Design, Synthesis, and Evaluation of a Low-Molecular-Weight ¹¹C-Labeled Tetrazine for Pretargeted PET Imaging Applying Bioorthogonal in Vivo Click Chemistry

Abstract

A low-molecular-weight tetrazine labeled with the short-lived positron emitter carbon-11 was developed as a bioorthogonal PET probe for pretargeted imaging. A method for efficient and fast synthesis of this imaging agent is presented using radiolabeling of a readily available precursor. High reactivity with trans-cyclooctenes was observed and in vivo investigations including PET/MR scanning showed homogeneous biodistribution, good metabolic stability, and rapid excretion in naive mice. These properties are key to the success of bioorthogonal (11)C-PET imaging, which has been shown in a simple pretargeting experiment using TCO-modified mesoporous silica nanoparticles. Overall, this (11)C-labeled tetrazine represents a highly versatile and advantageous chemical tool for bioorthogonal PET imaging and enables pretargeting approaches using carbon-11 for the first time.

Site-specific conjugation allows modulation of click reaction stoichiometry for pretargeted SPECT imaging

“…11 These IEDDA reactions have second-order rate constants ranging from k 2  = 10 3 –10 6 M −1 s −1 , which are primarily driven by expulsion of N 2 and TCO strain relief following the cycloaddition 12,13 Furthermore, electron withdrawing substituents attached to the tetrazine confer increased reaction rates between the dienophile and diene. 14,15 Successful pretargeted in vivo nuclear imaging has been demonstrated in preclinical models using PET isotopes, including 11 C (t 1/2 20.3 minutes), 16,17 18 F (t 1/2 110 minutes) 18–20 and 64 Cu (t 1/2 12.7 hours), 4,21–24 as well as SPECT isotopes including 99m Tc (t 1/2 6 hours), 25–27 111 In (t 1/2 2.8 days) 28–30 and 177 Lu (t 1/2 6.7 days). 27,31–33 The recent success of IEDDA reactions for in vivo pretargeting and other chemical biology applications has been reviewed by several groups.…”

Hybrid silica materials for detection of toxic species and clinical diagnosis

“…40 The other mechanism considers that liquidcrystalline phase is formed even at lower concentrations of surfactant molecules, for example, in a cooperative self-assembly of the template molecules and the added inorganic species. 41 Using this procedure, the original approach has been extended by a number of variations. As an example, the use of tri-block copolymer templates under acidic conditions was employed to prepare the so-called SBA (Santa Barbara Amorphous) silica phases, 42 whereas the use of cationic surfactants, such as hexadecyltrimethylammonium bromide (CTAB) was originally used in the synthesis of the first M41S materials, obtaining the hexagonal (MCM-41), the cubic (MCM-48) and lamellar (MCM-50) forms cited above.…”

“…This is a critical step, because depending on certain reaction parameters (temperature, polymeric precursor 40 Attard, G. S.; Glyde, J. C.; Göltner, C. G. Nature 1995, 378, 366. 41 concentration and reaction time) the particle morphology can be tuned from micrometric and heterogeneous particles to create various forms, including thin films, spherical nanoparticles or monoliths. 43 figure 11, in a work considered the first example of cocondensation functionalization of the MCM-41 inorganic scaffold.…”

“…15 In contrast, there are very few examples in which enzymes themselves are used as caps. 41 Based on these concepts, we report herein the preparation of mesoporous silica nanoparticles (MSNs) capable of selectively opening and releasing an entrapped cargo (we selected a dye as a proof of concept) in the presence of DFP, which is a mimic of nerve agents Sarin or Soman. We employed the acetylcholinesterase (AChE) enzyme as the cap, rhodamine B as the cargo and directed experiments to detect DFP in aqueous environments.…”

“…31 3+2 cycloadditions with labelled tetraazines and grafting complexes through amidation reactions) and have also been used for positron emission tomography (PET) and SPECT imaging. [37][38][39][40][41][42][43][44][45] However, a typical drawback of some of these labelled systems is poor tumour accumulation. 39,40 From another perspective, MUC-1 is a mucin glycoprotein expressed in the extracellular matrix by most glandular and ductal epithelial cells, and by several hematopoietic cell lineages.…”