Glioblastoma multiforme (GBM), the most common type of malignant brain tumor, has a very high mortality rate, due in part to poor responses to chemotherapy. Treatment of GBM requires anti-cancer agents to cross the blood-brain barrier (BBB), the biological membrane that protects the brain and other parts of the central nervous system from pathogens and toxins in the blood. While the BBB serves an important protective function, it also presents challenges to drug delivery.