Focus on the Flu : Treating, Drugs. Diagnosing

by National Institute of Health

(Page 9 of 15)

Blocking the Entryways

At the biotech company NexBio in San Diego, CA, NIAID grantee Mang Yu, Ph.D., is developing a kind of drug called a fusion protein, which is designed to guard against multiple flu strains. If successful, not only would such a drug be a strong weapon to fight the seasonal flu, but it could be on standby in case of an outbreak of pandemic flu.

Before it can cause disease, the flu virus must first enter a human cell. To enter, the virus passes through a gateway (receptor) on the cell's surface. NexBio is developing fusion proteins that disable receptors located on cells in the airway passages to render them inaccessible by flu virus particles.

Dr. Yu and his colleagues at NexBio are currently developing this fusion-protein drug, called Fludase, so that-as an inhalant-it can be applied to the upper airway surface for both prevention and treatment of flu viral infections. Whereas most inhalants are systemic drugs that enter the bloodstream and travel throughout the body, Fludase sticks onto the surfaces of the respiratory tract, allowing the drug to function only in the desired areas.

NexBio has successfully completed studies to assess Fludase efficacy and safety issues in two animal models. In 2005, the company began the application process for an Investigational New Drug with the U.S. Food and Drug Administration and is manufacturing Fludase for further laboratory studies and clinical trials.

Although NexBio is taking a novel approach to fight influenza virus, Dr. Yu and his colleagues are veteran drug developers in the field of respiratory viral infections. They have previously used special antibodies to block the entry of human rhinovirus, the cause of the common cold, into cells. Their cold virus research has led to a promising drug candidate, CFY 196, which was described in a 2003 paper in The Journal of Antimicrobial Chemotherapy.

For a Brighter Flu Picture, Change the Channel

Type A is the most serious of influenzas, responsible for widespread pandemics, but type B influenza can also exert a heavy hand during the fall and winter months, accounting for half of the flu cases diagnosed in most years.

Unfortunately, the popular antiviral treatment for type A flu, amantadine, as well as its derivative, rimantadine, doesn't work against a type B strain. Now NIAID-supported researchers Lawrence Pinto, Ph.D., and Robert A. Lamb, Ph.D., Sc.D., Northwestern University, have figured out why.

An influenza A virus is unable to do any real damage until its genetic material enters the host cell's nucleus, allowing it to make copies of itself. And it's the M2 protein, a pore-like "channel" on the surface of the virus, that allows this to happen by letting acid enter the virus particle to "loosen up" the virus's genetic material.

A flu virus's genetic material begins life securely locked up in the center of the virus. When a viral particle attaches to a host cell, it becomes surrounded by an acidic, membrane-bound bubble inside the cell. The M2 protein acts as a sort of "safecracker," allowing acid to move inside the virus, and causing the genetic material to loosen itself from other nearby parts. In addition, the bubble's acid environment causes hemagglutinin to change shape, poking a hole in the bubble. Together, these two actions allow the contents of the virus-namely, its RNA-to spill out, finding its way to the nucleus.

By binding to the M2 protein, however, amantadine plugs the channel's acid-conducting pore, keeping the genetic material locked safely away in the virus and preventing the virus from copying itself.

Drs. Pinto and Lamb have identified a protein on the B virus that, like A's M2 protein, helps move acid into the virus, unlocking the RNA from inside the virus particle. But instead of binding to amantadine, as A's M2 protein does, B's M2 protein repels the drug, explaining why amantadine doesn't work against a type B strain.

With better understanding of the biology of B's M2 protein, researchers may develop new drugs that can shut down the virus the same way amantadine shuts down the type A virus.

Diagnosing the Flu

Is it the Flu? Ask a Reporter ...

Clinical virologists are in need of a fast, simple, foolproof way to diagnose the flu. The most widely used method can eat up several days in the laboratory and relies on a ready supply of key antibodies.

Paul Olivo, M.D., Ph.D., president and CSO of Apath, LLC, of St. Louis, MO, and colleagues may have figured out a better way. The strategy: Dr. Olivo and others have found a method to outfox a flu virus into revealing itself.

The researchers' secret weapon is a reporter gene, which is derived from a gene that gives a firefly its luminescent glow, and which is encased within an artificial gene segment of the flu virus. While keeping the rest of the flu genome intact, the team removes the part of a flu gene that helps code for influenza A and replaces it with the "glow gene." (Although flu genes are made of RNA, the scientists first convert the RNA into DNA because DNA is easier to work with.) Special gene sequences are then added to help the gene replicate. The technology is based on a similar one Dr. Olivo developed 10 years ago for detecting the herpes simplex virus.

Once the new reporter DNA is made, it's injected into a cell, which makes RNA copies of the reporter DNA.

The process would end here, however, if it weren't for one final ingredient: the influenza virus itself. The glow gene, convinced that it's a fully functioning influenza gene, requires the flu virus to supply enzymes to catalyze the process by which RNA is translated into proteins-only this time, it's not a flu protein that's being made, but a reporter protein.

If a sample throat swab added to the cell contains influenza A, the reporter gene will be translated into a protein and the cell will glow bright. If the throat swab does not contain influenza A, the cell will remain clear.

Dr. Olivo is collaborating on the project with Andrew Pekosz, Ph.D., assistant professor in the Washington University School of Medicine, St. Louis, MO, who is working on other projects funded by NIAID, and Diagnostic Hybrids, of Athens, OH, which will develop and manufacture the reporter-equipped cells. The group is currently studying if the method can be used to identify all possible flu strains.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.