I017 Countering mHtt neurotoxicity by a small-molecule drug

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Background Neurotoxicity of mutant huntingtin (mHtt) with an expanded polyglutamine stretch is the driving force of neurodegeneration in Huntington’s disease (HD) patients. Aims Development of an oral, small-molecule drug inhibitor of mHtt neurotoxicity to treat HD patients. Methods/Techniques Phenotypic screening of small-molecules in a cell-based model of mHtt toxicity; efficacy studies using in-vivo models and iPSC patient-derived medium spiny neurons (MSNs); mitochondrial calcium imaging, gene silencing, electrophysiology Results/Outcome A potent lead compound was identified with excellent oral bioavailability and brain permeability which countered mHtt neurotoxicity in-cellulo. Validation in a mouse model of HD revealed full restoration of cortico-striatal transmission, rescued post-synaptic markers of MSNs and normalised phenotypes. Dose-response studies revealed an effective oral dose (ED50) of 0.11 mg/kg in line with its in vitro potency and translating to a projected human ED50 of 0.6 mg/day/subject. Target deconvolution studies identified an enzyme catalysing the formation of excessive ROS. Enzyme activity assays indicated that the compound inhibits the catalytic activity consistent with co-crystallisation data positioning the compound in the catalytic centre. In patient-derived MSNs, mitochondrial calcium excessively accumulates. Pharmacological inhibition of the target by the identified compound or genetic inhibition of the target-encoding gene mitigated this excessive accumulation of mitochondrial calcium. Conclusions A potent orally bioavailable candidate drug was developed with neuroprotective activity in HD models by targeting a ROS generating enzyme, indicating that excessive ROS production plays a prominent role in mediating mHtt-driven neurotoxicity (Figure 1). The identified lead compound is geared-up for clinical development in 2025.

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