First experience of 18F-alfatide in lung cancer patients using a new lyophilized kit for rapid radiofluorination

Recent Progress in Peptide-Based Molecular Probes for Disease Bioimaging

Recent strides in molecular pathology have unveiled distinctive alterations at the molecular level throughout the onset and progression of diseases. Enhancing the in vivo visualization of these biomarkers is crucial for advancing disease classification, staging, and treatment strategies. Peptide-based molecular probes (PMPs) have emerged as versatile tools due to their exceptional ability to discern these molecular changes with unparalleled specificity and precision. In this Perspective, we first summarize the methodologies for crafting innovative functional peptides, emphasizing recent advancements in both peptide library technologies and computer-assisted peptide design approaches. Furthermore, we offer an overview of the latest advances in PMPs within the realm of biological imaging, showcasing their varied applications in diagnostic and therapeutic modalities. We also briefly address current challenges and potential future directions in this dynamic field.

Optimization of a 1,4,7-Triazacyclononane-1,4-diacetic acid (NODA) Derivative Radiofluorination by Al18 F Complexation Using a Design of Experiments Approach

Fluorine-18 (18 F) is the most favorable positron emitter for radiolabeling Positron Emission Tomography (PET) probes. However, conventional 18 F labeling through covalent C-F bond formation is challenging, involving multiple steps and stringent conditions unsuitable for sensitive biomolecular probes whose integrity may be altered. Over the past decade, an elegant new approach has been developed involving the coordination of an aluminum fluoride {Al18 F} species in aqueous media at a late-stage of the synthetic process. The objective of this study was to implement this method and to optimize radiolabeling efficiency using a Design of Experiments (DoE). To assess the impact of various experimental parameters on {Al18 F} incorporation, a pentadentate chelating agent NODA-MP-C4 was prepared as a model compound. This model carried a thiourea function present in the final conjugates resulting from the grafting of the chelating agent onto the probe. The formation of the radioactive complex Al18 F-NODA-MP-C4 was studied to achieve the highest radiochemical conversion. A complementary "cold" series study using the natural isotope 19 F was also conducted to guide the radiochemical operating conditions. Ultimately, Al18 F-NODA-MP-C4 was obtained with a reproducible and satisfactory radiochemical conversion of 79±3.5 % (n=5).

CycloSiFA: The Next Generation of Silicon-Based Fluoride Acceptors for Positron Emission Tomography (PET)

The ring-opening Si-fluorination of a variety of azasilole derivatives cyclo-1-(iPr2 Si)-4-X-C6 H3 -2-CH2 NR (4: R=2,6-iPr2 C6 H3 , X=H; 4 a: R=2,4,6-Me3 C6 H2 , X=H; 9: R=2,6-iPr2 C6 H3 , X=tBuMe2 SiO; 10: R=2,6-iPr2 C6 H3 , X=OH; 13: R=2,6-iPr2 C6 H3 , X=HCCCH2 O; 22: R=2,6-iPr2 C6 H3 , X=tBuMe2 SiCH2 O) with different 19 F-fluoride sources was studied, optimized and the experience gained was used in a translational approach to create a straightforward 18 F-labelling protocol for the azasilole derivatives [18 F]6 and [18 F]14. The latter constitutes a potential clickable CycloSiFA prosthetic group which might be used in PET tracer development using Cu-catalysed triazole formation. Based on our findings, CycloSiFA has the potential to become a new entry into non-canonical labelling methodologies for radioactive PET tracer development.

Druggability of Targets for Diagnostic Radiopharmaceuticals

Targets play an indispensable and pivotal role in the development of radiopharmaceuticals. However, the initial stages of drug discovery projects are often plagued by frequent failures due to inadequate information on druggability and suboptimal target selection. In this context, we aim to present a comprehensive review of the factors that influence target druggability for diagnostic radiopharmaceuticals. Specifically, we explore the crucial determinants of target specificity, abundance, localization, and positivity rate and their respective implications. Through a detailed analysis of existing protein targets, we elucidate the significance of each factor. By carefully considering and balancing these factors during the selection of targets, more efficacious and targeted radiopharmaceuticals are expected to be designed for the diagnosis of a wide range of diseases in the future.

Automated Synthesis and Preclinical Evaluation of Optimized Integrin α6-Targeted Positron Emission Tomography Imaging of Pancreatic Cancer

Integrin α6 has been considered a promising biomarker, is overexpressed in many tumors, and plays a vital role in tumor formation, recurrence, and metastasis. In this study, we identified a novel high-affinity integrin α6-targeted peptide named RD2 (Arg-Trp-Tyr-Asp-PEG4)2-Lys-Lys and developed a 18F-radiolabeled peptide tracer ([18F]-AlF-NOTA-RD2) and evaluated its potential application in positron emission tomography (PET) imaging of pancreatic cancer. [18F]-AlF-NOTA-RD2 was produced using GMP (Good Manufacturing Practice of Medical Products)-compliant automatic radiosynthesis on a single GE FASTLab2 cassette-type synthesis module. The stability of [18F]-AlF-NOTA-RD2 was analyzed in phosphate-buffered saline (PBS) and fetal bovine serum (FBS). The cell uptake assay of the tracer was assessed using PANC-1 cells. In addition, small-animal PET imaging and biodistribution studies of [18F]-AlF-NOTA-RD2 were performed in pancreatic cancer subcutaneous tumor-bearing mice. The PET tracer [18F]-AlF-NOTA-RD2 was obtained with a radiochemical yield of 23.7 ± 4.7%, radiochemical purity of >99%, and molar activity of 165.7 ± 59.1 GBq/μmol. [18F]-AlF-NOTA-RD2 exhibited good in vitro stability in PBS and FBS. LogP octanol water value for the tracer was -2.28 ± 0.05 (n = 3). The binding affinity of RD2 to the integrin α6 protein (Kd = 0.13 ± 3.65 μM, n = 3) was significantly higher than that of the RWY (CRWYDENAC) (Kd = 6.97 ± 1.44 μM, n = 3). Small-animal PET imaging and biodistribution also revealed that [18F]-AlF-NOTA-RD2 displayed rapid and good tumor uptake and lower liver background uptake in PANC-1 tumor-bearing mice. [18F]-AlF-NOTA-RD2 showed significant radioactivity accumulation in tumors and was successfully blocked by NOTA-RD2. Compared with [18F]-FDG, [18F]-AlF-NOTA-RD2 PET imaging and biodistribution studies in PANC-1 xenograft tumor-bearing mice confirmed a good tumor-to-muscle ratio (8.69 ± 2.03 vs 1.41 ± 0.23, respectively) at 0.5 h and (2.99 ± 3.02 vs 1.43 ± 0.17, respectively) at 1 h post injection. Autoradiography of human pancreatic cancer tumor tissues further confirmed high accumulation of [18F]-AlF-NOTA-RD2. In summary, we developed an optimized integrin α6-targeted imaging tracer and obtained high radioactivity products with a cassette-type synthesis module; moreover, the tracer exhibited good binding affinity with integrin α6 and good target specificity for PANC-1 cells in xenograft pancreatic tumor-bearing mice, demonstrating its promising application as a noninvasive PET radiotracer of integrin α6 expression in pancreatic cancer.

Radionuclide-based theranostics - a promising strategy for lung cancer

PURPOSE

This review aims to provide a comprehensive overview of the latest literature on personalized lung cancer management using different ligands and radionuclide-based tumor-targeting agents.

BACKGROUND

Lung cancer is the leading cause of cancer-related deaths worldwide. Due to the heterogeneity of lung cancer, advances in precision medicine may enhance the disease management landscape. More recently, theranostics using the same molecule labeled with two different radionuclides for imaging and treatment has emerged as a promising strategy for systemic cancer management. In radionuclide-based theranostics, the target, ligand, and radionuclide should all be carefully considered to achieve an accurate diagnosis and optimal therapeutic effects for lung cancer.

METHODS

We summarize the latest radiotracers and radioligand therapeutic agents used in diagnosing and treating lung cancer. In addition, we discuss the potential clinical applications and limitations associated with target-dependent radiotracers as well as therapeutic radionuclides. Finally, we provide our views on the perspectives for future development in this field.

CONCLUSIONS

Radionuclide-based theranostics show great potential in tailored medical care. We expect that this review can provide an understanding of the latest advances in radionuclide therapy for lung cancer and promote the application of radioligand theranostics in personalized medicine.

Thermodynamic and Kinetic Stabilities of Al(III) Complexes with N2O3 Pentadentate Ligands

Al(III) complexes have been recently investigated for their potential use in imaging with positron emission tomography (PET) by formation of ternary complexes with the radioisotope fluorine-18 (¹⁸F). Although the derivatives of 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) are the most applied chelators for [Al¹⁸F]²⁺ labelling and (pre)clinical PET imaging, non-macrocyclic, semi-rigid pentadentate chelators having two N- and three O-donor atoms such as RESCA1 and AMPDA-HB have been proposed with the aim to allow room temperature labelling of temperature-sensitive biomolecules. The paucity of stability data on Al(III) complexes used for PET imaging instigated a complete thermodynamic and kinetic solution study on Al(III) complexes with aminomethylpiperidine (AMP) derivatives AMPTA and AMPDA-HB and the comparison with a RESCA1-like chelator CD3A-Bn (trans-1,2-diaminocyclohexane-N-benzyl-N,N',N'-triacetic acid). The stability constant of [Al(AMPDA-HB)] is about four orders of magnitude higher than that of [Al(AMPTA)] and [Al(CD3A-Bn)], highlighting the greater affinity of phenolates with respect to acetate O-donors. On the other hand, the kinetic inertness of the complexes, determined by following the Cu²⁺-mediated transmetallation reactions in the 7.5-10.5 pH range, resulted in a spontaneous and hydroxide-assisted dissociation slightly faster for [Al(AMPTA)] than for the other two complexes (t_1/2 = 4.5 h for [Al(AMPTA)], 12.4 h for [Al(AMPDA-HB)], and 24.1 h for [Al(CD3A-Bn)] at pH 7.4 and 25 °C). Finally, the [AlF]²⁺ ternary complexes were prepared and their stability in reconstituted human serum was determined by ¹⁹F NMR experiments.

18F-alfatide II internal dosimetry using the ICRP 110 adult reference phantoms and the ICRP 103 tissue weighting factors

PURPOSE

¹⁸F-alfatide II is an arginine-glycine-aspartate (RGD) peptide-based PET tracer with promising imaging properties and pharmacokinetics. This study aims to calculate the absorbed and effective doses of ¹⁸F-alfatide II using the ICRP 110 adult reference phantoms and the ICRP 103 tissue weighting factors.

METHODS

The MIRD method was used in this study to calculate the absorbed dose of organs and tissues. The biokinetic data were taken from a previous study. These data are based on the whole-body PET imaging of mice.

RESULTS

The results show that the effective dose per unit activity administered of ¹⁸F-alfatide II is 1.33E-02 mSv/MBq. The urinary bladder wall receives the highest absorbed dose due to the administration of this radiopharmaceutical. Also, the effective dose of ¹⁸F-alfatide II is lower than that of ¹⁸F-FDG and some other RGD peptide-based tracers.

CONCLUSIONS

Dose calculation using ICRP 110 voxelized adult reference phantoms and ICRP 103 tissue weighting factors leads to more realistic and accurate results for 18F-alfatide II compared to the stylized phantoms. The calculated effective dose of ¹⁸F-alfatide II in the present study is lower than that of previously published data.

An optimized radiosynthesis of [18 F]DK222, a PET radiotracer for imaging PD-L1

A radiochemical synthesis of [18 F]DK222, a peptide binder of programmed death ligand 1 protein, suitable for human PET studies is described, and results from validation productions are presented. The high specific activity radiotracer product is prepared as a sterile, apyrogenic solution that conforms to current Good Manufacturing Practice (cGMP) requirements. In addition, the production is extended to use a commercial synthesizer platform (General Electric FASTlab 2).

Skin Cancer Pathobiology at a Glance: A Focus on Imaging Techniques and Their Potential for Improved Diagnosis and Surveillance in Clinical Cohorts

Early diagnosis is essential for completely eradicating skin cancer and maximizing patients' clinical benefits. Emerging optical imaging modalities such as reflectance confocal microscopy (RCM), optical coherence tomography (OCT), magnetic resonance imaging (MRI), near-infrared (NIR) bioimaging, positron emission tomography (PET), and their combinations provide non-invasive imaging data that may help in the early detection of cutaneous tumors and surgical planning. Hence, they seem appropriate for observing dynamic processes such as blood flow, immune cell activation, and tumor energy metabolism, which may be relevant for disease evolution. This review discusses the latest technological and methodological advances in imaging techniques that may be applied for skin cancer detection and monitoring. In the first instance, we will describe the principle and prospective clinical applications of the most commonly used imaging techniques, highlighting the challenges and opportunities of their implementation in the clinical setting. We will also highlight how imaging techniques may complement the molecular and histological approaches in sharpening the non-invasive skin characterization, laying the ground for more personalized approaches in skin cancer patients.

High in-vivo stability in preclinical and first-in-human experiments with [18F]AlF-RESCA-MIRC213: a 18F-labeled nanobody as PET radiotracer for diagnosis of HER2-positive cancers

PURPOSE

[18F]AlF-RESCA was introduced as a core particularly useful for 18F-labeling of heat-sensitive biomolecules. However, no translational studies have been reported up to now. Herein, we reported the first-in-human evaluation of an 18F-labeled anti-HER2 nanobody MIRC213 as a PET radiotracer for imaging HER2-positive cancers.

METHODS

MIRC213 was produced by E. coli and conjugated with ( ±)-H3RESCA-Mal. [18F]AlF-RESCA-MIRC213 was prepared at room temperature. Its radiochemical purity and stability of were determined by radio-HPLC with the size-exclusion chromatographic column. Cell uptake was performed in NCI-N87 (HER2 +) and MCF-7 (HER2-) cells and the cell-binding affinity was verified in SK-OV-3 (HER2 +) cells. Small-animal PET/CT was performed using SK-OV-3, NCI-N87, and MCF-7 tumor-bearing mice at 30 min, 1 h, and 2 h post-injection. For blocking experiment, excess MIRC213 was co-injected with radiotracer. Biodistribution were performed on SKOV-3 and MCF-7 tumor-bearing mice at 2 h post-injection. For clinical study, PET/CT images were acquired at 2 h and 4 h after injection of [18F]AlF-RESCA-MIRC213 (1.85-3.7 MBq/kg) in six breast cancer patients (3 HER2-positive and 3 HER2-negative). All patients underwent [18F]-FDG PET/CT within a week for tissue selection purpose. Distribution and dosimetry were calculated. Standardized uptake values (SUV) were measured in tumors and normal organs.

RESULTS

MIRC213 was produced with > 95% purity and modified with RESCA to obtain RESCA-MIRC213. [18F]AlF-RESCA-MIRC213 was prepared within 20 min at room temperature with the radiochemical yield of 50.48 ± 7.6% and radiochemical purity of > 98% (n > 10), and remained stable in both PBS (88%) and 5% HSA (92%) after 6 h. The 2 h cellular uptake of [18F]AlF-RESCA-MIRC213 in NCI-N87 cells was 11.22 ± 0.60 AD%/105 cells. Its binding affinity Kd value was determined to be 1.23 ± 0.58 nM. Small-animal PET/CT with [18F]AlF-RESCA-MIRC213 can clearly differentiate SK-OV-3 and NCI-N87 tumors from MCF-7 tumors and background with a high uptake of 4.73 ± 1.18 ID%/g and substantially reduced to 1.70 ± 0.13 ID%/g for the blocking group (p < 0.05) in SK-OV-3 tumors at 2 h post-injection. No significant bone radioactivity was seen in the tumor-bearing animals. In all six breast cancer patients, there was no adverse reaction during study. The uptake of [18F]AlF-RESCA-MIRC213 was mainly in lacrimal gland, parotid gland, submandibular gland, thyroid gland, gallbladder, kidneys, liver, and intestines. There was no significant bone radioactivity accumulation in cancer patients. [18F]AlF-RESCA-MIRC213 had significantly higher tumor uptake in lesions from HER2-positive patients than that lesions from HER2-negative patients (SUVmax of 3.62 ± 1.56 vs. 1.41 ± 0.41, p = 0.0012) at 2 h post-injection. The kidneys received the highest radiation dose of 2.42 × 10-1 mGy/MBq, and the effective dose was 1.56 × 10-2 mSv/MBq.

CONCLUSIONS

[18F]AlF-RESCA-MIRC213 could be prepared with high radiolabeling yield under mild conditions. [18F]AlF-RESCA-MIRC213 has relatively high stability both in vitro and in vivo. The results from clinical transformation suggest that [18F]AlF-RESCA-MIRC213 PET/CT is a safe procedure with favorable pharmacokinetics and dosimetry profile, and it is a promising new PET radiotracer for noninvasive diagnosis of HER2-positive cancers.

Positron emission tomography imaging of lung cancer: An overview of alternative positron emission tomography tracers beyond F18 fluorodeoxyglucose

Lung cancer has been the leading cause of cancer-related mortality in China in recent decades. Positron emission tomography-computer tomography (PET/CT) has been established in the diagnosis of lung cancer. ¹⁸F-FDG is the most widely used PET tracer in foci diagnosis, tumor staging, treatment planning, and prognosis assessment by monitoring abnormally exuberant glucose metabolism in tumors. However, with the increasing knowledge on tumor heterogeneity and biological characteristics in lung cancer, a variety of novel radiotracers beyond ¹⁸F-FDG for PET imaging have been developed. For example, PET tracers that target cellular proliferation, amino acid metabolism and transportation, tumor hypoxia, angiogenesis, pulmonary NETs and other targets, such as tyrosine kinases and cancer-associated fibroblasts, have been reported, evaluated in animal models or under clinical investigations in recent years and play increasing roles in lung cancer diagnosis. Thus, we perform a comprehensive literature review of the radiopharmaceuticals and recent progress in PET tracers for the study of lung cancer biological characteristics beyond glucose metabolism.

Potential 18F-RGD PET/CT and DCE-MRI Imaging-Based Biomarkers for Postoperative Survival Prediction Among Patients With Newly Diagnosed Glioblastoma Treated With Bevacizumab and Chemoradiotherapy

Purpose

To investigate the ability of potential imaging biomarkers based on ¹⁸F-AlF-NOTA-PRGD2 positron emission tomography/computed tomography (¹⁸F-RGD PET/CT) and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) imaging to predict the response to bevacizumab combined with conventional therapy in postoperative newly diagnosed glioblastoma.

Methods

Twenty patients with newly diagnosed with glioblastoma after surgery were prospectively enrolled to receive bevacizumab plus conventional concurrent radiotherapy and temozolomide (CCRT). ¹⁸F-RGD PET/CT and DCE-MRI were performed at baseline, week 3, and week 10 for each patient. Statistical methods included the analysis of variance (ANOVA), Kaplan–Meier method and Cox proportional hazard analysis.

Results

All patients completed CCRT plus bevacizumab therapy without interruption. The median follow-up time was 33.9 months (95% confidence interval [CI], 28.3-39.5 months). The median progression-free survival (PFS) and overall survival (OS) was 9.66 months (95% CI, 6.20-13.12 months) and 15.89 months (95% CI, 13.89-17.78), respectively. Treatment was generally well tolerated, and there were no Treatment emergent adverse events (TEAEs) with a toxicity grade equal to or exceeding 3 or that led to termination of treatment or patient death.Over the treatment interval of bevacizumab therapy from week 3 to week 10, patients with a large decrease of SUVmean was associated with a better PFS with a hazard ratio (HR) of 6.562, 95% CI (1.318-32.667), p=0.022. According to Kaplan-Meier analysis, patients with a decrease in the SUVmean of more than 0.115 on ¹⁸F-RGD PET/CT had a longer PFS than those with a decrease in the SUVmean of 0.115 or less (12.25 months vs.7.46 months, p=0.009). For OS, only a small decrease of Ktrans was also found to have certain prognostic value (HR=0.986, 95% CI (0.975-0.998), p=0.023). Patients with a decrease in Ktrans larger than 37.03 (min-1) on DCE-MRI had worse OS than those with a decrease in Ktrans of 37.03 (min-1) or less (15.93 months vs. 26.42 months, p=0.044).

Conclusion

¹⁸F-RGD PET/CT and DCE-MRI may be valuable in evaluating the response of glioblastoma to treatment with the combination of bevacizumab and CCRT, with a greater decrease in SUV_mean predicting better PFS as well as a small decrease in K^trans predicting improved OS.

A Role of Non-FDG Tracers in Lung Cancer?

Since the introduction of PET/CT hybrid imaging about two decades ago the landscape of oncological imaging has fundamentally changed, opening a new era of molecular imaging with emphasis on functional characterization of biological processes such as metabolism, cellular proliferation, hypoxia, apoptosis, angiogenesis and immune response. The most commonly assessed functional hallmark of cancer is the increased metabolism in tumor cells due to well-known Warburg effect, because of which FDG has been the most employed radiotracer, the so-called pan-cancer agent, in oncological imaging. However, several limitations such as low specificity and low sensitivity for several histopathological forms of lung cancer as well as high background uptake in the normal tissue of FDG imaging lead to numerous serious pitfalls. This restricts its utilization and diagnostic value in lung cancer imaging, even though this is currently considered to be the method of choice in pulmonary cancer imaging. Accurate initial tumor staging and therapy response monitoring with respect to the TNM criteria plays a crucial role in therapy planning and management in patients with lung cancer. To this end, many efforts have been made for decades to develop novel PET radiopharmaceuticals with innovative approaches that go beyond the assessment of increased glycolytic activity alone. Radiopharmaceuticals targeting DNA synthesis, amino acid metabolism, angiogenesis, or hypoxia have been extensively studied, leading to the emergence of indications for specific clinical questions or as a complementary imaging tool alongside existing conventional or FDG imaging. Nevertheless, despite some initial encouraging results, these tracers couldn't gain a widespread use and acceptance in clinical routine. However, given its mechanism of action and some initial pilot studies regarding lung cancer imaging, FAPI has emerged as a very promising alternative tool that could provide superior or comparable diagnostic performance to FDG imaging in lung cancer entities. Thus, in this review article, we summarized the current PET radiopharmaceuticals, different imaging approaches and discussed the potential benefits and clinical applications of these agents in lung cancer imaging.

Synthesis of a new bifunctional NODA for bioconjugation with PSMA ligand and one-step Al18F labeling

The Al¹⁸F labeling method is a relatively new approach that allows radiofluorination of biomolecules such as peptides and proteins in a one-step procedure and in an aqueous solution. However, instability of the complex of [AlF]²⁺ with hexadentate chelator NOTA may attribute to the disassociation of free ¹⁸F^- and [Al¹⁸F]²⁺ and accumulation in bone. In this study, we designed and synthesized a new bifunctional pentadentate AlF-chelator p-SCN-PhPr-NODA as well as its nitro form p-NO₂-PhPr-NODA. Chelator p-NO₂-PhPr-NODA exhibited increased Al (III) complexation kinetics determined by AA III complexation kinetic studies and stronger coordination ability towards [AlF]²⁺ according to DFT calculation studies in comparison with hexadentate chelator NOTA. As a proof of concept, bifunctional chelator p-SCN-PhPr-NODA was furthermore conjugated to a PSMA targeting moiety Glu-urea-Lys to form NODA-PrPh-GuL. The conjugated peptide showed acceptable radiochemical yield (12.5-16.4%) and efficiency with an excellent radiochemical purity (∼100% after SPE purification) in Al¹⁸F labeling. The labeled peptide exhibited good in vitro stability and significant specificity for PSMA. Biodistribution study and MicroPET scan in healthy Kun Ming mice with the labeled peptide were performed and demonstrated excellent in vivo stability of Al¹⁸F-labeled construct. In general, the successful application of the new bifunctional chelator in labeling dipeptide Glu-urea-Lys with Al¹⁸F could facilitate its possibility in conjugating with other peptides for PET imaging with enhanced in vivo stability, thus providing better in vivo performances.

Preliminary Clinical Application of RGD-Containing Peptides as PET Radiotracers for Imaging Tumors

Angiogenesis is a common feature of many physiological processes and pathological conditions. RGD-containing peptides can strongly bind to integrin αvβ3 expressed on endothelial cells in neovessels and several tumor cells with high specificity, making them promising molecular agents for imaging angiogenesis. Although studies of RGD-containing peptides combined with radionuclides, namely, 18F, 64Cu, and 68Ga for positron emission tomography (PET) imaging have shown high spatial resolution and accurate quantification of tracer uptake, only a few of these radiotracers have been successfully translated into clinical use. This review summarizes the RGD-based tracers in terms of accumulation in tumors and adjacent tissues, and comparison with traditional 18F-fluorodeoxyglucose (FDG) imaging. The value of RGD-based tracers for diagnosis, differential diagnosis, tumor subvolume delineation, and therapeutic response prediction is mainly discussed. Very low RGD accumulation, in contrast to high FDG metabolism, was found in normal brain tissue, indicating that RGD-based imaging provides an excellent tumor-to-background ratio for improved brain tumor imaging. However, the intensity of the RGD-based tracers is much higher than FDG in normal liver tissue, which could lead to underestimation of primary or metastatic lesions in liver. In multiple studies, RGD-based imaging successfully realized the diagnosis and differential diagnosis of solid tumors and also the prediction of chemoradiotherapy response, providing complementary rather than similar information relative to FDG imaging. Of most interest, baseline RGD uptake values can not only be used to predict the tumor efficacy of antiangiogenic therapy, but also to monitor the occurrence of adverse events in normal organs. This unique dual predictive value in antiangiogenic therapy may be better than that of FDG-based imaging.

18F-Alfatide II for the evaluation of axillary lymph nodes in breast cancer patients: comparison with 18F-FDG

PURPOSE

¹⁸F-Alfatide II has been translated into clinical use and been proven to have good performance in identifying breast cancer. In this study, we investigated ¹⁸F-Alfatide II for evaluation of axillary lymph nodes (ALN) in breast cancer patients and compared the performance with ¹⁸F-FDG.

METHODS

A total of 44 female patients with clinically suspected breast cancer were enrolled and underwent ¹⁸F-Alfatide II and ¹⁸F-FDG PET/CT within a week. Tracer uptakes in ALN were evaluated by visual analysis, semi-quantitative analysis with maximum standardized uptake value (SUV_max), mean standardized uptake value (SUV_mean), and SUV_max ratio of target/non-target (T/NT).

RESULTS

Among 44 patients, 37 patients were pathologically diagnosed with breast cancer with metastatic (17 cases) or non-metastatic (20 cases) ALN. The sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) of visual analysis were 70.6%, 90%, 81.1%, 85.7%, and 78.3% for ¹⁸F-Alfatide II, 64.7%, 90%, 78.4%, 84.6%, and 75% for ¹⁸F-FDG, respectively. By combining ¹⁸F-Alfatide II and ¹⁸F-FDG, the sensitivity significantly increased to 82.4%, the specificity was 85%, the accuracy increased to 83.8%, the PPV was 82.4%, and the NPV significantly increased to 85.0%. Three cases of luminal B subtype were false negative for both ¹⁸F-Alfatide II and ¹⁸F-FDG. The other 2 false negative cases of ¹⁸F-Alfatide II were triple-negative subtype and 3 false negative cases of ¹⁸F-FDG were luminal B subtype too. The AUCs of three semi-quantitative parameters (SUV_max, SUV_mean, T/NT) for ¹⁸F-Alfatide II were between 0.8 and 0.9, whereas those for ¹⁸F-FDG were more than 0.9. ¹⁸F-Alfatide II T/NT had the highest Youden index (76.5%), specificity (100%), accuracy (89.2%), and PPV (100%) among these semi-quantitative parameters. ¹⁸F-Alfatide II uptake as well as ¹⁸F-FDG uptake in metastatic axillary lymph nodes (MALN) was significantly higher than that in benign axillary lymph nodes (BALN). Both ¹⁸F-Alfatide II and ¹⁸F-FDG did not show difference in primary tumor uptake irrespective of ALN status.

CONCLUSION

¹⁸F-Alfatide II can be used in breast cancer patients to detect metastatic ALN, however, like ¹⁸F-FDG, with high specificity but relatively low sensitivity. The combination of ¹⁸F-Alfatide II and ¹⁸F-FDG can significantly improve sensitivity and NPV. ¹⁸F-Alfatide II T/NT may serve as the most important semi-quantitative parameter to evaluate ALN.

Tumor angiogenesis at baseline identified by 18F-Alfatide II PET/CT may predict survival among patients with locally advanced non-small cell lung cancer treated with concurrent chemoradiotherapy

Background

The study investigated the predictive value of tumor angiogenesis observed by ¹⁸F-ALF-NOTA-PRGD2 II (denoted as ¹⁸F-Alfatide II) positron emission tomography (PET)/computed tomography (CT) before concurrent chemoradiotherapy (CCRT) for treatment response and survival among patients with locally advanced non-small cell lung cancer (LA-NSCLC).

Methods

Patients with unresectable stage IIIA or IIIB NSCLC (AJCC Cancer Staging 7th Edition) who received CCRT were included in this prospective study. All patients had undergone ¹⁸F-Alfatide PET/CT scanning before CCRT, and analyzed parameters included maximum uptake values (SUV_max) of primary tumor (SUV_P) and metastatic lymph nodes (SUV_LN) and mean uptake value of blood pool (SUV_blood). Tumor-to-background ratios (TBRs) and changes in tumor diameter before and after CCRT (ΔD) were calculated. The ratios of SUV_P to SUV_blood, SUV_LN to SUV_blood, and SUV_P to SUV_LN were denoted as TBR_P, TBR_LN, and T/LN. Short-term treatment response, progression-free survival (PFS), and overall survival (OS) were evaluated.

Results

Of 38 enrolled patients, 28 completed CCRT. SUV_P, SUV_LN, TBR_P, TBR_LN and T/LN showed significant correlation with PFS (all P < 0.05). SUV_P was negatively correlated with OS (P = 0.005). SUV_P and TBR_P were higher in non-responders than in responders (6.55 ± 2.74 vs. 4.61 ± 1.94, P = 0.039; 10.49 ± 7.58 vs. 7.73 ± 6.09, P = 0.023). ΔD was significantly greater in responders (2.78 ± 1.37) than in non-responders (-0.16 ± 1.33, P < 0.001). Exploratory receiver operating characteristic curve analysis identified TBR_P (area under the curve [AUC] = 0.764, P = 0.018), with a cutoff value of 6.52, as the only parameter significantly predictive of the response to CCRT, with sensitivity, specificity, and accuracy values of 71.43%, 78.57%, and 75.00%, respectively. ROC curve analysis also identified SUV_P (AUC = 0.942, P < 0.001, cutoff value 4.64) and TBR_P (AUC = 0.895, P = 0.001, cutoff value 4.95) as predictive of OS with high sensitivity (84.21%, 93.75%), specificity (100.00%, 66.67%), and accuracy (89.29%, 82.14%).

Conclusions

Evaluation of tumor angiogenesis by ¹⁸F-Alfatide II at baseline may be useful in predicting the short-term response to CCRT as well as PFS and OS in patients with LA-NSCLC.

Negative Correlation Between 18F-RGD Uptake via PET and Tumoral PD-L1 Expression in Non-Small Cell Lung Cancer

PURPOSE

We investigated the correlation of ¹⁸F-AlF-NOTAPRGD2 (¹⁸F-RGD) uptake during positron emission tomography (PET) with tumoral programmed death-ligand 1 (PD-L1) expression and explored its potential in immune checkpoint inhibitor treatment.

METHODS

Forty-two mice were subcutaneously injected with CMT-167 lung carcinoma cells. A total of 30 mice with good growth tumor and good general condition were selected. ¹⁸F-RGD PET scanning was performed on days 0, 2, 4, 6, 9, and 11 with five mice per day. Immunohistochemistry (IHC) for PD-L1 was performed on each specimen obtained from tumors. Thirty patients with advanced non-small cell lung cancer (NSCLC) were scanned using ¹⁸F-RGD PET/CT, and Milliplex multifactor detection analyzed serum PD-1/PD-L1 expression of twenty-eight of them. Thirteen of them were analyzed immunohistochemically using core needle biopsy samples obtained from primary tumors.

RESULTS

Thirty mice were scanned by ¹⁸F-RGD PET/CT and analyzed for PD-L1 expression in tumor cells by IHC finally. Maximum standard uptake value (SUVmax) and mean SUV (SUVmean) were significantly lower in relatively-higher-PD-L1-expression tumors than in relatively-low-PD-L1-expression tumors (P < 0.05). In patients, the SUVmax was significantly negatively correlated with tumoral PD-L1 expression by IHC (P=0.014). SUVmean, peak SUV (SUVpeak), and gross tumor volume (GTV) were also negatively correlated with PD-L1, but without significance (P > 0.05). SUVmax, SUVmean, SUVpeak, and GTV were negatively correlated with serum PD-1 and PD-L1, but not significantly. According to the receiver operating characteristic curve analysis, significant correlations between SUVmax and tumoral PD-L1 expression in both mice and patients were present (P < 0.05).

CONCLUSION

Higher ¹⁸F-RGD uptake is correlated with depressed PD-L1 expression in tumor cells, and SUVmax is the best parameter to display tumoral expression of PD-L1. ¹⁸F-RGD PET may be useful for reflecting the immune status of NSCLC.

Scintigraphic Imaging of Neovascularization With 99mTc-3PRGD2 for Evaluating Early Response to Endostar Involved Therapies on Pancreatic Cancer Xenografts In Vivo

Background

Molecular imaging targeting angiogenesis can specifically monitor the early therapeutic effect of antiangiogenesis therapy. We explore the predictive values of an integrin αvβ3-targeted tracer, 99mTc-PEG4-E[PEG4-c(RGDfK)]2 (99mTc-3PRGD2), for monitoring the efficacy of Endostar antiangiogenic therapy and chemotherapy in animal models.

Methods

The pancreatic cancer xenograft mice were randomly divided into four groups, with seven animals in each group and treated in different groups with 10 mg/kg/day of Endostar, 10 mg/kg/day of gemcitabine, 10 mg/kg/day of Endostar +10 mg/kg/day of gemcitabine at the same time, and the control group with 0.9% saline (0.1 ml/day). 99mTc-3PRGD2 scintigraphic imaging was carried out to monitor therapeutic effects. Microvessel density (MVD) was measured using immunohistochemical staining of the tumor tissues. The region of interest (ROI) of tumor (T) and contralateral corresponding site (NT) was delineated, and the ratio of radioactivity (T/NT) was calculated. Two-way repeated-measure analysis of variance (ANOVA) was used to assess differences between treatment groups.

Results

Tumor growth was significantly lower in treatment groups than that in the control group (p < 0.05), and the differences were noted on day 28 posttreatment. The differences of 99mTc-3PRGD2 uptakes were observed between the control group and Endostar group (p = 0.033) and the combined treatment group (p < 0.01) on day 7 posttreatment and on day 14 posttreatment between the control group and gemcitabine group (p < 0.01). The accumulation of 99mTc-3PRGD2 was significantly correlated with MVD (r = 0.998, p = 0.002).

Conclusion

With 99mTc-3PRGD2 scintigraphic imaging, the tumor response to antiangiogenic therapy, chemotherapy, and the combined treatment can be observed at an early stage of the treatments, much earlier than the tumor volume change. It provides new opportunities for developing individualized therapies and dose optimization.

18F-Fluorination: Challenge and Opportunity for Organic Chemists

18F-fluorination is an important and growing field in organic synthesis that has attracted many chemists in the recent past. Here we present our own, biased perspective with a focus on our own chemistry that evaluates recent advances in the field and provides our opinion on the challenges for the development of new chemistry, so that it may have an impact on imaging. We hope that the manuscript will provide a useful guide to chemists to develop reliable and robust reaction chemistry suitable for radiofluorination to have a real impact on human health.

ROS-Responsive Boronate-Stabilized Polyphenol-Poloxamer 188 Assembled Dexamethasone Nanodrug for Macrophage Repolarization in Osteoarthritis Treatment

Osteoarthritis (OA) is a disabling joint disease associated with chronic inflammation. The polarization of macrophages plays the key role in inflammatory microenvironment of joint which is a therapeutic target for OA treatment. Herein, a boronate-stabilized polyphenol-poloxamer assembled dexamethasone nanodrug with reactive oxygen species (ROS)-responsive drug release behavior and ROS scavenging ability is prepared. Thanks to that, the nanodrug can efficiently inhibit the ROS and nitric oxide production in lipopolysaccharide-activated RAW264.7 macrophages and modulate macrophages M2 polarization at a much lower concentration than free drug dexamethasone. Furthermore, the monosodium iodoacetate-induced OA mice treated with this nanodrug is very similar with the normal mice with the evaluation of body weight and scores including clinical arthritis scores, claw circumference, and kinematics score. The inflammation associated angiogenesis is also reduced which revealed by ⁶⁸ Ga-labeled arginine-glycine-aspartic acid peptide micro-positron emission tomography imaging. Cartilage degradation and bone erosion in the joints are also inhibited by the nanodrug, along with the inhibition of proinflammatory cytokines. In addition, the biosafety of this nanodrug is also verified. This nanodrug with excellent immunomodulation properties can be used not only for OA therapy but also for other inflammatory diseases associated with excess oxidative stress and macrophage polarization.

The aluminium-[18F]fluoride revolution: simple radiochemistry with a big impact for radiolabelled biomolecules

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.

18F-RGD PET/CT and Systemic Inflammatory Biomarkers Predict Outcomes of Patients With Advanced NSCLC Receiving Combined Antiangiogenic Treatment

Background

The aim of this study was to evaluate ¹⁸F-AlF-NOTA-PRGD2 positron emission tomography/computed tomography (¹⁸F-RGD PET/CT) and serum inflammation biomarkers for predicting outcomes of patients receiving combined antiangiogenic treatment for advanced non-small cell lung cancer (NSCLC).

Methods

Patients with advanced NSCLC underwent ¹⁸F-RGD PET/CT examination and provided blood samples before treatments commenced. PET/CT parameters included maximum standard uptake value (SUVmax) and mean standard uptake value (SUVmean), peak standard uptake value (SUVpeak) and metabolic tumor volume (MTV) for all contoured lesions. Biomarkers for inflammation included pretreatment neutrophil-to-lymphocyte ratio (PreNLR), pretreatment platelet-to-lymphocyte ratio (PrePLR), and pretreatment lymphocyte-to-monocyte ratio (PreLMR). Receiver operating characteristic (ROC) curve analysis was used to describe response prediction accuracy. Logistic regression and Cox’s regression analysis was implemented to identify independent factors for short-term responses and progression-free survival (PFS).

Results

This study included 23 patients. According to ROC curve analysis, there were significant correlations between the SUVmax, SUVmean, and ¹⁸F-RGD PET/CT MTV and short-term responses (p<0.05). SUVmax was identified using logistic regression analysis as a significant predictor of treatment sensitivity (p=0.008). Cox’s multivariate regression analysis suggested that high SUVpeak (p=0.021) and high PreLMR (p=0.03) were independent PFS predictors. Combining SUVpeak and PreLMR may also increase the prognostic value for PFS, enabling us to identify a subgroup of patients with intermediate PFS.

Conclusion

¹⁸F-RGD uptake on PET/CT and serum inflammation biomarker pretreatment may predict outcomes for combined antiangiogenic treatments for advanced NSCLC patients. Higher ¹⁸F-RGD uptake and higher PreLMR also appear to predict improved short-term responses and PFS. Combining biomarkers may therefore provide a basis for risk stratification, although further research is required.

Optimal 18F-fluorination conditions for the high radiochemical yield of [18F]AlF-NOTA-NHS complexes

18F-fluorination using aluminum-fluoride ([18F]AlF) chelate technique has been reported to give a low-to-moderate radiochemical yield, between 5 and 20%. Therefore, the work described here outlines the optimum 18F-fluorination condition for the formation of [18F]AlF2+ and [18F]AlF-NOTA-NHS complex with the radiochemical yield (RCY) and purity (RCP) of more than 90% as a prerequisite step before proceeding with the radiopharmaceutical preparation using the [18F]AlF-bifunctional chelator technique. As well as being simple, the suggested method is practical and relevant for beginners interested in 18F-fluorination with [18F]AlF-chelate complex technique or also for a researcher who aims to proceed on an extensive scale.

Non-oncological applications of RGD-based single-photon emission tomography and positron emission tomography agents

INTRODUCTION

Non-invasive imaging techniques (especially single-photon emission tomography and positron emission tomography) apply several RGD-based imaging ligands developed during a vast number of preclinical and clinical investigations. The RGD (Arg-Gly-Asp) sequence is a binding moiety for a large selection of adhesive extracellular matrix and cell surface proteins. Since the first identification of this sequence as the shortest sequence required for recognition in fibronectin during the 1980s, fundamental research regarding the molecular mechanisms of integrin action have paved the way for development of several pharmaceuticals and radiopharmaceuticals with clinical applications. Ligands recognizing RGD may be developed for use in the monitoring of these interactions (benign or pathological). Although RGD-based molecular imaging has been actively investigated for oncological purposes, their utilization towards non-oncology applications remains relatively under-exploited.

METHODS AND SCOPE

This review highlights the new non-oncologic applications of RGD-based tracers (with the focus on single-photon emission tomography and positron emission tomography). The focus is on the last 10 years of scientific literature (2009-2020). It is proposed that these imaging agents will be used for off-label indications that may provide options for disease monitoring where there are no approved tracers available, for instance Crohn's disease or osteoporosis. Fundamental science investigations have made progress in elucidating the involvement of integrin in various diseases not pertaining to oncology. Furthermore, RGD-based radiopharmaceuticals have been evaluated extensively for safety during clinical evaluations of various natures.

CONCLUSION

Clinical translation of non-oncological applications for RGD-based radiopharmaceuticals and other imaging tracers without going through time-consuming extensive development is therefore highly plausible. Graphical abstract.

18F-RGD PET/CT imaging reveals characteristics of angiogenesis in non-small cell lung cancer

Background

The objective of this study was to explore the benefit of ¹⁸F-AlF-NOTA-PRGD2 positron emission tomography/computed tomography (denoted as ¹⁸F-RGD PET/CT) imaging for determining the clinical pathologic features of non-small cell lung cancer (NSCLC).

Methods

Seventy-two patients with NSCLC (37 cases of adenocarcinoma and 35 cases of squamous carcinoma) were enrolled to receive ¹⁸F-RGD PET/CT scanning pretreatment. The peak standard uptake value (SUV_peak), mean standard uptake value (SUV_mean), angiogenic tumor volume (ATV) and total lesion angiogenesis (TLA) of tumors were determined using an automated contouring program. Cases were classified according to the tumor, lymph node, metastasis (TNM) stage.

Results

Significant differences in ATV and TLA were observed among T1, T2, T3 and T4 cases (ATV, P=0.000; TLA, P=0.000). ATV and TLA also differed significantly among cases of clinical stage I, II, III and IV (ATV, P=0.002; TLA, P=0.011). However, no significant differences in any values were observed between stage III and IV NSCLC cases (SUV_peak, P=0.675; SUV_mean, P=0.668; ATV, P=0.52; TLA, P=0.634). All assessed values were higher in squamous cell carcinoma cases than in adenocarcinoma cases (SUV_peak, P=0.045; SUV_mean, P=0.014; ATV, P=0.003; TLA, P=0.001). For clinical stage III and IV cases specifically, SUV_peak, SUV_mean, and TLA were higher for squamous cell carcinoma than for adenocarcinoma (SUV_peak, P=0.015; SUV_mean, P=0.009; TLA, P=0.036).

Conclusions:¹⁸F-RGD PET/CT imaging revealed the presence of increased angiogenesis in the tumor microenvironment of NSCLC, especially squamous cell carcinoma, and thus may be valuable in planning therapeutic regimens for individual patients.

[18F]-Alfatide PET imaging of integrin αvβ3 for the non-invasive quantification of liver fibrosis

BACKGROUND & AIMS

The vitronectin receptor integrin αvβ3 drives fibrogenic activation of hepatic stellate cells (HSCs). Molecular imaging targeting the integrin αvβ3 could provide a non-invasive method for evaluating the expression and the function of the integrin αvβ3 on activated HSCs (aHSCs) in the injured liver. In this study, we sought to compare differences in the uptake of [18F]-Alfatide between normal and injured liver to evaluate its utility for assessment of hepatic fibrogenesis.

METHODS

PET with [18F]-Alfatide, non-enhanced CT, histopathology, immunofluorescence staining, immunoblotting and gene analysis were performed to evaluate and quantify hepatic integrin αvβ3 levels and liver fibrosis progression in mouse models of fibrosis (carbon tetrachloride [CCl4] and bile duct ligation [BDL]). The liver AUC divided by the blood AUC over 30 min was used as an integrin αvβ3-PET index to quantify fibrosis progression. Ex vivo analysis of frozen liver tissue from patients with fibrosis and cirrhosis verified the animal findings.

RESULTS

Fibrotic mouse livers showed enhanced [18F]-Alfatide uptake and retention compared to control livers. The radiotracer was demonstrated to bind specifically with integrin αvβ3, which is mainly expressed on aHSCs. Autoradiography and histopathology confirmed the PET imaging results. Further, the mRNA and protein level of integrin αvβ3 and its signaling complex were higher in CCl4 and BDL models than controls. The results obtained from analyses on human fibrotic liver sections supported the animal findings.

CONCLUSIONS

Imaging hepatic integrin αvβ3 with PET and [18F]-Alfatide offers a potential non-invasive method for monitoring the progression of liver fibrosis.

LAY SUMMARY

Integrin αvβ3 expression on activated hepatic stellate cells (aHSCs) is associated with HSC proliferation during hepatic fibrogenesis. Herein, we show that a radioactive tracer, [18F]-Alfatide, binds to integrin αvβ3 with high affinity and specificity. [18F]-Alfatide could thus be used as a non-invasive imaging biomarker to track hepatic fibrosis progression.

Hexavalent lactoside labeled with [18F]AlF for PET imaging of asialoglycoprotein receptor

Several methods have been developed to label compounds with ¹⁸F. However, in general these are laborious and require a multistep synthesis. A method based on the chelation of ¹⁸F-aluminum fluoride ([¹⁸F]AlF) by 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) was developed recently. The present work was aimed to radiolabel hexavalent lactoside (NOTA-HL) by [¹⁸F]AlF method for PET imaging of asialoglycoprotein receptor (ASGPR).

METHODS

hexavalent lactoside was conjugated with the NOTA chelate and labeled with ¹⁸F in a one-pot method. The labeling procedure was investigated with different amounts of NOTA-HL and aluminum concentration. Radiochemical yield and radiochemical purity were determined by radio-TLC and radio-HPLC respectively. In vitro stability study of [¹⁸F]AlF-HL were carried out. PET/CT imaging of normal mice injected with [¹⁸F]AlF-NOTA-HL was performed.

RESULTS

The Radiochemical yield of [¹⁸F]AlF-NOTA-HL was higher with more precursor and optimal Al⁺ concentration. The radiochemical purity of labeled product was >95% after purified by Sep-Pak cartridge to remove unbound [¹⁸F]AlF. The radiolabeling, including purification, was performed in 30 min [¹⁸F]AlF-NOTA-HL exhibited good in vitro stability. PET studies in normal mice revealed high specific accumulation of activity in the liver.

CONCLUSION

NOTA-HL could be labeled rapidly and efficiently with aqueous ¹⁸F using AlF method. [¹⁸F]AlF-NOTA-HL would provide another efficient approach for PET imaging of ASGPR.

Insight into the Development of PET Radiopharmaceuticals for Oncology

While the development of positron emission tomography (PET) radiopharmaceuticals closely follows that of traditional drug development, there are several key considerations in the chemical and radiochemical synthesis, preclinical assessment, and clinical translation of PET radiotracers. As such, we outline the fundamentals of radiotracer design, with respect to the selection of an appropriate pharmacophore. These concepts will be reinforced by exemplary cases of PET radiotracer development, both with respect to their preclinical and clinical evaluation. We also provide a guideline for the proper selection of a radionuclide and the appropriate labeling strategy to access a tracer with optimal imaging qualities. Finally, we summarize the methodology of their evaluation in in vitro and animal models and the road to clinical translation. This review is intended to be a primer for newcomers to the field and give insight into the workflow of developing radiopharmaceuticals.

Radiolabelled Peptides for Positron Emission Tomography and Endoradiotherapy in Oncology

This review deals with the development of peptide-based radiopharmaceuticals for the use with positron emission tomography and peptide receptor radiotherapy. It discusses the pros and cons of this class of radiopharmaceuticals as well as the different labelling strategies, and summarises approaches to optimise metabolic stability. Additionally, it presents different target structures and addresses corresponding tracers, which are already used in clinical routine or are being investigated in clinical trials.

A Comprehensive Review of Non-Covalent Radiofluorination Approaches Using Aluminum [18F]fluoride: Will [18F]AlF Replace 68Ga for Metal Chelate Labeling?

Due to its ideal physical properties, fluorine-18 turns out to be a key radionuclide for positron emission tomography (PET) imaging, for both preclinical and clinical applications. However, usual biomolecules radiofluorination procedures require the formation of covalent bonds with fluorinated prosthetic groups. This drawback makes radiofluorination impractical for routine radiolabeling, gallium-68 appearing to be much more convenient for the labeling of chelator-bearing PET probes. In response to this limitation, a recent expansion of the 18F chemical toolbox gave aluminum [18F]fluoride chemistry a real prominence since the late 2000s. This approach is based on the formation of an [18F][AlF]2+ cation, complexed with a 9-membered cyclic chelator such as NOTA, NODA or their analogs. Allowing a one-step radiofluorination in an aqueous medium, this technique combines fluorine-18 and non-covalent radiolabeling with the advantage of being very easy to implement. Since its first reports, [18F]AlF radiolabeling approach has been applied to a wide variety of potential PET imaging vectors, whether of peptidic, proteic, or small molecule structure. Most of these [18F]AlF-labeled tracers showed promising preclinical results and have reached the clinical evaluation stage for some of them. The aim of this report is to provide a comprehensive overview of [18F]AlF labeling applications through a description of the various [18F]AlF-labeled conjugates, from their radiosynthesis to their evaluation as PET imaging agents.

Integrin α6 targeted positron emission tomography imaging of hepatocellular carcinoma in mouse models

Integrin α6 emerges to be a diagnostic biomarker for hepatocellular carcinoma (HCC). Here, we translated our previously identified integrin α6 targeted peptide RWY into a positron emission tomography (PET) tracer ¹⁸F-RWY for the detection of HCC lesions in following four HCC mouse models including subcutaneous, orthotopic, genetically engineered and chemical induced HCC mice. ¹⁸F-RWY produced high PET signals in liver tumor tissues that were reduced by blocking studies using nonradiolabeled RWY peptide. We compared the integrin α6 targeted PET tracer ¹⁸F-RWY with the integrin αvβ3-targeted PET tracer ¹⁸F-3PRGD₂ and the clinical PET tracer ¹⁸F-FDG in chemical induced HCC mice. Among 12 HCC identified by enhanced magnetic resonance imaging (MRI) with hepatocellular specific gadoxetate disodium Gd-EOB-DTPA, the sensitivities of ¹⁸F-RWY, ¹⁸F-3PRGD₂ and ¹⁸F-FDG were approximately 92%, 73% and 50% while the tumor-to-liver ratios were 4.36 ± 1.41, 1.97 ± 0.43 and 1.63 ± 0.23 respectively. Additionally, PET imaging with the integrin α6 targeted ¹⁸F-RWY enabled to visualize small HCC lesions with diameters approximately 0.2 cm that was hard to be distinguished from surround hepatic vascular by enhanced MRI with Gd-EOB-DTPA. These findings potentiate the use of integrin α6 targeted PET tracer ¹⁸F-RWY for the detection of HCC.

Al18F-labeled alpha-melanocyte-stimulating hormone (α-MSH) peptide derivative for the early detection of melanoma

OBJECTIVE

Early detection plays a role in the prognosis of melanoma, the most aggressive skin cancer. ⁶⁴Cu- and ⁶⁸Ga-labeled alpha-melanocyte-stimulating hormone (α-MSH) analogs targeting the melanocortin-1 receptor are promising positron emission tomography (PET) tracers for detecting melanoma, and the use of ¹⁸F-labeling will further contribute to the detectability and availability. However, the high radiochemistry demand related to the conventional ¹⁸F-labeling methods has restricted the development of ¹⁸F-labeled α-MSH analogs. A recently developed radiofluorination method using aluminum-fluoride (Al¹⁸F) offers a simple, efficient, and time-saving labeling procedure compared to the conventional ¹⁸F-labeling methods. Herein, we sought to establish a simple preparation method for an ¹⁸F-labeled α-MSH analog using Al¹⁸F, and we examined its potential for the early detection of melanoma.

METHODS

A 1,4,7-triazacyclononane-N,N',N″-triacetic acid (NOTA)-conjugated α-MSH analog (NOTA-GGNle-CycMSH_hex) was prepared by the Fmoc solid-phase strategy. NOTA-GGNle-CycMSH_hex was labeled with Al¹⁸F by heating at 105 °C using a microwave synthesizer for 15 min. Biodistribution study was conducted on B16/F10-luc melanoma-bearing mice at 30 min, 1 h and 3 h after injection of Al¹⁸F-NOTA-GGNle-CycMSH_hex. PET imaging was conducted on melanoma-bearing mice at 1 h post-injection. One day prior to the PET imaging, bioluminescence imaging was also performed.

RESULTS

Al¹⁸F-NOTA-GGNle-CycMSH_hex was readily prepared with a high radiochemical yield (94.0 ± 2.8%). The biodistribution study showed a high accumulation of Al¹⁸F-NOTA-GGNle-CycMSH_hex in the tumor at 30 min and 1 h post-injection (6.69 ± 1.49 and 7.70 ± 1.71%ID/g, respectively). The tumor-to-blood ratio increased with time: 3.46 ± 0.89, 12.67 ± 1.29, and 35.27 ± 9.12 at 30 min, 1 h, and 3 h post-injection, respectively. In the PET imaging, Al¹⁸F-NOTA-GGNle-CycMSH_hex clearly visualized the tumors and depicted very small tumors (< 3 mm).

CONCLUSIONS

We successfully prepared Al¹⁸F-NOTA-GGNle-CycMSH_hex in a simple and efficient manner. Al¹⁸F-NOTA-GGNle-CycMSH_hex showed high tumor accumulation and clearly visualized very small tumors in melanoma-bearing mice. These findings suggest that Al¹⁸F-NOTA-GGNle-CycMSH_hex will be a promising PET tracer for melanoma imaging at an earlier stage.

Pretreatment PET/CT imaging of angiogenesis based on 18F-RGD tracer uptake may predict antiangiogenic response

PURPOSE

To explore the relationship between metabolic uptake of the ¹⁸F-ALF-NOTA-PRGD₂ (¹⁸F-RGD) tracer on positron emission tomography/computerized tomography (PET/CT) and the antiangiogenic effect of apatinib in patients with solid malignancies.

MATERIALS AND PATIENTS

Patients with measurable lesions scheduled for second- or third-line single-agent therapy with apatinib were eligible for this prospective clinical trial. All patients underwent ¹⁸F-RGD PET/CT examination before the start of treatment. Standardized uptake values (SUVs) of contoured tumor lesions were computed and compared using independent sample t-tests or the Mann-Whitney U test. Receiver-operating characteristic (ROC) curve analysis was used to determine accuracy in predicting response. Survival curves were compared using the Kaplan-Meier method.

RESULTS

Of 38 patients who consented to study participation, 25 patients with 42 measurable lesions met the criteria for inclusion in this response assessment analysis. The median follow-up time was 3 months (range, 1-10 months), and the median progression-free survival (PFS) was 3 months (95% confidence interval, 1.04-4.96). The SUV_peak and SUV_mean were significantly higher in responding tumors than in non-responding tumors (4.98 ± 2.34 vs 3.59 ± 1.44, p = 0.048; 3.71 ± 1.15 vs 2.95 ± 0.49, P = 0.036). SUV_max did not differ between responding tumors and non-responding tumors (6.58 ± 3.33 vs 4.74 ± 1.83, P = 0.078). An exploratory ROC curve analysis indicated that SUV_mean [area under the ROC curve (AUC) = 0.700] was a better parameter than SUV_peak (AUC = 0.689) for predicting response. Using a threshold value of 3.82, high SUV_mean at baseline was associated with improved PFS (5.0 vs. 3.4 months, log-rank P = 0.036).

CONCLUSION

¹⁸F-RGD uptake on PET/CT imaging pretreatment may predict the response to antiangiogenic therapy, with higher ¹⁸F-RGD uptake in tumors predicting a better response to apatinib therapy.

Design of RGD-ATWLPPR peptide conjugates for the dual targeting of αVβ3 integrin and neuropilin-1

Targeting the tumour microenvironment is a promising strategy to detect and/or treat cancer. The design of selective compounds that co-target several receptors frequently overexpressed in solid tumours may allow a reliable and selective detection of tumours. Here we report the modular synthesis of compounds encompassing ligands of αVβ3 integrin and neuropilin-1 that are overexpressed in the tumour microenvironment. These compounds were then evaluated through cellular experiments and imaging of tumours in mice. We observed that the peptide that displays both ligands is more specifically accumulating in the tumours than in controls. Simultaneous interaction with αVβ3 integrin and NRP1 induces NRP1 stabilization at the cell membrane surface which is not observed with the co-injection of the controls.

Diagnostic and Predictive Value of Using RGD PET/CT in Patients with Cancer: A Systematic Review and Meta-Analysis

The purpose of this study was to assess the diagnostic value of arginine-glycine-aspartic acid (RGD) PET/CT for tumor detection in patients with suspected malignant lesions and to determine the predictive performance of RGD PET/CT in identifying responders. Methods. The PubMed (Medline), EMBASE, Cochrane Library, and Web of Science databases were systematically searched for potentially relevant publications (last updated on July 28th, 2018) reporting the performance of RGD PET in the field of oncology. Pooled sensitivities, specificities, and diagnostic odds ratios (DORs) were calculated for parameters. The areas under the curve (AUCs) and Q⁎ index scores were determined from the constructed summary receiver operating characteristic (SROC) curve. We explored heterogeneity by metaregression. Results. Nine studies, five including 216 patients that determined diagnostic performance and three including 75 patients that determined the predictive value of parameters, met our inclusion criteria. The pooled sensitivity, pooled specificity, DOR, AUC, and Q⁎ index score of RGD PET/CT for the detection of underlying malignancy were 0.85 (0.79-0.89), 0.93 (0.90-0.96), 48.35 (18.95-123.33), 0.9262 (standard error=0.0216), and 0.8606 for SUVmax and 0.86 (0.80-0.91), 0.92 (0.88-0.94), 40.49 (14.16-115.77), 0.9312 (SE=0.0177), and 0.8665 for SUVmean, respectively. The pooled sensitivity, pooled specificity, DOR, AUC, and Q⁎ index score of RGD PET/CT for identifying responders were 0.80 (0.59-0.93), 0.74 (0.60-0.85), 15.76 (4.33-57.32), 0.8682 (0.0539), and 0.7988, respectively, for SUVmax at baseline. Conclusion. The interesting but preliminary data in this meta-analysis demonstrate that RGD PET/CT may be an ideal diagnostic tool for detecting underlying malignancies in patients suspected of having tumors and may be able to efficiently predict short-term outcomes.

Al[18F]F-complexation of DFH17, a NOTA-conjugated adrenomedullin analog, for PET imaging of pulmonary circulation

INTRODUCTION

Adrenomedullin receptors are highly expressed in human alveolar capillaries and provide a molecular target for imaging the integrity of pulmonary microcirculation. In this work, we aimed to develop a NOTA-derivatized adrenomedullin analog (DFH17), radiolabeled with [¹⁸F]AlF, for PET imaging of pulmonary microcirculation.

METHODS

Highly concentrated [¹⁸F](AlF)²⁺ (15 μL) was produced from purified fluorine-18 in NaCl 0.9%. Various complexation experiments were carried out at Al-to-NOTA molar ratios ranging from 1:1 to 1:40 to assess optimal radiolabeling conditions before using the peptide. DFH17 peptide (2 mM, pH 4) was radiolabeled with [¹⁸F](AlF)²⁺ for 15 min at 100 °C in a total volume of 60 μL. As part of the radiolabeling process, parameters such as fluorine-18 activity (~37 and 1480 MBq), concentration of AlCl₃ (0.75, 2, 3, 6 or 10 mM) and the effects of hydrophilic organic solvent (aqueous vs ethanol 50%) were studied. The final formulation was tested for purity, identity and stability in saline. Initial in vivo evaluation of [¹⁸F]AlF-DFH17 was performed in normal rats by PET/CT.

RESULTS

The scaled-up production of [¹⁸F]AlF-DFH17 was performed in high radiochemical and chemical purities in an overall radiochemical yield of 22-38% (at end-of-synthesis) within 60 min. The final formulation was stable in saline at different radioactive concentrations for 8 h. PET evaluation in rats revealed high lung-to-background ratios and no defluorination in vivo up to 1 h post-injection.

CONCLUSION

The novel radioconjugate [¹⁸F]AlF-DFH17 appears to be a promising PET ligand for pulmonary microcirculation imaging.

Evaluation of A Novel GLP-1R Ligand for PET Imaging of Prostate Cancer

BACKGROUND

Glucagon-like peptide 1 receptor (GLP-1R) is an important biomarker for diagnosis and therapy of the endocrine cancers due to overexpression. Recently, in human prostate cancer cell lines the receptor was also observed, therefore it may be a potential target for the disease. 18F-Al-NOTA-MAL-Cys39- exendin-4 holds great promise for GLP-1R. Therefore, the feasibility of the 18F-labeled exendin-4 analog for prostate cancer imaging was investigated.

METHODS

New probe 18F-Al-NOTA-MAL-Cys39-exendin-4 was made through one-step fluorination. Prostate cancer PC3 cell xenograft model mice were established to primarily evaluate the imaging properties of the tracer via small animal PET studies in vivo. Pathological studies and Western Blots were also performed.

RESULTS

PC-3 prostate xenografts were clearly imaged under baseline conditions. At 30 and 60 min postinjection, the tumor uptakes were 2.90±0.41%ID/g and 2.26±0.32 %ID/g respectively. The presence of cys39-exendin-4 significantly reduced the tumor uptake to 0.82±0.10 %ID/g at 60 min p.i. Findings of ex vivo biodistribution studies were similar to those of in vivo PET imaging. The tumors to blood and muscles were significantly improved with the increase of time due to rapid clearance of the tracer from normal organs. Low levels of radioactivity were also detected in the GLP-1R positive tumor and normal organs after coinjection with excessive unlabeled peptides. Immunohistochemistry and Western Blots results confirmed that GLP-1R was widely expressed in PC-3 prostate cancers.

CONCLUSION

18F-Al labeled exendin-4 analog might be a promising tracer for in vivo detecting GLP-1R positive prostate cancer with the advantage of facile synthesis and favorable pharmacokinetics. It may be useful in differential diagnosis, molecularly targeted therapy and prognosis of the cancers.

Development of [18F]AlF-NOTA-NT as PET Agents of Neurotensin Receptor-1 Positive Pancreatic Cancer

Several studies have suggested that neurotensin receptors (NTRs) and neurotensin (NT) greatly affect the growth and survival of pancreatic ductal adenocarcinoma (PDAC). Developing NTR-targeted PET probes could therefore be important for the management of a pancreatic cancer patient by providing key information on the NTR expression profile noninvasively. Despite the initial success on the synthesis of ¹⁸F-labeled NT PET probes, the labeling procedure generally requires lengthy steps including azeotropic drying of ¹⁸F. Using a straightforward chelation method, here we report the simple preparation of aluminum-¹⁸F-NOTA-NT starting from aqueous ¹⁸F. The cell binding test demonstrated that [¹⁹F]AlF-NOTA-NT maintained high receptor-binding affinity to NTR1. This probe was then further evaluated in NTR1 positive pancreatic tumor models (AsPC-1 and PANC-1). After the administration of [¹⁸F]AlF-NOTA-NT, small animal PET studies showed a high contrast between tumor and background in both models at 1 and 4 h time points. A blocking experiment was performed to demonstrate the receptor specificity: the tumor uptake in AsPC1 without and with blocking agent was 1.0 ± 0.2 and 0.1 ± 0.0%ID/g, respectively, at 4 h post injection. In summary, a NTR specific PET agent, [¹⁸F]AlF-NOTA-NT, was prepared through the simple chelation method. This NTR-targeted PET probe may not only be used to detect NTR1 positive pancreatic tumors (diagnosis), but also it may be fully integrated to NTR target therapy leading to personalized medicine (theranostic).

Aluminum fluoride-18 labeled folate enables in vivo detection of atherosclerotic plaque inflammation by positron emission tomography

Inflammation plays an important role in the development of atherosclerosis and its complications. Because the folate receptor β (FR-β) is selectively expressed on macrophages, an FR targeted imaging agent could be useful for assessment of atherosclerotic inflammation. We investigated aluminum fluoride-18-labeled 1,4,7-triazacyclononane-1,4,7-triacetic acid conjugated folate (¹⁸F-FOL) for the detection of atherosclerotic plaque inflammation. We studied atherosclerotic plaques in mice, rabbits, and human tissue samples using ¹⁸F-FOL positron emission tomography/computed tomography (PET/CT). Compound 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) was used as a comparison. Firstly, we found that the in vitro binding of ¹⁸F-FOL co-localized with FR-β-positive macrophages in carotid endarterectomy samples from patients with recent ischemic symptoms. We then demonstrated specific accumulation of intravenously administered ¹⁸F-FOL in atherosclerotic plaques in mice and rabbits using PET/CT. We noticed that the ¹⁸F-FOL uptake correlated with the density of macrophages in plaques and provided a target-to-background ratio as high as ¹⁸F-FDG, but with considerably lower myocardial uptake. Thus, ¹⁸F-FOL PET/CT targeting of FR-β-positive macrophages presents a promising new tool for the in vivo imaging of atherosclerotic inflammation.