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.

Background: There have been few cohorts of neonates with coronavirus disease-2019 reported. As a result, there remains much to be learned about mechanisms of neonatal infection including potential vertical transmission, best methods of testing, and the spectrum of clinical findings. This communication describes the epidemiology, diagnostic test results and clinical findings of neonatal COVID-19 during the pandemic in Iran. Materials and methods: This is a retrospective cohort study of 19 neonates infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from 10 hospitals throughout Iran. We analyzed obstetrical information, familial COVID-19 status, neonatal medical findings, perinatal complications, hospital readmissions, patterns of repeated testing, and clinical outcomes. Results: Eleven neonates had family members infected. Five mothers were negative for COVID-19 and four neonates had no identifiable family source of infection. The neonatal mortality rate from COVID-19 was 10%. Seven newborns (37%) were discharged from the hospital as healthy but required readmission for symptoms of COVID-19. There were 2 multifetal gestationsone set each of twins and triplets, each with disparate testing and clinical outcomes. Premature delivery was common, occurring in 12 of 19 infants (63%). Initial testing for COVID-19 was negative in 4 of the 19 neonates (21%) who subsequently became positive. In 2 cases, neonates tested positive at 1 and 2 h after birth which was suspicious for vertical transmission of SARS-CoV-2. Conclusions: These cases have notable variation in the epidemiology, clinical features, results of testing and clinical outcomes among the infected newborns. Neonates initially testing negative for COVID-19 may require readmission due to infection. Two neonates were highly suspicious for intrauterine vertical transmission. Repeat testing of neonates who initially test negative for COVID-19 is recommended, without which 21% of neonatal infections would have been undiagnosed.

The bioorthogonal reaction between a tetrazine and strained trans-cyclooctene (TCO) has garnered success in pretargeted imaging. This reaction was first validated in nuclear imaging using an 111In-labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-linked bispyridyl tetrazine (Tz) ([111In]In-DOTA-PEG11-Tz) and a TCO functionalized CC49 antibody. Given the initial success of this Tz, it has been paired with TCO functionalized small molecules, diabodies, and affibodies for in vivo pretargeted studies. Furthermore, the single photon emission tomography (SPECT) radionuclide, 111In, has been replaced with the β-emitter, 177Lu and α-emitter, 212Pb, both yielding the opportunity for targeted radiotherapy. Despite use of the ‘universal chelator’, DOTA, there is yet to be an analogue suitable for positron emission tomography (PET) using a widely available radionuclide. Here, a 68Ga-labeled variant ([68Ga]Ga-DOTA-PEG11-Tz) was developed and evaluated using two different in vivo pretargeting systems (Aln-TCO and TCO-CC49). Small animal imaging and ex vivo biodistribution studies were performed and revealed target specific uptake of [68Ga]Ga-DOTA-PEG11-Tz in the bone (3.7 %ID/g, knee) in mice pretreated with Aln-TCO and tumor specific uptake (5.8 %ID/g) with TCO-CC49 in mice bearing LS174 xenografts. Given the results of this study, [68Ga]Ga-DOTA-PEG11-Tz can serve as an alternative to [111In]In-DOTA-PEG11-Tz.

Background Pretargeted imaging allows the use of short-lived radionuclides when imaging the accumulation of slow clearing targeting agents such as antibodies. The biotin-(strept)avidin and the bispecific antibody-hapten interactions have been applied in clinical pretargeting studies; unfortunately, these systems led to immunogenic responses in patients. The inverse electron demand Diels-Alder (IEDDA) reaction between a radiolabelled tetrazine (Tz) and a trans -cyclooctene (TCO)-functionalized targeting vector is a promising alternative for clinical pretargeted imaging due to its fast reaction kinetics. This strategy was first applied in nuclear medicine using an 111 In-labelled Tz to image TCO-functionalized antibodies in tumour-bearing mice. Since then, the IEDDA has been used extensively in pretargeted nuclear imaging and radiotherapy; however, these studies have only been performed in mice. Herein, we report the 44 Sc labelling of a Tz and evaluate it in pretargeted imaging in Wistar rats. Results 44 Sc was obtained from an in house 44 Ti/ 44 Sc generator. A 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-functionalized tetrazine was radiolabelled with 44 Sc resulting in radiochemical yields of 85–95%, a radiochemical purity > 99% at an apparent molar activity of 1 GBq/mmol. The 44 Sc-labelled Tz maintained stability in solution for up to 24 h. A TCO-functionalized bisphosphonate, which accumulates in skeletal tissue, was used as a targeting vector to evaluate the 44 Sc-labelled Tz. Biodistribution data of the 44 Sc-labelled Tz showed specific uptake (0.9 ± 0.3% ID/g) in the bones (humerus and femur) of rats pre-treated with the TCO-functionalized bisphosphonate. This uptake was not present in rats not receiving pre-treatment (< 0.03% ID/g). Conclusions We have prepared a 44 Sc-labelled Tz and used it in pretargeted PET imaging with rats treated with TCO-functionalized bisphosponates. This allowed for the evaluation of the IEDDA reaction in animals larger than a typical mouse. Non-target accumulation was low, and there was a 30-fold higher bone uptake in the pre-treated rats compared to the non-treated controls. Given its convenient half-life and the ability to perform positron emission tomography with a previously studied DOTA-functionalized Tz, scandium-44 ( t 1/2 = 3.97 h) proved to be a suitable radioisotope for this study. Electronic supplementary material The online version of this article (10.1186/s13550-019-0520-y) contains supplementary material, which is available to authorized users.