AstraZeneca and partner Targacept have announced disappointing top-line results from the first of four late-stage studies on their new antidepressant.

Specifically, the Renaissance 3 Phase III study investigated TC-5214 as an adjunct therapy to an antidepressant in patients with major depressive disorder who do not respond adequately to initial treatment. The study did not meet its primary endpoint of change on the commonly-used Montgomery-Asberg Depression Rating Scale after eight weeks of treatment with TC-5214 as compared to placebo.

AstraZeneca said the drug, a first-in-class nicotinic channel modulator,  was overall well tolerated in the study and showed an adverse event profile generally consistent with the earlier Phase IIb study. Analyses of the full data are ongoing.

The flexible dose study, conducted in Europe, was part of the Renaissance programme which consists of four Phase III studies and a fifth long-term safety trial. Reporting of all results is expected by the first half of 2012.

Despite the setback, AstraZeneca still has high hopes for TC-5214 and a New Drug Application in the USA s planned for the second half of 2012. A European filing is not expected before 2015.

Investors are not so confident, however, and at 9.45am (UK time), AstraZeneca shares were down 3.1% to £28.75.