ALKS-5461 failed to meet its primary efficacy endpoints in two trials from 2016. On the basis of a third study that did meet its primary endpoints, Alkermes initiated a rolling New Drug Application with the FDA.
In November 2018, an FDA panel voted against recommending approval, finding that evidence was insufficient. As such, approval of the medication was rejected in 2019. It is a κ-opioid receptor (KOR) antagonist and is being developed by Alkermes.
A mouse study found that knockout of the MOR or DOR or selective pharmacological ablation of the NOP did not affect the antidepressant-like effects of buprenorphine, whereas knockout of the KOR abolished the antidepressant-like effects of the drug, supporting the notion that the antidepressant-like effects of buprenorphine are indeed mediated by modulation of the KOR by the drug (and not of the MOR, DOR, or NOP). However, a subsequent study found that the MOR may play an important role in the antidepressant-like effects of buprenorphine in animals.
Buprenorphine is not a silent antagonist of the KOR but rather a weak partial agonist.In vitro, it has shown some activation of the KOR at concentrations of ≥ 100 nM, with an Emax of 22% at 30 µM; no plateau in maximal response (EC50) was observed at concentrations up to 30 µM. Samidorphan similarly shows activation of the KOR in vitro, but to an even greater extent, with an EC50 of 3.3 nM and an Emax of 36%. As such, ALKS-5461 may possess both antagonistic and agonistic potential at the KOR. Because antagonism of the KOR seems to be responsible for the antidepressant effects of ALKS-5461, this property could in theory limit the effectiveness of ALKS-5461 in the treatment of depression.
ALKS-5461 was granted Fast Track Designation by the Food and Drug Administration (FDA) for treatment-resistant depression in October 2013. During June and July 2014, three phase IIIclinical trials were initiated in the United States for treatment-resistant depression. Alkermes reported that the first two trials failed in 2016. In August 2017, based on the third trial, Alkermes announced the initiation of a rolling submission of a New Drug Application for ALKS-5461 to the FDA. On 31 January 2018, Alkermes submitted a New Drug Application for ALKS-5461 to the FDA for the adjunctive treatment of major depressive disorder. The submission was accepted by the FDA on 9 April 2018 after initially serving a refuse-to-file letter due to insufficient evidence of overall effectiveness.
In November 2018, an FDA advisory committee voted 21-2 against recommending approval of ALKS-5461 for MDD, setting the medication up for likely rejection. The main reason cited was insufficient evidence of effectiveness. Conversely, the panel voted in favor of adequate safety having been demonstrated.
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