Rheumatoid arthritis drug a potential targeted therapy for aggressive cancer

Mount Sinai researchers found that a rheumatoid arthritis drug shrinks breast cancer tumors in mice.

A mutation in the tumor-suppressing gene PTEN causes uncontrolled growth in several types of cancer. Mount Sinai researchers found an approved rheumatoid arthritis drug that stops this growth in its tracks and could be a possible new treatment for aggressive cancers.

PTEN mutations occur in many cancers, including the brain cancer glioblastoma, as well as lung, breast and prostate cancers. They modify a metabolic pathway in tumors, which accelerates DNA production and leads to the unchecked growth of the cancer.

The Mount Sinai team, led by Ramon Parsons, M.D., Ph.D., discovered that the drug leflunomide inhibits an enzyme in the pathway, which damages the DNA the pathway produces. This ends up destroying PTEN-mutant cancer cells while sparing healthy cells, according to the statement. Sanofi markets leflunomide as Arava.

To test the drug’s efficacy, the researchers transplanted human breast cancer cells into mice. Leflunomide “drastically” reduced the breast cancer tumors in the mice. The findings are published in Cancer Discovery.

A number of groups are studying PTEN to find new options for difficult-to-treat cancers. Earlier this year, Cold Spring Harbor scientists found that the protein Importin-11 protects the PTEN gene by transporting it into the nucleus of cells. They noticed that lung cancer patients with low levels of Importin-11 also lacked PTEN. Meanwhile, Ohio State researchers discovered that the enzyme PMRT5 blocked PTEN’s tumor-suppressing activity.

Mount Sinai's Parsons hopes to pit leflunomide against breast and colon cancer in a clinical trial. "Finding successful targeted therapies for cancer is a challenging but important goal in the face of insufficient treatment options," said Parsons in the statement. "Targeted therapies that are tumor-specific are much needed, and identifying changes based on specific tumor suppressor or oncogene alterations will facilitate this effort. Due to the high mutation rate of PTEN in cancer, the effects of PTEN could be at the heart of targeted therapy."