CHICAGO (Reuters) - An experimental drug that chokes off the blood supply to fat cells helped obese monkeys slim down, a sign that it may work in people, too, U.S. researchers said on Wednesday.

The drug, known as Adipotide, takes a different approach from other weight loss medicines, which have generally tried to control appetite, alter the absorption of fat or increase metabolism in order to help people lose weight.

"Development of this compound for human use would provide a non-surgical way to actually reduce accumulated white fat," said Renata Pasqualini of University of Texas MD Anderson Cancer Center, whose study appears in the journal Science Translational Medicine.

The drug works by seeking out and sticking to proteins on the surface of blood vessels that feed white fat cells -- the kind that gathers under the skin and around the middle.

Once attached, the drug releases a synthetic molecule that triggers a natural process of cell death that kills the fat cells.

Earlier tests of the drug on obese mice helped them lose 30 percent of their body weight.

The latest study involved 15 monkeys that became obese in much the same way humans do -- by overeating and getting too little exercise.

Ten monkeys were treated and five were the control group. At the end of the study, treated monkeys lost an average of 38.7 percent of their total body fat, compared to 14.8 percent for the control animals.

Treated monkeys also lost 27 percent of their abdominal fat.

Monkeys remained bright and alert throughout the study. The chief side effects were increased urine output and slight dehydration, both symptoms of mild kidney failure. But these were reversible and varied by dose.

The researchers are now planning to test the drug in obese patients being treated for prostate cancer.

"Obesity is a major risk factor for developing cancer, roughly the equivalent of tobacco use, and both are potentially reversible" Dr. Wadih Arap, also of MD Anderson, who worked on the study, said in a statement.

"Obese cancer patients do worse in surgery, with radiation or on chemotherapy -- worse by any measure."

Patients in the study will get daily injections of the drug for 28 consecutive days.

"The question is, will their prostate cancer become better if we can reduce their body weight and the associated health risks," Arap said.

Drug companies have had a difficult time getting new obesity drugs approved in the United States, with Vivus Inc, Arena Pharmaceuticals Inc and Orexigen Therapeutics Inc's all suffering setbacks this year over safety concerns.

More than a third of Americans are overweight and more than a quarter are obese, increasing their chances of developing health problems including type 2 diabetes, heart disease, high blood pressure, fatty liver disease and some cancers.

(Editing by Xavier Briand)