Novel VHH-Based Tracers with Variable Plasma Half-Lives for Imaging of CAIX-Expressing Hypoxic Tumor Cells.

Hypoxic areas are present in the majority of solid tumors, and hypoxia is associated with resistance to therapies and poor outcomes. A transmembrane protein that is upregulated by tumor cells that have adapted to hypoxic conditions is carbonic anhydrase IX (CAIX). Therefore, noninvasive imaging of CAIX could be of prognostic value, and it could steer treatment strategies. The aim of this study was to compare variants of CAIX-binding VHH B9, with and without a C-terminal albumin-binding domain with varying affinity (ABDlow and ABDhigh), for SPECT imaging of CAIX expression. The binding affinity and internalization of the various B9-variants were analyzed using SK-RC-52 cells. Biodistribution studies were performed in mice with subcutaneous SCCNij153 human head and neck cancer xenografts. Tracer uptake was determined by ex vivo radioactivity counting and visualized by SPECT/CT imaging. Furthermore, autoradiography images of tumor sections were spatially correlated with CAIX immunohistochemistry. B9-variants demonstrated a similar moderate affinity for CAIX in vitro. Maximal tumor uptake and acceptable tumor-to-blood ratios were found in the SCCNij153 model at 4 h post injection for [111In]In-DTPA-B9 (0.51 ± 0.08%ID/g and 8.1 ± 0.85, respectively), 24 h post injection for [111In]In-DTPA-B9-ABDlow (2.39 ± 0.44%ID/g and 3.66 ± 0.81, respectively) and at 72 h post injection for [111In]In-DTPA-B9-ABDhigh (8.7 ± 1.34%ID/g and 2.43 ± 0.15, respectively). An excess of unlabeled monoclonal anti-CAIX antibody efficiently inhibited tumor uptake of [111In]In-DTPA-B9, while only a partial reduction of [111In]In-DTPA-B9-ABDlow and [111In]In-DTPA-B9-ABDhigh uptake was found. Immunohistochemistry and autoradiography images showed colocalization of all B9-variants with CAIX expression; however, [111In]In-DTPA-B9-ABDlow and [111In]In-DTPA-B9-ABDhigh also accumulated in non-CAIX expressing regions. Tumor uptake of [111In]In-DTPA-B9-ABDlow and [111In]In-DTPA-B9-ABDhigh, but not of [111In]In-DTPA-B9, could be visualized with SPECT/CT imaging. In conclusion, [111In]In-DTPA-B9 has a high affinity to CAIX and shows specific targeting to CAIX in head and neck cancer xenografts. The addition of ABD prolonged plasma half-life, increased tumor uptake, and enabled SPECT/CT imaging. This uptake was, however, partly CAIX- independent, precluding the ABD-tracers for use in hypoxia quantification in this tumor type.

A Nanobody-on-Quantum Dot Displacement Assay for Rapid and Sensitive Quantification of the Epidermal Growth Factor Receptor (EGFR).

Biosensing approaches that combine small, engineered antibodies (nanobodies) with nanoparticles are often complicated. Here, we show that nanobodies with different C-terminal tags can be efficiently attached to a range of the most widely used biocompatible semiconductor quantum dots (QDs). Direct implementation into simplified assay formats was demonstrated by designing a rapid and wash-free mix-and-measure immunoassay for the epidermal growth factor receptor (EGFR). Terbium complex (Tb)-labeled hexahistidine-tagged nanobodies were specifically displaced from QD surfaces via EGFR-nanobody binding, leading to an EGFR concentration-dependent decrease of the Tb-to-QD Förster resonance energy transfer (FRET) signal. The detection limit of 80±20 pM (16±4 ng mL-1 ) was 3-fold lower than the clinical cut-off concentration for soluble EGFR and up to 10-fold lower compared to conventional sandwich FRET assays that required a pair of different nanobodies.

Structural insights into the role and targeting of EGFRvIII.

The epidermal growth factor receptor (EGFR) is a well-known oncogenic driver in lung and other cancers. In glioblastoma multiforme (GBM), the EGFR deletion variant III (EGFRvIII) is frequently found alongside EGFR amplification. Agents targeting the EGFR axis have shown limited clinical benefits in GBM and the role of EGFRvIII in GBM is poorly understood. To shed light on the role of EGFRvIII and its potential as a therapeutic target, we determined X-ray crystal structures of a monomeric EGFRvIII extracellular region (ECR). The EGFRvIII ECR resembles the unliganded conformation of EGFR, including the orientation of the C-terminal region of domain II. Domain II is mostly disordered, but the ECR structure is compact. We selected a nanobody with preferential binding to EGFRvIII relative to EGFR and structurally defined an epitope on domain IV that is occluded in the unliganded intact EGFR. These findings suggest new avenues for EGFRvIII targeting in GBM.

Structural insights into the non-inhibitory mechanism of the anti-EGFR EgB4 nanobody.

BACKGROUND: The epidermal growth factor receptor (EGFR) is involved in various developmental processes, and alterations of its extracellular segment are associated with several types of cancers, in particular glioblastoma multiforme (GBM). The EGFR extracellular region is therefore a primary target for therapeutic agents, such as monoclonal antibodies and variable domains of heavy chain antibodies (VHH), also called nanobodies. Nanobodies have been previously shown to bind to EGFR, and to inhibit ligand-mediated EGFR activation. RESULTS: Here we present the X-ray crystal structures of the EgB4 nanobody, alone (to 1.48 Å resolution) and bound to the full extracellular EGFR-EGF complex in its active conformation (to 6.0 Å resolution). We show that EgB4 binds to a new epitope located on EGFR domains I and II, and we describe the molecular mechanism by which EgB4 plays a non-inhibitory role in EGFR signaling. CONCLUSION: This work provides the structural basis for the application of EgB4 as a tool for research, for targeted therapy, or as a biomarker to locate EGFR-associated tumors, all without affecting EGFR activation.

Homogeneous tumor targeting with a single dose of HER2-targeted albumin-binding domain-fused nanobody-drug conjugates results in long-lasting tumor remission in mice.

Background: The non-homogenous distribution of antibody-drug conjugates (ADCs) within solid tumors is a major limiting factor for their wide clinical application. Nanobodies have been shown to rapidly penetrate into xenografts, achieving more homogeneous tumor targeting. However, their rapid renal clearance can hamper their application as nanobody drug conjugates (NDCs). Here, we evaluate whether half-life extension via non-covalent interaction with albumin can benefit the efficacy of a HER2-targeted NDC. Methods: HER2-targeted nanobody 11A4 and the irrelevant nanobody R2 were genetically fused to an albumin-binding domain (ABD) at their C-terminus. Binding to both albumin and tumor cells was determined by ELISA-based assays. The internalization potential as well as the in vitro efficacy of NDCs were tested on HER2 expressing cells. Serum half-life of iodinated R2 and R2-ABD was studied in tumor-free mice. The distribution of fluorescently labelled 11A4 and 11A4-ABD was assessed in vitro in 3D spheroids. Subsequently, the in vivo distribution was evaluated by optical molecular imaging and ex vivo by tissue biodistribution and tumor immunohistochemical analysis after intravenous injection of IRDye800-conjugated nanobodies in mice bearing HER2-positive subcutaneous xenografts. Finally, efficacy studies were performed in HER2-positive NCI-N87 xenograft-bearing mice intravenously injected with a single dose (250 nmol/kg) of nanobodies conjugated to auristatin F (AF) either via a maleimide or the organic Pt(II)­based linker, coined Lx®. Results: 11A4-ABD was able to bind albumin and HER2 and was internalized by HER2 expressing cells, irrespective of albumin presence. Interaction with albumin did not alter its distribution through 3D spheroids. Fusion to ABD resulted in a 14.8-fold increase in the serum half-life, as illustrated with the irrelevant nanobody. Furthermore, ABD fusion prolonged the accumulation of 11A4-ABD in HER2-expressing xenografts without affecting the expected homogenous intratumoral distribution. Next to that, reduced kidney retention of ABD-fused nanobodies was observed. Finally, a single dose administration of either 11A4-ABD-maleimide-AF or 11A4-ABD-Lx-AF led to long-lasting tumor remission in HER2-positive NCI-N87 xenograft-bearing mice. Conclusion: Our results demonstrate that genetic fusion of a nanobody to ABD can significantly extend serum half-life, resulting in prolonged and homogenous tumor accumulation. Most importantly, as supported by the impressive anti-tumor efficacy observed after a single dose administration of 11A4-ABD-AF, our data reveal that monovalent internalizing ABD-fused nanobodies have potential for the development of highly effective NDCs.

Implications for tetraspanin-enriched microdomain assembly based on structures of CD9 with EWI-F.

Tetraspanins are eukaryotic membrane proteins that contribute to a variety of signaling processes by organizing partner-receptor molecules in the plasma membrane. How tetraspanins bind and cluster partner receptors into tetraspanin-enriched microdomains is unknown. Here, we present crystal structures of the large extracellular loop of CD9 bound to nanobodies 4C8 and 4E8 and, the cryo-EM structure of 4C8-bound CD9 in complex with its partner EWI-F. CD9-EWI-F displays a tetrameric arrangement with two central EWI-F molecules, dimerized through their ectodomains, and two CD9 molecules, one bound to each EWI-F transmembrane helix through CD9-helices h3 and h4. In the crystal structures, nanobodies 4C8 and 4E8 bind CD9 at loops C and D, which is in agreement with the 4C8 conformation in the CD9-EWI-F complex. The complex varies from nearly twofold symmetric (with the two CD9 copies nearly anti-parallel) to ca. 50° bent arrangements. This flexible arrangement of CD9-EWI-F with potential CD9 homo-dimerization at either end provides a "concatenation model" for forming short linear or circular assemblies, which may explain the occurrence of tetraspanin-enriched microdomains.

Insights into maleimide-thiol conjugation chemistry: Conditions for efficient surface functionalization of nanoparticles for receptor targeting.

Maleimide-thiol chemistry is widely used for the design and preparation of ligand-decorated drug delivery systems such as poly(lactide-co-glycolide) (PLGA) based nanoparticles (NPs). While many publications on nanocarriers functionalized exploiting this strategy are available in the literature, the conditions at which this reaction takes place vary among publications. This paper presents a comprehensive study on the conjugation of the peptide cRGDfK and the nanobody 11A4 (both containing a free thiol group) to maleimide functionalized PLGA NPs by means of the maleimide-thiol click reaction. The influence of different parameters, such as the nanoparticles preparation method and storage conditions as well as the molar ratio of maleimide to ligand used for conjugation, on the reaction efficiency has been evaluated. The NPs were prepared by a single or double emulsion method using different types and concentrations of surfactants and stored at 4 or 20 °C before reaction with the targeting moieties. Several maleimide to ligand molar ratios and different reaction times were studied and the conjugation efficiency was determined by quantification of the not-bound ligand by liquid chromatography. The kind of emulsion used to prepare the NPs as well as the type and concentration of surfactant used had no effect on the conjugation efficiency. Reaction between the maleimide groups present in the NPs and cRGDfK was optimal at a maleimide to thiol molar ratio of 2:1, reaching a conjugation efficiency of 84 ±â€¯4% after 30 min at room temperature in 10 mM HEPES pH 7.0. For 11A4 nanobody the optimal reaction efficiency, 58 ±â€¯12%, was achieved after 2 h of incubation at room temperature in PBS pH 7.4 using a 5:1 maleimide to protein molar ratio. Storage of the NPs at 4 °C for 7 days prior to their exposure to the ligands resulted in approximately 10% decrease in the reactivity of maleimide in contrast to storage at 20 °C which led to almost 40% of the maleimide being unreactive after the same storage time. Our findings demonstrate that optimization of this reaction, particularly in terms of reactant ratios, can represent a significant increase in the conjugation efficiency and prevent considerable waste of resources.

TRIM46 Controls Neuronal Polarity and Axon Specification by Driving the Formation of Parallel Microtubule Arrays.

Axon formation, the initial step in establishing neuronal polarity, critically depends on local microtubule reorganization and is characterized by the formation of parallel microtubule bundles. How uniform microtubule polarity is achieved during axonal development remains an outstanding question. Here, we show that the tripartite motif containing (TRIM) protein TRIM46 plays an instructive role in the initial polarization of neuronal cells. TRIM46 is specifically localized to the newly specified axon and, at later stages, partly overlaps with the axon initial segment (AIS). TRIM46 specifically forms closely spaced parallel microtubule bundles oriented with their plus-end out. Without TRIM46, all neurites have a dendrite-like mixed microtubule organization resulting in Tau missorting and altered cargo trafficking. By forming uniform microtubule bundles in the axon, TRIM46 is required for neuronal polarity and axon specification in vitro and in vivo. Thus, TRIM46 defines a unique axonal cytoskeletal compartment for regulating microtubule organization during neuronal development.