Abstract

Stebbeds, Marta1*; Todd, Daniel1; Herva Moyano, Maria1; Iovino, Mariangela1; Jain, Shushant1; Mitchell, Philip1; Breccia, Perla2; Smith, David3; McAllister, George4; Haque, Tasir4; Somalinga, Balajee4; Dominguez, Celia4; Munoz-Sanjuan, Ignacio4 1 Discovery from Charles River, Chesterford Research Park, Saffron Walden, UK; 2 Neuroscience, BioPharmaceuticals R&D, AstraZeneca, Cambridge, UK; 3 Emerging Innovations Unit, Discovery Sciences, R&D, AstraZeneca, Cambridge, UK; 4 CHDI Management/CHDI Foundation, Los Angeles, United States *presenting author Lowering of the pathogenic mutant huntingtin (mHTT) protein in Huntington’s disease (HD) patients is one of the leading approaches to ameliorate the fatal neurodegeneration caused by the poly-CAG expansion in the Htt gene. Current therapeutics in development involve use of novel biological agents such as ASOs, RNAi, ZFTR and CRISPR/Cas9; however, these approaches require invasive administration and have relatively limited biodistribution. To overcome these challenges, we seek to identify brain penetrant small molecules with suitable oral dosing and systemic distribution that selectively lower human mHTT protein. To identify novel agents that reduce physiologically relevant mHTT levels, we have developed an unbiased phenotypic assay in HD-patient derived, polyQ48 embryonic stem cells (ESC) suitable for HTS of large compound collections. AstraZeneca’s Open Innovation HTS Collaboration provided CHDI/CRL access to two AZ compound libraries: EPEC Diverse collection (250k compounds) and Chemogenomics/CNS target collection (15k compounds). A mHTT HTRF-based assay was used to screen both libraries and reliably detect compounds that lower mHTT protein levels. Progressed hits showed good translation in an IC50 format and compounds that mediated effects via toxicity were removed from the screening cascade. Counter-screen and orthogonal assay formats were applied to define specificity and putative mechanisms of action. We will present the unbiased phenotypic HTT-lowering screening results along with the lessons learned and insights into new mechanism-focussed assay strategies in HD neurons.