Two oral agents with novel mechanisms of action in schizophrenia generated considerable audience interest after acing large phase 2 clinical trials presented at the virtual congress of the European College of Neuropsychopharmacology.
The two successful drugs moving on to definitive phase 3 studies after their performance at ECNP 2020 are KarXT, a proprietary combination of xanomeline and trospium chloride, and an inhibitor of glycine transporter 1 (Gly-T1) known for now as BI 425809.
Pimavanserin, an oral selective serotonin inverse agonist with a high affinity for 5-HT2A receptors and low affinity for 5-HT2C receptors, has taken a more convoluted path through the developmental pipeline for schizophrenia. It recently failed to outperform placebo as adjunctive treatment for schizophrenia on the primary endpoint of improvement in Positive And Negative Syndrome Scale (PANSS) total score in the 6-week, phase 3 ENHANCE (Efficacy and Safety of Adjunctive Pimavanserin for the Treatment of Schizophrenia) study. The drug did, however, show significant benefit on secondary endpoints involving negative symptoms.
And in the 400-patient, 26-week, placebo-controlled, phase 2 ADVANCE trial, adjunctive pimavanserin was positive for the primary endpoint of improvement in the Negative Symptom Assessment-16 (NSA-16) score. A phase 3 program evaluating the drug specifically for negative symptoms is underway.
Another novel therapy, an investigational selective estrogen receptor beta agonist, proved reassuringly safe but completely ineffective in men with schizophrenia in a study presented at ECNP 2020.
“The results, unfortunately, were disappointing. We saw no signal on cognition, no change on brain imaging with fMRI, and no improvement in negative symptoms or PANSS total score,” reported Alan Breier, MD, professor and vice chair of the department of psychiatry at Indiana University in Indianapolis.
Dr. Alan Breier
Broad agreement exists that current antipsychotics targeting D2 dopamine and serotonin receptors in schizophrenia leave much to be desired. They’re ineffective for two of the three major symptom categories that define schizophrenia: cognitive impairment and negative symptoms, such as apathy and social withdrawal. And even for the current antipsychotics’ forte – treatment of positive symptoms, including hallucinations and delusions – effectiveness is often only modest to moderate and accompanied by limiting side effects.
KarXT
KarXT combines xanomeline, a selective M1/M4 muscarinic receptor agonist exclusively licensed from Lilly to Karuna Therapeutics, with trospium chloride, a muscarinic antagonist approved for more than a decade in the United States and Europe for treatment of overactive bladder. Xanomeline was synthesized in the 1990s. It showed promising evidence of antipsychotic efficacy in schizophrenia and Alzheimer’s disease in yearlong clinical trials totaling more than 800 patients, but interest in further developing the drug cooled because of limiting GI and other cholinergic adverse events. KarXT, Karuna’s lead product candidate, is designed to maintain the efficacy of xanomeline while trospium, which doesn’t cross the blood-brain barrier, cancels out its side effects, explained Stephen Brannan, MD, a psychiatrist and chief medical officer at the company.
He presented the results of the phase 2 study, a multicenter, randomized, double-blind, placebo-controlled, 5-week trial conducted with 182 schizophrenia inpatients experiencing an acute psychotic exacerbation. All other antipsychotics were washed out before randomization to KarXT at 50 mg xanomeline/20 mg trospium twice daily, titrated to 100/20 twice daily on days 3-7 and 100/20 b.i.d. thereafter, with an optional increase to 125/30 twice daily.
The primary study endpoint was change from baseline to week 5 in PANSS total score. The results were positive at the P < .0001 level, with a mean 17.4-point reduction in the KarXT group, compared with a 5.9-point improvement in placebo-treated controls. The between-group difference was significant by the first assessment at week 2.
Four of five prespecified secondary endpoints were also positive in rapid and sustained fashion: improvement in the PANSS positive subscore, PANSS negative subscore, Marder PANSS negative subscore, and Clinical Global Impressions-Severity. The fifth secondary endpoint – the proportion of patients with a Clinical Global Impressions rating of 1 or 2, meaning normal or only mildly mentally ill – wasn’t significantly different with KarXT, compared with placebo, but Dr. Brannan shrugged that off.
“In hindsight, it was probably a little overly optimistic to think that after 5 weeks [patients with schizophrenia] would be either well or almost well,” he quipped.
An exploratory analysis of participants’ before-and-after scores on a battery of six cognitive tests showed an encouraging trend: Patients on KarXT performed numerically better than did controls on five of the six tests, albeit not significantly so. Moreover, in a further analysis stratified by baseline impairment, patients in the most impaired tertile showed a larger, statistically significant benefit in response to KarXT.
“We’re interested enough that we plan to continue to look at this in our upcoming larger and longer-term trials,” Dr. Brannan said.
As for safety and tolerability, he continued: “We were pleasantly surprised. We certainly see more side effects with KarXT than with placebo, but not by that much, and they’re much, much better than with xanomeline alone.”
The side effects, mostly cholinergic and anticholinergic, occurred 2-4 times more frequently than in controls. Notably, the rates of nausea, vomiting, and dry mouth – three of the five most common treatment-related adverse events in patients on KarXT – decreased over time to levels similar to placebo by week 5. In contrast, rates of constipation and dyspepsia remained stable over time. All side effects were mild to moderate, and none led to study discontinuation.
A key point was that the KarXT-related side effects were not the same ones that are commonly problematic and limiting with current antipsychotics. There was no weight gain or other metabolic changes, sleepiness or sedation, or extrapyramidal symptoms.
“These results show KarXT has the potential to offer patients a novel mechanism-of-action antipsychotic with a different efficacy and/or tolerability profile than current antipsychotic medications,” Dr. Brannan said.