OMNI: Gas Chromatograph Captures Seven Common PET Radiotracer Analytes in under 5 Minutes

A novel gas chromatography method was developed using automatic injections to identify and quantify the amount of residual solvents or analytes in samples of fluorine-18 and carbon-11 radiopharmaceuticals. This approach evaluates seven analytes in less than 5 versus 13 min of acquisition time. The method additionally includes a 3 min bakeout to aid in the removal and carry-over of higher-boiling impurities. Chromatographic parameters such as column temperature, hold time, column pressure, flow rate, and split ratios were adjusted and optimized to analyze radioactive drug samples containing analytes which include methanol, ethanol, acetone, acetonitrile, triethylamine, N,N-dimethylformamide, and dimethyl sulfoxide. The relative standard deviation for each solvent was determined to be no greater than 1.6%. The method limit of detection (LOD) and limit of quantification (LOQ) were between 0.053 and 0.163 and 0.000 (5.791 × 10-6) and 0.520 mg/mL, respectively. This GC technique, using flame ionization detection (FID), was validated and is currently employed for the routine quality control of all approved IND and RDRC PET radiopharmaceuticals at our center.

Radiosynthesis and evaluation of [11C]AG-488, a dual anti-angiogenetic and anti-tubulin PET ligand

Combinations of antiangiogenic and cytotoxic agents show promising results in the treatment of cancer. However, there is a lack of single agent with both antiangiogenic and cytotoxic activities for clinical application. AG-488 aka FLAG-003 is a novel ligand with established antiangiogenetic properties via activation of receptor thymidine kinase (RTK) and anti-tubulin properties in tumor cells. AG-488 is also reported to reduce tumor volume and prolong survival in preclinical animal models of glioblastoma multiforme, breast cancer and is in clinical stage. Higher expression of RTKs and tubulins is reported in various cancers. This study reveals the development of [¹¹C]AG-488, a high affinity dual target inhibitor binding to RTK and anti-tubulin activities. We rationale that antiangiogenic RTK and anti-tubulin activity of [¹¹C]AG-488 may enhance the tumor to tissue ratio, assisting in cancer drug development. [¹¹C]AG-488 was synthesized in 35 ± 5 % radiochemical yield by radiomethylating the corresponding phenolate using [¹¹C]CH₃I. MicroPET studies in mice indicated blood-brain barrier penetration of [¹¹C]AG-488 and retention in the brain. However, blocking studies with antitubulin and RTK agent HD-800 and microtubule depolymerizing agent MPC-6827 show increased binding of [¹¹C]AG-488 in brain. The pattern of tracer binding in blocking conditions is similar to the baseline conditions. The higher binding may be due to the increased plasma uptake of radiotracer or the formation of more free tubulins due to microtubule dynamic instability during the blocking conditions.

Preclinical evaluation of a microtubule PET ligand [11C]MPC-6827 in tau and amyotrophic lateral sclerosis animal models

BACKGROUND

Microtubules are abundant in brain and their malfunctioning occurs in the early-to-advanced stages of neurodegenerative disorders. At present, there is no in vivo test available for a definitive diagnosis of most of the neurodegenerative disorders. Herein, we present the microPET imaging of microtubules using our recently reported Positron Emission Tomography (PET) tracer, [¹¹C]MPC-6827, in transgenic mice models of tau pathology (rTg4510) and amyotrophic lateral sclerosis pathology (SOD1*G93A) and compared to corresponding age-matched controls.

METHODS

Automated synthesis of [¹¹C]MPC-6827 was achieved in a GE-FX2MeI/FX2M radiochemistry module. In vivo PET imaging studies of [¹¹C]MPC-6827 (3.7 ± 0.8 MBq) were performed in rTg4510 and SOD1*G93A mice groups and their corresponding littermates (n = 5 per group). Dynamic PET images were acquired using a microPET Inveon system (Siemens, Germany) at 55 min for rTg4510 and 30 min for SOD1*G93A and corresponding controls. PET images were reconstructed using the 3D-OSEM algorithm and analyzed using VivoQuant version 4 (Invicro, MA). Tracer uptake in ROIs that included whole brain was measured as %ID/g over time to generate standardized uptake values (SUV) and time-activity curves (TACs).

RESULTS

[¹¹C]MPC-6827 exhibit a trend of lower tracer binding in mouse models of Alzheimer's disease (tau pathology, line rTg4510) and Amyotrophic Lateral Sclerosis (line SOD1*G93A) compared to wild-type littermates.

CONCLUSIONS

Our finding indicates a trend of loss of microtubule binding of [¹¹C]MPC-6827 in the whole brain of AD and ALS transgenic mice models compared to control mice. The pilot studies described herein show that [¹¹C]MPC-6827 could be used as a PET ligand for preclinical and human brain imaging of Alzheimer's disease, ALS, and other neurodegenerative diseases. Preclinical Evaluation of a Microtubule PET Ligand [¹¹C]MPC-6827 in Tau and Amyotrophic Lateral Sclerosis Animal Models. J. S. Dileep Kumar, Andrei Molotkov, Jongho Kim, Patrick Carberry, Sidney Idumonyi, John Castrillon, Karen Duff, Neil A. Shneider, Akiva Mintz.

Real-Time Positron Emission Tomography Evaluation of Topotecan Brain Kinetics after Ultrasound-Mediated Blood-Brain Barrier Permeability

Glioblastoma (GBM) is the most common primary adult brain malignancy with an extremely poor prognosis and a median survival of fewer than two years. A key reason for this high mortality is that the blood-brain barrier (BBB) significantly restricts systemically delivered therapeutics to brain tumors. High-intensity focused ultrasound (HIFU) with microbubbles is a methodology being used in clinical trials to noninvasively permeabilize the BBB for systemic therapeutic delivery to GBM. Topotecan is a topoisomerase inhibitor used as a chemotherapeutic agent to treat ovarian and small cell lung cancer. Studies have suggested that topotecan can cross the BBB and can be used to treat brain metastases. However, pharmacokinetic data demonstrated that topotecan peak concentration in the brain extracellular fluid after systemic injection was ten times lower than in the blood, suggesting less than optimal BBB penetration by topotecan. We hypothesize that HIFU with microbubbles treatment can open the BBB and significantly increase topotecan concentration in the brain. We radiolabeled topotecan with 11C and acquired static and dynamic positron emission tomography (PET) scans to quantify [11C] topotecan uptake in the brains of normal mice and mice after HIFU treatment. We found that HIFU treatments significantly increased [11C] topotecan brain uptake. Moreover, kinetic analysis of the [11C] topotecan dynamic PET data demonstrated a substantial increase in [11C] topotecan volume of distribution in the brain. Furthermore, we found a decrease in [11C] topotecan brain clearance, confirming the potential of HIFU to aid in the delivery of topotecan through the BBB. This opens the potential clinical application of [11C] topotecan as a tool to predict topotecan loco-regional brain concentration in patients with GBMs undergoing experimental HIFU treatments.

Lipocalin-2 is an anorexigenic signal in primates

In the mouse, the osteoblast-derived hormone Lipocalin-2 (LCN2) suppresses food intake and acts as a satiety signal. We show here that meal challenges increase serum LCN2 levels in persons with normal or overweight, but not in individuals with obesity. Postprandial LCN2 serum levels correlate inversely with hunger sensation in challenged subjects. We further show through brain PET scans of monkeys injected with radiolabeled recombinant human LCN2 (rh-LCN2) and autoradiography in baboon, macaque, and human brain sections, that LCN2 crosses the blood-brain barrier and localizes to the hypothalamus in primates. In addition, daily treatment of lean monkeys with rh-LCN2 decreases food intake by 21%, without overt side effects. These studies demonstrate the biology of LCN2 as a satiety factor and indicator and anorexigenic signal in primates. Failure to stimulate postprandial LCN2 in individuals with obesity may contribute to metabolic dysregulation, suggesting that LCN2 may be a novel target for obesity treatment.

Binding of the D3-preferring antipsychotic candidate F17464 to dopamine D3 and D2 receptors: a PET study in healthy subjects with [11C]-(+)-PHNO

RATIONALE

F17464, a dopamine D3 receptor antagonist with relatively high D3 selectivity (70 fold vs D2 in vitro), exhibits an antipsychotic profile in preclinical studies, and therapeutic efficacy was demonstrated in a randomized placebo-controlled clinical trial in patients with schizophrenia (Bitter et al. Neuropsychopharmacology 44(11):1917-1924, 2019).

OBJECTIVE

This open-label study in healthy male subjects aimed at characterizing F17464 binding to D3/D2 receptors and the time course of receptor occupancy using positron emission tomography (PET) imaging with a D3-preferring tracer, [¹¹C]-(+)-PHNO.

METHODS

PET scans were performed at baseline and following a single 30 mg or 15 mg dose of F17464 (3 subjects/dose), and blood samples were collected for pharmacokinetic analysis. Receptor occupancy was calculated based upon reduction in binding potential of the tracer following F17464 administration. The relationship between plasma F17464 concentration and D3/D2 receptor occupancy was modeled and the plasma concentration corresponding to 50% receptor occupancy (EC₅₀) calculated.

RESULTS

Both doses of F17464 robustly blocked [¹¹C]-(+)-PHNO D3 receptor binding, with substantial occupancy from 1 h post-administration, which increased at 6-9 h (89-98% and 79-87% for the 30 mg and 15 mg groups, respectively) and remained detectable at 22 h. In contrast, D2 binding was only modestly blocked at all time points (< 18%). F17464 exhibited a combination of rapid peripheral kinetics and hysteresis (persistence of binding 22 h post-dose despite low plasma concentration). The best estimate of the EC₅₀ was 19 ng ml^-1 (~ 40 nM).

CONCLUSION

Overall, F17464 was strongly D3-selective in healthy volunteers, a unique profile for an antipsychotic candidate drug.

Fluoride-18 radiolabeling of peptides bearing an aminooxy functional group to a prosthetic ligand via an oxime bond

We have developed a novel F-18 prosthetic ligand named fluoro-PEG-benzaldehyde (FPBA) 1. [(18)F]-FPBA 1 is formed in situ from its radiolabeled precursor [(18)F]6. Compound 6 is efficiently synthesized in four steps starting from commercially available 6-bromo-3-pyridine carbaldehyde 2. [(18)F]-FPBA was evaluated as a prosthetic ligand to radiolabel three cyclic peptides bearing an aminooxy functional group at the N-terminus position. Acetal [(18)F]6 is purified by either solid-phase extraction (SPE) or reverse-phase HPLC with the overall radiochemical yields (RCY) and radiochemical purity (RCP) in very close agreement. The SPE purification process has the advantage of shorter reaction times (71-87 min for entire reaction sequence), while the use of the reverse-phase HPLC purification process allows the use of up to fifty times less of the expensive synthetic peptides (~ 50 nmol) in the oxime coupling reaction. We have demonstrated an efficient methodology in the production of [(18)F]-FPBA 1 and demonstrated its use as a prosthetic ligand for the labeling of peptides possessing an aminooxy functional group.

New F-18 prosthetic group via oxime coupling

A novel fluorine-18 prosthetic ligand, 5-(1,3-dioxolan-2-yl)-2-(2-(2-(2-fluoroethoxy)ethoxy)ethoxy)pyridine [(18)F]2, has been synthesized. The prosthetic ligand is formed in high radiochemical yield (rcy = 71 ± 2%, n = 3) with excellent radiochemical purity (rcp = 99 ± 1%, n = 3) in a short reaction time (10 min). [(18)F]2 is a small, neutral, organic complex, easily synthesized in four steps from a readily available starting material. It can be anchored onto a target molecule containing an aminooxy functional group under acidic conditions by way of an oxime bond. We report herein two examples [(18)F]23 and [(18)F]24, potential imaging agents for β-amyloid plaques, which were labeled with this prosthetic group. This approach could be used for labeling proteins and peptides containing an aminooxy group. Biodistribution in male ICR mice for both oxime labeled complexes [(18)F]23 and [(18)F]24 were compared to that of the known β-amyloid plaque indicator, [(18)F]-AV-45, florbetapir 1. Oximes [(18)F]23 and [(18)F]24 are larger in size and therefore should reduce the blood-brain barrier (BBB) penetration. The brain uptake for oxime [(18)F]23 appeared to be reduced, but still retained some capability to cross the BBB. Oxime [(18)F]24 showed promising results after 2 min post injection (0.48% dose/gram); however, the uptake increased after 30 min post injection (0.92% dose/gram) suggesting an in vivo decomposition/metabolism of compound [(18)F]24. We have demonstrated a general protocol for the fluoride-18 labeling with a new prosthetic ligand [(18)F]2 that is tolerant toward several functional groups and is formed via chemoselective oxime coupling.

Addition of alkynes to aldehydes and activated ketones catalyzed by rhodium-phosphine complexes

A mixture of 2-(di-tert-butylphosphino)biphenyl and dicarbonylacetonato rhodium(I) provides an effective catalyst system for the addition of alkynes to aldehydes and activated ketones. In contrast to the more common zinc-catalyzed processes, enolizable 1,2-dicarbonyls are excellent substrates for these rhodium-catalyzed additions. This reaction allows for the formation of propargylic alcohols under mild conditions, tolerating many functional groups (such as carboxylic acids) that are incompatible with other methods. Little selectivity was observed in cases of unsymmetrical 1,2-diketones. Addition of alkynes to aldehydes with an adjacent chirality center usually provides the Felkin addition product with excellent selectivity in some cases. Studies on the catalyst structure show that both the beta-diketonate and a carbon monoxide ligand appear to be bound to the active catalyst. The use of chiral phosphines to induce asymmetry in the propargyl alcohol products provided low enantioselectivity, which may be due to the phosphine having a distal relationship to the reacting centers. Modification of other ligands, such as the beta-diketonate, appears to be a more promising avenue for the development of an enantioselective variant.

The induction of reproductive activity in lactating ewes

In two experiments, Merino ewes that had lambed in either the autumn or spring were treated with various combinations of a progestagen (methylacetoxyprogesterone, MAP) and pregnant mare's serum gonadotrophin (PMSG), from 3 days post partum. Irrespective of the season of lambing, the treatments resulted in ovulation in nearly all ewes before day 15 post partum; oestrus was observed in all ewes that had lambed in the autumn but in only half the spring ewes. Regular oestrus activity was not resumed after the induced oestrus and/or ovulation. After further treatments with MAP and PMSG (days 15–26 post partum), 29% of the ewes showed oestrus (autumn and spring), with 47.1% and 58.3% of ewes ovulating in the autumn and spring respectively. Cystic and/or persistent corpora lutea (CP) were noted in 24% of the treated ewes. In spring-lambing ewes, 42% of ovulations before day 15 were judged to be abnormal. Fertilization rates were low in ewes that mated. The best results, 56% of ova fertilized, were from matings between 26 and 30 days post partum in spring-lambing ewes. In two further experiments, the fertility of ewes was examined at matings induced at various times post partum in crossbred ewes that had lambed in the spring. The fertility was low (=17%) up to 30 days post partum, but it improved in later matings (=30%). The incidence of a second oestrus succeeding the induced cycle was low (29%), but fertility was higher (50%). Approximately 50% of the untreated ewes lambed to matings between 30 and 60 days after lambing.

Induction of parturition in sheep using oestradiol benzoate

The efficacy of oestradiol benzoate (ODB) in inducing parturition in Dorset Horn x Merino ewes was examined in two trials conducted at the Agricultural Research Station, Condobolin during the autumn and spring of 1974. In the first trial ewes were given either 10, 20 or 40 mg of ODB i.m. as a single dose between days 140 and 144 of gestation. In the three days following treatment 50 per cent of untreated ewes lambed. Of the treated ewes, 14.7 per cent lambed on the first day after treatment, 79.4 per cent lambed on the second day after treatment and 5.9 per cent lambed on the third day after treatment. Abortion was induced in 40 to 70 per cent of ewes inadvertently treated on days 126 to 130 of gestation, with all lambs born dead or dying. In a second trial ODB was effective in inducing parturition at doses as low as 7.5 mg. For ewes treated at 141 days of gestation optimal synchrony of parturition, between 35 and 50 hours after treatment, was obtained with doses of 20 and 30 mg ODB. Lamb losses (19 to 23 per cent) in treated ewes were similar to those for untreated ewes. ODB was superior to either a short or long acting corticoid (Dexamethasone) in synchronizing and inducing parturition in ewes treated at 141 days of gestation. Lambs born prematurely grew at least as well as lambs born at the normal time.