19. Investigative Treatment Division
The main goal of the research of this division is innovation of a new
strategy for cancer diagnosis, treatment and prevention. For this purpose,
currently three projects are on going.
New Strategy for Gene Therapy
About 15% of mutations affecting tumor suppressor genes are reported to be
mutations disturbing RNA splicing. These mutations often result in a loss
of gene function but sometimes also result in production of a deleterious
product, a dominant negative effect. In the latter case, such as p53
gene mutation, supplementation with a wild type gene product is not enough
to overcome the effect of mutation; reduction of the mutated product is
necessary. However, so far no strategy for suppressing a splicing mutation
has been established. A series of mutant U1snRNA expression vectors was
constructed, which have various base substitutions in the 5'-portion that
hybridize with a splice-donor site of pre-mRNA, and some of the mutations
were found to effectively suppress the splice-donor site mutation in a
model system using Nagase analbuminemic rats.(37) These expression vectors
did not alter cell growth, morphology or anchorage independence in cultured
mammalian cells. This new strategy for manipulation of pre-mRNA splicing
should be very promising also for the treatment of diseases caused by RNA
tumor viruses. In addition, the pattern of alternative splicing often
changes during carcinogenesis in various genes such as fibronectin
troponiyosin, CD44, k-ras, and DCC. These changes in alternative
splicing are deeply involved in carcinogenesis. The present strategy for
manipulations of pre-mRNA splicing will open a new field of research on
tumor biology and cancer therapy.
Analysis of Minute Lesions of the Colon
In order to understand the carcinogenesis process completely,
identification of very early minute lesions which are potentially
precursors of advanced carcinomas is important. Aberrant crypt foci (ACF)
were extensively studied and activation of K-ras codons 12 and 13
was proved to be very frequent even in a very small ACF, less than 0.1 mm
in diameter. The incidence was increased to about 90% for the lesions 0.5
mm to 3 mm in diameter. Cell proliferation in ACF was studied in rat colon.
Increased cell proliferation in ACF was proved by the mitotic index, BrdU
labeling index and proliferating cell nuclear antigen (PCNA) staining and
this was also true even in ACF consisting of one crypt.(33) The same
increased cell proliferation in ACF was also demonstrated in human ACF by
PCNA staining. Histologically, small ACF, less than 0.1 mm in diameter,
were hyperplastic. The adenomatous component became prominent in the larger
ACF. Histological examination of larger ACF, 0.1 mm to 3 mm in diameter,
revealed that about 1/2 of the focus is hyperplastic, 1/5 is a mixture of
hyperplasia and adenoma and the remaining 1/3 is adenoma. PCNA staining was
clearly stronger in adenomatous lesions than in hyperplastic lesions. This
tendency was clear even in ACF consisting of a hyperplastic portion and an
adeno-matous portion. Therefore, an ACF seemed to be formed as a
hyperplastic lesion through K-ras activation and to progress into an
adenomatous lesion through so far unidentified genetic changes with further
increased cell proliferation. Macroscopically normal mucosa was examined
for a mutant K-ras gene by using the enriched polymerase chain
reaction. The mutant K-ras gene was detected in about 10% of the
samples of normal mucosa from the colon of patients with colorectal
cancer.(34) The origin of the mutant K-ras gene is not clear at
present but most likely these mutant k-ras genes represent the
existence of very minute neoplastic lesions such as ACF. Evaluation of
detection of mutant K-ras gene as a biomarker of the risk for
colorectal cancer is under investigation.
Implication of Nitric Oxide Synthase in Clinical Features of Cancer
Patients
Nitric oxide is a relatively newly identified signaling molecule in various
biological processes.(25-31) Therefore, it could be one of the new target
molecules for cancer therapy. Paclitaxel is one of the most promising
cancer chemotherapeutic agents and many clinical trials are ongoing. One
serious adverse effect of it is hypotension. Taxol has been shown to have a
bacterial lipopolysaccharide-like action. Taxol was found to induce nitric
oxide synthase mRNA in macrophages and endothelial cells and this induction
was considered to be one of the mechanisms of hypotension caused by the
drug. A study on the induction of nitric oxide synthase in patients
administered paclitaxel is ongoing. Induction of nitric oxide synthase is
also being studied in connection with the adverse effects of vincalkaloides
on the nervous system. The contribution of nitric oxide synthase to
diarrhea, lung fibrosis and hemorrhagic diathesis is also being
investigated.
List of papers
from this division
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