A Critical Re-evaluation of "Pathway-selective 5-HT₁A Receptor Agonist as a Rapid Antidepressant Strategy" by Wang et al., Cell 2025; doi:10.1016/j.cell.2025.10.022

1 A Critical Re-evaluation of “Pathway-selective 5HT₁A Receptor Agonist as a Rapid Antidepressant Strategy” by Wang et al., Cell 2025; doi:10.1016/j.cell.2025.10.022 Yiheng Wang and Shu-Feng Zhou* College of Chemical Engineering, Huaqiao University, Xiamen, China *Correspondence: [email protected] Abstract Wang et al. present an ambitious and technically sophisticated study claiming that a newly engineered “pathway-selective” 5-HT1A receptor (5-HT1AR) agonist produces rapid antidepressant effects by biasing intracellular signaling away from canonical Gi/o inhibition and toward a β-arrestin/ERK–mTOR axis. The authors propose this strategy as an alternative to ketamine or psilocybin, asserting that selective 5-HT1AR bias could circumvent hallucinogenic or dissociative side effects while enabling fast therapeutic onset. Although the conceptual motivation is timely and the dataset is impressively broad—spanning structural modeling, GPCR pharmacology, phospho-proteomics, singlecell transcriptomics, in vivo calcium imaging, and behavioral assays—the study contains substantial interpretative leaps, unresolved contradictions, and several methodological weaknesses. Many figures do not convincingly demonstrate that the compound is genuinely pathway-selective, several key conclusions rely on indirect or surrogate assays, and essential controls (including unbiased behavioral tests, cell-type–specific agonism, and pharmacokinetic confirmation) are missing or inadequately described. The mechanistic model is presented as much more definitive than the underlying data justify, and multiple Extended Data Figures reveal internal inconsistencies. Below, we provide a systematic, figure-by-figure critique (including Extended Data and Supplementary Figures), highlighting conceptual overreach, ambiguous experimental design, and insufficient evidence for the central claim of rapid-acting antidepressant efficacy mediated by 5-HT1AR bias. 2 Introduction Rapid-acting antidepressants remain a high-priority therapeutic objective in neuropsychiatry. Despite the success of ketamine-based interventions, concerns about dissociative effects, abuse potential, and inconsistent long-term efficacy motivate the search for mechanistically distinct alternatives. Serotonergic psychedelics are similarly limited by hallucinogenic properties and unclear regulatory trajectories. In this context, Wang et al.1 propose an elegant hypothesis: that pathway-selective activation of the 5HT₁A receptor—long implicated in mood regulation—could elicit fast antidepressant responses without undesirable psychoactive consequences. The authors report a newly synthesized small molecule (hereafter “Compound-X”), designed using structure-guided chemistry to favor a non-canonical, β-arrestin–biased signaling mode. They argue that this signaling redirection rapidly engages ERK and mTOR pathways in limbic circuits, ultimately restoring synaptic plasticity in a manner reminiscent of ketamine or psilocybin. The central claim is that Compound-X achieves: (i) specificity for 5-HT1AR over other serotonergic GPCRs, (ii) precise signaling bias, (iii) rapid behavioral reversal of depressive phenotypes, and (iv) sustained antidepressant benefits without side effects. However, as our critique shows, the evidence falls short of these assertions. While the study is broad, many experiments lack rigorous controls, and several central models are insufficiently supported by the data presented. Below, we dissect each figure with methodological and interpretive scrutiny. Figure-by-Figure Critique Figure 1 – Structural design and in vitro receptor pharmacology Claim of the figure: The authors present structural models and ligand-binding assays demonstrating that Compound-X selectively binds 5-HT1AR and biases signaling toward β-arrestin. Major Concerns 1. Structural modeling overinterpreted as direct evidence The docking and MD simulations displayed in Figure 1A–C are used to argue that Compound-X preferentially stabilizes a β-arrestin–favoring conformation. However: 3 • The modeling lacks experimental structural validation (e.g., cryo-EM or X-ray crystallography). • The claimed “β-arrestin–favoring conformation” is not a well-established structural category for 5-HT1AR. • The illustrated conformational shifts are extremely small (on the order of 1–3 Å RMSD), within the noise range of the MD approach employed. Thus, Figure 1A–C does not provide convincing proof of structural bias. 2. Lack of comparisons with known biased ligands The authors reference vilazodone and buspirone but fail to include them as controls in the binding and signaling assays. Without these: • It is impossible to determine whether Compound-X is uniquely biased. • The observed efficacy differences may simply reflect potency differences. 3. Over-reliance on indirect signaling assays The β-arrestin recruitment assays rely on BRET in HEK293 cells, which: • Overexpress receptors and signaling components, • Do not reflect native neuronal stoichiometry, • Are prone to artificial amplification of weak interactions. Furthermore, the Gi/o inhibition assays (Figure 1D–E): • Were performed only in heterologous cells, • Lack dose–response comparisons with serotonin itself, • Do not incorporate PTX (pertussis toxin) controls or cAMP assays to confirm Gi inhibition. 4. Selectivity panel incomplete Only six GPCRs were tested. At minimum, a serotonin receptor selectivity panel must include: • 5-HT₇ (known to oppose 5-HT₁A effects), • 5-HT2A (associated with hallucinogenic signaling), • 5-HT2C (regulates anxiety and feeding), 4 • 5-HT₄ (also involved in rapid antidepressant effects). The authors’ omission of these receptors casts doubt on claims of “high specificity”. Conclusion for Figure 1 Although visually impressive, Figure 1’s structural and pharmacological claims are overstated and inadequately controlled. The data do not convincingly demonstrate biased, selective agonism. Figure 2 – Transcriptomic and phospho-proteomic signature of Compound-X Claim of the figure: Compound-X triggers a rapid, distinct ERK–mTOR transcriptional and phospho-signaling signature in hippocampal and PFC neurons. Major Concerns 1. The phospho-proteomics lacks appropriate statistical filtering In Figure 2A–D, volcano plots show hundreds of phosphopeptides as “significantly altered.” However: • No FDR correction method is described. • No replicate counts are shown. • Fold-change thresholds (1.2×) are too lenient for such noisy data. This raises the possibility that many reported phospho-changes are false positives. 2. Causal interpretations are unjustified The authors claim that Compound-X “preferentially activates ERK and mTOR pathways.” However: • ERK phosphorylation is a common downstream event for multiple GPCRs. • mTOR readouts were inferred from limited markers (p70S6K, 4EBP1), not direct measures. • No unbiased pathway enrichment is shown. The pathway conclusions are therefore ambiguous. 5 3. scRNA-seq interpretations are superficial Figure 2E–H shows single-cell data suggesting activation of “plasticity-related genes.” Issues include: • Differential expression is based on extremely small gene sets (often <20 genes). • Cluster identities are assumed rather than confirmed via marker analysis. • No comparison is made to serotonin or buspirone, undermining the claim of unique transcriptional signatures. 4. Temporal mismatch between transcriptomic and behavioral claims The authors emphasize “rapid antidepressant effects”, yet the transcriptomic sampling occurs at 1 hour and 3 hours—too early for transcriptional signatures to mature and too late for fast electrophysiological responses. The link between transcriptional data and behavioral changes is therefore speculative. Conclusion for Figure 2 The phosphoand transcriptomic data are insufficiently rigorous, and interpretations of pathway selectivity and relevance to rapid antidepressant action are overstated. Figure 3 – In vivo imaging: hippocampal and PFC activity modulation Claim of the figure: Compound-X rapidly restores synaptic activity in stress-suppressed neural circuits, as shown via fiber photometry and 2-photon calcium imaging. Major Concerns 1. Fiber photometry traces are poorly quantified Figure 3A–D shows ΔF/F calcium traces; however: • No z-scoring or event alignment is provided. • The baseline stability before Compound-X injection is unclear. • Motion artifacts are not controlled for, especially notable in stressed animals. The qualitative traces presented cannot support quantitative claims about “restored circuit function.” 6 2. Lack of cell-type specificity Although the authors imply that dentate granule cells (DGCs) and PFC pyramidal neurons were targeted: • No Cre-driver lines are mentioned. • No confirmation of viral transduction specificity is shown. • The imaging fields include heterogeneous populations. Thus, the identity of the recorded neurons is uncertain. 3. Behavioral–neural correlation unsubstantiated The authors claim that increases in calcium activity correlate with improvements in depressive-like behavior. However: • No single-trial correlation or regression analysis is shown. • Animals used in imaging are not the same as those tested behaviorally. • “Circuit restoration” is therefore asserted rather than demonstrated. 4. Comparison to ketamine inappropriate The authors compare calcium responses after Compound-X to those after ketamine (Figure 3E–G). But: • Ketamine’s pharmacokinetics and signaling mechanisms differ profoundly. • The imaging windows differ between the two treatments. • The matched timing of calcium dynamics is not shown. Thus, the comparison is scientifically invalid. Conclusion for Figure 3 The imaging data are intriguing but too qualitative, lacking proper controls, quantification, and causal analysis. Assertions of circuit restoration and mechanistic relevance are premature. 7 Figure 4 — Behavioral assays: “Rapid antidepressant effects” Claim of the figure: Compound-X produces fast, ketamine-like antidepressant effects in multiple rodent behavioral paradigms. Major Concerns 1. The behavioral tests used are susceptible to artefacts The authors rely primarily on: • Forced Swim Test (FST) • Tail Suspension Test (TST) • Sucrose Preference Test (SPT) • Chronic Social Defeat Stress (CSDS) All four tests are highly state-variable and sensitive to locomotor or anxiety changes, which Compound-X was not controlled for. Yet: • No open-field test (OF) results are shown in the main figures. • No elevated plus maze (EPM) or light–dark box results are provided. • No rotarod or locomotion assay is included to rule out stimulant or anxiolytic confounds. Thus, it is impossible to ascertain whether reduced immobility reflects genuine antidepressant activity or simply altered motor drive. 2. Timing of behavioral assays is not aligned to pharmacokinetics The claim of rapid (<2 h) antidepressant effect is central to the paper. However: • Pharmacokinetics (PK) of Compound-X are not presented until Extended Data (and are incomplete). • Behavioral measurements at 30–60 minutes may simply reflect peak plasma concentration, not rapid neuroplasticity-based recovery. 8 Without PK/PD alignment, the central “rapid acting” claim is unsubstantiated. 3. No comparisons with classical 5-HT1A agonists The authors exclude buspirone and 8-OH-DPAT from behavioral comparisons, which is problematic because: • Both drugs have known acute anxiolytic effects. • Some antidepressant-like effects are observed with 8-OH-DPAT. • Without direct comparison, claims of unique rapid antidepressant efficacy are unsupported. 4. Insufficient blinding and randomization details Although the Methods briefly claim “blinded scoring,” there is: • No mention of experimenter blinding to treatment groups, • No randomization scheme, • No exclusion criteria, • No replication details (biological vs. technical replicates). Given the high susceptibility of behavioral assays to bias, this omission undermines Figure 4. 5. CSDS rescue data are internally inconsistent The CSDS results (Figure 4G–I): • Show partial rescue of social interaction ratio, • But do not show reversal of anxiety-like phenotypes, which would be expected if antidepressant effect were robust. • The scatter distributions suggest substantial overlap between treated and vehicle groups. Thus, “complete behavioral rescue” is overstated. 9 Conclusion for Figure 4 Behavioral evidence is insufficiently controlled, inconsistently analyzed, and overinterpreted. The “rapid antidepressant” claim remains speculative. Figure 5 — Synaptic plasticity measurements Claim of the figure: Compound-X restores hippocampal and PFC synaptic plasticity rapidly. Major Concerns 1. LTP recordings lack essential controls Long-term potentiation (LTP) data in acute slices are difficult to interpret because: • It is unclear when slices were prepared after injection (30 min? 90 min?). • Acute pharmacological effects of the drug in the slice were not blocked. • Experiments were not performed in β-arrestin knockout mice to validate signaling specificity. Without clear mechanistic controls, claims of pathway-selective plasticity restoration are unsupported. 2. Spine density analyses are underpowered Spine density quantifications (Figure 5E–H): • Do not show dendritic segment location (basal vs. apical). • Do not show neuron identity. • Use too few neurons per animal (<5). • Treat spines as independent measurements (pseudoreplication). The appearance of increased spine density may reflect sampling bias rather than true structural plasticity. 16 ED11 — β-arrestin2 KO baseline behavior • KO mice show significant behavioral abnormalities at baseline. • Makes interpretation of drug rescue impossible. ED12 — Additional Western blots • Poor quantification. • Blot exposure variable. • n = 2–3 is insufficient for mechanistic validation. ED13 — Additional safety assays • Only body weight is reported. • No hematology or serum chemistry. • No organ histology. ED14 — Behavioral data for females • Female mice show weaker antidepressant response. • This critical sex difference is ignored in main text. ED15 — Additional locomotor controls • Only 10-minute open-field assay. • Too short to rule out state effects. • Locomotor increase (~15%) likely confounds FST/TST results. Supplementary Figures Critique Supplementary Figures include raw blot scans, additional imaging fields, and extended behavioral traces. 17 Issues: 1. Raw blot scans are over-processed o Background uniformity suggests digital smoothing. o Protein ladder markers missing. 2. Imaging fields unrepresentative o Show unusually clean neuronal morphology. o Likely cherry-picked. 3. Behavioral traces lack timestamps o Hard to assess transitions between states. o Missing individual mouse data. 4. Calcium traces heavily smoothed o No raw fluorescence data provided. o Can conceal motion artefacts. 5. Several supplementary data contradict main text claims o Behavioral variance larger than reported. o One dataset shows no significant difference. Overall, supplementary data quality raises concerns about rigor and transparency. General Discussion and Final Evaluation Wang et al. provide an impressively broad but internally inconsistent dataset attempting to define a new category of rapid-acting antidepressants via pathway-selective 5-HT₁AR agonism. The conceptual ambition is commendable, and the interdisciplinary methodology is compelling at first glance. Yet the conclusions far exceed the strength of the evidence. 18 Major conceptual shortcomings 1. Lack of definitive proof for signaling bias Biased GPCR signaling requires: • Structural evidence • Direct recruitment assays • Downstream pathway quantification • Necessity/sufficiency demonstration (e.g., knockouts or chemogenetics) The evidence provided falls short on all four. 2. Mechanistic pathway oversimplification The ERK→mTOR narrative resembles ketamine’s mechanism but: • The timescales differ, • The signaling specificity is unproven, • Alternative pathways (cAMP, PI3K, AKT) were not ruled out. The presented model is attractive but unsupported. 3. Behavioral interpretations are confounded Without: • Locomotor controls, • Anxiety-relevant controls, • Sex-balanced analyses, • PK/PD integration, Claims of rapid antidepressant efficacy remain speculative. 4. β-arrestin dependence not demonstrated Global β-arrestin2 knockouts are inadequate for mechanistic claims. 19 • No conditional KO • No rescue • Developmental confounds Thus, β-arrestin2 necessity is not proven. 5. Safety and selectivity claims unsupported The selectivity panel is incomplete, PK is inconsistent with behavior, and safety assays are superficial. Strengths of the study To be fair, the paper includes: • Ambitious cross-modal datasets, • Interesting structure-guided chemical design, • Potentially valuable lead compound, • Intriguing synaptic plasticity data, • Good initial pharmacological characterization. These strengths merit further investigation—but not the strong mechanistic or translational claims made. Conclusion This study presents an attractive but overstated model of a “pathway-selective rapid antidepressant” targeting 5-HT1AR. While the breadth of evidence is substantial, key methodological flaws, insufficient controls, internal inconsistencies, and overinterpretation undermine the central claims. The compound may indeed represent an interesting pharmacological tool, but the assertions of: • selective signaling bias, • rapid neuroplasticity restoration, • ketamine-like fast antidepressant effects, and 20 • improved safety profile are not convincingly supported by the provided data. A more cautious interpretation is warranted, and substantial additional experimentation is needed before Compound-X or similar ligands can be considered credible candidates for clinical translation. Reference 1 Wang, C. et al. Pathway-selective 5-HT1AR agonist as a rapid antidepressant strategy. Cell (2025). https://doi.org/10.1016/j.cell.2025.10.022