Enhancement of Binding Affinity for Amyloid Aggregates by Multivalent Interactions of ^99mTc-Hydroxamamide Complexes

Abstract

Deposition of amyloid aggregates has been regarded as an early stage of amyloidosis progression. An imaging probe that can image amyloid aggregates enables the early diagnosis of amyloidosis and contributes to the development of new medical therapies. High binding affinity for amyloid aggregates is essential to develop a useful molecular imaging probe. This article describes a new strategy to enhance the binding affinity of imaging agents targeting amyloid aggregates. We designed and synthesized novel (99m)Tc-hydroxamamide ((99m)Tc-Ham) complexes with a bivalent amyloid ligand and evaluated their binding affinity for amyloid aggregates by using β-amyloid peptide (Aβ(1-42)) aggregates as a model. In vitro inhibition assay indicated that bivalent (99m)Tc-Ham complexes had much higher binding affinity for amyloid aggregates than monovalent complexes. In vitro autoradiography using Tg2576 mice showed the specific binding of bivalent (99m)Tc-Ham complexes to Aβ plaques in the mouse brain, as reflected in the results of the inhibition assay. The preliminary results suggest that a new molecular design based on bivalent (99m)Tc-Ham complexes may be reasonable to develop an imaging probe targeting amyloid aggregates.

Novel Bivalent 99mTc-Complex with N-Methyl-Substituted Hydroxamamide as Probe for Imaging of Cerebral Amyloid Angiopathy

“…The precursor for [ 99m Tc]MBT2 (MBTHam, 5 ) was prepared in four steps from the precursor for [ 99m Tc]BT2 (BTHam, 1 ) according to a previous report ( Fig 2 )[ 31 ]. BTHam was prepared according to our previous report[ 30 ]. Reaction of BTHam with ethyl chlorocarbonate provided compound 2 , which was cyclized to compound 3 in alkaline solution.…”

“…The 99m Tc labeling reaction was performed by the complexation reaction using the Ham precursor, 99m Tc-pertechnetate, and tin(II) tartrate hydrate as a reducing agent ( Fig 3 )[ 30 ]. The 99m Tc complexation reaction with MBTHam rendered a single peak at the retention time of 13.6 min on RP-HPLC, while the reaction with BTHam provided two peaks at the retention times of 11.5 and 14.3 min ( Fig 4 ).…”

“… a Values are the mean ± standard error of the mean of six independent experiments b Data from our previous study (Ref. 30 ). …”

Evaluation of the Relationship Between Cognitive Impairment, Glycometabolism, and Nicotinic Acetylcholine Receptor Deficits in a Mouse Model of Alzheimer’s Disease

“…Upon completion of the ex vivo dual autoradiography study, serial sections were stained with thioflavin-S using the same procedure as that stated by Iikuni et al [17]. The digital images (n = 4 per group) taken under the same conditions were analyzed with BZ-X analyzer ver.…”

Small Molecule Radiopharmaceuticals – A Review of Current Approaches

“…To assess the amyloid aggregation ( 18 ), synthesized bivalent amyloid ligand and labeled with 99m Tc leading to the formation of 99m Tc-Ham (Figure 2 D). Stilbene (SB) and benzothiazole (BT) derivatives were selected as amyloid binding units.…”