DBCO-C6-NHS ester

Establishment of an appropriate cell labeling and tracking method is essential for the development of cell-based therapeutic strategies. Here, we are introducing a new method for cell labeling and tracking by combining metabolic gylcoengineering and bioorthogonal copper-free Click chemistry. First, chondrocytes were treated with tetraacetylated N-azidoacetyl-D-mannosamine (Ac4ManNAz) to generate unnatural azide groups (-N3) on the surface of the cells. Subsequently, the unnatural azide groups on the cell surface were specifically conjugated with near-infrared fluorescent (NIRF) dye-tagged dibenzyl cyclooctyne (DBCO-650) through bioorthogonal copper-free Click chemistry. Importantly, DBCO-650-labeled chondrocytes presented strong NIRF signals with relatively low cytotoxicity and the amounts of azide groups and DBCO-650 could be easily controlled by feeding different amounts of Ac4ManNAz and DBCO-650 to the cell culture system. For the in vivo cell tracking, DBCO-650-labeled chondrocytes (1 × 10(6) cells) seeded on the 3D scaffold were subcutaneously implanted into mice and the transplanted DBCO-650-labeled chondrocytes could be effectively tracked in the prolonged time period of 4 weeks using NIRF imaging technology. Furthermore, this new cell labeling and tracking technology had minimal effect on cartilage formation in vivo.

Unnatural sugar-mediated metabolic labeling of cancer cells, coupled with efficient Click chemistry, has shown great potential for in vivo imaging and cancer targeting. Thus far, chemical labeling of cancer cells has been limited to the small-sized azido groups, with the large-sized and highly hydrophobic dibenzocyclooctyne (DBCO) being correspondingly used as the targeting ligand. However, surface modification of nanomedicines with DBCO groups often suffers from low ligand density, difficult functionalization, and impaired physiochemical properties. Here we report the development of DBCO-bearing unnatural sugars that could directly label LS174T colon cancer cells with DBCO groups and subsequently mediate cancer-targeted delivery of azido-modified silica nanoconjugates with easy functionalization and high azido density in vitro and in vivo. This study, for the first time, demonstrates the feasibility of metabolic labeling of cancer cells with large-sized DBCO groups for subsequent, efficient targeting of azido-modified nanomedicines.

Antibody-drug conjugates (ADCs) are a targeted chemotherapeutic currently at the cutting edge of oncology medicine. These hybrid molecules consist of a tumor antigen-specific antibody coupled to a chemotherapeutic small molecule. Through targeted delivery of potent cytotoxins, ADCs exhibit improved therapeutic index and enhanced efficacy relative to traditional chemotherapies and monoclonal antibody therapies. The currently FDA-approved ADCs, Kadcyla (Immunogen/Roche) and Adcetris (Seattle Genetics), are produced by conjugation to surface-exposed lysines, or partial disulfide reduction and conjugation to free cysteines, respectively. These stochastic modes of conjugation lead to heterogeneous drug products with varied numbers of drugs conjugated across several possible sites. As a consequence, the field has limited understanding of the relationships between the site and extent of drug loading and ADC attributes such as efficacy, safety, pharmacokinetics, and immunogenicity. A robust platform for rapid production of ADCs with defined and uniform sites of drug conjugation would enable such studies. We have established a cell-free protein expression system for production of antibody drug conjugates through site-specific incorporation of the optimized non-natural amino acid, para-azidomethyl-l-phenylalanine (pAMF). By using our cell-free protein synthesis platform to directly screen a library of aaRS variants, we have discovered a novel variant of the Methanococcus jannaschii tyrosyl tRNA synthetase (TyrRS), with a high activity and specificity toward pAMF. We demonstrate that site-specific incorporation of pAMF facilitates near complete conjugation of a DBCO-PEG-monomethyl auristatin (DBCO-PEG-MMAF) drug to the tumor-specific, Her2-binding IgG Trastuzumab using strain-promoted azide-alkyne cycloaddition (SPAAC) copper-free click chemistry. The resultant ADCs proved highly potent in in vitro cell cytotoxicity assays.