RxPG News : Drug Delivery

Nanoparticles hitchhike on red blood cells for drug delivery

Wed, 27 Jun 2007 03:59:37 PST

( from http://www.rxpgnews.com ) Researchers at the University of California, Santa Barbara have discovered that attaching polymeric nanoparticles to the surface of red blood cells dramatically increases the in vivo lifetime of the nanoparticles. The research, published in the July 07 issue of Experimental Biology and Medicine, could offer applications for the delivery of drugs and circulating bioreactors.

Polymeric nanoparticles are excellent carriers for delivering drugs. They protect drugs from degradation until they reach their target and provide sustained release of drugs. Polymeric nanoparticles, however, suffer from one major limitation: they are quickly removed from the blood, sometimes in minutes, rendering them ineffective in delivering drugs.

The research team, led by Samir Mitragotri, a professor of chemical engineering, and Elizabeth Chambers, a recent doctoral graduate, found that nanoparticles can be forced to remain in the circulation when attached to red blood cells. The particles eventually detach from the blood cells due to shear forces and cell-to-cell interactions, and are cleared from the system by the liver and spleen. Red blood cell circulation is not affected by attaching the nanoparticles.

"Attachment of polymeric nanoparticles to red blood cells combines the advantages of the long circulating lifetime of the red blood cell, and their abundance, with the robustness of polymeric nanoparticles," said Mitragotri. "Using red blood cells to extend the circulation time of the particles avoids the need to modify the surface chemistry of the entire particle, which offers the potential to attach chemicals to the exposed surface for targeting applications."

The researchers have learned that particles adhered to red blood cells can escape phagocytosis because red blood cells have a knack for evading macrophages. Nanoparticles aren't the first to be piggybacking on red blood cells; the strategy has already been adopted by certain bacteria, such as hemobartonella, that adhere to RBCs and can remain in circulation for several weeks.

The researchers say that it may be possible to keep the nanoparticles in circulation for a relatively long time, theoretically up to the circulation lifetime of a red blood cell - which is 120 days - if the binding between particles and the red blood cells is strengthened. The methodology is applicable to drugs that are effective while still attached to a red blood cell, although the researchers say that slow release from the red blood cell surface is also feasible.

Mitragotri says "this mode of prolonging particle circulation has significant implications in drug delivery, potentially leading to new treatments for a broad variety of conditions such as cancer, blood clots and heart disease". Dr. Steven R. Goodman, Editor-in-Chief of the journal, said "this study dealing with the attachment of nanoparticles to red blood cells may also have important implications for future treatment of hematologic disorders. This fusion of modern nanobioscience with cell biology and hematology is precisely the type of interdisciplinary study that the new Experimental Biology and Medicine is interested in publishing."

Using biologically compatible materials to fabricate a nanoshuttle

Tue, 24 Jan 2006 15:50:37 PST

( from http://www.rxpgnews.com ) Researchers at The University of Texas M. D. Anderson Cancer Center report that they have created a way for viral and gold particles to "directly assemble" and potentially seek out and treat disease where it resides in the body.

Their study, published in the online early edition of The Proceedings of the National Academy of Sciences (PNAS) the week of Jan. 23 - 27, 2006, shows the use of biologically compatible materials to fabricate a "nanoshuttle" - thousands of times smaller than a human hair - which can be harnessed to viral particles to precisely home to disease wherever it hides.

Once there, the nanoshuttle can perform a variety of functions. The study defines how assembled particles of gold - a metal that is not rejected by the body - could possibly be "tuned" to destroy tissue or emit signals that can be detected by imaging devices. The system also can be adapted to form a flexible scaffold that can carry drugs, genes or even cradle restorative stem cells.

"Gold is a perfect metal to perform these different functions, and scientists have been trying to find a way to target such particles to specific organs or tissues, but it has been extremely difficult," says the co-leader of the study, Renata Pasqualini, Ph.D., professor of medicine and cancer biology. "Instead of taking the usual approach by using a synthetic molecule or polymer, we have found a way to mix a 'genetically programmable' nanoparticle with a biologically compatible metal that together target specific locations in the body."

For example, these nanoplatforms could potentially locate damaged areas on arteries that have been caused by heart disease, and then deliver stem cells to the site that can build new blood vessel tissue. To treat cancer, they also may be able to locate specific tumors by using an array of imaging techniques. The tumors could then be treated by either heating the gold particles with laser light and/or using the nanoparticles to selectively deliver a drug to destroy the cancer.

"Gold nanoshells and laser light have been tested in pre-clinical models previously, but it has been difficult to accurately target the therapy," says Wadih Arap, M.D., professor of medicine and cancer biology, co-leader on the study.

These nanoplatforms and scaffolds have not as yet been tested in vivo, but this study is the first to show how, in a laboratory, gold and phage (viruses that infect only bacteria) can combine and build a matrix that can support stem cells.

The disease-finding capability of these scaffolds is due to the specially engineered virus that displays a peptide that matches a protein receptor "zip code" on the tissue of interest. This homing technique was pioneered by the lead authors on the current study, Pasqualini and Arap. Their previous work revealed that the human vascular system contains unique molecular addresses, depending on the site of an organ or tissue, and that blood vessels also acquire abnormal signatures on diseased organs. They were the first to attach such unique vascular "zip codes" to phage, engineering them in such a way that these viral particles would go to these target addresses.

This advance was only made possible, Pasqualini says, because she and Arap invited chemist Glauco Souza, Ph.D., the paper's first author, to work on the problem.

"This was truly a multidisciplinary approach, and it brings together something chemists, physicists and biologists have been trying to do, separately and unsuccessfully, for a long time," Souza says.

"The beauty of this approach is that the phage can already be screened and selected to either target a certain cell type in the body, or home to certain tissues," Pasqualini says.

During their preliminary work, Souza discovered that certain properties of the capsid (the outer shell of the phage virus) would allow it to spontaneously assemble with gold particles.

"So if you can assemble gold particles onto the phage and incorporate a 'signature' molecule like imidazole, you immediately have an entity that is both a sensor, because it binds to a specific molecular signature, and a reporter, because it picks up specific properties of the gold which can be measured in a number of ways," Souza says.

The team also found that by manipulating solution conditions, the network of scaffolds would form a "hydrogel," a bio-inorganic environment capable of sustaining and nurturing stem cells. This biological matrix can potentially be used in two ways, according to Pasqualini and Arap. First, it could be used to grow needed tissue in a laboratory, which could then be delivered to patients. Alternatively, the matrix could be directly injected so that it can implant at the site of injury. There, the stem cells could potentially morph into tissue needed to internally repair the wound, the researchers say.

"This is our vision of the future, and, of course, it all needs to be further studied and translated into real clinical applications," Arap says. "But we can now think in those terms because of this pioneering work that merges the fields of vascular targeting and nanotechnology."

DNA buckyballs for drug delivery created

Mon, 29 Aug 2005 22:35:38 PST

( from http://www.rxpgnews.com ) DNA isn't just for storing genetic codes any more. Since DNA can polymerize -- linking many molecules together into larger structures -- scientists have been using it as a nanoscale building material, constructing geometric shapes and even working mechanical devices.

Now Cornell University researchers have made DNA buckyballs -- tiny geodesic spheres that could be used for drug delivery and as containers for chemical reactions.

The term "buckyballs" has been used up to now for tiny spherical assemblies of carbon atoms known as Buckminsterfullerenes or just fullerenes. Under the right conditions, carbon atoms can link up into hexagons and pentagons, which in turn assemble into spherical shapes (technically truncated icosahedrons) resembling the geodesic domes designed by the architect-engineer Buckminster Fuller. Instead of carbon, the Cornell researchers are making buckyballs out of a specially prepared, branched DNA-polystyrene hybrid. The hybrid molecules spontaneously self-assemble into hollow balls about 400 nanometers (nm) in diameter. The DNA/polystyrene "rods" forming the structure are each about 15 nm long. (While still on the nanoscale, the DNA spheres are much larger than carbon buckyballs, which are typically around 7 nm in diameter.)

About 70 percent of the volume of the DNA buckyball is hollow, and the open spaces in the structure allow water to enter. Dan Luo, Cornell assistant professor of biological and environmental engineering in whose lab the DNA structures were made, suggests that drugs could be encapsulated in buckyballs to be carried into cells, where natural enzymes would break down the DNA, releasing the drug. They might also be used as cages to study chemical reactions on the nanoscale, he says.

The nanoscale, hollow buckyballs are also the first structures assembled from "dendrimerlike DNA." If three strands of artificial DNA are created such that portions of each strand are complementary to portions of another, the three strands will bind to each other over the complementary portions, creating a Y-shaped molecule. By joining several Y's in the same way, Luo's research group created molecules with several arms, a sort of tree shape (dendri- means tree in Greek). Then they attached polystyrene molecules to the dendrimerlike DNA forming a hybrid molecule called an amphiphile -- a molecule that both likes and hates water. DNA is hydrophillic -- attracted to water -- while polystyrene is hydrophobic -- water repels it.

The researchers expected the amphiphiles to assemble in water into some sort of solid structure arranged so that DNA would have a maximum interaction with water and polystyrene would avoid water as much as possible. Other researchers have used other amphiphiles to make spheres, rods and other solids. The hollow buckyballs were an intriguing and serendipitous surprise. A model suggests that one buckyball consists of about 19,000 amphiphiles, with their water-loving DNA mostly on the outside of the rods that form the structure. How these tens of thousands of molecules were able to self-organize to form such an intricate and complex structure is still an open question, the researchers say. They are seeking collaborators to solve the puzzle.

A scanning electron microscope photo of a self-assembled DNA buckyball.

Luo and Ph.D. graduate students Soong Ho Um, Sang Yeon Kwon and Jong Bum Lee described DNA buckyballs in an invited talk titled "Self-assembly of nanobuckyballs from dendrimer-like-DNA-polystyrene amphiphiles" Sunday, Aug. 28, at the 2005 annual meeting of the American Chemical Society in Washington, D.C. They reminded the audience that although the geometry of solid truncated icosahedrons was first described by Archimedes on paper more than 2,000 years ago, the skeletal, hollow-faced version of buckyballs had not been envisioned until Leonardo da Vinci's illustrations in 1494.

Luo added that DNA buckyballs may turn out to have unusual electronic, photonic and mechanical properties, and that because DNA is easily labeled and manipulated, his research group's work offers a way to study in detail the self-assembly process -- a process very important to the future development of nanotechnology.