Fenbendazole is an antihelmintic drug used to treat gastrointestinal parasites including pinworms, giardia, roundworms, hookworms, and Taenia solium. It is also used in some animals, such as cattle and dogs, to treat parasitic tapeworms and pulmonary paragonimiasis. Despite the fact that it is not intended for human use, the anecdotal account of Joe Tippens — an American diagnosed with cancer and who claims his tumor went into remission after taking fenbendazole on a veterinarian’s recommendation — has gained widespread traction on social media. The story was even reported in popular TikTok videos, which have millions of views. However, as the nonprofit organization Cancer Research UK told Full Fact, there is insufficient evidence to support Tippens’ claim that fenbendazole cures cancer.
Benzimidazoles, which include fenbendazole, are known to bind beta-tubulin, disrupt microtubules, and arrest cell division. The mechanism of action involves a complex interplay between the cell cycle machinery and mitotic spindles. These effects are attributed to the disruption of the adenosine triphosphate (ATP) cycle and inhibition of the formation of new microtubules [1,2].
The antiparasitic activity of benzimidazoles has made them attractive candidates for repurposing as an anticancer drug, and several studies have been conducted to determine whether fenbendazole has anticancer properties in cancer cells. In one study, fenbendazole significantly inhibited the growth of colorectal cancer cells in vitro. In addition, it induced autophagy, which is an important mechanism of resistance to chemotherapy drugs. This was due to the ability of fenbendazole to increase Beclin-1 expression in the cells. Moreover, it activated the caspase-8-dependent apoptosis pathway in cells by suppressing the expression of SLC7A11 and GPX4, which is involved in ferroptosis.
More recently, fenbendazole has been shown to induce apoptosis in hepatocellular carcinoma cells in vivo and in vitro. In addition, it has been shown to bind and block adenosine triphosphate in cancer cells. Its anticancer effects may be mediated by its binding to ATP and its inhibition of the adenosine triphosphate cycle, as well as its ability to promote autophagy.
However, the clinical relevance of fenbendazole for humans is questionable because it has not been tested for safety and tolerability in patients. Although fenbendazole is highly absorbed and reaches high concentrations in the bloodstream, it is quickly metabolized to its active metabolites, oxfendazole and fenbendazole sulfone, in the intestines, where it has the most potent biological activity. In addition, oxfendazole and its metabolites are known to be excreted into the urine, where they are readily eliminated by the body. Therefore, a phase 1 clinical trial to assess the safety and optimal dose of fenbendazole in healthy volunteers is required. The results should help guide the development of a safe and effective therapeutic strategy for fenbendazole for human cancer.