The human epidermal growth factor receptor 3 (HER3) is overexpressed in several cancers, being linked to a more resistant phenotype and hence leading to poor patient prognosis. Imaging HER3 is challenging owing to the modest receptor number (<50000 receptors/cell) in overexpressing cancer cells. Therefore, to image HER3 in vivo, high target affinity PET probes need to be developed. This work describes two different [(18)F]AlF radiolabeling strategies of the ZHER3:8698 affibody molecule specifically targeting HER3. The one-pot radiolabeling of ZHER3:8698 performed at 100 °C and using 1,4,7-triazanonane-1,4,7-triacetate (NOTA) as chelator resulted in radiolabeled products with variable purity attributed to radioconjugate thermolysis. An alternative approach based on the inverse electron demand Diels-Alder (IEDDA) reaction between a novel tetrazine functionalized 1,4,7-triazacyclononane-1,4-diacetate (NODA) chelator and the trans-cyclooctene (TCO) functionalized affibody molecule was also investigated. This method enabled the radiolabeling of the protein at room temperature. The [(18)F]AlF-NOTA-ZHER3:8698 and [(18)F]AlF-NODA-ZHER3:8698 conjugates showed a specific uptake at 1 h after injection in high HER3-expressing MCF-7 tumors of 4.36 ± 0.92% ID/g and 4.96 ± 0.65% ID/g, respectively. The current results are encouraging for further investigation of [(18)F]AlF-NOTA-ZHER3:8698 as a HER3 imaging agent.

The aluminium-[18F]fluoride ([18F]AlF) radiolabelling method combines the favourable decay characteristics of fluorine-18 with the convenience and familiarity of metal-based radiochemistry and has been used to parallel gallium-68 radiopharmaceutical developments. As such, the [18F]AlF method is popular and widely implemented in the development of radiopharmaceuticals for the clinic. In this review, we capture the current status of [18F]AlF-based technology and reflect upon its impact on nuclear medicine, as well as offering our perspective on what the future holds for this unique radiolabelling method.

The future of Zr-based immuno-PET is reliant upon the development of new chelators with improved stability compared to the currently used deferoxamine (DFO). Herein, we report the evaluation of the octadentate molecule DFO-HOPO (3) as a suitable chelator forZr and a more stable alternative to DFO. The molecule showed good potential for the future development of a DFO-HOPO-based bifunctional chelator (BFC) for the radiolabelling of biomolecules with Zr. This work broadens the selection of available chelators forZr in search of improved successors to DFO for clinical Zr-immuno-PET.

Background The histological evaluation of estrogen receptor (ER) and progesterone receptor (PR) expression in breast cancer lesions from biopsy tissue can stratify patients to receive endocrine therapy. Furthermore, PR expression can predict response to selective estrogen receptor modulators (SERMs). Current immunohistochemical approaches to PR detection are limited by sampling error associated with biopsy and lack of standardised protocols; positron emission tomography (PET) using receptor targeted radiopharmaceuticals to provide quantitative, whole-body imaging may overcome these limitations. PR expression has been successfully imaged with PET in the clinical setting, however investigation into new radioligands with improved pharmacokinetics and metabolic stability is desirable. Results We report the synthesis of a focused library of non-steroidal PR ligands evaluated for use as PET radioligands. A lead candidate ( [ 18 F]2 ) with low nanomolar activity was selected and radiolabelled with a radiochemical yield of 2.29 ± 2.31% (decay-corrected), radiochemical purity (RCP) > 95% and a molar activity of 2.5 ± 1.6 GBq/μmol. Cell uptake studies showed a significant and specific accumulation of [ 18 F]2 in T47D (PR++) breast cancer cell compared to MDA-MB-231 (PR-) control; however, in vivo evaluation was confounded by rapid defluorination of the radioligand. In vitro metabolite analysis of 2 in MLM confirmed defluorination and oxidative metabolism of the thiocarbamate to oxocarbamate moiety by mass spectrometry. Conclusions A route to access [ 18 F]2 was developed to allow in vitro and in vivo evaluation, albeit with low radiochemical yield and modest molar activity. [ 18 F]2 demonstrated selective uptake in PR++ T47D cells which could be blocked in a dose dependent manner with progesterone. However, [ 18 F]2 showed poor in vivo metabolic stability with rapid defluorination within the time frame of the imaging protocol. Electronic supplementary material The online version of this article (10.1186/s41181-018-0054-z) contains supplementary material, which is available to authorized users.

The first general [18F]AIF automated radiolabelling procedure developed on the GE Tracerlab FX FN (Left) and Trasis AllInOne (Right) platforms.

Synthesis of the first water-soluble porphyrin radiolabeled with fluorine-18 is described: a new molecular theranostic agent which integrates the therapeutic selectivity of photodynamic therapy (PDT) with the imaging efficacy of positron emission tomography (PET). Generation of the theranostic was carried out through the conjugation of a cationic water-soluble porphyrin bearing an azide functionality to a fluorine-18 radiolabeled prosthetic bearing an alkyne functionality through click conjugation, with excellent yields obtained in both cold and hot synthesis. Biological evaluation of the synthesized structures shows the first example of an (18)F-radiolabeled porphyrin retaining photocytotoxicity following radiolabeling and demonstrable conjugate uptake and potential application as a radiotracer in vivo. The promising results gained from biological evaluation demonstrate the potential of this structure as a clinically relevant theranostic agent, offering exciting possibilities for the simultaneous imaging and photodynamic treatment of tumors.

2 Translational RelevanceCurrently, inter-and intra-tumor heterogeneity is a clinical challenge, as histological techniques can fail to provide a representative indication of molecular variation, due to dependence on the section of tumor that is chosen for sampling. This underscores the need to introduce novel imaging biomarkers that allow the examination of the whole tumor mass and may significantly help to better understand and treat cancer. Therefore, we have developed a novel PET radiotracer that will provide information on heterogeneous HER3 expression and receptor expression changes due to downstream signaling inhibition, which is increasingly being recognized as a key player in therapeutic resistance. This would aid in the selection of patients for novel HER3 targeted therapies and potentially enable patients to be spared ineffective therapies, and, if necessary, being switched sooner to more effective therapeutic regimens.Research. Zr-DFO-Z HER3:8698 can track changes in receptor expression in HER3-positive xenograft models and monitor the outcome of AUY922 treatment. Our in vitro findings showed that MCF-7 cells, which are phenotypically different from BT474, develop resistance to AUY922 through HER3/IGF-1R-mediated signaling. Of note, the lack of response in vitro due to HER3 recovery was confirmed in vivo using 89 Zr-DFO-Z HER3:8698 -based imaging. Upon AUY922 treatment, higher radioconjugate uptake was detected in treated MCF-7 xenografts, correlating with an AUY922-induced HER3 up-regulation concomitant with an increase in IGF-1R expression. Conclusion: These data underline the potential of HER3-based PET imaging to noninvasively provide information about HER3 expression and to identify patients not-responding to targeted therapies due to HER3 recovery.

In head and neck squamous cell carcinoma (HNSCC), 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 mAb used for the treatment of HNSCC, 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 non-invasive measurement of EGFR expression across the entire tumor burden and also allow for dynamic monitoring of cetuximab-mediated changes in receptor expression. EGFR-specific Affibody molecule (ZEGFR:03115) was radiolabeled with zirconium-89 (Zr) and fluorine-18 (F). 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 Zr-DFO-ZEGFR:03115 (2.4-3.6 MBq, 2 µg) either together with or 30 mins after increasing amounts of unlabeled ZEGFR:03115 (1, 5, 10, 15 and 20 µg). PET images were acquired at 3, 24 and 48 h post-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 andF-AlF-NOTA-ZEGFR:03115 (12 µg, 1.5-2 MBq/mouse) used to monitor receptor changes. In vivo studies demonstrated that co-injecting 10 µg of non-labeled molecules withZr-DFO-ZEGFR:03115 allows for clear tumor visualization 3 h post-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, F-AlF-NOTA-ZEGFR:03115 could measure receptor downregulation in response to EGFR inhibition. ZEGFR03115-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.