Phase 3 trial on pimavanserin underway
Pimavanserin is an oral selective serotonin inverse agonist, or SSIA, with a high affinity for 5-HT2A receptors, very low affinity for 5-HT2C receptors, and “absolutely no affinity” for dopaminergic, histaminergic, adrenergic, or muscarinic receptors, explained Dragana Bugarski-Kirola, MD, a psychiatrist and vice president of clinical development at Acadia Pharmaceuticals in San Diego.
“Those sites are thought to contribute to sedation, cognitive impairment, and orthostatic hypotension,” she noted.
Pimavanserin is at present FDA approved for a narrow indication: Treatment of hallucinations and delusions associated with Parkinson’s disease psychosis. But the drug’s unique mechanism of action suggests broad efficacy across a range of psychiatric disorders.
Indeed, after a successful phase 2 clinical trial of pimavanserin for treatment of Alzheimer’s-related psychosis, a phase 3 randomized, double-blind, placebo-controlled clinical trial of the drug for relapse prevention in dementia-related psychosis is now enrolling a planned 360 outpatients at 95 centers in 13 countries. This 26-week study, known as HARMONY, is preceded by open-label psychotherapy to ensure that study participants truly need pharmacotherapy. Patients are eligible regardless of their type of dementia, because psychosis in patients with various forms of dementia is clinically pretty much the same, whether the underlying disorder is Alzheimer’s disease, vascular dementia, Parkinson’s disease, or Lewy body dementia, according to Dr. Bugarski-Kirola.
In addition, pimavanserin also is the subject of an ongoing phase 3 randomized trial in patients with major depressive disorder inadequately responsive to an selective serotonin reuptake inhibitor or a selective norepinephrine reuptake inhibitor. A 380-patient phase 2 study of the drug as adjunctive treatment for negative symptoms of schizophrenia also is underway based upon earlier promising results.
Across the board for these potential indications, the drug has been well tolerated, with a side effect profile similar to that of placebo. Importantly, pimavanserin has not been associated with cognitive impairment when used for dementia-related psychosis, unlike the antipsychotics now being used off label in clinical practice, the psychiatrist said.
SEP-363856 part of ‘novel class’
SEP-363856 is a nondopaminergic D2, trace amine-associated receptor agonist (TAAR1) under development for treatment of schizophrenia. Phase 3 trials in adults and adolescents with schizophrenia will begin before the end of the year on the strength of positive phase 2 results, according to, head of global translational medicine and early development, as well as head of discovery sciences, at Sunovion Pharmaceuticals, Marlborough, Mass.
“We believe that SEP-363856 actually represents the first candidate in a novel class of antipsychotics. It’s a monoamine receptor activator, unlike the atypical antipsychotics, which work through blockade of the monoamine receptor via dopamine and serotonin. We believe that it’s the monoamine receptor activation that leads to the safety and efficacy of the class,” he explained.
In the four-country, double-blind, 4-week phase 2 trial conducted in 245 hospitalized acutely psychotic patients, oral SEP-363856 flexibly dosed at 50 or 75 mg/day had a side effect profile like that of placebo. Negative symptoms as assessed via theimproved by an average of 7.1 points at 4 weeks with SEP-363856, significantly more than the 2.7-point improvement with placebo. The PANSS total score improved by 17.2 points in the SEP-363856 group and 9.7 points in controls at 4 weeks, with a further 10-point drop in PANSS during a 6-month open-label extension phase of the study. Moreover, the SEP-363856 cohort showed significant functional improvement at 4 weeks in the UCSD Performance-Based Skills Assessment, with continued improvement during the open-label extension study.
Dr. Koblan said the pharmaceutical industry has overemphasized the development of dopaminergic D2-based drugs for schizophrenia. In the past 2 decades, roughly 30,000 patients have been enrolled in industry-sponsored, placebo-controlled, phase 2 or 3 randomized trials of drugs with that mechanism. Many of the those drugs have reached the marketplace. In contrast, there have been far fewer RCTs – and no product launches – of antipsychotics with non-D2 mechanisms of action.
“When you consider that the cost is about $50,000 per research subject and 50,000 subjects have been studied since 2000, the pharmaceutical industry has invested on the order of billions of dollars to try to come up with the next breakthrough medication,” he said.