AMG 580: a novel small molecule phosphodiesterase 10A (PDE10A) positron emission tomography tracer

Phosphodiesterase 10A (PDE10A) inhibitors have therapeutic potential for the treatment of psychiatric and neurologic disorders, such as schizophrenia and Huntington's disease. One of the key requirements for successful central nervous system drug development is to demonstrate target coverage of therapeutic candidates in brain for lead optimization in the drug discovery phase and for assisting dose selection in clinical development. Therefore, we identified AMG 580 [1-(4-(3-(4-(1H-benzo[d]imidazole-2-carbonyl)phenoxy)pyrazin-2-yl)piperidin-1-yl)-2-fluoropropan-1-one], a novel, selective small-molecule antagonist with subnanomolar affinity for rat, primate, and human PDE10A. We showed that AMG 580 is suitable as a tracer for lead optimization to determine target coverage by novel PDE10A inhibitors using triple-stage quadrupole liquid chromatography-tandem mass spectrometry technology. [(3)H]AMG 580 bound with high affinity in a specific and saturable manner to both striatal homogenates and brain slices from rats, baboons, and human in vitro. Moreover, [(18)F]AMG 580 demonstrated prominent uptake by positron emission tomography in rats, suggesting that radiolabeled AMG 580 may be suitable for further development as a noninvasive radiotracer for target coverage measurements in clinical studies. These results indicate that AMG 580 is a potential imaging biomarker for mapping PDE10A distribution and ensuring target coverage by therapeutic PDE10A inhibitors in clinical studies.

Discovery of clinical candidate 1-(4-(3-(4-(1H-benzo[d]imidazole-2-carbonyl)phenoxy)pyrazin-2-yl)piperidin-1-yl)ethanone (AMG 579), a potent, selective, and efficacious inhibitor of phosphodiesterase 10A (PDE10A)

We report the identification of a PDE10A clinical candidate by optimizing potency and in vivo efficacy of promising keto-benzimidazole leads 1 and 2. Significant increase in biochemical potency was observed when the saturated rings on morpholine 1 and N-acetyl piperazine 2 were changed by a single atom to tetrahydropyran 3 and N-acetyl piperidine 5. A second single atom modification from pyrazines 3 and 5 to pyridines 4 and 6 improved the inhibitory activity of 4 but not 6. In the in vivo LC-MS/MS target occupancy (TO) study at 10 mg/kg, 3, 5, and 6 achieved 86-91% occupancy of PDE10A in the brain. Furthermore, both CNS TO and efficacy in PCP-LMA behavioral model were observed in a dose dependent manner. With superior in vivo TO, in vivo efficacy and in vivo PK profiles in multiple preclinical species, compound 5 (AMG 579) was advanced as our PDE10A clinical candidate.

Discovery of Novel Imidazo[4,5-b]pyridines as Potent and Selective Inhibitors of Phosphodiesterase 10A (PDE10A)

We report the discovery of novel imidazo[4,5-b]pyridines as potent and selective inhibitors of PDE10A. The investigation began with our recently disclosed ketobenzimidazole 1, which exhibited single digit nanomolar PDE10A activity but poor oral bioavailability. To improve oral bioavailability, we turned to novel scaffold imidazo[4,5-b]pyridine 2, which not only retained nanomolar PDE10A activity but was also devoid of the morpholine metabolic liability. Structure-activity relationship studies were conducted systematically to examine how various regions of the molecule impacted potency. X-ray cocrystal structures of compounds 7 and 24 in human PDE10A helped to elucidate the key bonding interactions. Five of the most potent and structurally diverse imidazo[4,5-b]pyridines (4, 7, 12b, 24a, and 24b) with PDE10A IC50 values ranging from 0.8 to 6.7 nM were advanced into receptor occupancy studies. Four of them (4, 12b, 24a, and 24b) achieved 55-74% RO at 10 mg/kg po.

Initial characterization of a PDE10A selective positron emission tomography tracer [11C]AMG 7980 in non-human primates

INTRODUCTION

Phosphodiesterase 10A (PDE10A) is an intracellular enzyme responsible for the breakdown of cyclic nucleotides which are important secondary messengers in the central nervous system. Inhibition of PDE10A has been identified as a potential therapeutic target for treatment of various neuropsychiatric disorders. To assist the drug development program, we have identified a selective PDE10A PET tracer, [(11)C]AMG 7980, for imaging PDE10A distribution using positron emission tomography.

METHODS

[(11)C]AMG 7980 was prepared in a one-pot, two-step reaction. Dynamic PET scans were performed in non-human primates following a bolus or bolus plus constant infusion tracer injection paradigm. Regions-of-interest were defined on individuals' MRIs and transferred to the co-registered PET images. Data were analyzed using Logan graphical analysis with metabolite-corrected input function, the simplified reference tissue model (SRTM) method and occupancy plots. A benchmark PDE10A inhibitor was used to demonstrate PDE10A-specific binding.

RESULTS

[(11)C]AMG 7980 was prepared with a mean specific activity of 99 ± 74 GBq/μmol (n=10) and a synthesis time of 45 min. Specific binding of the tracer was localized to the striatum and globus pallidus (GP) and low in other brain regions. Thalamus was used as the reference tissue to derive binding potentials (BPND). The BPND for caudate, putamen, and GP were 0.23, 0.65, 0.51, respectively by the graphical method, and 0.42, 0.76, and 0.75 from the SRTM method. A dose dependent decrease of BPND was observed with the pre-treatment of a PDE10A inhibitor. A bolus plus infusion injection paradigm yielded similar results.

CONCLUSION

[(11)C]AMG 7980 has been successfully used for imaging PDE10A in non-human primate brain. Despite the fast brain kinetics it can be used to measure target occupancy of PDE10A inhibitors in non-human primates and potentially applicable to humans.

A quality assurance initiative for commercial-scale production in high-throughput cryopreservation of blue catfish sperm

Cryopreservation of fish sperm has been studied for decades at a laboratory (research) scale. However, high-throughput cryopreservation of fish sperm has recently been developed to enable industrial-scale production. This study treated blue catfish (Ictalurus furcatus) sperm high-throughput cryopreservation as a manufacturing production line and initiated quality assurance plan development. The main objectives were to identify: (1) the main production quality characteristics; (2) the process features for quality assurance; (3) the internal quality characteristics and their specification designs; (4) the quality control and process capability evaluation methods, and (5) the directions for further improvements and applications. The essential product quality characteristics were identified as fertility-related characteristics. Specification design which established the tolerance levels according to demand and process constraints was performed based on these quality characteristics. Meanwhile, to ensure integrity throughout the process, internal quality characteristics (characteristics at each quality control point within process) that could affect fertility-related quality characteristics were defined with specifications. Due to the process feature of 100% inspection (quality inspection of every fish), a specific calculation method, use of cumulative sum (CUSUM) control charts, was applied to monitor each quality characteristic. An index of overall process evaluation, process capacity, was analyzed based on in-control process and the designed specifications, which further integrates the quality assurance plan. With the established quality assurance plan, the process could operate stably and quality of products would be reliable.

Hyperglycemia and prostate cancer recurrence in men treated for localized prostate cancer

BACKGROUND

Obesity is consistently linked with prostate cancer (PCa) recurrence and mortality, though the mechanism is unknown. Impaired glucose regulation, which is common among obese individuals, has been hypothesized as a potential mechanism for PCa tumor growth. In this study, we explore the relationship between serum glucose at time of treatment and risk of PCa recurrence following initial therapy.

METHODS

The study group comprised 1734 men treated with radical prostatectomy (RP) or radiation therapy (RT) for localized PCa between 2001-2010. Serum glucose levels closest to date of diagnosis were determined. PCa recurrence was determined based on PSA progression (nadir PSA+2 for RT; PSA≥0.2 for RP) or secondary therapy. Multivariate Cox regression was performed to determine whether glucose level was associated with biochemical recurrence after adjusting for age, race, body mass index, comorbidity, diagnosis of diabetes, Gleason Sum, PSA, treatment and treatment year.

RESULTS

Recurrence was identified in 16% of men over a mean follow-up period of 41 months (range 1-121 months). Those with elevated glucose (≥100 mg/dl) had a 50% increased risk of recurrence (HR 1.5, 95% CI: 1.1-2.0) compared with those with a normal glucose level (<100 mg/dl). This effect was seen in both those undergoing RP (HR 1.9, 95% CI: 1.0-3.6) and those treated with RT (HR 1.4, 95% CI: 1.0-2.0).

CONCLUSIONS

Glucose levels at the time of PCa diagnosis are an independent predictor of PCa recurrence for men undergoing treatment for localized disease.

Rapid identification of a novel small molecule phosphodiesterase 10A (PDE10A) tracer

A radiolabeled tracer for imaging therapeutic targets in the brain is a valuable tool for lead optimization in CNS drug discovery and for dose selection in clinical development. We report the rapid identification of a novel phosphodiesterase 10A (PDE10A) tracer candidate using a LC-MS/MS technology. This structurally distinct PDE10A tracer, AMG-7980 (5), has been shown to have good uptake in the striatum (1.2% ID/g tissue), high specificity (striatum/thalamus ratio of 10), and saturable binding in vivo. The PDE10A affinity (K(D)) and PDE10A target density (B(max)) were determined to be 0.94 nM and 2.3 pmol/mg protein, respectively, using [(3)H]5 on rat striatum homogenate. Autoradiography on rat brain sections indicated that the tracer signal was consistent with known PDE10A expression pattern. The specific binding of [(3)H]5 to rat brain was blocked by another structurally distinct, published PDE10A inhibitor, MP-10. Lastly, our tracer was used to measure in vivo PDE10A target occupancy of a PDE10A inhibitor in rats using LC-MS/MS technology.

Outlook for development of high-throughput cryopreservation for small-bodied biomedical model fishes

With the development of genomic research technologies, comparative genome studies among vertebrate species are becoming commonplace for human biomedical research. Fish offer unlimited versatility for biomedical research. Extensive studies are done using these fish models, yielding tens of thousands of specific strains and lines, and the number is increasing every day. Thus, high-throughput sperm cryopreservation is urgently needed to preserve these genetic resources. Although high-throughput processing has been widely applied for sperm cryopreservation in livestock for decades, application in biomedical model fishes is still in the concept-development stage because of the limited sample volumes and the biological characteristics of fish sperm. High-throughput processing in livestock was developed based on advances made in the laboratory and was scaled up for increased processing speed, capability for mass production, and uniformity and quality assurance. Cryopreserved germplasm combined with high-throughput processing constitutes an independent industry encompassing animal breeding, preservation of genetic diversity, and medical research. Currently, there is no specifically engineered system available for high-throughput of cryopreserved germplasm for aquatic species. This review is to discuss the concepts and needs for high-throughput technology for model fishes, propose approaches for technical development, and overview future directions of this approach.

Outlook for development of high-throughput cryopreservation for small-bodied biomedical model fishes

With the development of genomic research technologies, comparative genome studies among vertebrate species are becoming commonplace for human biomedical research. Fish offer unlimited versatility for biomedical research. Extensive studies are done using these fish models, yielding tens of thousands of specific strains and lines, and the number is increasing every day. Thus, high-throughput sperm cryopreservation is urgently needed to preserve these genetic resources. Although high-throughput processing has been widely applied for sperm cryopreservation in livestock for decades, application in biomedical model fishes is still in the concept-development stage because of the limited sample volumes and the biological characteristics of fish sperm. High-throughput processing in livestock was developed based on advances made in the laboratory and was scaled up for increased processing speed, capability for mass production, and uniformity and quality assurance. Cryopreserved germplasm combined with high-throughput processing constitutes an independent industry encompassing animal breeding, preservation of genetic diversity, and medical research. Currently, there is no specifically engineered system available for high-throughput of cryopreserved germplasm for aquatic species. This review is to discuss the concepts and needs for high-throughput technology for model fishes, propose approaches for technical development, and overview future directions of this approach.

High-throughput cryopreservation of spermatozoa of blue catfish (Ictalurus furcatus): Establishment of an approach for commercial-scale processing

Hybrid catfish created by crossing of female channel catfish (Ictalurus punctatus) and male blue catfish (Ictalurus furcatus) are being used increasingly in foodfish aquaculture because of their fast growth and efficient food conversion. However, the availability of blue catfish males is limited, and their peak spawning is at a different time than that of the channel catfish. As such, cryopreservation of sperm of blue catfish could improve production of hybrid catfish, and has been studied in the laboratory and tested for feasibility in a commercial dairy bull cryopreservation facility. However, an approach for commercially relevant production of cryopreserved blue catfish sperm is still needed. The goal of this study was to develop practical approaches for commercial-scale sperm cryopreservation of blue catfish by use of an automated high-throughput system (MAPI, CryoBioSystem Co.). The objectives were to: (1) refine cooling rate and cryoprotectant concentration, and evaluate their interactions; (2) evaluate the effect of sperm concentration on cryopreservation; (3) refine cryoprotectant concentration based on the highest effective sperm concentration; (4) compare the effect of thawing samples at 20 or 40°C; (5) evaluate the fertility of thawed sperm at a research scale by fertilizing with channel catfish eggs; (6) test the post-thaw motility and fertility of sperm from individual males in a commercial setting, and (7) test for correlation of cryopreservation results with biological indices used for male evaluation. The optimal cooling rate was 5°C/min (Micro Digitcool, IMV) for high-throughput cryopreservation using CBS high-biosecurity 0.5-ml straws with 10% methanol, and a concentration of 1×10(9)sperm/ml. There was no difference in post-thaw motility when samples were thawed at 20°C for 40s or 40°C for 20s. After fertilization, the percentage of neurulation (Stage V embryos) was 80±21%, and percentage of embryonic mobility (Stage VI embryo) was 51±22%. There was a significant difference among the neurulation values produced by thawed blue catfish sperm, fresh blue catfish sperm (P=0.010) and channel catfish sperm (P=0.023), but not for Stage VI embryos (P≥0.585). Cryopreserved sperm from ten males did not show significant variation in post-thaw motility or fertility at the neurulation stage. This study demonstrates that the protocol established for high-throughput cryopreservation of blue catfish sperm can provide commercially relevant quantities and quality of sperm with stable fertility for hybrid catfish production and provides a model for establishment of commercial-scale approaches for other aquatic species.

p38 mitogen-activated protein kinase targets the production of proinflammatory endothelial microparticles

BACKGROUND

Endothelial microparticles (EMPs) are irregularly shaped membrane fragments shed into the circulation in patients with vascular diseases, and may themselves act to enhance the endothelial response to inflammation. On the basis of the importance of p38 mitogen-activated protein kinase (MAPK) in endothelial responses to inflammatory stimuli, we sought to define the role of p38 in EMP generation and function.

METHODS

Microparticle generation from cultures of human aortic endothelial cells (hAECs) treated with tumor necrosis factor-alpha (TNF-alpha) and p38 inhibition was quantified via multiple modalities. The response of target endothelial cells was assessed by treatment of cells with EMPs generated under various conditions.

RESULTS

Inhibition of p38 in hAECs, using pharmacologic agents, resulted in a 50% reduction of TNF-alpha-induced EMPs. Importantly, suppression of microparticles was specific to p38 MAPK pathways. EMPs triggered by TNF-alpha activation induced an approximately four-fold increase in soluble intercellular adhesion molecule-1 (sICAM-1) release from targeted cells. However, inhibition of p38 MAPK in the targeted cell prior to EMP treatment did not alter the sICAM1 response.

CONCLUSIONS

Our findings implicate p38 MAPK signaling as significant and selective in the formation and maturation of EMPs. EMPs elicited a proinflammatory response from targeted hAECs that was dependent on the conditions under which EMPs were generated. However, our results imply a unidirectional model in which p38 MAPK is critical at the source of microparticle formation, but not the target cell response to EMPs. These findings indicate a novel mechanism by which p38 inhibition may offer therapeutic benefit in vivo via direct inhibition of EMP formation.

Allosteric inhibitors of Akt1 and Akt2: discovery of [1,2,4]triazolo[3,4-f][1,6]naphthyridines with potent and balanced activity

A series of [1,2,4]triazolo[3,4-f][1,6]naphthyridine allosteric dual inhibitors of Akt1 and 2 have been developed. These compounds have been shown to have potent dual Akt1 and 2 cell potency. The representative compound 13 provided potent inhibitory activity against Akt1 and 2 in vivo in a mouse model.