Syndeio Biosciences' precision neurotherapeutics are fundamentally differentiated from existing treatments for psychiatric and neurodegenerative disorders, co-founder and CEO Derek Small told FirstWord, because they're designed to "directly modulate synaptic structure and function — targeting the root cause of circuit dysfunction."The startup emerged from stealth on Tuesday with $90 million in funding and two assets in Phase II testing. Its investor syndicate includes Catalio Capital Management, Innoviva, Tenmile, Luson Bioventures and Palo Santo, while AbbVie and Eli Lilly are strategic shareholders.Syndeio's purview includes central nervous system (CNS) disorders that involve synaptic dysfunction, such as major depressive disorder (MDD), Alzheimer’s disease and schizophrenia.Traditional antipsychotics for MDD rely on neurotransmitter blockade, such as dopamine or serotonin antagonists, "which dull symptoms but fail to repair circuits," Small said. He added that, along the same lines, targeting amyloid or tau in Alzheimer’s has "limited cognitive impact unless synaptic integrity is restored."Syndeio is betting that its lead candidate, zelquistinel, can overcome those pitfalls in both diseases. The N-methyl-D-aspartate receptor (NMDAR) positive allosteric modulator (PAM), designed to enhance activity-dependent signaling and plasticity, is in Phase II testing for MDD, and is slated to shortly begin a synaptic function biomarker trial for Alzheimer's – a first-of-its-kind, according to the company."Our goal is not just to manage symptoms, but to repair the machinery of cognition and emotion," Small said. The biotech is also advancing a second NMDAR PAM, dubbed apimostinel, as an acute treatment of MDD. The candidate is being evaluated in an investigator-led Phase IIa study in collaboration with the University of Pittsburgh.Giving synapse repair a BoostWhile NMDAR is a well-known target, Small believes that the company's approach to modulating the receptor is unique, thanks to its Boost Synapse Pharmacology Platform. "We not only utilise scientifically-validated mechanisms, but we’ve also established the translational discipline needed to convert biological promise into therapeutic impact," Small said. "We’ve invested significant amounts to rigorously de-risk both our clinical and non-clinical programmes — not just to advance compounds, but to build a robust translational platform."Syndeio's platform integrates electrophysiology, behavioural assays, biomarker readouts such as EEG and polysomnography, as well as retrospective validation from past CNS programmes to predict treatment outcomes and dosing strategies for synaptogenic agents. According to Small, the Boost platform helps inform the company's asset selection, pipeline prioritisation, clinical trial design, patient selection and dose optimisation. Along with NMDAR, Syndeio is also exploring whether fine-tuning other synaptic targets, such as AMPAR, mGluR, 5HT2A, can restore synaptic plasticity. "Importantly, while these targets are not new, the field has historically applied outdated pharmacologic frameworks, primarily receptor occupancy and chronic exposure models," Small said. "This has overlooked the dynamic nature of synaptic potentiation and depotentiation, which has been well established since the 1970s. Sustained stimulation can paradoxically shut down synaptic function, negating therapeutic effects."