Book of abstract 2008

Increased tumour hypoxia and morphological blood vessel changes in
tumours after electrochemotherapy
Andrej Cör1, Mateja Legan1, Simona Kranjc2, Maja Čemažar2, Gregor Serša2
1Institute of Histology and Embryology, Medical Faculty, University of Ljubljana, Korytkova 2, Ljubljana,
Slovenia; 2Institute of Oncology Ljubljana, Zaloška 2, Ljubljana, Slovenia
It is widely accepted that no solid tumour can grow larger than a critical size of ~ 1mm3
without developing a blood supply network. Tumour vascular networks are chaotic,
featuring complex branching patterns and a lack of hierarchy. Vessel diameters are irregular
and blood flow rates are low (1). Evidences has accumulated showing that up to 50-60% of
locally advanced solid tumours may exhibit hypoxic and/or anoxic tissue areas, which are
heterogeneously distributed within the tumour mass.
The underlying mechanism of electrochemotherapy is electroporation of the cell
membrane, which facilitates access of poorly or non-permeable molecules into the
tumour cells. Additionally to the well-established direct cytotoxic effect on tumour cells,
blood flow measurements showed an immediate reduction of tumour blood flow after
application of electric pulses and electrochemotherapy (2).
In our study, SA-1 solid subcutaneous sarcoma tumours in A/J mice were treated by
bleomycin (BLM), the application of electric pulses (8 pulses, 1040V, 100 μs, 1Hz) or a
combination of both – electrochemotherapy. At various time points after therapy, tumours
were excised and analysed histochemically and immunohistochemically with antibodies
against CD-31 as endothelial cell marker, Glut-1 as intrinsic hypoxic marker and active
casapase-3 as apoptotic marker.
After application of electric pulses alone, as well as after electrochemotherapy, the extent
of tumour hypoxia, detected by Glut-1, reached its peak after 2h and lasted up to 8h after
the treatment. After the application of electric pulses, the recovery to pre-treatment level
lasted 14h, whereas
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after electrochemotherapy the recovery to pre-treatment level did not
occur for at least 48h.
To discover the cause of the increased hypoxia in the tumours after therapy, the
morphological characteristics of small tumour blood vessels were analysed. Changes in the
endothelial cells’ shape were observed 1h after the application of electric pulses. Endothelial
cells were rounded up and swollen, and the lumens of blood vessels were narrowed. The
same blood vessel morphological changes were also found after electrochemotherapy,
although at later times, approximately 14h after electrochemotherapy, some endothelial
cells with apoptotic characteristics and immunohistochemical active caspase-3 positivity
were found. Apoptotic endothelial cells were not observed in tumours treated with electric
pulses alone.
Our results demonstrate that electrochemotherapy also has a vascular disrupting action,
which can greatly increase the hypoxia in the tumours.
References:
1. Tozer GM, Kanthou C, Baguley BC. Disrupting tumour blood vesels. Nat Rev Cancer 2005; 5: 423-33.
2. Sersa G, Jarm T, Kotnik T, et al. Vascular disrupting action of electroporation and electrochemotherapy
with bleomycin in murine sarcoma. Br J Cancer 2008; 98: 388-98.
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