Biology Reference
In-Depth Information
In 2001, the tyrosine kinase inhibitor imatinib mesylate (IM) was ap-
proved as a first-line therapy for CML by the U.S. Food and Drug Admin-
istration (FDA). Emergence of this drug, the therapeutic outcomes of which
are better than those of other options, has radically improved therapy for
CML and has provided a strategy to control the disease, other than alloge-
neic hematopoietic stem cell transplantation (allo-HSCT).
111,112
On the
other hand, for a considerable number of patients, either IM fails to work
from the beginning or resistance to IM develops during treatment. The
mechanisms of IM resistance can be dependent or independent of
mutations in the Abl kinase domain; such mutations occur in
50% of
IM-resistant patients. In the former case, because the second-generation
drugs nilotinib (NL) and dasatinib are now available for the treatment of
IM-resistant patients, as well as for first-line treatment, the effectiveness
of these medicines may be predictable and dependent on the types of
mutation present.
113
When there is no mutation present, however, the
only way in which to evaluate drug efficacy is to actually prescribe the
drug and follow the course of treatment by blood and bone marrow tests
for several months to a year or more. Given that treatment with an
ineffective medicine cannot be expected to hamper progression of the
disease, the most suitable medication should, ideally, be used from the
start.
114
To solve this problem and to optimally select the most effective
drug for each individual patient, it is necessary to develop a technique(s)
that evaluates the effect of every available medication on each patient's
leukemic cells and detects
the presence of any resistant cells before
starting therapy.
7.1. Biosensor design and its specification
To address the aforementioned issues, we developed a novel biosensor to
monitor BCR-ABL activity in living cells.
5
CrkL,
115
an authorized repre-
sentative of the substrates of BCR-ABL,
116-118
was used for the backbone of
the biosensor. CrkL harbors one Src homology 2 (SH2) domain and two
SH3 domains in addition to the tyrosine residue that is phosphorylated
by BCR-ABL (
Fig. 8.5A
). Of these, the SH2 domain possesses the
ability to bind to phosphorylated tyrosine, leading to structural changes
upon phosphorylation by BCR-ABL or the inhibition of BCR-ABL
activity in response to drug treatment (
Fig. 8.5A
). The biosensor for
BCR-ABL activity was designed on the basis of this characteristic of
CrkL;
in our construct, CrkL is sandwiched between CFP and YFP.
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