Optimized Enzyme-Linked Immunosorbent Assay for Anti-PEG Antibody Detection in Healthy Donors and Patients Treated with PEGylated Liposomal Doxorubicin.

There is considerable interest in quantifying anti-PEG antibodies, given their potential involvement in accelerated clearance, complement activation, neutralization, and acute reactions associated with drug delivery systems. Published and commercially available anti-PEG enzyme-linked immunosorbent assays (ELISAs) differ significantly in terms of reagents and conditions, which could be confusing to users who want to perform in-house measurements. Here, we optimize the ELISA protocol for specific detection of anti-PEG IgG and IgM in sera from healthy donors and in plasma from cancer patients administered with PEGylated liposomal doxorubicin. The criterion of specificity is the ability of free PEG or PEGylated liposomes to inhibit the ELISA signals. We found that coating high-binding plates with monoamine methoxy-PEG5000, as opposed to bovine serum albumin-PEG20000, and blocking with 1% milk, as opposed to albumin or lysozyme, significantly improve the specificity, with over 95% of the signal being blocked by competition. Despite inherent between-assay variability, setting the cutoff value of the optical density at the 80th percentile consistently identified the same subjects. Using the optimized assay, we longitudinally measured levels of anti-PEG IgG/IgM in cancer patients before and after the PEGylated liposomal doxorubicin chemotherapy cycle (1 month apart, three cycles total). Antibody titers did not show any increase but rather a decrease between treatment cycles, and up to 90% of antibodies was bound to the infused drug. This report is a step toward harmonizing anti-PEG assays in human subjects, emphasizing the cost-effectiveness and optimized specificity.

Inhibition of acute complement responses towards bolus-injected nanoparticles using targeted short-circulating regulatory proteins.

Effective inhibition of the complement system is needed to prevent the accelerated clearance of nanomaterials by complement cascade and inflammatory responses. Here we show that a fusion construct consisting of human complement receptor 2 (CR2) (which recognizes nanosurface-deposited complement 3 (C3)) and complement receptor 1 (CR1) (which blocks C3 convertases) inhibits complement activation with picomolar to low nanomolar efficacy on many types of nanomaterial. We demonstrate that only a small percentage of nanoparticles are randomly opsonized with C3 both in vitro and in vivo, and CR2-CR1 immediately homes in on this subpopulation. Despite rapid in vivo clearance, the co-injection of CR2-CR1 in rats, or its mouse orthologue CR2-Crry in mice, with superparamagnetic iron oxide nanoparticles nearly completely blocks complement opsonization and unwanted granulocyte/monocyte uptake. Furthermore, the inhibitor completely prevents lethargy caused by bolus-injected nanoparticles, without inducing long-lasting complement suppression. These findings suggest the potential of the targeted complement regulators for clinical evaluation.

Molecular basis of conformational changes and mechanics of integrins.

Integrin, as a mechanotransducer, establishes the mechanical reciprocity between the extracellular matrix (ECM) and cells at integrin-mediated adhesion sites. This study used steered molecular dynamics (SMD) simulations to investigate the mechanical responses of integrin αvß3 with and without 10th type III fibronectin (FnIII10) binding for tensile, bending and torsional loading conditions. The ligand-binding integrin confirmed the integrin activation during equilibration and altered the integrin dynamics by changing the interface interaction between ß-tail, hybrid and epidermal growth factor domains during initial tensile loading. The tensile deformation in integrin molecules indicated that fibronectin ligand binding modulates its mechanical responses in the folded and unfolded conformation states. The bending deformation responses of extended integrin models reveal the change in behaviour of integrin molecules in the presence of Mn2+ ion and ligand based on the application of force in the folding and unfolding directions of integrin. Furthermore, these SMD simulation results were used to predict the mechanical properties of integrin underlying the mechanism of integrin-based adhesion. The evaluation of integrin mechanics provides new insights into understanding the mechanotransmission (force transmission) between cells and ECM and contributes to developing an accurate model for integrin-mediated adhesion. This article is part of a discussion meeting issue 'Supercomputing simulations of advanced materials'.

Promotion of Protein Solubility and Reduction in Stiffness in Human Lenses by Aggrelyte-1: Implications for Reversing Presbyopia.

With aging, human lenses lose the ability to focus on nearby objects due to decreases in accommodative ability, a condition known as presbyopia. An increase in stiffness or decrease in lens elasticity due to protein aggregation and insolubilization are the primary reasons for presbyopia. In this study, we tested aggrelyte-1 (S,N-diacetyl glutathione diethyl ester) for its ability to promote protein solubility and decrease the stiffness of lenses through its dual property of lysine acetylation and disulfide reduction. Treatment of water-insoluble proteins from aged human lenses (58-75 years) with aggrelyte-1 significantly increased the solubility of those proteins. A control compound that did not contain the S-acetyl group (aggrelyte-1C) was substantially less efficient in solubilizing water-insoluble proteins. Aggrelyte-1-treated solubilized protein had significant amounts of acetyllysine, as measured by Western blotting and LC-MS/MS. Aggrelytes increased the protein-free thiol content in the solubilized protein. Aged mouse (7 months) and human (44-66 years) lenses treated with aggrelyte-1 showed reduced stiffness accompanied by higher free thiol and acetyllysine levels compared with those treated with aggrelyte-1C or untreated controls. Our results suggested that aggrelyte-1 reduced lens stiffness through acetylation followed by disulfide reduction. This proof-of-concept study paves the way for developing aggrelyte-1 and related compounds to reverse presbyopia.

Aggrelyte-2 promotes protein solubility and decreases lens stiffness through lysine acetylation and disulfide reduction: Implications for treating presbyopia.

Aging proteins in the lens become increasingly aggregated and insoluble, contributing to presbyopia. In this study, we investigated the ability of aggrelyte-2 (N,S-diacetyl-L-cysteine methyl ester) to reverse the water insolubility of aged human lens proteins and to decrease stiffness in cultured human and mouse lenses. Water-insoluble proteins (WI) of aged human lenses (65-75 years) were incubated with aggrelyte-2 (500 µM) for 24 or 48 h. A control compound that lacked the S-acetyl group (aggrelyte-2C) was also tested. We observed 19%-30% solubility of WI upon treatment with aggrelyte-2. Aggrelyte-2C also increased protein solubility, but its effect was approximately 1.4-fold lower than that of aggrelyte-2. The protein thiol contents were 1.9- to 4.9-fold higher in the aggrelyte-2- and aggrelyte-2C-treated samples than in the untreated samples. The LC-MS/MS results showed Nε -acetyllysine (AcK) levels of 1.5 to 2.1 nmol/mg protein and 0.6 to 0.9 nmol/mg protein in the aggrelyte-2- and aggrelyte-2C-treated samples. Mouse (C57BL/6J) lenses (incubated for 24 h) and human lenses (incubated for 72 h) with 1.0 mM aggrelyte-2 showed significant decreases in stiffness with simultaneous increases in soluble proteins (human lenses) and protein-AcK levels, and such changes were not observed in aggrelyte-2C-treated lenses. Mass spectrometry of the solubilized protein revealed AcK in all crystallins, but more was observed in α-crystallins. These results suggest that aggrelyte-2 increases protein solubility and decreases lens stiffness through acetylation and disulfide reduction. Aggrelyte-2 might be useful in treating presbyopia in humans.

Topical ocular application of aggrelyte-2A reduces lens stiffness in mice.

Presbyopia is the progressive loss of the ability of the lens to focus on nearby objects due to its increased stiffness. It occurs in the mid-40s and continues to worsen until the mid-60s. The age-associated increase in protein cross-linking in the lens leads to protein aggregation and water insolubility, especially in the nuclear region, contributing to lens stiffness. This study reports the development of aggrelyte-2A (methyl S-acetyl-N-(3,3-dimethylbutanoyl) cysteinate, a derivative of our previously reported aggrelyte-2) for reversing the stiffness of aged lenses. Aggrelyte-2A showed minimal toxicity in cultured mouse lens epithelial cells (up to 2000 µM) and human lens epithelial cells (up to 250 µM). Lenses from aged mice (age: 24-25 months) treated with 1 mM aggrelyte-2A for 24 h, and human lenses (age: 47-67 years) treated with 250 µM aggrelyte-2A for 48 h showed 11-14% reductions in stiffness, accompanied by an increase in acetyllysine in lens proteins, and free-thiols in the lens. Topical application of aggrelyte-2A (40 mM, 5 µl twice daily for 4 weeks) on mouse eyes significantly reduced lens stiffness. The topical application showed no toxicity to the lens, cornea, or retina, as revealed by morphological examination, H&E staining, and optical coherence tomography. These data suggest that aggrelyte-2A could be developed as a presbyopia-reversing therapeutic.

Indocarbocyanine nanoparticles extravasate and distribute better than liposomes in brain tumors.

Glioblastoma (GBM) is the most devastating and aggressive brain tumor in adults. Hidden behind the blood-brain and blood-tumor barriers (BBTB), this invasive type of brain tumor is not readily accessible to nano-sized particles. Here we demonstrate that fluorescent indocarbocyanine lipids (ICLs: DiD, DiI) formulated in PEGylated lipid nanoparticle (PLN) exhibit highly efficient penetration and accumulation in GBM. PLN-formulated ICLs demonstrated more efficient penetration in GBM spheroids and organoids in vitro than liposomal ICLs. Over 82% of the tumor's extravascular area was positive for ICL fluorescence in the PLN group versus 13% in the liposomal group just one hour post-systemic injection in the intracranial GBM model. Forty-eight hours post-injection, PLN-formulated ICLs accumulated in 95% of tumor myeloid-derived suppressor cells and macrophages, 70% of tumor regulatory T cells, 50% of tumor-associated microglia, and 65% of non-immune cells. PLN-formulated ICLs extravasated better than PEGylated liposomal doxorubicin and fluorescent dextran and efficiently accumulated in invasive tumor margins and brain-invading cells. While liposomes were stable in serum in vitro and in vivo, PLNs disassembled before entering tumors, which could explain the differences in their extravasation efficiency. These findings offer an opportunity to improve therapeutic cargo delivery to invasive GBM.

Antibody-Dependent Complement Responses toward SARS-CoV-2 Receptor-Binding Domain Immobilized on "Pseudovirus-like" Nanoparticles.

Many aspects of innate immune responses to SARS viruses remain unclear. Of particular interest is the role of emerging neutralizing antibodies against the receptor-binding domain (RBD) of SARS-CoV-2 in complement activation and opsonization. To overcome challenges with purified virions, here we introduce "pseudovirus-like" nanoparticles with ∼70 copies of functional recombinant RBD to map complement responses. Nanoparticles fix complement in an RBD-dependent manner in sera of all vaccinated, convalescent, and naïve donors, but vaccinated and convalescent donors with the highest levels of anti-RBD antibodies show significantly higher IgG binding and higher deposition of the third complement protein (C3). The opsonization via anti-RBD antibodies is not an efficient process: on average, each bound antibody promotes binding of less than one C3 molecule. C3 deposition is exclusively through the alternative pathway. C3 molecules bind to protein deposits, but not IgG, on the nanoparticle surface. Lastly, "pseudovirus-like" nanoparticles promote complement-dependent uptake by granulocytes and monocytes in the blood of vaccinated donors with high anti-RBD titers. Using nanoparticles displaying SARS-CoV-2 proteins, we demonstrate subject-dependent differences in complement opsonization and immune recognition.

PEGylated Liposomes Accumulate in the Areas Relevant to Skin Toxicities via Passive Extravasation across "Leaky" Endothelium.

PEGylated liposome is the cornerstone platform for modern drug delivery. Unfortunately, as exemplified by PEGylated liposomal doxorubicin (aka Doxil), altered doxorubicin pharmacokinetics causes off-target accumulation in the skin, including the palms and feet, leading to severe dose-limiting toxicity. In addition to Doxil, other nanoparticles and PEGylated liposomes exhibit significant deposition in the skin, but mechanisms of accumulation are poorly understood. Using ex vivo imaging and ex vivo confocal microscopy, we show that PEGylated liposomes in mice accumulate predominantly in the areas subject to mechanical stress/pressure. Blood vessels in foot skin appear to be especially leaky, exhibiting burst-like extravasations. Using high-resolution confocal microscopy and liposomes labeled with different dyes in the membrane and/or interior, two modes of extravasation were observed: (1) as intact liposomes; (2) as separated liposomal components. On the other hand, stable cross-linked iron oxide nanoworms extravasated only as intact nanoparticles. There was no colocalization between liposomes and exosomal marker CD81, excluding the role of exocytosis. Also, in situ perfusion of formalin-fixed foot skin with labeled liposomes revealed that the extravasation is mediated by passive, energy-independent diffusion and not by leukocyte "hitchhiking". These findings improve our understanding of extravasation pathways of nanocarriers in the areas relevant to skin pathologies and could lead to strategies to prevent and treat liposome-induced skin toxicities.

Improved Cathepsin Probes for Sensitive Molecular Imaging.

Cysteine cathepsin proteases are found under normal conditions in the lysosomal compartments of cells, where they play pivotal roles in a variety of cellular processes such as protein and lipid metabolism, autophagy, antigen presentation, and cell growth and proliferation. As a consequence, aberrant localization and activity contribute to several pathologic conditions such as a variety of malignancies, cardiovascular diseases, osteoporosis, and other diseases. Hence, there is a resurgence of interest to expand the toolkit to monitor intracellular cathepsin activity and better ascertain their functions under these circumstances. Previous fluorescent activity-based probes (ABPs) that target cathepsins B, L, and S enabled detection of their activity in intact cells as well as non-invasive detection in animal disease models. However, their binding potency is suboptimal compared to the cathepsin inhibitor on which they were based, as the P1 positive charge was capped by a reporter tag. Here, we show the development of an improved cathepsin ABP that has a P1 positive charge by linking the tag on an additional amino acid at the end of the probe. While enhancing potency towards recombinant cathepsins, the new probe had reduced cell permeability due to additional peptide bonds. At a second phase, the probe was trimmed; the fluorophore was linked to an extended carbobenzoxy moiety, leading to enhanced cell permeability and superb detection of cathepsin activity in intact cells. In conclusion, this work introduces a prototype design for the next generation of highly sensitive ABPs that have excellent detection of cellular cathepsin activity.

Highly aminated iron oxide nanoworms for simultaneous manufacturing and labeling of chimeric antigen receptor T cells.

Cell based therapies including chimeric antigen receptor (CAR) T cells are promising for treating leukemias and solid cancers. At the same time, there is interest in enhancing the functionality of these cells via surface decoration with nanoparticles (backpacking). Magnetic nanoparticle cell labeling is of particular interest due to opportunities for magnetic separation, in vivo manipulation, drug delivery and magnetic resonance imaging (MRI). While modification of T cells with magnetic nanoparticles (MNPs) was explored before, we questioned whether MNPs are compatible with CAR-T cells when introduced during the manufacturing process. We chose highly aminated 120 nm crosslinked iron oxide nanoworms (CLIO NWs, ~36,000 amines per NW) that could efficiently label different adherent cell lines and we used CD123 CAR-T cells as the labeling model. The CD123 CAR-T cells were produced in the presence of CLIO NWs, CLIO NWs plus protamine sulfate (PS), or PS only. The transduction efficiency of lentiviral CD123 CAR with only NWs was ~23% lower than NW+PS and PS groups (~33% and 35%, respectively). The cell viability from these three transduction conditions was not reduced within CAR-T cell groups, though lower compared to non-transduced T cells (mock T). Use of CLIO NWs instead of, or together with cationic protamine sulfate for enhancement of lentiviral transduction resulted in comparable levels of CAR expression and viability but decreased the proportion of CD8+ cells and increased the proportion of CD4+ cells. CD123 CAR-T transduced in the presence of CLIO NWs, CLIO NWs plus PS, or PS only, showed similar level of cytotoxicity against leukemic cell lines. Furthermore, fluorescence microscopy imaging demonstrated that CD123 CAR-T cells labeled with CLIO NW formed rosettes with CD123+ leukemic cells as the non-labeled CAR-T cells, indicating that the CAR-T targeting to tumor cells has maintained after CLIO NW labeling. The in vivo trafficking of the NW labeled CAR-T cells showed the accumulation of CAR-T labeled with NWs primarily in the bone marrow and spleen. CAR-T cells can be magnetically labeled during their production while maintaining functionality using the positively charged iron oxide NWs, which enable the in vivo biodistribution and tracking of CAR-T cells.

Surface Modification of Erythrocytes with Lipid Anchors: Structure-Activity Relationship for Optimal Membrane Incorporation, in vivo Retention, and Immunocompatibility.

Red blood cells (RBCs) are natural carriers for sustained drug delivery, imaging, and in vivo sensing. One of the popular approaches to functionalize RBCs is through lipophilic anchors, but the structural requirements for anchor stability and in vivo longevity remain to be investigated. Using fluorescent lipids with the same cyanine 3 (Cy3) headgroup but different lipid chain and linker, the labeling efficiency of RBCs and in vivo stability are investigated. Short-chain derivatives exhibited better insertion efficiency, and mouse RBCs are better labeled than human RBCs. Short-chain derivatives demonstrate low retention in vivo. Derivatives with ester bonds are especially unstable, due to removal and degradation. On the other hand, long-chain, covalently linked derivatives show remarkably long retention and stability (over 80 days half life in the membrane). The clearance organs are liver and spleen with evidence of lipid transfer to the liver sinusoidal endothelium. Notably, RBCs modified with PEGylated lipid show decreased macrophage uptake. Some of the derivatives promote binding of antibodies in human plasma and mouse sera and modest increase in complement deposition and hemolysis, but these do not correlate with in vivo stability of RBCs. Ultra-stable anchors can enable functionalization of RBCs for drug delivery, imaging, and sensing.

Lipid nanoparticle formulation of niclosamide (nano NCM) effectively inhibits SARS-CoV-2 replication in vitro.

As exemplified by the COVID-19 pandemic, highly infective respiratory viruses can spread rapidly in the population because of lack of effective approaches to control viral replication and spread. Niclosamide (NCM) is an old anthelminthic drug (World Health Organization essential medicine list) with pleiotropic pharmacological activities. Several recent publications demonstrated that NCM has broad antiviral activities and potently inhibits viral replication, including replication of SARS-CoV-2, SARS-CoV, and dengue viruses. Unfortunately, NCM is almost completely insoluble in water, which limits its clinical use. We developed a cost-effective lipid nanoparticle formulation of NCM (nano NCM) using only FDA-approved excipient and demonstrated potency against SARS-CoV-2 infection in cells (Vero E6 and ACE2-expressing lung epithelium cells).

Liposomal Extravasation and Accumulation in Tumors as Studied by Fluorescence Microscopy and Imaging Depend on the Fluorescent Label.

Tumor trafficking of liposomes is routinely monitored via fluorescence microscopy and imaging. To investigate whether an accumulation of liposomes depends on the type of fluorescent label, we prepared PEGylated liposomes dual-labeled with indocarbocyanine lipids (ICLs: DiD or DiI) and fluorescent phospholipids (FPLs: Cy3-DSPE or Cy5-DSPE) with similar cyanine headgroups but different spectra. Using ex vivo confocal microscopy and imaging, we compared tumor extravasation and accumulation of ICLs and FPLs. After systemic injection in a syngeneic mouse model of 4T1 breast cancer, ICLs and FPLs initially colocalized in tumor blood vessels and perivascular space. At later time points, ICLs spread over a significantly larger tumor area and accumulated in tumor macrophages, whereas FPLs were mostly restricted to the vasculature with limited extravascular signal. This phenomenon was independent of liposomal composition and ICL/FPL type and was also observed in syngeneic intracranial GL261 glioma and LY2 head and neck cancer models. The dual-labeled liposomes were stable in plasma and delivered both dyes to tumors at early time points. Notably, while the level of ICLs increased over time, FPLs gradually disappeared from tumors and other organs in vivo, likely due to degradation of the phospholipid. These findings demonstrate that trafficking and stability of the label is of critical importance when assessing extravasation and accumulation of nanocarriers in tumors and other organs by fluorescence microscopy and imaging.

Delivery of a model lipophilic membrane cargo to bone marrow via cell-derived microparticles.

Bone marrow (BM) is the central immunological organ and the origin of hematological diseases. Efficient and specific drug delivery to the BM is an unmet need. We tested delivery of fluorescent indocarbocyanine lipids (ICLs, DiR, DiD, DiI) as a model lipophilic cargo, via different carriers. Systemically injected T-lymphocyte cell line Jurkat delivered ICLs to the BM more efficiently than erythrocytes, and more selectively than PEGylated liposomes. Near infrared imaging showed that the delivery was restricted to the BM, lungs, liver and spleen, with no accumulation in the kidneys, brain, heart, intestines, fat tissue and pancreas. Following systemic injection of ICL-labeled cells in immunodeficient or immunocompetent mice, few cells arrived in the BM intact. However, between 5 and 10% of BM cells were ICL-positive. Confocal microscopy of intact BM confirmed that ICLs are delivered independently of the injected cells. Flow cytometry analysis showed that the lipid accumulated in both CD11b + and CD11b- cells, and in hematopoietic progenitors. In a xenograft model of acute myeloid leukemia, a single injection of 10 million Jurkat cells delivered DiD to ~15% of the tumor cells. ICL-labeled cells disappeared from blood almost immediately post-intravenous injection, but numerous cell-derived microparticles continued to circulate in blood. The microparticle particle formation was not due to the ICL labeling or complement attack and was observed after injection of both syngeneic and xenogeneic cells. Injection of microparticles produced in vitro from Jurkat cells resulted in a similar ICL delivery as the injection of intact Jurkat cells. Our results demonstrate a novel delivery paradigm wherein systemically injected cells release microparticles that accumulate in the BM. In addition, the results have important implications for studies involving systemically administered cell therapies.

Complement Inhibitors Block Complement C3 Opsonization and Improve Targeting Selectivity of Nanoparticles in Blood.

Complement is one of the critical branches of innate immunity that determines the recognition of engineered nanoparticles by immune cells. Antibody-targeted iron oxide nanoparticles are a popular platform for magnetic separations, in vitro diagnostics, and molecular imaging. We used 60 nm cross-linked iron oxide nanoworms (CLIO NWs) modified with antibodies against Her2/neu and EpCAM, which are common markers of blood-borne cancer cells, to understand the role of complement in the selectivity of targeting of tumor cells in whole blood. CLIO NWs showed highly efficient targeting and magnetic isolation of tumor cells spiked in lepirudin-anticoagulated blood, but specificity was low due to high uptake by neutrophils, monocytes, and lymphocytes. Complement C3 opsonization in plasma was predominantly via the alternative pathway regardless of the presence of antibody, PEG, or fluorescent tag, but was higher for antibody-conjugated CLIO NWs. Addition of various soluble inhibitors of complement convertase (compstatin, soluble CD35, and soluble CD55) to whole human blood blocked up to 99% of the uptake of targeted CLIO NWs by leukocytes, which resulted in a more selective magnetic isolation of tumor cells. Using well-characterized nanomaterials, we demonstrate here that complement therapeutics can be used to improve targeting selectivity.

Cathepsins Drive Anti-Inflammatory Activity by Regulating Autophagy and Mitochondrial Dynamics in Macrophage Foam Cells.

BACKGROUND/AIMS: Atherosclerosis underlies the majority of cardiovascular events, consequent to non-resolving inflammation. Considerable evidence implicates autophagy dysfunction at the core of this inflammatory condition, but the basis of this dysfunction is not fully understood. METHODS: Using an in vitro model of lipid-laden macrophages, activity-based probes and high-throughput techniques, we studied the role of the cysteine proteases cathepsins in autophagy. RESULTS: We showed that cathepsin activity is suppressed by oxidized lipids and that cathepsin has an indispensable role in the autophagy-lysosomal degradation pathway. Accordingly, loss of cathepsin function resulted in autophagy derangement. Shotgun proteomics confirmed autophagy dysfunction and unveiled a pivotal role of cathepsin L in a putative cathepsin degradation network. At the physiological level, cathepsin inhibition resulted in mitochondrial stress, which translated into impaired oxidative metabolism, excessive production of reactive oxygen species and activation of the cellular stress response, driven by ATF4-CHOP transcription factors. In addition, transcriptomic analysis of these cells uncovered some genetic similarities with the inflammatory macrophage phenotype (a.k.a M1 macrophages) and increased expression of inflammatory cytokines. CONCLUSION: Our data highlight the importance of cathepsins for mitochondrial quality control mechanisms and amelioration of vascular inflammation.

Evaluation of Targeting Efficiency of Joints with Anticollagen II Antibodies.

Diseases of the joints affect over 10% of the world's population, resulting in significant morbidity. There is an unmet need in strategies for specific delivery of therapeutics to the joints. Collagen type II is synthesized by chondrocytes and is mainly restricted to the cartilage and tendons. Arthrogen-CIA is a commercially available anticollagen II antibody cocktail that reacts with 5 different epitopes on human, bovine, and mouse collagen II. Arthrogen has been used for induction of experimental rheumatoid arthritis (RA) in mice because of high complement activation on the cartilage surface. Native collagen II might serve as a useful target for potential delivery of therapeutics to the joint. To evaluate the efficiency and specificity of targeting collagen II, Arthrogen was labeled with near-infrared (NIR) dye IRDye 800 or IRDye 680. Using ex vivo NIR imaging, we demonstrate that Arthrogen efficiently and specifically accumulated in the limb joints regardless of the label dye or injection route (intravenous and subcutaneous). After subcutaneous injection, the mean fluorescence of the hind limb joints was 19 times higher than that of the heart, 8.7 times higher than that of the liver, and 3.7 times higher than that of the kidney. Control mouse IgG did not show appreciable accumulation. Microscopically, the antibody accumulated on the cartilage surface of joints and on endosteal surfaces. A monoclonal antibody against a single epitope of collagen II showed similar binding affinity and elimination half-life, but about three times lower targeting efficiency than Arthrogen in vitro and ex vivo, and about two times lower targeting efficiency in vivo. We suggest that an antibody against multiple epitopes of collagen II could be developed into a highly effective and specific targeting strategy for diseases of the joints or spine.

Clickable Methyltetrazine-Indocarbocyanine Lipids: A Multicolor Tool Kit for Efficient Modifications of Cell Membranes.

Cell-based therapeutics are one of the most promising and exciting breakthroughs in modern medicine. Modification of the cell surface with ligands, biologics, drugs, and nanoparticles can further enhance the functionality. Previously, we described the synthesis of a dioctadecyl indocarbocyanine Cy3 analog (aminomethyl-DiI) for efficient and stable modification (painting) of mouse erythrocytes with small molecules, enzymes, and biologics. Here, we synthesized a near-infrared aminomethyl dioctadecyl derivative of Cy7 (aminomethyl-DOCy7) and systematically compared it to aminomethyl-DiI as an anchor for the modification of human erythrocytes, Jurkat cells, and primary T cells with immunoglobulin G. To enable copper-free click chemistry modification of cell membranes, we conjugated a methyltetrazine (MTz) group to the amino-indocyanine lipids via a polyethylene glycol (PEG) linker. DOCy7-PEG3400-MTz showed over 99% modification efficiency of human red blood cells (RBCs) at 25 µM. Reaction of trans-cyclooctene (TCO) modified immunoglobulin G (IgG) with DOCy7-PEG4-MTz-modified RBCs (2-step method) resulted in ∼80,000 IgG molecules per erythrocyte, whereas modification with a preconjugated DOCy7-PEG3400-IgG construct (1-step method) resulted in ∼20,000 IgG molecules per erythrocyte as detected by immuno dot-blot. The number of IgG/RBC was controlled by the concentration of IgG. The incubation of RBCs with DiI-PEG3400-MTz resulted in a similar number of IgG/RBC. Modification of the T-lymphocyte cell line Jurkat with IgG resulted in ∼1 × 106 IgG/cell with the 1-step and 2-step methods, and the efficiency was similar for DOCy7 and DiI constructs. Finally, we used DOCy7 and DiI constructs to demonstrate efficient modification of primary CD3+T cells from healthy donors. In conclusion, click indocarbocyanine conjugates represent a novel multicolor chemical biology tool kit for efficient surface modification of different cells types and can be used for potential imaging and drug delivery applications involving engineered cells.