Pre-clinical evaluation of 99mTc-labeled chalcone derivative for amyloid-β imaging post-head trauma

Aβ42 plaque formation is one of the preliminary pathologic events that occur post traumatic brain injury (TBI) which is also among the most noteworthy hallmarks of AD. Their pre symptomatic detection is therefore vital for better disease management. Chalcone-picolinic acid chelator derivative, 6-({[(6-carboxypyridin-2-yl)methyl](2-{4-[(2E)-3-[4-(dimethyl amino)phenyl]prop-2-enoyl]phenoxy}ethyl)amino}methyl)pyridine-2-carboxylic acid, Py-chal was synthesized to selectively identify amyloid plaques formed post head trauma using SPECT imaging by stable complexation to 99mTc with > 97% efficiency without compromising amyloid specificity. The binding potential of the Py-chal ligand to amyloid plaques remained high as confirmed by in vitro binding assay and photophysical spectra. Further, the Py-chal complex stained amyloid aggregates in the brain sections of rmTBI mice model. In vivo scintigraphy in TBI mice model displayed high uptake followed by high retention while the healthy rabbits displayed higher brain uptake followed by a rapid washout attributed to absence of amyloid plaques. Higher uptake in brain of TBI model was also confirmed by ex vivo biodistribution analysis wherein brain uptake of 3.38 ± 0.2% ID/g at 2 min p.i. was observed for TBI mice model. This was followed by prolonged retention and more than twofold higher activity as compared to sham mice brain. This preliminary data suggests the specificity of the radiotracer for amyloid detection post head trauma and applicability of 99mTc labeled Py-chal complex for TBI-induced β-amyloid SPECT imaging.

Novel terpestacin derivatives with l-amino acid residue as anticancer agents against U87MG-derived glioblastoma stem cells

Based on the natural product terpestacin, seventeen derivatives (1-17) with various l-amino acid side chains were designed and synthesized. Their anticancer activities against U87MG-derived glioblastoma stem cells (GSCs) were evaluated, and compounds 5, 11, 13 and 15 showed strong abilities to inhibit the proliferation (IC₅₀ = 2.8-6.9 μM) and tumorsphere formation of GSCs. Besides, compounds 13 and 15 could effectively induce apoptosis and significantly inhibit the invasion of GSCs (95 and 97 % inhibition, respectively, at 2.5 μM). The levels of CD133 marker in GSCs also decreased in dose-dependent manners after the treatment of these active compounds. Compared to terpestacin and the positive control A1938, our derivatives showed stronger activities and compounds 13 and 15 are promising candidates for further development as anticancer agents by targeting GSCs.

A GdIII-Based Spin Label at the Limits for Linewidth Reduction through Zero-Field Splitting Optimization

The remarkably narrow central line in the electron paramagnetic resonance spectrum and the very weak zero-field splitting (ZFS) make [Gd^III(NO3Pic)] ([Gd^III(TPATCN)]) an attractive starting point for the development of spin labels. For retaining the narrow line of this parent complex when modifying it with a substituent enabling bioconjugation, alkyl with a somehow remote functional group as a substituent at the picolinate moiety was found to be highly suitable because ZFS stayed weak, even if the threefold axial symmetry was broken. The ZFS is so weak that hyperfine coupling and/or g-value variations noticeably determine the linewidth in Q band and higher fields when the biomolecule is protonated, which is the standard situation, and in W band and higher fields for the protonated complex in a fully deuterated surrounding. Clearly, [NDSE-{Gd^III(NO3Pic)}], a spin label targeting the cysteines in a peptide, is at a limit of linewidth narrowing through ZFS minimization. The labeling reaction is highly chemoselective and, applied to a polyproline with two cysteine units, it took no more than a minute at 7 °C and pH 7.8. Subsequent disulfide scrambling is very slow and can therefore be prevented. Double electron-electron resonance and relaxation-induced dipolar modulation enhancement applied to the spin-labeled polyproline proved the spin label useful for distance determination in peptides.

Bio-Evaluation of 99mTc-Labeled Homodimeric Chalcone Derivative as Amyloid-β-Targeting Probe

Chalcone derivatives have been successfully utilized for a range of biological applications and can cross the blood–brain barrier easily. β-amyloid-specific bis-chalcone derivative, 6,9-bis(carboxymethyl)-14-(4-[(E)-3-(4-(dimethylamino)phenyl)acryloyl]phenoxy)-3-(2-[(2-(4-[(E)-3-(4-(dimethylamino)phenyl)acryloyl]phenoxy)ethyl)amino]-2-oxoethyl)-11-oxo-3,6,9,12-tetraazatetradecanoic acid, DT(Ch)₂, was analyzed using molecular modeling to explain the binding modes of the ligand with amyloid fibril and monomer followed by ^99mTc-complexation in 95% yield and 98.7% efficiency. High-binding specificity of the radiocomplex was established following in vitro evaluation against 100-fold excess of DT(Ch)₂. ^99mTc–DT(Ch)₂ exhibited <3% trans-complexation in human serum after 24 h, indicating high stability. A fast clearance rate in pharmacokinetics studies displayed a biphasic pattern with t_1/2(F) = 30 min ± 0.09 and t_1/2(S) = 4 h 20 min ± 0.06. In vivo single-photon emission computed tomography (SPECT) imaging in rabbits reiterated the pharmacokinetics data with initially high brain uptake followed by rapid washout. Biodistribution studies confirmed the initial brain uptake as 1.16 ± 0.02% ID/g after 2 min and the brain_2min/brain_30min ratio was 3.74. Radioactivity distribution in the brain was >40% in the cingulate cortex followed by >25% in the hippocampus, a distribution pattern aligned to Alzheimer’s affected brain regions. Radiocomplex also displayed rapid plasma clearance followed by hepatobolic and renal modes of excretion.

Amino acid based gallium-68 chelators capable of radiolabeling at neutral pH

Herein we show a flexible synthesis for bifunctional chelators based on amino acids that rapidly complex ⁶⁸Ga under physiological conditions.