Evaluation of a Radiolabelled Macrocyclic Peptide as Potential PET Imaging Probe for PD-L1

The interaction between the immune checkpoint PD‐1 and PD−L1 promotes T‐cell deactivation and cancer proliferation. Therefore, immune checkpoint inhibition therapy, which relies on prior assessment of the target, has been widely used for many cancers. As a non‐invasive molecular imaging tool, radiotracers bring novel information on the in vivo expression of biomarkers (e. g., PD−L1), enabling a personalized treatment of patients. Our work aimed at the development of a PD−L1‐specific, peptide‐based PET radiotracer. We synthesized and evaluated a radiolabeled macrocyclic peptide adapted from a patent by Bristol Myers Squibb. Synthesis of [⁶⁸Ga]Ga‐NJMP1 yielded a product with a radiochemical purity>95 % that was evaluated in vitro. However, experiments on CHO−K1 hPD−L1 cells showed very low cell binding and internalization rates of [⁶⁸Ga]Ga‐NJMP1 in comparison to a control radiopeptide (WL12). Non‐radioactive cellular assays using time‐resolved fluorescence energy transfer confirmed the low affinity of the reported parent peptide and the DOTA‐derivatives towards PD−L1. The results of our studies indicate that the macrocyclic peptide scaffold reported in the patent literature is not suitable for radiotracer development due to insufficient affinity towards PD−L1 and that C‐terminal modifications of the macrocyclic peptide interfere with important ligand/receptor interactions.

Unexpected transformation of n.c.a. [111In]InCl3 in stock solutions into an unreactive [111In]In-species

While performing multiple indium-111 labeling of DOTA-modified peptides from a single batch of [¹¹¹In]InCl₃, inconsistent radiochemical yields were observed. We found that the formation of a radioactive impurity in the [¹¹¹In]InCl₃ stock solution hampered the reactivity of the indium-111 during radiolabeling reactions. The formation of this unknown ¹¹¹In-species could be successfully suppressed by increasing the concentration of chloride ions in the stock solution and [¹¹¹In]InCl₃ was "recovered". Radiolabeling of DOTA-peptides with the stabilized [¹¹¹In]InCl₃ resulted again in acceptable radiochemical yields. In addition, we report convenient iTLC systems that allow distinguishing between [¹¹¹In]InCl₃, the formed unknown ¹¹¹In-species, radiocolloids, and radiolabeled peptides (DOTANOC).

Original implementation of low-temperature SPS for bioactive glass used as a bone biomaterial

Alkali borated bioactive glasses powders with compositions based on the SiO₂-Na₂O-CaO-P₂O₅-x B₂O₃ system (0 < x < 20 wt%); have been consolidated at low temperature using Spark Plasma Sintering (SPS). Through SPS technique under 50 MPa, it was possible to achieve fully dense and completely amorphous borated glasses at temperatures as low as 420 °C. By increasing the sintering temperature up to 430 °C, the dense samples crystallized which is mostly achieved at higher temperatures. This study reveals that the mechanical properties of these new borated biomaterials are suitable to be used as a promising candidate for repairing defects in non-load-bearing bones as well as for coating on the metallic surface implants to improve the bioactivity process bone/implant. The pressure had a weak effect on the crystallization and densification of the glass compared to the temperature during the powder consolidation by SPS. Moreover, by increasing the boron content, the compressive strength and the elastic modulus of the elaborated glasses decreased for being close to those of the natural.

Mini-review: Targeted radiopharmaceuticals incorporating reversible, low molecular weight albumin binders

The combination of low molecular weight, reversible human serum albumin (HSA) binders with targeted radiopharmaceuticals in dual-targeted radioconjugates holds great promise, in particular for endoradiotherapy. Attachment of HSA-binders to radiopharmaceuticals extends their blood circulation time and results in an enhanced tumour uptake as well as often in an improved pharmacokinetic profile. In this mini-review, an overview of currently pursued approaches of this novel strategy is provided.

Ruthenium polypyridyl TG6 dye for the sensitization of nanoparticle and nanocrystallite spherical aggregate photoelectrodes

A ruthenium polypyridyl dye containing a hexasulfanyl-styryl modified bipyridyl group as ancillary ligand, coded TG6, is investigated as a sensitizer for ZnO-based dye-sensitized solar cells (DSSCs). The advantages of this dye are a broad wavelength absorption spectrum, a large loading in ZnO photoelectrodes, a significantly larger extinction coefficient compared to more classical Ru-polypyridyl dyes, and the formation of less agglomerate in the pores of the ZnO layers. TG6 has been used to sensitize ZnO nanorod particle layers of high structural quality and ZnO layers made of submicrometer spheres composed of aggregated nanocrystallites and that develop an internal surface area. The latter are highly light-scattering in the visible wavelength region but more difficult to sensitize correctly. The TG6 dye has been compared with the metal-free D149 dye and has been shown more efficient for photoconversion. The best performances have been obtained by combining TG6 with the nanorod layer, the optimal power conversion efficiency being measured at 5.30% in that case. The cells have been investigated by impedance spectroscopy over a large applied voltage range. We especially show that the submicrometer sphere layers exhibit lower conductivity and lower charge collection efficiency as compared to the nanorod particle ones.

Structure of di(salicylaldehyde benzoylhydrazonato) zinc (II), an unusual staircase polymeric structure formed via E → Z isomerization on complexation

A bicomplex of salicylaldehyde benzoylhydrazone (SBH) with Zn(II) was synthesized in ethanol and single crystals were obtained in DMSO. The compound crystallizes in the orthorhombic system with the space group Pna21(33) and crystal data: a = 22.573(3)Å, b = 6.1208(5) Å, c = 17.881(2) Å, V = 2470.5(5) Å3, Z = 4, d(calc) = 1.462 g⋅cm–3, (2633 reflections with I > 2 σ(I); final R = 0.0509; R w = 0.1099). The asymmetric unit is a nearly planar bicomplex built up from one Zn atom linked to two monodeprotonated SBH ligands. The compound can be described as formed of chains extended along the b axis. This linear polymeric character results from the linking of each asymmetric unit to two neighbouring ones via four (2x2) covalent Zn-O bonds involving three Zn atoms and four phenolic oxygens. These covalent bonds are related to the very unusual Z configuration of the ligand. The three-dimensional cohesion of the compound is obtained by van der Waals forces be-tween the polymeric chains.

Conducting-polymer electrochemical switching as an easy means for control of the molecular properties of grafted transition metal complexes

Copper(II) 3',4'-bis(N,N'-oxamato)terthiophene has been synthesized and electropolymerized. The copper(II)-complex centers are not affected by the polymerization process, which involves coupling between Calpha carbon atoms of the terthiophene units and leads to a new conjugated polymer consisting of polythiophene chains bearing bis(oxamato)-Cu(II) groups regioregularly grafted onto the polymer backbone. The polymer is stable with respect to polythiophene electroactivity, and no demetallation or modification of the Cu oxidation state occurs over a large potential range. In this material, the two moieties exhibit direct electronic interaction, which makes it possible to use the conductive polymer backbone as a molecular wire or a nanocontact capable of inputting to the bis(oxamato)-Cu(II) groups through the polythiophene-switching reaction. FTIR, XPS, and XAS spectroscopies have been used to study the effect of the state of the conducting polymer upon the properties of the copper(II) center (electron density, ligand field strength, size of cavity, force constants of some bonds). These properties can be controlled to some extent by the potential applied to this device. From the point of view of the copper(II) center, this effect is similar to the grafting of substituents with various electronic properties.