Biomedical Engineering Reference
In-Depth Information
identification of biological modulations theoretically exploited by the wide variabil-
ity of available natural and synthetic compounds acting on entities different from the
target selected. Given the availability of this wide number and variety of compounds,
neglecting their potential biological modulation activity would be an unquantifiable
waste of effort and opportunity. Obviously, the disposal of this vast plethora of com-
pounds is not related strictly to the ability to determine their biological potential.
When the number of variables increases, the use of rapid biological screenings, pro-
viding easily handled, exhaustive, extensive, and understandable results, becomes a
central quest.
14.1.1.1 The State of the Art: From Isolated Targets to Systems Over the years,
the pharmaceutical industry has relied on several different technologies to assess
the biological activities of screened compounds. For a long time, the initial bio-
logical screenings aimed at drug discovery purposes were carried out by means
of in vitro assays. Mainly, isolated entities (i.e., enzymes) were used to identify
compounds having functional effects; otherwise, conventional high-throughput LC-
MS-MS and newer MS approaches were used [9]. Although ligand-receptor binding
assays were considered the “gold standard,” many drawbacks are associated with
these approaches, and their fallouts are easily quantifiable when considering the high
rate of drug development abortions at the preclinical stage. The application of in silico
approaches, based on the modeling of novel compounds able to bind and modulate
targetable entities, only partially prevented the failure of new bioactive compounds.
Although the use of a molecule isolated from its natural environment clears the pres-
ence of eventual background noises, it forbids the prediction of characteristics that
make a selected compound a “druggable” molecule. As an example, the ability of
the molecule selected to permeate the cell membrane and its metabolism are often
unpredictable a priori. In addition, eventual side effects are hardly predictable. More-
over, the utilization of purified target molecules relies on the one target-one disease
concept [10]. On the contrary, a great many disorders, such as cancer and neurodegen-
erative diseases, revealed a higher complexity, often being associated with several
molecules or with complete pathway dysfunction. Cell-based assays thus became
a useful tool in the selection of bioactive compounds not biased by the problems
described above. A cell-based approach does not require the selection of a specific
target. A desirable phenotype such as fungal cell death when searching for novel
antifungals can be selected, and then the molecules are screened for their ability to
induce such a phenotype. At the same time, this approach allows for the identification
of compounds active in inducing the selected phenotype and the characterization of
otherwise hardly predictable mechanisms lying at the basis of this phenotype. The
other side of the coin is that, once a bioactive compound is selected, its cellular target
has to be identified.
The more is known about the cell system used for the assay, the less complicated is
the identification of molecular targets lying at the basis of the phenotype modulation
induced by a selected compound or perturbation. Aiming at this, the use of a model
system is preferable to utilization of the final (clinical) target, often represented by
the still poorly characterized Homo sapiens . Although there are obvious limitations
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