New Cancer Fighter May Help ICU Patients Beat Infections

Studies in an animal model of  sepsis, a major cause of ICU patient death, indicate HSP 90 inhibitors help degrade  proteins perpetuating inflammation, says Dr. John D. Catravas, director of the  Medical College of Georgia Vascular Biology Center.

Results include restored lung  function, reduced blood vessel leakage, which can lead to dangerous swelling in  the lungs, and fewer byproducts of inflammation such as white blood cells, MCG  researchers report in the American  Journal of Respiratory and Critical Care Medicine, a journal of the  American Thoracic Society.

They already have begun looking at  the impact of HSP 90 inhibitors on the function of other organs, such as the  liver and kidneys, also typically impacted by sepsis.

"We would die without an  inflammatory response, but unreined inflammation is bad," says Dr. Catravas. That's  just what happens with overwhelming infection; inflammation, which helps the  body eliminate invaders, essentially keeps working after invaders are gone and  the new target is the body.

"These are proteins that initially  are useful in combating an invading bacteria but then, in some of us that  develop sepsis for reasons that are poorly understood, the inflammatory  response is amplified and stays much longer than it should," says Dr. Catravas,  the paper's corresponding author.

Heat shock proteins carry proteins  where they are needed and fold them up nicely so they do the correct job. Dr.  Catravas compares their two-protein configuration to a lobster with its claws  closed while tending to "client" proteins.

"The hypothesis we worked on is that these HSP 90 inhibitors take the heat  shock protein and move it into a different conformation," says Dr. Catravas.  The published research indicates they were correct and that inhibitors, fortunately,  readily target proteins that no longer have a useful function.

"The HSP 90 inhibitor binds to a little pocket in the dimer, the two identical  proteins that make up HSP 90 complex, and forces the two claws open," he says.  "As soon as they open, as soon as the three-dimensional conformation of the HSP  dimer and the client protein change, other proteins start attaching to the complex."  The client protein then becomes susceptible to degradation. It was their  earlier finding that inducible nitric oxide synthase, a major mediator of  sepsis, is a client protein of HSP 90 that led to the inhibitor study.

For the study, researchers used what would be considered lethal doses of  endotoxin to create a worse-case infection and pretreated animals with smaller  doses of HSP 90 than those currently under study for a wide range of cancers.

They have begun looking at more clinically relevant infection levels and  identifying the best time after the insult to give the lowest dose. However,  Dr. Catravas has not ruled out HSP 90 inhibitors' potential to preventively  treat patients at risk because patients seem to tolerate it well in the cancer  clinical trials.

He hopes to move ahead soon with  clinical trials of HSP 90 inhibitors, used in conjunction with antibiotics, in  intensive care patients.

These manmade HSP 90 inhibitors work by attaching where the protein pair's energy  source, called ATP, should be. The body appears to have an endogenous version,  ADP, which has one less phosphate than ATP and binds at the same site, also  opening the protein claws and sending the client protein toward degradation.

The research was funded by the National Institutes of Health.