Research Report 2000 - MDC

Experimental
Pharmacology
Iduna Fichtner
The group is continuing with the
development of in vitro and in vivo
models of relevance to preclinical
investigations in cancer. With the help
of these models, we shall address
questions concerning :
• the expression of tumor markers in
relation to biological
characteristics, such as metastasis,
drug- or hormone resistance,
• the pharmacological potential of
novel therapeutic or diagnostic
approaches, or
• the possibility of mitigating
therapy-induced side-effects.
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Expression of tumor-related
markers
In this research, the occurrence of
markers for metastasis (CD44),
resistance (MDR), endocrine
dependence (estrogen receptor) or
immune defence (RANTES) have
been correlated with the properties of
tumor growth.
The surface marker CD44 and several
of its splice variants are expressed
in a very specific pattern in individual
breast cancer xenografts, as revealed
by RT-PCR and immunohistochemistry.
The detection of certain CD44isoforms
is not related to the hormone
dependence or metastasis capacity of
the tumors. Cytostatics and
antihormones used clinically for the
treatment of breast cancer do not
affect the expression pattern of CD44
in xenografts indicating that it is a
suitable target molecule for gene- or
immunotherapeutic approaches.
In a clinically related study in 14
human sarcomas, we have found a
close relationship between the
expression of the multidrug resistance
gene (mdr1) and the response to
doxorubicin, both in xenografts and
patient tumors, while for lung
reistance protein (LRP) and MDRassociated
protein (MRP) there was
only a poor correlation. We have
concluded that screening sarcomas for
MDR-related markers clearly predicts
chemoresistance and helps avoid
unnecessary and toxic treatment.
In cooperation with the University of
Mannheim, the chemokine RANTES
has been found to be expressed by
a subset of melanomas. It is
responsible for the recruitment of
monocytes, T-cells and dendritic cells
but, surprisingly, it favored tumor
formation in nude mice.
Models for novel therapeutic or
diagnostic approaches
In cooperation with the Department of
Pediatric Oncology/Hematology of the
Virchow-Clinics leukemic blasts of
patients have been transplanted to
severely immunodeficient NOD/SCID
mice. In all, 11/16 acute lymphatic
leukemias were successfully
established in vivo and shown to
maintain their immuno- and genotype
during passaging. The antileukemic
activity of allogeneic human
mononuclear cells as a graft versus
leukemia (GVL) reaction with an
accompanying graft versus host
disease (GVHD) was simulated in the
mouse model. The chemo- and
radiation sensitivity of the ALL lines
resembled that in a clinical situation.
We believe that xenotransplanted ALL
can be considered as clinically
relevant models mimicking human
conditions and are a useful preclinical
tool for the evaluation of novel
immuno- or gene therapeutic
approaches.
Another extended study deals with the
detection of minimal residual disease
(MRD) in the bone marrow of patients
with solid tumors. At present, occult
epithelial cells are determined by
immunohistochemical or PCR
methods in patient samples. However,
nothing is known about the viability
of these cells or their proliferating and
metastasizing potential. Therefore,
bone marrow samples of 13 patients
with breast cancer, 30 from colorectal
cancer (Robert-Rössle-Clinics) and 33
from head and neck cancers (Mund-
Kiefer-Gesichtschirurgie, Virchow
Clinics) were transplanted to NOD/
SCID mice. Human and epithelial
cell-specific detection methods have
been developed for a sensitive proof
of potential cancer cells in murine
organs. The results obtained show that
only in rare instances can vital cancer
cells be found. These findings
correlate with the poor prognosis for
the disease. Additionally, the results
suggest that the evidence of epithelial
cells in bone marrow samples results
in too many false positives concerning
the survival potential of those cells.
Engraftment of nonhematopoietic
progenitor cells
from human blood in
immundeficient mice
Human cord blood (CB) and human
mobilized peripheral blood (PB) are
attractive cell sources for hematopoietic
transplantation, but their potential to
form non-hematopoietic cells is as yet
poorly characterized. Six to nine
weeks after injection of separated
CD34 + -cells from CB and PB into
sublethally irradiated NOD/SCIDmice
we found besides human
hematopoietic cells (up to 40 %) in
chimeric bone marrow, cells staining
positive with antibodies specific for
human fibroblasts and human
endothelial cells. PB CD34 + -cells were
flow-cytometrically sorted into
CD34 + /CD38 low and CD34+/CD38 high -