Discovery of a highly specific ^(18)F-labeled PET ligand for phosphodiesterase 10A enabled by novel spirocyclic iodonium ylide radiofluorination

As a member of cyclic nucleotide phosphodiesterase(PDE)enzyme family,PDE10A is in charge of the degradation of cyclic adenosine(cAMP)and guanosine monophosphates(cGMP).While PDE10A is primarily expressed in the medium spiny neurons of the striatum,it has been implicated in a variety of neurological disorders.Indeed,inhibition of PDE10A has proven to be of potential use for the treatment of central nervous system(CNS)pathologies caused by dysfunction of the basal ganglia–of which the striatum constitutes the largest component.A PDE10A-targeted positron emission tomography(PET)radioligand would enable a better assessment of the pathophysiologic role of PDE10A,as well as confirm the relationship between target occupancy and administrated dose of a given drug candidate,thus accelerating the development of effective PDE10A inhibitors.In this study,we designed and synthesized a novel ^(18)F-aryl PDE10A PET radioligand,codenamed[^(18)F]P10A-1910([^(18)F]9),in high radiochemical yield and molar activity via spirocyclic iodonium ylide-mediated radiofluorination.[^(18)F]9 possessed good in vitro binding affinity(IC_(50)=2.1 nmol/L)and selectivity towards PDE10A.Further,[^(18)F]9 exhibited reasonable lipophilicity(logD=3.50)and brain permeability(P_(app)>10×10^(−6) cm/s in MDCK-MDR1 cells).PET imaging studies of[^(18)F]9 revealed high striatal uptake and excellent in vivo specificity with reversible tracer kinetics.Preclinical studies in rodents revealed an improved plasma and brain stability of[^(18)F]9 when compared to the current reference standard for PDE10A-targeted PET,[^(18)F]MNI659.Further,dose–response experiments with a series of escalating doses of PDE10A inhibitor 1 in rhesus monkey brains confirmed the utility of[^(18)F]9 for evaluating target occupancy in vivo in higher species.In conclusion,our results indicated that[^(18)F]9 is a promising PDE10A PET radioligand for clinical translation.

Stimulation of in vitro bone formation by canine prostate cancer

Aim:Patients with prostate cancer frequently develop osteoblastic bone metastases.Canine models are important because dogs are the only mammal to develop spontaneous prostate cancer with osteoblastic bone metastases similar to men.The mechanism by which prostate cancer induces bone formation is unclear;however,it depends on the complex interaction between prostate cancer cells and bone microenvironment.This study investigated the effects of three canine prostate cancer cell lines(Ace-1,LuMa,and Probasco)on bone formation and resorption in vitro.Methods:Mouse calvaria were treated with conditioned medium(CM)from cell lines.Calvaria were evaluated by histology,fluorescent calcein uptake at sites of bone mineralization,medium calcium assay,and alkaline phosphatase activity.The expression of bone-related genes was measured using quantitative reverse transcription PCR.Results:A novel calcein uptake assay was developed to measure bone formation and mineralization in vitro.Ace-1 CM induced predominantly bone resorption in calvaria,while Probasco CM induced marked bone formation,mineralization,and healing of calvaria defects.The expression of osteoblast-related genes in calvaria showed that Probasco CM stimulated the maturation and differentiation of osteoblasts and inhibited osteoclastogenesis.Both bone modeling and remodeling were involved in Probasco CM-induced bone formation and mineralization by inhibiting remodeling with zoledronic acid.Inhibition of WNT activity by DKK-1 decreased the osteoblastic activity of Probasco cells.Conclusion:Probasco cells induced bone formation and mineralization in vitro that depended on the WNT signaling pathway.Probasco cells will serve as a valuable model for studying the mechanisms of osteoblastic bone metastasis in prostate cancer.