This work features the synthesis and biological evaluation of a novel fluorinated derivative of tanaproget and a carbon-11 labelled analogue, a high affinity non-steroidal PR ligand, as a possible candidate for imaging PR expressionin vivo.
Positron emission tomography (PET) has proven to be an invaluable tool in the staging and management of disease in oncology; however, [18F]fluorodeoxyglucose ([18F]FDG) remains the most widely used PET radiopharmaceutical despite the large financial investment in novel radiotracer development. We report our perspective and experience of translating radiopharmaceuticals into clinical studies, discussing the PET development pipeline from a chemistry perspective. We hope that, by identifying potential points of attrition along the pipeline and suggesting solutions to these problems, we may help others take their preclinical radiotracers into human studies. This review focuses primarily on the development of fluorine-18 radiopharmaceuticals, although the broader field of radiometal chemistry is considered where the translation journey is similar.
The use of biologics in positron emission tomography (PET) imaging is an important area of radiopharmaceutical development and new automated methods are required to facilitate their production. We report an automated radiosynthesis method to produce a radiolabelled biologic via facile inverse electron demand Diels-Alder (IEDDA) "click" chemistry on a single GE FASTLab™ cassette. We exemplified the method by producing a fluorine-18 radiolabelled interleukin-2 (IL2) radioconjugate from a trans-cyclooctene (TCO) modified IL2 precursor. The radioconjugate was produced using a fully automated radiosynthesis on a single FASTLab™ cassette in a decay-corrected radiochemical yield (RCY, d.c.) of 19.8 ± 2.6% in 110 min (from start of synthesis); the molar activity was 132.3 ± 14.6 GBq μmol-1. The in vitro uptake of [18F]TTCO-IL2 correlated with the differential receptor expression (CD25, CD122, CD132) in PC3, NK-92 and activated human PBMCs. The automated method may be adapted for the radiosynthesis of any TCO-modified protein via IEDDA chemistry.
Abstract Background Glycogen is a multibranched polysaccharide of glucose produced by cells to store energy and plays a key role in cancer. A previously reported fluorescent probe (CDg4) was shown to selectively bind glycogen in mouse embryonic stem cells, however the molecule was not evaluated in cancer cells. We report the synthesis and biological evaluation of a dual-modality imaging probe based on CDg4, for positron emission tomography (PET) and fluorescence microscopy. Results A fluorine-18 radiolabelled derivative of CDg4, ( [ 18 F]5 ) for in vivo quantification of total glycogen levels in cancer cells was developed and synthesised in 170 min with a non-decay corrected radiochemical yield (RCY n.d.c) of 5.1 ± 0.9% ( n = 4) in > 98% radiochemical purity. Compound 5 and [ 18 F]5 were evaluated in vitro for their potential to bind glycogen, but only 5 showed accumulation by fluorescence microscopy. The accumulation of 5 was determined to be specific as fluorescent signal diminished upon the digestion of carbohydrate polymers with α-amylase. PET imaging in non-tumour bearing mice highlighted rapid hepato-biliary-intestinal elimination of [ 18 F]5 and almost complete metabolic degradation after 60 min in the liver, plasma and urine, confirmed by radioactive metabolite analysis. Conclusions Fluorescent compound 5 selectively accumulated in glycogen containing cancer cells, identified by fluorescence microscopy; however, rapid in vivo metabolic degradation precludes further investigation of [ 18 F]5 as a PET radiopharmaceutical.
In head and neck squamous cell cancer, the human epidermal growth factor receptor 1 (EGFR) is the dominant signaling molecule among all members of the family. So far, cetuximab is the only approved anti-EGFR monoclonal antibody used for the treatment of head and neck squamous cell cancer, but despite the benefits of adding it to standard treatment regimens, attempts to define a predictive biomarker to stratify patients for cetuximab treatment have been unsuccessful. We hypothesized that imaging with EGFR-specific radioligands may facilitate noninvasive measurement of EGFR expression across the entire tumor burden and allow for dynamic monitoring of cetuximab-mediated changes in receptor expression. Methods: EGFR-specific Affibody molecule (ZEGFR:03115) was radiolabeled with 89Zr and 18F. The radioligands were characterized in vitro and in mice bearing subcutaneous tumors with varying levels of EGFR expression. The protein dose for imaging studies was assessed by injecting 89Zr-deferoxamine-ZEGFR:03115 (2.4–3.6 MBq, 2 μg) either together with or 30 min after increasing amounts of unlabeled ZEGFR:03115 (1, 5, 10, 15, and 20 μg). PET images were acquired at 3, 24, and 48 h after injection, and the image quantification data were correlated with the biodistribution results. The EGFR expression and biodistribution of the tracer were assessed ex vivo by immunohistochemistry, Western blot, and autoradiography. To downregulate the EGFR level, treatment with cetuximab was performed, and 18F-aluminium fluoride-NOTA-ZEGFR:03115 (12 μg, 1.5–2 MBq/mouse) was used to monitor receptor changes. Results: In vivo studies demonstrated that coinjecting 10 μg of nonlabeled molecules with 89Zr-deferoxamine-ZEGFR:03115 allows for clear tumor visualization 3 h after injection. The radioconjugate tumor accumulation was EGFR-specific, and PET imaging data showed a clear differentiation between xenografts with varying EGFR expression levels. A strong correlation was observed between PET analysis, ex vivo estimates of tracer concentration, and receptor expression in tumor tissues. Additionally, 18F-aluminium fluoride-NOTA-ZEGFR:03115 could measure receptor downregulation in response to EGFR inhibition. Conclusion: ZEGFR:03115-based radioconjugates can assess different levels of EGFR level in vivo and measure receptor expression changes in response to cetuximab, indicating a potential for assessment of adequate treatment dosing with anti-EGFR antibodies.
The success of Lutathera™ ([177Lu]Lu-DOTA-TATE) in the NETTER-1 clinical trial as a peptide receptor radionuclide therapy (PRRT) for somatostatin receptor expressing (SSTR) neuroendocrine tumours (NET) is likely to increase the demand for patient stratification by positron emission tomography (PET). The current gold standard of gallium-68 radiolabelled somatostatin analogues (e.g., [68Ga]Ga-DOTA-TATE) works effectively, but access is constrained by the limited availability and scalability of gallium-68 radiopharmaceutical production. The aim of this review is three-fold: firstly, we discuss the peptide library design, biological evaluation and clinical translation of [18F]fluoroethyltriazole-βAG-TOCA ([18F]FET-βAG-TOCA), our fluorine-18 radiolabelled octreotide; secondly, to exemplify the potential of the 2-[18F]fluoroethylazide prosthetic group and copper-catalysed azide-alkyne cycloaddition (CuAAC) chemistry in accessing good manufacturing practice (GMP) compatible radiopharmaceuticals; thirdly, we aim to illustrate a framework for the translation of similarly radiolabelled peptides, in which in vivo pharmacokinetics drives candidate selection, supported by robust radiochemistry methodology and a route to GMP production. It is hoped that this review will continue to inspire the development and translation of fluorine-18 radiolabelled peptides into clinical studies for the benefit of patients.
Steroid hormone receptor (SHR) expression and changes in SHR expression compared to basal levels, whether upregulated, down-regulated, or mutated, form a distinguishing feature of some breast, ovarian, and prostate cancers. These receptors act to induce tumor proliferation. In the imaging context, total expression together with modulation of expression can yield predictive and prognostic information. Currently, biopsy for histologic assessment of SHR expression is routine for breast and prostate cancer; however, the technique is not well suited to the heterogeneous tumor environment and can lead to incorrect receptor expression assignment, which precludes effective treatment. The development of positron emission tomography (PET) radioligands to image receptor expression may overcome the difficulties associated with tumor heterogeneity and facilitate the assessment of metastatic disease.
This Tutorial Account aims to be a useful educational resource which describes how to automate fluorine-18 positron emission tomography (PET) radiochemistry using cassette-based automated radiosynthesis platforms.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
