DOI: 10.1002/cmdc.201500060
Full Papers
NIR Fluorogenic Dye as a Modular Platform for Prodrug
Assembly: Real-Time in vivo Monitoring of Drug Release
Orit Redy-Keisar,[a] Shiran Ferber,[b] Ronit Satchi-Fainaro,*[b] and Doron Shabat*[a]
The ability to monitor drug release in vivo provides essential
pharmacological information. We developed a new modular
approach for the preparation of theranostic prodrugs with
a turn-ON near-infrared (NIR) fluorescence mode of action. The
prodrugs release their chemotherapeutic cargo and an active
cyanine fluorophore upon reaction with a specific analyte. The
prodrug platform is based on the fluorogenic dye QCy7; upon
removal of a triggering substrate, the dye fluoresces, and the
free drug is released. The evaluated camptothecin prodrug
was activated by endogenous hydrogen peroxide produced in
tumor cells in vitro and in vivo. Drug release and in vitro cyto-
toxicity were correlated with the emitted fluorescence. The
prodrug activation was effectively imaged in real time in mice
bearing tumors. The modular design of the QCy7 fluorogenic
platform should allow the preparation of numerous other pro-
drugs with various triggering substrates and chemotherapeutic
agents. We anticipate that the development of real-time in
vivo monitoring tools such as that described herein will pave
the way for personalized therapy.
Introduction
With the recent remarkable advances in medicine, the need for
specific and personalized treatment has gained considerable
attention over the past few years.[1] The therapeutic approach
in which all patients who suffer from a particular disease re-
ceive similar treatment is now recognized as having many defi-
ciencies. One way to address this issue is to develop tools that
have the ability to simultaneously diagnose and treat a medical
condition. The relatively new term theranostic is used to de-
scribe a single agent that can function for both therapy and di-
agnosis.[2] The use of such agents will provide information on
the biodistribution, pharmacokinetics, pharmacodynamics, se-
lectivity, and mode of action of a given drug, thereby enabling
personalization of treatment.
rescence was observed. The amount of drug released was de-
termined by quantifying the emitted fluorescence. After our
report, a burst of studies on theranostic drug delivery systems
appeared in the literature,[4–19] including a recent one that used
our coumarin linker to assemble an activatable prodrug for the
treatment of metastatic tumors.[20]
The relatively short emission wavelength of the coumarin
linker enables monitoring of drug release and cytotoxic activity
in a cell-based assay. To monitor fluorescence in vivo, the
system should be designed based on a linker with emission in
the near-infrared (NIR) region.[21–23] The NIR region is optimal
for in vivo imaging applications, as live tissues have minimal
absorbance and emission at NIR wavelengths, and NIR photons
have the ability to penetrate through organic tissues. Two spe-
cific examples were recently reported in which a disulfide-
based linkage was used as a triggering substrate for gluta-
thione and a NIR dye as a fluorescent tracker.[9,12]
Nearly four years ago, we developed a unique latent fluoro-
genic linker (based on coumarin building block) that has been
used for the assembly of prodrug systems.[3] The prodrug is de-
signed to undergo specific activation by an analyte of interest;
activation releases the drug and turns on a fluorescence signal
through the formation of a coumarin derivative (Scheme 1).
This pioneering prodrug system was able to report its cytotox-
ic activity toward cancer cells in real time. A direct correlation
between the ability to inhibit cancer cell growth and emit fluo-
We recently developed a novel class of turn-ON NIR cyanine-
based probes.[24–27] The probes are based on quinone cyanine-
7 (QCy7), which is composed of a phenol donor conjugated to
two indolium acceptors. Deprotonation of the phenol causes
a distinct change in the p-electron system as a result of intra-
molecular charge transfer (ICT), leading to the generation of
a cyanine dye with strong NIR fluorescence (Scheme 2). Mecha-
nistically, deprotonation of the phenol results in the formation
of a phenolate active donor II that is able to donate a pair of
p-electrons to either one of the conjugated indolium acceptors
(structures III and IV). This ICT generates a resonance species
with a p-electron pattern similar to that of a cyanine fluoro-
chrome. QCy7 exhibits a relatively high quantum yield of 16%
under aqueous conditions, good photostability, and large ex-
tinction coefficient.[25]
[a] O. Redy-Keisar, Prof. D. Shabat
School of Chemistry, Department of Organic Chemistry
Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel)
[b] S. Ferber, Prof. R. Satchi-Fainaro
Department of Physiology and Pharmacology
Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978 (Israel)
Supporting information for this article is available on the WWW under
characterization data of all new compounds, spectroscopic assay condi-
tions, in vitro and in vivo experimental conditions.
ChemMedChem 0000, 00, 0 – 0
1
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ