¹⁸F-Labelled Pyrrolopyrimidines Reveal Leucine-rich Repeat Kinase 2 Expression-related Neurodegenerative Risk

Purpose:18F-labelled pyrrolopyrimidines for LRRK2 expression levels determination,[18F]FDG,[18F]AV-45,and[11C]CFT were used in positron emission tomography(PET)imaging of LRRK2 G2019S mice and LRRK2 wild-type(WT)mice to achieve comprehensive understanding of the role of Leucine-rich repeat kinase 2(LRRK2)in related neurodegenerative disorders.Methods:[18F]5-(6-fluoropyridin-3-yl)-N,N-dimethyl-7H-pyrrolo[2,3-d]pyrimidin-4-amine([18F]1)and its morpholine substituted analogue([18F]2)were synthesised using a nucleophilic substitution reaction.The Kd values of 1 and 2 were measured in saturation binding analysis with[18F]1 as the radio-standard.60 minutes dynamic PET scan was performed in LRRK2 G2019S mice and WT mice(n=3).Using brain stem(BS)as the reference tissue,the standardized uptake value ratios(SUVRs)of brain regions,including the olfactory,cortex,striatum,cerebellum,and hippocampus were compared between LRRK2 G2019S mice and WT mice.Besides the behaviours examination and immunohistochemistry(IHC),the neurodegenerative progress was explored using[18F]FDG,[18F]AV-45,and[11C]CFT.Two-way ANOVA and Tukey multiple comparison posttest were used for statistical analysis.Results:Two in vivo-stable 18F-labelled 5-(6-fluoropyridin-3-yl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine derivatives([18F]1 and[18F]2)were synthesised automatically at a 8-10%radiochemical yield(non-decay-corrected)and 0.5-0.95 GBq μmol-1 molar activity.The Kd values of 6.90 nM for 1 and of 14.27 nM for 2 demonstrated their high affinities to LRRK2.Subsequent in vivo microPET imaging indicated the LRRK2 G2019S mice was with high uptake of[18F]1 in olfactory,striatum and hippocampus(P<0.001)compare with WT mice,consistent with the immunohistology results.The results of multiprobe imaging showed that there was only difference in the expression of dopamine transporter between the two mice.Increased olfactory bulb,striatum and hippocampus uptakes was related to LRRK2 G2019S mice cognitive decline and LRRK2 kinase activity up regulate.Conclusion:18F-labelled pyrrolopyrimidines are able to reflect LRRK2 expression with PET,and predict the LRRK2 related risk for Parkinson’s disease.