Photodynamic therapy (PDT) requires a photosensitizer, light, and oxygen to induce cell death. The majority of efforts to advance PDT focus only on the first two components. Here, we employ perfluorocarbon nanoemulsions to simultaneously deliver oxygen and a photosensitizer. We find that the implementation of fluorous soluble photosensitizers enhances the efficacy of PDT.
Perfluorocarbon (PFC)
nanoemulsions, droplets of fluorous solvent stabilized by surfactants
dispersed in water, are simple yet versatile nanomaterials. The orthogonal
nature of the fluorous phase promotes the formation of nanoemulsions
through a simple, self-assembly process while simultaneously encapsulating
fluorous-tagged payloads for various applications. The size, stability,
and surface chemistry of PFC nanoemulsions are controlled by the surfactant.
Here, we systematically study the effect of the hydrophilic portion
of polymer surfactants on PFC nanoemulsions. We find that the hydrophilic
block length and identity, the overall polymer hydrophilic/lipophilic
balance, and the polymer architecture are all important factors. The
ability to modulate these parameters enables control over initial
size, stability, payload retention, cellular internalization, and
protein adsorption of PFC nanoemulsions. With the insight obtained
from this systematic study of polymer amphiphiles stabilizing PFC
nanoemulsions, design features required for the optimal material are
obtained.
Stimuli-responsive
materials are exploited in biological, materials,
and sensing applications. We introduce a new endogenous stimulus,
biomacromolecule crowding, which we achieve by leveraging changes
in thermoresponsive properties of polymers upon high concentrations
of crowding agents. We prepare poly(2-oxazoline) amphiphiles that
exhibit lower critical solution temperatures (LCST) in serum above
physiological temperature. These amphiphiles stabilize oil-in-water
nanoemulsions at temperatures below the LCST but are ineffective surfactants
above the LCST, resulting in emulsion fusion. We find that the transformations
observed upon heating nanoemulsions above their surfactant’s
LCST can instead be induced at physiological temperatures through
the addition of polymers and protein, rendering thermoresponsive materials
“crowding responsive.” We demonstrate that the cytosol
is a stimulus for nanoemulsions, with droplet fusion occurring upon
injection into cells of living zebrafish embryos. This report sets
the stage for classes of thermoresponsive materials to respond to
macromolecule concentration rather than temperature changes.
The clinical utility of emulsions as delivery vehicles is hindered by a dependence on passive release. Stimuliresponsive emulsions overcome this limitation but rely on external triggers or are composed of nanoparticle-stabilized droplets that preclude sizes necessary for biomedical applications. Here, we employ cleavable poly(2-oxazoline) diblock copolymer surfactants to form perfluorocarbon (PFC) nanoemulsions that release cargo upon exposure to glutathione. These surfactants allow for the first example of redoxresponsive nanoemulsions in cellulo. A noncovalent fluorous tagging strategy is leveraged to solubilize a GFP plasmid inside the PFC nanoemulsions, whereupon protein expression is achieved selectively when employing a stimuli-responsive surfactant. This work contributes a methodology for nonviral gene delivery and represents a general approach to nanoemulsions that respond to endogenous stimuli.
Fluorophores that are sensitive to their environment are useful tools for sensing chemical changes and probing biological systems. Here, we extend responsive fluorophores to the fluorous phase with the synthesis of a reduction-sensitive fluorous-soluble fluorogenic coumarin. We demonstrate that this fluorophore responds to various reducing agents, most notably glutathione, a key biological reductant. The fluorous solubility of this probe allows for its encapsulation into two different fluorous nanomaterials: perfluorocarbon nanoemulsions and fluorous core-shell micelles. The fluorogenic coumarin allows us to study how efficiently these vehicles protect the contents of their interior from the external environment. In the presence of glutathione, we observe different degrees of release for micelles and emulsions. This understanding will help guide future applications of fluorous nanomaterials as drug delivery vehicles.
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