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which contains two moieties that can be cleaved by different
mechanisms can generate a molecular “OR” logic gate
trigger. The gate is activated upon a cleavage signal from
either of the two input ports. The signal will be translated into
a bond cleavage that releases the active drug molecule.
Several anticancer prodrugs have been designed for
selective activation in malignant tissues by
a specific
enzyme secreted within the proximity of the tumor.[10]
A
prodrug with a molecular “OR” logic gate triggering device
could potentially target two different cancerous tissues with
different enzyme-expression patterns. There are several
examples for enzymes that are present in elevated levels in
malignant tissues.[11] The substrates of two of these enzymes
could be introduced in the molecular “OR” logic trigger to
generate an agent for dual-prodrug monotherapy. Prodrug
strategies are sometimes based on the assumption that a
particular enzyme is elevated in the tumor tissues and that
activation of a prodrug in the tumor tissue will result in a
significantly improved therapeutic index. While there is much
evidence for overexpression of particular enzymes in tumors,
consistent patterns of expression are elusive. Consequently,
attempts to develop drugs activated by tumor-specific
enzymes in general have not been very successful. Prodrugs
with two modes of activation could offer an advantage over
single-triggered prodrugs, particularly in circumstances where
two different enzymes are present in elevated levels in various
regions of the tumor. Herein, we report the design, synthesis,
and bioactivation of a molecular “OR” logic trigger which is
used to activate a prodrug with dual susceptibility to
enzymatic activity.
Prodrug Activation
Prodrug Activation Gated by a Molecular “OR”
Logic Trigger**
Roey J. Amir, Mikhail Popkov, Richard A. Lerner,
Carlos F. Barbas III, and Doron Shabat*
Molecular logic gates are increasingly important in attributing
chemical reactivity to molecular devices.[1–5] Specific input
signals of basic logic gates can be programmed into single
molecules that generate readable output signals, such as
fluorescence[6] or UV/Vis light.[7] Here we show that the
release of an active drug molecule through a prodrug
activation process is a viable output signal. The term
“prodrug” is used to indicate that a chemical derivatization
has been applied to alter the physicochemical properties of a
drug.[8,9] The prodrug is converted into the active drug in vivo
by metabolic processes or environmental conditions. Masking
of a functional group in a targeted drug with a simple linker
Classical “OR” logic gates have two input ports and one
output port.[12] An activating signal, which operates on either
one of the input ports, activates the output signal of the gate
(Figure 1). Obviously, positive input signals from both input
ports should also activate the gate.
Diethylenetriamine has previously been introduced in a
multitriggering mechanism[13] and is used as a linker in the
construction of the molecular “OR” logic trigger. The central
secondary amine is attached to a drug molecule while the two
primary amines are linked to different enzymatic substrates
(triggers 1 and 2). The enzymatic cleavage of either one of the
substrates generates a free-amine intermediate (intermedi-
ate 1 or 2) that initiates an intracyclization reaction to release
the free drug unit (Figure 2).
To provide a proof of concept for the “OR” triggering
release mechanism suggested in Figure 2, we prepared 1,
which contains two different enzymatic substrates and 4-
nitrophenol, as a model compound that represents a potential
drug. The two substrates were a phenylacetamide moiety,
which is the substrate for penicillin G amidase[14] (PGA), and
a retro-aldol retro-Michael substrate that is cleaved by
catalytic antibody (Ab) 38C2.[15–17] According to the proposed
pathway presented in Figure 3, cleavage by antibody 38C2 or
by PGA should catalyze the formation of intermediates 2 or 3,
respectively, and subsequent intracyclization will release 4-
nitrophenol.
[*] R. J. Amir, Dr. D. Shabat
Department of Organic Chemistry
School of Chemistry, Faculty of Exact Sciences
Tel Aviv University
Tel Aviv 69978 (Israel)
Fax: (+972)3-640-9293
E-mail: chdoron@post.tau.ac.il
Dr. M. Popkov, Prof. R. A. Lerner, Prof. C. F. Barbas III
The Skaggs Institute for Chemical Biology
Departments of Molecular Biology and Chemistry
The Scripps Research Institute
10550 North Torrey Pines Road
La Jolla, CA 92037 (USA)
[**] R.J.A. and M.P. contributed equally to this work. D.S. thanks the
Israel Science Foundation for financial support.
The “OR” logic trigger substrate 1 was incubated with
either antibody 38C2 or PGA in phosphate-buffered saline
(PBS) solution (pH 7.4) at 378C. The formation of 4-nitro-
Supporting information for this article is available on the WWW
4378
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/anie.200500842
Angew. Chem. Int. Ed. 2005, 44, 4378 –4381