Disialoganglioside 2 (GD2) is overexpressed in multiple cancers, such as melanoma and neuroblastoma, but also in peripheral nerves. To improve current GD2-targeting approaches, next-generation heterodimeric bispecific human IgG antibodies were created, each with one antibody binding fragment (Fab) arm specific for GD2 and the other Fab arm specific for B7-H3 (CD276) to drive tumor selectivity. The avidity and selectivity of our GD2-B7-H3 targeting bispecific antibodies (INV34-6, INV33-2, and INV36-6) were determined by flow cytometry and competition binding assays in GD2+/hB7-H3+ B78 cells. INV34-6 showed high avidity for GD2+/hB7-H3+ but not GD2+/hB7-H3- B78 cells, contrasting with the similar cell binding to these cells observed with the anti-GD2 antibody Dinutuximab (DINU). The bispecific antibodies, DINU, and a nontargeted bispecific control (bsAb CTRL) were conjugated with deferoxamine for radiolabeling with Zr-89 (t1/2 = 78.4 h). Positron emission tomography (PET) corroborated the in vivo avidity and selectivity of the GD2-B7-H3 targeting bispecific compared to bsAb CTRL and DINU in GD2+/hB7-H3+ and GD2+/hB7-H3- B78 tumor models. PET in mice bearing the GD2+/hB7-H3- and GD2+/hB7-H3+ B78 murine xenografts showed similar biodistribution in normal tissues for [89Zr]Zr-Df-INV34-6, [89Zr]Zr-Df-bsAb CTRL, and [89Zr]Zr-Df-DINU. Importantly, [89Zr]Zr-Df-INV34-6 tumor uptake was selective to GD2+/hB7-H3+ B78 over GD2+/hB7-H3- B78 tumors, unlike [89Zr]Zr-Df-DINU, which displayed elevated tumor uptake, irrespective of hB7-H3 expression. Nontargeted [89Zr]Zr-Df-bsAb CTRL isotype control showed markedly lower uptake in all tested tumor models. Overall, bispecific antibodies binding GD2 and B7-H3 showed improved selectivity for targeting tumor cells expressing both antigens. This approach may enhance antitumor efficacy while addressing the toxicity limitations of current GD2-targeting therapies by reducing off-tumor GD2 binding in nerves.

Triple-negative breast cancer (TNBC) and non-small cell lung cancer (NSCLC) are aggressive solid tumors with limited treatment options. Nectin cell adhesion molecule 4 (Nectin4) is a tumor-associated antigen frequently overexpressed in these cancers, making it a promising therapeutic and imaging target. Here, we report the development and evaluation of [89Zr]Zr-desferrioxamine (DFO)-Padcev, a radiolabeled antibody-drug conjugate targeting Nectin4, for immuno-positron emission tomography (ImmunoPET) imaging. [89Zr]Zr-DFO-Padcev is synthesized with a radiochemical yield of 88.87% ± 2.59% and a radiochemical purity above 99%. ImmunoPET imaging successfully visualizes Nectin4-positive tumors in TNBC (MDA-MB-468) and NSCLC (H1975) models as early as 6 h post-injection, with uptake progressively increasing and peaking at 48 h (14.57 ± 1.94 and 9.50 ± 0.76 %ID/g, respectively). Minimal tumor uptake is observed in blocking and Nectin4-negative controls, confirming specificity. Complementary fluorescence imaging further reveals the in vivo distribution of Padcev, providing valuable insights into optimal therapeutic time windows.

CD70 is an emerging biomarker for both solid tumors and hematologic malignancies, highlighting the urgent need for a molecular imaging tracer capable of visualizing CD70 with favorable pharmacokinetics. Methods: ABDB6 was prepared by fusing the albumin-binding domain ABD035 with the CD70-targeting single-domain antibody RCCB6, which we previously reported. The resulting ABDB6 was then conjugated to the bifunctional chelator p-SCN-NOTA and labeled with 64Cu to produce [64Cu]Cu-NOTA-ABDB6. Flow cytometry was used to screen 6 lymphoma cell lines with varying CD70 expression levels. Cell uptake and in vivo immuno-PET imaging studies were conducted to fully evaluate the pharmacokinetic properties and tumor-targeting efficacy of [64Cu]Cu-NOTA-ABDB6. An ABDB6 blocking study was performed to validate the targeting specificity of [64Cu]Cu-NOTA-ABDB6, followed by immunohistochemistry and fluorescent immunostaining studies to correlate tracer uptake with CD70 expression. Results: 64Cu labeling of ABDB6 achieved a high radiochemical yield and specific activity. Significant CD70 expression was observed in 5 lymphoma cell lines (TMD8, HBL1, OCI-LY10, LCL-EBV, and type III latency Burkitt lymphoma [BL] cells) but not in type I latency BL cells, which served as the negative control. [64Cu]Cu-NOTA-ABDB6 exhibited good affinity for CD70 protein at the nanomolar level (inhibitory concentration of 50%, 91.57 nM) and specificity in binding to human CD70. Immuno-PET imaging of [64Cu]Cu-NOTA-ABDB6 demonstrated excellent tumor uptake and retention in various CD70-positive lymphoma models (TMD8, type III latency BL, and LCL-EBV), with the highest tumor uptake values recorded as 24.67 ± 1.36, 18.02 ± 4.29, and 14.68 ± 1.20 percentage injected dose per gram of tissue (%ID/g) at 48 h after injection, respectively. These tumor uptake values were significantly higher than that of the CD70-negative type I latency BL tumor, which had an uptake of 3.59 ± 0.28 %ID/g at the same scanning time point (P < 0.05). In the TMD8 blocking group, tumor uptake was 5.99 ± 1.20 %ID/g at 48 h after injection, significantly lower than in the TMD8 control group (P < 0.01). Both biodistribution and histology results corroborated these imaging findings. Conclusion: [64Cu]Cu-NOTA-ABDB6 immuno-PET effectively visualized varying levels of CD70 in different lymphoma models. Its clinical potential may provide insights into CD70 expression in lymphoma patients.

Purpose:ImmunoPET imaging of PD-L1 has emerged as a promising strategy for patient stratification and treatment response monitoring in immunotherapy. This study aimed to evaluate [89Zr]Zr-DFO-Durvalumab in noninvasive imaging of PD-L1 expression in non-small cell lung cancer (NSCLC) and bladder cancer. Materials and methods:Durvalumab was conjugated with p-SCN-Bn-DFO and labeled with [89Zr]Zr-oxalate, achieving high radiochemical purity (> 99 %) and stability. PD-L1 expression in human NSCLC (H1975, A549) and bladder cancer (HT1376, T24) cell lines was characterized via flow cytometry and immunofluorescence. In vitro binding and uptake studies were conducted to assess specificity. ImmunoPET imaging and biodistribution analyses were performed in mouse xenograft models. Additionally, fluorescence-guided imaging using IRDye 800CW-labeled Durvalumab was evaluated. Results:H1975 and HT1376 cells exhibited strong PD-L1 expression and high tracer uptake, while A549 and T24 cells were low in PD-L1 expression. In vivo PET imaging revealed significantly higher uptake in PD-L1-positive tumors. At 48 h p.i., the accumulation in H1975 tumor was 10.73 ± 1.89 %ID/g, compared to 4.47 ± 0.55 %ID/g in A549 tumor (P = 0.0219) and 4.60 ± 0.46 %ID/g in blocking control (P = 0.0228). HT1376 tumor reached 10.63 ± 1.35 %ID/g, significantly higher than T24 (4.10 ± 0.89 %ID/g, P = 0.0037), blocking (4.10 ± 0.92 %ID/g, P = 0.0036), and [89Zr]Zr-DFO-IgG control (5.67 ± 0.90 %ID/g, P = 0.0089). Tumor-to-muscle ratios at 48 h for H1975 and HT1376 tumors were 14.30 ± 2.02 and 15.00 ± 1.62, respectively, indicating excellent contrast. Fluorescence imaging with IRDye 800CW-Durvalumab further confirmed the uptake in PD-L1-specific tumors. No significant histological abnormalities were observed in major organs. The estimated human effective dose was 0.0522 mSv/MBq. Conclusion:[89Zr]Zr-DFO-Durvalumab enables specific, high-contrast ImmunoPET and fluorescence imaging of PD-L1-expressing NSCLC and bladder cancers. This dual-modality imaging platform holds potential for noninvasive assessment of PD-L1 status and personalized immunotherapy planning.

Synaptic density loss is a major correlate of cognitive functioning in adults with and without significant impairment. It is also a feature of clinical Alzheimer’s disease (AD) and suspected to co-occur with neurofibrillary tau (NFT) accumulation. Previous studies using [ 11 C]UCB-J for in-vivo analysis of synaptic density have been restricted to unimpaired (CU) A- and impaired (CI) AD (A+) participants where within group analyses have shown no association between synaptic density and NFT. There is also little known about the relationship between synaptic density and NFT in AD without cognitive impairment. Here we evaluated the association between synaptic density and NFT in CU and CI AD. Participants were recruited from ongoing AD-related studies (Wisconsin Registry for Alzheimer’s Prevention, ADRC) at UW and from the community and underwent comprehensive clinical and cognitive evaluation to determine cognitive status. Pearson’s r was used to determine associations between synaptic density ([ 11 C]UCB-J DVR) and neurofibrillary tau ([ 18 F]MK-6240 SUVR) across all participants and within amyloid and cognitive groups. Participant demographics are reported in Table 1. Across all participants, synaptic density and ERC, Hp NFT were well correlated (ERC NFT: r = -.46, p < .001; Hp NFT: r = -.49, p < .001). Within groups, only the CU A+ correlation between synaptic density and NFT remained significant (ERC NFT: r = -.49, p = .02; Hp NFT: r = -.59, p = .003) with CI A+ showing only a moderate (insignificant) relationship with Hp NFT (ERC NFT: r = -.16, p = .44; Hp NFT: r = -.31, p = .14) (Figure 1). In agreement with previous work, CI AD has lower Hp synaptic density than CU A-, and no significant relationship between Hp synaptic density and NFT. However, CU AD participants showed a significant relationship between NFT and synaptic density. This may be explained by a floor effect of Hp synaptic density that is reached by participants with clinical AD, but not yet in preclinical AD, or the existence of non-AD pathologies contributing to synapse loss. These results can help better understand the process of neurodegeneration in AD as participants progress from preclinical to clinical AD.

CD70 is a promising target for advancing the diagnosis and treatment of Burkitt lymphoma (BL). A 44Sc-labeled single-domain antibody fragment tracer, [44Sc]Sc-CHX-A″-DTPA-RCCB6, was developed and assessed for its potential in CD70-targeted immuno-PET imaging using BL models. Methods: RCCB6 single-domain antibody was conjugated with CHX-A″-DTPA and radiolabeled with 44Sc. The final tracer, [44Sc]Sc-CHX-A″-DTPA-RCCB6, was assessed for stability both in vitro and in vivo. Cellular uptake, binding, and internalization assays were conducted using type III and type I latency BL cell lines to confirm the tracer's specificity for CD70. Immuno-PET and biodistribution studies were performed in type III and type I latency BL models, whereas near-infrared fluorescence imaging was used to validate tumor accumulation. Finally, immunohistochemistry analysis was conducted on tumor tissues from both latency types to correlate between tracer accumulation and CD70 expression. Results: Radiolabeling of CHX-A″-DTPA-RCCB6 with 44Sc achieved high radiochemical yield and specific activity. The tracer was highly stable both in vitro and in vivo. In vitro cellular uptake and internalization assays confirmed the specific binding of [44Sc]Sc-CHX-A″-DTPA-RCCB6 to CD70 in type III latency BL cells. An inhibitory concentration of 50% of 16.45 ± 2.82 nM for RCCB6 and 38.74 ± 4.66 nM for CHX-A″-RCCB6 was determined from competition binding studies. Saturation binding studies determined the maximum number of binding sites, the association constant, and receptor density values for [44Sc]Sc-CHX-A″-DTPA-RCCB6 in type III latency BL cells to be 4.83 ± 0.52 pM, 19.75 ± 5.97 nM, and (2.36 ± 0.26) × 106 receptors per cell, respectively. Immuno-PET imaging and ex vivo biodistribution revealed high tracer accumulation in type III latency BL tumors, with sustained retention up to 6 h after injection (2.85 ± 0.84 %ID/g). Tracer uptake was minimal in both the blocked group and in type I latency BL tumors, with values of 0.35 ± 0.03 %ID/g and 0.58 ± 0.16 %ID/g, respectively. Near-infrared fluorescence imaging further confirmed tracer accumulation in type III latency BL tumors. Immunohistochemistry analysis supported these results, showing more intense CD70 staining in type III latency BL tumors compared with type I latency BL tumors. Conclusion: This work highlights the robust capability of [44Sc]Sc-CHX-A″-DTPA-RCCB6 in delineating differential CD70 expression in BL models, demonstrating promising findings that underscore the necessity for clinical studies to validate its translational potential.

Synaptic loss is a key feature of Alzheimer’s disease (AD) dementia. In the entorhinal cortex (ERC) and hippocampus, phosphorylated tau (pTau) colocalizes with synaptosomes, and its presence may play a role in AD-related synaptic loss. However, the relationship between pTau and synaptic density is not well understood. Plasma pTau represents secreted tau pathology and among the available epitopes, pTau217 has emerged as an accurate biomarker of AD pathology. Here, we tested the relationship between secreted pTau217 and synaptic density. Participants were recruited from the Wisconsin Alzheimer’s Disease Research Center and the Wisconsin Registry for Alzheimer’s Prevention (N=38; Table 1). All participants underwent blood sampling for measurement of plasma pTau217 and [C-11]UCB-J PET to assess synaptic density in regions of interest (ROIs: hippocampus, ERC, and fusiform gyrus) known to show early AD tau accumulation. Synaptic density was quantified using [C-11]UCB-J DVR (LGA, whole cerebellar reference region) and ROIs were identified following FreeSurfer T1w-MRI parcellation. Plasma pTau217 was determined using the ALZpath pTau217 Simoa assay on the Quanterix HD-X platform. We utilized multiple regression analysis to examine the extent to which plasma pTau217 and gender predict synaptic density in ROIs controlling for age. All models were fitted in R and considered significant at Bonferroni-corrected (.05/3) p<.017. During analysis we discovered one outlier; a cognitively-unimpaired participant with pTau217 concentration >2.5 standard deviations above the mean and high UCB-J DVR in all ROIs. Results with and without the outlier were considered. Plasma pTau217 (b=-.07, p=0.01) and gender (b=-.05, p=0.008) predicted UCB-J DVR in the hippocampus, but not other ROIs (Table 2). The effect size of plasma pTau217 and gender, as measured by Cohen’s f 2 , was 0.23 and 0.34, respectively, indicating medium to large effects. Welch’s t-test showed a significant gender difference in hippocampal UCB-J DVR (Figure). Our results indicate that higher levels of plasma pTau217 associated with lower synaptic density in the hippocampus. However, given the individual with high pTau217 and synaptic density, it is possible other processes unaccounted for in this analysis are impacting this relationship. Further examinations could give insight into early processes that confer neuronal injury in the AD pathological cascade.

We report DGA extraction chromatography isolation of 51Mn from isotopically enriched 54Fe. The method has been studied in semi-automated and automated realizations. The former achieves a decay corrected radiochemical yield of 78 f 1 % (n = 3) and a separation factor of (1.0 f 0.8) x 105 (n = 3). With GE HealthCare's Solid Target Platform (STP) and FASTlab the latter, fully automated method achieves a decay corrected radiochemical yield of 87 f 1 % (n = 3) and a separation factor of (2.7 f 0.9) x 104 (n = 3). Both setups efficiently isolate cyclotron-produced 51MnCl2 suitable for human administration as determined by developed Chemistry, Manufacturing, and Controls (CMC) acceptance criteria, and support exploration of 51Mn as a clinical diagnostic tool.

Trophoblast cell-surface antigen 2 (Trop2) is overexpressed in various solid tumors and contributes to tumor progression, while its expression remains low in normal tissues. Trop2-targeting antibody–drug conjugate (ADC), sacituzumab govitecan-hziy (Trodelvy), has shown efficacy in targeting this antigen. Leveraging the enhanced specificity of ADCs, we conducted the first immunoPET imaging study of Trop2 expression in gastric cancer (GC) and triple-negative breast cancer (TNBC) models using 89Zr-labeled Trodelvy ([89Zr]Zr-DFO-Trodelvy). This approach enables preclinical screening to identify patients who may benefit from targeted therapies. Trop2 expression levels in GC and TNBC cell lines (NCI-N87, HGC-27, MDST8, and MDA-MB-468) were assessed via flow cytometry and immunofluorescence staining. Labeling of DFO-Trodelvy with 89Zr was performed in Na2CO3 buffer at pH 7 (37 °C, 1.5 h). In vitro stability was analyzed using radio-thin layer chromatography. Biological properties were evaluated through cell uptake, saturation binding assays, and biodistribution experiments. ImmunoPET imaging with [89Zr]Zr-DFO-Trodelvy was performed at various time points to confirm its in vivo targeting. Immunohistochemical and immunofluorescence analyses were conducted on tumor tissues from tumor-bearing mice. The radiochemical yield of [89Zr]Zr-DFO-Trodelvy exceeded 90

This work reports an effective and scalable radiochemical separation process for isolating terbium from Gd2O3. The separation process uses three commercially available extraction chromatography resin columns, has been implemented on a computer-controlled chemistry module, and tested with 100 mg quantities of proton-irradiated natGd2O3. The 4 h separation procedure isolated radioterbium in 1.3 mL of 0.01 M HCl with 80 ± 8 % radiochemical yield and a Gd decontamination factor >(1.2 ± 0.3)·105.

The widely established PET isotope 18F does not have a therapeutic partner. We have recently established that the Sc-F bond can be formed under aqueous, high yielding conditions, paving the way to providing 18F as diagnostic partners to 47Sc and 177Lu radiotherapeutics. Here, we synthesized a library of tacn-based chelators comprised of 10 structurally unique permutations incorporating acetate, methyl-benzylamide and picolinate donor arms. The chelator library encompasses chelators ranging from 6- to 9-dentate, and produces complex changes ranging from +3 to -1. The corresponding Sc-F/Sc and Lu chelate complexes were characterized using computational, spectroscopic and potentiometric methods, followed by optimization of radiolabeling with 18F, 44Sc and 177Lu and concluded by in vivo validation. We identify characterization benchmarks that chart the coordinative landscape of radiochelation approaches for this unusual triad. Our screening identifies two ligand systems, H2L111 and H3L201 as ideal, readily functionalizable constructs for prospective, targeted theranostic applications with 18F/44Sc/177Lu.

The development of inert, biocompatible chelation methods is required to harness the emerging positron emitting radionuclide 45 Ti for radiopharmaceutical applications. Herein, we evaluate the Ti (IV) -coordination chemistry of four catechol-based, hexacoordinate chelators using synthetic, structural, computational, and radiochemical approaches. The siderophore enterobactin (Ent) and its synthetic mimic TREN-CAM readily form mononuclear Ti (IV) species in aqueous solution at neutral pH. Radiolabeling studies reveal that Ent and TREN-CAM form mononuclear complexes with the short-lived, positron-emitting radionuclide 45 Ti (IV) , and do not transchelate to plasma proteins in vitro and exhibit rapid renal clearance in naïve mice. These features guide efforts to target the 45 Ti isotope to prostate cancer tissue through the design, synthesis, and evaluation of Ent-DUPA, a small molecule conjugate composed of a prostate specific membrane antigen (PSMA) targeting peptide and a monofunctionalized Ent scaffold. The [ 45 Ti][Ti(Ent-DUPA)] 2− complex forms readily at room temperature. In a tumor xenograft model in mice, selective tumor tissue accumulation (8±5 %, n =5), and low off-target uptake in other organs is observed. Overall, this work demonstrates targeted imaging with 45 Ti (IV) , provides a foundation for advancing the application of 45 Ti in nuclear medicine, and reveals that Ent can be repurposed as a 45 Ti-complexing cargo for targeted nuclear imaging applications.

The elementally matched 55 Co 2+/3+ (t 1/2 =17.53 h, I β+ =77 %)/ 58m Co 2+/3+ (t 1/2 =9.10 h, internal conversion=100 %) radioisotope pair is of interest for development of paired diagnostic/therapeutic radiopharmaceuticals. Due to the accessibility of the nat/55 Co 2+/3+ redox couple, the redox state can be readily modulated. Here, we show that macroscopic and radiochemical redox reactions can be closely monitored and controlled using spectroscopic and radiochemical methods. We employ model systems to inform how to selectively synthesize thermodynamically favored oxidation state coordination complexes. In addition to exogenous oxidants, our data indicates that 55 Co-induced radiolysis of water efficiently and directly drives selective oxidation to the 55 Co 3+ species under no-carrier added (n.c.a.) conditions. Our synthetic strategies subsequently stabilize the respective 55 Co 2+ or 55 Co 3+ species for targeted positron emission tomography imaging in a mouse tumor model.

The development of theranostic radiotracers relies on their binding to specific molecular markers of a particular disease and the use of corresponding radiopharmaceutical pairs thereafter. This study reports the use of multiamine macrocyclic moieties (MAs), as linkers or chelators, in tracers targeting the neurotensin receptor-1 (NTSR-1). The goal is to achieve elevated tumor uptake, minimal background interference, and prolonged tumor retention in NTSR-1-positive tumors. Methods: We synthesized a series of neurotensin antagonists bearing MA linkers and metal chelators. The MA unit is hypothesized to establish a strong interaction with the cell membrane, and the addition of a second chelator may enhance water solubility, consequently reducing liver uptake. Small-animal PET/CT imaging of [64Cu]Cu-DOTA-SR-3MA, [64Cu]Cu-NT-CB-NOTA, [68Ga]Ga-NT-CB-NOTA, [64Cu]Cu-NT-CB-DOTA, and [64Cu]Cu-NT-Sarcage was acquired at 1, 4, 24, and 48 h after injection using H1299 tumor models. [55Co]Co-NT-CB-NOTA was also tested in HT29 (high NTSR-1 expression) and Caco2 (low NTSR-1 expression) colorectal adenocarcinoma tumor models. Saturation binding assay and internalization of [55Co]Co-NT-CB-NOTA were used to test tracer specificity and internalization in HT29 cells. Results: In vivo PET imaging with [64Cu]Cu-NT-CB-NOTA, [68Ga]Ga-NT-CB-NOTA, and [55Co]Co-NT-CB-NOTA revealed high tumor uptake, high tumor-to-background contrast, and sustained tumor retention (≤48 h after injection) in NTSR-1-positive tumors. Tumor uptake of [64Cu]Cu-NT-CB-NOTA remained at 76.9% at 48 h after injection compared with uptake 1 h after injection in H1299 tumor models, and [55Co]Co-NT-CB-NOTA was retained at 60.2% at 24 h compared with uptake 1 h after injection in HT29 tumor models. [64Cu]Cu-NT-Sarcage also showed high tumor uptake with low background and high tumor retention 48 h after injection Conclusion: Tumor uptake and pharmacokinetic properties of NTSR-1-targeting radiopharmaceuticals were greatly improved when attached with different nitrogen-containing macrocyclic moieties. The study results suggest that NT-CB-NOTA labeled with either 64Cu/67Cu, 55Co/58mCo, or 68Ga (effect of 177Lu in tumor to be determined in future studies) and NT-Sarcage labeled with 64Cu/67Cu or 55Co/58mCo may be excellent diagnostic and therapeutic radiopharmaceuticals targeting NTSR-1-positive cancers. Also, the introduction of MA units to other ligands is warranted in future studies to test the generality of this approach.

Objectives:Disialoganglioside 2 (GD2), overexpressed by cancers such as melanoma and neuroblastoma, is a tumor antigen for targeted therapy. The delivery of conventional IgG antibody technologies targeting GD2 is limited clinically by its co-expression on nerves that contributes to toxicity presenting as severe neuropathic pain. To improve the tumor selectivity of current GD2-targeting approaches, a next-generation bispecific antibody targeting GD2 and B7-H3 (CD276) was generated. Methods:Differential expression of human B7-H3 (hB7-H3) was transduced into GD2+ B78 murine melanoma cells and confirmed by flow cytometry. We assessed the avidity and selectivity of our GD2-B7-H3 targeting bispecific antibodies (INV34-6, INV33-2, and INV36-6) towards GD2+/hB7-H3- B78 cells relative to GD2+/hB7-H3+ B78 cells using flow cytometry and competition binding assays, comparing results an anti-GD2 antibody (dinutuximab, DINU). The bispecific antibodies, DINU, and a non-targeted bispecific control (bsAb CTRL) were conjugated with deferoxamine for radiolabeling with Zr-89 (t1/2 = 78.4 h). Using positron emission tomography (PET) studies, we evaluated the in vivo avidity and selectivity of the GD2-B7-H3 targeting bispecific compared to bsAb CTRL and DINU using GD2+/hB7-H3+ and GD2+/hB7-H3- B78 tumor models. Results:Flow cytometry and competition binding assays showed that INV34-6 bound with high avidity to GD2+/hB7-H3+ B78 cells with high avidity but not GD2+/hB7-H3+ B78 cells. In comparison, no selectivity between cell types was observed for DINU. PET in mice bearing the GD2+/hB7-H3- and GD2+/hB7-H3+ B78 murine tumor showed similar biodistribution in normal tissues for [89Zr]Zr-Df-INV34-6, [89Zr]Zr-Df-bsAb CTRL, and [89Zr]Zr-Df-DINU. Importantly, [89Zr]Zr-Df-INV34-6 tumor uptake was selective to GD2+/hB7-H3+ B78 over GD2+/hB7-H3- B78 tumors, and substantially higher to GD2+/hB7-H3+ B78 than the non-targeted [89Zr]Zr-Df-bsAb CTRL control. [89Zr]Zr-Df-DINU displayed similar uptake in both GD2+ tumor models, with uptake comparable to [89Zr]Zr-Df-INV34-6 in the GD2+/hB7-H3+ B78 model. Conclusion:The GD2-B7-H3 targeting bispecific antibodies successfully improved selectivity to cells expressing both antigens. This approach should address the severe toxicities associated with GD2-targeting therapies by reducing off-tumor GD2 binding in nerves. Continued improvements in bispecific antibody technologies will continue to transform the therapeutic biologics landscape.

Radiopharmaceutical therapy (RPT) uses radionuclides that decay via one of three therapeutically relevant decay modes (alpha, beta, and internal conversion (IC) / Auger electron (AE) emission) to deliver short range, highly damaging radiation inside of diseased cells, maintaining localized dose distribution and sparing healthy cells. Antimony-119 (119Sb, t1/2 = 38.19 h, EC = 100

Down syndrome (DS) is the most prevalent genetic cause of intellectual disability, resulting from trisomy 21. Recently, positron emission tomography (PET) imaging has been used to image synapses in vivo. The motivation for this pilot study was to investigate whether synaptic density in low functioning adults with DS can be evaluated using the PET radiotracer [11C]UCB-J. Data were acquired from low functioning adults with DS (n = 4) and older neurotypical (NT) adults (n = 37). Motion during the scans required the use of a 10-minute acquisition window for the calculation of synaptic density using SUVR50–60,CS which was determined to be a suitable approximation for specific binding in this analysis using dynamic data from the NT group. Of the regions analyzed a large effect was observed when comparing DS and NT hippocampus and cerebral cortex synaptic density as well as hippocampus and cerebellum volumes. In this pilot study, PET imaging of [11C]UCB-J was successfully completed and synaptic density measured in low functioning DS adults. This work provides the basis for studies where synaptic density may be compared between larger groups of NT adults and adults with DS who have varying degrees of baseline cognitive status.

CD93 is overexpressed in multiple solid tumor types, serving as a novel target for antiangiogenic therapy. The goal of this study was to develop a 64Cu-based positron emission tomography (PET) tracer for noninvasive imaging of CD93 expression. Antimouse-CD93 mAb (mCD93) and the CD93 ligand IGFBP7 were conjugated to a bifunctional chelator, p-isothiocyanatobenzyl-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-NOTA) and labeled with 64Cu. To evaluate the pharmacokinetic properties and tumor-targeting efficacy of [64Cu]Cu-NOTA-mCD93 and [64Cu]Cu-NOTA-IGFBP7, PET imaging and biodistribution were performed on both 4T1 murine breast tumor-bearing mice and MDA-MB-231 human breast tumor-bearing mice. The tumor model HT1080-FAP, which does not overexpress CD93, was used as a negative control. Fluorescent immunostaining was conducted on different tissues to correlate radiotracer uptake with CD93 expression. 64Cu-labeling was achieved with high yield and specific activity. Serial PET imaging revealed that the in vivo performance of [64Cu]Cu-NOTA-IGFBP7 was superior to that of [64Cu]Cu-NOTA-mCD93, and that the tracer [64Cu]Cu-NOTA-IGFBP7 exhibited elevated tumor uptake values and excellent tumor retention in MDA-MB-231 mice, rather than in 4T1 murine mice. The MDA-MB-231 tumor uptake of [64Cu]Cu-NOTA-IGFBP7 was 2.85 ± 0.15, 3.69 ± 0.60, 6.91 ± 0.88, and 6.35 ± 0.55%ID/g at 1, 4, 24, and 48 h p.i., respectively, which were significantly higher than that in the CD93-negative HT1080-FAP tumor (0.73 ± 0.15, 0.97 ± 0.31, 1.00 ± 0.07, and 1.02 ± 0.11%ID/g, respectively). The significant difference between positive and negative tumors indicated [64Cu]Cu-NOTA-IGFBP7 was specifically binding to CD93. Biodistribution data as measured by gamma counting were consistent with the PET analysis. Ex vivo histology further confirmed the high CD93 expression on MDA-MB-231 tumor tissues. Herein, we prepared two novel radiotracers, [64Cu]Cu-NOTA-mCD93 and [64Cu]Cu-NOTA-IGFBP7, for the first immune-PET imaging of CD93 expression. Our results suggest that [64Cu]Cu-NOTA-IGFBP7 is a more potential radiotracer for visualizing angiogenesis due to its sensitive, persistent, and CD93-specific characteristics.