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Five Cystic Fibrosis Questions for Vertex Pharma

CAMBRIDGE, Mass. ( TheStreet) -- Deutsche Bank Securities biotech analyst Robyn Karnauskas says Vertex Pharmaceuticals (VRTX - Get Report) needs to come up with good answers to five key questions about its VX-809/Kalydeco cystic fibrosis therapy to boost investor confidence in the program as it moves into a phase III study early next year.

Detailed and final data from the phase II study of VX-809/Kalydeco will be presented Thursday at 11:40 am EDT at the 2012 North American Cystic Fibrosis (NACF) conference.

Here are Karnauskas' five key questions:

1. Was there a dose-response trend with the lower doses of VX-809 (200 mg and 400 mg) not reported in June?

Vertex has previously disclosed the 200 mg and 400 mg doses of VX-809 reported statistically significant improvements in lung function compared to placebo although those improvements were lower than what was observed in the highest, 600 mg dose of VX-809 studied in the phase II trial. [At the 600 mg dose, lung function improvement as measured by FEV1 was 6.1% within group and 8.6% relative to placebo.]

"We would like to see a dose response and a reasonable relationship between all three doses on FEV1% response," writes Karnauskas.

2. Did huge outliers drive the FEV1 benefit in the 600 mg dose arm that will be studied in phase III?

In June, Vertex disclosed that 55% of responders in the VX-809 600 mg arm had an FEV1 (lung function) improvement of more than 5%, while 25% of responders have an FEV1 improvement of more than 10%.

Among the slides presented Thursday should be a waterfall plot depicting the FEV1 lung function improvements for each patient treated with VX-809 600 mg or a placebo.

Investors will be comforted if the waterfall plot shows consistent efficacy for VX-809 across most patients. What the Street doesn't want to see are a small handful of outliers or "super responders" driving most of the lung function improvements, says Karnauskas.

3. Was the sweat chloride change at 200 mg and 400 mg statistically significant?

Reduction in sweat chloride is a laboratory marker for improved CFTR protein function (missing or malfunctioning CFTR proteins causes cystic fibrosis) and is a co-primary endpoint of the phase II study.

Conventional wisdom held that if drugs like VX-809 and Kalydeco are working as designed, a direct correlation between reduced sweat chloride levels and improvements in lung function should be evident. That was the case for Kalydeco monotherapy in cystic fibrosis patients with the G551D mutation.
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