CAMBRIDGE, Mass., Aug. 21, 2025 — Allos Pharma Inc., announces key milestones advancing its mission to deliver effective treatments for Autism Spectrum Disorder (ASD), Fragile X Syndrome, and related neurodevelopmental disorders. Global…
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Arbaclofen delivers clinically meaningful improvements in social functioning and irritability across Fragile X Syndrome and Autism Spectrum Disorder.
ABOUT US
Allos Pharma is committed to delivering science-based treatments for underserved neurodevelopmental and neurological disorders. Arbaclofen is the first therapy to show replicated improvements in social functioning and irritability in children with Fragile X Syndrome and ASD — with additional promise in genetically defined subgroups like 16p11.2 deletion syndrome.
Disease Area
Arbaclofen works by modulating GABA-B receptors, restoring inhibitory balance in key brain circuits implicated in Fragile X Syndrome and Autism Spectrum Disorder. Clinical trials have demonstrated statistically significant improvements in social functioning, irritability, and daily living skills — with a safety profile comparable to placebo over 3 years of use in over 700 patients.
SCIENCE
Increases in relative excitatory:inhibitory balance are commonly observed in humans with, and animal models of, autism spectrum disorders
Arbaclofen selectively activates GABA-B receptors to decrease presynaptic release of excitatory neurotransmitters while simultaneously decreasing excitability of the postsynaptic neuron.
Activation of GABA-B receptors effectively normalizes excitatory: inhibitory balance in animal models of ASD and FXS.
Arbaclofen treatment produces broad phenotypic improvements in animal models and humans
Arbaclofen is a potent and selective agonist of GABA-B receptors
Preclinical: Arbaclofen is 10 times more potent than GABA itself
Excellent safety & tolerability confirmed in 360 humans with fragile X syndrome, including >200 subjects treated for over a year
Founders
Mark Bear, PhD, Professor
Dr. Mark Bear is Picower Professor of Neuroscience in The Picower Institute for Learning and Memory and the Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology. He was an Investigator of the Howard Hughes Medical Institute for 22 years from 1994 to 2015 and served as Director of the Picower Institute from 2007 to 2009. Prior to moving to MIT in 2003, Dr. Bear was on the faculty of Brown University School of Medicine for 17 years.
Dr. Carpenter’s career experience includes leadership positions in academic medicine, pharmaceutical, and biotechnology companies. He previously founded Seaside Therapeutics to leverage breakthrough scientific discoveries and develop therapeutics capable of correcting molecular perturbations that increase vulnerability to intellectual disability and autism. He currently serves as the CMO of the Rett Syndrome Research Trust, is a member of the advisory boards of EU-AIMS and the Translational Neuroscience Center of Boston Children’s Hospital, and is a research affiliate in the Department of Brain and Cognitive Sciences at MIT.
While in industry, he led translational medicine teams responsible for eight successful IND submissions and dozens of FDA-compliant clinical trials. Prior to joining industry, he held academic faculty appointments at the University of Washington and Wake Forest University, where he specialized in anesthesiology, pain management, and translational medicine.
Randall Carpenter, MD
Fragile X Syndrome:
National Fragile X Foundation – www.fragilex.org
FRAXA Research Foundation – www.fraxa.org
RESOURCES
Autism Spectrum Disorder:
Autism Speaks – www.autismspeaks.org
Autism Science Foundation – autismsciencefoundation.org
SFARI – www.sfari.org
Selected publications
- Arbaclofen in Children and Adolescents with Autism Spectrum Disorder: A Randomized, Controlled, Phase 2 Trial.Veenstra-VanderWeele JM, Cook EH, King BH, Zarevics P, Cherubini M,Walton-Bowen K, Bear MF, Wang PP, Carpenter RL. Neuropsychopharmacology. 2016, 1-9 Oct 17. doi: 10.1038/npp.2016.237 [Epub ahead of print]
- STX209 (Arbaclofen) for Autism Spectrum Disorders: An 8-Week Open-Label Study. Erickson CA, Veenstra-Vanderweele JM, Melmed RD, McCracken JT, Ginsberg LD, Sikich L, Scahill L, Cherubini M, Zarevics P, Walton-Bowen K, Carpenter RL, Bear MF, Wang PP, King BH. J Autism Dev Disord. 2014 44(4):958-64.
- Effects of STX209 (arbaclofen) on neurobehavioral function in children and adults with fragile X syndrome: A randomized, controlled, Phase 2 trial. Berry-Kravis E, Hessl D, Rathmell B, Zarevics P, Cherubini M, Walton-Bowen K, Gonzales-Heydrich J, Wang P, Carpenter RL, Bear MF, Hagerman R. Science Translational Medicine. 2012 19;4(152):152ra127.
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The mGluR theory of Fragile X mental retardation M.F. Bear, K. M. Huber and S.T. Warren, 2004 July. Trends in Neuroscience; 27(7): 370-377
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The Autistic Neuron: Troubled Translation? R.J. Kelleher and M.F.Bear, 2008 Oct. Cell. 135(3): 401-6
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Arbaclofen in fragile X syndrome: results of phase 3 trials E. Berry-Kravis, R. Hagerman, J. Visootsak, D. Budimirovic, WE. Kaufmann ,M. Cherubini, P. Zarevics, K. Walton-Bowen, P. Wang,M. Bear MF9, R. Carpenter, 2017 June. Journal of Neurodevelopmental Disorders; 12;9:3
- Arbaclofen produces clinically meaningful improvements in individuals with Fragile X: R. L. Carpenter, M. E. Matthiesen, D. C. Stoppel, S. Hudgens, M. F. Bear, 2022 July. NFXF International Fragile X Conference.
- Reversal of disease phenotypes in the Fragile X mouse model by selective activation of GABA-B receptors.Henderson C, Wijetunge L, Nakamoto Kinoshita M, Shumway M, Postma FR, Brynczka C, Hammond RS, Rush R, Thomas A, Paylor R, Warren ST, Vanderklish PW, Kind PC, Carpenter RL, Bear MF, Healy AH. Science Translational Medicine. 2012 19;4(152):152ra128.
- R-baclofen reverses cognitive deficits and improves social interactions in two lines of 16p11.2 deletion mice.Stoppel LJ, Kazdoba TM, Schaffler MD, Preza AR, Heynen A, Crawley JN, Bear MF. Neuropsychopharmacology. 2018 Feb;43(3):513-524
- Identification of small molecules rescuing fragile X syndrome phenotypes in Drosophila. Chang S, Bray SM, Li Z, Zarnescu DC, He C, Jin P, Warren ST. Nat Chem Biol.2008 Apr;4(4):256-6
News
Allos announced today that it has held a meeting with the U.S. Food and Drug Administration (FDA) to optimize the design of their Phase 3 trial.
Allos announced presentation of “Arbaclofen produces clinically meaningful improvements in individuals with Fragile X” at the 18th NFXF International Fragile X Conference, July 14-17th, 2022.
Allos announced the exclusive license rights on arbaclofen in Fragile X Syndrome (FXS). The company is preparing the regulatory path for market authorization.
