Cancer Research in Switzerland - Krebsliga Schweiz

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Pruschy Martin | Microtubule interference as target
for combined cancer therapy with ionizing radiation
(OCS 02129­08­2007)
Interference with microtubule function is a promising approach
for anti­cancer therapy that has been extensively
validated by the use of taxanes for the treatment of a wide
variety of human malignancies. However, treatment with
taxanes is limited by taxane­related toxicities and the development
of multidrug resistance. This has prompted an
ongoing worldwide search for novel microtubule­targeting
agents (MSA), e. g. epothilones. We recently demonstrated
that epothilones also offer a significant therapeutic
potential in combination with ionizing radiation (IR).
Thus this potent, combined treatment modality represents
a promising strategy for efficacy­enhancement of
tumour­directed radiotherapy and systemic but tumouroriented
and rationally designed anticancer agents. Treatment
with MSAs alone or in combination with IR directly
targets tumour cells, but it also affects other critical structures
of the tumour, e. g. the tumour vasculature, which
co­determines the tumour treatment response. However,
these processes and the signalling consequences relevant
for their cytotoxic effect are far from clear.
In this research project we investigated in a multilayered
approach the mechanisms underlying the antitumour effects
of microtubule interference with epothilones alone
and in combination with IR. In multiple tumour cell lines
(lung and colon adenocarcinoma cell lines, fibrosarcoma,
glioblastoma and medulloblastoma) and in murine tumour
models derived from these cells, the efficacy of
epothilones and IR alone and in combination was determined.
Having access to a genetically­defined tumour cell
system (wild­type lung adenocarcinoma cell line A549
and the mutant A549EpoB40 cell line, which are resistant
to epothilones due to a b­tubulin mutation) we could perform
complementary in vitro and in vivo experiments
specifically investigating the role of the tumour microenvironment
to this combined treatment modality. We could
demonstrate that the major cytotoxic effect of the combined
treatment modality of IR and patupilone is directed
against the tumour cell compartment and that the induced
anti­angiogenic effect, which contributes to the
supra­additive treatment response of this combined
treatment modality, derives indirectly from the tumour
cell. At the same time, we demonstrated that the potency
of patupilone alone is independent of tumour hypoxia.
Besides classic additive cytotoxicity determined on the
single cell level, we identified that microtubule interference
counteracts radiation­induced stress responses and
thereby downregulates treatment thresholds. In particular,
we determined interference on the level of VEGF
secretion and matrix metalloproteinase activity and demonstrated
that regulation of these paracrine effects contributes
to the supra­additive treatment response of this
combined treatment modality on the in vivo level.
Besides these mechanistic insights, these new data in
combination with our previous studies have already contributed
to the design and launch of clinical trials with this
combined treatment modality at the international level.
Furthermore, and based on our data, we are currently
outlining several options to combine IR not only with
epothilones but also with other microtubule de­/stabilizing
agents for clinical trials.
Project coordinator
Prof. Dr. Martin Pruschy
Labor für molekulare Radiobiologie
Klinik für Radio­Onkologie
UniversitätsSpital Zürich
Rämistrasse 100
CH­8091 Zürich
Phone +41 (0)44 255 85 49
martin.pruschy@usz.ch
Radtke Freddy | The role of Notch2 in murine
epidermis (OCS 01560­08­2004)
The skin epidermis and its appendages represent a constantly
renewing physical barrier that protects against
mechanical injuries, infective organisms and excessive loss
of water. Cellular processes such as proliferation, migration
and cell death must be highly regulated in order to
ensure lifelong homeostasis. The Notch pathway plays a
key role in differentiation of the epidermis and its appendages.
Notch proteins comprise a family of four type I transmembrane
receptors that influence cell fate decision and
differentiation processes in multiple organisms and tissues.
In the haematopoietic system, signalling via Notch1 or
Notch2 is important for the generation of T cells and a certain
subpopulation of B cells, both of which have an important
function in the immune system. Moreover, aberrant
Notch1 signalling in the haematopoietic system is
oncogenic and causative of T cell leukaemia. Results from
the blood system but also other tissues suggested that aberrant
Notch signalling is mostly associated with oncogenic
properties.
However, evidence from our own laboratory and from
others has shown that Notch1 can also function as a tumour
suppressor in particular in the skin. Conditional inactivation
of Notch1 in the mouse epidermis leads to the
development of spontaneous basal cell carcinoma­like tumours
within 1 year after loss of Notch1 function. The relatively
long latency for skin tumour development suggests
that during this period additional mutations have to be acquired
to cause malignant growth of Notch1 deficient
skin. The murine skin expresses mostly two Notch receptors,
Notch1 and Notch2. The function of the second
Notch receptor in the skin was completely unknown. We
therefore generated mice in which Notch2 alone or both
Notch1 and Notch2 could be inactivated simultaneously
in the skin.
Our study showed that inactivation of Notch2 in the skin
did not lead to any apparent phenotype, because loss of
Notch2 function was fully compensated by the presence