100th Anniversary of Macromolecular Science Viewpoint: Re-Engineering Cellular Interfaces with Synthetic Macromolecules Using Metabolic Glycan Labeling

Abstract

Cell-surface functionality is largely programmed by genetically encoded information through modulation of protein expression levels, including glycosylation enzymes. Genetic tools enable control over protein-based functionality, but are not easily adapted to recruit non-native functionality such as synthetic polymers and nanomaterials to tune biological responses and attach therapeutic or imaging payloads. Similar to how polymer-protein conjugation evolved from nonspecific PEGylation to site-selective bioconjugates, the same evolution is now occurring for polymer-cell conjugation. This Viewpoint discusses the potential of using metabolic glycan labeling to install bio-orthogonal reactive cell-surface anchors for the recruitment of synthetic polymers and nanomaterials to cell surfaces, exploring the expanding therapeutic and diagnostic potential. Comparisons to conventional approaches that target endogenous membrane components, such as hydrophobic, protein coupling and electrostatic conjugation, as well as enzymatic and genetic tools, have been made to highlight the huge potential of this approach in the emerging cellular engineering field.

Figure 1

Metabolic oligosaccharide engineering with unnatural derivatives of glycan’s allows “hijacking” of biosynthetic pathways of endogenous glycan analogues to install biorthogonal handles (R₁) for chemoselective ligation. R₂ = OH or Ac.

Figure 2

Metabolic glycoengineering with Ac₄ManNAz provides bioorthogonal azide handles for cell-surface recruitment of pHEA polymers bearing DBCO and abiotic fluorescent cargos (green). Adapted from ref (81) and reproduced with permission. Copyright 2019 American Chemical Society.

Figure 3

Comparisons between nonspecific conjugation and metabolic cell labeling approaches. Confocal images of live HEK293 cells nonspecifically labeled with (A) poly(ethylene imine), (B) PEG-lipid, and (C) PEG-NHS (from ref (88)); and (D) live A549 cells metabolically labeled with Ac₄ManNAz and pHEA-DBCO (from ref (81)). All images were taken both immediately and 24 h following polymer grafting to assess surface retention. Confocal images: green = fluorescent polymer; blue = nuclear DAPI stain. Criteria: green tick = positive outcome; amber tick = results vary; red cross = negative outcome. (A)–(C) are adapated from ref (88) with permission. Copyright 2008 Elsevier. (D) is adapted with permission from ref (81). Copyright 2019 American Chemical Society.

Figure 4

Heterolytic cell adhesion with MOE. (A) Cyclodextrin conjugation to cell surfaces using MOE; (B) recruitment of photoactive azobenzene MUC1 aptamers to Hela (green) and PBMC (blue) cell surfaces for subsequent photoswitchable adhesion to MCF-7 cells (red) expressing mucin 1. Heterolytic adhesion enhances cytotoxicity of PBMCs toward MCF-7 cells. Scale bar = 50 μm. Figure is adapted with permission from ref (117). Copyright 2016 SpringerNature.

Figure 5

(A) BCN-CNPs are self-assembled under aqueous conditions possessing imaging agents (Cy5.5, iron and gold) and a strained alkyne for (B) cell surface binding and internalization by hMSCs. (C) Subcutaneous implantation into mice allowed noninvasive optical, MR, and CT stem cell tracking. Figure adapted with permission from ref (49). Copyright 2017 Elsevier.

Figure 6

(A) Metabolically glycoengineered stem cells were labeled with DBCO-Cy5.5 and injected intraperitoneally into MA148-Luc ovarian tumor bearing mice to determine tumor tropism capabilities. Tumor-free mice are shown as controls. (B) Intraperitoneal injection of metabolically labeled stem cells was completed again, but followed by intraperitoneal injection of DBCO-PLGA-PAX nanoparticles with all relevant controls. Tumor growth and mice survival were measured over 65 days (n = 4). Figure adapted with permission from ref (129). Copyright 2016 Elsevier.

Figure 7

Microtissues by DNA conjugation. (A) Metabolic labeling of Jurkat cells allows cell surface recruitment of complementary ssDNA to form cell assemblies; (B) Construction of a microtissue possessing a paracrine signaling network using complementary DNA strands. CHO cells expressing murine IL-3 (and GFP) supply IL-3 for growth of murine pro-B cell line FL5.12, whereas in its absence apoptosis occurs. Figure adapted with permission from (140). Copyright 2009 NAS.