in 5-fluorouracil-resistant SNU-C5/5-FUR cancer cells is largely due to its ability to increase apoptosis and ferroptosis and partly by decreasing p53 expression and GPX4 expression.