3 research outputs found
Development of an Azo-Based Photosensitizer Activated under Mild Hypoxia for Photodynamic Therapy
Photodynamic therapy
(PDT) utilizes photoirradiation in the presence
of photosensitizers to ablate cancer cells via generation of singlet
oxygen (<sup>1</sup>O<sub>2</sub>), but it is important to minimize
concomitant injury to normal tissues. One approach for achieving this
is to use activatable photosensitizers that can generate <sup>1</sup>O<sub>2</sub> only under specific conditions. Here, we report a novel
photosensitizer that is selectively activated under hypoxia, a common
condition in solid tumors. We found that introducing an azo moiety
into the conjugated system of a seleno-rosamine dye effectively hinders
the intersystem crossing process that leads to <sup>1</sup>O<sub>2</sub> generation. We show that the azo group is reductively cleaved in
cells under hypoxia, enabling production of <sup>1</sup>O<sub>2</sub> to occur. In PDT <i>in vitro</i>, cells under mild hypoxia,
within the range typically found in solid tumors (up to about 5% O<sub>2</sub>), were selectively ablated, leaving adjacent normoxic cells
intact. This simple and practical azo-based strategy should be widely
applicable to design a range of activatable photosensitizers
Reversible Off–On Fluorescence Probe for Hypoxia and Imaging of Hypoxia–Normoxia Cycles in Live Cells
We
report a fully reversible off–on fluorescence probe for
hypoxia. The design employs QSY-21 as a Förster resonance energy
transfer (FRET) acceptor and cyanine dye Cy5 as a FRET donor, based
on our finding that QSY-21 undergoes one-electron bioreduction to
the radical under hypoxia, with an absorbance decrease at 660 nm.
At that point, FRET can no longer occur, and the dye becomes strongly
fluorescent. Upon recovery of normoxia, the radical is immediately
reoxidized to QSY-21, with loss of fluorescence due to restoration
of FRET. We show that this probe, RHyCy5, can monitor repeated hypoxia–normoxia
cycles in live cells
Development of an Azoreductase-based Reporter System with Synthetic Fluorogenic Substrates
Enzyme/substrate
pairs, such as β-galactosidase with chromogenic
x-gal substrate, are widely used as reporters to monitor biological
events, but there is still a requirement for new reporter systems,
which may be orthogonal to existing systems. Here, we focused on azoreductase
(AzoR). We designed and synthesized a library of azo-rhodamine derivatives
as candidate fluorogenic substrates. These derivatives were nonfluorescent,
probably due to ultrafast conformational change around the Nî—»N
bond after photoexcitation. We found that AzoR-mediated reduction
of the azo bond of derivatives bearing an electron-donating group
on the azobenzene moiety was followed by nonenzymatic cleavage to
afford highly fluorescent 2-methyl-rhodamine green (2-Me RG), which
was well retained in cells. We show that the AzoR/compound <b>9</b> reporter system can detect azoreductase-expressing live cells at
the single cell level