Biomedical Engineering Reference
In-Depth Information
and was therefore one of the earliest applications in cancer research. Although this
work has so far not achieved the original goal of transforming the science of
combination chemotherapy in the clinic, there has been a recent convergence
involving detailed understanding of the basic mechanisms of cell cycle regulation
and the development of novel anticancer agents that selectively target these mechan-
isms. Importantly, specific and high-affinity antibodies directed toward the key
molecular regulators are becoming available, opening up the potential to develop
a new generation of flow cytometry protocols to study cell cycle regulation in
experimental cancer models and in patients [33]. Combined with the capabilities
of modern data analysis software and multilaser flow cytometers, this is likely to
become a very productive area for research over the next few years.
7.3.2.1 Aurora Kinase Inhibitors
Aurora kinases play an important role inmitotic
progression and are frequently overexpressed in cancers. There is therefore interest in
the development of anticancer agents that target the two main forms, Aurora A and
Aurora B, and these can be considered representative of a broader range of potential
drug targets that is emerging from recent research into cell cycle regulation [34, 35].
Wilkinson et al. recently tested a novel Aurora B inhibitor, AZD1152, in a human
tumor xenograft models [36]. To monitor in vivo pharmacodynamic effects, they
combined a standard DNA content protocol with an antibody to phosphorylated
histone H3, which is an important Aurora B target. As expected, in control tumors
the P-H3 positive cells were confined to the G
2
/M peak. Drug treatment produced a
striking decrease in P-H3, accompanied by the emergence of a population of cells with
a 4C DNA content consistent with Aurora B inhibition (Figure 7.5). These results
suggest the potential to develop this application for the study of other cell cycle
disrupting agents in animal models, as well as in samples obtained frompatients during
drug treatment.
7.3.3 Histone Modification
In addition to mutational loss of tumor suppressors, their expression can be silenced
epigenetically by histone modifications that involve deacetylation. Histone deace-
tylase (HDAC) inhibitors are therefore novel and potentially effective anticancer
agents, and several have now been introduced into clinical trial [37, 38]. As with other
novel agents discussed in this chapter, although HDAC inhibitors differ in their effects
from classical chemotherapy agents, they have the potential for major side effects
[39]. Furthermore, there appears to be considerable interpatient variability in their
effects, indicating a need for laboratory methods able to monitor drug effects in
patients. An interesting paper by Kummar et al. describes the use of a flow cytometry
technique for surrogate measurement of HDAC inhibition in peripheral blood
samples, based on an antiacetylated lysine antibody combined with surface immu-
nophenotypic markers [40]. This was applied to a phase I clinical trial of the novel
HDAC inhibitor MS-275, treating patients with refractory cancers. The results show a
clear increase in acetylated proteins in subpopulations of normal blood cells that was
dependent on the dose of drug given [40]. Although the antibody used was not specific
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