US researchers have modified a drug used to treat parasitic infections that reduced pain sensitivity and endometriosis-like lesions in mice, offering a potential alternative to hormone-based treatments and surgery. 

Endometriosis affects around one in ten women worldwide and occurs when tissue similar to the lining of the uterus grows elsewhere in the body, causing inflammation, pain and scar tissue. Current treatments include surgery and hormone therapy, but lesions can return after surgery, while hormonal treatments can affect fertility and potentially cause severe side effects. 

Researchers from Washington State University, Washington, had previously found that niclosamide, a drug used to treat tapeworm infections, could reduce the growth of endometriosis-like lesions in mice. However, the drug dissolves poorly in water, limiting its absorption. To overcome this, the team attached niclosamide to a tiny, water-soluble carrier called a dendrimer. They also added folic acid, which binds to the surface of macrophages, immune cells involved in the development of endometriosis lesions, helping direct the drug towards these cells. 

To test the treatment, researchers injected fragments of uterine lining tissue into the abdominal cavities of anaesthetised female mice. After a single injection of the modified drug, mice developed fewer and smaller lesions and showed reduced sensitivity to pain compared with control animals. The drug remained inside the macrophages for at least two weeks, raising the possibility of future treatments being administered at intervals of several weeks. 

“Although we still need to clear multiple phases, this study is telling us the efficacy is strong, and this nanocarrier is stable, so far, for two weeks—and we think we can go longer,” said Kanako Hayashi, professor at the Washington State University and lead author of the study published in Advanced Healthcare Materials.