title: SMN Protein Can Be Reliably Measured in Whole Blood with an Electrochemiluminescence (ECL) Immunoassay: Implications for Clinical Trials.
abstract: Spinal muscular atrophy (SMA) is caused by defects in the survival motor neuron 1 (SMN1) gene that encodes survival motor neuron (SMN) protein. The majority of therapeutic approaches currently in clinical development for SMA aim to increase SMN protein expression and there is a need for sensitive methods able to quantify increases in SMN protein levels in accessible tissues. We have developed a sensitive electrochemiluminescence (ECL)-based immunoassay for measuring SMN protein in whole blood with a minimum volume requirement of 5μL. The SMN-ECL immunoassay enables accurate measurement of SMN in whole blood and other tissues. Using the assay, we measured SMN protein in whole blood from SMA patients and healthy controls and found that SMN protein levels were associated with SMN2 copy number and were greater in SMA patients with 4 copies, relative to those with 2 and 3 copies. SMN protein levels did not vary significantly in healthy individuals over a four-week period and were not affected by circadian rhythms. Almost half of the SMN protein was found in platelets. We show that SMN protein levels in C/C-allele mice, which model a mild form of SMA, were high in neonatal stage, decreased in the first few weeks after birth, and then remained stable throughout the adult stage. Importantly, SMN protein levels in the CNS correlated with SMN levels measured in whole blood of the C/C-allele mice. These findings have implications for the measurement of SMN protein induction in whole blood in response to SMN-upregulating therapy.
authors.affiliation: PharmOptima, Portage, Michigan, United States of America.
authors.forename: Phillip
authors.initials: P
authors.lastname: Zaworski
authors.affiliation: Spinal Muscular Atrophy Foundation, New York, New York, United States of America.
authors.forename: Katharine M
authors.initials: KM
authors.lastname: von Herrmann
authors.affiliation: PharmOptima, Portage, Michigan, United States of America.
authors.forename: Shannon
authors.initials: S
authors.lastname: Taylor
authors.affiliation: Spinal Muscular Atrophy Foundation, New York, New York, United States of America.
authors.forename: Sara S
authors.initials: SS
authors.lastname: Sunshine
authors.affiliation: Spinal Muscular Atrophy Foundation, New York, New York, United States of America.
authors.forename: Kathleen
authors.initials: K
authors.lastname: McCarthy
authors.affiliation: PTC Therapeutics, South Plainfield, New Jersey, United States of America.
authors.forename: Nicole
authors.initials: N
authors.lastname: Risher
authors.affiliation: Department of Neurology, University of Utah School of Medicine, Salt Lake City, Utah, United States of America.
authors.forename: Tara
authors.initials: T
authors.lastname: Newcomb
authors.affiliation: PTC Therapeutics, South Plainfield, New Jersey, United States of America.
authors.forename: Marla
authors.initials: M
authors.lastname: Weetall
authors.affiliation: Department of Molecular Pathology, Wexner Medical Center, Ohio State University, Columbus, Ohio, United States of America.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Prior
authors.affiliation: Department of Neurology, University of Utah School of Medicine, Salt Lake City, Utah, United States of America.
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Swoboda
authors.affiliation: Spinal Muscular Atrophy Foundation, New York, New York, United States of America.
authors.forename: Karen S
authors.initials: KS
authors.lastname: Chen
authors.affiliation: Spinal Muscular Atrophy Foundation, New York, New York, United States of America.
authors.forename: Sergey
authors.initials: S
authors.lastname: Paushkin
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D016022:Case-Control Studies; D004195:Disease Models, Animal; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D008163:Luminescent Measurements / Q000379:methods*; D051379:Mice; D009134:Muscular Atrophy, Spinal / Q000097:blood / Q000175:diagnosis / Q000628:therapy; D055550:Protein Stability; D055532:SMN Complex Proteins / Q000097:blood* / Q000134:cerebrospinal fluid / Q000378:metabolism
chemical_list: D055532:SMN Complex Proteins