A novel imaging ligand as a biomarker for mutant huntingtin-lowering in Huntington’s disease

Huntington’s disease (HD) is a dominantly inherited neurodegenerative disorder caused by a CAG trinucleotide expansion in the huntingtin ( HTT ) gene that encodes the pathologic mutant HTT (mHTT) protein with an expanded polyglutamine (PolyQ) tract. While several therapeutic programs targeting mHTT expression have advanced to clinical evaluation, no method is currently available to visualize mHTT levels in the living brain. Here we demonstrate the development of a positron emission tomography (PET) imaging radioligand with high affinity and selectivity for mHTT aggregates. This small molecule radiolabeled with 11C ([11C]CHDI-180R) enables non-invasive monitoring of mHTT pathology in the brain and can track region-and time-dependent suppression of mHTT in response to therapeutic interventions targeting mHTT expression. We further show that therapeutic agents that lower mHTT in the striatum have a functional restorative effect that can be measured by preservation of striatal imaging markers, enabling a translational path to assess the functional effect of mHTT lowering. ### Competing Interest Statement This work was supported by the non-profit CHDI Foundation, Inc. J.B., L.L., L.M., V.K., Y.W., D.M., M.S., C.D., I.M.-S. are employed by CHDI Management, Inc. as advisors to CHDI Foundation, Inc., and declare no conflict of interest. CHDI Foundation, Inc. is a nonprofit biomedical research organization exclusively dedicated to developing therapeutics that substantially improve the lives of those affected by Huntington's disease, and conducts research in a number of different ways.