Dual-Purpose Polymer Labels for Fluorescent and Mass Cytometric Affinity Bioassays

Hybrid Macromolecular Constructs as a Platform for Spectral Nanoprobes for Advanced Cellular Barcoding in Flow Cytometry

Herein, an advanced bioconjugation technique to synthesize hybrid polymer-antibody nanoprobes tailored for fluorescent cell barcoding in flow cytometry-based immunophenotyping of leukocytes is applied. A novel approach of attachment combining two fluorescent dyes on the copolymer precursor and its conjugation to antibody is employed to synthesize barcoded nanoprobes of antibody polymer dyes allowing up to six nanoprobes to be resolved in two-dimensional cytometry analysis. The major advantage of these nanoprobes is the construct design in which the selected antibody is labeled with an advanced copolymer bearing two types of fluorophores in different molar ratios. The cells after antibody recognition and binding to the target antigen have a characteristic double fluorescence signal for each nanoprobe providing a unique position on the dot plot, thus allowing antibody-based barcoding of cellular samples in flow cytometry assays. This technique is valuable for cellular assays that require low intersample variability and is demonstrated by the live cell barcoding of clinical samples with B cell abnormalities. In total, the samples from six various donors were successfully barcoded using only two detection channels. This barcoding of clinical samples enables sample preparation and measurement in a single tube.

Hybrid Fluorescent Mass-Tag Nanotrackers as Universal Reagents for Long-Term Live-Cell Barcoding

Barcoding and pooling cells for processing as a composite sample are critical to minimize technical variability in multiplex technologies. Fluorescent cell barcoding has been established as a standard method for multiplexing in flow cytometry analysis. In parallel, mass-tag barcoding is routinely used to label cells for mass cytometry. Barcode reagents currently used label intracellular proteins in fixed and permeabilized cells and, therefore, are not suitable for studies with live cells in long-term culture prior to analysis. In this study, we report the development of fluorescent palladium-based hybrid-tag nanotrackers to barcode live cells for flow and mass cytometry dual-modal readout. We describe the preparation, physicochemical characterization, efficiency of cell internalization, and durability of these nanotrackers in live cells cultured over time. In addition, we demonstrate their compatibility with standardized cytometry reagents and protocols. Finally, we validated these nanotrackers for drug response assays during a long-term coculture experiment with two barcoded cell lines. This method represents a new and widely applicable advance for fluorescent and mass-tag barcoding that is independent of protein expression levels and can be used to label cells before long-term drug studies.

Polymeric dipicolylamine based mass tags for mass cytometry

Mass cytometry is an emerging powerful bioanalytical technique for high-dimensional single-cell analysis. In this technique, cells are stained with metal-isotope-tagged antibodies and are analyzed by an inductively coupled plasma time-of-flight mass spectrometer. While there are more than 100 stable isotopes available in the m/z 75 to 209 detection range of the instrument, only about 50 parameters can be measured per cell because current reagents are metal-chelating polymers with pendant aminocarboxylate chelators that only bind hard metal ions such as the rare earths and Bi³⁺. Here we describe the synthesis and characterization of a new type of metal-chelating polymer with pendant dipicolylamine chelators suited to binding intermediate to soft metals such as rhenium and platinum. We introduce two different conjugation strategies, a thiol–maleimide reaction that works well for rhenium, and a DBCO-azide click reaction designed to avoid potential complications of Pt and other heavy metals interacting with thiol groups. We show that these polymers can serve as new elemental mass tags for mass cytometry. Antibody-polymer conjugates of CD20 and CD8a prepared by both coupling reactions were employed in conjunction with commercial metal-conjugated antibodies for multi-parameter single-cell immunoassays.

A new type of metal-chelating polymer with pendant dipicolylamine chelators that bind rhenium and platinum has been developed for mass cytometry applications.

Modular synthesis and modification of novel bifunctional dendrons

The modular synthesis of two generations of highly branched bifunctional dendrons is reported. The first generation dendron–antibody conjugate is shown to selectively detect CD4⁺ T cells in the PBMC culture.

Glycan-Directed Grafting-from Polymerization of Immunoglobulin G: Site-Selectively Modified IgG-Polymer Conjugates with Preserved Biological Activity

Antibody and related antibody drugs for the treatment of malignancies have led to progress in targeted cancer therapy. Preparation of diverse antibody conjugates is critical for preclinical and clinical applications. However, precise control in tagging molecules at specific locations on antibodies is essential to preserve their native function. In this study, a synthetic boronic acid (BA)-tosyl initiator was used to trigger a glycan-directed modification of IgGs, and the obtained IgG macroinitiators allowed a growth of the poly N-isopropylacrylamide (PNIPAAm) chains specifically at Fc-domains. Therefore, the PNIPAAm chains are located away from the critical antigen-binding domains (Fab), which could reasonably prevent the loss of biological activity after the attachment of polymer chains. According to the proposed strategy, a site-selectively modified anticoncanavalin A (Con A) antibody-PNIPAAm conjugate showed 6-times higher efficiency in the binding of targeted Con A antigen to a randomly conjugated anti-Con A antibody-PNIPAAm conjugate. In this study, we developed the first chemical strategy for the site-specific preparation of IgG-polymer conjugates with conserved biological activity as well as intact glycan structures.

Clickable and High-Sensitivity Metal-Containing Tags for Mass Cytometry

Mass cytometry is a highly multiplexed single-cell analysis platform that uses metal-tagged reagents to identify multiple cellular biomarkers. The current metal-tagged reagent preparation employs thiol-maleimide chemistry to covalently couple maleimide-functionalized metal-chelating polymers (MCPs) with antibodies (Abs), a process that requires partial reduction of the Ab to form reactive thiol groups. However, some classes of Abs (for example, IgM) as well as biomolecules lacking cysteine residues have been challenging to label using this method. This inherent limitation led us to develop a new conjugation strategy for labeling a wide range of biomolecules and affinity reagents. In this report, we present a metal tagging approach using a new class of azide- or transcyclooctene-terminated MCPs with copper(I)-free strain-promoted alkyne-azide cycloaddition or tetrazine-alkene click chemistry reactions, in which biomolecules with -NH₂ functional groups are selectively activated with a dibenzocyclooctyne or tetrazine moiety, respectively. This approach enabled us to generate highly sensitive and specific metal-tagged IgGs, IgMs, small peptides, and lectins for applications in immunophenotyping and glycobiology. We also created dual-tagged reagents for simultaneous detection of markers by immunofluorescence, mass cytometry, and imaging mass cytometry using a two-step conjugation process. The Helios mass cytometer was used to test the functionality of reagents on suspension human leukemia cell lines and primary cells. The dual-tagged Abs, metal-tagged lectins, and phalloidin staining reagent were used to visualize target proteins and glycans on adherent cell lines and frozen/FFPE tissue sections using the Hyperion Imaging System. In some instances, reagents produced by click conjugation showed superior sensitivity and specificity compared to those of reagents produced by thiol-maleimide chemistry. In general, the click chemistry-based conjugation with new MCPs could be instrumental in developing a wide range of highly sensitive metal-containing reagents for proteomics and glycomics applications.

Labeling of native proteins with fluorescent RAFT polymer probes: application to the detection of a cell surface protein using flow cytometry

Fluorescent RAFT polymer probes with an activated ester reactive end-group can be advantageously used to label native proteins.

Pre-clinical Evaluation of a Cyanine-Based SPECT Probe for Multimodal Tumor Necrosis Imaging

PURPOSE

Recently we showed that a number of carboxylated near-infrared fluorescent (NIRF) cyanine dyes possess strong necrosis avid properties in vitro as well as in different mouse models of spontaneous and therapy-induced tumor necrosis, indicating their potential use for cancer diagnostic- and prognostic purposes. In the previous study, the detection of the cyanines was achieved by whole body optical imaging, a technique that, due to the limited penetration of near-infrared light, is not suitable for investigations deeper than 1 cm within the human body. Therefore, in order to facilitate clinical translation, the purpose of the present study was to generate a necrosis avid cyanine-based NIRF probe that could also be used for single photon emission computed tomography (SPECT). For this, the necrosis avid NIRF cyanine HQ4 was radiolabeled with ¹¹¹indium, via the chelate diethylene triamine pentaacetic acid (DTPA).

PROCEDURES

The necrosis avid properties of the radiotracer [¹¹¹In]DTPA-HQ4 were examined in vitro and in vivo in different breast tumor models in mice using SPECT and optical imaging. Moreover, biodistribution studies were performed to examine the pharmacokinetics of the probe in vivo.

RESULTS

Using optical imaging and radioactivity measurements, in vitro, we showed selective accumulation of [¹¹¹In]DTPA-HQ4 in dead cells. Using SPECT and in biodistribution studies, the necrosis avidity of the radiotracer was confirmed in a 4T1 mouse breast cancer model of spontaneous tumor necrosis and in a MCF-7 human breast cancer model of chemotherapy-induced tumor necrosis.

CONCLUSIONS

The radiotracer [¹¹¹In]DTPA-HQ4 possessed strong and selective necrosis avidity in vitro and in various mouse models of tumor necrosis in vivo, indicating its potential to be clinically applied for diagnostic purposes and to monitor anti-cancer treatment efficacy.

Lanthanide-Coordinated Semiconducting Polymer Dots Used for Flow Cytometry and Mass Cytometry

Simultaneous monitoring of biomarkers as well as single-cell analyses based on flow cytometry and mass cytometry are important for investigations of disease mechanisms, drug discovery, and signaling-network studies. Flow cytometry and mass cytometry are complementary to each other; however, probes that can satisfy all the requirements for these two advanced technologies are limited. In this study, we report a probe of lanthanide-coordinated semiconducting polymer dots (Pdots), which possess fluorescence and mass signals. We demonstrated the usage of this dual-functionality probe for both flow cytometry and mass cytometry in a mimetic cell mixture and human peripheral blood mononuclear cells as model systems. The probes not only offer high fluorescence signal for use in flow cytometry, but also show better performance in mass cytometry than the commercially available counterparts.

Site-selective in situ growth of fluorescent polymer-antibody conjugates with enhanced antigen detection by signal amplification

This paper reports a new and general in situ methodology to grow fluorescent polymer conjugates from the interchain disulfide bridging sites of a monoclonal antibody. Atom transfer radical polymerization (ATRP) initiators were attached to a monoclonal antibody at its interchain disulfide bridging sites by disulfide re-bridging to yield a macroinitiator. Subsequent in situ ATRP of PEG-like monomers with dye-functionalized monomers from the macroinitiator formed antibody-polymer-dye conjugates with site-selectivity and tunable dye-to-antibody ratios. Notably, these conjugates can amplify antigen detection signal by reducing label-density dependent fluorescence quenching and by increasing dye-to-antibody ratios. The method developed may be applicable to a variety of antibodies, dyes and drugs to create a number of antibody-polymer-dye/drug conjugates for advanced diagnosis and therapy of diseases.

Polarity-tunable and wavelength-tunable bacteriochlorins bearing a single carboxylic acid or NHS ester. Use in a protein bioconjugation model system

10 new near-infrared absorbing bacteriochlorins (soluble in aqueous or membranous media) are equipped for protein bioconjugation.