Improved Nanoparticles Designed to Deliver Drugs into Brain

Scientists have reported they are closer to having a drug-delivery system adaptable enough to overcome some major challenges posed by brain cancer and possibly other disorders affecting that organ.

In a report published online on August 29, 2012, in the journal Science Translational Medicine, the Johns Hopkins University (JHU; Baltimore, MD, USA) investigators reported that its bioengineers have devised nanoparticles that can safely and predictably infiltrate deep into the brain when evaluated in lab rat and human tissue.

“We are pleased to have found a way to prevent drug-embedded particles from sticking to their surroundings so that they can spread once they are in the brain,” said Justin Hanes, PhD, a professor of ophthalmology, with secondary appointments in chemical and biomolecular engineering, biomedical engineering, oncology, neurological surgery, and environmental health sciences, and director of the Johns Hopkins Center for Nanomedicine.

After surgery to remove a brain tumor, standard treatment protocols include the application of chemotherapy directly to the surgical site to destroy any cells left behind that could not be surgically removed. Up to now, this technique of preventing tumor recurrence is only somewhat effective, in part, because it is difficult to administer a dose of chemotherapy high enough to adequately penetrate the tissue to be effective and low enough to be safe for the patient and healthy tissue.

To overcome this dosage challenge, engineers designed nanoparticles--about one-thousandth the diameter of a human hair--that deliver the drug in small, gradual quantities over a period of time. Traditional drug-delivery nanoparticles are made by entrapping drug molecules together with microscopic, string-like molecules in a tight ball, which slowly breaks down when it comes in contact with water. According to Charles Eberhart, MD, a Johns Hopkins pathologist and contributor to this work, these nanoparticles historically have not worked very well because they stick to cells at the application site and tend to not migrate deeper into the tissue.

Elizabeth Nance, a graduate student in chemical and biomolecular engineering at Hopkins, and Hopkins neurosurgeon Graeme Woodworth, MD, suspected that drug penetration might be improved if drug-delivery nanoparticles interacted minimally with their environment. Ms. Nance first coated nanosized plastic beads with a clinically tested molecule called PEG (polyethyleneglycol), that had been shown by others to protect nanoparticles from the body’s defense mechanisms. The team thought that a dense layer of PEG might also make the beads more slippery.

The researchers then injected the coated beads into slices of rodent and human brain tissue. They first labeled the beads with glowing tags that enabled them to visualize the beads as they moved through the tissue. Compared to non-PEG-coated beads, or beads with a less dense PEG coating, they found that a dense coating of PEG allowed larger beads to penetrate the tissue, even those beads that were nearly twice the size earlier believed to be the maximum possible for penetration within the brain. They then tested these beads in live rodent brains and found the same results.

The researchers then took biodegradable nanoparticles carrying the chemotherapy drug paclitaxel and coated them with PEG. As expected, in rat brain tissue, nanoparticles without the PEG coating moved very little, while PEG-covered nanoparticles distributed themselves quite well.

“It’s really exciting that we now have particles that can carry five times more drug, release it for three times as long and penetrate farther into the brain than before,” said Ms. Nance. “The next step is to see if we can slow tumor growth or recurrence in rodents.”

Dr. Woodworth added that the team “also wants to optimize the particles and pair them with drugs to treat other brain diseases, like multiple sclerosis, stroke, traumatic brain injury, Alzheimer’s and Parkinson’s.”

Another objective for the investigators is to be able to administer their nanoparticles intravenously, for which research has already begun.

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