Japanese pharmaceutical company Shionogi and Co. on July 10th announced mildly encouraging results from a highly unusual Phase IIa trial of a new weight-loss pill called S-2367.

In one arm of the 12-week trial, obese participants spent four weeks on a very low-calorie (900-to-950 calories a day) diet before they started taking the experimental diet drug. The results for this group -- which continued on a reduced-calorie diet while taking S-2367 -- appeared somewhat promising.

In the other more conventional arm of the trial, participants started on a trial of the S-2367 without any run-in period. The results for this group -- which also was put on a reduced-calorie diet during the 12-week trial -- were positive but "not statistically significant."

Shionogi said it conducted the trials on 342 obese patients at 20 centers around the United States to test the efficacy and safety of a novel drug that blocks receptor binding of neuropeptide Y (NPY), a neurotransmitter involved in regulation of energy balance and food consumption.

"NPY levels are particularly elevated in reduced weight or food deprived subjects, resulting in stimulation of food intake," a Shionogi spokesperson said. "S-2367 was designed to counteract elevated NPY levels, thereby promoting weight loss and continued weight loss maintenance."

In the first study, participants who had lost 6.8 pounds during their four-week pretrial diet period then lost an additional 4.8 pounds while treated for the next 12 weeks with S-2367 once a day. The pretrial dieters who were given a placebo lost weight during the run-in period, but lost no further weight during the 12-week trial.

In the second study (which had no-run in period, but where all patients followed a reduced-calorie diet for the 12 weeks of the trial), patients treated with S-2367 lost an average 7.9 pounds while placebo patients lost an average 5.3 pounds. 

A Shionogi spokesperson termed the results of the second study a "positive trend," and said "we believe longer duration studies will also demonstrate the clear benefit of S-2367 in this setting."

No major safety problems were observed during the trial, the company said.

Stan Heshka, PhD., a statistics specialist at the New York Obesity Research Center who played a major role in conceiving the unique study design, said:

"With these study results, S-2367 has demonstrated its potential to help obese individuals maintain and increase their achieved weight loss. These results are particularly encouraging since weight regain is one of the major problems with current obesity treatments."

Shionogi said it plans to unveil results of the final analysis of the Phase IIa trials in October.

"The current Phase IIa results with S-2367 are very exciting and represent a significant milestone for Shionogi as we seek to further establish our global presence," said Dr. Sapan Shah, President & CEO of Shionogi USA.

"We look forward to working closely with obesity experts and regulatory authorities to design and execute longer-term clinical studies which we hope will confirm the unique profile, safety and benefit of S-2367 treatment for patients."