Alto Neuroscience Shares Topline Results from Phase 2 Proof-of-Concept Trial of ALTO-101 and Highlights Ongoing Pipeline Progress
Alto Neuroscience, Inc. has announced topline results from its Phase 2 proof-of-concept (POC) clinical trial evaluating ALTO-101 for the treatment of cognitive impairment associated with schizophrenia (CIAS), alongside a broader update on its development pipeline and strategic priorities. While the study did not meet its primary endpoints, the findings offer nuanced insights into the therapy’s potential, as well as the company’s evolving focus within the neuropsychiatric treatment landscape.
CIAS remains one of the most challenging aspects of schizophrenia to treat, with patients often experiencing persistent deficits in attention, memory, and executive function despite stabilization of psychotic symptoms. These cognitive impairments significantly affect daily functioning, employment, and overall quality of life, and there are currently no widely approved pharmacological treatments specifically targeting this domain. As such, the development of therapies for CIAS represents a critical unmet need in psychiatry.
The Phase 2 trial evaluated ALTO-101, a phosphodiesterase 4 (PDE4) inhibitor, in patients with CIAS using a range of electroencephalography (EEG) biomarkers and cognitive performance measures. Despite the scientific rationale supporting PDE4 inhibition as a mechanism for enhancing cognitive function, ALTO-101 did not achieve statistical significance compared to placebo on the study’s primary EEG or cognitive endpoints.
However, a closer examination of the data reveals several encouraging signals. The study demonstrated directional improvements across multiple EEG-based biomarkers, including theta inter-trial coherence (theta-ITC), a neurophysiological measure associated with cognitive processing and neural synchronization. In the overall study population (n=83), ALTO-101 showed a near-significant effect on theta-ITC, with a moderate effect size (d=0.34) and a p-value of 0.052, suggesting a trend toward improvement that approached conventional thresholds for statistical significance.
More notably, in a pre-specified subgroup of patients with more severe cognitive impairment (n=59), ALTO-101 achieved nominal statistical significance on theta-ITC (d=0.44, p=0.03) compared to placebo. This finding suggests that the drug’s effects may be more pronounced in patients with greater baseline deficits, a hypothesis that could inform future study designs and patient selection strategies.
In addition to subgroup effects, temporal trends observed during the trial provided further insights. Certain EEG measures, including theta-ITC, showed progressive improvement between day 5 and day 10 of treatment. This pattern raises the possibility that a longer treatment duration could yield more robust and clinically meaningful effects, highlighting a potential limitation of the current study design and an area for further exploration.
From a safety and tolerability perspective, ALTO-101 demonstrated a favorable profile. Rates of nausea and vomiting—common adverse events associated with the PDE4 inhibitor class—were comparable to those observed in the placebo group. This is a noteworthy finding, as tolerability challenges have historically limited the clinical utility of PDE4 inhibitors. Alto Neuroscience attributes this improved tolerability to the pharmacokinetic properties of ALTO-101, which may allow for more consistent drug exposure while minimizing peak-related side effects.
That said, the study did report high rates of application site skin reactions in both the active treatment and placebo arms, suggesting that these effects may be related to the delivery method rather than the drug itself. While not uncommon in trials involving topical or transdermal formulations, such reactions remain an important consideration for patient adherence and overall treatment experience.
In parallel with the clinical trial, Alto Neuroscience has been advancing a modified-release oral formulation of ALTO-101. This new formulation has demonstrated improved pharmacokinetic characteristics and enhanced tolerability compared to the original immediate-release version. By optimizing drug absorption and reducing variability in plasma concentrations, the modified-release formulation may offer broader therapeutic potential across multiple indications.
The company has indicated that this formulation is covered by a pending patent application and could represent a valuable asset for future development. Rather than continuing to independently advance ALTO-101 in CIAS, Alto plans to explore strategic partnering opportunities to further develop and potentially commercialize the program. This approach allows the company to preserve optionality while reallocating internal resources toward higher-priority assets.
Based on the overall results of the Phase 2 study, Alto Neuroscience has decided not to pursue further internal development of ALTO-101 for CIAS. Instead, the company will prioritize its lead program, ALTO-207, which is being developed for treatment-resistant depression (TRD). This decision reflects a strategic shift toward programs with stronger clinical validation and a clearer path to value creation.
Dr. Amit Etkin, founder and Chief Executive Officer of Alto Neuroscience, acknowledged the mixed outcome of the ALTO-101 trial, noting that while the results were not as robust as hoped, the program remains exploratory in nature. He emphasized the company’s continued confidence in ALTO-207, which is supported by compelling prior clinical data and external validation of its underlying mechanism.
ALTO-207 is expected to enter a Phase 2b clinical trial in the near future, representing a key inflection point for the company. Treatment-resistant depression is another area of significant unmet need, with many patients failing to respond to existing antidepressant therapies. By focusing on this indication, Alto aims to leverage its precision medicine approach to identify and treat patient subgroups most likely to benefit from targeted interventions.
Beyond its individual programs, Alto Neuroscience highlighted its strong overall position as it moves forward. The company reported a cash balance of approximately $275 million, providing substantial financial runway to support ongoing clinical development and strategic initiatives. In addition, multiple programs within its pipeline continue to advance, reflecting a diversified approach to addressing complex neuropsychiatric conditions.
The company also plans to present additional data from the ALTO-101 study at a future medical conference, which may provide further insights into the drug’s effects and inform potential next steps for the program. Such data could be particularly valuable in refining hypotheses around patient selection, dosing strategies, and treatment duration.
In summary, while ALTO-101 did not meet its primary endpoints in the Phase 2 CIAS trial, the study generated important scientific insights, including evidence of biological activity in specific patient subgroups and a favorable tolerability profile. These findings, combined with advancements in formulation technology, support the potential for future development through partnerships.
At the same time, Alto Neuroscience is sharpening its strategic focus on higher-priority programs, particularly ALTO-207 in treatment-resistant depression. With a strong financial position, multiple clinical assets, and a commitment to precision medicine, the company remains well-positioned to advance its mission of developing targeted therapies for neuropsychiatric disorders and addressing some of the most pressing unmet needs in mental health.
ALTO-207 in Treatment-Resistant Depression
Alto’s most advanced and differentiated program, ALTO-207, remains on track to initiate a Phase 2b clinical trial in the first half of 2026. ALTO-207 is a fixed-dose combination of pramipexole (a dopamine D3/D2 agonist) and ondansetron (a 5-HT3 antagonist), designed to enable rapid titration to higher pramipexole doses by mitigating dose-limiting nausea and vomiting. The planned Phase 2b trial is a randomized, double-blind, placebo-controlled study evaluating ALTO-207 as an adjunctive treatment in approximately 178 adults with treatment-resistant depression who have experienced two to five prior treatment failures.
The core mechanism of ALTO-207 is supported by the PAX-D study, published in The Lancet Psychiatry and conducted by the University of Oxford, which demonstrated a Cohen’s d=0.87 effect size for pramipexole versus placebo at 12 weeks — substantially larger than the effect sizes observed for current approved treatment resistant depression (TRD) treatments. The Phase 2a trial of ALTO-207 met primary and secondary endpoints. Following a successful FDA meeting in 2025, Alto is positioned to advance ALTO-207 through Phase 3 and a potential NDA submission.
About Alto Neuroscience
Alto Neuroscience is a clinical-stage biopharmaceutical company with a mission to redefine psychiatry by leveraging neurobiology to develop personalized and highly effective treatment options. Alto’s Precision Psychiatry Platform™ measures brain biomarkers by analyzing EEG activity, neurocognitive assessments, wearable data, and other factors to better identify which patients are more likely to respond to Alto product candidates. Alto’s clinical-stage pipeline includes novel drug candidates in bipolar depression, major depressive disorder, treatment resistant depression, schizophrenia, and other mental health conditions.
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