A high yield synthesis of a novel, small molecule, bisphosphonate-modified trans-cyclooctene (TCO-BP, 2) that binds to regions of active bone metabolism and captures functionalized tetrazines in vivo, via the bioorthogonal inverse electron demand Diels-Alder (IEDDA) cycloaddition, was developed. A Tc-labeled derivative of 2 demonstrated selective localization to shoulder and knee joints in a biodistribution study in normal mice. Compound 2 reacted rapidly with aLu-labeled tetrazine in vitro, and pretargeting experiments in mice, using 2 and the Lu-labeled tetrazine, yielded high activity concentrations in shoulder and knee joints, with minimal uptake in other tissues. Pretargeting experiments with 2 and a novelTc-labeled tetrazine also produced high activity concentrations in the knees and shoulders. Critically, both radiolabeled tetrazines showed negligible uptake in the skeleton and joints when administered in the absence of 2. Compound 2 can be utilized to target functionalized tetrazines to bone and represents a convenient reagent to test novel tetrazines for use with in vivo bioorthogonal pretargeting strategies.

Hydrocyanine dyes are sensitive "turn-on" type optical probes that can detect reactive oxygen species (ROS). We have developed a method to prepare an F-labeled hydrocyanine dye as a multi-modal PET and optical "turn-on" probe. A commercially available near infrared (NIR) dye was modified with a fluorinated prosthetic group that did not alter its ROS sensing properties in the presence of superoxide and hydroxyl radicals. The F-labeled analogue was produced using a single-step terminal fluorination procedure. Positron emission tomography (PET) imaging and quantitative in vivo biodistribution studies indicated this novel probe had remarkably different pharmacokinetics compared to the oxidized cyanine analogue. The chemistry reported enables the use of quantitative and dynamic PET imaging for the in vivo study of hydrocyanine dyes as ROS probes.

A new prosthetic group referred to as the triazole appending agent (TAAG) was developed as a means to prepare targeted radioiodine-based molecular imaging and therapy agents. Tributyltin-TAAG and the fluorous analogue were synthesized in high yield using simple click chemistry and the products labeled in greater than 95% RCY with 123 I. A TAAG derivative of an inhibitor of prostate-specific membrane antigen was prepared and radiolabeled with 123 I in 85% yield where biodistribution studies in LNCap prostate cancer tumor models showed rapid clearance of the agent from nontarget tissues and tumor accumulation of 20% injected dose g −1 at 1 h. The results presented demonstrate that the TAAG group promotes minimal nonspecific binding and that labeled conjugates can achieve high tumor uptake and exquisite target-to-nontarget ratios.

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Dipeptidyl (acyloxy)methyl ketones (AOMKs) were functionalized with different iodine-containing prosthetic groups to generate a library of candidate cathepsin B probes. Compound 23a, (S)-20-[(S)-2-{[(benzyloxy)carbonyl]amino}-3-phenylpropanamido]-1-(4-iodophenyl)-1,14,21-trioxo-5,8,11-trioxa-2,15-diazadocosan-22-yl 2,4,6-trimethylbenzoate, was identified as a potential lead through in vitro screening, having a Ki = 181 ± 9 nM and demonstrating the ability to effectively label active cathepsin B in vitro. Its less potent analogue 11a, (S)-3-[(S)-2-{[(benzyloxy)carbonyl]amino}-3-phenylpropanamido]-7-[6-(4-iodobenzamido)hexanamido]-2-oxoheptyl 2,4,6-trimethylbenzoate, was also tested as a comparison. Biodistribution studies of the iodine-125-labeled compounds in MDA-MB-231 mouse xenografts exhibited tumor uptake of 0.58% ± 0.06% injected dose per gram (ID/g) for [(125)I]11a and 1.12% ± 0.08% ID/g for [(125)I]23a at 30 min. The tumor-to-blood ratios reached 1.2 for [(125)I]23a and 1.6 for [(125)I]11a after 23 h. The more hydrophilic [(125)I]23a showed an improved clearance profile with a superior tumor-to-muscle ratio of 7.0 compared to 3.4 for [(125)I]11a at 23 h. Iodinated AOMK ligands are suitable in vitro probes for cathepsin B and hold promise as a platform to develop molecular imaging probes.