Boehringer Ingelheim said it plans to shift the focus of its investigational compound BI 409306 to ongoing clinical trials with schizophrenia patients after the drug failed to outperform a placebo in Phase II trials with 450 patients for the indication Alzheimer's disease (AD).

The German drugmaker said plans for further trials with the compound in the AD application will not be pursued. It said future investigations will focus on two studies in schizophrenia, aimed at prevention of relapse and at prevention of occurrence of a first psychotic episode.

Boehringer’s Alzheimer’s candidate was an inhibitor of the phosphodiesterase 9 (PDE9) enzyme, which is involved in cognitive function. The trials were part of an extensive clinical trial program exploring the efficacy of compounds targeting the malfunctioning of specific (glutamatergic) brain circuits as potential new treatments for specific symptoms and traits of mental illness.

 Researchers had hoped that this approach would enhance glutamatergic signaling in the brain to increase synaptic strength and plasticity, which are important for memory and learning.

Patients receiving BI 409306 and the placebo included those suffering from with cognitive impairment and others with memory dysfunction in schizophrenia and in Alzheimer's disease.

Boehringer said its continued engagement in the dementia field will focus on the planned Phase II trials investigating another compound, BI 425809, a GlyT1 inhibitor, in a range of central nervous system (CNS) indications that also include Alzheimer's disease.

"We recognize the immense anticipation around any progress in brain research that brings us closer to finding solutions for the many millions of people living with dementia," said Jan Poth, therapeutic area head CNS Diseases at the company. He stressed, however, that "even these clinical trial results will add to the understanding of brain function and contribute to future progress in this area."

Following a comprehensive review of the complete trial data, Boehringer said it intends to present the full results at the Alzheimer's Association International Conference (AAIC) 2018 in July.