Human epidermal growth factor receptor 2 (HER2) status is one of the major tumor characteristics in breast cancer to guide therapy. Anti-HER2 treatment has clear survival advantages in HER2-positive breast carcinoma patients. Heterogeneity in HER2 expression between primary tumor and metastasis has repeatedly been described, resulting in the need to reassess HER2 status during the disease course. To avoid repeated biopsy with potential bias due to tumor heterogeneity, Nanobodies directed against HER2 have been developed as probes for molecular imaging. Nanobodies, which are derived from unique heavy-chain-only antibodies, are the smallest antigen-binding antibody fragments and have ideal characteristics for PET imaging. The primary aims were assessment of safety, biodistribution, and dosimetry. The secondary aim was to investigate tumor-targeting potential. Methods: In total, 20 women with primary or metastatic breast carcinoma (score of 21 or 31 on HER2 immunohistochemical assessment) were included. Anti-HER2-Nanobody was labeled with 68 Ga via a NOTA derivative. Administered activities were 53-174 MBq (average, 107 MBq). PET/CT scans for dosimetry assessment were obtained at 10, 60, and 90 min after administration. Physical evaluation and blood analysis were performed for safety evaluation. Biodistribution was analyzed for 11 organs using MIM software; dosimetry was assessed using OLINDA/EXM. Tumor-targeting potential was assessed in primary and metastatic lesions. Results: No adverse reactions occurred. A fast blood clearance was observed, with only 10% of injected activity remaining in the blood at 1 h after injection. Uptake was seen mainly in the kidneys, liver, and intestines. The effective dose was 0.043 mSv/MBq, resulting in an average of 4.6 mSv per patient. The critical organ was the urinary bladder wall, with a dose of 0.406 mGy/MBq. In patients with metastatic disease, tracer accumulation well above the background level was demonstrated in most identified sites of disease. Primary lesions were more variable in tracer accumulation. Conclusion: 68 Ga-HER2-Nanobody PET/CT is a safe procedure with a radiation dose comparable to other routinely used PET tracers. Its biodistribution is favorable, with the highest uptake in the kidneys, liver, and intestines but very low background levels in all other organs that typically house primary breast carcinoma or tumor metastasis. Tracer accumulation in HER2-positive metastases is high, compared with normal surrounding tissues, and warrants further assessment in a phase II trial. One in 8 women develops breast cancer, and it remains the second leading cause of cancer death in women. Identification of cancer subtypes based on biologic markers has led to the introduction of targeted therapies, with improved survival and morbidity. Besides hormone receptor expression, human epidermal growth factor receptor 2 (HER2) is used for breast cancer classification. Breast cancers with HER2 overexpression in primary or metastatic sites will benefit from HER2-targeted therapie...

Nanobodies are the smallest fully functional antigen-binding antibody fragments possessing ideal properties as probes for molecular imaging. In this study we labeled the anti-human epidermal growth factor receptor type 2 (HER2) Nanobody with 68 Ga via a 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) derivative and assessed its use for HER2 iPET imaging. Methods: The 2Rs15dHis 6 Nanobody and the lead optimized current-good-manufacturing-practice grade analog 2Rs15d were conjugated with S-2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) to enable fast and efficient 68 Ga labeling. Biodistribution and PET/CT studies were performed on HER2-positive and -negative tumor xenografts. The effect of injected mass on biodistribution was evaluated. The biodistribution data were extrapolated to calculate radiation dose estimates for the adult female using OLINDA software. A single-dose extended-toxicity study for NOTA2Rs15d was performed on healthy mice up to a dose of 10 mg/kg. Results: Radiolabeling was quantitative (.97%) after 5 min of incubation at room temperature; specific activity was 55-200 MBq/nmol. Biodistribution studies showed fast and specific uptake (percentage injected activity [%IA]) in HER2-positive tumors (3.13 6 0.06 and 4.34 6 0.90 %IA/g for 68 Ga-NOTA-2Rs15dHis 6 and 68 Ga-NOTA-2Rs15d, respectively, at 1 h after injection) and high tumor-to-blood and tumor-to-muscle ratios at 1 h after injection, resulting in high-contrast PET/CT images with high specific tumor uptake. A remarkable finding of the biodistribution studies was that kidney uptake was reduced by 60% for the Nanobody lacking the C-terminal His 6 tag. The injected mass showed an effect on the general biodistribution: a 100-fold increase in NOTA-2Rs15d mass decreased liver uptake from 7.43 6 1.89 to 2.90 6 0.26 %IA/g whereas tumor uptake increased from 2.49 6 0.68 to 4.23 6 0.99 %IA/g. The calculated effective dose, based on extrapolation of mouse data, was 0.0218 mSv/MBq, which would yield a radiation dose of 4 mSv to a patient after injection of 185 MBq of 68 Ga-NOTA2Rs15d. In the toxicity study, no adverse effects were observed after injection of a 10 mg/kg dose of NOTA-2Rs15d. Conclusion:A new anti-HER2 PET tracer, 68 Ga-NOTA-2Rs15d, was synthesized via a rapid procedure under mild conditions. Preclinical validation showed high-specific-contrast imaging of HER2-positive tumors with no observed toxicity. 68 Ga-NOTA2Rs15d is ready for first-in-human clinical trials.

Tumor-associated macrophages constitute a major component of the stroma of solid tumors, encompassing distinct subpopulations with different characteristics and functions. We aimed to identify M2-oriented tumor-supporting macrophages within the tumor microenvironment as indicators of cancer progression and prognosis, using PET imaging. This can be realized by designing 18 F-labeled camelid single-domain antibody fragments (sdAbs) specifically targeting the macrophage mannose receptor (MMR), which has been identified as an important biomarker on this cell population. Methods: Crossreactive anti-MMR sdAbs were generated after immunization of an alpaca with the extracellular domains of both human and mouse MMR. The lead binder was chosen on the basis of comparisons of binding affinity and in vivo pharmacokinetics. The PET tracer 18 F-fluorobenzoate (FB)-anti-MMR sdAb was developed using the prosthetic group N-succinimidyl-4-18 F-fluorobenzoate ( 18 F-SFB), and its biodistribution, tumor-targeting potential, and specificity in terms of macrophage and MMR targeting were evaluated in mouse tumor models. Results: Four sdAbs were selected after affinity screening, but only 2 were found to be cross-reactive for human and mouse MMR. The lead anti-MMR 3.49 sdAb, bearing an affinity of 12 and 1.8 nM for mouse and human MMR, respectively, was chosen for its favorable in vivo biodistribution profile and tumor-targeting capacity. 18 F-FB-anti-MMR 3.49 sdAb was synthesized with a 5%-10% radiochemical yield using an automated and optimized protocol. In vivo biodistribution analyses showed fast clearance via the kidneys and retention in MMRexpressing organs and tumor. The kidney retention of the fluorinated sdAb was 20-fold lower than a 99m Tc-labeled counterpart. Compared with MMR-and C-C chemokine receptor 2-deficient mice, significantly higher uptake was observed in tumors grown in wild-type mice, demonstrating the specificity of the 18 F tracer for MMR and macrophages, respectively. Conclusion: Anti-MMR 3.49 was denoted as the lead cross-reactive MMR-targeting sdAb. 18 F radiosynthesis was optimized, providing an optimal probe for PET imaging of the tumor-promoting macrophage subpopulation in the tumor stroma. Dur ing tumor development, myeloid cells are attracted to the tumor stroma. These infiltrating immune cells are versatile, adopting different activation states in response to a changing microenvironment, leading to subsets of tumor-associated macrophages (TAMs) with specialized functions (1,2). Two main morphologically distinct TAM subsets can be distinguished on the basis of major histocompatibility complex (MHC) class II expression levels in multiple mouse tumor models. Tumor promotion has been linked with an accumulation of M2-oriented MHC II low TAMs in lung and breast carcinoma (3,4). Accordingly, MHC II low TAMs were found to reside primarily in less oxygenated zones, express hypoxia-regulated genes, and facilitate the angiogenic switch (5). Interestingly, the macrophage mannose receptor (MMR, CD206), a typical M2...

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Antisense oligonucleotides (AONs) can be used to correct the disrupted reading frame of Duchenne muscular dystophy patients (DMD). We have a collection of 121 AONs, of which 79 are effective in inducing the specific skipping of 38 out of the 79 different DMD exons. All AONs are located within exons and were hypothesized to act by steric hindrance of serine-arginine rich (SR) protein binding to exonic splicing enhancer (ESE) sites. Indeed, retrospective in silico analysis of effective versus ineffective AONs revealed that the efficacy of AONs is correlated to the presence of putative ESE sites (as predicted by the ESEfinder and RESCUE-ESE software). ESE predicting software programs are thus valuable tools for the optimization of exon-internal antisense target sequences.