Nanomotor Assessed for Treating AIDS, Cancer

The National Institutes of Health recently awarded a multidisciplinary team $7 million over five years to study the potential use of a nanomotor -- a microscopic biological machine -- in diagnosing and treating diseases such as cancer, AIDS, hepatitis B and influenza.

The Purdue University team will lead one of eight national nanomedicine development centers and take the first steps in research that could lead to using nanomotors to package and deliver therapeutic DNA or RNA to disease-causing cells. This is a feat that could revolutionize medicine, but it faces many challenges, said Peixuan Guo, director of the center and a professor of molecular virology with joint appointments in Purdue's Cancer Research Center, School of Veterinary Medicine and Weldon School of Biomedical Engineering.

An image of the phi29 nanomotor illustrates the ring of six pRNA molecules processing a strand of DNA through its center. With National Institutes of Health funding, a Purdue University research team will study the potential use of the nanomotor in diagnosing and treating diseases such as cancer and AIDS. (Image: Guo laboratories)

"Nanomedicine, a branch of nanotechnology, calls upon many fields, including engineering, biology, chemistry, mathematics, computation and physics," Guo said. "The NIH centers bring these scientists together and that is the most exciting aspect of this project. We hope to create a medical tool using a device that mimics a natural biological structure. This biomimetic tool will be a hybrid of natural biological structures and synthetic structures that will operate on the nanoscale."

Nanotechnology is defined as structures, devices and systems 1 to 100 nanometers in size that possess novel properties and functions due to the arrangement of their atoms and molecules. A nanometer is one-billionth of a meter, or 100,000 times smaller than the diameter of a human hair.

The NIH nanomedicine initiative is a network of centers studying biological systems at the nanoscale in an effort to understand and control the molecular complexes responsible for cellular processes. The long-term goal is to develop devices that can control these processes for disease diagnosis and treatment. Four nanomedicine centers were funded last year, and the NIH recently announced the final four centers. Other nanomedicine centers are located at Baylor College of Medicine, University of Illinois, University of California at San Francisco, Columbia University, Georgia Institute of Technology, University of California at Los Angeles and the University of California Lawrence Berkeley National Laboratory.

Researchers are only beginning to scratch the surface of nanotechnology and the potential benefits to medicine, said David Thompson, a professor of organic chemistry.

"One of the major challenges in nanomedicine is merging new nanoscale fabrication tools with classical synthetic methods and delicate biomolecular building blocks to create materials with unique biomedical properties," he said.

The nanomedicine center will employ these tools by adapting a viral motor to package therapeutic cargo within a drug-delivery system that is already widely used in cancer clinics and in infectious disease treatments, he said.

Scientists worldwide have been trying for more than two decades to solve the problem of developing a delivery method that protects fragile deoxyribonucleic acid (DNA) and does not cause an adverse reaction in the patient. There are multiple barriers to realizing the potential of DNA therapeutics: DNA must be delivered in a protective vehicle that is of the right size, targets specific disease cells and unloads the DNA once inside the cell, Thompson said.

"We are optimistic that with the nanomotor created by Peixuan Guo and by pooling our research strengths, we can create a hybrid system that combines the strengths of biological and synthetic DNA delivery systems that may be the answer," Thompson said. "However, we are only at the beginning stages of research, and we are several steps away from that end goal."

Peixuan Guo, professor of molecular virology and director of the Purdue Nanomedicine Development Center, observes biological processes at the nanoscale. The National Institutes of Health recently selected Guo's team as one of eight national nanomedicine development centers. (Purdue News Service photo/David Umberger)

Guo's nanomotor is derived from the biological motor of bacteriophage phi29, a virus that infects bacteria. The virus uses the motor to package DNA and move it into the capsid, a shell made of proteins, as part of the viral reproduction process. The viral motor is geared by six packaging ribonucleic acid (pRNA) molecules arranged in a ring. Adenosine triphosphate (ATP), the same biological energy used for muscle movement, fuels the RNA motor. The DNA is cranked through the center of the RNA ring and into the capsid like a screw through a bolt.

Guo discovered this pRNA in 1987, and his research was published in the journal Science. In 1986 he was able to achieve a functional phi29-imitating nanomotor in a cell-free system, and his research was published in the Proceedings of the National Academy of Sciences. The team now will work to use the nanomotor to package DNA in the same way, but move it into and out of a therapeutic delivery vehicle.

Guo and his team constructed the DNA-packaging systems of the nanomotors to contain modified synthetic pRNA and reengineered protein molecules. The nanomotors retain the modified and reengineered viral components, which are harmless to human cells because the phi29 bacteriophage only infects bacteria. The modified nanomotors have the additional advantage of lowering the chance of an adverse immunologic response in a patient.

"The phi29 motor is considered to be the most powerful biological motor constructed to date and is well-characterized and understood due to Guo's extensive research," said Rashid Bashir, professor of electrical and computer engineering in the Weldon School of Biomedical Engineering. "Nature has created this highly efficient biological machine through billions of years of evolution. We are attempting to harness this delivery process. We want to learn from nature to make our approaches better."

The motor also has the advantage of being the correct size.

"The nanoscale size range is ideal for delivery inside the body," Guo said. "Anything smaller would be filtered out through the kidneys too quickly to be effective, and larger molecules would not be able to enter cells."

The team plans to attach the nanomotor to a lipid sheet, cell membrane and liposome. A liposome is a pocket made up of fat molecules. The liposome would, in effect, take the place of the capsid into which the phi29 biological motor pumps DNA. The nanomotor, once embedded into the outer wall of the liposome or cell membrane would pump DNA, drugs or other therapeutic molecules into the liposome pocket's open space, or directly into the cell through a controlled mechanism.

Liposomes have been clinically accepted as safe and should be able to protect the DNA and cause no harm to the human body, Thompson said. They also can be engineered to target a specific pathologic cell. The team will have to create a synthetic liposome compatible with the nanomotor and find a way to combine the two into a functioning drug-delivery device.

"This project is unprecedented," said Carlo Montemagno, dean of engineering at the University of Cincinnati, who is part of the research team. "It involves placing a biological motor into an entirely different context. It is an extremely difficult task to embed a viral motor into a lipid and to have it continue to function efficiently. It is a challenging research proposal, but if we are successful, the rewards to the field of medicine will be great."

The team also will work to develop new diagnostic methods to test for disease using the nanomotor. The long-term goal is to place thousands of nanomotors in an array assembled on a porous surface, such as silicon, and to have them function for use in biosensing, Bashir said.

"It could be a great analysis tool able to assess thousands of molecules at once to detect specific DNA or genes," he said. "An array of this type on silicon surfaces has never been done before."

In addition to working toward the goals of creating therapeutic and diagnostic tools, the team will expand understanding of the structure and function of the lipid membrane-embedded artificial motor and other possible applications.

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