Enabling In Vivo Photocatalytic Activation
of Rapid Bioorthogonal Chemistry by Repurposing Silicon-Rhodamine
Fluorophores as Cytocompatible Far-Red Photocatalysts
posted on 2021-07-12, 11:04authored byChuanqi Wang, He Zhang, Tao Zhang, Xiaoyu Zou, Hui Wang, Julia E. Rosenberger, Raghu Vannam, William S. Trout, Jonathan B. Grimm, Luke D. Lavis, Colin Thorpe, Xinqiao Jia, Zibo Li, Joseph M. Fox
Chromophores that absorb in the tissue-penetrant
far-red/near-infrared
window have long served as photocatalysts to generate singlet oxygen
for photodynamic therapy. However, the cytotoxicity and side reactions
associated with singlet oxygen sensitization have posed a problem
for using long-wavelength photocatalysis to initiate other types of
chemical reactions in biological environments. Herein, silicon-Rhodamine
compounds (SiRs) are described as photocatalysts for inducing rapid
bioorthogonal chemistry using 660 nm light through the oxidation of
a dihydrotetrazine to a tetrazine in the presence of trans-cyclooctene dienophiles. SiRs have been commonly used as fluorophores
for bioimaging but have not been applied to catalyze chemical reactions.
A series of SiR derivatives were evaluated, and the Janelia Fluor-SiR
dyes were found to be especially effective in catalyzing photooxidation
(typically 3%). A dihydrotetrazine/tetrazine pair is described that
displays high stability in both oxidation states. A protein that was
site-selectively modified by trans-cyclooctene was
quantitatively conjugated upon exposure to 660 nm light and a dihydrotetrazine.
By contrast, a previously described methylene blue catalyst was found
to rapidly degrade the protein. SiR-red light photocatalysis was used
to cross-link hyaluronic acid derivatives functionalized by dihydrotetrazine
and trans-cyclooctenes, enabling 3D culture of human
prostate cancer cells. Photoinducible hydrogel formation could also
be carried out in live mice through subcutaneous injection of a Cy7-labeled
hydrogel precursor solution, followed by brief irradiation to produce
a stable hydrogel. This cytocompatible method for using red light
photocatalysis to activate bioorthogonal chemistry is anticipated
to find broad applications where spatiotemporal control is needed
in biological environments.