In vivo efficacy of a kinase inhibitor, roscovitine, in HD mouse model

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Project Summary (Abstract): Huntington’s disease (HD) is caused by a mutation in the huntingtin gene (HTT). Expanded CAG trinucleotide repeats in exon 1 encode polyglutamine in the mutant huntingtin protein (mHTT), causing preferential neurodegeneration in striatum, cortex and other regions. No disease-modifying treatment is available. Mutant HTT lowing approaches are very promising; However, the delivery agents are mostly large molecules with limited brain penetration, requiring invasive procedures. Small molecule RNA-directed therapies are also emerging, but they are generally non-allele specific and may have off target effects on other mRNAs. Huntingtin protein (HTT) has many sites of post-translational modification (PTM). As part of a long-standing program to study PTMs of HTT, we have identified a small number of PTM sites can modify mHTT toxicity, especially those sites with serine and targeting by phosphorylation. Using in vitro kinase screens, we have found that one of those serines, S1181, is actively phosphorylated by CDKs, including CDK1, CDK2 and CDK5, etc. A CDK inhibitor, roscovitine (also known as seliciclib, CYC202), is highly neuroprotective against mHTT toxicity in our HD cell model. As a proof of principle for this strategy, we now propose to determine whether roscovitine can be therapeutically efficacious in an HD mouse model in vivo. Roscovitine is a well-known CDKs inhibitor and has been in several human phase II clinical trials. One previous study in an HD mouse model showed that roscovitine can ameliorate depressive-like behavior in HD mice. However, this study used intracerebral infusion to deliver roscovitine into the brain for a short period of time. Other studies have found that a single oral administration of roscovitine can penetrate brain. We hypothesize that chronic peripheral administration of roscovitine can achieve adequate brain concentrations to inhibit overactivated CDK5, which involves in HD pathogenesis. Thus, it will have beneficial effect in HD mouse model. We have confirmed that single injection of roscovitine can penetrate brain. Three weeks of daily injection is well tolerable in zQ175 HD mice, which is a knock-in mouse express full length human exon1 HTT under mouse huntingtin gene with approximate of 175 CAG repeats. We will inject roscovitine in manifested zQ175 HD mice for long term (6 months). Body weight, behavioral task and MRI scan will be used to compare HD mice treated with or without roscovitine. Brain samples will be collected and brain pathology, molecular biological changes will be examined in HD mice. We expect that roscovitine protect HD mice and can be further translate into HD clinic.