Browsing by Subject "VHH"

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    Astatine-211 labeled anti-HER2 5F7 single domain antibody fragment conjugates: radiolabeling and preliminary evaluation.
    (Nucl Med Biol, 2017-09-19) Choi, Jaeyeon; Vaidyanathan, Ganesan; Koumarianou, Eftychia; Kang, Choong Mo; Zalutsky, Michael R
    INTRODUCTION: Derived from heavy chain only camelid antibodies, ~15-kDa single-domain antibody fragments (sdAbs) are an attractive platform for developing molecularly specific imaging probes and targeted radiotherapeutics. The rapid tumor accumulation and normal tissue clearance of sdAbs might be ideal for use with (211)At, a 7.2-h half-life α-emitter, if appropriate labeling chemistry can be devised to trap (211)At in cancer cells after sdAb binding. This study evaluated two reagents, [(211)At]SAGMB and iso-[(211)At]SAGMB, for this purpose. METHODS: [(211)At]SAGMB and iso-[(211)At]SAGMB, and their radioiodinated analogues [(131)I]SGMIB and iso-[(131)I]SGMIB, were synthesized by halodestannylation and reacted with the anti-HER2 sdAb 5F7. Radiochemical purity, immunoreactivity and binding affinity were determined. Paired-label internalization assays on HER2-expressing BT474M1 breast carcinoma cells directly compared [(131)I]SGMIB-5F7/[(211)At]SAGMB-5F7 and iso-[(131)I]SGMIB-5F7/iso-[(211)At]SAGMB-5F7 tandems. The biodistribution of the two tandems was evaluated in SCID mice with subcutaneous BT474M1 xenografts. RESULTS: Radiochemical yields for Boc2-iso-[(211)At]SAGMB and Boc2-[(211)At]SAGMB synthesis, and efficiencies for coupling of iso-[(211)At]SAGMB and [(211)At]SAGMB to 5F7 were similar, with radiochemical purities of [(211)At]SAGMB-5F7 and iso-[(211)At]SAGMB-5F7 >98%. iso-[(211)At]SAGMB-5F7 and [(211)At]SAGMB-5F7 had immunoreactive fractions >80% and HER2 binding affinities of less than 5 nM. Internalization assays demonstrated high intracellular trapping of radioactivity, with little difference observed between corresponding (211)At- and (131)I-labeled 5F7 conjugates. Higher BT474M1 intracellular retention was observed from 1-6 h for the iso-conjugates (iso-[(211)At]SAGMB-5F7, 74.3 ± 2.8%, vs. [(211)At]SAGMB-5F7, 63.7 ± 0.4% at 2 h) with the opposite behavior observed at 24 h. Peak tumor uptake for iso-[(211)At]SAGMB-5F7 was 23.4 ± 2.2% ID/g at 4 h, slightly lower than its radioiodinated counterpart, but significantly higher than observed with [(211)At]SAGMB-5F7. Except in kidneys and lungs, tumor-to-normal organ ratios for iso-[(211)At]SAGMB-5F7 were greater than 10:1 by 2 h, and significantly higher than those for [(211)At]SAGMB-5F7. CONCLUSION: These (211)At-labeled sdAb conjugates, particularly iso-[(211)At]SAGMB-5F7, warrant further evaluation for targeted α-particle radiotherapy of HER2-expressing cancers.
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    ItemOpen Access
    Low-level whole-brain radiation enhances theranostic potential of single-domain antibody fragments for human epidermal growth factor receptor type 2 (HER2)-positive brain metastases.
    (Neuro-oncology advances, 2022-01) Procissi, Daniele; Jannetti, Stephen A; Zannikou, Markella; Zhou, Zhengyuan; McDougald, Darryl; Kanojia, Deepak; Zhang, Hui; Burdett, Kirsten; Vaidyanathan, Ganesan; Zalutsky, Michael R; Balyasnikova, Irina V

    Background

    Single-domain antibody fragments (aka VHH, ~ 13 kDa) are promising delivery systems for brain tumor theranostics; however, achieving efficient delivery of VHH to intracranial lesions remains challenging due to the tumor-brain barrier. Here, we evaluate low-dose whole-brain irradiation as a strategy to increase the delivery of an anti- human epidermal growth factor receptor type 2 (HER2) VHH to breast cancer-derived intracranial tumors in mice.

    Methods

    Mice with intracranial HER2-positive BT474BrM3 tumors received 10-Gy fractionated cranial irradiation and were evaluated by noninvasive imaging. Anti-HER2 VHH 5F7 was labeled with 18F, administered intravenously to irradiated mice and controls, and PET/CT imaging was conducted periodically after irradiation. Tumor uptake of 18F-labeled 5F7 in irradiated and control mice was compared by PET/CT image analysis and correlated with tumor volumes. In addition, longitudinal dynamic contrast-enhanced MRI (DCE-MRI) was conducted to visualize and quantify the potential effects of radiation on tumor perfusion and permeability.

    Results

    Increased 18F-labeled 5F7 intracranial tumor uptake was observed with PET in mice receiving cranial irradiation, with maximum tumor accumulation seen approximately 12 days post initial radiation treatment. No radiation-induced changes in HER2 expression were detected by Western blot, flow cytometry, or on tissue sections. DCE-MRI imaging demonstrated transiently increased tumor perfusion and permeability after irradiation, consistent with the higher tumor uptake of 18F-labeled anti-HER2 5F7 in irradiated mice.

    Conclusion

    Low-level brain irradiation induces dynamic changes in tumor vasculature that increase the intracranial tumor delivery of an anti-HER2 VHH, which could facilitate the use of radiolabeled VHH to detect, monitor, and treat HER2-expressing brain metastases.