Common antiparasitic drug shows promise in halting growth of aggressive skin cancer

A common pinworm medication may stop and reverse cancer growth in Merkel cell carcinoma, an aggressive form of skin cancer, according to research led by University of Arizona Cancer Center researchers and published in the Journal of Clinical Investigation.

Merkel cell carcinoma is a rare but fast-growing neuroendocrine cancer that is three to five times more likely than melanoma to be deadly. Response rates to current therapies—surgery, radiation and immunotherapy—are limited, resulting in a need for effective and broadly applicable therapeutics.

“Merkel cell carcinoma is increasing in incidence,” said senior author Megha Padi, Ph.D., a U of A Cancer Center member and an assistant professor in the U of A College of Science. “Even though it’s a rare cancer type, it mimics a lot of properties that other cancers have.”

Pyrvinium pamoate, a medication approved by the Food and Drug Administration in 1955 to treat pinworms, has been shown to have antitumor potential in several different cancers, including breast, colorectal, pancreatic and bladder cancers. This is the first time it has been studied in models of Merkel cell carcinoma.

Padi and the research team found that in laboratory models of Merkel cell carcinoma, pyrvinium pamoate inhibited cancer cell growth and reversed the cancer’s neuroendocrine features. In mouse models of Merkel cell carcinoma, pyrvinium pamoate reduced tumor growth.

“This is a hypothesis, but some people think the reason an antiparasitic agent could be effective against cancers is because tumors are a little bit like parasites in our body,” Padi said.

“Parasites and tumors must develop ways to use scarce resources in their host to feed themselves and allow for unlimited multiplication. If the pathways that they have hijacked to feed themselves are the same, then you get lucky, and you have a tumor type that could be amenable to killing by these antiparasitic drugs.”

Padi and the research team chose to test pyrvinium pamoate after identifying the Wnt signaling pathway as one of the molecular mechanisms that drives the transition of normal cells into Merkel cell carcinoma. Pyrvinium pamoate is a known Wnt pathway inhibitor.

Further research is needed to optimize treatment protocols for the development of pyrvinium pamoate as a clinically useful medication for Merkel cell carcinoma.