An experimental drug appears to cross a protective barrier in the brain that screens out most chemicals, offering potentially better ways to treat brain tumors, U.S. researchers said on Sunday.

The drug, made by privately held Angiochem Inc of Montreal was safe and showed evidence it could shrink tumors in two separate early phase studies totaling more than 100 people with a brain cancer called glioblastoma.

It also worked among people whose cancers had spread or metastasized to the brain, the researchers reported at the annual meeting of the Society for Neuroscience in Chicago.

In both studies, tumors shrank in patients who got a higher dose of the drug, called ANG1005. The drug also showed signs of working in patients whose cancers resisted the chemotherapy drug taxane.

"It is highly encouraging to see that ANG1005 has shown the potential to be effective in metastatic brain cancers and against drug-resistant tumors," Dr. Jan Drappatz of Dana-Farber Cancer Institute and Brigham and Women's Hospital in Boston, who is studying the drug, said in a statement.

Drappatz said tumors shrank significantly in some patients and some neurological problems were reversed in several.

Studies of brain tumor samples showed concentrations of the drug in the tumors, proving it successfully crossed the blood-brain barrier and accumulated.

Made up of a network of blood vessels, the blood-brain barrier prevents 95 percent of all chemicals from leaving the bloodstream and entering the brain.

It protects the brain from harmful chemicals, bacteria and other substances. But it also presents major challenges for treating disease in the brain, such as Alzheimer's or cancers -- which must typically be treated by surgery and radiation.

To cross this barrier, the Angiochem drug hijacks a protein called low-density lipoprotein receptor-related protein that is commonly found on the surface of the blood-brain barrier.

"The development of novel ways to cross the blood-brain barrier has considerable potential for treating a host of debilitating and prevalent diseases and disorders," Dr. John Kessler of Northwestern University said in a statement.