NSI-189

Synthetic small molecule originally from Neuralstem that genuinely promotes hippocampal neurogenesis in animals (~36-66% volume increase in mouse dentate gyrus) but failed its primary depression endpoint TWICE — once at Neuralstem in 2017, again at Alto Neuroscience in October 2024 even after biomarker-stratifying for the patients most likely to respond. For Dylan: WATCH-LIST. Hippocampal neurogenesis is theoretically valuable for memory + brain-priority + MMA subconcussive load, but the human translation is unproven, the molecular target is still unidentified, and research-chem identity verification is non-trivial. Cerebrolysin already covers the neurotrophic axis with vastly better evidence.

NSI-189 (amdiglurax / ALTO-100) is a benzylpiperazine-aminopyridine small molecule: (4-benzylpiperazin-1-yl)-[2-(3-methyl-butylamino)pyridin-3-yl] methanone, CAS 1270138-40-3. Originally developed by Neuralstem, Inc. (Maryland) with DARPA + NIH support, screened from a stem-cell-based phenotypic library specifically for "compounds that make hippocampal neural progenitors proliferate." It is one of the few synthetic small molecules in the literature with hippocampal neurogenesis as its declared primary mechanism (others in the same conceptual bucket: P7C3 series, dihexa for synaptogenesis, BPN14770 for cAMP/PDE4D — all earlier-stage).

Molecular target: still unidentified after 15+ years of work. This is unusual and important. NSI-189 does not bind:

• Monoamine transporters (SERT, DAT, NET) — distinguishes it from SSRIs, SNRIs, stimulants
• NMDA, AMPA, kainate (glutamate receptors)
• Classical monoamine receptors (5-HT, DA, adrenergic)
• The pharmacology is "phenotypic" — we know what it does to neural progenitor cells, not why.

Downstream pathway effects (proposed):

1. Neural progenitor cell proliferation in the subgranular zone of the hippocampal dentate gyrus — the canonical adult-neurogenesis niche. EC₅₀ in vitro ~0.1-1 µM (low-micromolar).
2. BDNF upregulation — robust, with corresponding TrkB activation → PI3K/Akt + MAPK/ERK survival/plasticity cascades.
3. GDNF, VEGF, SCF also upregulated; SCF (stem cell factor) effect particularly strong, fitting the progenitor-proliferation phenotype.
4. Putative GABA-A negative allosteric modulation — a secondary signal in some assays that may explain part of the antidepressant-like behavior in animals; not the primary story.
5. Hippocampal volume expansion in animals. Mouse studies show ~36% dentate gyrus volume increase at 10 mg/kg, ~66% at 30 mg/kg, bell-shaped curve (higher doses lose the effect). This is the headline preclinical finding.
6. Behavioral effects in animal models — antidepressant-like in forced-swim and tail-suspension, cognitive improvement in Morris water maze, recovery in stroke models (Tajiri 2017), and synaptic plasticity rescue in an Angelman Syndrome mouse model.

Plain English: It tells the brain's adult stem-cell niche (the dentate gyrus) to make more new neurons and to release more growth factors. In mice, this expands the hippocampus measurably. In humans, the expansion did not show on MRI — and the depression benefit that this expansion was supposed to deliver has now failed two Phase 2b trials.

Pharmacokinetics (human):

• Oral absorption, peak plasma 1-2 hr post-dose
• Half-life ~17.4-20.5 hours — long enough for once-daily dosing, fits 4-5 days to steady state
• Linear PK in 40-120 mg/day range
• Limited metabolism (oxidation + glucuronidation per unpublished in-vitro data); no CYP characterization in public literature
• BBB penetration: yes, presumed (effect would be impossible otherwise) — formal CNS Cmax data not public