In Vivo Imaging of Bone Using a Deep-Red Fluorescent Molecular Probe Bearing Multiple Iminodiacetate Groups

Abstract

Deep-red fluorescent molecular probes are described that have dendritic molecular architecture with a squaraine rotaxane core scaffold and multiple peripheral iminodiacetate groups as the bone targeting units. Iminodiacetates have inherently lower bone affinity than bisphosphonates and a major goal of the study was to determine how many appended iminodiacetate groups are required for effective deep-red fluorescence imaging of bone in living rodents. A series of in vitro and in vivo imaging studies showed that a tetra(iminodiacetate) probe stains bones much more strongly than an analogous bis(iminodiacetate) probe. In addition, a control tetra(iminodiapropionate) probe exhibited no bone targeting ability. The tetra(iminodiacetate) probe targeted the same regions of high bone turnover as the near-infrared bisphosphonate probe OsteoSense®750. Longitudinal studies showed that the fluorescence image signal from living mice treated with the tetra(iminodiacetate) probe was much more stable over 19 days than the signal from OsteoSense®750. The narrow emission band of the tetra(iminodiacetate) probe makes it very attractive for inclusion in multiplex imaging protocols that employ a mixture of multiple fluorescent probes in preclinical studies of bone growth or in fluorescence guided surgery. The results also suggest that molecules or nanoparticles bearing multivalent iminodiacetate groups have promise as bone targeting agents with tunable properties for various pharmaceutical applications.

Pre-Assembly of Near-Infrared Fluorescent Multivalent Molecular Probes for Biological Imaging

“…Three years ago, we discovered that fluorescent probes with appended iminodiacetate groups have affinity for regions of living bone that are undergoing high turnover. 39 The iminodiacetate groups associate with the hydroxyapatite mineral within the bone. 40 Moreover, a comparative in vivo imaging study showed that a fluorescent probe with four iminodiacetate groups exhibited more bone accumulation in living mice than a probe with two iminodiacetate groups.…”

“…Previously, we have shown that bone section staining with a fluorescent probe containing multiple iminodiacetate groups is lost if the bone section is decalcified by pre-treatment with EDTA. 39 …”

Direct or indirect stimulation of adenosine A 2A receptors enhances bone regeneration as well as bone morphogenetic protein‐2

“…This fluorescence reagent targets hydroxyapatite, and in combination with the IVIS imaging system (Caliper), allows in vivo detection and measurement of skeletal changes (26)(27)(28). Fluorescence images were taken with an excitation peak of 681 nm and an emission peak of 696 nm.…”

Synthesis of a disulfonated derivative of cucurbit[7]uril and investigations of its ability to solubilise insoluble drugs

“…1 Encapsulation of a guest inside a molecular container by formation of the container•guest complex often confers new properties or reactivity upon the guest. For example, molecular containers have been used to tame otherwise unstable species like cyclobutadiene, P 4 , and o -benzyne, 2 to protect π-conjugated chromophores for molecular electronic and imaging applications, 3 to promote and control supramolecular polymerization processes, 4 to catalyze bimolecular reactions, 5 and to control the conformational properties of the guest. We, and others, have been very interested in an alternate class of molecular containers known as cucurbit[n]urils (CB[n], n = 5, 6, 7, 8, 10, 14; Figure 1) 6,7 which are composed of n glycoluril units connected by 2n CH 2 -bridges and that are formed in high yield in a single condensation reaction under hot concentrated aqueous acidic conditions.…”