Gene therapy for Cystic fibrosis updates

Two new studies from the University of Iowa suggest that gene therapy may be a viable approach for treating or preventing lung disease caused by cystic fibrosis (CF).

Working with CF pigs, the researchers, based in the UI Pappajohn Biomedical Institute (PBI), have shown that two different virus-based vectors can restore a working version of a protein—the cystic fibrosis transmembrane conductance regulator (CFTR)—that is faulty in CF to the pigs’ airway cells. Moreover, this gene replacement normalizes important aspects of the lung biology and improves the ability of airway secretions to kill bacteria.

“This is an important proof of principle for the idea that gene therapy for CF could work because we used an animal model that we know develops lung disease like people,” says Paul McCray Jr., professor of pediatrics in the UI Carver College of Medicine and principal investigator for one of the studies, both of which were published Sept. 8 in the journal JCI Insight. “In our short-term experiments we saw evidence of correction of some of the known problems of CF, including salt movement across the cell membrane, the pH (acidity) of the airway surface liquid, and the ability of respiratory secretions to kill bacteria. This shows that the gene therapy has an effect that appears to be therapeutically relevant.”

In the new studies, two teams tested two different gene therapy strategies to get functional CFTR into the airway cells of CF pigs. One group, led by McCray and Patrick Sinn, UI research associate professor of pediatrics and director of the UI Viral Vector Core, focused on a lentivirus. This type of virus has been successfully and safely used as a gene therapy vector for patients with rare immune diseases. A major advantage of lentiviruses is the delivered gene is directly incorporated (integrated) in to the cell’s genome, meaning the fix is permanent. However, it is challenging to produce large quantities of lentivirus, and this virus has not yet been tested for safety in human lungs.

The other research team, led by Zabner and David Schaffer at the University of California, Berkeley, focused on the adeno-associated virus AAV2. AAVs are safe for use in humans, including human lungs, and relatively easy to produce in large quantities. Genes delivered by AAV vectors are not permanently incorporated into the cell’s genome, but expression of the gene is often long-lived. An important aspect of the AAV study was the molecular customization of the virus such that it efficiently targeted pig airway cells. Zabner and Schaffer created an AAV2 virus with five mutations that was 240 times more efficient than AAV2 at infecting pig airway cells. The team previously used the same directed evolution strategy to create an AAV virus that preferentially infects human airway cells.

The researchers showed that both gene therapies restored chloride currents in pig airway cells, indicating that both vectors delivered working CFTR to the correct location in the airways. Both approaches also increased the pH and the bacterial-killing ability of the pigs’ airway secretions.

The vectors the UI researchers are developing could also have uses beyond CF gene therapy as multifaceted gene-delivery tools.

The current studies resulted from highly collaborative science among teams from the UI, the University of California, Berkeley, and Wright State University in Ohio, as well as among multiple departments within the UI Carver College of Medicine. The two lead authors of the studies are both UI graduate students: Ashley Cooney, in the microbiology program, and Benjamin Steines, in the molecular and cellular biology program. The research was funded in part by grants from the National Heart, Lung, and Blood Institute and the National Institute for Diabetes and Digestive and Kidney Diseases, both part of the National Institutes of Health, and the Cystic Fibrosis Foundation.

Press release from University of Iowa

Uncovering antibiotic resistance in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a common bacterium of our environment. It can however become a formidable pathogen causing fatal infections, especially in intubated patients, people suffering from cystic fibrosis or severe burns. The presence of certain metals in the natural or human environment of the bacterium makes it more dangerous and, in particular, resistant to antibiotics of last resort. A team of researchers from the University of Geneva (UNIGE), Switzerland, has shown that a specific protein of P. aeruginosa, called Host factor q (Hfq), is essential for reacting to these metals and acquire these new properties. The results, presented in the special issue Virulence Gene Regulation in Bacteria of the journal Genes, single out the Hfq protein as the Achilles heel of P. aeruginosa. Indeed, blocking its action could make this pathogen unable to adapt to a new environment and to resist to certain antibiotics.

‘We had discovered that high concentrations of metals, such as zinc, could induce a resistance to carbapenems, which are antibiotics of last resort, as well as an increase in the production of virulence factors’, says Karl Perron, researcher at the Department of Botany and Plant Biology of the UNIGE Faculty of Science. This metal may be present in abnormal amounts in the lung secretions of cystic fibrosis patients and in some urinary catheters, contributing to an increase in the pathogenicity of the bacterium and to treatment failure.

Some antibiotics must penetrate the bacteria to exert their effect. Carbapenems, for example, pass through a specific porin, a sort of channel normally used to import nutrients. When the bacterium is present in an environment containing an excess of zinc, it becomes resistant to carbapenems. ‘We had observed that zinc and other metals induce a suppression of the production of this porin, but we did not know exactly how’, specifies Verena Ducret, biologist in the Geneva group and first author of the article.

The team of Karl Perron has solved this enigma by uncovering the central role of a bacterial protein called Host factor q (Hfq). ‘This chaperone, a molecular assistant that allows the bacterium to adjust the synthesis of various proteins according to its needs, inhibits the synthesis of certain porins by intervening at several levels of the production chain’, explains Verena Ducret. By studying a bacterium that does not express Hfq, the scientists have thus discovered a real Achilles heel, because the mutant is unable to respond to zinc and other metals. Therefore, it cannot express its virulence or become resistant to carbapenems in the presence of these metals.

Since the different pathways leading to the inhibition of the production of this porin use Hfq, this chaperone becomes a promising therapeutic target. ‘We are looking for different inhibitors of Hfq that act on Pseudomonas aeruginosa strains. These drugs should counter all of the pathogen’s direct and indirect effects without affecting the host cells, because they do not have proteins such as Hfq’, says Karl Perron.

Publication: OprD Repression upon Metal Treatment Requires the RNA Chaperone Hfq in Pseudomonas aeruginosa
Press release from University of Geneva faculty of science