Microscopy helps discover potential new drug target for cystic fibrosis

Sept. 24, 2013
An international team of scientists, using automated microscopy and genetics, have discovered a promising potential drug target for cystic fibrosis.

Scientists at the European Molecular Biology Laboratory (EMBL; Heidelberg, Germany), Regensburg University (Regensburg, Germany), and the University of Lisbon (Lisbon, Portugal), using automated microscopy and genetics, have discovered a promising potential drug target for cystic fibrosis. Their work also uncovers a large set of genes not previously linked to the disease, demonstrating how their screening technique can help identify new drug targets.

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Cystic fibrosis is a hereditary disease caused by mutations in a single gene called cystic fibrosis transmembrane conductance regulator (CFTR). These mutations cause problems in various organs, most notably making the lining of the lungs secrete unusually thick mucus. This leads to recurrent life-threatening lung infections, which make it increasingly hard for patients to breathe.

In patients with cystic fibrosis, the mutations to CFTR render it unable to carry out its normal tasks. Among other things, this means CFTR loses the ability to control a protein called the epithelial sodium channel (ENaC). Released from CFTR’s control, ENaC becomes hyperactive, cells in the lungs absorb too much sodium and--as water follows the sodium--the mucus in patients’ airways becomes thicker and the lining of the lungs becomes dehydrated. The only drug currently available that directly counteracts a cystic fibrosis-related mutation only works on the three percent of patients that carry one specific mutation out of the almost 2,000 CFTR mutations scientists have found so far.

A more efficient way to fight cystic fibrosis would be finding a therapy that would act upon ENaC instead of trying to correct that multitude of CFTR mutations. But unfortunately, the drugs that inhibit ENaC, mostly developed to treat hypertension, don’t transfer well to cystic fibrosis, where their effects don’t last very long.

Inhibiting DGKi reduces ENaC activity, reversing the effects of cystic fibrosis. In this assay, active ENaC dims the cells’ green glow (bottom), so the scientists screened for cases where the cells’ glow didn’t change (top). (Image courtesy of EMBL/Pepperkok)

So the team of scientists attempted to mimic a drug treatment, according to Rainer Pepperkok, whose team at EMBL developed the technique, by knocking down a gene and seeing if ENaC became inhibited. Starting with a list of around 7,000 genes, the scientists systematically silenced each one, using a combination of genetics and automated microscopy, and analyzed how this affected ENaC. They found over 700 genes which, when inhibited, brought down ENaC activity, including a number of genes no one knew were involved in the process. Among their findings was a gene called DGKi; when they tested chemicals that inhibit DGKi in lung cells from cystic fibrosis patients, the scientists discovered that it appears to be a very promising drug target.

“Inhibiting DGKi seems to reverse the effects of cystic fibrosis, but not block ENaC completely,” says Margarida Amaral from the University of Lisboa. Inhibiting DGKi reduces ENaC activity enough for cells to go back to normal, but not so much that they cause other problems, like pulmonary edema, she adds.

These promising results have already raised the interest of the pharmaceutical industry and led the researchers to patent DGKi as a drug target, as they are keen to explore the issue further, searching for molecules that strongly inhibit DGKi without causing side effects.

The work appears in the journal Cell; for more information, please visit http://www.cell.com/abstract/S0092-8674%2813%2901076-3.

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