Synthesis and biological evaluation of [¹¹C]AZ12504948; a novel tracer for imaging of glucokinase in pancreas and liver

Characterization of a Novel M4 PAM PET Radioligand [11C]PF06885190 in Nonhuman Primates (NHP)

Muscarinic acetylcholine receptors (mAChR), including M4, draw attention as therapeutic targets for several neurodegenerative diseases including Alzheimer's disease (AD). PET imaging of M4 positive allosteric modulator (PAM) allows qualification of the distribution as well as the expression of this receptor under physiological conditions and thereby helps to assess the receptor occupancy (RO) of a drug candidate. In this study, our aims were (a) to synthesize a novel M4 PAM PET radioligand [11C]PF06885190 (b) to evaluate the brain distribution of [¹¹C]PF06885190 in nonhuman primates (NHP) and (c) to analyze its radiometabolites in the blood plasma of NHP. Radiolabeling of [¹¹C]PF06885190 was accomplished via N-methylation of the precursor. Six PET measurements were performed using two male cynomolgus monkeys, where three PET measurements were at baseline, two after pretreatment with a selective M4 PAM compound CVL-231 and one after pretreatment with donepezil. The total volume of distribution (V_T) of [¹¹C]PF06885190 was examined using Logan graphical analysis with arterial input function. Radiometabolites were analyzed in monkey blood plasma using gradient HPLC system. Radiolabeling of [¹¹C]PF06885190 was successfully accomplished and the radioligand was found to be stable in the formulation, with radiochemical purity exceeding 99% 1 h after the end of the synthesis. [¹¹C]PF06885190 was characterized in the cynomolgus monkey brain where a moderate brain uptake was found at the baseline condition. However, it showed fast wash-out as it dropped to half of the peak at around 10 min. Change of V_T from baseline was around -10% after pretreatment with a M4 PAM, CVL-231. Radiometabolite studies showed relatively fast metabolism. Although sufficient brain uptake of [¹¹C]PF06885190 was observed, these data suggest that [¹¹C]PF06885190 might have too low specific binding in the NHP brain to be further applied in PET imaging.

An Overview of Prospective Drugs for Type 1 and Type 2 Diabetes

Aims:

The aim of this study is to provide an overview of several emerging anti-diabetic molecules.

Background:

Diabetes is a complex metabolic disorder involving the dysregulation of glucose homeostasis at various levels. Insulin, which is produced by β-pancreatic cells, is a chief regulator of glucose metabolism, regulating its consumption within cells, which leads to energy generation or storage as glycogen. Abnormally low insulin secretion from β-cells, insulin insensitivity, and insulin tolerance lead to higher plasma glucose levels, resulting in metabolic complications. The last century has witnessed extraordinary efforts by the scientific community to develop anti-diabetic drugs, and these efforts have resulted in the discovery of exogenous insulin and various classes of oral anti-diabetic drugs.

Objective:

Despite these exhaustive anti-diabetic pharmaceutical and therapeutic efforts, long-term glycemic control, hypoglycemic crisis, safety issues, large-scale economic burden and side effects remain the core problems.

Method:

The last decade has witnessed the development of various new classes of anti-diabetic drugs with different pharmacokinetic and pharmacodynamic profiles. Details of their FDA approvals and advantages/disadvantages are summarized in this review.

Results:

The salient features of insulin degludec, sodium-glucose co-transporter 2 inhibitors, glucokinase activators, fibroblast growth factor 21 receptor agonists, and GLP-1 agonists are discussed.

Conclusion :

In the future, these new anti-diabetic drugs may have broad clinical applicability. Additional multicenter clinical studies on these new drugs should be conducted.

Imaging pancreatic islet cells by positron emission tomography

It was estimated that every year more than 30000 persons in the United States - approximately 80 people per day - are diagnosed with type 1 diabetes (T1D). T1D is caused by autoimmune destruction of the pancreatic islet (β cells) cells. Islet transplantation has become a promising therapy option for T1D patients, while the lack of suitable tools is difficult to directly evaluate of the viability of the grafted islet over time. Positron emission tomography (PET) as an important non-invasive methodology providing high sensitivity and good resolution, is able to accurate detection of the disturbed biochemical processes and physiological abnormality in living organism. The successful PET imaging of islets would be able to localize the specific site where transplanted islets engraft in the liver, and to quantify the level of islets remain alive and functional over time. This information would be vital to establishing and evaluating the efficiency of pancreatic islet transplantation. Many novel imaging agents have been developed to improve the sensitivity and specificity of PET islet imaging. In this article, we summarize the latest developments in carbon-11, fluorine-18, copper-64, and gallium-68 labeled radioligands for the PET imaging of pancreatic islet cells.

Systematic screening of imaging biomarkers for the Islets of Langerhans, among clinically available positron emission tomography tracers

INTRODUCTION

Functional imaging could be utilized for visualizing pancreatic islets of Langerhans. Therefore, we present a stepwise algorithm for screening of clinically available positron emission tomography (PET) tracers for their use in imaging of the neuroendocrine pancreas in the context of diabetes.

METHODS

A stepwise procedure was developed for screening potential islet imaging agents. Suitable PET-tracer candidates were identified by their molecular mechanism of targeting. Clinical abdominal examinations were retrospectively analyzed for pancreatic uptake and retention. The target protein localization in the pancreas was assessed in silico by -omics approaches and the in vitro by binding assays to human pancreatic tissue.

RESULTS

Six putative candidates were identified and screened by using the stepwise procedure. Among the tested PET tracers, only [(11)C]5-Hydroxy-tryptophan passed all steps. The remaining identified candidates were falsified as candidates and discarded following in silico and in vitro screening.

CONCLUSIONS

Of the six clinically available PET tracers identified, [(11)C]5-HTP was found to be a promising candidate for beta cell imaging, based on intensity of in vivo pancreatic uptake in humans, and islet specificity as assessed on human pancreatic cell preparations. The flow scheme described herein constitutes a methodology for evaluating putative islet imaging biomarkers among clinically available PET tracers.