NNZ-2591

At a glance

Overview

NNZ-2591 is modeled on cyclic glycine-proline, a metabolite associated with insulin-like growth factor 1 biology. It is being developed for conditions with substantial developmental and behavioral needs, including Phelan-McDermid syndrome. These are disease-specific programs, not evidence for general cognitive enhancement. The published phase 2 Phelan-McDermid study provides useful information about exposure, short-term tolerability, and possible outcome measures. However, all participants received active treatment. Caregiver expectation, natural variation, and changes in support can influence observed improvement when there is no concurrent placebo group. Controlled studies are therefore an essential next step.

Supporting sources [1] [2] [3] [4] [5]

How it works

The development hypothesis involves modulation of IGF-1-related signaling and downstream processes affecting neuronal development and connectivity. NNZ-2591 is an analog of cyclic glycine-proline, whereas trofinetide is an analog of glycine-proline-glutamate. That chemical distinction matters: one compound’s approval and trial outcomes cannot be transferred to the other. The exact connection between proposed signaling effects and meaningful functional benefit remains under clinical investigation.

Supporting sources [1] [2] [3] [4] [5]

What the published phase 2 study shows

Eighteen children with Phelan-McDermid syndrome received NNZ-2591 in a 13-week open-label study. Several secondary efficacy assessments improved from baseline, and most reported adverse events were mild or moderate. Safety and pharmacokinetics were primary objectives. Multiple secondary outcomes and the small uncontrolled sample make these signals preliminary rather than confirmatory.

Supporting sources [1]

Current development context

Neuren uses ercanetide as another name for NNZ-2591 and reported initiation of the randomized phase 3 Koala program in Phelan-McDermid syndrome in 2026. The program is designed to resolve uncertainties that an open-label study cannot. A sponsor report establishes the developer’s program description, not independent confirmation that eventual results will be positive.

Supporting sources [2] [4]

Avoid double-counting publications

The 2026 publication with DOI ending 0200405 is an erratum to the phase 2 article, not another clinical trial. A correction to one report should not be mistaken for an additional trial or independent replication of the original findings. Long-term safety also remains a separate question from short-term tolerability.

Supporting sources [1] [3]