Scientists have found that a 70-year-old malaria drug can block immune cells in the liver so nanoparticles can arrive at their intended tumour site, overcoming a significant hurdle of targeted drug delivery. Many cancer patients do not respond to chemotherapy because the drugs never reach the cancer cells. Even in nanomedicine, only about 1% of a dose of nanoparticles will successfully arrive at the intended tumour site, while the rest are filtered out by the immune cells of the liver and spleen.

However, using the drug chloroquine not only increased the circulation of nanoparticles in the body but also reduced the body’s filtration of nanoparticles, as well as improved drug delivery to breast tumours, the researchers said. The research, led by Mauro Ferrari, nanoscientist at the Houston Methodist Research Institute in the US, showed that chloroquine interfered with immune cells called macrophages, which are used by the body to identify microscopic foreign objects and destroy them. For the study, published in the journal Scientific Reports, the team injected mice with chloroquine and followed it by an injection of nanoparticles.

Chloroquine decreased the macrophages’ ability to clean up the nanoparticles. The findings are significant because the nanoparticles not only remained in circulation but also accumulated in mouse tumours, as well as in the lungs of healthy mice, suggesting that the approach also may enhance treatment for lung diseases, the researchers noted.

Chloroquine was invented in the 1940s for the prevention and treatment of malaria. Since it mildly suppresses the immune system, the drug is also used in some autoimmune disorders, such as rheumatoid arthritis and lupus.