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(Reuters) - Arena Pharmaceuticals Inc said on Tuesday it submitted an official response addressing safety concerns of U.S. health regulators over the company's experimental weight loss drug lorcaserin, and believes it will gain U.S. approval.
Lorcaserin, which is being developed in partnership with Japanese drugmaker Eisai Co Ltd, is one of three new potential obesity treatments rejected by the Food and Drug Administration over safety issues.
New data included in Arena's response to the FDA's complete response letter is intended to alleviate agency concerns over cancerous tumors found in rats in two-year animal studies of lorcaserin.
"With these last group of experiments, which had to do with mammary tumors in female rats, we believe that we have addressed all of the issues that the FDA raised in the complete response letter," Christy Anderson, head of Arena's lorcaserin development program, said in a telephone interview.
However, the companies cautioned that "the FDA may analyze or weigh the data differently than Arena and Eisai."
Arena expects that the FDA later this month will confirm acceptance of the official response and set a new action date for an approval decision, likely about six months from the time of submission.
Obesity, a leading cause of diabetes, heart disease and other serious health problems, has reached epidemic proportions in the United States with nearly a third of the population falling into the growing category. But the FDA has set a very high approval bar for weight loss drugs because such a large portion of the general population is likely to want to take them.
Many industry observers believe approval of any new weight loss drug is a longshot. Arena's Chief Executive Jack Lief, however, remains optimistic.
"We believe that lorcaserin will be approved both in this country as well as in Europe and other countries," Lief said.
Vivus Inc and Orexigen Therapeutics are also working to convince the FDA of the worth of their weight loss drugs after initial rejections.
In data submitted to the FDA last week, Arena said it found that the rats that received the highest dose of lorcaserin without developing malignant tumors were getting 24 times more of the drug than a person taking the recommended dose. The rats that did develop tumors were taking even more of the drug than that, Anderson explained.
In addition to demonstrating what they called a safety margin of 24, the companies believe they have shown that the mechanism for tumor formation was relevant to rats but not humans. The drug leads to an increase in the hormone prolactin.
"Prolactin is a hormone that can cause mammary tumors in rats but is not known to cause mammary tumors in people," Anderson said.
In clinical trials of some 7,000 patients taking lorcaserin for up to two years there was "no excess of any sort of tumors in humans," Lief said.
Arena does not believe the FDA will require a lengthy, expensive study to show that its drug does not cause heart problems -- a so-called outcomes study -- as a condition of approval.
"We think that is not likely primarily because we haven't shown any increase in any risk factors in clinical trials," Lief said.
Added Anderson: "We Showed beneficial effects on blood pressure and heart rate in some of our Phase III studies, so there would be no reason to pursue an outcomes study based on data."
Arena's shares rose 5 cents to $1.97 in extended trading.
Reporting by Bill Berkrot; editing by Carol Bishopric