Biomedical Engineering Reference
In-Depth Information
an initial hit and can streamline an efficient scaled synthesis of an optimized probe.
The logic underlying a variety of DOS strategies was reviewed extensively in earlier
chapters.
Integration of the DOS approach into chemical genetics has emerged as a powerful
tool for systematic probing of the chemical space relevant to the biological processes
inherent in a wide range of human diseases [6]. Efforts in this regard have produced
new and important probes for dissecting complex biological processes and lead
compounds for developing novel treatments of diseases. In this chapter we present
several recent studies aimed at identifying novel small-molecule probes from DOS-
based libraries and DOS-based optimization strategies.
18.2 DOS-DERIVED SMALL-MOLECULE PROBES
Growing efforts directed to discovering bioactive molecules from DOS libraries
have led to many important new biological probes. Tables 18.1 and 18.2 provide a
summary of recent DOS-derived bioactive small molecules identified using a forward
and reverse chemical genetics approach. A set of examples are discussed below, with
a particular focus on representing the extensive utilities of a DOS strategy in probe
development, ranging from targeting challenging biological pathways and expanding
the collections of important biological probes to achieving therapeutically desirable
phenotypes.
18.3 DEVELOPING SMALL-MOLECULE PROBES OF COMPLEX
BIOLOGICAL PATHWAYS
18.3.1
Inhibitors of Sonic Hedgehog Signaling
The Hedgehog (Hh) signaling pathway plays an important role in embryonic devel-
opment and cellular differentiation [52]. In mammals, the major components in the
Hh signaling pathway include the Hh ligands (Sonic, Desert, and Indian), the 12-
transmembrane receptor Patched (Ptc1), the pseudo-G-protein-coupled signal trans-
ducer Smoothened (Smo), and the glial (Gli) family of transcription factors [52,53].
The Hh ligands are secreted glycoproteins, among which the Sonic Hedgehog protein
(Shh) is best characterized. In the absence of ligands, Ptc1 binds to and inhibits the
signal transducer Smo on the cell membrane. The inhibitory effect of Ptc1 on Smo
is reversed upon binding of ShhN, the active 20-kDa N-terminal fragment of Shh, to
the extracellular domain of Ptc1, which initiates downstream signaling by enhancing
the expression and nuclear translocation of the Gli transcription factors (Gli1, Gli2,
and Gli3) and subsequent up-regulation of the Shh target genes (Figure 18.1) [43,54].
Aberrant activity of the Shh signaling pathway is associated with the development of
various cancers [53]. For example, mutations in the
Ptch1
gene cause nevoid basal
cell carcinoma syndrome, in which excessive ectopic activation of Shh signaling is
observed. Individuals having the mutations exhibit an increased risk of developing
