(Adds that companies seeking priority regulatory review, updates shares)
By Ransdell Pierson and Natalie Huet
NEW YORK/PARIS, July 30 (Reuters) - A new drug being developed by Sanofi SA and Regeneron Pharmaceuticals Inc significantly cut cholesterol in nine late-stage clinical trials, the companies said on Wednesday, and provided the first glimpse of its potential to prevent heart attacks and strokes.
The injectable drug, alirocumab, is from a new class of medicines called PCSK9 inhibitors, which are also being developed by Amgen Inc and Pfizer Inc. If approved, they could lower "bad" LDL cholesterol in a new way and reap multibillion-dollar sales.
An interim safety analysis of one of the Phase III studies showed patients on alirocumab were less prone, versus those on placebo, to a combination of cardiovascular events, including cardiac death, heart attack, stroke, and chest pain requiring hospitalization.
That ongoing 2,341-patient study, called Odyssey Long Term, is expected to conclude early next year. Data were examined when all patients had been in the trial for a year, and about 25 percent had reached 18 months of treatment.
No other drugmaker has released data suggesting reduced cardiovascular risk from PCSK9 inhibitors.
But Regeneron Chief Executive Leonard Schleifer, in an interview, played down the favorable cardiovascular data. He said the trial was not designed to show reduced cardiovascular risk, but to assess safety and effectiveness in lowering LDL.
"One should not draw any conclusions from this," Schleifer said, adding that the definitive word on alirocumab's potential to cut heart risk will come from an ongoing 18,000-patient study called Odyssey Outcomes.
Schleifer said, however, the favorable cardiovascular data offers encouragement that Sanofi and Regeneron are testing "the right hypothesis".
PCSK9 inhibitors cut cholesterol by blocking a protein that prevents the body from eliminating LDL from the bloodstream.
In earlier mid-stage studies, alirocumab and Amgen's own anti-PCSK9 drug, when combined with statins, cut LDL by almost 70 percent beyond reductions seen with statins alone.
Data from the nine large Odyssey trials showed that after 24 weeks, LDL reductions with alirocumab were consistent with results seen in previous trials.
The trials involve patients whose high LDL cholesterol levels are not sufficiently controlled by statins and other existing treatments, and patients who cannot tolerate statins or who have a high cardiovascular risk.
In eight of the studies, all patients received alirocumab in addition to standard treatments such as statins and Merck & Co's Zetia.
Sanofi and Regeneron plan to seek approvals for alirocumab by year-end. The companies said they would seek a priority review from U.S. regulators that would allow for an approval decision in six months rather than the usual 10 months.
The most common side effects of alirocumab in the trials included stuffy nose and upper respiratory tract infections.
Regeneron is best known for its hot-selling Eylea treatment for macular degeneration. Late on Tuesday, it said U.S. regulators had approved Eylea to treat diabetic macular edema.
Regeneron shares closed up 5.8 percent at $322.18 on Nasdaq, while Sanofi shares were little changed. (Additional reporting by Bill Berkrot; Editing by Peter Galloway)