Immunotheranostic Polymersomes Modularly Assembled from Tetrablock and Diblock Copolymers with Oxidation-Responsive Fluorescence
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Intracellular delivery is a key step for many applications in medicine and for investigations into cellular function. This is particularly true for immunotherapy, which often requires controlled delivery of antigen and adjuvants to the cytoplasm of immune cells. Due to the complex responses generated by the stimulation of diverse immune cell populations, it is critical to monitor which cells are targeted during treatment. To address this issue, we have engineered an immunotheranostic polymersome delivery system that fluorescently marks immune cells following intracellular delivery.
Amine functionalized poly(ethylene glycol)-bl-poly(propylene sulfide) (PEG-PPS-NH2) was synthesized by anionic ring opening polymerization and bridged via perylene bisimide (PBI) to form a tetrablock copolymer (PEG-PPS-PBI-PPS-PEG). Block copolymers were assembled into polymersomes by thin film hydration in phosphate buffered saline and characterized by dynamic light scattering, cryogenic electron microscopy and fluorescence spectroscopy. Polymersomes were injected subcutaneously into the backs of mice, and draining lymph nodes were extracted for flow cytometric analysis of cellular uptake and disassembly.
Modular self-assembly of tetrablock/diblock copolymers in aqueous solutions induced π–π stacking of the PBI linker that both red-shifted and quenched the PBI fluorescence. Reactive oxygen species within the endosomes of phagocytic immune cell populations oxidized the PPS blocks, which disassembled the polymersomes for dequenching and shifting of the PBI fluorescence from 640 to 550 nm emission. Lymph node resident macrophages and dendritic cells were found to increase in 550 nm emission over the course of 3 days by flow cytometry.
Immunotheranostic polymersomes present a versatile platform to probe the contributions of specific cell populations during the elicitation of controlled immune responses. Flanking PBI with two oxidation-sensitive hydrophobic PPS blocks enhanced π stacking and introduced a mechanism for disrupting π–π interactions to shift PBI fluorescence in response to oxidative conditions. Shifts from red (640 nm) to green (550 nm) fluorescence occurred in the presence of physiologically relevant concentrations of reactive oxygen species and could be observed within phagocytic cells both in vitro and in vivo.
KeywordsPolymersome Fluorescence Theranostics Perylene Macrophage Dendritic cell
Antigen presenting cells
Cryogenic transmission electron microscopy
Dynamic light scattering
Fetal bovine serum
Gel permeation chromatography
Major histocompatibility complex I
Poly(ethylene glycol)-bl-poly(propylene sulfide)
Reactive oxygen species
Toll like receptors
We would like to thank J. Remis for CryoTEM assistance and the following facilities at Northwestern University: Robert H. Lurie Comprehensive Cancer Center Flow Cytometry Core; Center for Advanced Molecular Imaging; Biological imaging facility; Mouse Histology and Phenotyping Laboratory; and the Keck Interdisciplinary Surface Science Facility. This work was supported by the National Institutes of Health Director’s New Innovator Award (grant no. 1DP2HL132390-01), the Louis A. Simpson & Kimberly K. Querrey Center for Regenerative Nanomedicine Regenerative Nanomedicine Catalyst Award.
Conflict of Interest
Fanfan Du, Yu-Gang Liu, and Evan A. Scott declare that they have no conflicts of interest.
No human studies were carried out by the authors for this article. All institutional and national guidelines for the care and use of laboratory animals were followed and approved by the Northwestern University Institutional Animal Care and Use Committee.
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