Comparison of the Tissue Distribution of a Long-Circulating Glucagon-like Peptide-1 Agonist Determined by Positron Emission Tomography and Quantitative Whole-Body Autoradiography.

Positron emission tomography (PET) is a molecular imaging modality that enables non-invasive visualization of tracer distribution and pharmacology. Recently, peptides with long half-lives allowed once-a-week dosing of glucagon-like peptide-1 receptor (GLP-1R) agonists with therapeutic applications in diabetes and obesity. PET imaging for such long-lived peptides is hindered by the typically used short-lived radionuclides. Zirconium-89 (89Zr) emerged as a promising PET radionuclide with a sufficiently long half-life to be applied for biodistribution studies of long-circulating biomolecules. A comparison between the biodistribution profiles obtained via 89Zr-PET and the current standard, quantitative whole-body autoradiography (QWBA), will be valuable for the development of novel peptide drugs. We determined the PET biodistribution of a 89Zr-labeled acylated peptide agonist of GLP-1R and compared it to the profile obtained by QWBA using analogous tritiated tracers for up to 1 week after administration. The plasma metabolic profile was obtained and identification was done for the tritiated tracers. We found that, at early time points, the biodistribution profiles agreed between PET and QWBA. At the latertime points, the 89Zr tracer remained primarily trapped in the kidneys. The introduction of desferrioxamine (DFO) chelator reduced the peptide stability, and UPLC-MS analysis identified a circulating metabolite arising from DFO hydrolysis. Kidney accumulation of radiolabeled peptides and DFO metabolic instability may compromise biodistribution studies using 89Zr-PET to support the development of new biopharmaceuticals. PET and QWBA biodistribution data correlated well during the absorption phase, but new and more stable 89Zr chelators are needed for a more accurate description of the elimination phase.

Synthesis and evaluation of zirconium-89 labelled and long-lived GLP-1 receptor agonists for PET imaging.

INTRODUCTION: Lately, zirconium-89 has shown great promise as a radionuclide for PET applications of long circulating biomolecules. Here, the design and synthesis of protracted and long-lived GLP-1 receptor agonists conjugated to desferrioxamine and labelled with zirconium-89 is presented with the purpose of studying their in vivo distribution by PET imaging. The labelled conjugates were evaluated and compared to a non-labelled GLP-1 receptor agonist in both in vitro and in vivo assays to certify that the modification did not significantly alter the peptides' structure or function. Finally, the zirconium-89 labelled peptides were employed in PET imaging, providing visual verification of their in vivo biodistribution. METHODS: The evaluation of the radiolabelled peptides and comparison to their non-labelled parent peptide was performed by in vitro assays measuring binding and agonistic potency to the GLP-1 receptor, physicochemical studies aiming at elucidating change in peptide structure upon bioconjugation and labelling as well as an in vivo food in-take study illustrating the compounds' pharmacodynamic properties. The biodistribution of the labelled GLP-1 analogues was determined by ex vivo biodistribution and in vivo PET imaging. RESULTS: The results indicate that it is surprisingly feasible to design and synthesize a protracted, zirconium-89 labelled GLP-1 receptor agonist without losing in vitro potency or affinity as compared to a non-labelled parent peptide. Physicochemical properties as well as pharmacodynamic properties are also maintained. The biodistribution in rats shows high accumulation of radiolabelled peptide in well-perfused organs such as the liver, kidney, heart and lungs. The PET imaging study confirmed the findings from the biodistribution study with a significant high uptake in kidneys and presence of activity in liver, heart and larger blood vessels. CONCLUSIONS AND ADVANCES IN KNOWLEDGE: This initial study indicates the potential to monitor the in vivo distribution of long-circulating incretin hormones using zirconium-89 based PET.

Direct comparison of the in vitro and in vivo stability of DFO, DFO* and DFOcyclo* for 89Zr-immunoPET.

PURPOSE: Currently, the most commonly used chelator for labelling antibodies with 89Zr for immunoPET is desferrioxamine B (DFO). However, preclinical studies have shown that the limited in vivo stability of the 89Zr-DFO complex results in release of 89Zr, which accumulates in mineral bone. Here we report a novel chelator DFOcyclo*, a preorganized extended DFO derivative that enables octacoordination of the 89Zr radiometal. The aim was to compare the in vitro and in vivo stability of [89Zr]Zr-DFOcyclo*, [89Zr]Zr-DFO* and [89Zr]Zr-DFO. METHODS: The stability of 89Zr-labelled chelators alone and after conjugation to trastuzumab was evaluated in human plasma and PBS, and in the presence of excess EDTA or DFO. The immunoreactive fraction, IC50, and internalization rate of the conjugates were evaluated using HER2-expressing SKOV-3 cells. The in vivo distribution was investigated in mice with subcutaneous HER2+ SKOV-3 or HER2- MDA-MB-231 xenografts by PET/CT imaging and quantitative ex vivo tissue analyses 7 days after injection. RESULTS: 89Zr-labelled DFO, DFO* and DFOcyclo* were stable in human plasma for up to 7 days. In competition with EDTA, DFO* and DFOcyclo* showed higher stability than DFO. In competition with excess DFO, DFOcyclo*-trastuzumab was significantly more stable than the corresponding DFO and DFO* conjugates (p < 0.001). Cell binding and internalization were similar for the three conjugates. In in vivo studies, HER2+ SKOV-3 tumour-bearing mice showed significantly lower bone uptake (p < 0.001) 168 h after injection with [89Zr]Zr-DFOcyclo*-trastuzumab (femur 1.5 ± 0.3%ID/g, knee 2.1 ± 0.4%ID/g) or [89Zr]Zr-DFO*-trastuzumab (femur 2.0 ± 0.3%ID/g, knee 2.68 ± 0.4%ID/g) than after injection with [89Zr]Zr-DFO-trastuzumab (femur 4.5 ± 0.6%ID/g, knee 7.8 ± 0.6%ID/g). Blood levels, tumour uptake and uptake in other organs were not significantly different at 168 h after injection. HER2- MDA-MB-231 tumour-bearing mice showed significantly lower tumour uptake (p < 0.001) after injection with [89Zr]Zr-DFOcyclo*-trastuzumab (16.2 ± 10.1%ID/g) and [89Zr]Zr-DFO-trastuzumab (19.6 ± 3.2%ID/g) than HER2+ SKOV-3 tumour-bearing mice (72.1 ± 14.6%ID/g and 93.1 ± 20.9%ID/g, respectively), while bone uptake was similar. CONCLUSION: 89Zr-labelled DFOcyclo* and DFOcyclo*-trastuzumab showed higher in vitro and in vivo stability than the current commonly used 89Zr-DFO-trastuzumab. DFOcyclo* is a promising candidate to become the new clinically used standard chelator for 89Zr immunoPET.

Azotides as Modular Peptide-Based Ligands for Asymmetric Lewis Acid Catalysis.

Synthesis of azotides and evaluation of these as ligands for enantioselective Lewis acid catalysis is reported. The ligands were readily prepared from the chiral pool of amino acids and perform well in the cobalt(II)-catalyzed formation of asymmetric hetero Diels-Alder adducts. A rational for the observed enantioselectivity and conversion rate supported by computational calculations is provided.

Stable gold(III) catalysts by oxidative addition of a carbon-carbon bond.

Low-valent late transition-metal catalysis has become indispensable to chemical synthesis, but homogeneous high-valent transition-metal catalysis is underdeveloped, mainly owing to the reactivity of high-valent transition-metal complexes and the challenges associated with synthesizing them. Here we report a carbon-carbon bond cleavage at ambient conditions by a Au(i) complex that generates a stable Au(iii) cationic complex. In contrast to the well-established soft and carbophilic Au(i) catalyst, this Au(iii) complex exhibits hard, oxophilic Lewis acidity. For example, we observed catalytic activation of α,ß-unsaturated aldehydes towards selective conjugate additions as well as activation of an unsaturated aldehyde-allene for a [2 + 2] cycloaddition reaction. The origin of the regioselectivity and catalytic activity was elucidated by X-ray crystallographic analysis of an isolated Au(iii)-activated cinnamaldehyde intermediate. The concepts revealed suggest a strategy for accessing high-valent transition-metal catalysis from readily available precursors.

1,4-Naphthoquinones in H-bond-directed trienamine-mediated strategies.

The synthesis of optically active, carboannulated dihydronaphthoquinone and naphthoquinone derivatives with up to four stereogenic centers is demonstrated by H-bond-directed, trienamine-mediated [4 + 2]-cycloadditions. The outcome of the reaction between 2,4-dienals and 1,4-naphthoquinones is controlled by the substituent in the 2-position of the 1,4-naphthoquinone. In the case of sterically demanding 2-substituted derivatives, dihydronaphthoquinones are obtained. However, when a hydrogen atom is present in the 2-position, a subsequent oxidation of the initially formed cycloadducts occurs yielding naphthoquinones.

Enantioselective formation of substituted 3,4-dihydrocoumarins by a multicatalytic one-pot process.

The formation of optically active 3,4-dihydrocoumarins is presented by merging aminocatalysis with an N-heterocyclic carbene-catalyzed internal redox reaction. The products are formed in good to excellent yields and in general with excellent enantioselectivities. Moreover, the developed procedure demonstrates the potential of enantioselective, multicatalytic sequences. By employing an enantiopure aminocatalyst in the enantiodifferentiating step, the challenges related to achieving high stereoinductions by deployment of optically active NHC-catalysts can be circumvented.

Organocatalytic iminium ion/carbene reaction cascade for the formation of optically active 2,4-disubstituted cyclopentenones.

An organocatalytic iminium ion/N-heterocyclic carbene (NHC) cascade reaction between ß-keto phenyltetrazolesulfones and α,ß-unsaturated aldehydes, providing direct access to optically active 2,4-disubstituted cyclopent-2-enones, has been developed. The products are isolated in good yields with high enantioselectivities.

Asymmetric organocatalytic monofluorovinylations.

The development of highly enantio- and diastereoselective organocatalytic monofluorovinylations is presented. Based on the application of α-fluoro-ß-keto-benzothiazolesulfones, the formal addition of a monofluorovinylic anion synthon to a range of acyclic and cyclic enones, as well as imines, is shown. These procedures give selective access to both E- and Z-isomers of the monofluorovinylated products, which are isolated as the pure diastereoisomers in good to excellent yields with up to 99% ee. Furthermore, the application of this concept for the formation of highly enantioenriched bicylic compounds containing a monofluorovinyl moiety is also described. In addition, a mechanistic rationale for the observed E:Z-selectivities is presented.

Asymmetric organocatalysis with sulfones.

Asymmetric organocatalysis has become a powerful tool for the synthesis of optically active compounds. Whereas early research mainly focused on combining simple reagents as a proof-of-concept for asymmetric organocatalysis, recent investigations are directed towards extending the concept to more target- and diversity-oriented synthesis. As a result of the many transformation possibilities and their ability to generate both nucleophilic and electrophilic reaction partners, sulfones have become especially important substrates in the field of organocatalysis.

Transition-metal-free formal Sonogashira coupling and alpha-carbonyl arylation reactions.

Transition-metal-free formal Sonogashira coupling and alpha-carbonyl arylation reactions have been developed. These transformations are based on the nucleophilic aromatic substitution (S(N)Ar) of beta-carbonyl sulfones to electron-deficient aryl fluorides, producing a key intermediate that, depending on the reaction conditions, gives the aromatic alkynes or alpha-aryl carbonyl compounds. The development of these reactions is presented and, based on investigations under basic and acidic conditions, mechanisms have been proposed. To develop the formal Sonogashira coupling further, a milder, two-step protocol is also disclosed that expands the reaction concept. The scope of these reactions is demonstrated for the synthesis of Sonogashira and alpha-carbonyl arylated products from a range of electron-deficient aryl fluorides with a variety of functional groups and aryl-, heteroaryl-, alkyl-, and alkoxy-substituted sulfone nucleophiles. These transition-metal-free reactions complement the metal-catalyzed versions in terms of substitution patterns, simplicity, and reaction conditions.

An asymmetric organocatalytic approach towards allylic amines and beta-keto amino compounds.

The enantioselective organocatalysed addition of beta-keto benzothiazolesulfones to N-Boc-protected imines, leading to intermediates easily transformed into optically active allylic amines or beta-keto amino compounds, is presented.

Asymmetric organocatalytic formal alkynylation and alkenylation of alpha,beta-unsaturated aldehydes.

A highly stereoselective organocatalytic one-pot protocol for the formal alkynylation and alkenylation of alpha,beta-unsaturated aldehydes using novel chemistry based on beta-keto heterocyclic sulfones is presented. The organocatalytic step is catalyzed by a prolinol derivative and allows for the formation of important optically active compounds. Further transformations of the beta-keto heterocyclic sulfone moiety, based on new developments of the Smiles rearrangement through a process parallel to the Julia-Kocienski reaction, were performed leading to beta-alkynylated aldehydes and 3-alkenylated alcohols. The scopes of both transformations are demonstrated by the synthesis of various optically active alkynes and alkenes. Furthermore, different transformations of the aldehyde and the alcohol functionality were performed. Finally, the proposed mechanisms for both the alkynylation and alkenylation of alpha,beta-unsaturated aldehydes are outlined.

Organocatalytic asymmetric ring-opening of aziridines.

The organocatalytic ring-opening of N-tosyl protected aziridines by beta-ketoesters under chiral PTC-conditions, leading to the formation of optically active aminoethyl functionalised compounds with up to 99% ee, has been developed.

Organocatalytic asymmetric vinylogous addition to quinones - formation of optically active alpha-aryl ketones.

The first organocatalytic addition of dicyanoalkylidenes to quinones catalyzed by Cinchona alkaloids leading to formation of 1,4-diketone derivatives with high diastereomeric ratios (up to >98 : <2 dr) and enantioselectivities (up to 99% ee) has been developed; the optically active compounds obtained are useful for a number of transformations, e.g. the synthesis of optically active alpha-aryl ketones.