Repurposed Drugs for Cancer

by | Feb 10, 2023 | Articles, Cancer, Conditions

Many drugs have “pleotropic” properties, meaning they have actions other than those for which the agent was specifically developed.  While the quest for better treatments for cancer is ongoing, there is still a large unmet need and increasing interest in the potential of existing drugs and natural substances for their possible pleotropic role in cancer treatment.

The “repurposing” of old medications comes about given the shortcomings of existing chemotherapy options, the high cost and time input for new drug development, and the need for more tumor specific therapies.  Drugs such as ivermectin, fenbendazole, metformin, doxycycline, and others that have a history of known safety and efficacy for other conditions may prove to be valuable additions to conventional cancer therapies.

Note these drugs are not FDA approved to treat cancer.  There may be only a few, or no clinical trials to date that confirm their safety and efficacy as anticancer drugs for humans.  The information in this article is for education purposes only.


Ivermectin is well known as an incredibly safe and effective drug for treating gastrointestinal parasitic nematodes, lungworms, lice, and mange, but it may also hold potential for treating cancer.  The story of Ivermectin starts with its origin from a soil sample from the south east coast of Honshu, Japan.  In 1970, microbiologist Satoshi Omura collected the soil and isolated an unknown species of Streptomyces bacterium.  He sent the sample to an an Irish biologist and parasitologist named Dr William Campbell who worked at Merck.  Dr Campbell noted the cultures show potent anti-parasitic effects against roundworms and isolated the active compounds.  He gave these compounds the name avermectins due to the “averminous” lack of worms that resulted.  One of the best synthetic derivatives of the naturally occurring avermectins turned out to be Ivermectin.

By the 1980s Ivermectin was being used within the veterinary realm as the largest selling animal health product in the world.  Also during this time another Merck researcher, Dr. Mohammed Aziz, helped develop a program to donate Ivermectin for treating a devastating disease called river blindness that plagued remote communities in Africa and Latin America.  In collaboration with the World Health Organization the drug continues to be distributed to these regions in an effort to completely eliminate river blindness as well as elephantiasis.  In 1987, Merck committed to donate Ivermectin – as much as needed, for as long as needed – with the goal to help eliminate river blindness.  At this time more than 4 billion doses have been given to people in 49 countries.

Satoshi Omura and William Campbell won the 2015 Nobel Prize in Physiology or Medicine for the discovery of the excellent efficacy of ivermectin against parasitic diseases.

Ivermectin as an Anti Cancer Drug

In recent years Ivermectin has been examined for its anticancer potential.  Ivermectin has been shown in laboratory research to be effective against a wide variety of cancers through multiple mechanisms, including:

  • Inhibiting tumor cell proliferation via
    • increased programmed cell death through apoptosis, autophagy and pyroptosis
    • influcence on multipl molecular targets and signaling pathways
  • Decreasing angiogenesis and metastases
  • Enhancing conventional drug activity and reducing multi-drug resistance

Ivermectin, a potential anticancer drug derived from an antiparasitic drug


Fenbendzaole, commonly known as Fenben, is a broad spectrum anti-parasitic drug widely used in veterinary medicine

Fenbendazole acts as a moderate microtubule destabilizing agent and causes cancer cell death by modulating multiple cellular pathways

“The results, in conjunction with our earlier data, suggest that FZ is a new microtubule interfering agent that displays anti-neoplastic activity and may be evaluated as a potential therapeutic agent because of its effect on multiple cellular pathways leading to effective elimination of cancer cells.”


The beneficial effects of metformin on cancer prevention and therapy: a comprehensive review of recent advances

“Therefore, this drug can be used as a complementary therapeutic agent for cancer treatment and prevention.  In this review, we have summarized the data from various experimental and clinical studies and highlight the possible potential effects of metformin on cancer therapeutic responses.”




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