A homogeneous fluorescence-based method to measure antibody internalization in tumor cells

Towards targeted Cas9 (CRISPR-Cas) delivery: Preparation of IgG antibody-Cas9 conjugates using a split intein

The CRISPR-Cas9 system has revolutionized the field of genetic engineering, but targeted cellular delivery remains a central problem. The delivery of the preformed ribonuclease-protein (RNP) complex has the advantages of fewer side effects and avoidance of potential permanent effects. We reasoned that an internalizing IgG antibody as a targeting device could address the delivery of Cas9-RNP. We opted for protein trans-splicing mediated by a split intein to facilitate posttranslational conjugation of the two large protein entities. We recently described the cysteine-less CL split intein that efficiently performs under oxidizing conditions and does not interfere with disulfide bonds or thiol bioconjugation chemistries. Using the CL split intein, we report for the first time the ligation of monoclonal IgG antibody precursors, expressed in mammalian cells, and a Cas9 precursor, obtained from bacterial expression. A purified IgG-Cas9 conjugate was loaded with sgRNA to form the active RNP complex and introduced a double-strand break in its target DNA in vitro. Furthermore, a synthetic peptide variant of the short N-terminal split intein precursor proved useful for chemical modification of Cas9. The split intein ligation procedure reported here for IgG-Cas9 provides the first step towards a novel CRISPR-Cas9 targeting approach involving the preformed RNP complex.

Targeting cancer with mRNA-lipid nanoparticles: key considerations and future prospects

Harnessing mRNA-lipid nanoparticles (LNPs) to treat patients with cancer has been an ongoing research area that started before these versatile nanoparticles were successfully used as COVID-19 vaccines. Currently, efforts are underway to harness this platform for oncology therapeutics, mainly focusing on cancer vaccines targeting multiple neoantigens or direct intratumoural injections of mRNA-LNPs encoding pro-inflammatory cytokines. In this Review, we describe the opportunities of using mRNA-LNPs in oncology applications and discuss the challenges for successfully translating the findings of preclinical studies of these nanoparticles into the clinic. We critically appraise the potential of various mRNA-LNP targeting and delivery strategies, considering physiological, technological and manufacturing challenges. We explore these approaches in the context of the potential clinical applications best suited to each approach and highlight the obstacles that currently need to be addressed to achieve these applications. Finally, we provide insights from preclinical and clinical studies that are leading to this powerful platform being considered the next frontier in oncology treatment.

Multiplexed non-invasive tumor imaging of glucose metabolism and receptor-ligand engagement using dark quencher FRET acceptor

Rationale: Following an ever-increased focus on personalized medicine, there is a continuing need to develop preclinical molecular imaging modalities to guide the development and optimization of targeted therapies. Near-Infrared (NIR) Macroscopic Fluorescence Lifetime Förster Resonance Energy Transfer (MFLI-FRET) imaging offers a unique method to robustly quantify receptor-ligand engagement in live intact animals, which is critical to assess the delivery efficacy of therapeutics. However, to date, non-invasive imaging approaches that can simultaneously measure cellular drug delivery efficacy and metabolic response are lacking. A major challenge for the implementation of concurrent optical and MFLI-FRET in vivo whole-body preclinical imaging is the spectral crowding and cross-contamination between fluorescent probes. Methods: We report on a strategy that relies on a dark quencher enabling simultaneous assessment of receptor-ligand engagement and tumor metabolism in intact live mice. Several optical imaging approaches, such as in vitro NIR FLI microscopy (FLIM) and in vivo wide-field MFLI, were used to validate a novel donor-dark quencher FRET pair. IRDye 800CW 2-deoxyglucose (2-DG) imaging was multiplexed with MFLI-FRET of NIR-labeled transferrin FRET pair (Tf-AF700/Tf-QC-1) to monitor tumor metabolism and probe uptake in breast tumor xenografts in intact live nude mice. Immunohistochemistry was used to validate in vivo imaging results. Results: First, we establish that IRDye QC-1 (QC-1) is an effective NIR dark acceptor for the FRET-induced quenching of donor Alexa Fluor 700 (AF700). Second, we report on simultaneous in vivo imaging of the metabolic probe 2-DG and MFLI-FRET imaging of Tf-AF700/Tf-QC-1 uptake in tumors. Such multiplexed imaging revealed an inverse relationship between 2-DG uptake and Tf intracellular delivery, suggesting that 2-DG signal may predict the efficacy of intracellular targeted delivery. Conclusions: Overall, our methodology enables for the first time simultaneous non-invasive monitoring of intracellular drug delivery and metabolic response in preclinical studies.

Multifaceted characterization of recombinant protein-based vaccines: An immunochemical toolbox for epitope-specific analyses of the hepatitis E vaccine

The integrity of functional epitopes is a critical quality attribute for recombinant protein based vaccines since the presence of these native-like epitopes is the structural basis for vaccines to elicit functional antibodies. To demonstrate the quality and quantity of functional epitopes on vaccine antigens, a toolbox of assessing antigen characteristics is essential. Among the physicochemical, biophysical, immunochemical and in vivo potency analyses, the epitope-specific assays are most critical assessment of the antigen functionality. In this study, we used hepatitis E virus vaccine as an example to illustrated how the monoclonal antibody (mAb) based immunochemical assays were established for in-depth and multifaceted antigen characterization. A large panel of mAbs were developed and characterized using epitope clustering analysis. A subset of these mAbs recognizing non-overlapping epitopes were chosen to be used for assay development. Orthogonal methods, including surface plasma resonance-based BIAcore, solution competitive ELISA and sandwich ELISA, were developed for the antigenicity assessment. The sandwich ELISA with a pair of mAbs, recognizing two different epitopes, was used to assess the accelerated antigen stability, showing enhanced stability with adjuvant adsorption. Such a sandwich ELISA with robust performance has the potentials to be used for in vitro potency analysis to replace animal-based potency assay as product release test. In summary, using hepatitis E vaccine as an example, we demonstrated the importance and establishment of a mAb-based immunochemical toolbox for multifaceted antigen characterization. This is particularly important to demonstrate the successful reconstruction of the native-like and functional epitopes on a recombinant antigen post expression and purification. These epitope-specific and multifaceted assays serve as critical tools for process monitoring or lot consistency tests in support of vaccine development and manufacturing.

Functional evaluation of fluorescein-labeled derivatives of a peptide inhibitor of the EGF receptor dimerization

A cyclic decapeptide (1, ), which acts on the extracellular region of the EGF receptor, preventing it from dimerizing, has been developed. Peptide 2, which was labeled with fluorescein at the N-terminus of peptide 1, was synthesized based on structure-activity relationship studies. Peptide 2 essentially retained the inhibitory activity of peptide 1 against the receptor autophosphorylation. Confocal microscopy studies revealed that in carcinoma cells, the fluorescence of peptide 2 was localized inside some vesicles. Treatment of intact cells by peptide 1 in combination with peptide 2 decreased the fluorescence intensity significantly compared to treatment with only peptide 2. These results indicate that peptide 2 competes with peptide 1 for binding to the cellular surface. Six derivatives of peptide 2, in which constituent amino acids, with the exception of two cysteines and proline were randomized, were synthesized and used to treat the cells. Peptides 6 and 9 showed the highest fluorescence intensity in cells. From the results of the EGF receptor autophosphorylation assay, these two derivatives were proven to have higher inhibitory activity than peptide 2, which would therefore be a useful delivery peptide and fluorescent probe to find new inhibitors against the EGF receptor. Peptides 6 and 9 are promising leads for EGF receptor inhibitors.

Bright Fluorescent Nanotags from Bottlebrush Polymers with DNA-Tipped Bristles

Bright signal outputs are needed for fluorescence detection of biomolecules at their native expression levels. Increasing the number of labels on a probe often results in crowding-induced self-quenching of chromophores, and maintaining the function of the targeting moiety (e.g., an antibody) is a concern. Here we demonstrate a simple method to accommodate thousands of fluorescent dye molecules on a single antibody probe while avoiding the negative effects of self-quenching. We use a bottlebrush polymer from which extend hundreds of duplex DNA strands that can accommodate hundreds of covalently attached and/or thousands of noncovalently intercalated fluorescent dyes. This polymer-DNA assembly sequesters the intercalated fluorophores against dissociation and can be tethered through DNA hybridization to an IgG antibody. The resulting fluorescent nanotag can detect protein targets in flow cytometry, confocal fluorescence microscopy, and dot blots with an exceptionally bright signal that compares favorably to commercially available antibodies labeled with organic dyes or quantum dots.