Potent anticancer drug isolated from weed

Washington - Scientists have isolated a potent anticancer compound from a Mediterranean weed that acts like 'molecular grenade'.

In lab studies, researchers said they found that a three-day course of the drug called G202 reduced the size of human prostate tumours grown in mice by an average of 50 percent within 30 days.

G202 outdid the chemotherapy drug docetaxel, reducing seven of nine human prostate tumours in mice by more than 50 percent in 21 days. Docetaxel reduced one of eight human prostate tumours in mice by more than 50 percent in the same time period, the journal Science Translational Medicine reports.

Researchers from the Johns Hopkins Kimmel Cancer Centre and Denmark also reported that G202 produced at least 50 percent regression in models of human breast cancer, kidney cancer and bladder cancer, according to a Johns Hopkins statement

Based on these results, Johns Hopkins physicians have performed a phase I clinical trial to assess safety of the drug and have thus far treated 29 patients with advanced cancer. Besides, the University of Wisconsin and the University of Texas San Antonio are participating in the trial. A phase II trial to test the drug in patients with prostate cancer and liver cancer is planned.

The drug G202 is chemically derived from a weed called Thapsia garganica that grows naturally in the Mediterranean region. The plant makes a product, dubbed thapsigargin, that since the time of ancient Greece has been known to be toxic to animals.

"Our goal was to try to re-engineer this very toxic natural plant product into a drug we might use to treat human cancer," says Samuel Denmeade, professor of oncology, urology, pharmacology and molecular sciences, who led the study. "We achieved this by creating a format that requires modification by cells to release the active drug."

The drug can be injected and can travel through the bloodstream until it finds the site of cancer cells and hits a protein called prostate-specific membrane antigen (PSMA).

PSMA is released by cells lining tumours of the prostate and other areas, and in effect "pulls the pin" on G202, releasing cell killing agents into the tumour and the blood vessels that feed it, as well as to other cells in the vicinity.