Experimental Pfizer cholesterol drug promising in study LOS ANGELES (Reuters) - An experimental Pfizer Inc cholesterol drug showed promise in a small midstage trial, putting the world's largest drugmaker in the race to develop a medicine from a promising new class, albeit behind similar programs by Regeneron Pharmaceuticals Inc and Amgen Inc. The drug, RN316, which Pfizer acquired with its purchase of Rinat Neuroscience, is a PCSK9 inhibitor, a class of biotech medicines that has generated great excitement in the industry. The drugs work by blocking a protein that slows removal of bad LDL cholesterol from the blood and are considered potentially the most important advance in the field since widely used statin drugs, such as Pfizer's Lipitor. In a 12-week trial of about 130 patients already on high doses of cholesterol-lowering statins, Pfizer's PCSK9 drug cut LDL cholesterol by 56 percent at the highest dose of 6 milligrams/kilogram of weight. The 3 mg/kg dose lowered LDL levels by 46 percent on top of statins, according to data unveiled on Monday. Barry Gumbiner, executive director of clinical research for Pfizer's PCSK9 program, said the results were somewhat misleading because any patient whose LDL level fell below 25 had doses withheld as a precaution, skewing the overall results. After four weeks, patients on the highest dose had LDL reductions of up to 80 percent before some had doses withheld, Pfizer explained. The data was presented at the American Heart Association scientific meeting in Los Angeles. PCSK9 drugs are intended for use by the millions of people who either cannot tolerate statins or cannot get their LDL levels down to target goals with statins and other drugs, including patients with a genetic condition that makes them predisposed to extreme, dangerously high cholesterol. Analysts have said the PCSK9 drugs could generate billions of dollars in annual sales. The Pfizer drug was administered intravenously once every four weeks for a total of three dosings in the brief proof-of-concept trial. Subsequent trials will use a version injected under the skin, with the next Phase II study designed to determine which doses of the drug will be advanced into much larger, late-stage studies, the company said. Patients on the higher doses who were not taken off the drug over the 12 weeks experienced sustained LDL level declines of 75 percent, said Gumbiner, who presented the data at the meeting. The drug was also tested at doses of 0.25 mg/kg and 1 mg/kg against a placebo. Pfizer researchers said the drug appeared to be well-tolerated, with no allergic reactions or safety issues of concern cropping up in the small study. Earlier on Monday, U.S. biotech Regeneron Pharmaceuticals Inc and its partner, French drugmaker Sanofi, announced plans to begin enrolling subjects in an 18,000-patient study to determine whether its PCSK9 drug can reduce heart attacks, strokes and death. That and an ambitious program that includes several smaller Phase III studies solidify Regeneron as the clear front-runner in the race to bring one of these new medicines to market. Amgen Inc, which is also aggressively pursuing a rival PCSK9 drug, is somewhat further along than Pfizer. The world's largest biotech company presented data from two Phase II studies at the heart meeting on Monday and planned to present the results of two more midstage trials on Tuesday. Sean Harper, Amgen's research chief, said in a telephone interview that the company expects to begin its Phase III trials early next year. Reporting by Bill Berkrot and Deena Beasley; editing by Matthew Lewis