Posted on by Lawrence Tabak, D.D.S., Ph.D.
The human brain is profoundly complex, consisting of tens of billions of neurons that form trillions of interconnections. This complex neural wiring that allows us to think, feel, move, and act is surrounded by what’s called the blood-brain barrier (BBB), a dense sheet of cells and blood vessels. The BBB blocks dangerous toxins and infectious agents from entering the brain, while allowing nutrients and other essential small molecules to pass right through.
This gatekeeping function helps to keep the brain healthy, but not when the barrier prevents potentially life-saving drugs from reaching aggressive, inoperable brain tumors. Now, an NIH-funded team reporting in the journal Nature Materials describes a promising new way to ferry cancer drugs across the BBB and reach the sites of disease . While the researchers have not yet tried this new approach in people, they have some encouraging evidence from studies in mouse models of medulloblastoma, an aggressive brain cancer that’s diagnosed in hundreds of children each year.
The team, including Daniel Heller, Memorial Sloan Kettering Cancer Center, New York, NY, and Praveen Raju, Icahn School of Medicine at Mount Sinai, New York, NY, wanted to target a protein called P-selectin. The protein is found on blood vessel cells at sites of infection, injury, or inflammation, including cancers. The immune system uses such proteins to direct immune cells to the places where they are needed, allowing them to exit the bloodstream and enter other tissues.
Heller’s team thought they could take advantage of P-selectin and its molecular homing properties as a potential way to deliver cancer drugs to patients. But first they needed to package the drugs in particles tiny enough to stick to P-selectin like an immune cell.
That’s when they turned to a drug-delivery construct called a nanoparticle, which can have diameters a thousand times smaller than that of a human hair. But what’s pretty unique here is the nanoparticles are made from chains of sugar molecules called fucoidan, which are readily extracted from a type of brown seaweed that grows in Japan. It turns out that this unlikely ingredient has a special ability to attract P-selectin.
In the new study, the researchers decided to put their novel fucoidan nanoparticles to the test in the brain, while building on their previous animal work in the lungs . That work showed that when fucoidan nanoparticles bind to P-selectin, they trigger a process that shuttles them across blood vessel walls.
This natural mechanism should also allow nanoparticle-packaged substances in the bloodstream to pass through vessel walls in the BBB and into the surrounding brain tissue. The hope was it would do so without damaging the BBB, a critical step for improving the treatment of brain tumors.
In studies with mouse models of medulloblastoma, the team loaded the nanoparticles with a cancer drug called vismodegib. This drug is approved for certain skin cancers and has been tested for medulloblastoma. The trouble is that the drug on its own comes with significant side effects in children at doses needed to effectively treat this brain cancer.
The researchers found that the vismodegib-loaded nanoparticles circulating in the mice could indeed pass through the intact BBB and into the brain. They further found that the particles accumulated at the site of the medulloblastoma tumors, where P-selectin was most abundant, and not in other healthy parts of the brain. In the mice, the approach allowed the vismodegib treatment to work better against the cancer and at lower doses with fewer side effects.
This raised another possibility. Radiation is a standard therapy for children and adults with brain tumors. The researcher found that radiation boosts P-selectin levels specifically in tumors. The finding suggests that radiation targeting specific parts of the brain prior to nanoparticle treatment could make it even more effective. It also may help to further limit the amount of cancer-fighting drug that reaches healthy brain cells and other parts of the body.
The fucoidan nanoparticles could, in theory, deliver many different drugs to the brain. The researchers note their promise for treating brain tumors of all types, including those that spread to the brain from other parts of the body. While much more work is needed, these seaweed-based nanoparticles may also help in delivering drugs to a wide range of other brain conditions, such as multiple sclerosis, stroke, and focal epilepsy, in which seizures arise from a specific part of the brain. It’s a discovery that brings new meaning to the familiar adage that good things come in small packages.
 P-selectin-targeted nanocarriers induce active crossing of the blood-brain barrier via caveolin-1-dependent transcytosis. Tylawsky DE, Kiguchi H, Vaynshteyn J, Gerwin J, Shah J, Islam T, Boyer JA, Boué DR, Snuderl M, Greenblatt MB, Shamay Y, Raju GP, Heller DA. Nat Mater. 2023 Mar;22(3):391-399.
 P-selectin is a nanotherapeutic delivery target in the tumor microenvironment. Shamay Y, Elkabets M, Li H, Shah J, Brook S, Wang F, Adler K, Baut E, Scaltriti M, Jena PV, Gardner EE, Poirier JT, Rudin CM, Baselga J, Haimovitz-Friedman A, Heller DA. Sci Transl Med. 2016 Jun 29;8(345):345ra87.
Medulloblastoma Diagnosis and Treatment (National Cancer Institute/NIH)
Brain Basics: Know Your Brain (National Institute of Neurological Disorders and Stroke/NIH)
The Daniel Heller Lab (Memorial Sloan Kettering Cancer Center, New York, NY)
Praveen Raju (Mount Sinai, New York, NY)
NIH Support: National Cancer Institute; National Institute of Neurological Disorders and Stroke
Posted on by Dr. Francis Collins
Nanoparticles hold great promise for delivering next-generation therapeutics, including those based on CRISPR gene editing tools. The challenge is how to guide these tiny particles through the bloodstream and into the right target tissues. Now, scientists are enlisting some surprising partners in this quest: magnetic bacteria!
First a bit of background. Discovered in the 1960s during studies of bog sediments, “magnetotactic” bacteria contain magnetic, iron-rich particles that enable them to orient themselves to the Earth’s magnetic fields. To explore the potential of these microbes for targeted delivery of nanoparticles, the NIH-funded researchers devised the ingenious system you see in this fluorescence microscopy video. This system features a model blood vessel filled with a liquid that contains both fluorescently-tagged nanoparticles (red) and large swarms of a type of magnetic bacteria called Magnetospirillum magneticum (not visible).
At the touch of a button that rotates external magnetic fields, researchers can wirelessly control the direction in which the bacteria move through the liquid—up, down, left, right, and even “freestyle.” And—get this—the flow created by the synchronized swimming of all these bacteria pushes along any nearby nanoparticles in the same direction, even without any physical contact between the two. In fact, the researchers have found that this bacteria-guided system delivers nanoparticles into target model tissues three times faster than a similar system lacking such bacteria.
How did anyone ever dream this up? Most previous attempts to get nanoparticle-based therapies into diseased tissues have relied on simple diffusion or molecular targeting methods. Because those approaches are not always ideal, NIH-funded researchers Sangeeta Bhatia, Massachusetts Institute of Technology, Cambridge, MA, and Simone Schürle, formerly of MIT and now ETH Zurich, asked themselves: Could magnetic forces be used to propel nanoparticles through the bloodstream?
As a graduate student at ETH Zurich, Schürle had worked to develop and study tiny magnetic robots, each about the size of a cell. Those microbots, called artificial bacterial flagella (ABF), were designed to replicate the movements of bacteria, relying on miniature flagellum-like propellers to move them along in corkscrew-like fashion.
In a study published recently in Science Advances, the researchers found that the miniature robots worked as hoped in tests within a model blood vessel . Using magnets to propel a single microbot, the researchers found that 200-nanometer-sized polystyrene balls penetrated twice as far into a model tissue as they did without the aid of the magnet-driven forces.
At the same time, others in the Bhatia lab were developing bacteria that could be used to deliver cancer-fighting drugs. Schürle and Bhatia wished they could direct those microbial swarms using magnets as they could with the microbots. That’s when they learned about the potential of M. magneticum and developed the experimental system demonstrated in the video above.
The researchers’ next step will be to test their magnetic approach to drug delivery in a mouse model. Ultimately, they think their innovative strategy holds promise for delivering nanoparticles carrying a wide range of therapeutic payloads right to a tumor, infection, or other diseased tissue. It’s yet another example of how basic research combined with outside-the-box thinking can lead to surprisingly creative solutions with real potential to improve human health.
 Synthetic and living micropropellers for convection-enhanced nanoparticle transport. Schürle S, Soleimany AP, Yeh T, Anand GM, Häberli M, Fleming HE, Mirkhani N, Qiu F, Hauert S, Wang X, Nelson BJ, Bhatia SN. Sci Adv. 2019 Apr 26;5(4):eaav4803.
What are genome editing and CRISPR-Cas9? (National Library of Medicine/NIH)
Sangeeta Bhatia (Massachusetts Institute of Technology, Cambridge, MA)
Simone Schürle-Finke (ETH Zurich, Switzerland)
NIH Support: National Cancer Institute; National Institute of General Medical Sciences
Posted on by Dr. Francis Collins
Great things sometimes come in small packages. That’s certainly true in the lab of Eun Ji Chung at the University of Southern California, Los Angeles. Chung and her team each day wrap their brains around bioengineering 3-D nanoparticles, molecular constructs that measure just a few billionths of a meter.
Chung recently received an NIH Director’s 2018 New Innovator Award to bring the precision of nanomedicine to autosomal dominant polycystic kidney disease (ADPKD), a relatively common inherited disorder that affects about 600,000 Americans and 12 million people worldwide.
By age 60, about half of those battling ADPKD will have kidney failure, requiring dialysis or a kidney transplant to stay alive. For people with ADPKD, a dominantly inherited gene mutation causes clusters of fluid-filled cysts to form in the kidneys that grow larger over time. The cysts can grow very large and displace normal kidney tissue, progressively impairing function.
For Chung, the goal is to design nanoparticles of the right size and configuration to deliver therapeutics to the kidneys in safe, effective amounts. Our kidneys constantly filter blood, clearing out wastes that are removed via urine. So, Chung and her team will exploit the fact that most molecules in the bloodstream measuring less than 10 nanometers in diameter enter the kidneys, where they are gradually processed and eliminated from the body. This process will give nanoparticles time to bind there and release any therapeutic molecules they may be carrying directly to the cysts that cluster on the kidneys of people with ADPKD.
Chung’s research couldn’t be more timely. Though ADPKD isn’t curable right now, the Food and Drug Administration (FDA) last year approved Jynarque™ (tolvaptan), the first treatment in the United States to slow the decline in kidney function in ADPKD patients, based on tests of the rate of kidney filtration. Other approved drugs, such as metformin and rapamycin, have shown potential for repurposing to treat people with ADPKD. So, getting these and other potentially life-saving drugs directly to the kidneys, while minimizing the risk of serious side effects in the liver and elsewhere in the body, will be key.
Most FDA-approved nanoparticle therapies are administered intravenously, often for treatment of cancer. Because ADPKD is chronic and treatment can last for decades, Chung wants to develop an easy-to-take pill to get these nanoparticles into the kidneys.
But oral administration raises its own set of difficulties. The nanoparticles must get from the stomach and the rest of the gastrointestinal tract to the bloodstream. And then if nanoparticles exceed 10 nanometers in diameter, the body typically routes them to the liver for clearance, rather than the kidneys.
While Chung brainstorms strategies for oral administration, she’s also considering developing a smart bandage to allow the nanoparticles to pass readily through the skin and, eventually, into the bloodstream. It would be something similar to the wearable skin patch already featured on the blog.
In the meantime, Chung continues to optimize the size, shape, and surface charge of her nanoparticles. Right now, they have components to target the kidneys, provide a visual signal for tracking, enhance the nanoparticle’s lifespan, and carry a therapeutic molecule. Because positively charged molecules are preferentially attracted to the kidney, Chung has also spent untold hours adjusting the charge on her nanoparticles.
But through all the hard work, Chung and her team continue to prove that great things may one day come in very small packages. And that could ultimately prove to be a long-awaited gift for the millions of people living with ADPKD.
Polycystic Kidney Disease (National Institute of Diabetes and Digestive and Kidney Diseases/NIH)
Video: Faculty Profile – Eun Ji Chung (University of Southern California, Los Angeles)
Chung Laboratory (USC)
Chung Project Information (NIH RePORTER)
NIH Director’s New Innovator Award (Common Fund)
NIH Support: Common Fund; National Institute of Diabetes and Digestive and Kidney Diseases
Posted on by Dr. Francis Collins
If you think this soup looks unappealing for this year’s Thanksgiving feast, you’re right! If you were crazy enough to take a sip, you’d find it to be virtually flavorless—just a salty base (red) with greasy lipid globules (green) floating on top. But what this colorful concoction lacks in taste, it makes up for as a valuable screening tool for peptides, miniature versions of proteins that our bodies use to control many cellular processes.
In this image, William Wimley, an NIH-supported researcher at Tulane University, New Orleans, has stirred up the soup and will soon add some peptides. These peptides aren’t made by our cells, though. They’re synthesized in the lab, allowing Wimley and team to tweak their chemical structures and hopefully create ones with therapeutic potential, particularly as smart-delivery systems to target cells with greater precision and deliver biological cargoes such as drugs .