SEALS Phase II Failure Leaves NX210c Dependent on Post-Hoc Signals No Regulator Has Yet Accepted

Axoltis' ALS Trial Misses Primary Endpoint, Shows Exploratory Benefits

Axoltis Pharma's Phase II SEALS study for NX210c in amyotrophic lateral sclerosis (ALS) failed to meet its primary endpoint, showing no significant benefit in neurofilament light chain (NfL) levels or albumin quotient (Qalb) after six weeks. Despite this, the company reported "consistent positive trends" in secondary and exploratory parameters. Post-hoc analyses indicated a substantial reduction in the decline rate of clinical function, assessed by ALSFRS-R slope, and benefits in motor function. Data also suggested blood-brain barrier recovery. Axoltis plans further analyses, including a 10-month follow-up, and aims to present detailed data at Neuroscience 2026 to determine the optimal treatment regimen.

• The SEALS study (NCT06365216) for NX210c in ALS patients did not meet its primary endpoint, which assessed neurofilament light chain (NfL) levels and albumin quotient (Qalb) between cerebrospinal fluid and blood after six weeks. While a numerical benefit in blood NfL decrease was observed (25.4% in NX210c arms vs. 11.8% in placebo), it was not statistically significant, indicating the trial's primary objective of demonstrating a clear benefit on these biomarkers was not achieved.
• Despite the primary endpoint miss, Axoltis reported "consistent positive trends" in secondary and exploratory parameters. Post-hoc analyses revealed a substantial reduction in the decline rate of clinical function, measured by the Harmonised Revised Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R) slope. This reduction was 0.67 point/month for the 5mg/kg arm and 0.9 for the 10mg/kg cohort, compared to 1.14 for placebo, corresponding to average reductions of 41% and 21% respectively, which improved through week 10 and four months.
• Further exploratory data showed benefits on the motor function subscale of ALSFRS-R, with average reductions of approximately 64% for 5mg/kg and 33% for 10mg/kg at weeks six and ten. Additionally, the 10mg cohort demonstrated a significant decrease in blood claudin-5, a biomarker for blood-brain barrier (BBB) disruption, suggesting potential barrier recovery. These findings are guiding Axoltis's next clinical steps for NX210c, including further analyses and a 10-month follow-up of the Phase II trial patients.

NX210c's SEALS Study: Mixed Primary and Exploratory Outcomes

Several recent clinical trials have advanced the understanding of therapeutic options in amyotrophic lateral sclerosis (ALS), spanning pharmacological agents, biological interventions, and microbiome-targeted approaches. A randomized, double-blind, placebo-controlled trial enrolling 27 sporadic ALS patients evaluated fecal microbiota transplantation (FMT) against sham transplantation over 35 weeks. The primary efficacy outcome — change in ALSFRS-R total score from baseline to week 35 — showed no significant difference between groups (FMT: 6.1 [SD, 3.11]; placebo: 6.41 [SD, 2.73]). Secondary outcomes including respiratory function, muscle strength, autonomic function, cognition, quality of life, and plasma neurofilament light chain also showed no significant differences. Notably, the FMT group demonstrated improvements in constipation, depression, and anxiety symptoms, and FMT induced a shift in gut microbiome composition marked by increased abundance of Bifidobacterium persisting until week 15 (95% CI, 0.04 to 0.28; p = 0.01). Gastrointestinal adverse events were the primary FMT-related side effects.

A pooled safety analysis across three randomized, placebo-controlled studies examined edaravone (MCI-186) over the first six cycles (24 weeks) of ALS therapy in 368 patients (184 per group). Treatment-emergent adverse event (TEAE) incidence was comparable between groups (87.5% edaravone vs. 87.0% placebo). TEAEs occurring at ≥2% incidence more frequently in the edaravone group included contusion (14.7% vs. 8.7%), gait disturbance (12.5% vs. 9.2%), headache (8.2% vs. 5.4%), eczema (6.5% vs. 2.2%), dermatitis contact (6.0% vs. 3.3%), respiratory disorder (4.3% vs. 1.1%), and glucose urine present (3.8% vs. 1.6%). Discontinuations due to adverse events were lower in the edaravone group (2.2%) than placebo (5.4%), serious adverse event incidence was 17.4% versus 22.3%, and treatment-emergent deaths — all respiratory in nature and attributed to worsening ALS — occurred in 2.2% of the edaravone group versus 1.1% of placebo.

A real-world retrospective chart review at the Massachusetts General Hospital ALS Clinic described clinical experience with sodium phenylbutyrate and taurursodiol (PB and TURSO), which was approved in the United States in 2022 and voluntarily withdrawn in 2024 following negative phase 3 results. Of 441 patients who received a prescription, 329 (75%) initiated treatment, with an average treatment duration of 285 days. The drug discontinuation rate during the study period was 41% (N=135), with side effects accounting for the most common reason for discontinuation (N=93, 69%), predominantly gastrointestinal issues (N=69). No hospitalizations, deaths, or serious adverse events were considered related to treatment with PB and TURSO.

The Evolving and Challenging ALS Treatment Landscape

The ALS treatment landscape has undergone meaningful expansion over the past several years, with regulatory approvals reflecting both mechanistic diversity and the persistent challenge of demonstrating durable clinical benefit. As of the end of 2023, five therapies carried FDA approval for ALS: riluzole, edaravone, dextromethorphan hydrobromide + quinidine sulfate, tofersen, and sodium phenylbutyrate-tauroursodeoxycholic acid (PB-TUDCA). Among these, tofersen — an antisense oligonucleotide targeting mutant SOD1 mRNA — represents a paradigm shift toward precision medicine, receiving accelerated approval based in part on reductions in neurofilament light chain (NfL), a surrogate biomarker recognized by the FDA as reasonably likely to predict clinical benefit. The phase 3 VALOR trial did not meet its primary ALSFRS-R endpoint at 28 weeks, yet extension data from the open-label phase demonstrated that earlier initiation of tofersen was associated with numerically less decline across measures of clinical function (ALSFRS-R score, -9.9 vs -13.5 points), respiratory function (slow vital capacity, -13.8% vs -18.1%), muscle strength (handheld dynamometry megascore, -0.38 vs -0.43 points), and quality of life over 148 weeks, alongside prolonged survival relative to the expected natural history of SOD1-ALS.

The trajectory of PB-TUDCA illustrates the volatility of the ALS development landscape. The phase 2 CENTAUR trial demonstrated a statistically significant reduction in ALSFRS-R decline (-1.24 points per month with active drug vs -1.66 points per month with placebo; difference 0.42 points per month; 95% CI, 0.03–0.81; P = 0.03), with post hoc analysis suggesting a median survival benefit of 4.8 months. However, the phase 3 PHOENIX trial (NCT05021536) showed no change in ALSFRS-R total score at 48 weeks, prompting the sponsor to initiate voluntary withdrawal of marketing authorizations with both the US FDA and Health Canada. In parallel, a retrospective population-based cohort study of TUDCA monotherapy in the Emilia Romagna Region of Italy reported a median overall survival of 49.6 months (95% CI 41.7–93.5) in TUDCA-treated patients versus 36.2 months (95% CI 32.7–41.6) in controls, with a reduced risk of death in patients receiving ≥1000 mg/day (HR 0.56; 95% CI 0.38–0.83; P = 0.0042), though the authors noted the exploratory nature of these findings and the need for prospective randomized confirmation.

Beyond approved agents, the investigational pipeline reflects growing interest in immunomodulatory and cell-based strategies. A phase 2A open-label study of tegoprubart, an anti-CD40L antibody, enrolled 54 participants across four dose cohorts (1, 2, 4, and 8 mg/kg) and demonstrated dose-dependent target engagement alongside reductions in 18 pro-inflammatory biomarkers, with the most common treatment-emergent adverse events being fatigue (25.9%), falls (22.2%), headaches (20.4%), and muscle spasms (11.1%). A phase I trial of autologous stromal vascular fraction (SVF) therapy in 26 patients reported significant reductions in CSF NfL (Δ530.29 pg/mL, P = 0.039) and GFAP (Δ622.23 pg/mL, P = 0.038), though ALSFRS-R scores showed no significant change (Δ-0.53, P = 0.384). Collectively, these data underscore both the expanding mechanistic breadth of ALS drug development and the continued difficulty of translating biomarker signals and phase 2 findings into confirmed phase 3 efficacy — a challenge that remains central to strategic planning across the field.

Emerging Endpoints Guiding NX210c's Path Forward

The ALS clinical research landscape has seen a meaningful expansion in endpoint diversity over the past three years, moving beyond traditional functional scales toward multimodal, remote, and biomarker-driven measures. This shift reflects both the complexity of ALS disease biology and the growing demand for trial designs that are sensitive, patient-centric, and capable of capturing progression across cognitive, motor, and respiratory domains.

• Survival and ventilation-free endpoints: The CENTAUR trial demonstrated that tracheostomy/permanent assisted ventilation (PAV)-free survival and time to first hospitalisation are clinically meaningful endpoints. Early sodium phenylbutyrate/taurursodiol (PB/TURSO) treatment reduced the risk of death or tracheostomy/PAV (HR = 0.51; 95% CI 0.32 to 0.84; p = 0.007) and delayed first hospitalisation (HR = 0.56; 95% CI 0.34 to 0.95; p = 0.03), validating these composite endpoints for long-term ALS trials.

• Novel disability and functional rating scales: The Rasch-Built Overall ALS Disability Scale (ROADS) is emerging as a reliable outcome measure. Multivariate Cox models confirmed that baseline ROADS positively correlated with ALS survival (HR = 0.95, p < 0.001) and that ΔROADS negatively correlated with survival (HR = 1.26, p < 0.001). ROADS declined significantly over time in a pattern similar to ALSFRS-R, supporting its use as a complementary or alternative functional endpoint in clinical trials.

• Blood neurofilament biomarkers: Blood neurofilament light chain (NfL) and phosphorylated neurofilament heavy chain (pNfH) are consolidating as prognostic endpoints. A meta-analysis of 1,619 ALS patients found that higher blood NfL levels were associated with a significantly higher risk of death (high vs. low NfL: HR = 4.51; 95% CI 2.45–8.32; p < 0.01), and both NfL and pNfH positively correlated with disease progression rate (NfL: summary r = 0.53; pNfH: summary r = 0.51; both p < 0.01).

• Digital and remote speech biomarkers: The PROSA study is developing low-burden, telephone-based speech biomarkers capable of objectively measuring cognitive, motor, and respiratory symptoms. Collected at four longitudinal time points across 75 ALS and 75 FTD patients, these speech-based phenotypes are intended to support diagnostic and prognostic modelling, with direct implications for clinical trial stratification.

• Remote respiratory function monitoring: Home-based spirometry is emerging as a feasible and reliable endpoint modality. In the Radcliff Study (67 people with ALS), home-measured Slow Vital Capacity (SVC) and Forced Vital Capacity (FVC) followed a linear trajectory over 7.7 ± 4.0 months, aligning with in-clinic pulmonary test results and supporting less frequent monitoring without compromising assessment precision.

• Neuroimaging and oxidative stress biomarkers: Diffusion tensor imaging (DTI) parameters — particularly Peduncle-MD (AUC = 0.896) and Peduncle-FA (AUC = 0.890) — are being evaluated as diagnostic and progression endpoints, with Capsule-FA identified as a potential surrogate biomarker for disease severity. Concurrently, the EPIC-ALS trial incorporates plasma and CSF oxidative stress markers (8-OHdG, 3-NT) alongside NfL and pNfH as mechanistic biomarker endpoints.

NX210c's ALS Journey: Beyond Initial Biomarker Hurdles

The journey to develop effective treatments for amyotrophic lateral sclerosis (ALS) is fraught with complexity, a reality underscored by Axoltis Pharma's recent Phase II SEALS study for NX210c. While the trial did not meet its primary endpoints of neurofilament light chain (NfL) and albumin quotient (Qalb) levels at six weeks, the company reported 'consistent positive trends' in secondary and exploratory measures, including a reduction in the decline rate of the ALS Functional Rating Scale-Revised (ALSFRS-R) and improvements in motor function.

This outcome highlights a critical tension in ALS drug development: the challenge of aligning short-term biomarker endpoints with long-term clinical benefit. Research consistently shows that NfL is a robust prognostic biomarker for ALS, strongly correlating with disease progression and survival. In contrast, while CNS barrier impairment, indicated by elevated Qalb, is observed in ALS patients and linked to functional decline and survival (particularly in males), its prognostic value is considered limited compared to NfL. NX210c's preclinical data demonstrating its capacity to strengthen the blood-brain barrier (BBB) aligns with the observed 'BBB recovery' trend, suggesting a plausible mechanism of action.

However, the reliance on post-hoc analyses and positive trends, rather than statistically significant primary endpoint achievement, introduces a degree of uncertainty. The 6-week timeframe for primary endpoints might be too brief to capture the full impact of a potential disease-modifying therapy in a chronic condition like ALS. Axoltis's plan for further analysis, including a 10-month follow-up, and presentation at Neuroscience 2026 will be pivotal. These longer-term data are essential to determine if the observed functional benefits are sustained and clinically meaningful, and to guide future trial designs that may need to consider different endpoints or patient stratification strategies, perhaps focusing on specific patient populations where BBB integrity plays a more pronounced role.