Safety and efficacy of N-acetylmannosamine (ManNAc) in patients with GNE myopathy: an open-label phase 2 study

Abstract

Purpose: To evaluate the safety and efficacy of N-acetylmannosamine (ManNAc) in GNE myopathy, a genetic muscle disease caused by deficiency of the rate-limiting enzyme in N-acetylneuraminic acid (Neu5Ac) biosynthesis.

Methods: We conducted an open-label, phase 2, single-center (NIH, USA) study to evaluate oral ManNAc in 12 patients with GNE myopathy (ClinicalTrials.gov NCT02346461). Primary endpoints were safety and biochemical efficacy as determined by change in plasma Neu5Ac and sarcolemmal sialylation. Clinical efficacy was evaluated using secondary outcome measures as part of study extensions, and a disease progression model (GNE-DPM) was tested as an efficacy analysis method.

Results: Most drug-related adverse events were gastrointestinal, and there were no serious adverse events. Increased plasma Neu5Ac (+2,159 nmol/L, p < 0.0001) and sarcolemmal sialylation (p = 0.0090) were observed at day 90 compared to baseline. A slower rate of decline was observed for upper extremity strength (p = 0.0139), lower extremity strength (p = 0.0006), and the Adult Myopathy Assessment Tool (p = 0.0453), compared to natural history. Decreased disease progression was estimated at 12 (γ = 0.61 [95% CI: 0.09, 1.27]) and 18 months (γ = 0.55 [95% CI: 0.12, 1.02]) using the GNE-DPM.

Conclusion: ManNAc showed long-term safety, biochemical efficacy consistent with the intended mechanism of action, and preliminary evidence clinical efficacy in patients with GNE myopathy.

Conflict of interest statement

N.C. has been funded by NIAMS grant UO1AR070498-01A1 to conduct a multicenter study of ManNAc for GNE myopathy. N.C., M.C.M., M.H., and W.A.G. obtained funding through Cooperative Research and Development Agreements with Leadiant Biosciences and Escala Therapeutics and donations from the Neuromuscular Disease Foundation and Lumos Pharma. S.V.W. received funding from NIH to perform population PK analysis. C.S.C. received funding from the NIH. M.Q. and S.M.B. received personal fees from the NIH and Leadiant Biosciences for statistical analysis. M.H. and W.A.G. are co-inventors on US patent 8,410,063, entitled N-acetylmannosamine as a therapeutic agent, with royalties paid to NHGRI. The other authors declare no competing interests.

© 2021. This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.

Figures

Fig. 1. Flow diagram.

*Of the 24 planned muscle biopsy pairs, 18 pairs were included in the analysis. BID twice daily.

Fig. 2. Neu5Ac production.

(a) Decreased enzymatic activity of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) results in impaired Neu5Ac production and glycoprotein sialylation. The rate-limiting step in the pathway is catalyzed by UDP-GlcNAc 2-epimerase. ManNAc is phosphorylated by ManNAc kinase. Neu5Ac is activated in the cell nucleus to CMP-Neu5Ac, which acts as the donor of Neu5Ac in the reactions catalyzed by sialyltransferases to sialylate nascent glycoproteins in the Golgi. Sialylated glycoproteins are abundant on plasma membranes where they mediate several biological processes such as cellular adhesion, cell interactions, and signal transduction. FITC-labeled SNA lectin (green), which predominantly binds to terminal α2,6-linked Neu5Ac (Neu5Acα2,6Galβ), and antibodies against the sarcolemmal residence protein Caveolin-3 (Cav-3), are shown. Figure courtesy of Julia Fekecs. (b) Plasma peak concentrations of Neu5Ac by timepoint and dose. The dotted line denotes mean plasma concentration at baseline. To obtain SI units, multiply plasma Neu5Ac in ng/ml by 3.237 to obtain the concentration in nmol/L. (c) Intracellular CMP-Neu5Ac concentrations (mean, SD) measured by liquid chromatography/tandem mass spectrometry (LC/MS-MS) in white blood cells (WBCs) at baseline, 6 and 12 hours after initial dosing, and trough on day 7.

Fig. 3. Sarcolemmal sialylation.

(a, b) Selection of muscle biopsy sites by muscle magnetic resonance image (MRI) in lower extremity muscles. Muscle regions with active disease (arrow) were identified by (a) absence of significant fat replacement on T1-weighted (T1W) and (b) short tau inversion recovery (STIR) hyperintensity (arrow). (c, d) Staining of muscle cryosections with the sarcolemmal marker Caveolin-3 (Cav-3, red) and the SNA lectin that recognizes sialylation (green-blue) at (c) baseline and (d) following 90 days of daily ManNAc administration. (e, f) Sarcolemmal sialylation increased at day 90 compared to baseline as measured by (e) mean and (f) normalized SNA intensities. Each symbol represents a muscle biopsy pair at baseline and day 90 (n = 18), and the line connects the means of both timepoints.

Fig. 4. Clinical efficacy of ManNAc.

(a–f) Clinical efficacy evaluated as the estimated decline for various exploratory clinical efficacy measures in patients with GNE myopathy treated with ManNAc (blue) compared with previously reported natural history (NH) estimates (black), including for (a) lower extremity (LE) strength, (b) upper extremity (UE) strength, (c) Adult Myopathy Assessment Tool (AMAT) total score, (d) 6-minute walk test (6MWT), (e) human activity profile maximum activity score (HAP MAS) and (f) Inclusion Body Myositis Functional Rating Scale (IBMFRS). (g–j) Posterior distribution of treatment effect as estimated by the GNE Myopathy Disease Progression Model (GNE-DPM) at (g) 12 months, (h) 18 months, (i) 24 months, and (j) 30 months, showing the posterior mean (blue marker) with 95% confidence intervals (blue line) of the treatment effect parameter (gamma, γ), and the posterior probability that ManNAc decreased disease progression [Pr(γ < 1)].