Scientific scandal hinders the development of new flu drugs
In the fall of 2007, the scientific advisory committee of the biotech company Influmedix specializing in the development of anti-influenza drugs from Radnor, Pennsylvania, convened a conference dedicated to the discussion of an important protein of the influenza virus – proton channel M2. The reason for the debate was the contradictory results obtained by two independent researchers working for the company, who almost simultaneously deciphered the structure of this protein at the atomic level. The problem was that the structural models of the same protein, which were not published at that time, interacted with two anti-influenza drugs in completely different ways.
The founder of Influmedix, William DeGrado from the University of Pennsylvania, believed that the drugs amantadine and remantadine prevent the opening of the channel by directly blocking it. On the other hand, James Chou, a scientific consultant at Harvard Medical School (Boston, Massachusetts), received evidence that drugs bind to a fragment of a protein molecule located outside the pore and modulate its activity by changing the shape of the molecule. As a result, both researchers found themselves at a dead end.
Currently, most influenza viruses, including the H1N1 strain that has made a lot of noise, are resistant to amantadine, rimantadine and other drugs that affect the M2 protein – one of two proven therapeutic targets on the virus envelope. The creation of new drugs capable of affecting the proton channel M2 of resistant influenza strains is possible only if an approach based on a detailed study of the structure of a protein molecule is used. However, as noted by Lawrence Pinto, who collaborates with Degrado and advises Influmedix from Northwestern University (Evanston, Illinois), this is impossible without resolving academic differences.
A month later, in January 2008, Degrado and Chou published their data in parallel published articles. At the same time, everyone claimed that his model explains the mechanism of action of drugs. Since then, the researchers have not spoken to each other, only exchanging rare emails. A few months later, Chow voluntarily left the Influmedix scientific advisory committee.
To date, the dispute is deeply bogged down in scientific publications, as both scientists continue to publish additional data confirming their points of view.
When Chou organized his own laboratory at Harvard University five years ago, he decided to use his knowledge in the field of magnetic resonance imaging to decipher the structure of membrane ion channels, in particular M2, a small protein involved in the replication of influenza virus particles. No one has ever used this method to solve such problems before.
Like most specialists, initially Chou assumed that the drugs blocking the work of the M2 channel act on the principle of a "bottle stopper", that is, they simply close the lumen of the channel. However, something in this idea did not add up. According to Chow's reasoning, M2 blockers are small molecules, so the question arises: how can several completely dissimilar mutations of a protein forming a much larger pore provide resistance to drugs binding to the same protein fragment?
As a result of a year of work, Chou and his colleagues came to the conclusion that the mechanism of action of drugs is not based on direct blockage of the canal. The images obtained by magnetic resonance imaging showed that the drugs bind to the outer part of the channel molecule, fixing it in a blocked state.
Degrado got completely different results. An employee of his laboratory, Amanda Stouffer, spent a year crystallizing the transmembrane region of the protein using X-ray crystallography and as a result came to the conclusion that the binding site of the drugs is located inside the pores of the channel.
The figure above shows a model of the M2 proton channel complex with amantadine (William Degrado), below is a model of the M2 complex with rimantadine (James Chow).
Both researchers are confident in the unambiguity of the data they received and, perhaps, both are right. Degrado does not question the results obtained by Chou, but suspects that Chou observed a non-specific binding of the drug to a protein fragment that is not important from a pharmacological point of view. He explains this by the fact that in his experiments Chou used an excessive amount of drugs, the molecules of which were "stuck" on the outer part of the protein molecule of the channel.
Chou, on the contrary, insists on the correctness of his results and claims that the object that Degrado saw inside the channel is not a drug molecule at all. He claims that the available Degradation resolution equal to 3.5 angstroms does not allow us to state with certainty that the channel pore was filled with a drug molecule, and not with residues of reagents used in crystallography.
A virologist from Northwestern University, Robert Lamb, who is the scientific founder of Influmedix, admits that improving the resolution of the methods used is necessary for the final solution of the controversial issue. However, he points to a growing body of evidence for a model of direct channel pore blocking (Degrado model).
Last year, Lamb and Pinto used directional mutation to change the outer fragments of the M2 channel, which, according to Chow, bind to drugs. The measurement of the electrophysiological parameters of the channel in cell models and live viral particles showed the preservation of the sensitivity of the mutated virus to drugs, which indicates against the model proposed by Chou. Chow, however, states that he analyzed similar mutations using a different method and found that changes in the order of amino acids still affect the sensitivity of the virus to the drug.
The only person actively publishing data supporting Chou's hypothesis is his father, Kuo-Chen Chou, founder and president of the San Diego, California-based nonprofit Gordon Natural Sciences Research Institute. In July, Ko-Chen Chou and his colleagues published two articles containing data based on the results of computer analysis and confirming the structural model of the M2 proton channel obtained by Chou Jr.
James Chow emphasizes that he has nothing to do with his father's research and that he personally does not trust conclusions made solely on the basis of computer simulation results.
Degrado and his colleagues want to finally resolve the conflict that has arisen. According to Degrado, he does not state that the existence of a second binding site of drugs is excluded, but in this connection the question arises: "Do they matter from a pharmacological point of view?" And the answer to this question is unequivocal: "No."
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of The Scientist: Flu-drug flap.
23.11.2009