Fibroblast growth factor 21 is an emerging metabolic regulator that was recently proposed to be a fed-state inducible factor in adipose tissue. As mice lacking FGF21 were refractory to treatment with rosiglitazone, FGF21 was suggested to underlie PPARγ-driven pharmacology and side effect profile (Dutchak et al., 2012 [12]). To evaluate FGF21/PPARγ cross-talk we conducted experiments in control and FGF21 null animals and found that rosiglitazone was equally efficacious in both strains. Specifically, diverse endpoints ranging from enhanced glycemic control, improved lipid homeostasis and side effects such as adipose accumulation were evident in both genotypes. Furthermore, the transcriptional signature and cytokine secretion profile of rosiglitazone action were maintained in our FGF21KO animals. Finally, we found that FGF21 in adipose was expressed at comparable levels in fasted and fed states. Thus, our data present a new viewpoint on the FGF21/PPARγ interplay whereby FGF21 is not necessary for the metabolic events downstream of PPARγ.

We aimed to develop effective radioligands for quantifying brain O-linked-β-N-acetyl-glucosamine (O-GlcNAc) hydrolase (OGA) using positron emission tomography in living subjects as tools for evaluating drug target engagement. Posttranslational modifications of tau, a biomarker of Alzheimer’s disease, by O-GlcNAc through the enzyme pair OGA and O-GlcNAc transferase (OGT) are inversely related to the amounts of its insoluble hyperphosphorylated form. Increase in tau O-GlcNAcylation by OGA inhibition is believed to reduce tau aggregation. LSN3316612, a highly selective and potent OGA ligand [half-maximal inhibitory concentration (IC50) = 1.9 nM], emerged as a lead ligand after in silico analysis and in vitro evaluations. [3H]LSN3316612 imaged and quantified OGA in postmortem brains of rat, monkey, and human. The presence of fluorine and carbonyl functionality in LSN3316612 enabled labeling with positron-emitting fluorine-18 or carbon-11. Both [18F]LSN3316612 and [11C]LSN3316612 bound reversibly to OGA in vivo, and such binding was blocked by pharmacological doses of thiamet G, an OGA inhibitor of different chemotype, in monkeys. [18F]LSN3316612 entered healthy human brain avidly (~4 SUV) without radiodefluorination or adverse effect from other radiometabolites, as evidenced by stable brain total volume of distribution (VT) values by 110 min of scanning. Overall, [18F]LSN3316612 is preferred over [11C]LSN3316612 for future human studies, whereas either may be an effective positron emission tomography radioligand for quantifying brain OGA in rodent and monkey.

The muscarinic M 1 receptor (M 1 R) is highly involved in cognition, and selective M 1 agonists have procognitive properties. Loss of M 1 R has been found in postmortem brain tissue for several neuropsychiatric disorders and may be related to symptoms of cognitive dysfunction. 123 I-iododexetimide is used for imaging muscarinic acetylcholine receptors (mAchRs). Considering its high brain uptake and intense binding in M 1 R-rich brain areas, 123 I-iododexetimide may be an attractive radiopharmaceutical to image M 1 R. To date, the binding affinity and selectivity of 123 I-iododexetimide for the mAchR subtypes has not been characterized, nor has its brain distribution been studied intensively. Therefore, this study aimed to address these topics. Methods: The in vitro affinity and selectivity of 127 I-iododexetimide (cold-labeled iododexetimide), as well as its functional antagonist properties (guanosine 5′-[γ-35 S-thio]triphosphate [GTPγ 35 S] assay), were assessed on recombinant human M 1 R-M 5 R. Distributions of 127 I-iododexetimide and 123 I-iododexetimide in the brain were evaluated using liquid chromatography-mass spectrometry and storage phosphor imaging, respectively, ex vivo in rats, wild-type mice, and M 1 -M 5 knock-out (KO) mice. Inhibition of 127 I-iododexetimide and 123 I-iododexetimide binding in M 1 R-rich brain areas by the M 1 R/ M 4 R agonist xanomeline, or the antipsychotics olanzapine (M 1 R antagonist) and haloperidol (low M 1 R affinity), was assessed in rats ex vivo. Results: In vitro, 127 I-iododexetimide displayed high affinity for M 1 R (pM range), with modest selectivity over other mAchRs. In biodistribution studies on rats, ex vivo 127 I-iododexetimide binding was much higher in M 1 R-rich brain areas, such as the cortex and striatum, than in cerebellum (devoid of M 1 Rs). In M 1 KO mice, but not M 2 -M 5 KO mice, 127 I-iododexetimide binding was strongly reduced in the frontal cortex compared with wild-type mice. Finally, acute administration of both an M 1 R/M 4 R agonist xanomeline and the M 1 R antagonist olanzapine was able to inhibit 123 I-iododexetimide ex vivo, and 123 I-iododexetimide binding in M 1 -rich brain areas in rats, whereas administration of haloperidol had no effect. Conclusion: The current results suggest that 123 I-iododexetimide preferentially binds to M 1 R in vivo and can be displaced by M 1 R ligands. 123 I-iododexetimide may therefore be a useful imaging tool as a way to further evaluate M 1 R changes in neuropsychiatric disorders, as a potential stratifying biomarker, or as a clinical target engagement biomarker to assess M 1 R.

Background LY3372689, an O‐GlcNAcase (OGA) enzyme inhibitor, is being developed as a potential treatment of tauopathies, including Alzheimer’s disease. OGA inhibition is proposed to delay the progression of tau‐related diseases by slowing the accumulation of hyper‐phosphorylated, insoluble tau filaments. Herein, we report on nonclinical and clinical studies that assessed the effect of LY3372689 on brain OGA enzyme occupancy (EO). Method Brain OGA EO of LY3372689 was measured in the frontal cortex of rats using tracer LSN3291920, a non‐fluorinated analog of a positron emission tomography (PET) radioligand 18F‐ LY3316612. A single oral dose study in healthy volunteers (HV) utilizing18F‐LY3316612 is ongoing to assess brain OGA EO of LY3372689 (NCT03944031). The study consists of up to 5 Cohorts (N = 3 – 6 subjects per Cohort). Upon completion, each subject will have participated in one cohort and have received a baseline PET scan and up to two post‐dose PET scans. In the initial cohorts, the post‐dose PET scans were conducted at approximately 2 and 24 hours after LY3372689 administration. The study design is adaptive to allow adjustment of the LY3372689 dose, timing of PET scans and pharmacokinetic samples, and number of subjects, pending results of prior cohorts. Result In rat studies, LY3372689 demonstrated a dose‐dependent change in OGA EO following a single oral dose with a maximum EO of greater than 90%. In the human PET study, a total of 12 healthy volunteers across 3 dose cohorts (N = 4 HV per cohort) have been enrolled to date. A plasma concentration‐dependent increase in brain OGA EO was observed with EO exceeding 90% at 24 hours following the highest dose of LY3372689 administered. Conclusion Non‐clinical and clinical EO studies demonstrated that occupancy of the OGA enzyme effectively translated from rats to humans after single doses of LY3372689. The human PET data can be used to support LY3372869 dose selection for efficacy trials in tauopathies.

Prostaglandins E1 and E2 are synthesized in the intestine and mediate a range of gastrointestinal functions via activation of the prostanoid E type (EP) family of receptors. We examined the potential role of EP receptors in the regulation of gut hormone secretion from L cells. Analysis of mRNA expression in mouse enteroendocrine GLUTag cells demonstrated the abundant expression of EP4 receptor, whereas expression of other EP receptors was much lower. Prostaglandin E1 and E2, nonselective agonists for all EP receptor subtypes, triggered glucagon like peptide 1 (GLP-1) secretion from GLUTag cells, as did the EP4-selective agonists CAY10580 and TCS2510. The effect of EP4 agonists on GLP-1 secretion was blocked by incubation of cells with the EP4-selective antagonist L161,982 or by down-regulating EP4 expression with specific small interfering RNA. Regulation of gut hormone secretion with EP4 agonists was further studied in mice. Administration of EP4 agonists to mice produced a significant elevation of plasma levels of GLP-1, glucagon like peptide 2 (GLP-2) and peptide YY (PYY), whereas gastric inhibitory peptide (GIP) levels were not increased. Thus, our data demonstrate that activation of the EP4 receptor in enteroendocrine L cells triggers secretion of gut hormones.