There is an accumulating body of evidence implicating the muscarinic acetylcholine receptor4(M4)in schizophrenia and dementia with Lewy bodies,however,a clinically validated M4positron emission tomography(PET)radiolig...There is an accumulating body of evidence implicating the muscarinic acetylcholine receptor4(M4)in schizophrenia and dementia with Lewy bodies,however,a clinically validated M4positron emission tomography(PET)radioligand is currently lacking.As such,the aim of this study was to develop a suitable M4PET ligand that allows the non-invasive visualization of M4in the brain.Structure-activity relationship studies of pyrazol-4-yl-pyridine derivates led to the discovery of target compound 12—a subtype-selective positive allosteric modulator(PAM).The radiofluorinated analogue,[18F]12,was synthesized in 28±10%radiochemical yield,>37 GBq/μmol and an excellent radiochemical purity>99%.Initial in vitro autoradiograms on rodent brain sections were performed in the absence of carbachol and showed moderate specificity as well as a low selectivity of[18F]12 for the M4-rich striatum.However,in the presence of carbachol,a significant increase in tracer binding was observed in the rat striatum,which was reduced by>60%under blocking conditions,thus indicating that orthosteric ligand interaction is required for efficient binding o f[18F]12 to the allosteric site.Remarkably,however,the presence of carbachol was not required for high specific binding in the non-human primate(NHP)and human striatum,and did not further improve the specificity and selectivity of[18F]12 in higher species.These results pointed towards significant species-differences and paved the way for a preliminary PET study in NHP,where peak brain uptake of[18F]12 was found in the putamen and temporal cortex.In conclusion,we report on the identification and preclinical development of the first radiofluorinated M4PET radioligand with promising attributes.The availability of a clinically validated M4PET radioligand harbors potential to facilitate drug development and provide a useful diagnostic tool for non-invasive imaging.展开更多
基金supported by the Swiss National Science Foundation(SNSF)supported by the National Health and Medical Research Council(NHMRC)Program Grant(APP1055134,USA)+1 种基金the Australian Research Council(ARC)Discovery Project(DP190102950,USA)supported by grants from Fulbright Denmark,The Lundbeck Foundation,Eva and Henry Frònkels foundation,The Danish Cancer Society,The Harboe Foundation。
文摘There is an accumulating body of evidence implicating the muscarinic acetylcholine receptor4(M4)in schizophrenia and dementia with Lewy bodies,however,a clinically validated M4positron emission tomography(PET)radioligand is currently lacking.As such,the aim of this study was to develop a suitable M4PET ligand that allows the non-invasive visualization of M4in the brain.Structure-activity relationship studies of pyrazol-4-yl-pyridine derivates led to the discovery of target compound 12—a subtype-selective positive allosteric modulator(PAM).The radiofluorinated analogue,[18F]12,was synthesized in 28±10%radiochemical yield,>37 GBq/μmol and an excellent radiochemical purity>99%.Initial in vitro autoradiograms on rodent brain sections were performed in the absence of carbachol and showed moderate specificity as well as a low selectivity of[18F]12 for the M4-rich striatum.However,in the presence of carbachol,a significant increase in tracer binding was observed in the rat striatum,which was reduced by>60%under blocking conditions,thus indicating that orthosteric ligand interaction is required for efficient binding o f[18F]12 to the allosteric site.Remarkably,however,the presence of carbachol was not required for high specific binding in the non-human primate(NHP)and human striatum,and did not further improve the specificity and selectivity of[18F]12 in higher species.These results pointed towards significant species-differences and paved the way for a preliminary PET study in NHP,where peak brain uptake of[18F]12 was found in the putamen and temporal cortex.In conclusion,we report on the identification and preclinical development of the first radiofluorinated M4PET radioligand with promising attributes.The availability of a clinically validated M4PET radioligand harbors potential to facilitate drug development and provide a useful diagnostic tool for non-invasive imaging.
