Tuning through-space interactions via the secondary coordination sphere of an artificial metalloenzyme leads to enhanced Rh(iii)-catalysis.

We report computationally-guided protein engineering of monomeric streptavidin Rh(iii) artificial metalloenzyme to enhance catalysis of the enantioselective coupling of acrylamide hydroxamate esters and styrenes. Increased TON correlates with calculated distances between the Rh(iii) metal and surrounding residues, underscoring an artificial metalloenzyme's propensity for additional control in metal-catalyzed transformations by through-space interactions.

Disparities between Antibody Occupancy, Orientation, and Cytotoxicity in Immunotherapy.

We report fusion proteins designed to bind spatially distinct epitopes on the extracellular portion of HER2, a breast cancer biomarker and established therapeutic target, and recruit IgG (either anti-His6 or serum IgG) to the cell surface. When the proteins were incubated with anti-His6 antibody and various concentrations of a single HER2-binding protein His6 fusion, we observed interference and a decrease in antibody recruitment at HER2-binding protein concentrations exceeding ∼30 nM. In contrast, concomitant treatment with two or three distinct HER2-binding protein His6 fusions, and anti-His6 , results in increased antibody recruitment, even at relatively high HER2-binding protein concentration. In some instances, increased antibody recruitment leads to increased antibody-dependent cellular cytotoxicity (ADCC) activity. While a fusion protein consisting of a HER2-binding nanobody and Sac7d, a protein evolved to recognize the Fc domain of IgG, binds IgG from serum, antibody recruitment does not lead to ADCC activity. Rationales for these disparities are provided. Collectively, our findings have implications for the design of efficacious targeted immunotherapeutic biologics, and ensembles thereof.

Asymmetric δ-Lactam Synthesis with a Monomeric Streptavidin Artificial Metalloenzyme.

Reliable design of artificial metalloenzymes (ArMs) to access transformations not observed in nature remains a long-standing and important challenge. We report that a monomeric streptavidin (mSav) Rh(III) ArM permits asymmetric synthesis of α,ß-unsaturated-δ-lactams via a tandem C-H activation and [4+2] annulation reaction. These products are readily derivatized to enantioenriched piperidines, the most common N-heterocycle found in FDA approved pharmaceuticals. Desired δ-lactams are achieved in yields as high as 99% and enantiomeric excess of 97% under aqueous conditions at room temperature. Embedding a Rh cyclopentadienyl (Cp*) catalyst in the active site of mSav results in improved stereocontrol and a 7-fold enhancement in reactivity relative to the isolated biotinylated Rh(III) cofactor. In addition, mSav-Rh outperforms its well-established tetrameric forms, displaying 11-33 times more reactivity.

Fluorine-18 Labeling of the HER2-Targeting Single-Domain Antibody 2Rs15d Using a Residualizing Label and Preclinical Evaluation.

PURPOSE: Our previous studies with F-18-labeled anti-HER2 single-domain antibodies (sdAbs) utilized 5F7, which binds to the same epitope on HER2 as trastuzumab, complicating its use for positron emission tomography (PET) imaging of patients undergoing trastuzumab therapy. On the other hand, sdAb 2Rs15d binds to a different epitope on HER2 and thus might be a preferable vector for imaging in these patients. The aim of this study was to evaluate the tumor targeting of F-18 -labeled 2Rs15d in HER2-expressing breast carcinoma cells and xenografts. PROCEDURES: sdAb 2Rs15d was labeled with the residualizing labels N-succinimidyl 3-((4-(4-[18F]fluorobutyl)-1H-1,2,3-triazol-1-yl)methyl)-5-(guanidinomethyl)benzoate ([18F]RL-I) and N-succinimidyl 4-guanidinomethyl-3-[125I]iodobenzoate ([125I]SGMIB), and the purity and HER2-specific binding affinity and immunoreactivity were assessed after labeling. The biodistribution of I-125- and F-18-labeled 2Rs15d was determined in SCID mice bearing subcutaneous BT474M1 xenografts. MicroPET/x-ray computed tomograph (CT) imaging of [18F]RL-I-2Rs15d was performed in this model and compared to that of nonspecific sdAb [18F]RL-I-R3B23. MicroPET/CT imaging was also done in an intracranial HER2-positive breast cancer brain metastasis model after administration of 2Rs15d-, 5F7-, and R3B23-[18F]RL-I conjugates. RESULTS: [18F]RL-I was conjugated to 2Rs15d in 40.8 ± 9.1 % yield and with a radiochemical purity of 97-100 %. Its immunoreactive fraction (IRF) and affinity for HER2-specific binding were 79.2 ± 5.4 % and 7.1 ± 0.4 nM, respectively. [125I]SGMIB was conjugated to 2Rs15d in 58.4 ± 8.2 % yield and with a radiochemical purity of 95-99 %; its IRF and affinity for HER2-specific binding were 79.0 ± 12.9 % and 4.5 ± 0.8 nM, respectively. Internalized radioactivity in BT474M1 cells in vitro for [18F]RL-I-2Rs15d was 43.7 ± 3.6, 36.5 ± 2.6, and 21.7 ± 1.2 % of initially bound radioactivity at 1, 2, and 4 h, respectively, and was similar to that seen for [125I]SGMIB-2Rs15d. Uptake of [18F]RL-I-2Rs15d in subcutaneous xenografts was 16-20 %ID/g over 1-3 h. Subcutaneous tumor could be clearly delineated by microPET/CT imaging with [18F]RL-I-2Rs15d but not with [18F]RL-I-R3B23. Intracranial breast cancer brain metastases could be visualized after intravenous administration of both [18F]RL-I-2Rs15d and [18F]RL-I-5F7. CONCLUSIONS: Although radiolabeled 2Rs15d conjugates exhibited lower tumor cell retention both in vitro and in vivo than that observed previously for 5F7, given that it binds to a different epitope on HER2 from those targeted by the clinically utilized HER2-targeted therapeutic antibodies trastuzumab and pertuzumab, F-18-labeled 2Rs15d has potential for assessing HER2 status by PET imaging after trastuzumab and/or pertuzumab therapy.

Minimalist Antibodies and Mimetics: An Update and Recent Applications.

The immune system utilizes antibodies to recognize foreign or disease-relevant receptors, initiating an immune response to destroy unwelcomed guests. Because researchers can evolve antibodies to bind virtually any target, it is perhaps unsurprising that these reagents, and their small-molecule conjugates, are used extensively in clinical and basic research environments. However, virtues of antibodies are countered by significant challenges. Foremost among these is the need for expression in mammalian cells (largely due to often necessary post-translational modifications). In response to these challenges, researchers have developed an array of minimalist antibodies and mimetics, which are smaller, more stable, simpler to express in Escherichia coli, and amendable to laboratory evolution and protein engineering. Here we describe these scaffolds and discuss recent applications of minimalist antibodies and mimetics.