Cancer Research in Switzerland - Krebsliga Schweiz

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Clinical research
Presentation of completed research projects from July 2008 to December 2010
Aebersold Daniel M. | The role of activating point
mutations in the met receptor tyrosine kinase in tumor
radioresistance (OCS 1681-02-2005)
The growth factor receptor Met activates various pathways
and corresponding biological functions that are implicated
in the development of malignant tumours, including
critical roles in tumour progression and metastasis.
Moreover, it was demonstrated that the activation of this
receptor can adversely affect the response of malignant
tumour cells to chemotherapy and radiotherapy. Consequently,
Met is considered to be a promising molecular
target for the development of new cancer drugs. Various
mechanisms that can lead to excessive activation of the
Met receptor in tumours have been described. In this regard,
Met receptor overexpression and the occurrence of
activating point mutations are the most prevalent. The
aim of this research project was to investigate in more detail
the importance of activating Met mutations, from
both the biological and clinical point of view. For this purpose,
the following sub-projects were pursued:
1) The clinical study focused on the potential role of the
MET variant Y1253D, for which we previously suggested
a role in tumour response to radiation therapy, in metastatic
head and neck squamous cells carcinoma. This work
– performed on biopsy samples from a prospective randomised
trial combining radiotherapy and chemotherapy
– confirmed a role for an activating MET mutation in metastasis
of these tumours.
2) The scope of this sub-study was to perform a characterization
of the response of four MET mutated variants,
all of clinical significance, to the small molecule inhibitor
SU11274 before a combination treatment with IR could be
performed. The data obtained suggest that although all
four mutants are responsive to SU11274, considerable differences
in IC50 were observed on various MET-dependent
biochemical and biological endpoints. Those response
differences would have to be taken into consideration
once SU11274 is combined with IR.
3) This study focused on mechanistic aspects that underlie
the molecular cross-talk between MET and the DNA
damage response in cells harbouring both overexpression
of MET and MET mutations. The work shows that MET
inhibition results in reduced clonogenic survival of cells
to IR, which is accompanied by increased apoptosis. The
work also shows that MET inhibition cooperates with
DNA damaging agents to induce double strand DNA
breaks (DSBs) in a synergistic manner, and one of the reasons
for this synergism is the fact the MET inhibition alone
results in high levels of DSBs. The study also shows that
Met inhibition results in blocking of a major checkpoint
signalling pathway, the ATR-CHK1-CDC25, which results
in disruption of a post-damage S-phase associated cell cycle
arrest, which could eventually lead to mitotic entry of
cells that harbour high levels of unrepaired DSBs.
4) In this study we further explored previous findings,
published in 2008, coupling MET to effectors of DSBs repair
via homologous recombination. In that respect, by
using the DR-GFP homologous recombination (HR) assay,
we show that MET inhibition results in attenuation of HR
in a dose-dependent manner in cells harbouring MET
overexpression and MET mutants. Moreover, mechanistically
the study shows that this MET-dependent inhibition
of HR is coupled to a reduction of nuclear RAD51 and a
disruption of the physical association between RAD51
and BRCA2, which is crucial for successful HR.
The overall objective of the research project was to pave
the way for the implementation of genetic and mechanistic
evidence related to the growth factor receptor Met in
clinical research protocols to test the combination of Met
inhibition with conventional radiotherapy or chemotherapy.
Project coordinator
Prof. Dr. Daniel M. Aebersold
Universitätsklinik für Radio-Onkologie
Inselspital/Universität Bern
Freiburgstrasse
CH-3010 Bern
Phone +41 (0)31 632 24 31
Fax +41 (0)31 382 23 42
daniel.aebersold@insel.ch
Baege Astrid | The role of adult stem cells in HPV-
associated carcinogenesis: Identification of the HPV
target cell capable of driving viral persistence
(KLS 02220-02-2008)
Objective
Cervical cancer is still the second most common malignancy-related
cause of death worldwide. Persistent infection
with high risk human papillomavirus (HPV) is necessary
for the emergence of cervical cancer, but the crucial
factors determining persistence are largely unknown. The
overall goal is to identify stem cells within the human cervical
epithelium to further investigate their role during
HPV-transmission, establishment of persistent infection
and HPV-induced transformation.
Methods
Epithelial cells are isolated from fresh human cervical tissue
and fractionated by FACS sorting. Subpopulations of
putative stem cells, transit amplifying cells and differentiating
cells are sequentially subjected to microarray analysis
to compare gene expression pattern. Recruited stem
cell markers will be used to localize stem cells within the
cervical epithelium. Advanced organotypic cervical explant
models will be infected with fluorescent high risk
HPV pseudoviruses, and the course of infection will be
monitored to identify the HPV target cell capable of maintaining
the viral DNA over a course of time.