Research Report 2000 - MDC

Phospholipids
Dietrich Arndt
Cytotoxic effects of antitumor
agents induced at the plasma
membrane level
We are investigating the anticancer
properties of special phospholipids.
These compounds, ether lipids and
alkylphospholipids (APLs), represent
a new class of non-DNA-interactive
compounds for cancer therapy. They
act as growth factor antagonists,
growth factor receptor blockers, and
interfere with mitogenic signal
transduction, modulate phospholipid
turnover, induce differentiation and
apoptosis and activate macrophages to
a tumoricidal state.
The aim of our research is to
investigate the correlation between
antineoplastic activity and the
supramoleculare structure of
phospholipids with antitumor
properties. Thus, we are concentrating
mainly on the investigation,
characterization and use of liposomes
prepared from phospholipids with
inherent antineoplastic activity
Antineoplastic activity of
alkylphospholipid liposomes in
human breast carcinomas
We have developed sterically
stabilized APL liposomes which avoid
uptake by the reticuloendothelial
system and can be targeted passively
to tumor tissue by increased
microvascular permeability in the
tumor area. The bilayer of such
sterically stabilized liposomes consists
of hexadecylphosphocholine,
cholesterol and polyethylene glycollinked
phosphoethanol-amine. The
reduced uptake of sterically stabilized
APL liposomes correlates in vitro
(J774 cells) with an increased
thickness of the fixed aqueous layer
around these liposomes and supports
the hypothesis that the thickness of
this aqueous layer is an important
factor responsible for preventing
opsonization, thereby resulting in
reduced macrophage uptake. The
pharmacokinetics of free and different
liposomal APLs is in agreement with
these assumptions; the serum levels of
APL obtained with sterically
stabilized liposomes are consistently
higher than with conventional
vesicles and free APL. In xenografted
MaTu carcinoma, the differences in
APL content between the different
groups are unexpectedly low and do
not reflect the high therapeutic
activity of sterically stabilized APL
liposomes. Detailed analysis shows
that the liposomal drug displays
modified pharmacokinetics which
may also involve lymphatic
absorption of the liposomal APL.
The physical properties and
pharmacological activity of liposomes
made from a new, highly active
alkylphospholipid (OPP) have been
optimized with special reference to
the composition of the vesicles. The
strongest antitumor effect on
xenotransplanted human breast cancer
MT-3 on nude mice was obtained with
sterically stabilized OPP liposomes
with a low cholesterol content. The
beneficial therapeutic effect of these
vesicles was accompanied by better
tolerance and a significant inhibition
of hemolysis, compared with micellar
OPP.
Immunoliposomes from
alkylphospholipids
For active targeting, we have
investigated the preparation of
immunoliposomes using
hexadecylphosphocholine and the
monoclonal antibody fragment 4D5,
specific against the p185 HER2 protein, a
growth factor receptor-tyrosine kinase.
Conjugation was achieved by
coupling the protein via a thioether
linkage to the liposomal surface. To
investigate the cellular uptake and
endocytosis by tumor cells, a pHsensitive
fluorescence marker was
encapsulated into the liposomes.
Experiments in vitro demonstrated a
difference in binding of liposomes,
with and without antibody, to cells
with different receptor expressions.
For active targeting of the
endothelium of the tumor
neovasculature, we are investigating
the preparation of immunoliposomes
using APL and peptides that
specifically target distinct blood
vessels. Each of these peptides binds
to different receptors that are
selectively expressed on the
vasculature of the target tissue. The
tumor-binding peptides, e.g peptides
containing an integrin-binding Arg-
Gly-Asp motif or the Asn-Gly-Arg
motif, bind to receptors that are
upregulated in tumor angiogenic
vasculature.
Selected Publications
Zeisig, R., Arndt, D., Stahn, R., and
Fichtner, I. (1998) Physical properties
and pharmacological activity in vitro
and in vivo of optimised liposomes
prepared from a new cancerostatic
alkylphospholipid. Biochim. Biophys.
Acta 1414, 238-248.
Arndt, D., Zeisig, R., and Fichtner, I.
(1998) Alkylphospholipid liposomes:
preparation, properties and use in
cancer research. Drugs of Today 34,
83-96.
Arndt, D., Zeisig, R., Fichtner, I.,
Teppke, A.D., and Fahr, A. (1999)
Pharmacokinetics of sterically
stabilized hexadecylphosphocholine
liposomes versus conventional
liposomes and free
hexadecylphosphocholine in tumor
free and human breast carcinoma
bearing mice. Breast Cancer Res.
Treat. 58, 71-80.
Patent Application
DE 198 55 953.4. Mittel zur
Tumortherapie. Erfinder: Zeisig, R.,
Fichtner, I., and Arndt, D.
DE 198 55 952.6 Mittel zum
nichtviralen Transfer von DNS in
eukaryotische Zellen. Erfinder: Zeisig,
R., and Walther, W.
Structure of the Group
Group leader
Dr. Dietrich Arndt
Scientists
Dr. Reiner Zeisig
Technical assistants
Anne-Dorothee Teppke
Adnan Ibikli*
* part of the period reported
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