Immunotheranostic Polymersomes Modularly Assembled from Tetrablock and Diblock Copolymers with Oxidation-Responsive Fluorescence

Abstract

Introduction 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. Methods N-(3-bromopropyl)phthalimide end-capped poly(ethylene glycol)-bl-poly(propylene sulfide) (PEG-PPS-PI) was synthesized by anionic ring opening polymerization and linked with PEG-PPS-NH2 via a perylene bisimide (PBI) bridge 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. Results 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 nm 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. Conclusions 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.

The Combination of Morphology and Surface Chemistry Defines the Biological Identity of Nanocarriers in Human Blood

“…S18). The non-cytotoxic nature of PEG-b-PPS nanocarriers observed here is consistent with previously published studies (22,23,33,72). To ensure that cytotoxicity would not influence our ensuing cell uptake studies, we used a BCP concentration of 0.5 mg/mL.…”

Sustained micellar delivery via inducible transitions in nanostructure morphology

“…Having produced FM-based scaffolds and demonstrated their unique degradation mechanism in vitro, we aimed to investigate their ability to release MCs in vivo. While difficult to quantify, biologically relevant concentrations of reactive oxygen species (ROS) have been estimated to range from 50–100 µM 63 , and we have previously demonstrated that H 2 O 2 at as low as 5 µM can induce changes in PEG-bl-PPS nanocarrier morphology 6 . We therefore hypothesized that continuous exposure of FM-scaffolds to physiologic levels of oxidation could be sufficient to induce sustained FM-to-MC transitions in vivo following subcutaneous injection in mice.…”

“…Nanocarriers present a versatile means of delivering therapeutic and diagnostic agents to specific cells and tissues and have become a primary basis for theranostic strategies 1 – 6 . Targeted nanocarrier delivery systems are primarily administered by bolus intermittent injections and infusions, with few options available for sustained delivery 7 .…”

Homopolymer self-assembly of poly(propylene sulfone) hydrogels via dynamic noncovalent sulfone–sulfone bonding

“…Synthesis and characterization of PPSU homopolymer. PPSU can be synthesized from the complete oxidation of poly(propylene sulfide) (PPS) 14,15 , which is known for its hydrophobic-hydrophilic transition upon oxidation [16][17][18] . However, complete oxidation of PPS had not been previously achieved, since standard oxidation of PPS generates random copolymers of poly(propylene sulfoxide)co-poly(propylene sulfone) 19 .…”