A first-of-its-kind 18F pretargeted PET imaging approach based on the bioorthogonal inverse electron demand Diels–Alder (IEDDA) reaction between tetrazine (Tz) and trans-cyclooctene (TCO) is presented. As proof-of-principle, a TCO-bearing immunoconjugate of the anti-CA19.9 antibody 5B1 and an Al[18F]NOTA-labeled tetrazine radioligand were harnessed for the visualization of CA19.9-expressing BxPC3 pancreatic cancer xenografts. Biodistribution and 18F-PET imaging data clearly demonstrate that this methodology effectively delineates tumor mass with activity concentrations up to 6.4 %ID/g at 4 h after injection of the radioligand.

Although aminoglycosides have been used as antibacterials for decades, their use has been hindered by their inherent toxicity and the resistance that has emerged to these compounds. It seems that such issues have relegated a formerly front-line class of antimicrobials to the proverbial back shelf. However, recent advances have demonstrated that novel aminoglycosides have a potential to overcome resistance as well as to be used to treat HIV-1 and even human genetic disorders, with abrogated toxicity. It is not the end for aminoglycosides, but rather, the challenges faced by researchers have led to ingenuity and a change in how we view this class of compounds, a renaissance.

This article is available online at http://www.jlr.org Cardiovascular disease (CVD) remains a leading cause of morbidity and mortality in the Western world ( 1 ). Elevated levels of LDL-cholesterol (LDL-C) have consistently shown a positive association with the development of CVD, justifying the current therapeutic strategies to prevent CVD primarily by the use of statins. Members of this drug class inhibit HMG-CoA reductase (HMGR), the rate-limiting enzyme for de novo cholesterol synthesis, thereby leading to decreased LDL-C ( 2-4 ). While the benefi ts of statins have been documented ( 2 ), many individuals on statin therapy still remain at a higher risk of developing CVD. It is possible this residual risk is a result of other metabolic syndrome (MetS) risk factors characterized by dyslipidemia and insulin resistance and is also in part due to statin intolerance ( 5-7 ) and noncompliance often related to statininduced myalgia ( 8, 9 ). Statins are effective at decreasing LDL-C and CVD; however, frequent muscle-related side effects limit dosage and impede maximal risk reduction in dyslipidemic patients ( 10 ). Furthermore, recent evidence suggests that high-dose statins may increase the risk of developing type 2 diabetes (T2D) ( 11 ), further justifying the need for alternative therapeutic interventions that have statin-like effects for lowering LDL-C and are designed to Abstract ETC-1002 (8-hydroxy-2,2,14,14-tetramethylpentadecanedioic acid) is a novel investigational drug being developed for the treatment of dyslipidemia and other cardio-metabolic risk factors. The hypolipidemic, anti-atherosclerotic, anti-obesity, and glucose-lowering properties of ETC-1002, characterized in preclinical disease models, are believed to be due to dual inhibition of sterol and fatty acid synthesis and enhanced mitochondrial long-chain fatty acid ␤ -oxidation. However, the molecular mechanism(s) mediating these activities remained undefi ned.

5B1 is a fully human, monoclonal antibody that has shown promise for the PET imaging of cancers expressing carbohydrate antigen 19.9 (CA19.9)—a carbohydrate prevalent in cells with aberrant glycosylation and an established effector of metastasis. The long physiologic half-life of the antibody and interference from circulating CA19.9 may increase the time required to generate quality images as well as the risk of radiation exposure to healthy tissues during repeated PET imaging. Pretargeting methodologies are an effective approach to expeditiously acquire PET images, but in this case, the pretargeting approach is complicated by the internalization of 5B1 by CA19.9-expressing cells. We sought to adapt and optimize a pretargeting strategy that exploits the bioorthogonal reaction between transcyclooctene (TCO) and tetrazine (Tz) to overcome these complications. Methods 5B1 was modified with TCO, and a novel NOTA-PEG7-Tz radioligand was synthesized with the goal of improving on a previously reported analog. BxPC3 and Capan-2 cells were evaluated for their ability to internalize anti-CA19.9 antibodies using a fluorometric assay, and xenografts of the same lines were used for in vivo studies. The pretargeting approach was optimized, and the 2 radioligands were compared using biodistribution and PET imaging in murine models of pancreatic cancer. Results BxPC3 and Capan-2 cells were shown to rapidly internalize anti-CA19.9 monoclonal antibodies, including 5B1. 64Cu-NOTA-PEG7-Tz showed improved in vivo pharmacokinetics relative to 64Cu-NOTA-Tz using 5B1-TCO as the targeting vector. PET imaging and biodistribution studies showed that injecting the radioligand 72 h after the administration of 5B1-TCO resulted in the best uptake (8.2 ± 1.7 percentage injected dose per gram at 20 h after injection) and tumor-to-background activity concentration ratios. Dosimetry calculations revealed that the pretargeting system produced a greater than 25-fold reduction in total body radiation exposure relative to 89Zr-desferrioxamine-5B1. PET/CT imaging in an orthotopic Capan-2 xenograft model—which secretes large amounts of CA19.9 and more rapidly internalizes anti-CA19.9 antibodies—showed that this approach is viable even in the difficult circumstances presented by a circulating antigen and internalized targeting vector. Conclusion The 5B1-TCO and 64Cu-NOTA-PEG7-Tz system evaluated in these studies can delineate CA19.9-positive xenografts in murine models of pancreatic cancer despite the challenges posed by the combination of circulating antigen and internalization of the 5B1-TCO.