Japanese drugmaker Shionogi said that results from a Phase IIa clinical trial of its obesity drug S-2367 indicate that it can cause weight loss.

If borne out in future studies, the results suggest S-2367 could provide a new treatment option in an underserved market which, until very recently, only had two products on the market.

For some years the only approved pharmacologic treatment options for obese patients have been Roche’s lipase inhibitor Xenical (orlistat) and Abbott’s Meridia (sibutramine), which together account for a market valued at a little over $1 billion, held back by what is seen as relatively limited efficacy in promoting weight loss.

The third, most recent entrant is Sanofi-Aventis’ Acomplia (rimonabant), which went on sale in the UK at the end of June and is expected to win US approval later this year. Sanofi has said it expects Acomplia to become a $3 billion product at peak.

S-2367 works via a different mechanism to the established products, blocking the binding of the neurotransmitter neuropeptide Y, involved in regulation of energy balance and food consumption, to its receptors.

In the Phase IIa study a once-daily dose of S-2367 or matched placebo were given to 342 obese subjects. The subjects were randomised to 12 weeks of either drug treatment or placebo with a reduced calorie diet, with one of the groups undertaking a month-long low-calorie diet before treatment got underway.

“This innovative study design allowed for the clinical assessment of the S-2367

concept and its utility as a weight-loss maintenance and continuation treatment,” said Shionogi.

Among those who underwent the four-week low-calorie diet followed by drug treatment or placebo, there was an additional weight loss during the treatment phase of 2.5% of body weight for the highest dose of S-2367 (1,600mg), with no change observed for placebo.

Similarly, for those randomised at the outset to drug or placebo alongside a reduced calorie diet, the weight loss for the high-dose S-2367 group was 3.7%, while those on placebo lost 2.4% of their total body weight. This result failed to reach statistical significance, but Shionogi said it believes ‘longer duration studies will demonstrate the clear benefit of S-2367 in this setting’.