Vertex falls on cystic fibrosis study data

Shares of Vertex Pharmaceuticals Inc. skidded today after the Cambridge company reported initial results from a study of two drugs designed to treat cystic fibrosis, a genetic disease that causes thick mucus buildup in the lungs.

The mid-stage study is primarily designed to show that the regimen of Vertex drug candidates VX-770 and VX-809 is safe. Vertex said it met that goal and there were no serious side effects associated with treatment. While the Cystic Fibrosis Foundation said the results are a milestone, the combination therapy did not appear to be as effective as Wall Street hoped.

The results were seen as a setback for Vertex, whose hepatitis C drug Incivek received Food and Drug Administration approval May 23. Vertex shares slumped $4.51, or 8.5 percent, to $48.63 in morning trading. Earlier the stock fell 13.2 percent.

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Cystic fibrosis causes breathing problems and lung damage. Vertex says about 70,000 people have the disease, including about 30,000 in the US. While treatments have improved in recent years, Vertex said patients are currently expected to live to about 36 years on average.

The drugs are designed to treat the defective protein that causes the disease, and in the study, Vertex tested the drugs against the most common genetic mutation that causes cystic fibrosis. In patients with that form of the disease, a specific protein does not reach the surface of the cell in normal amounts. Because there isn’t enough of the protein, not enough chloride flows across the cell surface and mucus is not effectively cleared from the airways. VX-809 is designed to help the protein reach the cell surface and VX-770 helps the protein function more normally.

The first part of the trial involved 62 patients. They were treated with either VX-809 or placebo alone for two weeks, then the combination therapy or placebo for another week. The drug’s effectiveness was evaluated by measuring the amount of chloride in the patients’ sweat. The excess chloride is removed by sweating and cystic fibrosis patients generally have at least 50 percent more chloride in their sweat than people without the disease.

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Vertex said the higher-dose combination therapy reduced patients’ sweat chloride levels by 9.1 millimoles per liter. Citi Investment Research analyst Yaron Werber said that was less than investors were hoping for.

“The data (…) technically falls a bit lower than the 15 mmol/L reduction that the Street wanted to see,’’ Werber said.

In a note published before the results were released, RBC Capital Markets analyst Jason Kantor wrote that a 10 mmol/L reduction would be the lowest result considered positive.

However, Werber said the study was very short and the regimen looks more effective than VX-770 alone.

Vertex said it will start the second part of the trial during the fourth quarter.

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