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The expression status of human epidermal growth factor receptor 2 (HER2) in cancer predicts response to HER2-targeted therapy. Therefore, its accurate determination is of utmost importance. In recent years, there has been an increase in research on noninvasive techniques for molecular imaging, as this method offers the advantages of a more accurate determination of HER2 status without the need for multiple biopsies. The technetium-labeled single-domain antibody RAD201, previously known as 99mTc-NM-02, has been shown to be safe for use in breast cancer imaging with reasonable radiation doses, favorable biodistribution, and imaging characteristics. Methods: A total of six HER2-positive, heavily pretreated patients with different cancer types aged between 42 and 69 years (5 women and 1 man; the median age of 55.5) have been examined. In six of seven scans, the patients were administered 500 ml of Gelofusine® solution (40 mg/ml) for radiation protection before the tracer injection (434 ± 42 MBq). Planar scans were acquired with the patient supine at 10 min, 60 min, 160 min, 20 h, and 24 h after injection. A CT scan was acquired at 95 min, followed by local tomographic SPECT imaging. Results: One patient was scanned twice with RAD201, 3 months apart, resulting in a total of seven scans for six patients. Here, we show that the use of RAD201 in our patient group shows the same favorable biodistribution as in a previous study with RAD201 (NCT04040686) and that the radiation dose to the critical organ kidney can be reduced by the application of the plasma expander Gelofusine® by almost 50%. Conclusion: RAD201 appears safe for use in humans and is a promising noninvasive tool for discriminating HER2 status in metastatic (breast) cancer, regardless of ongoing HER2-targeted antibody treatment. [ABSTRACT FROM AUTHOR]

Due to its long half-life (78 h) and decay properties (77% electron capture, 23% β+, Emax = 897 keV, Eav = 397 keV, Eγ = 909 keV, Iγ = 100%) 89Zr is an appealing radionuclide for immunoPET imaging with whole IgG antibodies. Derivatives of the siderophore desferrioxamine-B (H3DFO) are the most widely used bifunctional chelators for coordination of 89Zr4+ because the radiolabeling of the resulting immunoconjugates is rapid under mild conditions. 89Zr-DFO complexes are reportedly stable in vitro but there is evidence that 89Zr4+ is released in vivo, and subsequently taken up by the skeleton. We have evaluated a novel tripodal tris(hydroxypyridinone) chelator, H3CP256 and its bifunctional maleimide derivative, H3YM103, for coordination of Zr4+ and compared the NMR spectra, and the 89Zr4+ radiolabeling, antibody conjugation, serum stability and in vivo distribution of radiolabelled immunoconjugates with those of H3DFO and its analogues. H3CP256 coordinates 89Zr4+ at carrier-free concentrations forming [89Zr(CP256)]+. Both H3DFO and H3CP256 were efficiently radiolabelled using [89Zr(C2O4)4]4− at ambient temperature in quantitative yield at pH 6–7 at millimolar concentrations of chelator. Competition experiments demonstrate that 89Zr4+ dissociates from [89Zr(DFO)]+ in the presence of one equivalent of H3CP256 (relative to H3DFO) at pH 6–7, resulting largely in [89Zr(CP256)]+. To assess the stability of H3DFO and H3YM103 immunoconjugates radiolabelled with 89Zr, maleimide derivatives of the chelators were conjugated to the monoclonal antibody trastuzumab via reduced cysteine side chains. Both immunoconjugates were labelled with 89Zr4+ in ＞98% yield at high specific activities and the labeled immunoconjugates were stable in serum with respect to dissociation of the radiometal. In vivo studies in mice indicate that 89Zr4+ dissociates from YM103-trastuzumab with significant amounts of activity becoming associated with bones and joints (25.88 ± 0.58% ID g−1 7 days post-injection). In contrast, ＜8% ID g−1 of 89Zr activity becomes associated with bone in animals administered 89Zr-DFO-trastuzumab over the course of 7 days. The tris(hydroxypyridinone) chelator, H3CP256, coordinates 89Zr4+ rapidly under mild conditions, but the 89Zr-labelled immunoconjugate, 89Zr-YM103-trastuzumab was observed to release appreciable amounts of 89Zr4+in vivo, demonstrating inferior stability when compared with 89Zr-DFO-trastuzumab. The significantly lower in vivo stability is likely to be a result of lower kinetic stability of the Zr4+ tris(hydroxypyridinone complex) relative to that of DFO and its derivatives. [ABSTRACT FROM AUTHOR]

Hexadentate tris(3,4-hydroxypyridinone) ligands (THP) complex Fe3+ at very low iron concentrations and their high affinities for oxophilic trivalent metal ions have led to their development for new applications as bifunctional chelators for the radiometal gallium-68 (68Ga). THP-peptide bioconjugates rapidly and quantitatively complex 68Ga at room temperature, neutral pH, and micromolar ligand concentrations, making them amenable to kit-based radiosynthesis of 68Ga PET radiopharmaceuticals. With the aim to produce an N-hydroxysuccinimide-(NHS)-THP reagent for kit-based 68Ga-labeling and PET imaging, THP-derivatives were designed and synthesized to exploit the advantages of NHS chemistry for coupling with peptides, proteins, and antibodies. The more stable five-carbon atoms linker product was selected for a proof-of-concept conjugation and radiolabeling study with an anti-programmed death ligand 1 (PD-L1) camelid single domain antibody (sdAb) under mild conditions and further evaluated for site-specific amide bond formation with a synthesized glucagon-like peptide-1 (GLP-1) targeting peptide using solid-phase synthesis. The obtained THP-GLP-1 conjugate was tested for its 68Ga chelating ability, demonstrating to be a promising candidate for the detection and monitoring of GLP-1 aberrant malignancies. The obtained sdAb-THP conjugate was radiolabeled with 68Ga under mild conditions, providing sufficient labeling yields after 5 min, demonstrating that the novel NHS-THP bifunctional chelator can be widely used to easily conjugate the THP moiety to different targeting molecules (e.g., antibodies, anticalins, or peptides) under mild conditions, paving the way to the synthesis of different imaging probes with all the advantages of THP radiochemistry. [ABSTRACT FROM AUTHOR]

The level of expression of programmed cell death-1 (PD-1)/programmed death ligand-1 (PD-L1) is a predictive biomarker for cancer immunotherapy, however, its detection remains challenging due to tumour heterogeneity and the influence from the binding of therapeutic agents. We recently developed [ 99m Tc]-NM-01 as a companion diagnostic imaging agent for non-invasive molecular imaging of PD-L1 by single-photon emission computed tomography (SPECT). The aim of the study was to evaluate the [ 99m Tc] radiolabelling of GMP graded NM-01 and its pharmacology, pharmacokinetics and toxicology. NM-01 bound specifically to human PD-L1 (K d =0.8 nM) and did not interfere with the binding of the anti-PD-L1 antibody atezolizumab. NM-01 can bind various PD-L1-positive cancer cell lines and only interact with PD-L1 expressed on the cell surface. In SPECT/CT imaging, high [ 99m Tc]-NM-01 accumulation was observed in the HCC827 mouse xenografted tumour model (30-min: 1.50 ± 0.27 %ID/g; 90-min: 1.23 ± 0.18 %ID/g), demonstrated a predominantly renal elimination (high uptake in bladder and kidney), while activity in the blood pool and other major organs remained low. The tumour-to-muscle and tumour-to-blood ratios were comparable with/without atezolizumab (P<0.04) but were significantly lowered when co-injected with excess NM-01 (P=0.04 and P=0.01, respectively.) The blood clearance of [ 99m Tc]-NM-01 is bi-phasic; consisting of an initial fast washout phase with half-life of 2.1 min and a slower clearance phase with half-life of 25.4 min. In an intravenous extended single-dose toxicity study, no treatment-related changes were observed and the maximum tolerated dose of [ 99m Tc]-NM-01 was 2.58 mg/kg. [ 99m Tc]-NM-01 has suitable properties as a potential candidate for SPECT/CT imaging of PD-L1 assessment in cancer patients., Competing Interests: N.C.L.W., Y.C., L.K.M. and H.H.T. are employees of NanoMab Technology Ltd. H.J.B. is an advisor for NanoMab Technology Ltd. G.J.R.C. is a consultant and receive research support for NanoMab Technology Ltd, Theragnostics Ltd and Serac Healthcare Ltd. F. M. M is on the advisory board of Advanced Accelerator Applications GmbH and has received institutional grants from GE Healthcare, Siemens, and NanoMab Technology Ltd., (AJNMMI Copyright © 2021.)

Immunotherapy with checkpoint inhibitor programmed cell death 1 (PD-1)/programmed death ligand-1 (PD-L1) antibodies demonstrates improvements in treatment of advanced non-small cell lung cancer. Treatment stratification depends on immunohistochemical PD-L1 measurement of biopsy material, an invasive method that does not account for spatiotemporal heterogeneity. Using a single-domain antibody, NM-01, against PD-L1, radiolabeled site-specifically with 99m Tc for SPECT imaging, we aimed to assess the safety, radiation dosimetry, and imaging characteristics of this radiopharmaceutical and correlate tumor uptake with PD-L1 immunohistochemistry results. Methods: Sixteen patients (mean age, 61.7 y; 11 men) with non-small cell lung cancer were recruited. Primary tumor PD-L1 expression was measured by immunohistochemistry. NM-01 was radiolabeled with [ 99m Tc(OH 2 ) 3 (CO) 3 ] + complex binding to its C-terminal hexahistidine tag. Administered activity was 3.8-10.4 MBq/kg, corresponding to 100 μg or 400 μg of NM-01. Whole-body planar and thoracic SPECT/CT scans were obtained at 1 and 2 h after injection in all patients, and 5 patients underwent additional imaging at 10 min, 3 h, and 24 h for radiation dosimetry calculations. All patients were monitored for adverse events. Results: No drug-related adverse events occurred in this study. The mean effective dose was 8.84 × 10 -3 ± 9.33 × 10 -4 mSv/MBq (3.59 ± 0.74 mSv per patient). Tracer uptake was observed in the kidneys, spleen, liver, and bone marrow. SPECT primary tumor-to-blood-pool ratios (T:BP) varied from 1.24 to 2.3 (mean, 1.79) at 1 h and 1.24 to 3.53 (mean, 2.22) at 2 h ( P = 0.005). Two-hour primary T:BP ratios correlated with PD-L1 immunohistochemistry results ( r = 0.68, P = 0.014). Two-hour T:BP was lower in tumors with ≤1% PD-L1 expression (1.89 vs. 2.49, P = 0.048). Nodal and bone metastases showed tracer uptake. Heterogeneity (>20%) between primary tumor and nodal T:BP was present in 4 of 13 patients. Conclusion: This first-in-human study demonstrates that 99m Tc-labeled anti-PD-L1-single-domain antibody SPECT/CT imaging is safe and associated with acceptable dosimetry. Tumor uptake is readily visible against background tissues, particularly at 2 h when the T:BP ratio correlates with PD-L1 immunohistochemistry results., (© 2019 by the Society of Nuclear Medicine and Molecular Imaging.)

The efficient delivery of nanomaterials to specific targets for in vivo biomedical imaging is hindered by rapid sequestration by the reticuloendothelial system (RES) and consequent short circulation times. To overcome these two problems, we have prepared a new stealth PEG polymer conjugate containing a terminal 1,1-bisphosphonate (BP) group for strong and stable binding to the surface of ultrasmall-superparamagnetic oxide nanomaterials (USPIOs). This polymer, PEG(5)-BP, can be used to exchange the hydrophobic surfactants commonly used in the synthesis of USPIOs very efficiently and at room temperature using a simple method in 1 h. The resulting nanoparticles, PEG(5)-BP-USPIOs are stable in water or saline for at least 7 months and display a near-zero ζ-potential at neutral pH. The longitudinal (r(1)) and transverse (r(2)) relaxivities were measured at a clinically relevant magnetic field (3 T), revealing a high r(1) of 9.5 mM(-1) s(-1) and low r(2)/r(1) ratio of 2.97, making these USPIOs attractive as T1-weighted MRI contrast agents at high magnetic fields. The strong T1-effect was demonstrated in vivo, revealing that PEG(5)-BP-USPIOs remain in the bloodstream and enhance its signal 6-fold, allowing the visualization of blood vessels and vascular organs with high spatial definition. Furthermore, the optimal relaxivity properties allow us to inject a dose 4 times lower than with other USPIOs. PEG(5)-BP-USPIOs can also be labeled using a radiolabeled-BP for visualization with single photon emission computed tomography (SPECT), and thus affording dual-modality contrast. The SPECT studies confirmed low RES uptake and long blood circulation times (t(1/2) = 2.97 h). These results demonstrate the potential of PEG(5)-BP-USPIOs for the development of targeted multimodal imaging agents for molecular imaging.