Jered B. Haun

Magnetic nanoparticle biosensors

One of the major challenges in medicine is the rapid and accurate measurement of protein biomarkers, cells, and pathogens in biological samples. A number of new diagnostic platforms have recently been developed to measure biomolecules and cells with high sensitivity that could enable early disease detection or provide valuable insights into biology at the systems level. Most biological samples exhibit negligible magnetic susceptibility; therefore, magnetic nanoparticles have been used for diverse applications including biosensing, magnetic separation, and thermal ablation therapy. This review focuses on the use of magnetic nanoparticles for detection of biomolecules and cells based on magnetic resonance effects using a general detection platform termed diagnostic magnetic resonance (DMR). DMR technology encompasses numerous assay configurations and sensing principles, and to date magnetic nanoparticle biosensors have been designed to detect a wide range of targets including DNA/mRNA, proteins, enzymes, drugs, pathogens, and tumor cells. The core principle behind DMR is the use of magnetic nanoparticles as proximity sensors that modulate the spin-spin relaxation time of neighboring water molecules, which can be quantified using clinical MRI scanners or benchtop nuclear magnetic resonance (NMR) relaxometers. Recently, the capabilities of DMR technology were advanced considerably with the development of miniaturized, chip-based NMR (microNMR) detector systems that are capable of performing highly sensitive measurements on microliter sample volumes and in multiplexed format. With these and future advances in mind, DMR biosensor technology holds considerable promise to provide a high-throughput, low-cost, and portable platform for large scale molecular and cellular screening in clinical and point-of-care settings.

Fast and Sensitive Pretargeted Labeling of Cancer Cells through a Tetrazine/trans-Cyclooctene Cycloaddition†

There is considerable interest in the use of bioorthogonal covalent chemistry such as “click” chemistries to label small molecules located on live or fixed cells.[1] Such labeling has been used for the visualization of glycans, activity based protein profiling, site-specific tagging of proteins, detection of DNA and RNA synthesis, revealing the fate of small molecules in plants, and detection of post-translational modification in proteins.[2-4] Most reported applications rely on either the copper catalyzed azide-alkyne cycloaddition, which is limited to in vitro application due to the cytotoxicity of copper, or the elegant strain-promoted azide-alkyne cycloaddition, which permits live cell and in vivo application use but is hindered by relatively slow kinetics and often difficult synthesis of cyclooctyne derivatives.[4-5] New bioorthogonal reactions that do not require catalyst and show rapid kinetics are therefore of interest for different molecular imaging applications at the cellular level. In this report we demonstrate the use of inverse electron demand Diels-Alder cycloaddition between a serum stable 1,2,4,5 tetrazine and a highly strained trans-cyclooctene to covalently label live cells. This chemistry has been applied to the pretargeted labeling of Cetuximab (Erbitux) tagged epidermal growth factor receptor (EGFR) on A549 cancer cells. We find that the tetrazine cycloaddition to trans-cyclooctene labeled cells is fast and can be amplified by increasing the loading of dienophile on the antibody. This results in a highly sensitive targeting strategy that can be used to label proteins using nanomolar concentrations of a secondary agent for short durations of time.

Bioorthogonal chemistry amplifies nanoparticle binding and enhances the sensitivity of cell detection

Nanoparticles have emerged as key materials for biomedical applications because of their unique and tunable physical properties, multivalent targeting capability, and high cargo capacity. Motivated by these properties and by current clinical needs, numerous diagnostic and therapeutic nanomaterials have recently emerged. Here we describe a novel nanoparticle targeting platform that uses a rapid, catalyst-free cycloaddition as the coupling mechanism. Antibodies against biomarkers of interest were modified with trans-cyclooctene and used as scaffolds to couple tetrazine-modified nanoparticles onto live cells. We show that the technique is fast, chemoselective, adaptable to metal nanomaterials, and scalable for biomedical use. This method also supports amplification of biomarker signals, making it superior to alternative targeting techniques including avidin/biotin.

Micro-NMR for Rapid Molecular Analysis of Human Tumor Samples

A portable micro-NMR device enables rapid molecular diagnosis from scarce cancer cells in fine-needle aspirates from human tumors. A Micro-NMR Smart Phone for Detecting Cancer Smart phones may have provided millions of people with hours of mindless entertainment, but their real value may lie in the hands of clinicians at the patient’s bedside. Accurate diagnosis and staging of tumors through analysis of core biopsies is essential for ensuring that patients receive rapid treatment with the most appropriate cancer drugs. However, current techniques for analyzing tumor biopsies such as immunohistochemistry and flow cytometry are costly and time-consuming and require more tissue than biopsies often contain, necessitating that patients be subjected to repeat biopsies. Enter Weissleder and his team with their portable micro-NMR (nuclear magnetic resonance) device operated by smart phone technology that enables accurate diagnosis of malignant tumors from the scarce cancer cells present in fine-needle aspirate biopsies. Weissleder’s micro-NMR system uses nanoparticle-based magnetic affinity ligands to detect expression of protein markers that are associated with cancer. First, the investigators looked at the expression of nine protein markers in fine-needle aspirates taken from suspected malignant abdominal lesions in a cohort of 50 patients. Using detection of their nine-marker signature by micro-NMR, they correctly identified 44 patients as having malignant tumors, with verification of the diagnoses by standard techniques such as core biopsy, imaging, and clinical assessment. Using a four-protein marker signature (MUC-1, HER2, epidermal growth factor receptor, and EpCAM), Weissleder and his team were able to increase the diagnostic accuracy of their micro-NMR system still further to 96%. This exceeded the 84% accuracy of immunohistochemistry, a gold standard of cancer diagnosis, and was much faster, providing a diagnosis within 1 hour instead of 3 days. To validate their findings, the investigators tested their four-protein marker signature in another 20 patients with suspected abdominal malignancies and this time obtained a 100% accurate diagnosis. The micro-NMR cancer diagnostic system has the advantages of speed and accuracy, but the authors do point out several caveats. They discovered that protein marker expression is heterogeneous within and between tumors and varies depending on the location of the final needle aspirate site. They also point out that because of rapid protein degradation even at 4°C, the biopsies either should be analyzed immediately or should be carefully preserved. Despite these caveats, this portable micro-NMR device, which is easy to operate with smart phone technology, could improve the speed and accuracy of cancer diagnosis, leading to earlier and more effective treatments for cancer patients. Although tumor cells obtained from human patients by image-guided intervention are a valuable source for diagnosing cancer, conventional means of analysis are limited. Here, we report the development of a quantitative micro-NMR (nuclear magnetic resonance) system for rapid, multiplexed analysis of human tumors. We implemented the technology in a clinical setting to analyze cells obtained by fine-needle aspirates from suspected lesions in 50 patients and validated the results in an independent cohort of another 20 patients. Single fine-needle aspirates yielded sufficient numbers of cells to enable quantification of multiple protein markers in all patients within 60 min. Moreover, using a four-protein signature, we report a 96% accuracy for establishing a cancer diagnosis, surpassing conventional clinical analyses by immunohistochemistry. Our results also show that protein expression patterns decay with time, underscoring the need for rapid sampling and diagnosis close to the patient bedside. We also observed a surprising degree of heterogeneity in protein expression both across the different patient samples and even within the same tumor, which has important implications for molecular diagnostics and therapeutic drug targeting. Our quantitative point-of-care micro-NMR technique shows potential for cancer diagnosis in the clinic.

Quantifying nanoparticle adhesion mediated by specific molecular interactions.

Receptor-mediated targeting of nanometric contrast agents or drug carriers holds great potential for treating cardiovascular and vascular-associated diseases. However, predicting the ability of these vectors to adhere to diseased cells under dynamic conditions is complex due to the interplay of transport, hydrodynamic force, and multivalent bond formation dynamics. Therefore, we sought to determine the effects of adhesion molecule density and flow rate on adhesion of 210 nm particles, with the goal of identifying criteria to optimize binding efficiency and selectivity. Our system employed a physiologically relevant ligand, the vascular adhesion molecule ICAM-1, and an ICAM-1 specific antibody tethered to the nanoparticle using avidin-biotin chemistry. We measured binding and dissociation of these particles in a flow chamber as a function of antibody density, ligand density, and flow rate, and using a transport-reaction model we distilled overall kinetic rate constants for adhesion and detachment from the binding data. We demonstrate that both attachment and detachment of 210 nm particles can be correlated with receptor and ligand valency and are minimally affected by shear rate. Furthermore, we uncovered a time-dependent mechanism governing particle detachment, in which the rate of detachment decreases with contact time according to a power law. Finally, we use our results to illustrate how to engineer adhesion selectivity for specific molecular targeting applications. These results establish basic principles dictating nanoparticle adhesion and dissociation and can be used as a framework for the rational design of targeted nanoparticle therapeutics that possess optimum adhesive characteristics.

Probing intracellular biomarkers and mediators of cell activation using nanosensors and bioorthogonal chemistry.

Nanomaterials offer unique physical properties that make them ideal biosensors for scant cell populations. However, specific targeting of nanoparticles to intracellular proteins has been challenging. Here, we describe a technique to improve intracellular biomarker sensing using nanoparticles that is based on bioorthogonal chemistry. Using trans-cyclooctene-modified affinity ligands that are administered to semipermeabilized cells and revealed by cycloaddition reaction with tetrazine-conjugated nanoparticles, we demonstrate site-specific amplification of nanomaterial binding. We also show that this technique is capable of sensing protein biomarkers and phosho-protein signal mediators, both within the cytosol and nucleus, via magnetic or fluorescent modalities. We expect the described method will have broad applications in nanomaterial-based diagnostics and therapeutics.

Tunable leuko-polymersomes that adhere specifically to inflammatory markers.

The polymersome, a fully synthetic cell mimetic, is a tunable platform for drug delivery vehicles to detect and treat disease (theranostics). Here, we design a leuko-polymersome, a polymersome with the adhesive properties of leukocytes, which can effectively bind to inflammatory sites under flow. We hypothesize that optimal leukocyte adhesion can be recreated with ligands that mimic receptors of the two major leukocyte molecular adhesion pathways, the selectins and the integrins. Polymersomes functionalized with sialyl Lewis X and an antibody against ICAM-1 adhere avidly and selectively to surfaces coated with inflammatory adhesion molecules P-selectin and ICAM-1 under flow. We find that maximal adhesion occurs at intermediate densities of both sialyl Lewis X and anti-ICAM-1, owing to synergistic binding effects between the two ligands. Leuko-polymersomes bearing these two receptor mimetics adhere under physiological shear rates to inflamed endothelium in an in vitro flow chamber at a rate 7.5 times higher than those to uninflamed endothelium. This work clearly demonstrates that polymersomes bearing only a single ligand bind less avidly and with lower selectivity, thus suggesting proper mimicry of leukocyte adhesion requires contributions from both pathways. This work establishes a basis for the design of polymersomes for targeted drug delivery in inflammation.

Carboxymethylated Polyvinyl Alcohol Stabilizes Doped Ferrofluids for Biological Applications

[∗] Dr. M. Liong , H. Shao , Dr. J. B. Haun , Dr. H. Lee , Prof. R. Weissleder Center for Systems Biology Massachusetts General Hospital and Harvard Medical School 185 Cambridge Street, Boston, Massachusetts, 02114 (USA) E-mail: hlee@mgh.harvard.edu ; rweissleder@mgh.harvard.edu Prof. R. Weissleder Department of Systems Biology Harvard Medical School 200 Longwood Avenue, Boston, Massachusetts, 02115 (USA)

Enhancing Reactivity for Bioorthogonal Pretargeting by Unmasking Antibody Conjugated trans-Cyclooctenes

The bioorthogonal cycloaddition reaction between tetrazine and trans-cyclooctene (TCO) is rapidly growing in use for molecular imaging and cell-based diagnostics. We have surprisingly uncovered that the majority of TCOs conjugated to monoclonal antibodies using standard amine-coupling procedures are nonreactive. We show that antibody-bound TCOs are not inactivated by trans-cis isomerization and that the bulky cycloaddition reaction is not sterically hindered. Instead, TCOs are likely masked by hydrophobic interactions with the antibody. We show that introducing TCO via hydrophilic poly(ethylene glycol) (PEG) linkers can fully preserve reactivity, resulting in >5-fold enhancement in functional density without affecting antibody binding. This is accomplished using a novel dual bioorthogonal approach in which heterobifunctional dibenzylcyclooctyne (DBCO)-PEG-TCO molecules are reacted with azido-antibodies. Improved imaging capabilities are demonstrated for different cancer biomarkers using tetrazine-modified fluorophore and quantum dot probes. We believe that the PEG linkers prevent TCOs from burying within the antibody during conjugation, which could be relevant to other bioorthogonal tags and biomolecules. We expect the improved TCO reactivity obtained using the reported methods will significantly advance bioorthogonal pretargeting applications.

Molecular Detection of Biomarkers and Cells Using Magnetic Nanoparticles and Diagnostic Magnetic Resonance

The rapid and sensitive detection of molecular targets such as proteins, cells, and pathogens in biological specimens is a major focus of ongoing medical research, as it could promote early disease diagnoses and the development of tailored therapeutic strategies. Magnetic nanoparticles (MNP) are attractive candidates for molecular biosensing applications because most biological samples exhibit negligible magnetic susceptibility, and thus the background against which measurements are made is extremely low. Numerous magnetic detection methods exist, but sensing based on magnetic resonance effects has successfully been developed into a general detection platform termed diagnostic magnetic resonance (DMR). DMR technology encompasses numerous assay configurations and sensing principles, and to date magnetic nanoparticle biosensors have been designed to detect a wide range of targets including DNA/mRNA, proteins, enzymes, drugs, pathogens, and tumor cells with exquisite sensitivity. The core principle behind DMR is the use of MNP as proximity sensors that modulate the transverse relaxation time of neighboring water molecules. This signal can be quantified using MR imagers or NMR relaxometers, including miniaturized NMR detector chips that are capable of performing highly sensitive measurements on microliter sample volumes and in a multiplexed format. The speed, sensitivity, and simplicity of the DMR principle, coupled with further advances in NMR biosensor technology should provide a high-throughput, low-cost, and portable platform for large-scale parallel sensing in clinical and point-of-care settings.