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Drug Annotation Cite This: J. Med. Chem. 2018, 61, 11021−11036
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Discovery of Small Molecule Splicing Modulators of Survival Motor Neuron‑2 (SMN2) for the Treatment of Spinal Muscular Atrophy (SMA) Atwood K. Cheung,*,† Brian Hurley,† Ryan Kerrigan,† Lei Shu,† Donovan N. Chin,†,∥ Yiping Shen,† Gary O’Brien,† Moo Je Sung,† Ying Hou,† Jake Axford,† Emma Cody,† Robert Sun,†,⊥ Aleem Fazal,† Cary Fridrich,† Carina C. Sanchez,† Ronald C. Tomlinson,†,# Monish Jain,† Lin Deng,† Keith Hoffmaster,† Cheng Song,†,∇ Mailin Van Hoosear,†,○ Youngah Shin,† Rebecca Servais,† Christopher Towler,‡ Marc Hild,† Daniel Curtis,†,◆ William F. Dietrich,† Lawrence G. Hamann,†,¶ Karin Briner,† Karen S. Chen,§ Dione Kobayashi,§,∞ Rajeev Sivasankaran,† and Natalie A. Dales*,† †
Novartis Institutes for BioMedical Research, 250 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States Novartis Pharmaceuticals, 250 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States § SMA Foundation, 888 Seventh Avenue, Suite 400, New York, New York 10019, United States ‡
S Supporting Information *
ABSTRACT: Spinal muscular atrophy (SMA), a rare neuromuscular disorder, is the leading genetic cause of death in infants and toddlers. SMA is caused by the deletion or a loss of function mutation of the survival motor neuron 1 (SMN1) gene. In humans, a second closely related gene SMN2 exists; however it codes for a less stable SMN protein. In recent years, significant progress has been made toward disease modifying treatments for SMA by modulating SMN2 pre-mRNA splicing. Herein, we describe the discovery of LMI070/branaplam, a small molecule that stabilizes the interaction between the spliceosome and SMN2 pre-mRNA. Branaplam (1) originated from a high-throughput phenotypic screening hit, pyridazine 2, and evolved via multiparameter lead optimization. In a severe mouse SMA model, branaplam treatment increased full-length SMN RNA and protein levels, and extended survival. Currently, branaplam is in clinical studies for SMA.
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INTRODUCTION SMA is a rare autosomal recessive neuromuscular disorder, occurring in approximately 1 in every 11 000 live births worldwide; however, this deadly disease is the number 1 monogenic cause of death in infants and toddlers.1 SMA is caused by the deletion or mutation of the survival motor neuron 1 (SMN1) gene.2 A closely related gene, survival of motor neuron 2 (SMN2), exists in humans which can partially compensate for the loss of SMN1; however, a single nucleotide mutation in exon7 of SMN2 leads to the exclusion of exon7 from the mature RNA transcript, resulting in a truncated and unstable SMN protein.3 The loss of SMN protein leads to premature degeneration of motor neurons and progressive loss of peripheral and central motor control.2a Infants with the most severe form of SMA (type 1) will never sit and require © 2018 American Chemical Society
interventions such as ventilator assistance and feeding tubes. Milder forms include SMA type 2 (patients sit up but never walk) and type 3 (patients walk but may eventually lose that ability), which manifest at later ages (6−36 months).2 The recently approved (December 2016) splice correcting antisense oligonucleotide (ASO) nusinersen is the only marketed disease-modifying treatment for SMA.4 Nusinersen is administered via an intrathecal injection, and although it provides a valuable treatment option for SMA patients, an orally bioavailable small molecule treatment would have several advantages, including delivery route and wider tissue distribution. Recently, progress has been made toward geneReceived: August 15, 2018 Published: November 8, 2018 11021
DOI: 10.1021/acs.jmedchem.8b01291 J. Med. Chem. 2018, 61, 11021−11036
Journal of Medicinal Chemistry
Drug Annotation
replacement therapy5 and small molecule disease modifying treatments for SMA.6 Publications from PTC Therapeutics and F. Hoffmann-La Roche and our laboratories have described promising orally available small molecule therapies.7−9 We have demonstrated that LMI070/branaplam (1, NVS-SM1, Figure 1) can correct the splicing defect in the
The 3,6-disubstituted pyridazine compound 2 (Figure 2a) was an attractive starting point confirmed through the hit finding efforts. Compound 2 demonstrated activation of the SMN2 reporter of 1700% over DMSO control with an EC50 of 3.5 μM. Moreover, in a mouse SMN ELISA assay, 2 displayed significant increase in SMN protein levels (EC50 = 0.6 μM, 2.5fold increase) and 1.5-fold increase in human patient-derived fibroblasts.9 On the basis of the promising activity data and favorable physicochemical and in vitro profiling data (Table 1), Table 1. ADME/PK Profile of Compound 2 physicochemical properties MW PSA, cLogD (pH 7.4) pKa ADME profile Sol pH 6.8 (mM) Clint (μL min−1 mg−1) in vitro safety hERG binding IC50 (μM) mouse PKa CL (mL min−1 kg−1) oral BAV (%) AUC 0−7 h (μM·h) plasma/brain
Figure 1. Structure of SMN2 splicing modulator NVS-SM1/LMI070/ branaplam (1).
SMN2 gene through stabilizing the interaction between the U1-snRNP complex and SMN2 pre-messenger RNA, leading to generation of functionally competent full length SMN protein.9 Additionally, when administered to transgenic mice bearing the human SMN2 gene, 1 increased levels of full length SMN protein in the central nervous system and extended the lifespan of the diseased mice to match that of their healthy littermates. Clinical trials in type 1 SMA patients are ongoing to evaluate the safety, tolerability, PK/PD, and efficacy of orally dosed 1. Herein, we describe the identification, via highthroughput phenotypic screening, of a pyridazine SMN2 premRNA splicing modulator and medicinal chemistry optimization to the clinical compound branaplam, the first oral small molecule splicing modulator tested in SMA type 1 patients.10
366.5 49.8, 2.67 10.0 >1 22.6 (R), 23.5 (M) 0.6 113 18 0.40/BQLb
a
C57BL/6 mouse PK. Animals were dosed iv at 1 mg/kg; po at 5 mg/ kg, n = 2; 10% 0.1 N HCl, 10% PG, 25 (20%) Solutol, 100 mM pH 5 citrate buffer formulation. bBQL,
